05 - 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

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).

Image 1, Angle’s 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.: 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: 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: If the lower molar was behind the upper molar (remember, for Angle the upper 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.
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.

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.

Image 1, Ideal occlusion viewed from the facial side, the way we usually see it.(for a skull called “Old Glory”): As predicted by Angle, with the first molars in an ideal relationship, the other teeth interdigitate perfectly around the arch.	Image 2, Ideal occlusion from the lingual: Perfect, or nearly perfect, interdigitation of the teeth viewed from the lingual on a dissected skull. For patients, this view requires dental casts.

The Goal of Classification (cont.)

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

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.

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.

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.

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.

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.

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.

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.

Analagous 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.

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.

Image 1, Analagous malocclusions, different underlying causes: The considerable difference in jaw relationships is apparent on clinical examination of the two faces.	Image 2, Analagous malocclusions, different skeletal relationships: The cephs are quite different—one of the patients has a Class II malocclusion because of mandibular deficiency, a skeletal problem. The other’s Class II is due largely to displacement of the teeth relative to their supporting bone—the jaws are about the same size.

Overcoming the Limitations

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).

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).

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.

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 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.

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 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.

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).	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.
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.

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.

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 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.

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.

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.

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 cephs as well as almost any other radiographic view.

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.

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.

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.

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?

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.

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.

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?

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?
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.

Image 1: This patient has a vertically increased lower third of the face and increased mandibular plane angle.	Image 2, Orientation of horizontal planes: This patient has a less severe problem than the one above, but you can see the downward-backward pitch of the palaal plane on the ceph tracing. Pitch discrepancies often contribute to both open bite and deep bite.

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.

Self-Test

Question 1

(A) The Angle classification ignored the possibility of excessive protrusion of the teeth that compromised esthetics because (B) Angle believed that everyone had the potential to have 32 teeth in ideal occlusion without an esthetic problem.

1. A true, B true, A and B related ✓
2. A true, B true, A and B not related
3. A true, B false
4. A false, B true
5. A and B false

Correct

That is correct. Angle strongly opposed the extraction of teeth for orthodontic purposes, and justified the protrusion that aligning crowded teeth could produce by insisting that the patient looked best that way, whatever they might think.

Incorrect

No, that’s wrong. The statements are true and related. Angle strongly opposed the extraction of teeth for orthodontic purposes, and justified the protrusion that aligning crowded teeth could produce by insisting that the patient looked best that way, whatever they might think.

Question 2

Which of the following terms are inappropriate to use within the original Angle classification system?

1. incisor crowding
2. deep bite
3. posterior crossbite
4. skeletal Class III
5. 1 and 2
6. 3 and 4
7. 1, 2, and 3
8. 2, 3, and 4 ✓
9. all the above

Correct

That’s right. The Angle system recognizes incisor crowding as a deviation of tooth position from the line of occlusion, but does not include descriptions of vertical, transverse or skeletal relationships.

Incorrect

No, that’s wrong. The Angle system recognizes incisor crowding as a deviation of tooth position from the line of occlusion, but does not include descriptions of vertical, transverse or skeletal relationships.

Question 3

How does the addition of protrusion to the characteristics considered in classification affect the way crowding is measured?

1. requires lip prominence to be considered
2. requires cephalometric analysis
3. requires adjustment of arch length discrepancy
4. 1 and 2
5. 2 and 3
6. 1 and 3
7. all the above
8. none of the above ✓

Correct

That’s right, adding a consideration of protrusion to the classification system has no effect on how the amount of crowding is measured. The effect is on the interpretation of arch length deficiency or spacing, not on how the space analysis itself.

Incorrect

No, that’s wrong. Adding a consideration of protrusion to the classification system has no effect on how the amount of crowding is measured. The effect is on the interpretation of arch length deficiency or spacing, not on how the space analysis itself.

Question 4

Which of the following characteristics of malocclusion would be most likely to be associated with a pitch of the maxilla down posteriorly?

1. anterior open bite ✓
2. anterior deep bite
3. posterior crossbite
4. posterior open bite
5. all are equally possible

Correct

That’s right, if the maxilla is pitched down posteriorly, the mandible also is likely to rotate down and back, and anterior open bite is likely. Pitch is not related to crossbite. Pitch in the other direction would be associated with anterior deep bite, and perhaps (though that is unlikely) with posterior open bite.

Incorrect

No, that’s incorrect. If the maxilla is pitched down posteriorly, the mandible also is likely to rotate down and back, and anterior open bite is likely. Pitch is not related to crossbite. Pitch in the other direction would be associated with anterior deep bite, and perhaps (though that is unlikely) with posterior open bite.

Question 5

(A) The Ackerman-Proffit classification scheme uses five characteristics of malocclusion because (B) the five-characteristic scheme is quite compatible with computer data base management and computerized diagnosis.

1. A true, B true, A and B related
2. A true, B true, A and B not related ✓
3. A true, B false
4. A false, B true
5. A and B false

Correct

That’s correct, both statements are true but they have no cause-effect relationship. Five characteristics are the smallest number that allow a complete description of the malocclusion. Almost any scheme could be used in a computer data base.

Incorrect

No, that’s incorrect. Both statements are true but they have no cause-effect relationship. Five characteristics are the smallest number that allow a complete description of the malocclusion. Almost any scheme could be used in a computer data base.

Question 6

Which of the following types of malocclusion is most likely to be associated with a roll of the maxilla to the left?

1. posterior crossbite
2. anterior deep bite
3. anterior open bite
4. crowded incisors
5. all are equally likely ✓

Correct

That is correct. A roll discrepancy is perceived as a tilt of the dentition relative to the inter-commisure and inter-ocular lines, but does not necessarily affect the dental occlusion at all, i.e., a patient with a roll to the left could have ideal occlusion as perceived from examination of dental casts (unless they were carefully oriented on an articulator). The patient also could have any type of malocclusion, depending on factors other than the roll.

Incorrect

No, that’s incorrect. A roll discrepancy is perceived as a tilt of the dentition relative to the inter-commisure and inter-ocular lines, but does not necessarily affect the dental occlusion at all, i.e., a patient with a roll to the left could have ideal occlusion as perceived from examination of dental casts (unless they were carefully oriented on an articulator). The patient also could have any type of malocclusion, depending on factors other than the roll.

Question 7

What is the greatest risk of an inadequate classification that confuses analogous and homologous patients?

1. important aspect overlooked
2. esthetic outcome jeopardized
3. risk of not obtaining ideal occlusion
4. improper treatment plan ✓
5. they’re all equally important risks

Correct

That’s right, the greatest risk of a classification that confuses analogous with homologous problems is that an improper treatment plan will be selected. The improper treatment plan could relate to any or all the other risks listed here.

Incorrect

That’s wrong. The greatest risk of a classification that confuses analogous with homologous problems is that an improper treatment plan will be selected. The improper treatment plan could relate to any or all the other risks listed here.

Question 8

In the first step in Ackerman-Proffit classification, which of the following are major items for evaluation?

1. facial proportions
2. tooth-lip relationships
3. occlusal relationships
4. skeletal vs dental relationships
5. 1 and 2 ✓
6. 2 and 3
7. 3 and 4
8. 1, 2, and 4
9. all the above

Correct

That’s right. The first step is to consider facial proportions and tooth-lip relationships. Occlusal relationships and skeletal vs. dental relationships are considered in steps 3-5, using both clinical and radiographic data.

Incorrect

No, that’s wrong. The first step is to consider facial proportions and tooth-lip relationships. Occlusal relationships and skeletal vs. dental relationships are considered in steps 3-5, using both clinical and radiographic data.

Question 9

Which of the following is not a possible explanation of Class I molars in a child who has excessive face height?

1. distal position of the maxilla
2. mesial shift of the lower molar
3. large mandible
4. excessive eruption of the maxillary teeth ✓

Correct

That’s right, excessive eruption of the upper teeth would not compensate for the excess face height and downward-backward rotation of the mandible, but the other three things could.

Incorrect

No, that’s wrong. Excessive eruption of the upper teeth would not compensate for the excess face height and downward-backward rotation of the mandible, but the other three things could.

Question 10

Which of the following is most likely to be associated with anterior open bite?

1. increased distance from nose to upper incisor
2. increased distance from lower lip to chin
3. increased distance from nose to chin ✓
4. increased distance from condyle to chin

Correct

That’s right, if anterior face height is increased, it is likely that the patient will have anterior open bite. An increased distance from nose to upper incisor, indicating excessive eruption of the maxillary anterior teeth, would decrease the chance of open bite. The other two are not related to open bite.

Incorrect

No, that’s wrong. If anterior face height is increased, it is likely that the patient will have anterior open bite. An increased distance from nose to upper incisor, indicating excessive eruption of the maxillary anterior teeth, would decrease the chance of open bite. The other two are not related to open bite.

Question 11

On clinical examination, in assessing whether incisor protrusion is excessive, exactly what do you look for?

1. protrusion of the upper incisor relative to the lower
2. protrusion of the upper incisor relative to the maxilla
3. protrusion of the lower incisor relative to the mandible
4. protrusion of the lips
5. separation of the lips at rest
6. 1 only
7. 2 and 3
8. 4 and 5 ✓
9. 2, 3, 4, 5
10. all of the above

Correct

That’s right, the lips are the key to judging whether incisor protrusion is excessive. Incisor protrusion is measured by the relationship of the upper incisor to the maxilla and the lower incisor to the mandible, but the judgment as to whether this amount of protrusion is excessive is based on whether the lips are both protruded and separated at rest so that they are strained when brought together.

Incorrect

No, that’s incorrect. The lips are the key to judging whether incisor protrusion is excessive. Incisor protrusion is measured by the relationship of the upper incisor to the maxilla and the lower incisor to the mandible, but the judgment as to whether this amount of protrusion is excessive is based on whether the lips are both protruded and separated at rest so that they are strained when brought together.

Question 12

What is the characteristic that would be most useful in distinguishing a skeletal from a dental posterior crossbite?

1. transverse relationship of upper to lower molar
2. maxillary intermolar width
3. mandibular intermolar width
4. width of palatal vault ✓
5. width of gonial angles

Correct

That’s right. The key measurement for assessment of skeletal crossbite is the width of the maxilla at the height of the palatal vault, which often is narrow. The width of the gonial angles is less relevant because it’s not as closely related to the dental occlusion. Intermolar width tells you nothing about whether a crossbite is skeletal or dental.

Incorrect

No, that’s wrong. The key measurement for assessment of skeletal crossbite is the width of the maxilla at the height of the palatal vault, which often is narrow. The width of the gonial angles is less relevant because it’s not as closely related to the dental occlusion. Intermolar width tells you nothing about whether a crossbite is skeletal or dental.

Question 13

Which of the following is least likely to produce Class II malocclusion?

1. maxillary dentition positioned upward relative to maxilla ✓
2. maxillary dentition positioned anteriorly relative to maxilla
3. maxilla positioned anteriorly relative to cranial base
4. mandible retrusive relative to cranial base
5. mandibular dentition retrusive relative to mandible

Correct

That’s right, moving the maxillary teeth upward relative to the maxilla tends to produce Class III, not Class II malocclusion because the mandible would rotate up and forward. All the other relationships increase the tendency toward Class II.

Incorrect

No, that’s wrong. Moving the maxillary teeth upward relative to the maxilla tends to produce Class III, not Class II malocclusion because the mandible would rotate up and forward. All the other relationships increase the tendency toward Class II.

Question 14

Which of the following are characteristics of skeletal deep bite?

1. excessive vertical overlap of the upper and lower incisors
2. short posterior face height
3. short anterior face height
4. low mandibular plane angle
5. 1 and 2
6. 1 and 3
7. 2 and 3
8. 3 and 4 ✓
9. 1, 3, and 4

Correct

That’s right. Short anterior face height and a low mandibular plane angle are characteristics of skeletal deep bite. Long, not short posterior face height is the skeletal characteristic, and of course the dental relationship is irrelevant in determining the skeletal condition. That’s true even though too much vertical overlap of the incisors is likely in a patient with a skeletal deep bite jaw relationship.

Incorrect

No, that’s wrong. Short anterior face height and a low mandibular plane angle are characteristics of skeletal deep bite. Long, not short posterior face height is the skeletal characteristic, and of course the dental relationship is irrelevant in determining the skeletal condition. That’s true even though too much vertical overlap of the incisors is likely in a patient with a skeletal deep bite jaw relationship.

Question 15

Which of the following is least likely to produce a Class III malocclusion?

1. maxillary dentition posteriorly positioned relative to maxilla
2. maxilla posteriorly positioned relative to cranial base
3. mandibular dentition anteriorly positioned relative to mandible
4. mandible prominent relative to cranial base
5. mandible rotated to steep mandibular plane angle ✓

Correct

That’s right, rotation of the mandible downward and backward decreases the its prominence in the a-p plane of space, and is more associated with Class II than Class III malocclusion. The other relationships increase the tendency toward Class III.

Incorrect

That’s wrong. Rotation of the mandible downward and backward decreases the its prominence in the a-p plane of space, and is more associated with Class II than Class III malocclusion. The other relationships increase the tendency toward Class III.

Question 16

Which of the following are likely to be noted in a patient with a severe yaw of the maxillary dentition to the right?

1. maxillary midline to the right of the facial midline
2. buccal posterior crossbite on the right
3. Class II molar relationship on the left
4. anterior open bite
5. 1 and 2
6. 3 and 4
7. 1, 2, and 3 ✓
8. 1, 2, and 4
9. all the above

Correct

That’s right. A severe yaw to the right definitely would bring the maxillary midline to the right, and is likely to produce buccal crossbite on the right and a Class II molar relationship on the left side as the dentition is rotated forward on that side. Anterior open bite is not related to yaw.

Incorrect

That’s wrong. A severe yaw to the right definitely would bring the maxillary midline to the right, and is likely to produce buccal crossbite on the right and a Class II molar relationship on the left side as the dentition is rotated forward on that side. Anterior open bite is not related to yaw.