02 - To Extract or Not To Extract Part 1

Background

Reasons for Orthodontic Extraction

There are two reasons for extracting teeth in orthodontic treatment:

• correction of crowding/protrusion
• camouflage of jaw discrepancy

As a general rule, extraction for crowding/protrusion is done for patients with Class I malocclusion, i.e., no skeletal problem. Extraction for camouflage is done for patients with Class II or (less frequently) Class III problems.

It is important to keep the purpose of extractions in mind. Because some patients with a skeletal problem (mandibular deficiency, for instance) also have crowded teeth, extractions for crowding/protrusion sometimes are needed in patients who also have a Class II or Class III problem. The same extraction space can’t be used to correct crowding and again for camouflage, so crowded teeth in a Class II or Class III patient can greatly limit the possibility for camouflage.

This program focuses on crowding/protrusion in patients with normal jaw relationships (Class I malocclusion). Part 2 of To Extract or Not to Extract reviews extraction for camouflage of skeletal problems.

Crowding and Protrusion: Aspects of the Same Thing

An important concept: crowding and protrusion are really two different aspects of the same thing.

If there isn’t enough room for the teeth:

• either they remain upright and become crowded and irregular
• or they align themselves on the arc of a larger circle and protrude

Both of the patients shown here have the same amount of room for the teeth in the lower jaw. Note the crowding in both arches for the patient in image 1. Even with this degree of crowding, some protrusion also may be present. You wouldn’t know until you looked at the patient’s face.

In image 2, the lower incisors are aligned, and there is moderate crowding in the upper arch. The incisors are aligned because, although the patient had had no treatment, they protruded forward during growth, at the expense of the lip. The prominence of the roots of the lower incisors suggests protrusion, but you would have to look at the face to evaluate how protrusive they are.

The important point: if there’s not enough room for the teeth, soft tissue characteristics of individual patients determine whether they’re crowded, are protrusive, or have some aspects of both.

Image 1: crowding: Crowding expressed in both arches.	Image 2: protrusion?: Potential crowding expressed largely as protrusion.

Facial Impact of Protrusion

How do you evaluate protrusion when you look at the patient’s face? It’s hard to see from the frontal but can be observed in oblique and profile views.

An important guideline:

The teeth are too protrusive if:

• the lips are separated at rest, and
• strained and everted on closure

This is the face that goes with the intraoral picture of protrusion that you just saw. In the oblique view, with the lips relaxed, note that the lips are separated at rest. More than 4 mm lip separation at rest is excessive.

In the profile view, with the lips together, you can see that the lips are both strained and everted. Eversion refers to the prominence of the lip relative to its base. For the upper lip, that is the base of the nose; for the lower lip, it is the sulcus between the lip and chin. Lip eversion and lip protrusion are the same thing. Our terminology is that protrusion of the incisors is reflected in eversion of the lips.

Remember that both of these findings, lip separation at rest and strain/eversion on closure, must be present to make the diagnosis of excessive incisor protrusion. Prominent, protrusive, or everted lips can be present as a soft tissue characteristic that is not due to protrusion of the incisors.

Oblique view: >4 mm lip separation at rest is excessive.	Profile view: Note the lip strain on closure and lip protrusion.
Combined views: Combination of lip separation at rest and lip strain on closure indicates excessive incisor protrusion.

Extraction for Crowding/Protrusion

The purpose of extraction in the treatment of crowding/protrusion, of course, would be to:

• provide space to align crowded teeth without protruding them, or
• provide space to retract protruded teeth to a normal relationship with the lips and jaw
• or perhaps something of both (though, as we have already noted, the same space can’t be used twice to obtain both alignment and retraction)

Conversely, expansion of the arches—aligning the teeth without extraction—would be the best treatment if the teeth were retruded, not providing enough lip support.

You’d have to look at the face, not just the teeth, to determine that as well. These two patients illustrate the extremes in lip support from the teeth.

The woman in image 1 has too little lip support, so her profile is concave. Her lips are thin and lack normal prominence. Her incisors are retrusive, not prominent enough for best esthetics. Appropriate treatment for her would be to move the incisors facially—certainly they should not be retracted any further.

The woman in image 2 has a convex profile, with prominent lips that are separated at rest. Though you can’t see it here, her lips also are strained on closure. She has protrusive incisors, especially relative to her chin, and in orthodontic treatment, she would be a candidate for premolar extraction so that the incisors could be retracted.

image1, retrusive: Concave profile, inadequate lip support: retrusive incisors.	image 2, protrusive: Convex profile, excessive lip support: protrusive incisors.

Extraction Percentages over Time

Dentists’ opinions about extraction for crowding/protrusion have changed dramatically over time.

Early in the 20th century, as orthodontics developed, expansion of the arches was the usual treatment. By mid-century, extraction of first premolars was used frequently to provide space for alignment and/or retraction of canines and incisors. By the end of the century, expansion again was used more often than extraction.

This graph shows data from the graduate orthodontic clinic at UNC and illustrates the shift from expansion to extraction and back again. The percentage of patients treated in the clinic who had extraction of first premolars, the typical extraction pattern used to treat Class I crowding/protrusion, increased sharply in the late 1950s, then slowly declined over the next 30 years. The same type of change occurred in most American locations, although the increase in extraction percentages occurred earlier in many areas.

Reasons for Increase in Extraction Percentage

Why did extraction replace expansion as the usual treatment, at least for a while? The reason is critically important in understanding the whole issue of extraction versus arch expansion (nonextraction) in orthodontic treatment of crowding/protrusion:

It was a search for stability of the result.

By the mid-20th century, both doctors and patients observed that all too often after the arches were expanded to correct crowding of the teeth, relapse occurred. Prominent orthodontists reported that after premolar extraction, relapse problems disappeared.

The increasing use of bands on all (instead of just some) of the teeth to provide more precise orthodontic tooth movement also had an effect on the expansion/extraction decision. Although each band is quite thin, the cumulative effect of band material at every contact point can be several millimeters of arch length. So fully banded treatment tended to mean a higher percentage of patients with extractions.

But the big reason for extraction was to improve the chance that once the teeth were straight, they would stay straight and not relapse into crowding.

Reasons for Decrease in Extraction Percentage

Why did the pendulum swing back toward nonextraction (expansion) more recently? There are several reasons:

1. Retracting incisors too much can harm facial esthetics in some patients, and the first (small) decrease in the extraction percentage in the late 1960s probably was related to a better appreciation of this problem.
2. Research data in the 1970s, from long-term (>10 year) recall of patients treated for Class I crowding, showed that relapse into crowding still occurred in some patients even after extraction. That reduced the enthusiasm for extraction as a guarantee of long-term stability.
3. In the 1980s, bonding of attachments largely replaced banding (typically, except for molars), and band space no longer was a major consideration. This made it possible to align crowded teeth without so much protrusion—so the number of extraction cases decreased further.
4. In the 1990s, some practitioners linked premolar extraction—wrongly—to the development of TMD. Those claims, though false, led to a widely reported lawsuit and a more defensive approach by some practitioners.
5. Finally, most clinicians agree that it is more difficult and takes longer to treat extraction cases well, which tends to reduce enthusiasm for extraction in borderline cases.

The interesting result: a complete cycle, so that the extraction percentages in 1955 and 1995 were the same. In the first decade of the 21st century, as you can see, extraction percentages have remained at about the same level.

Current Spread in Extraction Percentages

There was an interesting public debate in the late 1990s between two longtime friends who practice in Texas and differ on the indications for extraction. Both kept up with the percentage of extractions in their practices for a year—more than 200 consecutively treated patients for each. Both felt that the great majority of their patients had a satisfactory outcome from treatment.

The extraction advocate had a 50% extraction rate (for all types of cases, not just crowding/protrusion); the nonextraction advocate had a 20% rate. Probably extractions in 5-10% of the patients were for camouflage, not crowding/protrusion. So for Class I patients, the expansion advocate was extracting premolars in 10-15%, the extraction advocate in 40-45%.

Those numbers probably illustrate the bounds for extraction at present and outline the area of debate. It appears that extraction or expansion is a clear-cut decision for two-thirds of the patients, i.e., both doctors would treat them the same way, while one-third perhaps could be treated either way.

Further evidence on the minimum extraction percentage was presented recently by an advocate of expansion who reported that 10% of a large sample of his patients required extraction to prevent excessive protrusion.

The bottom line: not all patients can be expanded successfully. Judicious extractions are necessary for some patients and may facilitate treatment in others.

Scientific Knowledge: Extraction Effect on Jaw Function

Let’s look at what we know about the extraction decision and the three important aspects of orthodontic treatment outcomes, starting with the impact of premolar extraction and jaw function. What difference does it make if your premolars are present or absent, in terms of occlusion and jaw function?

Does it affect how well you can eat? Almost surely not—there’s no evidence at all to support the idea that you need 8 premolars for normal mastication.

Are you more likely to develop TM dysfunction if your first premolars have been extracted? That claim, as we have noted, was made in the 1990s, without any scientific data to support it, and it has been totally refuted by research. It is interesting that the dentists who offered this idea were quite prepared to extract second molars instead. No explanation was offered as to why first premolars were vital components of the dental occlusion and second molars were not.

The bottom line: the presence or absence of premolars has little or no effect on function, and premolar extraction does not lead to TM joint dysfunction.

Esthetics

Extraction to Improve Facial Esthetics

The esthetic effect of extraction has been debated for a long time. In the early 20th century, concerns were expressed about esthetic problems created by too much protrusion, and this remains a potential problem to this day. If the arches are expanded too much to correct crowding of the teeth, there are two problems: the result tends to be unstable, and the excessive protrusion of the incisors is unesthetic.

This patient sought retreatment after expansion of her crowded dental arches because she and her parents didn’t like the way it looked. After premolar extraction allowed retraction of the protruding teeth, she was elected Miss Alabama. It’s a dramatic illustration that too much protrusion damages esthetics and retracting teeth to correct protrusion can improve it. (Courtesy Dr. David Sarver)

After initial treatment: Age 16, after orthodontic expansion of both arches that resulted in excessive protrusion.	After retreatment: Age 17, after retreatment with premolar extraction and retraction of incisors.
Profile change: Profile views before/after retraction of protruding incisors.	As Miss Alabama: Age 18, Miss Alabama.

Expansion to Improve Facial Esthetics

By the same token, as you have seen already, lack of lip support also can decrease profile esthetics.

In evaluating esthetics, however, it isn’t enough to look just at the profile. What really counts is what the smile looks like. Changing the width of the dental arches can improve smile esthetics for some patients—and of course, if the arches were expanded too much, also could make smile esthetics worse.

This girl’s narrow upper arch, which contributed to moderate crowding, also gave her wide buccal corridors, i.e., too much space between the cheeks and the teeth when she smiled.

Note the esthetic improvement from transverse expansion that also created enough space to allow the teeth to be aligned without excessive protrusion of the incisors.

Narrow arch: Prior to treatment: narrow arch, teeth too far from cheeks.	Transverse expansion: After expansion of the maxillary arch: better esthetics.
Before/after expansion: Comparison of smile esthetics after transverse expansion.

Extraction versus Expansion: Effect on Esthetics

Exactly how do expansion and extraction affect esthetics? By changing the prominence of the teeth. All other things being equal, expanding the arches would move the incisors facially and make them more prominent, and extracting would have the opposite effect. Obviously, this could be controlled to some extent by how much the expansion moved the posterior teeth laterally rather than forward and by how extraction spaces were closed (with more or less retraction of the incisors versus forward movement of the posterior teeth).

This diagram indicates the amount of change that might occur in typical treatment of crowding/protrusion. If you were close to the maximum amount of acceptable protrusion before treatment, expansion could move you outside the acceptable range. If you were too retrusive initially, expansion would move you into the acceptable range. If you were near the center of the acceptable range, expansion would simply leave you esthetically acceptable, as you were to start with.

Extraction, of course, would move you in the other direction. For some patients, extraction would be necessary to move into the esthetically acceptable range; for some others, extraction would definitely be contraindicated because it would move the patient outside the acceptable range; and for others, the esthetic outcome would be to leave the patient acceptable, as he or she was before treatment.

How can two doctors disagree about the need for extraction, when both insist (correctly) that the esthetic outcomes are satisfactory? Because of the expansion/extraction decision is not critical for esthetics in many patients, who stay in the acceptable range either way.

How Many Need Extraction for Esthetics?

How many patients would need extraction for esthetics? One recent and extensive data set, from patients treated by Dr. James McNamara, who used extractions only when it was deemed absolutely necessary, shows a 10% extraction rate. This suggests that at least 10% need extraction to be treated without being moved outside the acceptable range in the direction of too much protrusion.

How many crowded patients would be moved outside the esthetically acceptable range in the other direction, by extraction? There are no data, but perhaps the same 10-15% estimate would be a good guess as to the number who would be esthetically unacceptable with premolar extraction.

The bottom line: the effect on esthetics is a critical consideration in the extraction versus expansion decision for some (but by no means all) patients with crowding/protrusion. It is better to treat without extractions if this is possible, so the number of patients for whom there is an esthetic limitation from too much expansion is the important thing to remember.

Stability

Extraction and Stability

The same thinking applies to the relationship between extraction and stability, but it’s a bit more complicated.

The orthodontists of the mid-20th century, when the extraction percentage increased, made an assumption about stability that was based on clinical observations, not on carefully collected data. The assumption was that moving the patient toward full lips by expanding the arches caused increased pressure by the lips and cheeks, which promoted relapse, and that flattening the lips by making the teeth less prominent reduced lip-cheek pressures and made the tooth position more stable.

Stability is not that simple, but it seems reasonable that extraction would be:

• critical for stability in some patients who were borderline initially, i.e., who already had as much prominence of the teeth as the lips and cheeks would tolerate,
• wouldn’t make much difference for others,
• and might actually make some patients less stable because lip-cheek pressure would be too low relative to tongue pressure.

That concept is expressed in a diagram similar to the one for esthetics.

Greater Stability in Extraction Cases?

We know now that many patients have relapse into crowding of teeth after orthodontic treatment. Especially, lower incisors tend to become irregular long-term no matter what was done during treatment in adolescence. Because lower incisor crowding occurs in nearly everyone in their late teens and early twenties, even in those who naturally had nicely aligned incisors up to that time, it is not surprising that incisor crowding can happen after orthodontic treatment.

It’s clear that some extraction patients experience relapse. That doesn’t mean that relapse isn’t an even bigger problem after arch expansion. Unfortunately, there are no good data to document the chance of relapse into crowding with the alternative forms of treatment.

The difficulty in obtaining good data for treatment outcomes is that you have to carefully follow patients for a long time, and that’s hard to do. How many patients treated in early adolescence can be brought back for 10-year recall? Not all, for sure, and there is a chance that the ones who respond to recall are those who are unusually proud of their treatment outcome or unusually critical of it.

Nevertheless, there is some evidence that extraction helps with stability, as for instance the findings that on long-term recall, nonextraction cases have the highest irregularity and that patients who had serial extraction have relatively low irregularity. But the relationship is not nearly as clear-cut as was thought at one time.

Why Should Expansion Be More Successful Now?

An important question is, “If nonextraction treatment led to so many relapse problems years ago, why should we expect it to be more successful now?”

There are two answers. The first is that if you can keep the first permanent molars from shifting forward so that the leeway space is available, research data show that about 70% of the Class I crowded patients would have enough room to align the rest of the teeth. Leeway space, of course, is the difference in size of the second primary molars and second premolars.

Is it possible to maintain the leeway space? Yes, in most instances, so the ideal time to treat most children with crowding/protrusion problems is to start at the very end of the mixed dentition, just as the second primary molars are ready to exfoliate. Maintaining leeway space minimizes the need for arch expansion, so this approach would be expected to be more stable long-term. Of course, there still would be the normal tendency for lower incisors to become crowded toward the end of growth.

The second answer is that transverse expansion of the dental arches has been shown to be more stable than antero-posterior expansion. Perhaps you could say that the cheeks are more tolerant than the lips when the teeth are moved facially. So in current treatment, transverse expansion is emphasized, and protrusion of the incisors is not as great as it would have been if all the expansion were in the incisor region.

Leeway space: Maintaining leeway space allows about 70% of Class I crowding patients to be corrected without arch expansion.	Transverse expansion: Transverse expansion limits incisor protrusion.

Ways to Produce Transverse Expansion

There are three ways to produce transverse expansion:

• arch wires
• passive devices to hold lips/cheeks away
• opening of the midpalatal suture

Arch wires can be expanded to increase the circumference of the dental arch, and can be manipulated to create more or less of the total expansion transversely or anteriorly.

Passive devices that hold the lips away from the lower incisors can and do result in more prominence of the incisors, because of the change in the balance between tongue vs. lip forces that this produces. There is no evidence to show that this type of change in tooth position is more stable than changes created by orthodontic tooth movement. Stability, after all, is determined by the lip pressure after the device is removed, and the extent to which the lips change when these devices are used is debatable.

The current favorite approach is to open the midpalatal suture to widen the maxilla, then use arch wires to expand the mandibular arch, but no data exist to show that this method gives better results long-term.

Moderate transverse expansion by any of these methods seems to be acceptable.

Palatal expander, frontal: Bonded appliance in place, to expand across midpalatal suture.	Palatal expander, occlusal: Bonded appliance with jackscrew to expand across midpalatal suture.

How Much Expansion Can Be Tolerated?

Perhaps the most important question of all, from the perspective of stability, is: “How much expansion can be tolerated?”

Orthodontists often have compared individual patients to population averages and decided how much to move teeth based on what it would take to make the patient more like the average. For stability after treatment, that doesn’t work. The lower arch is the key, and you must look not at the original arch dimensions but at the amount of change that would be produced by treatment. Let’s look again at a slide you saw in Level III in the discussion of equilibrium effects on the dentition. The best evidence suggests that:

• the lower incisors can be moved forward 2 mm, if they’re not already protrusive
• very little if any expansion across the canines is stable
• 2-3 mm expansion across the premolars and molars is tolerated

The combination of 2 mm forward movement of incisors and 2-3 mm transverse expansion can provide a 6-7 mm increase in arch length for most patients. Beyond that, although further expansion is possible, stability becomes a real concern.

Summary/Conclusions

What Do You Do with the Child with Class I Crowding/Protrusion?

So what do you do with the child in your practice who has Class I crowding and perhaps some protrusion as well?

Three thoughts:

• be sure that treatment starts in the late mixed dentition, so that leeway space will be available if needed. Don’t wait until all the permanent teeth erupt—but there’s no advantage for most children to start before the late mixed dentition. With very few exceptions, enthusiasm for treating 8-year-olds for crowding is not supported by evidence.
• be sure that dental and facial esthetics are considered on both sides of the extraction/nonextraction decision. For some children, extraction is the only way to get good esthetics. For others, expansion is the only way.
• be sure that expansion/extraction decisions are made in the context of the amount of change for an individual patient, not from comparing his or her arch dimensions to some population average. Stability, after all, is a function of the change produced within an individual patient.

What Do You Do with the Adult with Class I Crowding/Protrusion?

An adult who is concerned about Class I crowding almost surely is concerned about the dental and/or facial esthetics but may also hope that TM pain-dysfunction would disappear if the occlusion were better. In that case, there also are three thoughts to keep in mind:

• fortunately, orthodontic treatment almost never is the primary cause of TMD. Unfortunately, orthodontics also rarely corrects it. So orthodontics to treat TM joint problems should be approached with great caution.
• often, the best esthetic outcomes in adults will require permanent retention
• computer simulations of treatment outcomes can help adults understand the esthetic implications of treatment decisions in a way they can’t from words

Let’s look at an adult in whom computer simulation of probable outcomes was important in deciding on extraction or nonextraction treatment.

Computer Simulations

This woman was concerned about mildly crowded upper and more severely crowded lower incisors, especially the lip irritation that the lower incisors produced. She admitted that she hoped to improve her appearance by getting treatment at age 45. Her lip support, as seen in the profile view (image

1. reflected the thinning of lips that occurs with increasing age.

Using computer-generated simulations of the profile effects of treatment, she was told that her teeth could be aligned with the extraction of one lower incisor, with a slight flattening of her profile and somewhat more thinning of the lips (image 2), or she could be treated by expanding the arches (image 3) but then would benefit from augmentation genioplasty (image 4) to obtain better chin-lip balance and stability. The technique for simulating the profile effect of treatment is reviewed in more detail in part 2 of “To Extract or Not to Extract?” on extraction for camouflage.

What do you think she said on seeing these?

“Oh, if that’s all the difference it makes, go ahead and extract the tooth.”

For her, both extraction and expansion were feasible treatment plans, and the esthetic impact of the treatment was important. She would have had more lip fullness and a better smile with expansion, but only she could decide if the more complex treatment would be worth it. After all, it’s the patient’s decision, and computer simulation of the facial effects of treatment helps significantly in obtaining true informed consent that is based on understanding the treatment alternatives.

Pretreatment profile: Profile prior to treatment, age 45.	Extraction prediction: Profile prediction, alignment with extraction of one lower incisor.
Expansion prediction: Profile prediction, arch expansion.	Expansion plus genioplasty: Profile prediction, arch expansion plus genioplasty.

Summary

In summary, important points to remember are:

• For patients with Class I crowding/protrusion, both esthetics and stability are important considerations in planning orthodontic treatment—but jaw function and TMD are not.
• If extraction is planned, usually four first premolars are removed, because this provides the greatest flexibility in aligning the incisors and obtaining appropriate lip support. Other extractions occasionally are preferred.
• Evaluation of esthetics requires consideration of both frontal (smile) tooth-lip-cheek relationships and lip support at rest. Excessive lip separation at rest and lip strain on closure are indications for retraction of the incisors. Lack of lip fullness is an indication for bringing them forward.
• Stability is affected by the amount of change within the dental arches, particularly when the arches are expanded.
• For perhaps 30% of patients, excellent results can be obtained by either arch expansion or appropriate extractions.
• With either approach, controlling the position of the incisors is the key. Extraction is acceptable esthetically if the incisors are not retracted too much, and may improve stability; expansion is acceptable for stability if not overdone and may have esthetic advantages.
• Computer image simulation of treatment effects can help adults understand the implications of the extraction/nonextraction decision (but this works only for adults, because growth in children is so unpredictable).

Self-Test Referral

The self-test section of this program is designed to help you be sure you have understood the material. Read the assigned material in Contemporary Orthodontics (5th ed., pages ; 4th ed., pages ). Then take the self-test, and use it as a guide for further study and review. Be sure you understand why various possible answers were correct or incorrect.

Copyright 2013, UNC Dept. of Orthodontics

Self-Test

Question 1

Which of the following are major reasons for tooth extraction in orthodontic treatment?

a. Protruding upper incisors

b. Protruding lower incisors

c. Severely crowded incisors

d. Impacted maxillary canines

1. a and b
2. b and c
3. a and c
4. a, b, and c ✓
5. all of the above

Correct

That’s right, the major reasons for extraction are severe crowding and protrusion of incisors that creates lip separation at rest and lip strain on closure. Protruding incisors in both arches, of course, are just another outcome of lack of space to accommodate the teeth in the dental arches. Impacted canines rarely are an indication for extraction.

Incorrect

No, that’s wrong. The major reasons for extraction are severe crowding and protrusion of incisors that creates lip separation at rest and lip strain on closure. Protruding incisors in both arches, of course, are just another outcome of lack of space to accommodate the teeth in the dental arches. Impacted canines rarely are an indication for extraction.

Question 2

Which of the following is an indication for expansion of the arches to deal with crowding of the incisors?

1. < 3 mm crowding
2. < 5 mm crowding
3. < 7 mm crowding
4. any could be correct ✓

Correct

That’s right, the decision to expand the arches can’t be made just from the degree of crowding. Any of those measurements might be consistent with a decision to expand the arches (or to extract). Because crowding and protrusion are aspects of the same thing, it’s necessary also to determine whether incisor protrusion is masking the space discrepancy. To do that, you have to look at the patient.

Incorrect

No, that’s wrong. Any of those measurements might be consistent with a decision to expand the arches (or to extract). Because crowding and protrusion are aspects of the same thing, it’s necessary also to determine whether incisor protrusion is masking the space discrepancy. To do that, you have to look at the patient.

Question 3

(A) Full and everted lips indicate excessive protrusion of incisors because (B) The position of the incisors determines the amount of lip support provided by these teeth.

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 right, the first statement is false and the second one is true. Excessive incisor protrusion is indicated by the combination of two things, full and everted lips and lip separation at rest with strain on closure. Lip fullness varies greatly with racial and ethnic characteristics, but when lip separation at rest is present, that is viewed as a problem. The teeth are too prominent only when you have to strain to close your lips over them.

Incorrect

No, that’s wrong. The first statement is false and the second one is true. Excessive incisor protrusion is indicated by the combination of two things, full and everted lips and lip separation at rest with strain on closure. Lip fullness varies greatly with racial and ethnic characteristics, but when lip separation at rest is present, that is viewed as a problem. The teeth are too prominent only when you have to strain to close your lips over them.

Question 4

How does the percentage of orthodontic patients with premolar extraction at present (at a reasonably typical location, like UNC) compare to the percentage with premolar extraction in 1950?

1. Much lower
2. A little lower
3. About the same ✓
4. A little higher
5. Much higher

Correct

That’s right, the percentage now and 50 years ago is about the same. Premolar extraction was introduced in the 1940s and 1950s as a way to improve the stability of results of orthodontic treatment, peaked in popularity in the 1960s, and its use has declined since then.

Incorrect

No, that’s wrong. The percentage now and 50 years ago is about the same. Premolar extraction was introduced in the 1940s and 1950s as a way to improve the stability of results of orthodontic treatment, peaked in popularity in the 1960s, and its use has declined since then.

Question 5

Which of the following are reasons for the decline in the percentage of patients with premolar extraction to treat crowding/protrusion?

a. Effects on facial esthetics

b. Instability even after extractions

c. Introduction of bonded brackets to replace bands

d. Considerations of treatment efficiency

1. a and b
2. b and c
3. a, b, and c
4. c and d
5. all of the above ✓

Correct

That’s right, all these factors contributed to the decrease in the number of patients having premolar extraction. As time passed, it was realized that retracting the incisors too much can affect facial esthetics unfavorably. Extraction treatment decreases the chance of long-term instability but does not eliminate it. Bonded brackets remove the need for interproximal space for band material and make nonextraction treatment easier, and nonextraction treatment tends to take less time and effort.

Incorrect

No, that’s wrong. All these factors contributed to the decrease in the number of patients having premolar extraction. Retracting the incisors too much can affect facial esthetics unfavorably. Extraction treatment decreases the chance of long-term instability but does not eliminate it. Bonded brackets remove the need for interproximal space for band material and make nonextraction treatment easier, and nonextraction treatment tends to take less time and effort.

Question 6

What is now considered the minimum percentage of patients with Class I crowding/protrusion who would need extractions rather than expansion?

1. 5%
2. 10% ✓
3. 26%
4. 50%
5. 65%

Correct

That’s right, the best current estimate of the minimum extraction percentage (by McNamara in 2002, who extracts only when it is absolutely necessary), is 10%. That is based on his survey of consecutive patients in his practice. On the other extreme, no one any longer advocates extraction in more than 50%, though extraction percentages often were higher than that in the 1960-85 period.

Incorrect

No, that’s wrong. The best current estimate of the minimum extraction percentage (by McNamara in 2002, who extracts only when it is absolutely necessary), is 10%. That is based on his survey of consecutive patients in his practice. On the other extreme, no one any longer advocates extraction in more than 50%, though extraction percentages often were higher than that in the 1960-85 period.

Question 7

Which of the following are ways by which arch expansion in patients with Class I crowding/protrusion can improve dentofacial esthetics?

a. Increasing the prominence of the incisors

b. Increasing the amount of lip support

c. Decreasing the width of buccal corridors

d. Altering the width of the alar base of the nose

1. a and b
2. b and c
3. c and d
4. a, b, and c ✓
5. all of the above

Correct

That’s right, the first 3 items affect tooth-lip-cheek relationships and dentofacial esthetics, but moving the teeth does not affect the width of the base of the nose (it takes surgery to do that). Esthetic effects must be considered from both the frontal and lateral views of the face and are not limited to the effect on the incisors, although those are the most visible teeth.

Incorrect

No, that’s wrong. The first 3 items affect tooth-lip-cheek relationships and dentofacial esthetics, but moving the teeth does not affect the width of the base of the nose (it takes surgery to do that). Esthetic effects must be considered from both the frontal and lateral views of the face and are not limited to the effect on the incisors, although those are the most visible teeth.

Question 8

Which of these choices is the major way extraction would affect long-term stability?

1. Decreasing tongue pressure
2. Disrupting the gingival fiber network
3. Decreasing lip/cheek pressure ✓
4. Decreasing bite force against the teeth

Correct

That’s right. Extraction has the potential to decrease pressure by the lips and cheeks against the dentition, if the incisors are retracted. If it affected tongue pressure at all, retracting the incisors would increase it. There’s little or no effect from extraction with space closure on either the gingival fiber network or bite force.

Incorrect

That’s wrong. Extraction has the potential to decrease pressure by the lips and cheeks against the dentition, if the incisors are retracted. If it affected tongue pressure at all, retracting the incisors would increase it. There’s little or no effect from extraction with space closure on either the gingival fiber network or bite force, so 3 is the only appropriate choice.

Question 9

On long-term recall, how does incisor irregularity with nonextraction (expansion) patients compare to patients who had early (serial) extraction?

1. Much greater
2. A little greater ✓
3. About the same
4. A little less
5. Much less

Correct

That’s right, the existing data indicate that irregularity on long-term recall tends to be a little greater in nonextraction patients and that 70% of long-term serial extraction patients have only minimal incisor crowding. But the differences are smaller than was expected at the height of enthusiasm for extraction to prevent relapse into crowding.

Incorrect

No, that’s wrong. The existing data indicate that irregularity on long-term recall tends to be a little greater in nonextraction patients and that 70% of long-term serial extraction patients have only minimal incisor crowding. But the differences are smaller than was expected at the height of enthusiasm for extraction to prevent relapse into crowding.

Question 10

What’s the current recommendation as to the best time to start treatment of patients with moderate crowding/protrusion?

1. Primary dentition, so that permanent teeth erupt in the correct position
2. Early mixed dentition, to take maximum advantage of growth
3. Late mixed dentition, to maintain leeway space when 2nd primary molars are lost ✓
4. Early permanent dentition, to keep treatment time to a minimum

Correct

That’s right, beginning treatment in the late mixed dentition, so that leeway space can be maintained when 2nd primary molars are lost, is now considered the best time to start treatment. Even if primary teeth are moved, permanent teeth do not necessarily erupt where their predecessors were located, so that doesn’t work. For Class I crowding/protrusion, changes in jaw relationships are not necessary, and early treatment has not been shown to be more effective than later treatment in obtaining alignment of the teeth. If leeway space is lost before treatment begins, treatment time is likely to be increased rather than decreased.

Incorrect

No, that’s wrong. Beginning treatment in the late mixed dentition, so that leeway space can be maintained when 2nd primary molars are lost, is now considered the best time to start treatment. Even if primary teeth are moved, permanent teeth do not necessarily erupt where their predecessors were located, so that doesn’t work. For Class I crowding/protrusion, changes in jaw relationships are not necessary, and early treatment has not been shown to be more effective than later treatment in obtaining alignment of the teeth. If leeway space is lost before treatment begins, treatment time is likely to be increased rather than decreased.

Question 11

Which one of the following statements about the limits of arch expansion for stability is incorrect?

1. Dimensions of the upper arch are more important than the lower ✓
2. Incisors can be advanced 2 mm in most patients
3. Intercanine expansion of any magnitude is unstable
4. Expansion of 2-3 mm per side in the premolar-molar region is acceptable

Correct

That’s right, it’s the lower arch whose dimensional changes are the key to evaluating likely stability. In the lower arch, as a general rule, the incisors can be advanced 2 mm in most patients, but more than that is likely to be unstable. Expansion across the mandibular canines is unstable, but 2-3 mm expansion per side in the lower premolar-molar regions is acceptable.

Incorrect

No, that’s wrong. It’s the lower*,* not the upper, arch whose dimensional changes are the key to evaluating likely stability. In the lower arch, as a general rule, the incisors can be advanced 2 mm in most patients, but more than that is likely to be unstable. Expansion across the mandibular canines is unstable, but 2-3 mm expansion per side in the lower premolar-molar regions is acceptable.

Question 12

For an adult considering orthodontic treatment, which of the following would be most likely to help her understand the esthetic implications of arch expansion versus extraction?

1. Informed consent booklet
2. Dental cast set-up, showing the tooth movement in each instance
3. Computer simulation of profile change ✓
4. Discussion with another patient who had the same kind of treatment

Correct

That’s right. Of the items on the list (all of which could be helpful), computer simulations are particularly important in helping patients understand the esthetic impact of alternative treatment approaches, and most likely to be helpful in making the decision. This is a good illustration of the adage that “a picture is worth a thousand words.” Computer simulations can be quite accurate in nongrowing individuals, but it is very difficult to accurately predict growth, so the simulations are much more useful for adults.

Incorrect

No, that’s not the best answer. Of the items on the list (all of which could be helpful), computer simulations are particularly important in helping patients understand the esthetic impact of alternative treatment approaches, and most likely to be helpful in makign the decision. This is a good illustration of the adage that “a picture is worth a thousand words.” Computer simulations can be quite accurate in nongrowing individuals, but it is very difficult to accurately predict growth, so the simulations are much more useful for adults.