Level II Diagnosis - Unit B__formatted_raw__v1

{{PAGE_1}} LEVEL II · DIAGNOSIS

Unit B Facial Form Analysis · Cephalometric Tracing Techniques · Cephalometric Superimposition · Space Analysis and Its Interpretation · Ackerman-Proffit Classification

Proffit Instruction — generated for offline reference

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Contents

1. Facial Form Analysis
2. Cephalometric Tracing Techniques
3. Cephalometric Superimposition
4. Space Analysis and Its Interpretation
5. Ackerman-Proffit Classification

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1. Facial Form Analysis

Frontal View: Symmetry and Facial Proportions

Learning Objectives

In your clinical evaluation of a patient, analysis of facial proportions and dental-facial relationships is an essential step in the diagnosis of malocclusion. You must develop something like x-ray vision, visualizing the underlying jaw relationships from looking at the patient, and you also must be aware of how the teeth relate to the lips and cheeks. The purpose of this program is to teach you how to do that.

This program will cover the following major topics:

Frontal view:

• symmetry
• vertical and transverse facial proportions
• tooth display

Lateral view:

• anteroposterior jaw relationships
• incisor protrusion or retrusion?

Normal Facial Asymmetry

The first step in facial form analysis is to examine the patient from the frontal (full face) view, and to evaluate whether there is enough facial asymmetry to create a problem.

All normal faces have some asymmetry, and in most people the right side of the face is slightly larger than the left side (but it can be the other way around). The best way to appreciate the degree of normal asymmetry is to look at the difference in facial appearance between the real image, in the center in the illustration here, and the same face with the left and right sides duplicated. A perfectly symmetrical face doesn’t look real, because we almost never encounter an individual with no difference in the two sides of the face.

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{{PAGE_5}} to be corrected. The midline of the upper arch relative to the face is important because it is displayed with every smile. Getting the dental midlines so they coincide is important, too—but not if that would require displacing the maxillary teeth to one side. Studies with computer-altered images suggest that a dental midline off the center of the face becomes noticeable, and a potential problem, when it exceeds about 3 mm (image 3).

{{PAGE_6}} Image 1: Complaint: “My smile is crooked.” The problem: the maxillary dental midline is displaced from the midline of the face. Image 2: Maxillary dental midline displaced from facial midline in a child. Correcting this would be a priority item in an orthodontic treatment plan.

Median Value		Depiction
Maximum Tolerable Value	2.9 mm
Ideal	0 mm

Figure 14 Maxillary Midline to Face Image 3: Evaluation of patient/parent reactions to a displaced midline created by computer graphics indicates that the maximum tolerable deviation (before it is noticed and becomes a potential problem for the patient) is just under 3 mm.

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Transverse Facial Proportions

The second goal of frontal facial analysis is to evaluate facial proportions across the width of the face. In the frontal view the face can be divided into a central region and two lateral regions on each side. The five regions normally are quite close to the same width. They may not be when noticeable asymmetry exists.

This image illustrates the transverse proportions of the face and the relationships of the mouth, nose and eyes in the transverse plane of space. Note that in a well-proportioned face:

• the distance between the eyes is the same as the width of the eye
• the width of the nose is about the same as the distance between the eyes
• the width of the mouth equals the inter-pupillary distance
• the width of the mandible at the gonial angles equals the width across the eyes

Vertical Facial Proportions

Vertical facial proportions are seen in both the frontal (image 1) and lateral (image 2) views. The face can be divided into three vertical regions that are normally about the same size: hairline to bridge of nose (upper face), bridge of nose to bottom of nose (mid-face), and bottom of nose to bottom of chin (lower face). The medieval artists (da Vinci, Durer) who wrote the guidelines for drawing the human face expected the three regions to be the same size. In modern populations the lower third of the face usually is a little (but only a little) longer.

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{{PAGE_8}} It is interesting, and important to dentists, that the lower facial third has thirds. From the base of the nose to the mouth ideally is one-third of the total height of the lower third of the face, and from the mouth to the bottom of the chin is two-thirds.

Deviations from these proportions quickly are perceived as abnormal, and if other people perceive your facial proportions to be abnormal, that can become a problem that you’d like your dentist / orthodontist to help you overcome.

Frontal View: Tooth Display

Anterior Tooth Display

An important aspect of dental-facial proportions is the extent to which the maxillary incisors can be seen when the patient is at rest and on smile. In planning dental treatment of any kind, an important objective is to obtain the appropriate amount of tooth display.

The amount of tooth display at rest, of course, is determined by the amount of lip separation at rest. This can be zero but usually is 2-4 mm, more in younger children than older ones, and less or zero in

{{PAGE_9}} adults. The amount of lip elevation in the “enjoyment smile” (“That’s the funniest thing I’ve heard in years!”) varies but is great enough to display much of the gingiva as well as the teeth. It’s the “social smile” that we use all the time (“Glad to meet you.”) to which dentists relate tooth display. For the social smile, the guideline is that 100% exposure of the maxillary incisor and perhaps exposure of a small amount of maxillary gingiva is ideal (image 1), and 75% exposure of the incisor is about the minimum for the best appearance (image 2).

Image 1: An ideal social smile for a patient in late adolescence displays 100% of the crown of the incisors and a small amount of gingiva.

Image 2: Display of 75% of the maxillary incisors on a social smile is about the minimum for good facial esthetics.

Anterior Tooth Display (cont.)

Perhaps the best way to appreciate the impact of incisor display is to look at the difference it can make to change incisor display with treatment.

The girl in these before / after images had orthodontic treatment (with premolar extractions) to align her teeth and decrease their protrusion, and then (just before the braces were removed) had a lower border osteotomy of the mandible to bring her chin upward and forward. The genioplasty didn’t affect her dental occlusion, which was quite good before it was done, but it was an important part of

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{{PAGE_10}} the overall treatment. It elevated the lower lip, greatly decreased lip separation at rest and strain on closure, and improved the relationship of the lower lip with the maxillary incisors on smile. That’s the smile arc, which you’re going to learn more about as this module continues.

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{{PAGE_11}} Image 1: Pre-treatment, age 11. Image 2: Completion of orthodontics, age 15, before genioplasty to reduce the height of the lower 2/3rds of the lower third of the face.

{{PAGE_12}} Image 3: Post-treatment, age 15. Note that the upper incisor display now is close to ideal, and the lower incisors are no longer exposed. Exposing those teeth on smile is a sign of aging.

Posterior Tooth Display: Buccal Corridors On smile it also is possible to see the maxillary posterior teeth, and their relationship to the cheeks should be noted during frontal facial examination. There should be a small separation between the teeth and the cheeks, which forms the buccal corridor. A wide buccal corridor detracts from the appearance of the smile and is an indication that widening the maxillary arch may be indicated in orthodontic treatment, just as it is in replacement of missing posterior teeth with full or partial dentures. By the same token, absence of a buccal corridor also detracts from the appearance of the smile—anything can be overdone, and that includes transverse expansion of the dental arch.

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{{PAGE_13}} Image 1: Narrow maxillary arch with wide buccal corridors. Image 2: 5-year recall (same patient—she changed her hair color) after orthodontic treatment with widening of maxillary arch.

Smile Arc The smile arc is the relationship of the curvature of the lower lip on smile to the contour of the maxillary dentition. These curves should match, as they do in the patient shown here. Evaluating the smile arc is an important aspect of evaluating tooth-lip relationships. A flat smile arc detracts from the appearance of the smile, and correcting this is a goal of orthodontic or prosthodontic treatment.

{{PAGE_14}} Smile Arc (cont.)

Studies with composite images have given different results as to what aspect of incisor display is most important in determining smile esthetics. It is apparent, however, that the smile arc is an important aspect of smile attractiveness. One recent study (which has not been widely replicated) called it the “deal breaker” as smiles are evaluated, i.e., if the smile arch is incorrect, other aspects of positioning the teeth relative to the lips for best appearance can’t overcome it.

This girl’s treatment consisted of lengthening her maxillary incisors so that their vertical position matched the lip contour, and was done with dental laminates rather than orthodontics. The same guidelines for tooth-lip relationships apply to all types of dental treatment. Modern restorative dentistry can be an effective way of creating more display of the upper incisors.

{{PAGE_15}} Clinical photo showing a patient with a flattened smile arc prior to treatment.

Lateral View: A-P Jaw Relationships

Detecting Jaw Relationships

It’s in evaluation of jaw relationships from a profile view that you really need to develop x-ray vision. Cephalometric radiographs make it easier to see the details of how the jaws relate to each other, but you can see abnormal versus normal jaw relationships well enough from careful clinical examination of the profile to make a correct diagnosis and determine which patients may need further evaluation. This works because the soft tissue contours usually reflect the hard tissue contours that underlie them. The position of the soft tissue chin is a function of the position of the bony chin beneath it. The base of the upper lip and nose reflects the position of the anterior maxilla, and the position of the upper incisor determines lip contour at the vermillion border. The contour of the lower lip similarly reflects the contours of the mandibular alveolar process and may be affected by the upper teeth. For this reason, profile analysis can tell you a lot about the position of the jaws and teeth. We don’t yet routinely have images like the one shown here, which was specially made to superimpose the soft tissue profile over the cephalometric radiograph. In profile analysis your goal is

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{{PAGE_16}} to infer the jaw and tooth positions from what you see of the facial soft tissue relationships.

Class II Profile A skeletal Class II problem means, of course, that the lower jaw is enough behind the upper jaw to make normal dental occlusion almost impossible. Can you see that in the profile appearance? Indeed you can. Sometimes it helps to quickly sketch the profile—because to draw it accurately, you have to look closely.

Is it easier to see that the lower jaw is too far back in this patient (image 1) if you draw it (image 2)? For students who are just learning to evaluate jaw relationships, the drawing seems to help. Until you sharpen your eye, developing the x-ray vision we’ve talked about, a good way to be sure you see it is to look carefully so you can draw the profile accurately. What you’re trying to see is the relationship of the jaws, and of the teeth to the jaws, as in image 3. The underlying hard tissue relationships are reflected in the soft tissue profile.

{{PAGE_17}} Image 1: Do you see the mandibular deficiency that predicts she has a Class II malocclusion?

Image 2: A drawing of the profile seen in image 1. A drawing like this, of course, is only valuable if it’s accurate—and to draw it accurately, you have to look at it carefully.

Image 3: The view of the facial skeleton and dentition that you would get from a radiograph.

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{{PAGE_18}} You can predict what this view would be like from careful examination of the overlying soft tissues.

Class I Profile In a normal face like this one (image 1), the bridge of the nose, the base of the nose, and the chin line up reasonably well in a straight or slightly curved convex line. Note that same relationship of the underlying bony structures can be seen in a lateral cephalometric relationship (image 2).

Image 1: Normal (Class I) profile—which means there is no jaw discrepancy, but is equally compatible with ideally aligned or crowded incisors.

Image 2: Cephalometric radiograph, same patient.

Class III Profile This patient (image 1) has a concave facial profile that suggests a moderately severe skeletal Class III relationship. Note the relationships of the bridge of the nose, base of the upper lip, and chin. This is described as a Class III skeletal pattern because it usually accompanies Class III molar and canine

{{PAGE_19}} dental relationships and negative (usually zero or less) overjet. Approximately 1-2% of the US population has this type of skeletal relationship, which is more prevalent (up to 14%) in Asians. In this girl, the Class III problem is due to a combination of a maxilla that is not as far forward as it should be, while the mandible is somewhat large. The profile sketch of a different individual (image 2) shows a similar situation. You already know that a skeletal Class III problem can be due to any combination of small / short maxilla and large / long mandible. You don’t need an x-ray to differentiate maxillary deficiency from mandibular excess.

Image 1: Class III profile, with a combination of mandibular excess and maxillary deficiency.

Short Face / Deep Overbite Vertical jaw relationships also are seen in the profile view, and appear as disproportions in the middle and/or lower thirds of the face. A patient with a short face usually is disproportionately short in the lower third (image 1). What dental relationship would you expect to find when you look at this patient’s dental occlusion? That’s right, she almost surely has a deep overbite. A short face is also called a skeletal deep bite, simply because the jaw relationship predisposes to that dental relationship. You can see that better in a lateral cephalometric radiograph (image 2), but you can detect it just from the profile analysis.

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Long Face / Open Bite

A patient with a long anterior face height is likely to be disproportionately long in middle third of the face because the maxilla has grown down more than normal. One of the effects is an increased display of maxillary gingiva (image 1). Excessive downward growth of the maxilla causes a downward-backward rotation of the mandible, shown diagrammatically in image 2. The profile view of this patient (image 3) shows the rotation.

An easy way to detect downward-backward rotation of the mandible is to use a mirror handle to demonstrate the mandibular plane angle (image 4). The steeper the angle, the more likely it is that rotation has occurred.

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{{PAGE_22}} Image 3: Downward-backward rotation of mandible (same patient as image 1). Image 4: Clinical determination of mandibular plane angle, which for this patient is within the normal range, but on the steep side.

Critical Questions for Facial Form Analysis

There are six major questions to be answered in facial form analysis, though not necessarily in this order:

The first relates to anteroposterior skeletal jaw relationships: What is the anteroposterior position of each jaw and how do the jaws relate to each other?

The second is the vertical jaw relationship: What are the vertical facial proportions, especially in the lower 1/3 of the face?

The third is the transverse jaw relationship: Is the face symmetric?

Fourth is the transverse position of the upper dental arch relative to the face: Are the upper incisors in the center of the face? Are the buccal corridors wide, normal or narrow?

Fifth is the vertical incisor position: Are the incisors correctly positioned vertically relative to the lips, so that incisor display is optimal?

We’ve answered these. Now let’s consider the last one:

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{{PAGE_23}} Do the incisors provide proper lip support, or are they retrusive or protrusive?

Facial form analysis and space analysis are the key diagnostic procedures in evaluating potential orthodontic problems in children, and this is where they overlap. As we will emphasize further in the module on space analysis, you can’t interpret the result of space analysis until you know where the incisors are positioned in the a-p plane of space and, if the incisors need to be repositioned, the direction in which they would be moved.

Lateral View: Tooth-Lip Relationships

Lip Position Related to Incisor Position

Lip position and incisor prominence are evaluated by viewing the profile with the patient’s lips relaxed, and observing the position of the upper lip relative to a true vertical line through the concavity at the base of the upper lip (soft tissue point A) (image 1). Then the position of the lower lip relative to a true vertical line through the bottom of the concavity between the lip and chin (soft tissue point B) is observed.

If either lip is significantly forward from the reference line, it can be judged as protrusive; if it falls behind this line, it’s retrusive. For this girl, the lower lip is quite protrusive relative to the chin, while the prominence of the upper lip is normally-related to the base of the lip. If the lips are prominent, incompetent (separated at rest by more than 3-4 mm) (image 2) and strained on closure (image 3), the anterior teeth are excessively protrusive.

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{{PAGE_24}} Image 1: Note the difference in the position of the upper lip to its base (soft tissue point A) and the lower lip relative to its base (soft tissue point B).

Image 2: Excessive separation of the lips is seen particularly well in an oblique (three-quarter) view of the face.

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{{PAGE_25}} Lip Position Related to Incisor Position (cont.)

Remember, if the lips are prominent, incompetent (separated at rest by more than 3-4 mm) (image 1) and strained on closure (image 2), the anterior teeth are excessively protrusive (image 3).

The incisor protrusion is more obvious in the radiograph, but it can be detected easily from examining the profile, and you can judge just from the profile that in this girl the incisor protrusion is severe.

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{{PAGE_26}} Image 1: Prominent and incompetent lips. Image 2: Lip strain on closure.

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Lip Support by Incisors

Can orthodontic movement of the anterior teeth affect the prominence of the lips? Yes, it can. Moving the incisors forward (facially) increases the amount of support for the lips and increases their prominence. Moving the incisors back (lingually) decreases lip support and lip prominence.

For this reason, evaluating lip prominence and incisor protrusion is a particularly important aspect of facial form analysis. This is a primary determinant of whether arch expansion or tooth extraction to make space for crowded teeth is indicated (images 1-4).

{{PAGE_28}} Image 1: Protrusive incisors, appearance on smile. Image 2: Appearance after premolar extraction and retraction of incisors.

{{PAGE_29}} Image 3: Clinical photo showing prominent and incompetent lips with protrusive incisors. Image 4: Clinical photo showing reduction in lip prominence after retraction of incisors.

Facial Form Analysis Exercises: Frontal

Patient #1

For this patient: What’s your judgment as to facial symmetry?

• within normal limit or asymmetric
• if present, location of asymmetry incisor tooth display?
• OK, too little, too much (excess gingiva) buccal corridor width
• OK, too little, too much smile arc

{{PAGE_30}} OK, flat, excessive

Patient #1 (cont.) You should see that this patient has

• significant asymmetry: note that her face is larger on the right side
• tooth display: relatively normal on left side, affected by asymmetry on right side
• buccal corridor width: excessive on right, OK on left
• smile arc: abnormal because of asymmetry

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{{PAGE_31}} Patient #2

For this patient: What’s your judgment as to facial symmetry?

• within normal limit or asymmetric
• if present, location of asymmetry

incisor display?

• OK, too little, too much (excess gingiva)

buccal corridor width

• OK, too little, too much

smile arc

• OK, flat, excessive

{{PAGE_32}} Patient #2 (cont.)

You should see that this patient has

• mild mandibular asymmetry, with his chin off to the left—but probably not enough for it to be a problem
• normal incisor display
• excessive buccal corridor width: too much space between the posterior teeth and the cheeks
• normal smile arc

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{{PAGE_33}} Patient #3

For this patient: What’s your judgment as to facial symmetry?

• within normal limit or asymmetric
• if present, location of asymmetry incisor display?
• OK, too little, too much (excess gingiva) buccal corridor width
• OK, too little, too much smile arc
• OK, flat, excessive

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Patient #3 (cont.)

You should see that this patient has

• significant mandibular asymmetry. Compare him to Patient #1 (seen in Image 2). Can you see that for him the asymmetry is just in the lower face, instead of affecting the entire face as in #1? This time the problem is due to excessive growth of the mandible on the left side.
• incisor display: inadequate display of upper incisors, displays lower incisors that should not be seen at this age
• buccal corridor width: not seen well enough to evaluate
• smile arc: flattened (upper teeth are hardly visible but don’t follow the lip line)

{{PAGE_35}} Image 1

Image 2, Patient #1

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{{PAGE_36}} Patient #4 For this patient: What’s your judgment as to facial symmetry?

• within normal limit or asymmetric
• if present, location of asymmetry incisor display?
• OK, too little, too much (excess gingiva) buccal corridor width
• OK, too little, too much smile arc
• OK, flat, excessive

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{{PAGE_37}} Patient #4 (cont.) You should see that this patient has

• no asymmetry
• too little display of maxillary incisors
• normal buccal corridor width
• flattened smile arc

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Patient #5

For this patient: What’s your judgment as to facial symmetry?

• within normal limit or asymmetric
• if present, location of asymmetry

incisor display?

• OK, too little, too much (excess gingiva)

buccal corridor width

• OK, too little, too much

smile arc

• OK, flat, excessive

{{PAGE_39}} Patient #5 (cont.)

You should see that this patient has

• a mild chin asymmetry, not enough to be a problem
• marginally adequate maxillary tooth display, some display of lower incisors
• minimal buccal corridor width, perhaps too little
• slightly flattened smile arc

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{{PAGE_40}} Facial Form Analysis Exercises: Profile

Patient #6 For this patient: What’s your judgment as to antero-posterior skeletal jaw relationship Class I (normal) Class II Class III vertical skeletal jaw relationship normal long face short face tooth support for lip ⇒ lip prominence excessive normal

{{PAGE_41}} inadequate

Patient #6 (cont.) For this patient you should say

• skeletal A-P: Class II
• skeletal vertical: long face
• lip prominence: OK
• tooth support for lip: OK (a little deficient for upper lip, a little excessive for lower?)

{{PAGE_42}} Patient #7 For this patient: What’s your judgment as to antero-posterior skeletal jaw relationship

• Class I (normal)
• Class II
• Class III vertical skeletal jaw relationship
• normal
• long face
• short face tooth support for lip ⇒ lip prominence
• excessive
• normal
• inadequate

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{{PAGE_43}} Patient #7 (cont.) For this patient you should see:

• skeletal A-P: Class II
• skeletal vertical: long face
• lip prominence: OK upper, excessive lower
• tooth support for lip OK upper, excessive lower

{{PAGE_44}} Patient #8 For this patient: What’s your judgment as to antero-posterior skeletal jaw relationship

• Class I (normal)
• Class II
• Class III vertical skeletal jaw relationship
• normal
• long face
• short face tooth support for lip ⇒ lip prominence
• excessive
• normal
• inadequate

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{{PAGE_45}} Patient #8 (cont.) For this patient you should see

• skeletal A-P: Class II (despite prominent chin)
• skeletal vertical short face
• lip prominence: normal
• tooth support for lip: upper, normal; lower, inadequate

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{{PAGE_46}} Patient #9 For this patient: What’s your judgment as to antero-posterior skeletal jaw relationship

• Class I (normal)
• Class II
• Class III vertical skeletal jaw relationship
• normal
• long face
• short face tooth support for lip ⇒ lip prominence
• excessive
• normal
• inadequate

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{{PAGE_47}} Patient #9 (cont.) For this patient you should see

• A-P skeletal: Class III: Is it apparent to you that she has some maxillary deficiency, although the large mandible is the major contributor to the skeletal Class III?
• vertical skeletal: normal
• lip prominence: inadequate upper, OK lower
• tooth support for lip: inadequate upper, OK lower

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{{PAGE_48}} Patient #10 For this patient: What’s your judgment as to antero-posterior skeletal jaw relationship

• Class I (normal)
• Class II
• Class III vertical skeletal jaw relationship
• normal
• long face
• short face tooth support for lip ⇒ lip prominence
• excessive
• normal
• inadequate

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Patient #10

For this patient you should see

• skeletal A-P: Class III
• skeletal vertical: long face
• lip prominence: inadequate (note that the upper lip is worse than the lower lip)
• tooth support for lip: inadequate

{{PAGE_50}} Summary

What difference does it make if a dentist can or can’t recognize facial disproportions? Why do you need to develop the ability to evaluate facial and dental proportions?

The answer is straightforward: this is the process you will use to evaluate the severity of an orthodontic problem and whether you would refer the patient to a specialist for treatment of this problem or treat it yourself. The process is referred to as “orthodontic triage”. It’s just an organized way to sort patients by the severity of their orthodontic problems (triage comes from the French verb trier, to sort). As you move on to Levels 3 and 4 in the Growth & Development sequence, you’ll be applying your ability to detect jaw relationships and tooth-lip relationships as you conduct orthodontic triage.

Referral to Self-Test

Before you take the self-test, be sure to read the assignment in Contemporary Orthodontics: pages 158-172 in the 5th edition, pages 176-189 in the 4th edition. Then use the self-test to be sure you have understood this important material.

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2. Cephalometric Tracing Techniques

Overview of Cephalometric Technique and Analysis

Learning Objectives

Cephalometric radiographs (often called “cephs” for short) have been an important part of orthodontic diagnostic records since the mid-20th century. They offer two important advantages:

1. The radiographic view makes it possible to directly view the relationship of the dental arches to the underlying jaw structures, and to evaluate the relationship of the jaws to each other and to the cranial base. Although careful clinical examination of patients can yield most of this information, diagnostic precision increases significantly; and
2. Serial cephalometric radiographs make it possible to evaluate both growth changes and the response to treatment in a way that was not possible previously.

In this module, we will focus on the first of these advantages, the use of cephs in the analysis of facial form. This extends what you learned in the previous module on facial form analysis, and will help you to further develop the “x-ray vision” needed in clinical examination of patients.

The next module, on cephalometric superimposition, is devoted to the second advantage, using serial cephs and various superimpositions to evaluate patients’ response to treatment.

Early Cephalometrics: America vs Europe

It has happened repeatedly in science (and in other creative areas as well) that a new idea appeared simultaneously in more than one location. You know already that Broadbent in the US and Hofrath in Germany independently realized that serial radiographs of the head and face could be used to study growth. This would allow evaluation of skeletal growth in a way that could not be done with cross-sectional measurements on skulls (craniometry) and longitudinal measurements across the soft tissues that cover the skeleton (anthropometry). Both Broadbent and Hofrath used a head holder so that the individual could be positioned in the same way repeatedly. And you’re already at least somewhat familiar with superimposed cephalometric tracings to view growth changes.

Now let’s look at cephalometric radiology in more detail, focusing on it as a diagnostic tool, not a tool for studying growth. The first thing to remember is that although Broadbent and Hofrath had the same idea, they didn’t standardize the technique in the same way. To this day, cephalometric radiographs (henceforth called cephs) made in Europe differ from those made in the US in one obvious way and one that’s not so obvious. The obvious way is that the patient looks to the right in an American ceph, and to the left in a European one. The not so obvious way is that the American radiograph usually is somewhat more magnified because the x-ray source is closer. Small details in positioning can differ between one machine and another on both sides of the Atlantic, so serial radiographs on the same machine are the most reliable way to detect small differences.

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{{PAGE_52}} Why Trace Cephalometric Radiographs?

The second thing to consider is why comparisons of the same patient at different times, or comparisons of one patient to another, are based on comparisons of tracings of the cephs instead of direct comparison of the images themselves. The tracings show only a few of the anatomic characteristics that can be seen in the ceph.

The problem is that the x-ray image contains so much information that it’s overwhelming. For both growth studies and cephalometric diagnosis, what you want to know is how the jaws relate to the cranium and cranial base, and how the maxillary and mandibular teeth relate to their own jaw (image 1). To see that clearly, it’s necessary to eliminate most of the detailed image so the areas of interest can be seen clearly (image 2). This was done originally by carefully tracing the outline of the cranial base, maxilla, mandible, teeth of both arches, and the soft tissue profile on a sheet of clear film laid over the illuminated radiograph. Now something that looks a lot like a tracing is generated by a computer program.

The goal was—and is—to evaluate those important relationships. This is the same goal, of course, as the goal of clinical evaluation of facial form.

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{{PAGE_53}} Image 1: This drawing shows the five major components of the face. An important goal of orthodontic diagnosis is to carefully establish their proportional relationships; cephalometric radiographs are the major tool for doing that.

Image 2: The five major components as seen in a typical ceph.

Cephalometric Analysis: Comparison with Numerical Norms

It did not take long for clinicians who had access to cephs to consider them as possible diagnostic records. The thought was that an individual’s dental and facial proportions could be compared to a population average, or to proportions that were selected as ideal for that person’s racial and ethnic group. This would focus attention on what was different about an individual patient. A comparison of this type is referred to as “cephalometric analysis”.

The first cephalometric analysis (the Downs analysis, named for the faculty member who produced it) was developed at the Univ. of Illinois, where one of the original three Broadbent-Bolton cephalometers was in use. (The Bolton family supported Broadbent’s work with cephalometrics, thus the dual name on the cephalometer). The Downs analysis, and its many successors, were based on defining skeletal landmarks on cephalometric tracings. The key landmarks that can be seen in a lateral ceph are shown on a dissected skull in image 1. The selected measurements in contemporary analyses are different now from those used originally (images 2 and 3), but the procedure still is to

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{{PAGE_54}} compare the patient’s measurements to “normal” values from cephs of a small group of individuals with ideal dental occlusion.

By now, numerical “norms” have been published for most racial and ethnic groups, so you can measure distances and angles for your patient and compare them to norms for the appropriate reference group.

Image 1: Anatomic location of major cephalometric landmarks. Image 2: Linear measurements frequently made on a ceph tracing. Image 3: Angular measurements frequently made on a ceph tracing.

Cephalometric Analysis: Comparison with Templates With the measurement approach, the norms for the various measurements were the averages from a selected reference group. Another way to represent the norms would be to locate landmarks, then

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{{PAGE_55}} create a composite tracing based on the average angles and distances within the reference group. The composite tracing, which contained the same information as a table of numbers but displayed it in a very different way, could be superimposed on the tracing of an individual patient. Then the way the patient differed from the ideal, and by how much, could simply be observed. Broadbent took this approach with the serial cephs he collected with financial support from the Bolton family, using his original cephalometer. Acknowledging the family support in producing them by using their name, the resulting Bolton templates show the average proportions at each year of age of 16 males and 16 females who were selected by Broadbent as having ideal facial proportions. He ended up averaging the combined gender groups, so the Bolton templates can be considered unisex data. Looking at the difference between a Bolton standard template (red) and the patient’s tracing (black), it’s easy to see that the patient differs from the norm in two ways: the maxilla is rotated down posteriorly, and the mandible is rotated down and back. The result is a long face with mandibular deficiency largely due to the rotation.

Cephalometric Analysis in the Era of Digital Radiographs

By the end of the 20th century, film was being replaced by digital images in radiography just as it was in every day use. It’s almost impossible to accurately trace a ceph that exists only on a computer screen. Now what?

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{{PAGE_56}} The answer is to digitize the location of landmarks on the ceph (which also could be done on a tracing from a film image, so that the tracing could be included in a computer data set). This creates a digital model that, like a tracing, removes most of the extraneous information. Then a computer program can be used to quickly generate as many linear and angular measurements as you want.

More landmarks would be needed in the digital model than usually were identified on a tracing, but otherwise the output would be similar to the tabulated numbers from measurements on a tracing—and the time spent in digitizing landmarks would be regained in not having to make the measurements manually.

Different computer programs require different landmarks. A typical set of landmarks for digitization is shown in this image. You have to digitize a set of at least 40-50 points to get an accurate representation of the patient into computer memory.

With the advent of digital radiographs, it has become the standard to use imaging software (which specifies the landmarks and sequence in which they are to be located) to digitize landmarks and create virtual ceph tracings. This practice has essentially replaced the use of acetate tracings.

Computer Templates Could you use the template approach to comparisons if your radiographs existed only in computer memory? Yes, if the templates for the normal comparison group also were in computer memory, so they could be called up and superimposed.

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{{PAGE_57}} In fact, with that approach it wouldn’t be necessary to digitize the patient’s radiograph. You could just pull up the digital ceph on your computer screen (images 1 and 2), then superimpose the reference tracing on the ceph (images 3 and 4), and you’d be able to see the differences between the patient and the template.

A new computer program, developed in 2008 (SmartCeph, OrthoII), offers the ability to bring up the correct Bolton template and superimpose it on the digital ceph. The correct template matches the length of the patient’s anterior cranial base rather than chronologic age, which matches them on developmental status instead of age. Only a couple of clicks of the computer mouse are required. After looking at the template comparison, you can go ahead with digitizing the patient’s landmarks—but that’s not really necessary in most cases.

Just from examining image 4, could you describe how this patient differs from the ideal facial proportions shown in the tracing? You’re going to get some experience doing just that later in this module, but already you can come pretty close—just by looking at it.

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{{PAGE_58}} Image 1: Digital ceph displayed on laptop computer (probably downloaded from a distant server). Image 2: Close-up of digital ceph on computer screen. Image 3: Template (blue-green lines) superimposed (cranial base superimposition) on the patient’s ceph. Image 4: Close-up of the superimposition, which allows observation of the differences between the patient’s facial proportions and the average for his population group as shown by the template.

3-D Imaging and Synthetic Cephs

At present, there is a strong trend toward replacing radiographs of individual dental and facial areas with a cone-beam computed tomographic (CBCT) image of the head. One CBCT scan could replace the panoramic, lateral ceph and a-p ceph images for a given patient, although there is a modest increase in cost and radiation exposure.

The good news is that the CBCT image can be viewed from any direction, and provides significantly more information than 2-D radiographs. The bad news for orthodontic diagnosis is that the information on a lateral ceph was overwhelming and needed to be reduced for analysis. With a 3-D image, the amount of information is so much greater that a stronger adjective is needed—overwhelming doesn’t describe it.

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{{PAGE_59}} Radiograph showing lateral view of skull and cervical spine with measurement scale.

{{PAGE_60}} The original cephalometric technique used the standard method for orienting dry skulls for craniometrics (image 1). This called for having the Frankfort plane, an imaginary line extending from the superior portion of the external auditory meatus to the inferior margin of the orbit, parallel to the floor—a position called Frankfort horizontal. Frankfort horizontal is the best estimate of how a skull would have been oriented when the living individual had his head level.

For a living patient, of course, it would make sense to capture the actual orientation of the head in life. Every individual has a reproducible head position in which he or she “knows” that the head is level, and that’s the head orientation that is presented to the world. It’s the head position you adopt when you look at something on the horizon, or into your own eyes in a mirror if you’re in a small room like an x-ray room. This natural head position (NHP) now is the preferred orientation for taking a ceph (image 2). NHP cephs typically show a hanging chain as a true vertical reference across the front of the image, and the true horizontal line is perpendicular to it. This ceph was taken in NHP with filters in the x-ray beam, so that an outline of the soft tissue profile as well as the hard tissue structures could be obtained.

Landmark Positions

Until the advent of digital radiography in the 1990s, a cephalometric radiograph was exposed and developed on plain film. A tracing was created by placing a thin semi-transparent sheet of acetate tracing paper on top of the film. The tracing paper was taped to the film to prevent movement, and the film was placed on a light box to improve the visualization of the anatomic structures. Using a pencil, the functional units of the facial skeleton were outlined and traced onto the acetate paper, and the landmarks were marked with dots.

To create a digital model of a ceph, you still have to find the landmarks accurately, and tracing the anatomic structures that indicate the key landmarks is still a good way to learn where the landmarks are. The most important landmarks for cephalometric analysis are shown on this tracing. We’ll identify them more clearly on the next screen.

{{PAGE_61}} Regardless of whether you trace a plain film by hand or digitize landmarks using computer software, the goal is to get the same information—a description of the 5 functional units and their relationships to each other.

Landmark Positions: Cranial Base

Since we are trying to understand the relationships between the 5 functional units of the craniofacial complex, it is important to identify consistent landmarks on each of these functional units. A cephalometric landmark is defined as an anatomic structure that meets two criteria:

1. It can be identified accurately on a cephalometric film.
2. It represents a known part of one of the five major functional units.

Let’s begin with the landmarks for the cranial base. Two critically important landmarks identify its orientation:

Sella (S) – indicates the posterior end of the anterior cranial base, and is located in the center of the cavity of sella turcica (image 1).

Nasion (Na) – indicates the front end of the anterior cranial base, and is located at the anterior end of the junction between the nasal and frontal bones (image 2).

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Landmark Positions: Maxilla

Three critically important landmarks for position and orientation of the maxilla (image 1) are:

Anterior nasal spine (ANS) – indicates the front end of the maxilla, and is located at the tip of the anterior nasal spine (image 2).

Point A (A) –another landmark associated with the anterior maxilla, located at the innermost point of the contour of the premaxilla between the anterior nasal spine and the incisor tooth (image 2).

Posterior nasal spine (PNS) – indicates the posterior end of the maxilla, and is located at the tip of the posterior spine of the palatine bone, at the junction of the hard and soft palates (image 3).

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Landmark Positions: Mandible

There are 5 important landmarks for position and orientation of the mandible (image 1): Point B (B) – indicates the anterior part of the bony base of the mandibular dentition, and is located at the innermost point on the contour of the mandible between the incisor tooth and bony chin (image 2). Pogonion (Pg) – the most anterior point on the contour of the chin (image 3). Menton (Me) – the most inferior point on the mandibular symphysis (i.e., the bottom of the chin) (image 3). Gnathion (Gn) – the center of the inferior contour of the chin, halfway between pogonion and menton (image 3). Gonion (Go) – indicates the angle of the mandible, and is located at the center of the inferior contour of the mandibular angle (image 4).

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Landmark Positions: Max / Mand Dentition

Four landmarks typically represent the a-p and vertical position of the incisor and molar teeth in each arch:

• Upper incisor (U1) – maxillary central incisor tip)
• Lower incisor (L1) – mandibular central incisor tip)
• Upper molar (U6) – maxillary 1st molar, mesial cusp tip
• Lower molar (L6) – mandibular 1st molar, mesial cusp tip

These points are indicated on the attached ceph.

{{PAGE_65}} Image 1: Close-up view of the maxillary and mandibular teeth as seen on a ceph, with the tooth landmarks identified.

Image 2

Tracing the Cranial Base Landmarks: S and Na

Even if you are in a digital world, if you can trace the areas around the important landmarks, it makes it easier to accurately locate them. Let’s begin some tracing by working with the cranial base landmarks.

Sella (S) appears as a depression in the sphenoid bone that contains the pituitary gland. To trace this area and identify the point (image 1):

• First draw the contour of the depression in the bone, extending anteriorly and posteriorly over the edges of the concavity; then mark point S in the center of the concavity. Extend your line forward along the floor of the anterior cranial base as shown (because this helps when and if you need to do superimpositions).

Nasion (N), the front end of the anterior cranial base, is the anterior end of the junction of the nasal and frontal bones. To trace this area and identify the point (image 2):

• Draw the outer surface of the nasal and frontal bones past the junction; then draw a suture between the bones. Identify point Na as the place where these lines intersect.

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Tracing the Maxillary Landmarks: ANS, Pt A, PNS

ANS is the tip of the anterior nasal spine. Point A, the junction between the skeletal maxilla and the maxillary dentoalveolar process, is the innermost point on the contour of the premaxilla between the anterior nasal spine and the incisor.

To trace this area and identify the points (image 1):

• Trace the superior and inferior surfaces of the anterior nasal spine and mark its tip as ANS; then follow the external contour of the bone downward toward the upper incisor, and mark point A at the depth of this concave line.

PNS is the back end of the bony palate, the point where the hard palate ends and the soft palate begins.

To trace this area and identify the point (image 2):

• Trace the inner contour of the anterior maxillary alveolar process, and continue posteriorly along the roof of the mouth to the end of the bony outline. Mark the end of the palatal bone contour as PNS.

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{{PAGE_67}} Image 1: Tracing the contours of the anterior maxilla to locate ANS and point A.

Image 2: Tracing the contour of the posterior maxilla to locate PNS.

Tracing the Anterior Mandibular Landmarks (Pt B, Pg, Me, Gn)

Point B, the junction between the skeletal mandible and the mandibular dentoalveolar process, is the innermost point on the contour of the anterior mandible between the incisor and the bony chin.

Pogonion (Pg), Gnathion (Gn) and Menton (Me) are points on the contour of the chin. To trace this area and identify the point (image):

Trace the bony chin. Include the inner aspect of the symphysis as shown (useful for superimposition). Follow the external contour of the bone from the chin upward toward the incisor, and mark point B as the depth of this concave line (image 1).

Pogonion is the most prominent point on the anterior aspect of the bony chin. Menton is the most inferior point on the bony chin, and Gnathion is the point on the anterior inferior contour of the chin halfway between pogonion and menton (image 2).

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{{PAGE_68}} Image 1: Tracing the contour of the mandibular symphysis to locate point B. Image 2: Locating pogonion, gnathion and menton (top to bottom order) on the contour of the bony chin.

Tracing the Mandibular Gonial Angle Area (Go) Gonion (Go) is the center of the inferior contour of the mandibular angle. To trace this area and identify the point:

• Follow the lower border of the mandible posteriorly around the mandibular angle and up the posterior surface of the ramus. Mark the center of the curvature at the gonial angle point Go. Often because of the mild asymmetry that almost everyone has, two shadows of the lower border of the mandible can be seen in the mandibular angle area. In that case, trace both sides, using a solid line for one and a dotted line for the other, and mark point Go as the midpoint between the two sides. (In cases of severe asymmetry, Go for the left and right sides would be the base for separate measurements.)

{{PAGE_69}} Orbitale, Mandibular Canal, 3rd Molar To complete the tracing of the jaws: trace the orbital rims and note point orbitale (Or), the most inferior point on the lower border of the orbit (image 1). The orbits are bilateral structures, and if you can see both sides separately, trace both and locate point Or halfway between the two sides. Also trace the shadow of the inferior alveolar canal and the crown of the unerupted third molar if present (image 2). These structures are especially useful as stable areas for superimposition.

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{{PAGE_70}} Tracing the orbital rim to locate point Or. Don’t confuse the dotted line behind the orbit with the orbital rim—a common tracing mistake. Tracing the outline of the neurovascular bundle below where it enters the lower part of the ramus, and the outline of a third molar at the stage of crown formation.

Adding the Incisor Teeth

At this point, you’re ready to trace the teeth. It’s important to locate accurately:

• the facial surface of the crowns of the upper and lower incisors
• the inclination of the roots of the incisors
• the position of the upper and lower first molars.

Templates that represent the typical dimensions of these teeth can make tracing them easier. If you are tracing by hand, you can use a tooth template which helps you draw teeth that are a uniform but consistent size. If tracing with a computer program, the program has a digital template you can use to trace the shapes of the incisors and molars (it requires the additional points shown in this figure). Remember that the templates are only guides, and if your patient’s teeth differ significantly from the templates, try to trace the real thing.

To trace the upper and lower central incisors:

• Orient your tooth template to accurately represent the axial inclination of the incisor and the position of the tooth’s facial surface. Then use the template to draw in the outline of the incisors.

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{{PAGE_71}} Adding the Molars and Occlusal Plane

Because the molars are bilateral structures, often two partially superimposed images can be seen. By convention we trace the tooth on the left side, the side closest to the film when the radiograph was taken.

This means that the tooth you want to trace is the one of a nearly-superimposed pair that is slightly above and behind the image of the other side. To place the first molar template accurately, it can help to first trace the sides of the second molar.

To complete the teeth, it is not necessary to trace all the other teeth, but it is important to outline the occlusal plane of the cheek teeth (2nd molar to 1st premolar). To do this digitally, a point on the crown of the first premolar can be added to orient a line across the crown of the first molar.

{{PAGE_72}} Completing the Tracing: Soft Tissue Profile To complete the tracing, add the outline of the soft tissue profile, from the bridge of the nose to the chin. Your completed tracing should look like the image here.

At this point, it’s ready to use, either by adding reference lines (which already has been done with the tracing shown here), making measurements, or superimposing it on another tracing.

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{{PAGE_73}} Digitization Rather Than Tracing

Let’s think about what would be different if you were sitting at the computer, as you almost surely will be in your professional future, rather than tracing at a light box.

What would be different if you digitized a digital ceph, instead of tracing a film image? Basically, you’d have to have more points so that the lines you would have traced can added by the computer software.

A minimal digital model (image 1) would ask you to add to the landmarks we’ve identified so far:

• points along the cranial base
• points to mark the posterior maxilla instead of just the orbital rim
• a point at the mandibular condyle and another where the shadow of the zygomatic arch crosses the upper mandibular ramus
• a series of points along the curvatures of the soft tissue profile
• additional points to define the incisor positions instead of just the tips
• points to mark the mesial and distal contact points of the molars.

It would be easier to do that if you had some experience doing ceph tracings—which is one of the reasons we’re doing a little tracing within these modules. More precise digital models would require more points, so to get something that was close to a traced image, you’d have to add additional points as shown in image 2—but if you add the extra points and the the computer program connects them,

{{PAGE_74}} you do get a reasonable representation of a rather complete tracing. This is what you’ll see most of the time in the future.

Cephalometric Analysis

Measurement Analysis

The objective of cephalometric analysis is to establish the relationship of the facial units in the antero-posterior and vertical planes of space. Cephalometric analysis is done by drawing reference lines on the tracing or digital model, to make relationships more visible. Then data are obtained for comparing an individual patient to a reference group, by measuring angles between reference lines, and by measuring distances between landmarks.

Remember, your objective is to define the relationships of the major elements of the head and face. Specifically, you want to know if the relationships, in the a-p and vertical planes of space, are normal or not, and if they’re abnormal, exactly what’s wrong.

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{{PAGE_75}} Vertical Proportions The first step in analysis is to examine vertical proportions. Start by drawing five horizontal reference lines:

1. S-N, the inclination of the anterior cranial base.
2. True horizontal, the visual axis, which is drawn perpendicular to true vertical (the chain) through the lower border of the orbit (Or).
3. ANS-PNS, the palatal plane.
4. Functional occlusal plane, drawn along the occluding surfaces of the posterior teeth.
5. Go-Gn, the mandibular plane.

In a well-proportioned face, the horizontal planes project posteriorly toward an approximate common meeting point, as shown in this image.

{{PAGE_76}} Vertical Proportions (cont.)

For the patient we have been tracing (image 1), the palatal plane is tilted down posteriorly and meets the occlusal and mandibular planes at a common point relatively close to the back of the jaws, and the SN plane is tilted up anteriorly. This amount of variation would have to be kept in mind as the relationships of the functional components were considered, but it is within normal limits.

Sometimes one or both of the jaws are rotated, or the teeth have not erupted properly. This shows up clearly because then one or more of the planes projects differently from normal. The patient seen in image 2 obviously has a mandible that is rotated down and back, creating a long face and an open bite. Just looking at the orientation of these horizontal planes gives excellent insight into vertical proportions.

If you needed to be more precise, you could measure angles (for instance, the angle between S-N and Go-Gn) or linear distances (Na-Me, the anterior face height) and check them against the norms for your patient’s group.

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{{PAGE_77}} Image 1: For this patient, angular measurements relative to SN would have to be adjusted because of its inclination to the true horizontal line. Often it is more important to look carefully at the ceph than to depend on measurements to determine relationships of the functional components.

Image 2: Note that the mandibular plane is very steep and projects well forward of the other planes. The downward-backward rotation of the mandible is obvious, and is the major cause of the anterior open bite.

Antero-Posterior Jaw Relationships

The second step in analysis is to evaluate the a-p relationships of the jaws. An excellent way to do this is to draw a true vertical line that extends downward from nasion, and examine the position of points A and B relative to this.

In a normally proportioned face, point A is on or slightly in front of this line; point B is slightly but not very far behind it. More precisely, point A should be about 2 mm in front of the Nasion vertical line, with a range of 0-4 mm. Point B should be about 2 mm behind it, with a range of -4 to zero. But the difference between the vertical lines through points A and B should not be more than 4 mm, otherwise the teeth can’t occlude properly.

For this patient, both jaws are a bit more forward from the cranium than in most individuals, so points A and B are forward from the usual position—but the jaws are positioned closely enough together than normal occlusion is quite possible. The relationships of the jaws to the cranium in this patient would be an example of normal variation.

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Antero-Posterior Jaw Relationships (cont.)

In a patient with an antero-posterior displacement of one or both jaws, it will be apparent that the maxilla and/or mandible are not well related to the cranial structures.

Both of the patients seen in images 1 and 2 have the maxilla in a reasonable position relative to the true vertical line dropped from nasion, but there is a large discrepancy in the size and position of the mandible. It’s obvious that the patient in image 1 has a skeletal Class III problem that is due almost completely to a large mandible. The one in image 2 has a skeletal Class II problem that is due to mandibular deficiency.

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{{PAGE_79}} Image 1: Skeletal Class III due mostly to a very large mandible. Image 2: Skeletal Class II due mostly to a small mandible, with protrusion of mandibular incisors.

A-P Jaw Relationships: Measurements

There are other measurements that you could make to estimate a-p jaw relationships.

For instance, you could draw the NA and NB lines (image 1), and measure the angle between them (ANB) to judge how great the difference in jaw position was.

And you could measure the SNA and SNB angles to estimate whether the maxilla or mandible was in the wrong position (image 2).

Standards for these and many other measurements have been published and are readily available.

But remember, these measurements are estimates of the vertical and a-p jaw relationships we’re ultimately interested in. The goal of cephalometric analysis is to accurately describe the facial and dental relationships, not to measure some specific characteristic.

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{{PAGE_80}} Image 1: The ANB angle is an estimator of the a-p relationship of the jaws. It is quite small in patients with normal jaw relationships, like this one. Image 2: The SNA and SNB angles indicate the degree of protrusion of the jaws relative to the cranial base, but they must be used carefully because the reference standards assume a normal inclination of SN, and we have seen already that this is not always correct.

A-P Relationship of Teeth to Jaw

The third step in analysis is to examine the a-p relationship of the upper teeth to the maxilla and lower teeth to the mandible.

Let’s consider the maxlla first. The question is, do the upper teeth protrude relative to the maxilla, is their a-p position within normal limits, or are they too far back?

A good way to answer that is to move the true vertical line so that it runs through point A, and examine the position of the upper incisor to the line. The incisor should be slightly but not very much ahead of the line, as it is in the patient shown here—so the a-p position of the upper incisors is normal.

A-P Relationship of Teeth to Jaw (cont.)

In the patient shown here, when the upper incisor position is compared to the position of point A, it becomes obvious that the upper teeth are a little forward from the maxilla. This individual’s overjet is due largely to a deficient mandible (note where point B is), but some protrusion of the maxillary teeth relative to the maxilla contributes to it.

In the same way, we can examine the position of the lower teeth relative to the mandible, by moving the true vertical line through point B and looking at how the incisor teeth relate to it. The guideline is

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{{PAGE_81}} the same: the lower incisors should be slightly but not very far in front of the line. More precisely, the lower incisors should be about 2 mm in front of point B, with a range of 1-5 mm. The prominence of the chin is a factor in how much lower incisor protrusion is appropriate. The position of Pg can be noted relative to the line through point B. The lower incisor can be 2 mm more forward than Pg, but not a lot more than that, and should not be a great deal more prominent than the chin. Note that this patient has a lot of protrusion of the lower incisors relative to the mandible—which is why his overjet is smaller than the discrepancy between maxilla and mandible.

Incisor Angulation and Vertical Position

There are a number of other measurements you might make, to establish more precisely how the incisors are angulated and positioned vertically.

Incisor angulation usually is measured relative to the S-N line (cranial base plane) for the maxillary incisors, and relative to the Go-Gn line (mandibular plane) for the lower incisors (image 1). Remember, though, that an angle that is larger or smaller than the ideal could be due to the inclination of the S-N or Go-Gn line, so if one of the reference lines is tipped, you might not want to judge incisor inclination from this angle. You could see inclination of the cranial base or mandibular planes by drawing the lines as illustrated in the previous screens. If you want to measure, the S-N line should be about 6° up relative to the true horizontal line.

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{{PAGE_82}} You also might note some excess overbite (image 2) (you can see that on a ceph, but of course it’s also obvious clinically), and suspect that the incisors have erupted more or less than they should have. One way to check that would be to measure how far the maxillary incisor root apices are from the palatal plane, or the how far the mandibular incisors root apices are from the mandibular plane (image 3). The normal distances are part of the data available for comparison.

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Image 1: Evaluating maxillary incisor inclination from the angle between the upper incisors and SN, and mandibular incisor inclination from the angle between the incisors and the mandibular plane (Go-Gn) will be accurate only if the reference lines (SN, Go-Gn) are normally inclined.

Image 2: Overbite can be measured on a ceph, but that doesn’t tell you the underlying cause of excess overbite.

Image 3: One way to judge whether maxillary or mandibular incisors have erupted too much or too little is to measure the

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{{PAGE_84}} distance from the root apices to the palatal or mandibular planes and compare this to the normative values.

Cephalometric Analysis: Summary

This combination of inspection of relationships seen on a ceph tracing or digital model, and measurements to confirm discrepancies from the normal, is a simplified approach to cephalometric analysis.

Perhaps one way to look at it is that the more your patient differs from the norm, the more measurements you might have to make to determine exactly what the discrepancies really are. Cephalometric analysis shouldn’t become a “numbers game”, with a standard set of measurements for every patient. The objective, as we have emphasized, is to determine the relationships between the components of the face. The analysis succeeds or fails depending on how well it defines those relationships.

Referral to Self-Test

Before you go to the self-test, be sure you read the material in Contemporary Orthodontics: pages 184-199 in the 5th edition, and 202-218 in the 4th edition. Then use the self-test to be sure you have understood the basics of cephalometric analysis.

{{PAGE_85}} 3. Cephalometric Superimposition

Purpose of Cephalometric Superimposition

Learning Objectives This program describes and demonstrates methods of cephalometric superimposition. The learning objectives are to:

• Understand the purpose of cephalometric superimpositions
• Learn the method for overall (cranial base) superimpositions
• Learn the method for regional superimpositions on the maxilla and mandible
• Gain experience in the interpretation of cephalometric superimpositions

After viewing this program, you should be able to:

• Superimpose cephalograms of the same patient from two time points
• Assess changes in dental and jaw relationships as well as soft tissue changes in profile
• Determine whether changes in dental relationships are due to jaw growth, tooth movement, or both

Cephalometric Superimposition Technique Cephalometric superimposition is the technique of overlaying a ceph tracing from one time point on another tracing from a ceph of the same individual at a different time point.

The purpose of ceph superimposition is to evaluate changes in jaw and tooth relationships in the same individual between different points in time, and to determine whether these changes occurred as a consequence of growth, dental maturation, or orthodontic tooth movement. Changes from orthognathic surgery also are evaluated in this way.

One strategy to make these comparisons is to take angular and linear measurements from a ceph at one time point and compare them to the measurements from another ceph at a later time. This strategy can be quite laborious. It would give some idea of the changes, but it is often difficult to visualize the changes that numbers represent and hard to differentiate between the skeletal and dental changes.

A better strategy is to compare tracings by overlaying them. This technique reduces the amount of information to a manageable level and provides a visual overview of the changes that occurred between two time points.

{{PAGE_86}} Cephalometric Superimposition Technique (cont’d) Cephalometric tracings are overlaid on defined anatomic landmarks that serve as registration points or lines. When tracings are superimposed, all changes are shown relative to the registration point(s) or lines. This view may or may not accurately reflect what you know from other sources of information about the patient, and the interpretation of any given superimposition must always be reconciled with clinical findings or clinical history.

{{PAGE_87}} Regional Superimpositions

Ceph tracings are commonly superimposed on three regions:

1. Cranial base
2. Maxilla
3. Mandible

Your finished superimpositions, done on tracing paper, will look similar to these. As you can see, in each one different anatomical features are precisely overlapped, or superimposed.

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{{PAGE_88}} Cephalometric Superimposition: View of Changes

In the cranial base superimposition, changes in the jaws and face relative to the cranial base are demonstrated. Because cranial base growth follows the neural growth curve and is completed by age 7, cranial base superimposition for orthodontic patients (who are older than 7 when treated) reveals changes in facial hard and soft tissues relative to a stable reference area. This superimposition compares cephs just before and after the adolescent growth spurt, which affects the facial structures but not the cranial base. Note the downward and somewhat forward growth of the face in this individual.

Cephalometric Superimposition: View of Changes (cont’d)

In the maxillary superimposition, the skeletal changes are canceled out and only dental changes relative to the maxilla are demonstrated. Note that for this individual (the same as on the previous screen), there was a little uprighting of the central incisors relative to their supporting bone, and a little mesial movement of the upper first molar. You’d expect to see that mesial movement at the time the second primary molars were lost. The mandibular superimposition is a little trickier than the maxillary one. It’s done anteriorly on the lingual outline of the symphysis and posteriorly on the canal that contains the mandibular neurovascular bundle, for reasons that we’ll explore in detail later in this module. Note that relative to the supporting bone, the mandibular teeth moved mesially and erupted slightly, while the ramus grew longer. The dental changes seen in these regional superimpositions are due to a combination of tooth eruption and (in treated patients) orthodontic tooth movement.

{{PAGE_89}} Cranial Base Superimposition

Technique To understand the technique, you will complete 3 superimposition tracings while using this program. Before proceeding, you will need to gather the following supplies, as shown in this image:

• sharp black and red pencils
• a sheet of acetate tracing paper, from a tablet such as “ortho/trace”. Remember that the tissue paper between the acetate pages functions only to separate the acetate and may be discarded.
• the original tracing from your patient’s initial ceph, time point 1 (which is done with green lines)
• the original tracing from your patient’s final ceph, time point 2 (blue lines)
• masking tape

For the rest of this program, these will be called the “initial tracing” (i.e., time point 1) and the “final tracing” (i.e., time point 2).

The two tracings you will work with are for the same patient before and after orthodontic treatment during the adolescent growth spurt. So the changes you’ll see with the cranial base superimposition will be due to a combination of growth and effects of treatment.

The time interval between initial and final tracings will depend on the patient’s problem and the nature of the information you are looking for.

Evaluating growth changes may require a year or longer. In contrast, a few months may be all that is necessary to visualize changes due to treatment.

Level II Diagnosis — Unit B · 89 / 204

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Technique (cont’d)

Begin by taping the initial tracing (green) to a smooth surface. Then place the final tracing (blue) over it, and superimpose the blue tracing over the green one at sella (S). Then rotate the blue tracing until it is oriented with the S-N line over the green S-N line. At that point it should look like what you see in this image.

This registration on the sella-nasion line registered at sella is a simple and reasonably accurate method to superimpose on the anterior cranial base.

Because the area around S is unaffected by growth after age 7, it makes an ideal registration point. Nasion can move forward relative to sella because of growth, but the inclination of the S-N line also is reasonably constant.

{{PAGE_91}} Cranial Base Superimposition Tracing The first step in producing a cranial base superimposition tracing is to tape a clean sheet of acetate tracing paper over your superimposed tracings. Make sure the shiny side of the acetate tracing paper faces down and that you trace on the dull side.

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{{PAGE_92}} Cranial Base Superimposition Tracing (cont.) Using your black pencil (image 1), retrace the initial tracing (green lines) onto the clean acetate paper, including the soft tissue profile. Include the sella-nasion (S-N) line on the new tracing (image 2).

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{{PAGE_93}} Cranial Base Superimposition Tracing (cont.)

Now, on the same acetate sheet with the copied initial tracing (black lines), retrace the hard and soft tissues of the final tracing, in red, wherever they are different. You don’t need to trace the cranial base in red, because the black and red are superimposed and the red line wouldn’t show anyway.

{{PAGE_94}} Cranial Base Superimposition Tracing (cont.)

You should now have an overall composite tracing with black and red lines superimposed on the anterior cranial base registered at sella. The black lines represent the first time point, and the red lines represent the second time point.

Before proceeding to the next screen, take the time to examine the overall skeletal and soft tissue growth in your patient, both in magnitude and in direction.

{{PAGE_95}} Regional Superimpositions: Maxillary and Mandibular

Maxillary Superimposition Next, let’s do the maxillary superimposition. Superimposition on the maxilla helps you visualize how the maxillary incisors and molars changed position between the two tracings. To do this, remove your new composite tracing, untape the blue tracing and superimpose it on the lingual contour of the palate behind the upper incisors, then rotate it so that the palatal plane is level (image 1), and again tape it so it can’t move (image 2). Note that the teeth aren’t superimposed. The objective here is to visualize any changes in the position of the teeth relative to the maxilla. Then place your composite tracing over the superimposed tracings, with a blank area over the maxilla superimposition, and tape it into position.

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Maxillary Superimposition Tracing

Now, using your black pencil, retrace the maxillary outline and teeth from the new composite tracing onto your copy of the maxilla from the initial tracing (images 1,2). Also trace any changes in the maxillary contour if there are noticeable differences (there probably won’t be).

Then trace in red any areas where the green and blue lines around the maxilla are different (image 3).

You now have the maxillary superimposition tracing (image 4). By inspecting where the incisors and molars started (black tracing) and where they ended up (red tracing), you can visualize how these teeth changed their position and/or angulation relative to the maxilla during the time interval between the two tracings.

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{{PAGE_97}} Image 1 Image 2 Image 3 Image 4

Mandibular Superimposition

The last superimposition tracing you will make is the mandibular superimposition. Superimposition on the mandible helps you see how the mandibular incisors and molars changed position and/or angulation between the two tracings.

In the mandibular superimposition, the tracings are registered as shown here: along the inner aspect of the mandibular symphysis, the unerupted third molar crypt, and the inferior alveolar nerve canal. Studies of children who had metallic implants placed in their jaws have demonstrated that these anatomic landmarks don’t change as the mandible grows.

The mandibular superimposition tracing demonstrates changes in the mandibular dentition relative to stable mandibular points.

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{{PAGE_98}} Mandibular Superimposition Tracing

The mandibular superimposition is accomplished in much the same manner as the maxillary superimposition. Place the initial tracing (green lines) on the viewbox. Place the final tracing (blue lines), positioning it so that lingual outline of the symphysis superimposes on that area of the initial tracing, then rotate it to also superimpose on the mandibular canal and unerupted third molar, and tape it into position. Take the acetate paper on which you have now traced cranial base and maxillary superimpositions and tape it over the original tracing so that the clean area of the page on the bottom left portion is placed over the mandibular area of the superimposed tracings. Using a black pencil (image 1), retrace the mandibular anatomy of the initial tracing, including the incisor and first molar (or second primary molar if no permanent teeth are present) (image 2).

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{{PAGE_99}} Mandibular Superimposition Tracing (cont.)

Now, using your red pencil (image 1), trace the teeth and areas of the mandibular outline onto the composite tracing. Remember, do not try to make the teeth coincide.

You now have a mandibular superimposition tracing which demonstrates mandibular dental changes, relative to the mandible itself (image 2). By comparing where the mandibular incisors and molars started (in black) to where they ended up (in red), you can see how they changed position relative to the basal bone of the mandible.

You also can see the amount of growth at the condyle and the remodeling of the mandible in the gonial angle area as it grows (note the resorption of bone at the angle even though the ramus grew longer).

Interpretation of Superimpositions

The Standard Superimpositions for Orthodontic Applications

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{{PAGE_100}} You now have produced a series of superimposition tracings for this patient, which should resemble the superimposition set shown here.

The cranial base superimposition reveals skeletal and soft tissue profile changes relative to the stable cranial base (image 1).

The maxillary superimposition demonstrates changes of the maxillary dentition relative to the palate (image 2).

The mandibular superimposition illustrates mandibular dentition changes and changes in the shape of the mandible relative to the stable mandibular landmarks that are not on the surface of the bone (image 3).

Interpretation of Cranial Base Superimposition, Patient #1

Let’s use these superimpositions to evaluate what happened in this patient. His Class II malocclusion was treated with extra-oral force (headgear) to restrain growth of the maxilla, and with a fixed appliance with brackets on the upper incisors to close the “gaps” (as he called them) between those teeth. Changes due to growth and treatment can be seen.

From the cranial base superimposition, it is apparent that the maxilla grew downward only and the upper lip became less prominent, while the mandible grew downward and forward.

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{{PAGE_101}} This skeletal change was due to headgear wear that minimized forward growth of the maxilla. The mandible, which was not affected by the extraoral force to the maxilla, grew forward as well as downward, improving the jaw relationship—which was very favorable in this patient.

Interpretation of Max / Mand Superimpositions, Patient #1 In the same patient, the maxillary superimposition (image 1) illustrates that the maxillary anterior teeth were retracted, while the maxillary posterior teeth remained in nearly the same place in the a-p plane of space. The maxillary molar moved down as the maxilla grew downward (which you saw in the cranial base superimposition), but now you can see in the maxillary superimposition that the molar also erupted downward relative to the maxilla, perhaps a bit more than ideal. How would you know this eruption was unfavorable? Look back at the cranial base superimposition and note that the mandibular plane angle increased a little, which is undesirable in a Class II patient because it takes away some of the effect of the forward growth. The mandibular superimposition (image 2) demonstrates that the lower molars were maintained in the same anteroposterior relationship within the mandible, so the improvement in molar relationship for this patient was due almost totally to favorable growth rather than forward movement of the lower teeth relative to the mandible. Note the amount of mandibular growth at the condyle. A small amount of uprighting of the lower incisors is also evident. There was only a little eruption of the lower molar relative to the mandible.

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{{PAGE_102}} Superimpositions, Pt #1

Combining the findings from these 3 superimpositions, one concludes that the correction from Class II to Class I molars was accomplished largely by maintaining the A-P position of the maxilla and upper teeth with the headgear while forward growth of the mandible occurred.

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{{PAGE_103}} Interpretation of Superimpositions, Pt. #2 Let’s look at the changes in this patient during late adolescence. From this cranial base superimposition, how would you describe her? I hope you now would say “long face Class III” at a glance.

For a patient like this, the timing of surgery to reposition the jaws is determined primarily from superimpositions like this. The closer the superimposition in areas that are not registered, the less change has occurred. That would indicate that growth has stopped or almost stopped, and that it would be safe to go ahead with the surgery. If surgery is done too soon, further growth in the Class III pattern would cause the lower jaw to again be in front of the upper jaw.

Do you think this patient is ready for surgery? The black lines are the progress radiograph, the green lines the previous year. It certainly looks as if there has been very little change during the year, with a bit of change in tooth positions related to the orthodontics she’s undergoing to get her ready for surgery. This small amount of change would support going ahead with the surgical phase of treatment.

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{{PAGE_104}} Interpretation of Superimpositions, Patient #2 (cont.)

In the maxillary superimposition for this patient, you can see more clearly that the maxillary molar actually was intruded relative to the maxilla, which is a reflection of orthodontic treatment in preparation for the surgery. The upper incisor moved forward a little.

The mandibular superimposition shows that the lower incisors also were intruded during the orthodontic treatment. The changes in tooth position in both arches were created by treatment to level out the arches.

It won’t matter whether you go into orthodontics or surgery in the future—you’re going to have a Class III patient who is a candidate for orthognathic surgery, and somebody will be showing you superimpositions like this as evidence that it is, or isn’t, time to proceed with surgery. Learning how to intepret superimpositions is an important tool for your professional future.

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{{PAGE_105}} Superimposing Digital Cephalograms

Superimposition of Digital Cephs: Overview Digital radiographs are rapidly becoming the norm. Lateral cephs obtained in digital format can be digitized to create a digital model, then superimposed using the same principles of landmark identification and superimposition as hand-traced cephalograms. Imaging software (e.g., Dolphin Imaging [tm]) has been developed with the capability of “tracing” and superimposing cephalograms. The ceph “tracing” shown here was created in Dolphin from the series of digitized landmarks.

{{PAGE_106}} Digital Cephalograms: Superimpositions, Patient #3 The software also permits you to superimpose cephalograms from different time points after you’ve digitally traced them. Cranial base and regional superimpositions are registered in the same way, but now you only have to tell the software to do it. You must select the registration lines or points, and the program superimposes and displays a digital image of the superimposed tracings for you to interpret.

Interpretation proceeds in the same manner as with hand-traced cephs; that is, you must examine and infer whether changes you see are due to skeletal growth, dental maturation, and/or orthodontic tooth movement.

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{{PAGE_107}} Cephalometric superimposition has two overlapping purposes:

1. to evaluate changes over time in untreated individuals as they grow (which was the original goal)
2. to evaluate changes during orthodontic treatment, so that the response to treatment procedures can be evaluated more accurately (which is now the major reason for obtaining cephs before, during and after treatment)

All change is relative to some reference. Three references are used routinely in cephalometric superimposition:

1. cranial base: to demonstrate growth of the face and jaws, and any growth modification induced by treatment, relative to cranial base structures that are not growing during the time period of greatest interest clinically (>7 years)
2. maxilla: to demonstrate movement of maxillary teeth relative to the maxilla
3. mandible: to demonstrate movement of mandibular teeth relative to the mandible, and also growth changes in the ramus (both remodeling and condylar growth)

Measurements of the amount of change between two time points often are used in research, but in some contrast to analysis of individual cephs, clinical interpretation is done almost totally from observation of superimpositions. Humans are, after all, walking analog computers, and even when

{{PAGE_108}} digital records are routinely obtained, a digital-to-analog conversion is required if the changes are to be understood.

Referral to Self-Test Before going to the self-test, it’s a good idea to review some of the material on cephalometrics that you have previously studied in Contemporary Orthodontics. Then use the self-test to demonstrate to yourself that you have understood how regional superimpositions can provide important clinical information on how growth and treatment are interacting.

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4. Space Analysis and Its Interpretation

Space Analysis Introduction

Learning Objectives

This program provides:

• An overview of mixed dentition space analysis, reviewing the possible ways to estimate the size of unerupted teeth and to judge the amount of space available
• A review of the assumptions about growth and development on which space analysis is based
• A detailed examination of the steps in carrying out the space analysis procedure
• A test of your ability to interpret the results of space analysis.

Space Analysis

One of the questions you will face when assessing a mixed dentition patient, like the one whose dental alignment is seen in these photos, is whether there will be adequate space for the succedaneous teeth.

To answer the question, you must measure the space within the arches after the permanent incisors and first molars have erupted and compare it to the space required to align the as yet unerupted permanent teeth.

Because the permanent teeth have not all erupted, their size must be estimated. Space analysis usually is done early in the mixed dentition, because this is when parents first notice crowding of the erupting permanent incisors.

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{{PAGE_110}} Available versus Required Space

The critical determination of a space analysis in the mixed dentition is to compare the space available in the dental arches to the space required for the eruption and alignment of the permanent teeth.

{{PAGE_111}} Space Available

The amount of space available is defined as the distance around the arch circumference from the mesial of one permanent first molar to the mesial of the other permanent first molar. It is measured as a series of straight-line segments, as shown here. Two lateral segments, from the mesial of the first molar to a point on the alveolar process in the canine region, and two anterior segments, from the canine region point to the midline, are used.

Note that the canine region and midline points are on the alveolar process, not the teeth.

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{{PAGE_112}} Space Required The space required is the sum of the width of the incisors that have erupted plus the width of the canines and premolars that have not erupted.

The incisor widths are measured directly on the dental casts. Prediction of the space required for the unerupted permanent teeth (canine and premolars) can be accomplished in three basic ways:

1. Measurement of the unerupted teeth on radiographs
2. Estimation of the width of the unerupted teeth from a correlation with the width of the erupted lower incisors
3. A combination of measurement on radiographs and correlation statistics

Radiographic Prediction Accurate measurement of teeth on periapical radiographs requires undistorted images, and these can be difficult to obtain, especially on children in the mixed dentition due to their smaller mouths and cooperation problems.

Individual periapical radiographs usually are needed, because panoramic radiographs tend to non-uniformly distort the images of the teeth.

Even with individual images, it is often difficult to obtain an undistorted view of the canines (especially the lower ones), and this inevitably reduces the accuracy.

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{{PAGE_113}} Radiographic Prediction (cont.) With any type of radiograph, it is necessary to compensate for enlargement of the radiographic image. This is done by measuring the same object (such as a primary second molar) in the radiograph and on the cast. The difference in the size of the images gives the percentage of magnification, which is used to correct the magnification of the unerupted permanent teeth.

A simple proportional relationship can be set up: True width of primary molar / Apparent width of primary molar = True width of unerupted premolar / Apparent width of unerupted premolar.

Accuracy is fair to good with this method of measuring radiographs, depending on the quality of the radiographs and the position of the teeth in the arch.

The advantages are that it can be used in maxillary and mandibular arches for all ethnic groups. The disadvantages are the additional radiation required, questionable accuracy in some instances and potential behavior problems with young children.

{{PAGE_114}} Moyers Prediction: Proportionality Tables

The second method to determine the size of the unerupted permanent teeth uses estimations from proportionality tables. There is a reasonably good correlation between the size of the erupted permanent LOWER incisors and the unerupted canines and premolars in both dental arches. To utilize the Moyers method, the mesiodistal width of the lower incisors is measured, and this number is used along with the table below to predict the size of BOTH the lower and upper unerupted canines and premolars.

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Moyers Prediction Values

mm, 75% Level

Total Mandibular Incisor Width	Predicted Width Maxillary Canines/Premolars	Predicted Width Mandibular Canines/Premolars
20.0	20.9	20.4
21.0	21.3	21.0
22.0	22.0	21.6
23.0	22.6	22.2
24.0	23.1	22.8
25.0	23.7	23.4
26.0	24.2	24.0
27.0	24.8	24.6
28.0	25.3	25.1
20.0	25.9	25.7

Tanaka-Johnston Prediction: Proportionality Formulas

Tanaka and Johnston developed another way to use the width of the lower incisors to predict the size of unerupted canines and premolars. The Tanaka-Johnston method has good accuracy, despite a small bias toward overestimating the unerupted tooth sizes.

It requires neither radiographs nor reference tables, which makes it very convenient. This is essentially another proportionality table method, but it has been greatly simplified so that no table is necessary—just two simple formulas that are easy to recall or that can be printed right on the analysis form.

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{{PAGE_116}} Hixon-Oldfather Prediction: Combination Method The third method is a combination of radiographic and proportionality table methods.

The major problem with using radiographic images is obtaining a good canine view. The size of permanent incisors measured from the dental casts and the size of unerupted premolars measured from periapical radiographs can be used together to predict the size of the unerupted canines.

This approach was developed by Hixon and Oldfather and revised and improved by Staley and Kerber. Their graph allows canine and premolar widths to be read directly from the sum of lower incisor widths on the cast and premolar widths on the radiographs.

Even though this method is quite accurate in its predictions for Caucasian children of northern European descent, because that was the group used to derive the prediction tables, the accuracy is somewhat questionable for children of African or Asian descent. Two other significant shortcomings: it can be used only for the mandibular arch and requires periapical radiographs.

Tanaka & Johnston Prediction Method

• Measure the width of each of the four lower incisors, add up the total, and divide by two Example: 5 + 4.5 + 4.5 + 4.5 = 18.5 / 2 = 9.25
• To estimate the size of the unerupted mandibular canine and premolars on each side, add 10.5 mm Example: 9.25 + 10.5 = 19.75 mm each side
• To estimate the size of the unerupted maxillary canine and premolars on each side, add 11.0 mm Example: 9.25 + 11.0 = 20.25 mm each side

Tanaka-Johnston Advantages For general clinical use, the most practical approach to space analysis is the Tanaka and Johnston method because it:

• requires no radiographs
• requires no lengthy prediction tables, graphs or equations

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• can be used for both arches
• is reasonably predictable (good correlation)

The method was derived using a sample of Caucasian children, which must be considered when using the technique in children of different ethnicities.

Assumptions

Tanaka-Johnston Assumptions: Tooth Size Correlation

When doing a mixed dentition space analysis, you must keep the assumptions in mind that underlie the procedure. Consider the assumptions that go with the use of the Tanaka-Johnston method.

The first assumption is that there is a correlation between the size of the erupted mandibular incisors and the size of the remaining unerupted maxillary and mandibular canines and premolars.

A significant correlation has been demonstrated by numerous researchers, but there are individual variations in the size of teeth. Maxillary lateral incisors and mandibular second premolars are the most variable teeth (except third molars, which do not figure in space analysis). If these teeth are obviously large or small, the correlations will be incorrect.

Tanaka and Johnston Assumptions: Caucasian Population

A second assumption is that your patient fits the population that was used to derive the prediction tables or formula. Because tooth size and morphology are distinct racial and ethnic traits, this must be taken into account for accurate prediction in any successful space analysis.

The prediction values used for the method advocated in this program were derived from a sample of children of northern European descent. You must decide if your patient is a member of the same population group. The prediction formulas are not nearly as accurate for other populations.

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Patient from Different Population

If your patient does not fit the population to which the prediction formulas apply, you can use one of three strategies:

1. complete the space analysis recognizing these limitations, and use great care when interpreting your results.
2. use a different prediction table or formula that is specific for your patient’s racial group, if such a table exists; or
3. use the individualized radiographic technique described earlier. Use of multiple periapical radiographs is not justified in all cases, but may be appropriate for these selected patients.

{{PAGE_119}} Tanaka-Johnston Assumptions: Normal Development A third assumption about space required is that all succedaneous teeth are developing normally (image 1). This may be difficult to ascertain in some early mixed dentition children, since the premolars are often late in forming and not visible on radiographs. It makes no sense to assume normal-sized teeth if the presence of all the teeth is not assured, or if there are obvious anomalies in tooth size (image 2) when the radiographs are examined.

Image 1: Panoramic radiograph showing missing mandibular second premolars in the mixed dentition—obviously, space analysis must take this into consideration. Image 2: Maxillary peg lateral incisors, which will affect the amount of space available in the maxillary arch. The variability of maxillary laterals is why only lower incisor widths are used in the prediction formulas.

General Assumptions: Space Available Level II Diagnosis — Unit B · 119 / 204

{{PAGE_120}} There are also some important assumptions about the amount of space available. Obviously, space analysis only works if space available can be predicted accurately.

Space analysis assumes that arch dimensions DO NOT increase during growth. Of course, the maxilla and mandible grow and increase in size, but this growth occurs in areas away from the dentition (for example, distal to the first molar), so that little extra space for the teeth is created. For normal growth and development, this is a valid assumption.

General Assumptions: Stable Position of Incisors

Another important assumption is that the position of the incisors will not change in a way that increases or decreases arch circumference and available space.

In fact, after the eruption of the lateral incisors, little increase in arch circumference can be expected and incisor stability can be assumed—but only in children with a Class I growth pattern, so assessment of space available is less accurate in Class II and Class III children.

In a child with a Class II growth pattern, the lower incisors tend to tip facially, increasing space in the lower arch, while the upper incisors may move either facially or lingually; in a Class III growth pattern, the lower incisors are likely to tip lingually, decreasing space in the lower arch, while the upper incisors often tip facially, increasing space in the upper arch.

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Transition of Molar Relationships

Because the primary molars are larger than the premolars that replace them (image 1), the position of the permanent first molars can be expected to change when the primary second molars are lost. The space analysis procedure assumes that the mesial shift of the first molars can be predicted accurately, at least in a child with a Class I skeletal pattern.

Even in skeletal Class I children, an end-to-end molar relationship is likely to be present during the mixed dentition, and molar shift occurs in these children when the primary molars are lost, so a correction for molar shift is necessary in space analysis. The different pattern of molar shift in children with skeletal Class II or Class III growth patterns is another reason for restricting space analysis to skeletal Class I children (image 2).

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Image 1: Size relationships of primary molars and the premolars that replace them.

Image 2: Effect of forward movement of molars in the transition of molar relationships from the mixed to the permanent dentition.

Procedures - Steps Involved

Dental Casts for Space Analysis

Let’s go over the steps in carrying out mixed dentition space analysis. A number of materials are required.

First, accurate study casts are required of a patient in the mixed dentition whose maxillary and mandibular permanent first molars, and maxillary and mandibular central and lateral incisors, all have erupted (images 1 and 2).

Occasionally, a space analysis is completed on only the mandibular arch, before it’s possible to do it for the maxillary arch, to begin preliminary planning prior to eruption of the maxillary incisors. If such a preliminary analysis is accomplished, it should be repeated when the maxillary lateral incisors erupt to provide a definitive result.

All study casts should be carefully trimmed to establish correct occlusal relationships. The accuracy of your analysis will depend upon the accuracy of your study casts. These relationships must be checked against the results of the clinical exam.

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Measuring Instrument equipment

Second, you will need some type of measuring device. Measurements can best be made with a Boley gauge.

The beaks of the Boley gauge should be sharpened, as illustrated here, to permit better access to the interproximal areas. Measurements must be made to the nearest tenth of a millimeter, so accurate instruments are imperative.

Steps in Space Analysis (cont.) Level II Diagnosis — Unit B · 123 / 204

{{PAGE_124}} This is the space analysis form you will use. When measurements are made and information is collected, it will be entered on this form.

As a guide to completing the space analysis and its interpretations, we will follow the space analysis form in a section-by-section manner.

Space Analysis Form, Section 1

Section 1 on the space analysis form is a determination of the available mandibular arch length. This is calculated by measuring the continuous arch length over the contacts of the mandibular teeth between the mesial of the permanent first molar on the right, and the mesial of the permanent first molar on the left.

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UNIVERSITY OF NORTH CAROLINA AT CHAPEL HILL

SCHOOL OF DENTISTRY

SPACE ANALYSIS FORM

Patient’s Name: L.N. McGil

SECTION 1	SECTION 5
AVAILABLE MANDIBULAR SPACE	MANDIBULAR SPACE ANALYSIS
	a. TOTAL SPACE AVAILABLE (from Section 1)
RIGHT	b. SUM OF MAND. INCISOR WID (from Section 2)
LEFT	c. SUM OF LEFT CANINE & PREMOLARS (estimated below from mand. incisors)
Arch Segment Lengths	d. SUM OF RIGHT CANINE & PREMOLARS (estimated below from mand. incisors)
a: mm	e. TOTAL SPACE REQUIRED (b + d)
b: mm	f. DISCREPANCY (a - e)
c: mm
d: mm
TOTAL: mm
SECTION 2	SECTION 6
MANDIBULAR INCISOR WIDTH	MAXILLARY SPACE ANALYSIS
#23: mm	a. TOTAL SPACE AVAILABLE (from Section 3)
#24: mm	b. SUM OF MAX. INCISOR WIDTH

Space Analysis Form, Section 1 (cont.)

A simple way to accomplish this is to divide the arch into segments in the area of certain teeth. Remember, you’re not measuring teeth. You’re measuring the dimensions of the alveolar process, so the lines separating the segments are marked on the alveolar process, below the teeth.

Segment “a” extends from the mesial of the permanent first molar on the right to the mesial of the primary right canine, not along the facial surface, but approximately over the contacts.

Segment “b” is from the mesial of the primary right canine to the midline, again over the contacts.

Segment “c” is from the midline to the mesial of the primary left canine.

Segment “d” is from the mesial of the primary left canine to the mesial of the permanent left first molar.

Other segments can be measured as long as one is careful not to measure the same space twice.

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{{PAGE_126}} Space Analysis Form, Section 1 (cont.) The length of each segment should be measured precisely, using the Boley gauge as shown in these images. Segments A and D, and segments B and C, are measured the same way on each side.

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Space Analysis Form, Section 1 (cont.)

These measured dimensions are recorded under Section 1 and totaled. The total of the segments is the available mandibular space. Straight-line segments, obviously, are an approximation of the curved space, but the error is small enough to be acceptable.

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Space Analysis Form, Section 2

L.N. McGill

SECTION 1

AVAILABLE MANDIBULAR SPACE

RIGHT	LEFT
a	d
b	c

Arch Segment Lengths a: 20.0 mm b: 9.6 mm c: 9.3 mm d: 20.3 mm TOTAL: 59.2 mm

The next step is to complete Section 2, which is measurement of the mesiodistal width of the lower incisors (teeth #23, 24, 25 and 26) (image 1).

The greatest mesiodistal width of each tooth should be measured accurately with a sharp Boley gauge as shown in image 1. This time you are measuring individual teeth.

These measurements are then recorded on the form and totaled under Section 2 (image 2).

SECTION 2

MANDIBULAR INCISOR WIDTH

#23: 6.1 mm #24: 5.2 mm #25: 5.1 mm #26: 5.9 mm TOTAL: 22.3 mm

Image 2: Section 2 completed

Space Analysis Form, Section 3

Level II Diagnosis — Unit B · 128 / 204

{{PAGE_129}} Space Analysis Form, Section 3 (cont). Segment “e” is marked along the alveolar process from the mesial of the permanent right first molar to the mesial of the primary right canine. Segment “f” is from the mesial of the primary right canine to the midline. Segment “g” is from the midline to the mesial of the primary left canine. Segment “h” is from the mesial of the primary left canine to the mesial of the permanent left first molar.

{{PAGE_130}} Space Analysis Form, Section 3 (cont). The dimensions for each of the segments are recorded on the form in Section 3 and totaled. This total is the available maxillary space.

Level II Diagnosis — Unit B · 130 / 204

{{PAGE_131}} SECTION 3 AVAILABLE MAXILLARY SPACE

Arch Segment Lengths e: 19.8 mm f: 15.0 mm g: 14.9 mm h: 19.0 mm TOTAL: 68.7 mm

Space Analysis Form, Section 4 Section 4 calculates the mesiodistal maxillary incisor width. The maxillary incisors are measured at their greatest width for teeth 7, 8, 9 and 10 (image 1).

After measuring these teeth, the dimensions should be recorded in the appropriate spaces and totaled. This will give the combined maxillary incisor width (image 2).

Image 1: Each individual maxillary incisor is accurately measured

SECTION 4 MAXILLARY INCISOR WIDTH #7: 7.1 mm #8: 8.5 mm #9: 8.6 mm #10: 6.8 mm TOTAL: 31.0 mm

INTERPRETATION OF NUMERICAL RESULTS Image 2: Section 4 completed

Space Analysis Form, Section 5 Section 5 is completion of the mandibular space analysis. The first step (5a) is to transcribe the total mandibular space available from Section 1.

Level II Diagnosis — Unit B · 131 / 204

{{PAGE_132}} UNIVERSITY OF NORTH CAROLINA AT CHAPEL HILL SCHOOL OF DENTISTRY

SPACE ANALYSIS FORM

Patient’s Name: L. N. McGILL

SECTION 1 AVAILABLE MANDIBULAR SPACE

Arch Segment Lengths a: 20.0 mm b: 9.6 mm c: 9.3 mm d: 20.3 mm

TOTAL: 59.2 mm

SECTION 2 MANDIBULAR INCISOR WIDTH

#23: 6.1 mm #24: 5.2 mm #25: 5.1 mm #26: 5.9 mm

TOTAL: 22.3 mm

SECTION 5 MANDIBULAR SPACE ANALYSIS

a. TOTAL SPACE AVAILABLE (from Section 1) 59.2

b. SUM OF MAND. INCISOR WIDTHS (from Section 2) 22.3

c. SUM OF LEFT CANINE & PREMOLARS (estimated below from mand. incisors)

d. SUM OF RIGHT CANINE & PREMOLARS (estimated below from mand. incisors)

e. TOTAL SPACE REQUIRED (b + c + d)

f. DISCREPANCY (a - e)

SECTION 6 MAXILLARY SPACE ANALYSIS

a. TOTAL SPACE AVAILABLE (from Section 3)

b. SUM OF MAX. INCISOR WIDTHS (from Section 4)

c. SUM OF RIGHT CANINE & PREMOLARS (estimated below from mand. incisors)

d. SUM OF LEFT CANINE & PREMOLARS (estimated below from mand. incisors)

e. TOTAL SPACE REQUIRED (b + c + d)

f. DISCREPANCY (a - e)

Space Analysis Form, Section 5 (cont.) The second step (5b) is to transcribe total measured mandibular incisor width from Section 2. This total will also be used in the next step.

Space Analysis Form, Section 5 (cont.)

Level II Diagnosis — Unit B · 132 / 204

{{PAGE_133}} To complete steps 5c and 5d, one must refer to the formula for the mandibular space prediction at the bottom of the form. The total mandibular incisor width from Section 2 is divided by 2, and 10.5 mm is added to produce a sum that is an estimation of the width of the mandibular unerupted canine and premolars in one mandibular quadrant.

Space Analysis Form, Section 5 (cont.) The estimated size of the unerupted mandibular canine and premolars in one quadrant is recorded twice, at lines 5c and 5d for the right and left sides respectively.

Space Analysis Form, Section 5 (cont.) Lines 5b, 5c and 5d are then added together to give the total space required. This sum is entered on line 5e.

Level II Diagnosis — Unit B · 133 / 204

{{PAGE_134}} 59.2 22.3 21.65 21.65 65.60

Space Analysis Form, Section 5 (cont.)

Line 5e is then subtracted from 5a to determine the estimate of the space discrepancy for the mandibular arch (5f).

If space required is larger than space available, the discrepancy is recorded as a negative number. If there is more space available than required, the number is positive. In this example the patient has a -6.4mm discrepancy.

59.2 22.3 21.65 21.65 65.60 -6.4

Space Analysis Form, Section 6

Level II Diagnosis — Unit B · 134 / 204

{{PAGE_135}} In Section 6, the maxillary space analysis is completed by first transcribing on to 6a the results of the measurements from Section 3 (total available maxillary space).

Space Analysis Form, Section 6 (cont.) Next transcribe to line 6b the total maxillary incisor width derived from Section 4.

Level II Diagnosis — Unit B · 135 / 204

{{PAGE_136}}

Space Analysis Form, Section 6 (cont.)

Next transcribe to line 6b the total maxillary incisor width derived from Section 4.

Level II Diagnosis — Unit B · 136 / 204

{{PAGE_137}}

Space Analysis Form, Section 7

In order to interpret the numerical results of the space analysis, additional information must be evaluated for each individual patient. This additional information is compiled in Sections 7-10. First, it is necessary to determine the skeletal status of the patient. This will enable us to project the mandibular incisor stability and its space implications. Remember, the position of the lower incisors is likely to change as a child with a skeletal Class II or Class III malocclusion grows. It also allows us to determine whether the mesial molar shift should be calculated.

PREMOLARS (estimated below from mand. incisors) 22.15

d. SUM OF LEFT CANINE & PREMOLARS (estimated below from mand. incisors) 22.15

e. TOTAL SPACE REQUIRED (b + c + d) 75.3

f. DISCREPANCY (a - e) -6.6

SECTION 7 SKELETAL JAW RELATIONSHIP (from Facial Profile Analysis)

( ) CLASS I; ( ) CLASS II; ( ) CLASS III

SECTION 8 OCCLUSION OF PERMANENT FIRST MOLARS

RIGHT SIDE ( ) ANGLE CLASS I ( ) LEFT SIDE ( ) END-TO-END ( ) ( ) ANGLE CLASS II ( ) ( ) ANGLE CLASS III ( )

Space Analysis Form, Section 7 (cont.)

The information for Section #7 is obtained from the results of the facial profile analysis that is found on the reverse side of the space analysis form. The facial profile analysis for the patient used in this example revealed a Class I skeletal pattern. If a patient has a Class I skeletal pattern, one would not expect mandibular incisor compensation with growth. Therefore, the space available would remain unchanged.

Level II Diagnosis — Unit B · 137 / 204

{{PAGE_138}} Space Analysis Form, Section 7 (cont.)

The information for Section #7 is obtained from the results of the facial profile analysis that is found on the reverse side of the space analysis form.

The facial profile analysis for the patient used in this example revealed a Class I skeletal pattern. If a patient has a Class I skeletal pattern, one would not expect mandibular incisor compensation with growth. Therefore, the space available would remain unchanged.

{{PAGE_139}}

Space Analysis Form, Section 7 (cont.)

However, in a Class II skeletal pattern (image 1), it is necessary to realize that the space available may change with growth.

In this mandibular composite tracing of a Class II patient, the original tracing is a solid line and the progress tracing is a dashed line (image 2).

It is evident that the mandibular incisors moved in a facial direction during growth. The lower incisors tend to compensate in a facial direction for the retrusive (Class II) mandible in some Class II patients, and this may actually increase the space available in the mandibular arch.

{{PAGE_140}} Image 1: Class II patient profile and facial form analysis Image 2: Mandibular superimposition for Class II patient: note space changes

Space Analysis Form, Section 7 (cont.)

This patient demonstrates a Class III skeletal pattern. In such cases, the mandibular incisor often compensates by tipping lingually (image 1).

In this mandibular composite tracing of a Class III patient, the original tracing is a solid line and the progress tracing is a dashed line (image 2). Note that the lower incisors moved lingually to compensate for the protrusive mandible. When a patient has a Class III skeletal pattern, the space analysis results can be misleading, because the space available is subject to change and may actually be reduced in the mandibular arch. This should be noted in your interpretation.

Image 1: Class III patient profile and facial form analysis Image 2: Mandibular superimposition for changes in a Class III patient

Level II Diagnosis — Unit B · 140 / 204

{{PAGE_141}}

Space Analysis Form, Section 8

Section 8 deals with molar relationships.

This image shows the profile analysis and the casts viewed from the right for the Class I example patient. The existing molar relationships should correlate with the skeletal relationships. If they do not, you should be able to explain this inconsistency.

Dental relationships for the right and left sides should be recorded on the form after viewing the articulated casts.

Space Analysis Form, Section 8 (cont.)

If the jaw relationship is Class I and there is a Class II molar relationship, this usually indicates maxillary space loss (image 1). One would suspect a maxillary space shortage, which should be confirmed by the numerical data of the space analysis.

Remember, canine relationships are often a useful clue to the previous dental relationships even when posterior teeth have drifted.

The casts of this patient show a Class II molar relationship and a maxillary space shortage of 5 mm, both of which are due to the patient’s maxillary right first molar moving mesially after premature loss of the 2nd primary molar (image 2).

Level II Diagnosis — Unit B · 141 / 204

{{PAGE_142}} Bridge of nose Porion (External Auditory Canal) Orbitale (Lower Rim of Orbit)

Steps Section 8

Another possibility is a Class III molar relationship in combination with a Class I skeletal pattern. (Image 1). This often indicates mandibular space loss, which would be confirmed by a space shortage in the lower arch space analysis figures.

These casts illustrate such a patient. The Class III molar relationship and a mandibular space shortage of 5mm are due to the mandibular right first molar moving mesially (image 2).

Level II Diagnosis — Unit B · 142 / 204

{{PAGE_143}} Image 1: Class I skeletal patient with a Class III molar relationship Image 2: Class III molar relationship on the right side is due to mesial movement of the mandibular right first molar. Note the forward drift of the maxillary left first molar in the same patient

Steps Section 8 Another possibility is a Class III molar relationship in combination with a Class I skeletal pattern. (Image 1). This often indicates mandibular space loss, which would be confirmed by a space shortage in the lower arch space analysis figures. These casts illustrate such a patient. The Class III molar relationship and a mandibular space shortage of 5mm are due to the mandibular right first molar moving mesially (image 2).

{{PAGE_144}} Image 1: Class I skeletal patient with a Class III molar relationship Image 2: Class III molar relationship on the right side is due to mesial movement of the mandibular right first molar. Note the forward drift of the maxillary left first molar in the same patient

Steps Section 8 (cont.) Likewise, if a patient has a Class III skeletal pattern, one would expect a bilateral Class III molar relationship. Caution must be exercised in interpreting the results in a Class III patient because as growth continues, the lower incisors may move lingually and the upper incisors facially. Note that this patient is Class III skeletally and dentally. Mixed dentition space analysis probably would underestimate the potential mandibular space discrepancy and severity of mandibular incisor crowding, but might overestimate the situation for the maxillary arch.

{{PAGE_145}} Steps Section 8 (cont.)

Even in a skeletal Class I child like our example, the molar relationship may not be Class I. For this patient, the right side is Class I and needs no adjustment for molar shift. But the left side, shown in the lower half of this frame, is end-to-end, and the magnitude of the molar shift needs to be measured.

This is the distance between the two lines marked on the casts. The mesio-buccal cusp of the upper 1st molar should occlude in the buccal groove of the lower first molar. The distance we’re interested in is the discrepancy between those two points.

Level II Diagnosis — Unit B · 145 / 204

{{PAGE_146}} Steps Section 8 (cont.) Even in a skeletal Class I child like our example, the molar relationship may not be Class I. For this patient, the right side is Class I and needs no adjustment for molar shift. But the left side, shown in the lower half of this frame, is end-to-end, and the magnitude of the molar shift needs to be measured.

This is the distance between the two lines marked on the casts. The mesio-buccal cusp of the upper 1st molar should occlude in the buccal groove of the lower first molar. The distance we’re interested in is the discrepancy between those two points.

Level II Diagnosis — Unit B · 146 / 204

{{PAGE_147}} Level II Diagnosis — Unit B · 147 / 204

Steps Section 8 (cont.) The skeletal Class I patient whose space anlysis we’ve been doing has a Class I molar relationship on the right side and end-to-end on the left side. This has been indicated in Section 8. Section #9 should be completed ONLY if the patient exhibits a Class I skeletal relationship and one or both molars are in an end-to-end relationship or not quite Class I.

SECTION 8 OCCLUSION OF PERMANENT FIRST MOLARS RIGHT SIDE (X) ANGLE CLASS I ( ) LEFT SIDE ( ) END-TO-END (X) ( ) ANGLE CLASS II ( ) ( ) ANGLE CLASS III ( )

Steps Section 9 With a Class I skeletal relationship and an end-to-end molar relationship, a Class I molar relationship may be achieved during development in one of three ways:

1. A shift of the mandibular first permanent molar mesially into the leeway space

{{PAGE_148}} 2. More mandibular than maxillary growth, which will move the mandible forward relative to the maxilla 3. A combination of molar shift and growth.

Steps Section 9: Leeway Space

The leeway space is simply the difference in the total widths of the primary molars and canines as compared to the combined width of the permanent teeth which replace them.

In this image, dimension “A” represents the width of the permanent teeth and is somewhat smaller than dimension “B”, which represents the width of the primary teeth.

Level II Diagnosis — Unit B · 148 / 204

{{PAGE_149}} Steps Section 9: Leeway Space (cont.)

In the late mixed dentition when the primary molars are exfoliated, arch length decreases. As shown here, distance “B” decreases to distance “B prime” when the primary teeth are replaced.

Since this shift is likely to occur when a Class I skeletal relationship and end-to-end molars are present, it is necessary to record the magnitude of this change.

Level II Diagnosis — Unit B · 149 / 204

{{PAGE_150}} Steps Section 9: Leeway Space (cont.)

To determine how much shortening of available space will occur due to a mesial shift, draw a vertical line at the mesiobuccal cusp tip of the permanent maxillary first molar and another line in the buccal groove of the permanent mandibular first molar. The distance between these lines with the models in occlusion represents the space required to achieve a Class I occlusion.

The total of this space for right and left sides will not be available for eruption of the permanent premolars and canines.

Level II Diagnosis — Unit B · 150 / 204

{{PAGE_151}} Steps Section 10 The next section, Section 10, lip posture of the patient, was assessed during the facial profile analysis. The lip posture should have been recorded as protrusive, normal or retrusive. You made this judgment by looking at the lip prominence relative to the base of the nose and the chin, the nasolabial angle, and lip competence. On a sketch of the profile or a cephalometric tracing, it can be helpful to draw the “E line” from the nose to the chin as shown in this image, and examine the position of the lips relative to it. The lips should be about on the line. If they’re well ahead of it, they’re probably protrusive; if they’re behind it, they’re retrusive. But the size of the nose and chin obviously affect this line, which only works if nose and chin are normal.

Level II Diagnosis — Unit B · 151 / 204

{{PAGE_152}} Steps Section 10 (cont.) If the lips are over-supported and protrusive, the incisors usually are protrusive.

Conversely, if the lips are under-supported, a retrusive relationship of the incisors can be inferred. In either case, correction of incisor position will generally be desirable, and this correction will definitely influence the amount of space available.

Moving incisors lingually to reduce incisor protrusion also reduces the amount of space available. Conversely, if the incisors are tipped facially to provide more lip support, an increase in space available is realized.

Level II Diagnosis — Unit B · 152 / 204

{{PAGE_153}} Steps Section 10 (cont.) This patient illustrates the use of the E-line in judging protrusion. The E line is constructed by connecting the tip of the nose to the most anterior point of the soft tissue pogonion. Normally, the lower lip should lie just behind the line, as this patient. A change in lower incisor position or lip posture would be inadvisable in this patient. But remember that the E line can be altered by large chins and noses, and you can’t judge protrusion just from it.

Level II Diagnosis — Unit B · 153 / 204

{{PAGE_154}} Steps Section 10 (cont.)

In the patient shown here, the lips are considerably in front of the E-line, which serves to confirm the clinical judgment that the lips and incisors are protrusive.

A reduction of incisor and lip protrusion in this patient, while esthetically desirable, would reduce the available arch length. Since he’s skeletal Class II, there already were concerns about the accuracy of space analysis for him, and the space analysis would not be the major factor in determining his treatment plan.

Remember, the degree of acceptable protrusion is influenced by racial and ethic considerations.

Level II Diagnosis — Unit B · 154 / 204

{{PAGE_155}}

Steps Section 10 (cont.)

This patient’s upper and lower lips are situated behind the E line, which confirms the clinical judgment that they are retrusive and under-supported by the incisors.

It would be possible to move the maxillary and mandibular incisors facially in this patient if an increase in arch length were necessary.

One must be cautious and realize that there is not always a direct relationship between incisor position and lip posture.

{{PAGE_156}} Steps Section 10 (cont.)

This patient’s upper and lower lips are situated behind the E line, which confirms the clinical judgment that they are retrusive and under-supported by the incisors.

It would be possible to move the maxillary and mandibular incisors facially in this patient if an increase in arch length were necessary.

One must be cautious and realize that there is not always a direct relationship between incisor position and lip posture.

{{PAGE_157}} Cases

Case Review #1 Now you will be asked to apply some common sense in your observations. On this screen and the ones following, study the casts shown to determine whether the space analysis result that one of your fellow students calculated is correct, or instead is an over- or under-estimate of the space needed. Assume normal skeletal and soft tissue relationships and no molar shift. Is this patient really 4 mm short in the lower arch?

Level II Diagnosis — Unit B · 157 / 204

{{PAGE_158}} Case Review #1 (cont.) Because of the minimal irregularity of the incisors and the available leeway space, this is an overestimation of the space needed. If there is a space discrepancy, it is quite small.

{{PAGE_159}} Case Review #2 The space analysis form produced for this patient shows a -1 mm space discrepancy for both arches. Is this patient really only 1 mm short of space?

{{PAGE_160}} Case Review #2 (cont.)

Given the availability of leeway space, this appears to be a good estimation (if the patient is skeletal Class I). Crowding of this extent in the early mixed dentition has the potential to improve during the transition to the full permanent dentition.

Level II Diagnosis — Unit B · 160 / 204

{{PAGE_161}} Case Review #3 Based on your observation of these casts, is this patient really 3 mm short of space in both arches, as the space analysis form shows?

Level II Diagnosis — Unit B · 161 / 204

{{PAGE_162}} Case Review #3 (cont.) For this patient, the space analysis result almost surely underestimates the size of the discrepancy. You can see on the casts that the mandibular teeth are aligned, but no primary canines are present. In the maxillary arch the permanent lateral incisors have not erupted, and there is almost no space available for them. This patient is really closer to -7 mm in each arch.

Level II Diagnosis — Unit B · 162 / 204

{{PAGE_163}}

Performing a Space Analysis

Now it is time to apply what has been presented in this program. Let’s perform a space analysis for the patient whose casts are shown here (image 1). Notice that there is irregularity in both the maxillary and mandibular arches.

Using the method previously described for measurement and the prediction formula at the bottom of the form, Sections 1 through 6 have been completed (Image 2).

{{PAGE_164}} UNIVERSITY OF NORTH CAROLINA AT CHAPEL HILL SCHOOL OF DENTISTRY SPACE ANALYSIS FORM

Patient’s Name: A. FARGOULT

SECTION 1 AVAILABLE MANDIBULAR SPACE a) Arch Segment Lengths (from Section 2) Right: 25.0 mm Left: 24.7 mm b) Sum of Mand Incisor Widths (from Section 2) c) Sum of Left Canine & Premolars (estimated below from mand incisors) 22.7 mm d) Sum of Right Canine & Premolars (estimated below from mand incisors) 22.7 mm e) Total Space Required (3 + 4 + 5) 67.4 mm f) Discrepancy (6 - 5) -2.6 mm

SECTION 2 MANDIBULAR INCISOR WIDTH #21 6.8 mm #22 5.6 mm #23 5.6 mm #24 5.6 mm TOTAL 23.6 mm

SECTION 3 AVAILABLE MAXILLARY SPACE a) Arch Segment Lengths Right: 25.1 mm Left: 24.7 mm b) Sum of Max Incisor Widths (from Section 4) c) Sum of Right Canine & Premolars (estimated below from max incisors) 22.5 mm d) Sum of Left Canine & Premolars (estimated below from max incisors) 22.5 mm e) Total Space Required (3 + 4 + 5) 67.4 mm f) Discrepancy (6 - 5) -2.2 mm

SECTION 4 MAXILLARY INCISOR WIDTH #11 6.0 mm #12 5.8 mm #13 5.8 mm #14 5.8 mm TOTAL 23.4 mm

SECTION 5 MANDIBULAR SPACE ANALYSIS a) TOTAL SPACE AVAILABLE (from Section 1) 65.4 mm b) SUM OF MAND INCISOR WIDTHS (from Section 2) 23.0 mm c) SUM OF LEFT CANINE & PREMOLARS (estimated below from mand incisors) 22.7 mm d) SUM OF RIGHT CANINE & PREMOLARS (estimated below from mand incisors) 22.7 mm e) TOTAL SPACE REQUIRED (3 + 4 + 5) 67.4 mm f) DISCREPANCY (6 - 5) -2.6 mm

SECTION 6 MAXILLARY SPACE ANALYSIS a) TOTAL SPACE AVAILABLE (from Section 3) 71.6 mm b) SUM OF MAX INCISOR WIDTHS (from Section 4) 23.7 mm c) SUM OF RIGHT CANINE & PREMOLARS (estimated below from max incisors) 22.5 mm d) SUM OF LEFT CANINE & PREMOLARS (estimated below from max incisors) 22.5 mm e) TOTAL SPACE REQUIRED (3 + 4 + 5) 67.4 mm f) DISCREPANCY (6 - 5) -2.2 mm

SECTION 7 SKELETAL JAW RELATIONSHIP (from Facial Profile Analysis) ( ) CLASS I ( ) CLASS II ( ) CLASS III

SECTION 8 OCCLUSION OF PERMANENT FIRST MOLARS RIGHT SIDE | END-TO-END | LEFT SIDE END-TO-END | ANGLE CLASS I | LEFT SIDE END-TO-END | ANGLE CLASS II | LEFT SIDE

SECTION 9 MOLAR SHIFT (from end-to-end to Class I) For Simple Class I only RIGHT SIDE = LEFT SIDE = TOTAL SHIFT

SECTION 10 LIP POSTURE (from Facial Profile Analysis) ( ) ACCEPTABLE | ( ) PROTRUSIVE | ( ) RETRUSIVE MANDIBULAR INCISOR POSITION (from Facial Profile Analysis) ( ) ACCEPTABLE | ( ) PROTRUSIVE | ( ) RETRUSIVE

INTERPRETATION OF NUMERICAL RESULTS (based on observations in Sections 7-10)

To estimate the size of the unuprighted canine and premolars in each quadrant (Method of Tanaka and Johnston, Am Dent Assoc 68:754, 1974)

Mandibular quadrant: ½ x the sum of the widths of the mandibular incisors, plus 10.5 mm. 11.5 + 14.5 = 22.7 [ENTER ON LINE 3c AND 3d ABOVE]

Maxillary quadrant: To the sum of the widths of the mandibular incisors, plus 11.0 mm. 11.5 + 11.0 = 22.5 [ENTER ON LINE 3c AND 3d ABOVE]

{{PAGE_165}} Interpretation of Space Analysis Result How does your interpretation compare with the one below?

Level II Diagnosis — Unit B · 165 / 204

{{PAGE_166}} In this case, there are small maxillary (-0.9mm) and mandibular (-1.6mm) space deficiencies predicted when space required is compared to space available. When this is combined with the molar shift (3.4mm), there appears to be a more significant demand for space in the mandibular arch (1.6mm + 3.4mm). The upright lower incisor position seen in the dental casts suggests that additional arch circumference could be created by proclining the lower incisors. But this patient’s lips appear well related or slightly protrusive, so proclining the lower incisors might make her lips protrusive or incompetent. Her face is not compatible with more than a very little forward movement of the incisors.

An alternate approach, which will be discussed in detail in Level 3, might be to try space management with a lower lingual arch in the late mixed dentition to prevent loss of the leeway space and prevent the molar shift. The lower incisors can be proclined slightly to accommodate the 1.6mm of predicted crowding. The upper molars will then have to be distalized to obtain a Class I molar relationship.

Alternate Technique: Digital Models With the development of advanced computer technology, digital dental models are becoming more widely used in dental and orthodontic practices. Digital models can be easily manipulated in three dimensions and also eliminate physical storage space requirements (image 1). Note that they are displayed with symmetric bases, so that they look like actual casts that have been trimmed in the standard way. A symmetric base makes it easier to pick up asymmetries in the dental arch.

A virtual space analysis can be preformed on the digital models on a computer screen. Using an on-screen tool, the user measures the individual size of the teeth (image 2) and the circumference of the dental arches. With this information, the computer program can perform different predictions of the size of the unerupted teeth (for instance, Tanaka-Johnston or Moyers) as selected.

Whether the measurements are done on the computer or using a form as we have described, it is important to take everything into account that was considered in the sequence of steps in the space analysis procedure. The computer is just a tool to help you get the information—it can’t be expected to do your thinking for you. Either way, you have to come to a conclusion as to what the space analysis result means and how you would use it in treatment planning.

Level II Diagnosis — Unit B · 166 / 204

{{PAGE_167}} Image 1, Virtual dental casts.: These images, scanned from actual casts or from impressions, are quite accurate and can be used for space analysis in the same way as dental casts. Image 2, Tooth width measurements: Tooth width is measured for each tooth as shown here, using the cursor.

Referral to Self-Test To develop skill in space analysis, you will need to do this a number of times—and that’s true whether you do it with actual dental casts or digital models. The self-test for this module is to help you confirm why space analysis is carried out the way it is, and evaluate your understanding of the underlying principles.

Before you take the self-test, be sure you do the assigned reading: pages 427-429 in the 5th edition of Contemporary Orthodontics; pages 195-201 in the 4th edition. Then use the self-test to be sure you have understood the material—and refer to this instructional module when you are assigned child patients who need space analysis as part of their diagnostic evaluation.

Level II Diagnosis — Unit B · 167 / 204

{{PAGE_168}}

5. Ackerman-Proffit Classification

Angle Classification and Treatment Goals

Learning Objectives

Conceptually, classification can be viewed as an orderly way to derive a list of the patient’s problems from the database of diagnostic information. In the early 1900s, Edward Angle proposed a simple classification system that remains in regular use. A century later, both the diagnostic evaluation of patients with dentofacial problems and the goals of treatment are much more extensive. Orthodontic diagnosis requires an accurate description of the characteristics of malocclusion. The Ackerman-Proffit classification provides a systematic way to review those characteristics, so that nothing important is overlooked. The objectives of this program are to help you understand how this modern classification system was developed to overcome the limitations of the Angle system, and to illustrate how it is used.

Angle Classification: Normal Occlusion vs Malocclusion

Level II Diagnosis — Unit B · 168 / 204

{{PAGE_169}} In the 1890’s, Edward Angle made a major contribution to dentistry when he described the ideal arrangement of teeth that had been proposed originally by his teacher Bonwill as “normal occlusion”, and used it as the basis for a description of malocclusion. Only after normal occlusion had been defined, of course, was it possible to describe deviations from normal occlusion as malocclusion.

Almost no one has the perfect alignment and occlusion of the teeth that Angle called “normal occlusion”, and as you saw in the first teaching program in Level II, a high percentage of the population have significant enough deviations from it that we put them in the malocclusion category.

Remember that Angle defined normal occlusion in the context of two characteristics: the arrangement of the teeth relative to the “line of occlusion” (image 1), and the arrangement of the maxillary teeth relative to the mandibular teeth (which is occlusion itself) (images 2-5).

Level II Diagnosis — Unit B · 169 / 204

{{PAGE_170}}

Angle’s Classification of Malocclusion

Image 1: Angle’s Line of Occlusion

Line of Occlusion: The line of occlusion, along which the teeth in both arches should be aligned, runs along the buccal cusps and incisal edges of the mandibular teeth, and along the central groove of the upper posterior teeth and across the cingulum of the anterior teeth.

Image 2: Normal Molar Relationship

Normal molar relationship: Angle assumed that the maxillary first molar was always appropriately located at the base of the zygomatic process, and that if the first molars were in this relationship, the rest of the teeth would interdigitate normally.

Image 3: Class I Malocclusion

Class I malocclusion: With the molars in the normal relationship but teeth not aligned along the line of malocclusion, the result was Class I malocclusion.

Image 4: Class II Malocclusion

Class II malocclusion: If the lower molar was behind the upper molar (remember, for Angle the upper…

Level II Diagnosis — Unit B · 170 / 204

{{PAGE_171}}

<table border="1">
	<tr>
		<td></td>
		<td>molar was presumed to be in the right place), the result was Class II malocclusion, excess overjet was expected, and malalignment was no longer part of the classification. Angle did recognize a variant based on alignment of the upper incisors, which sometimes protrude but are well aligned (because the lower lip is beneath them), but sometimes are severely tipped lingually and overjet is minimal (because the lower lip is in front of them). The usual version with overjet was called Class II, division 1; the version with lingually tipped maxillary incisors was called Class II, division 2.</td>
	</tr>
	<tr>
		<td></td>
		<td>Image 5, Class III malocclusion: If the lower molar was ahead of the upper molar, the result was Class III malocclusion. Reverse overjet was expected and malalignment was part of the classification.</td>
	</tr>
</table>
 
The Goal of Classification
The Angle classification has the great virtue of being simple and easy to understand, which is why it was widely adopted and now is universally understood by dentists. But the goal of classification is to describe patient problems in a way that facilitates their treatment. From that perspective, Angle classification is incomplete in significant ways. You need to understand how and why Angle classification was extended to form the systematic description method we currently use.
 
During Angle’s search for the ideal relationship of the teeth, he came across a number of skulls which seemed to him to have the characteristics of the ideal dental relationships for which he was searching. On one of these skulls, ideal occlusion viewed from the facial is shown in image 1, the view from the lingual in image 2. The key characteristic was having all 32 teeth (including third molars) in excellent alignment and occlusion. Angle called one of these skulls “Old Glory” (image 1) because it had such a perfect arrangement of the teeth, and said that this arrangement of the teeth should be the goal of treatment.
 
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{{PAGE_172}} Angle adopted the philosophic view popular in the late 19th century of the “noble savage”, whose perfection had not been impaired by civilization. He came to believe that every individual had the potential for dental occlusion like Old Glory’s, that everyone would look their best when ideal occlusion was obtained, and that forces against the teeth from function in ideal occlusion would maintain them in that relationship. He therefore taught that the primary goal of orthodontic treatment should be to align all 32 of the natural teeth (more practically, at least all but the 3rd molars) in this type of perfect relationship. When ideal occlusion was obtained, everything else would take care of itself.

If lining up all the teeth and placing them in ideal occlusion always was the approach to treatment, Angle’s simple classification scheme should be adequate. After all, the aim of classification is to organize information about patients in a way that facilities planning their treatment.

As you already have learned, the goals of modern orthodontic treatment go far beyond a focus only on occlusion. A modern classification system, of course, must relate to those broadened goals.

Limitations of Angle Classification Angle Classification: Protrusion / Esthetics

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{{PAGE_173}} Edward Angle’s great professional rival in the early twentieth century was Calvin Case. Case disagreed with Angle’s focus on ideal occlusion of all the teeth, which led to the concept that extraction for orthodontic purposes was never necessary, and with Angle’s insistence that ideal occlusion always produced an ideal facial appearance.

As you can see from this quote, which I have taken the liberty of arranging as blank verse, Case agreed with Angle that it was possible to bring even the most irregular teeth into an ideal or nearly ideal relationships.

“No matter how irregular the teeth, however bucked, malaligned or malposed, they could always be placed in their respective places in the arches and in normal occlusion. Therefore, so far as the relations of the teeth to each other are concerned, no dental malposition should be taken as a basis for extraction.”

Calvin Case, 1912

Angle Classification: Protrusion / Esthetics (cont.)

In essence, Case criticized the Angle classification for not recognizing dental protrusion as a problem. Certainly it is correct to think of crowding of the teeth and protrusion of the teeth as two aspects of the same thing, and if you think of crowding as having deleterious effects on facial esthetics, of course you should be able to think of protrusion as creating an equally negative impact.

“My teeth stick out too much” is as valid a complaint as “my teeth are crooked”, and because of the association of protruding upper incisors with stupidity, may have an even greater impact.

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{{PAGE_174}} Angle Classification: Protrusion / Esthetics (cont.) Case did not agree, however, that expanding the dental arches always should be the goal of treatment. He pointed out, correctly from a modern point of view, that the cost of expanding the dental arches might be the creation of a facial deformity because of the excessive protrusion of the teeth that would be produced.

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{{PAGE_175}} “The only excuse then for the extraction of savable teeth must be that it is inexpedient or impossible to correct their position in that way without producing facial protrusion.”

Calvin Case, 1912

Arch Length Discrepancy?

Both excessive protrusion and crowding of the teeth can be evaluated in the context of arch length discrepancy, which of course is the difference between the size of the dental arch and the size of the teeth it was meant to accommodate. You’ve already become used to calculating arch length discrepancy, in the form of mixed dentition space analysis, and have already learned that the calculated number must be interpreted in the light of incisor protrusion or retrusion.

Because Angle thought that all dental arches could and should be expanded, he saw no reason to include arch length discrepancy in evaluating patients. With extraction as a possibility in modern treatment, the extent of crowding or protrusion has to be evaluated.

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{{PAGE_176}} 68.7 31.0 22.15 22.15 75.30 -6.60

Class I = (?)

Another problem with Angle classification that became increasingly apparent was that malocclusions receiving the same classification, particularly Class I malocclusions, were often not at all the same. As Robert Strang put it in an orthodontic text written soon after Angle’s death, “When one says Class I malocclusion, the next question immediately has to be what kind of Class I malocclusion?” Class I malocclusion includes three major types of problems that may or may not overlap, and for that reason is not a useful characterization of a particular patient’s problems.

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Class I Malocclusion:

Any combination of:

• Dental crowding
• Crossbite (buccal or lingual)
• Open bite, deep bite

Transverse / Vertical Planes of Space

The Strang criticism can be focused more succinctly by saying that Angle classification evaluates dental occlusion only in the anteroposterior plane of space, and does not indicate how the teeth fit either transversely or vertically.

Occlusion is a three-dimensional, not a one-dimensional phenomenon. The Angle classification for this patient is Class I malocclusion, which hardly serves to specify her problems. Both the posterior crossbite and anterior open bite simply weren’t included in the classification scheme. They would certainly have to be considered in planning modern treatment, however.

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Skeletal vs Dental Problems

As cephalometric analysis was developed, it became clear that sometimes a Class II or Class III malocclusion was due to the jaw relationship, and sometimes was due just to displacement of teeth. The descriptive terms “skeletal Class II” and “skeletal Class III” were added to Angle’s terminology to describe the jaw relationships that predispose a patient to Class II or Class III malocclusion. Now, as you already know, “Class II growth pattern” or “Class III growth pattern” also are frequently used to describe the pattern of growth that leads to skeletal Class II or III jaw relationships.

Because of the three-dimensional nature of occlusion, it also is necessary to evaluate the skeletal vs. dental nature of transverse and vertical problems.

In a modern classification, differentiating dental and skeletal components of a malocclusion is a critically important distinction. In the lateral ceph for the patient whose dental relationships were pictured in the previous screen, the posterior crossbite can’t be seen, but it’s obvious that there’s a skeletal component to the open bite. The palatal plane is rotated down posteriorly, and anterior face height is too great.

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{{PAGE_179}} Radiograph showing lateral cephalometric view of a human skull. UNC SCHOOL OF DENTISTRY Digora pcr SN28333

Analogous or Homologous?

Taking skeletal as well as dental relationships into account is particularly important in differentiating patients whose malocclusions are merely analogous from those with homologous problems. Analogous problems are similar, homologous problems are identical. Mistakes in treatment can arise if analogous problems, which appear to be the same but really aren’t, receive the same classification. Consider the two patients whose dental casts are shown here. Note the similarity in the occlusion of the posterior teeth, which is Angle Class II but not a full-cusp Class II relationship (images 1 and 2). Both patients have the same overjet. From the frontal view (image 3), you can appreciate the similarity in arch form, and now you can see that both patients have an almost identical anterior deep bite. From the occlusal view (image 4), the lower arches are almost identical in arch dimensions and proportions, and in the degree of (mild) crowding. One has mild irregularity of his upper incisors, the other doesn’t.

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{{PAGE_180}} Image 1, Similar malocclusions, right lateral view: These two unrelated patients have quite similar Class II malocclusions.

Image 2, Similar malocclusions, left lateral view: Note the similar Class II molar relationships for both patients.

Image 3, similar malocclusions, frontal view: The frontal view shows a similar deep overbite for both patients, and normal transverse relationships of the posterior teeth.

Image 4, Alignment: Alignment of the teeth also is quite similar for both patients, with good alignment in the maxillary arch and mild irregularity of the lower incisors.

Analagous or Homologous? (cont.)

As you saw, the occlusion and alignment of the teeth of the two patients are remarkably similar. Only when you look at the faces (image 1) and the cephs (image 2) of these two individuals can you appreciate the considerable difference between them.

Note that the skeletal patterns are not at all the same. The patient on the left has a normal skeletal relationship, with the upper teeth displaced anteriorly and the lower teeth displaced lingually—in other words, a dental Class II. The one on the right, in contrast, is mandibular deficient but has the teeth well-related to each jaw—almost completely a skeletal Class II.

The skeletal difference means that the treatment plan for these patients will have to be quite different. These patients have analgous malocclusions—the teeth look the same, and they would get the same Angle classification—but they don’t have homologous malocclusions that would be treated in the same way.

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Symbolic Logic: Venn Diagrams

Now let’s begin to augment the Angle scheme to overcome its limitations. A good way to express the relationship among sets of variables is to use a Venn diagram to show them symbolically.

If that were done for the Angle classification, the resulting diagram might look like this image. The relationship of the teeth to the line of occlusion, Angle’s first consideration, is the outer frame. All patients have some characteristic alignment, either normal or not.

As a subset within the alignment field, the patient also would have Angle’s second consideration, the anteroposterior relationship of the first molars, which would determine the a-p relationship of the dental arches. If the molar relationship, and the a-p relationship more generally, is not ideal, the patient would be located within the anteroposterior circle, and would then be described as having Class II or Class III malocclusion (with the alignment of the teeth no longer specified).

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{{PAGE_182}} Venn Diagram, Ackerman-Proffit Classification

Now let’s alter the Venn diagram to show a more complete evaluation. We choose now to represent facial proportions and the relationship of the dentition to the soft tissues as the frame of the diagram, and dental alignment and symmetry as a major field within the frame (image 1). Initially, the frame was alignment and the large inner circle was labeled as profile / esthetic considerations. The modern focus on the facial soft tissues and the impact of the dentition on them makes it more logical to start with the face.

It is helpful in doing this to recognize that there are both a functional line of occlusion (Angle’s line) and an esthetic line of the dentition which runs along the outer surface of the upper teeth (image 2). Both are important. The esthetic line defines the extent of incisor display (and is evaluated in the context of dentofacial appearance), while the functional line allows an estimation of the extent of malalignment of the teeth (and is evaluated in the context of arch alignment and symmetry). Views of the two lines in an actual patient are shown in images 3 and 4, obtained from cone-beam computed tomography (CBCT).

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Image 1, incomplete Venn diagram, 2 characteristics: Venn diagram, frame = facial proportions, relationship of the dentition to the soft tissues; inner circle = dental alignment / symmetry

Image 2, functional and esthetic lines of occlusion: Green line, esthetic line of the dentition; red line, functional line of occlusion (Angle’s line)

Image 3, Cone-beam CT view of functional and esthetic lines of occlusion: CBCT submental vertex view of the dentition (looking up from below), with the esthetic line in green and the functional line in red.

Image 4, Cone-beam CT frontal view of the esthetic line of occlusion: CBCT frontal view of the dentition (another perspective of the patient shown in image 2), with the esthetic line in green.

{{PAGE_184}} Venn Diagram, Ackerman-Proffit Classification (cont.)

So now we would have a more complete description of dentofacial appearance, and would have a place to specifically consider the relationship of the dentition to the lips as it affects incisor display (excessive — normal — inadequate).

In the alignment field (relationship of the teeth to the functional line of occlusion), we would want to specify the severity of the alignment problems. This is done best by calculating the space discrepancy, by comparing the space available for the teeth with the space required (which is exactly what you have already learned to do in mixed dentition space analysis).

The treatment plan will be greatly affected by how large or small the space discrepancy is, so it is very important to specify that. For treatment planning purposes, precise measurements really are not necessary. Severe, moderate, mild crowding or spacing are adequate descriptions. This is true for asymmetry as well.

Now we could specifically locate a patient who had good alignment but suffered from dental protrusion, for instance; and there would also be a way to account for other esthetic problems related to the patient’s dentition and occlusion.

Venn Diagram, Ackerman-Proffit Classification (cont.)

The third criticism of the Angle classification is that it includes only the a-p plane of space. We need to add the transverse and vertical planes of space. A patient could have transverse, a-p or vertical

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{{PAGE_185}} deviations from normal occlusion, but he or she could also have any combination of problems in the three planes, so these fields must overlap.

Finally, we need to distinguish between skeletal and dental components of malocclusion, and the appropriate place to do this is when we consider the relationships in each of the three planes of space. For each one, we must evaluate skeletal as well as dental relationships, not just the way the teeth fit together.

The Venn diagram shown here symbolically represents the logic used in the late 20th century, with minimal changes from its introduction in 1970. It largely overcomes the limitations of Angle classification while incorporating the essence of that method. Although this classification is widely used now, it’s still incomplete in one important way for use in the 21st century.

On the next screen, let’s look at this final aspect of modern classification, evaluation of the orientation as well as the position of the jaws and dental arches.

Position and Orientation

Although this classification, based on 5 characteristics of malocclusion and dentofacial deformity, solved the major problems with Angle classification and became widely used, the version we just looked at was still incomplete in one important way for use in the 21st century.

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{{PAGE_186}} An important aspect of the classification system was, and is, its incorporation of systematic analysis of skeletal and dental characteristics in all three planes of space.

A complete description, however, requires consideration of both the position of the jaws and dental arches (forward-backward, up-down, right-left) in three-dimensional space, which the initial Ackerman-Proffit scheme included, and their orientation relative to three perpendicular axes (pitch, roll and yaw), which was not included initially. Specification of both location and orientation is necessary to describe the position of an airplane in space (image 1). It is equally necessary to describe dentofacial relationships (image 2), and the rotational axes must be considered both for the jaws and for the esthetic line of the dentition.

Image 1, Orientation of aircraft: To accurately describe an airplane in flight, it is necessary to specify its position in all three planes of space, and also to specify its orientation relative to the three axes of rotation. Pitch describes up-down orientation of the body of the plane relative to the route of flight; roll describes the up-down orientation of the wings; yaw describes the side-to-side orientation of the plane relative to its direction of movement.

Image 2, Orientation around axes of rotation in the head and face: As with aircraft, it is necessary to specify not only the location of skeletal components and teeth in all 3 planes of space, but also to specify their orientation to possible axes of rotation. Pitch, roll and yaw need to be evaluated in orthodontic diagnosis to complete a systematic description that will specify the patient’s problems in a way that leads to the appropriate treatment plan.

Pitch

An excessive upward/downward rotation of the dentition relative to natural head position and to the lips and cheeks would be noted as pitch (up or down, in the front or back). This can be picked up in photographs (image 1) but is best detected on clinical examination. Note that for this boy, the lower lip almost covers the esthetic line of the dentition.

Pitch of the jaws and teeth relative to each other also can and should be noted clinically. Image 2, the same boy as image 1, shows the anterior deep bite that usually accompanies a downward pitch of the

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{{PAGE_187}} dentition. For the girl in image 3, who does not have anterior open bite despite her long lower face, the entire dentition is translated down, but a downward pitch posteriorly can be observed in the photograph. Note that the esthetic line of the dentition tilts down posteriorly relative to the intercommisure line and that there is greater display of posterior than anterior gingivae.

Pitch of the jaws and teeth can be picked up from the lateral cephalogram in the last stage of systematic description, where it is revealed by the orientation of the palatal, occlusal and mandibular planes relative to each other and to the true horizontal plane.

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Image 1, Pitch of the anterior maxillary teeth down anteriorly: Downward pitch of the anterior teeth. Compare the position of the esthetic line of the dentition (out of sight behind the lower lip) to the inter-commisure line (which connects the corners of the mouth). </td> <td> Image 2, Pitch as a component of overbite: Intra-oral view, same patient as image 1. Anterior deep bite usually accompanies a downward pitch of the maxillary dental arch. </td>

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{{PAGE_189}} Image 3, Pitch as a component of long face / open bite: Downward pitch of the dentition posteriorly. Note that you can see more of the gingiva in the molar/premolar regions than in the incisor region, due to the rotation of the palatal plane down posteriorly. Pitch of one of the horizontal planes is easier to see on a lateral ceph but can be detected clinically.

Roll Roll of facial components is analogous to banking of an airplane. It is described as up or down on one side or the other. On clinical examination, the relationship of the dentition to the facial soft tissues is evaluated from the orientation of the esthetic line of the dentition to the inter-commisure line (connecting the corners of the lips) (image 1). The relationship to the facial skeleton is evaluated relative to the inter-ocular line (image 2). The use of a Fox plane (a thin metal sheet) to mark a cant of the occlusal plane makes it easier to visualize how the dentition relates to the inter-ocular line (image 3). But with this device in place, it is impossible to see how the teeth relate to the inter-commisure line.

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{{PAGE_190}} Image 1, Roll, downward on the right, of the maxillary dentition: Note the downward roll of the dentition on the right side relative to the inter-commisure line (yellow). Image 2, Roll, downward on the right, of both jaws: Roll of the both jaws down on the right side and slightly up on the left side, relative to the inter-commisure line. Image 3, Roll evaluated with a Fox plane: Use of a Fox plane against the posterior teeth makes it easier to evaluate the relationship of the dentition to the inter-ocular line.

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{{PAGE_191}} Yaw

Rotation of the jaw or dentition to one side, around a vertical axis, creates a skeletal or dental midline discrepancy that is best described as yaw. Dental midline deviations can be due just to displaced incisors because of crowding, and should be distinguished from yaw.

The effect of yaw, in addition to the midline discrepancy, usually is a unilateral Class II or Class III molar relationship. Severe yaw is associated with asymmetric posterior crossbites, buccal on one side and lingual on the other.

If yaw (the whole dentition rotated to one side) is present, it is necessary to determine whether the problem is primarily a deviation of the dentition relative to the jaw or primarily a deviation of the jaw itself. The girl in image 1 has yaw of the dentition to the left, and a slight yaw of the mandible in the same direction. Note that the yaw of the esthetic line of the dentition is greater than the yaw of the inter-commisure line. A compensatory yaw of the mandibular dentition back toward the facial midline often is present in patients like this.

Image 2 shows severe yaw of the maxillary dentition to the right in a woman with almost no yaw of the mandible. Note that she has more elevation of the lip on the right side, so she also has downward roll of the dentition on the right side relative to the inter-commisure line.

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{{PAGE_192}} Image 1, Yaw of both jaws: Yaw of the maxilla and maxillary dentition to the left, with mild yaw of the mandible in the same direction. This is a largely skeletal problem.

Image 2, Yaw of the dentition: Severe yaw of the maxillary dentition to the right, with almost no yaw of the maxilla itself or the mandible. This is a largely dental problem.

Current Classification Scheme Incorporating pitch, roll and yaw (which occur as an interaction between planes of space) completes the current classification scheme. It’s still a systematic description based on 5 characteristics, with some recent important modifications and additions. The complete Venn diagram is shown here.

If the logic associated with Venn diagrams helps you understand how this scheme was developed and would be used, that’s good. If it doesn’t, you can forget the diagrams now and concentrate on how to use this approach to systematic description as shown in the following section.

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Steps in Systematic Description

Classification by the Five Characteristics of Dentofacial Traits

Systematic description requires evaluation of the five key characteristics of dentofacial traits and malocclusion, with related findings grouped into one of the five characteristics. The key characteristics and the types of findings in each area are shown in the attached box. It also is important to detect any pathologic or functional problems (for example, periodontal disease or TMD). These findings are not included in the systematic description of malocclusion, but obviously must be taken into account when any treatment plan is formulated.

{{PAGE_194}} Classification: The Five Key Characteristics

• Dentofacial Appearance Frontal, oblique and profile facial proportions; anterior tooth display; orientation of esthetic line of occlusion
• Dental Arches: Symmetry, Alignment Symmetry; arch form; crowding/spacing relative to the functional line of occlusion
• Transverse Relationships Posterior crossbite (arch widths), skeletal and dental
• Anteroposterior Relationships Angle classification (overjet), skeletal and dental
• Vertical Relationships Bite depth (face height), skeletal and dental

Step 1: Facial Proportions and Esthetics

The first step in systematic description of malocclusion and dentofacial deformity is evaluation of facial proportions and esthetics. This is carried out during clinical examination of the patient. At this point, antero-posterior and vertical facial proportions (image 1), lip-tooth relationships at rest and at smile (image 2), and facial asymmetry (including roll and yaw) are evaluated.

The results are summarized as the positive findings (problems) from this part of the examination. The clinical findings can be checked against the facial photographs and lateral cephalometric radiograph (and other radiographs, if they were obtained). Cone-beam CT examination of orthodontic patients is becoming increasingly common, and can be used to provide the information from ceph’s as well as almost any other radiographic view.

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{{PAGE_195}} Image 1, Normal vertical proportions: Clinical examination of the patient is necessary in evaluation of dentofacial proportions and symmetry. The descriptive terms are listed in the outer part of the Venn diagram that concluded the previous section.

Image 2, Incisor display: The relationship of the lips to the maxillary dentition on smile (or at rest) determines the amount of display of the incisors. On the left, normal display on social smile; on the right, inadequate display.

Step 2: Alignment and Symmetry Within the Dental Arches

This step is carried out by examining the dental arches (usually, the dental casts) from the occlusal view. The evaluation is first of symmetry or asymmetry within the dental arch, and then of the amount of crowding or spacing that is present.

In a mixed dentition child, the space analysis form with which you are familiar is used. In an adolescent or adult, crowding or spacing is assessed directly by measuring the dental arch length (from the mesial of one first molar to the mesial of the other) and comparing this to the sum of the width of all the teeth (premolars, canines, incisors).

This initial measurement assumes that the form of the dental arch will be maintained, but the amount of crowding must be interpreted in the light of incisor protrusion or retrusion, and also relative to buccal corridor width. If the incisors should be retracted, that would reduce arch length and the amount of space to align the teeth; if arch width should be increased, that would increase arch length.

For the patient whose digital casts are seen here, the observation is reasonable symmetry and moderate crowding in both arches (arch length discrepancy approximately -6 mm). Interpretation of that amount of crowding will have to take into account the relationship of the dentition to the facial soft tissues.

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{{PAGE_196}} Step 3: Transverse Plane, Skeletal and Dental Relationships At this stage, the dental casts are viewed in occlusion and the occlusal relationships are observed, beginning with the transverse plane of space. The goal is to accurately describe the occlusion and distinguish between skeletal and dental contributions to the malocclusion. Malocclusion in the transverse plane is primarily posterior crossbite. Midline discrepancies usually are due just to malposition of incisors due to crowding, and if so are not a transverse problem—but both roll and yaw affect transverse relationships, and a shift of the entire dentition is a transverse problem. As in all three planes of space, it is important to evaluate the underlying skeletal relationships to answer the question, “Is this primarily a skeletal or dental problem?” For the other planes of space, this requires examination of radiographs, but the width of the palate can be seen in the maxillary cast. If the patient has a posterior crossbite due to a narrow maxillary arch, and you need to establish whether the problem is skeletal or dental, how do you do that? You measure the inter-molar width and compare it to the width across the palate as shown in this figure. If the palate is narrow, it’s a skeletal crossbite; if the palate is normal or wide, it’s a dental crossbite. It also is possible, of course, for a posterior crossbite to be due to a wide mandibular arch and a normal maxillary arch. Posterior crossbite usually is a maxillary problem, but not always.

{{PAGE_197}} Step 3: Transverse Plane, Skeletal and Dental Relationships (cont.)

After a discussion at a meeting some years ago of how to differentiate skeletal vs. dental width of the maxillary arch, an elderly gentleman suggested using the rule of thumb. I told him I knew several rules of thumb, which one was he talking about? He said, “No, no, the rule of thumb. If you take the upper cast, and you put your thumb into the palatal vault, if it fits comfortably the vault is wide enough. But if you can’t get your thumb down into the the palatal vault, it’s too narrow.”

That seems like a joke, and of course it isn’t totally serious, but really the width of the thumb and the normal width of the palatal vault are about the same, and this gives you a quick way of checking a skeletal width dimension. Of course you’d have to do some calibration of the width of your own thumb—and you can’t do that with a digital model. A real cast is required.

It’s also possible that a posterior crossbite like the one shown here can be due to a mandible that’s too wide. The width of the mandible can be estimated reasonably accurately from the mandibular inter- molar width. If maxillary dimensions are normal and the mandibular inter-molar width is large, a skeletal problem in the width of the mandible probably is present.

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{{PAGE_198}} Step 4: A-P Plane, Skeletal and Dental Relationships

The Angle classification, in its extended form, serves well to evaluate the a-p plane of space. A key question, of course, is the extent to which excessive overjet (and Class II molars) or reverse overjet (and Class III molars) are due to a jaw discrepancy or to displaced teeth on a normal skeletal base. Careful observation clinically (facial form analysis) usually is adequate to make the decision, but cephalometric analysis makes it possible to answer this question more precisely.

This patient has a Class II malocclusion. Is this a skeletal or dental problem? You will have to look at the facial photographs (and perhaps the cephalometric radiograph) to find out. From this image, what do you think?

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Step 4: A-P Plane, Skeletal and Dental Relationships (cont.)

That’s right, the photograph shows obvious mandibular deficiency, so it’s primarily a skeletal problem like the one diagrammed in image 1, except that there is a strong chin (i.e., the mandibular dentition is a bit retrusive relative to the mandible, not protrusive relative to the mandible as shown in the diagram). If you wanted to know more precisely, a lateral ceph would let you do that (image 2, same patient as previous screen). Now you can see that the maxillary incisors are somewhat proclined, so that the lower incisors are quite upright, and that there is a moderately severe mandibular deficiency.

As you have already learned, cephalometric analysis isn’t a group of measurements of angles and distances. You can use measurements to help you analyze how the dental and facial components fit together, but understanding the relationships is the goal. Often only careful observation is needed to accomplish that.

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{{PAGE_200}} Image 1, Diagrammatic skeletal Class II: This diagram shows the relationship of the facial components, and that is what you want to know from your examination of the patient. Image 2, Ceph of patient seen on the previous page: The ceph confirms that mandibular deficiency is the main problem, but the upright lower incisors contribute to the excessive overjet. If you have a good eye for proportions, the ceph confirms what you had already observed clinically.

Step 4: A-P Plane, Skeletal and Dental Relationships (cont.)

Occasionally, in a patient with excessive overjet the molar relationship is Class II on one side and Class I on the other. Angle called this a Class II subdivision, but this label is not useful because it does not describe the real problem.

Often the Class I side is due to early loss of a lower 2nd primary molar and mesial drift of the first molar, but the problem may be a yaw discrepancy of the dentition or jaw. If so, that should have been detected in the clinical examination but can be confirmed now. The major indication for taking a P-A ceph or a large-field-of-view cone beam CT is to more completely evaluate a jaw asymmetry.

The patient shown here (image 1) has both a roll of the mandible down on the right and yaw of the mandible to the left. The P-A ceph (image 2) makes it easier to see both of these characteristics, but you can pick up both on examination of the face.

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{{PAGE_201}} Image 1, Asymmetry: due to?: Note the yaw of the chin to the left, and the roll of the mandible down on the right (look at the vertical location of the gonial angles. Image 2, PA ceph for evaluation of asymmetry: In the PA ceph, both the yaw and roll aspects of the facial deformity can be seen clearly—but both were detectible on clinical examination.

Step 5: Vertical Plane, Skeletal and Dental Relationships

The fifth and final step in the classification procedure is to consider the vertical plane of space, in exactly the same way that the anteroposterior plane of space was considered. Now we need to know whether an open bite or deep bite is present, whether the patient has a skeletal open bite (long anterior face height) or skeletal deep bite (short anterior face height), and whether there is a pitch discrepancy.

On clinical examination this patient’s anterior open bite is obvious (image 1). What you can’t tell by looking at the occlusion, of course, is whether this open bite is due to lack of vertical development of the alveolar process, in other words to incisor teeth that did not erupt enough; or whether the problem is a vertical displacement of the jaw, so that the teeth do not come together anteriorly. To determine that, a close look at facial proportions and tooth-lip relationships is needed.

Look at images 2 and 3. What do you think?

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{{PAGE_202}} Image 1, Anterior open bite: The open bite is obvious on clinical examination, but to determine its cause you have to look at facial proportions and evaluate whether pitch of the maxilla or mandible is present. Image 2, Frontal facial view (same patient): Long face or normal face height? Harder to see in the presence of the beard, isn’t it?

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Image 3, Lateral facial view: Long face? Pitch discrepancy? (Look at the mandibular plane angle, you can see that.)

Step 5: Vertical Plane, Skeletal and Dental Relationships

This time the beard makes it a little harder (image 1), but clinically you saw it correctly: lower face height is too long, the maxilla probably is rotated down posteriorly (you can see that in an intraoral view—look again at image 1 on the previous page), and the mandible appears to be rotated down and back—so it’s largely a problem of too little vertical growth of the mandibular ramus relative to downward growth of the posterior maxilla and/or excessive eruption of posterior teeth. That increases anterior face height and causes an anterior open bite, unless the incisor teeth erupt much more than normal. This is shown in a tracing from a different patient in image 2.

It’s an important and sometimes difficult concept: a patient with a skeletal open bite has rotation of the jaws, with excessive downward growth of the posterior maxilla, downward rotation of the mandible, and normal (or even excessive) eruption of anterior teeth. Characterizing the problem in that way will prevent a common mistake in treatment planning, the thought that elongating the incisors is the appropriate way to correct the open bite. Sometimes that’s true, but not for patients with skeletal open bite.

Skeletal or dental vertical problems often can be described as pitch discrepancies. As we noted above, this can be seen in the orientation of the mandiblar, occlusal and palatal planes. Drawing those planes on a cephalometric tracing can help considerably in recognizing where the problem arises. Note in image 2 that the palatal plane is rotated down posteriorly and the mandibular plane is rotated down anteriorly.

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{{PAGE_204}} Classification - Problem List The positive findings from the five steps in systematic description form the developmental problem list for the patient. Following the steps in the sequence outlined above, and taking care to group findings in the five major areas, results in a thorough analysis without becoming overwhelmed with details. The more complex the case, the more a systematic approach is likely to be required to clarify the situation—but thinking your way through your patient’s situation in this way quickly becomes a mental checklist to prevent overlooking something important.

Take a good look at the work-up for an interesting patient that is shown in pages 214-219 of the 5th edition of Contemporary Orthodontics (pages 229-223 in the 4th edition)**, and at her treatment plan and outcome in pages 259-265 (258-267 in 4th edition).

Before you take the self-test, also do the reading about the classification method (pages 204-214 in 5th edition, 218-229 4th edition). The use the self-test to be sure you have understood how systematic description is used as a way to cover all aspects of a patient’s orthodontic problems without becoming confused by too much detail.

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