Orthodontic Treatment Planning
From Problem List to Specific Plan
Orthodontic diagnosis is complete when a comprehensive list of the patient’s problems has been developed and pathologic and developmental problems have been separated. At that point, the objective in treatment planning is to design the strategy that a wise and prudent clinician, using his or her best judgment, would employ to address the problems while maximizing benefit to the patient and minimizing cost and risk.
It is important to view the goal of treatment in that way. Otherwise, an inappropriate emphasis on some aspect of the case is likely, whether the proposed treatment is medical, dental, or just orthodontics. For example, consider a patient who seeks orthodontics because she is concerned about mildly crowded lower incisors. For that individual, controlling periodontal disease might be more beneficial than aligning teeth that would require permanent retention, and this should be emphasized when a treatment plan is discussed with the patient, even though she initially sought only orthodontic treatment. Any treatment plan should be developed, in collaboration with the patient, to do what on balance would be best for that individual.
When a group of dentists and dental specialists meet to plan treatment for a patient with complex problems, questions for the orthodontist often are along the lines of “Could you retract the incisors enough to correct the overjet?” or “Could you develop incisal guidance for this patient?” To a question phrased as, “Could you …?” the answer often is yes, given an unlimited commitment to treatment. The more appropriate question is not “Could you …?” but “Should you …?” or “Would it be best for the patient to …?” Cost-benefit and risk-benefit analyses (Figure 7-1) are introduced appropriately when the question is rephrased that way.
FIGURE 7-1 The treatment planning sequence. In treatment planning, the goal is wisdom, not scientific truth—judgment is required. Interaction with the patient and parent, so that they are involved in the decisions that lead to the final plan, is the key to informed consent.
A treatment plan in orthodontics, as in any other field, may be less than optimal if it does not take full advantage of the possibilities or if it is too ambitious. There is always a temptation to jump to conclusions and proceed with a superficially obvious plan without considering all the pertinent factors. The treatment planning approach advocated here is specifically designed to avoid both missed opportunities (the false negative or undertreatment side of treatment planning) and excessive treatment (the false positive or overtreatment side), while appropriately involving the patient in the planning.
At this point, before we talk in detail about the steps in going from the problem list to the final treatment plan that are outlined in Figure 7-1, let us examine some important concepts that underlie orthodontic treatment planning more generally.
Modern treatment planning must be an interactive process. No longer can the doctor decide, in a paternalistic way, what is best for a patient. Both ethically and practically, patients and parents must be involved in the decision-making process. Ethically, patients have the right to control what happens to them in treatment—treatment is something done for them not to them. Practically, the patient’s compliance is likely to be a critical issue in success or failure, and there is little reason to select a mode of treatment that the patient would not support. Informed consent, in its modern form, requires involving the patient in the treatment planning process. This is emphasized in the procedure for presenting treatment recommendations that is presented below.
If alternative methods of treatment are available, as usually is the case, which one should be chosen? Data gradually are accumulating to allow choices to be based on evidence of outcomes rather than anecdotal reports and the claims of advocates of particular approaches. The quality of evidence for clinical decisions and how to evaluate the data as reports of treatment outcomes become available are emphasized in Chapter 1.
The complexity of the proposed treatment affects treatment planning, especially in the context of who should do the treatment. The focus of this chapter is on planning comprehensive orthodontic treatment. In orthodontics as in all areas of dentistry, it makes sense that the less complex cases would be selected for treatment in general or family practice, while the more complex cases would be referred to a specialist. In family practice, an important issue is how you rationally select patients for treatment or referral. A formal scheme is presented in Chapter 11 for separating child patients most appropriate for orthodontic treatment in family practice from those more likely to require complex treatment, and a similar scheme for adults appears in Chapter 18.
As further background for planning comprehensive treatment, it is important to consider two controversial aspects of current orthodontic treatment planning: the extent to which arch expansion versus extraction is indicated as a solution for crowding in the dental arches and the extent to which growth modification versus extraction for camouflage or orthognathic surgery should be considered as solutions for skeletal problems.
From the beginning of the specialty, orthodontists have debated the limits of expansion of the dental arches and whether the advantages of extraction of some teeth to provide space for the others outweigh the disadvantages. With extraction, the loss of a tooth or teeth is a disadvantage, greater stability of the result is likely and is an advantage, and there may be positive or negative effects on facial esthetics. But in fact for any individual patient the decision is a value judgment. It is not only appropriate but necessary to discuss the pros and cons with the patient and parent before making the expansion-extraction decision.
In a rational contemporary view, the majority of orthodontic patients can and should be treated without removal of teeth, but some will require extraction to compensate for crowding, incisor protrusion that affects facial esthetics, or jaw discrepancy. Their number varies, depending on the population being treated. Extraction for camouflage is considered separately later in this chapter, in the context of treatment for skeletal problems. The next section is a discussion of the limits of expansion, and therefore the indications for extraction, for patients with the normal jaw relationships that underlie Class I crowding/protrusion. Facial and dental esthetics, posttreatment stability, and dental occlusion are the key considerations.
If the major factors in extraction decisions are stability and esthetics, it is worthwhile to review existing data that relate these factors to expansion and extraction. Consider esthetics first. The conceptual relationship between expansion/extraction and esthetics is illustrated in Figure 7-2. All other things being equal, expansion of the arches moves the patient in the direction of more prominent teeth, while extraction tends to reduce the prominence of the teeth. Facial esthetics can become unacceptable on either the too-protrusive or too-retrusive side.
FIGURE 7-2 Expansion of the dental arches tends to make the teeth more prominent and extraction makes them less prominent. The choice between extraction and nonextraction (expansion) treatment is a critical esthetic decision for some patients who are toward the extremes of incisor protrusion or retrusion initially, but because there is an acceptable range of protrusion, many if not most can be treated with satisfactory esthetics either way. This is especially true if expansion is managed so as not to produce too much incisor protrusion or space closure after extraction is controlled so as not to produce too much incisor retraction. Similarly, expansion tends to make arches less stable and extraction favors stability, but the extraction/nonextraction decision probably is a critical factor in stability largely for patients who are toward the extremes of the protrusion-retrusion distribution. There are no data to show the percentage of patients who could be treated satisfactorily with either extraction or arch expansion versus the number for whom the extraction/nonextraction decision is critical in determining a satisfactory outcome.
At what point have the incisors been moved too far forward so that facial appearance is compromised? The answer is found in soft tissue not hard tissue relationships: When the prominence of the incisors creates excessive lip separation at rest so that the patient must strain to bring the lips together, the teeth are too protrusive and retracting the incisors improves the facial appearance (Figure 7-3). Note that this has remarkably little to do with the prominence of the teeth relative to the supporting bone as seen in a profile view. An individual with thick, full lips looks good with incisor prominence that would not be acceptable in someone with thin, tight lips. You simply cannot determine the esthetic limit of expansion from tooth–bone relationships on a cephalometric radiograph.
FIGURE 7-3 In patients with excessive incisor protrusion, retracting the incisors improves facial esthetics. This young woman sought treatment because of dissatisfaction with the appearance of her teeth. After orthodontic treatment with premolar extraction and incisor retraction, dental and facial appearance were significantly improved. A and B, Appearance on smile before and after treatment. C and D, Profile before and after treatment.
At what point are the incisors retracted to the point of adversely affecting facial esthetics? This too depends largely on the soft tissues. The size of the nose and chin has a profound effect on relative lip prominence. For a patient with a large nose and/or a large chin, if the choices are to treat without extraction and move the incisors forward or to extract and retract the incisors at least somewhat, moving the incisors forward is better, provided it does not separate the lips too much. The upper incisors are too far lingually if the upper lip inclines backward—it should be slightly forward from its base at soft tissue point A (Figure 7-4, A). For best esthetics, the lower lip should be at least as prominent as the chin (Figure 7-4, B). Variations in chin morphology may put the proper incisor–chin relationship beyond the control of orthodontics alone, in which case chin surgery perhaps should be considered (see the sections in this chapter on Class II camouflage and maximizing esthetic changes in treatment and Chapter 19).
FIGURE 7-4 A, An upper lip that inclines backward relative to the true vertical line, which can result from retraction of upper incisors to correct excessive overjet, tends to compromise facial esthetics, as does a poorly-defined labiomental sulcus when lip strain is required to bring the lips together. B, Retroclined mandibular incisors, as in this patient with a prominent chin and dental compensation for a skeletal Class III jaw relationship, are another cause of a poorly-defined labiomental sulcus.
For stable results, how much can arches be expanded? The lower arch is more constrained than the upper, and so its limitations for stable expansion may be somewhat tighter than the upper arch. Current guidelines for the limits of expansion of the lower arch, admittedly based on limited data, are presented in Figure 7-5. The 2 mm limitation for forward movement of the lower incisors obviously is subject to considerable individual variation but makes sense in light of the observation that lip pressure increases sharply 2 mm out into space usually occupied by the lip (see Chapter 5). If lip pressure is the limiting factor in forward movement, as it probably is, the initial position of the incisors relative to the lip would be a consideration in how much movement could be tolerated. This suggests and clinical observation seems to confirm (again, limited data!) that incisors tipped lingually away from the lip can be moved farther forward than upright incisors. Incisors tipped labially and crowded probably represent the equivalent of a titrated end point in a chemical reaction, in that they have already become as protrusive as the musculature will allow. Moving them any further forward carries great risk of instability (see Figure 7-2).
FIGURE 7-5 Because the lower arch is more constrained, the limits of expansion for stability seem to be tighter for it than the maxillary arch. The available data suggest that moving lower incisors forward more than 2 mm is problematic for stability, probably because lip pressure seems to increase sharply at about that point. A considerable body of data shows that expansion across the canines is not stable, even if the canines are retracted when they are expanded. Expansion across the premolars and molars, in contrast, can be stable if it is not overdone.
There also is a soft tissue limitation in how far the incisors, especially the lower incisors, can be moved facially. Fenestration of the alveolar bone and stripping of the gingiva become increasingly likely as the incisors are advanced. The amount of attached gingiva is a critical variable. It is important to carefully monitor patients who have a marginal amount of attached gingiva so that they can be treated promptly if a problem arises (Figure 7-6). Pretreatment consultation with a periodontist often is advisable, and depending on the amount and direction of planned tooth movement, placing a gingival graft before orthodontic treatment begins may be the best option for these patients.
FIGURE 7-6 A, Gingival recession beginning to appear in a patient whose crowded lower incisors were aligned with some advancement despite premolar extraction to provide space. B, Preparation of a bed for a free gingival graft. C, The graft (tissue taken from the palate) sutured in position. D, 2 weeks later. (Courtesy Dr. J. Moriarty.)
Figure 7-5 suggests that there is more opportunity to expand transversely than anteroposteriorly—but only posterior to the canines. Numerous reports show that transverse expansion across the canines is almost never maintained, especially in the lower arch. In fact, intercanine dimensions typically decrease as patients mature, whether or not they had orthodontic treatment, probably because of lip pressures at the corners of the mouth. Expansion across the premolars and molars is much more likely to be maintained, presumably because of the relatively low cheek pressures.
One approach to arch expansion is to expand the upper arch by opening the midpalatal suture. If the maxillary base is narrow, this is appropriate treatment (see the discussion of transverse maxillary deficiency below). Some clinicians theorize (with no supporting evidence) that generously expanding the upper arch by opening the suture, temporarily creating a buccal crossbite, allows the lower arch then to be expanded more than otherwise would have been possible. If the limiting factor is cheek pressure, it seems unlikely that the method of expansion would make any difference. Excessive expansion carries the risk of fenestration of premolar and molar roots through the alveolar bone. There is an increasing risk of fenestration beyond 3 mm of transverse tooth movement.1
• Less than 4 mm arch length discrepancy: Extraction rarely indicated (only if there is severe incisor protrusion or in a few instances, a severe vertical discrepancy). In some cases, this amount of crowding can be managed without arch expansion by slightly reducing the width of selected teeth, being careful to coordinate the amount of reduction in the upper and lower arch.
• Arch length discrepancy 5 to 9 mm: Nonextraction or extraction treatment possible. The decision depends on both the hard- and soft-tissue characteristics of the patient and on how the final position of the incisors will be controlled; any of several different teeth could be chosen for extraction. Nonextraction treatment usually requires transverse expansion across the molars and premolars, and additional treatment time if the posterior teeth are to be moved distally, to increase arch length.
• Arch length discrepancy 10 mm or more: Extraction almost always required. For these patients, the amount of crowding virtually equals the amount of tooth mass being removed, and there would be little or no effect on lip support and facial appearance. The extraction choice is four first premolars or perhaps upper first premolars and mandibular lateral incisors. Second premolar or molar extraction rarely is satisfactory because it does not provide enough space near crowded anterior teeth or options to correct midline discrepancies (Table 7-1).
The presence of protrusion in addition to crowding, of course, complicates the extraction decision. Retracting the incisors to reduce lip prominence requires space within the dental arch. The effect is to increase the amount of arch length discrepancy. With that adjustment, the guidelines above can be applied. As a general rule, the lips will move two-thirds of the distance that the incisors are retracted (i.e., 3 mm of incisor retraction will reduce lip protrusion by 2 mm), but there is a great deal of individual variation, especially in the change that occurs when lip competence is reached. Two to three mm of lip retraction is a usual outcome.
It is interesting but not surprising that retrospective studies of changes in dental arch dimensions and facial appearance in extraction versus nonextraction cases show highly variable changes in both groups. The idea that extraction leads to incisor retraction and narrower arches and that nonextraction leads to incisor protrusion and wider arches is not well supported.2,3 The amount of change in both groups, of course, would be related to the amount of crowding and protrusion that was present initially and to the clinician’s decision as to how to manage arch expansion or closure of extraction spaces. Perhaps a final set of guidelines could be as follows:
• The more you can close extraction spaces without overretracting the incisors, the more patients you can treat satisfactorily (again, from the perspective of both esthetics and stability) with extraction.
If it were possible, the best way to correct a jaw discrepancy would be to get the patient to grow out of it. Because the pattern of facial growth is established early in life and rarely changes significantly (see Chapter 2), this is unlikely without treatment. The important questions in planning treatment are the extent to which growth can be modified, and how advantageous it is to start treatment prior to adolescence. Now that data from randomized clinical trials are available for Class II treatment outcomes, there is less reason for controversy about the best way to treat those patients (discussed in detail below), but skeletal problems in other planes of space remain controversial. Additional information on methods for early treatment of skeletal problems is presented in Chapter 12.
It is appropriate to discuss maxillary deficiency at the beginning of this discussion of skeletal problems because of its relationship to the extraction–nonextraction decision that was just reviewed. In a child with crowded teeth, a diagnosis of deficient maxillary width can become a convenient rationale for enough transverse expansion to align the teeth. If the maxilla is narrow relative to the rest of the face, a diagnosis of transverse maxillary deficiency is justified and skeletal expansion probably is appropriate. Both the width of the maxillary premolar teeth (via Pont’s index, an old and now-discredited approach)4 and the width of the palate compared to population norms have been advocated as methods to diagnose maxillary deficiency. As we have emphasized in Chapter 6, the appropriate comparison of maxillary width should be to other transverse proportions in the same patient (for example, bizygomatic width), not to population averages.
Like all craniofacial sutures, the midpalatal suture becomes more tortuous and interdigitated with increasing age (see Figure 8-30). Almost any expansion device (a lingual arch, for example) will tend to separate the midpalatal suture in addition to moving the molar teeth in a child up to age 9 or 10. By adolescence, relatively heavy force from a rigid jackscrew device (Figure 7-7) is needed to separate the partially interlocked suture, which must be microfractured. The maxilla opens as if on a hinge superiorly at the base of the nose and also opens more anteriorly than posteriorly.
FIGURE 7-7 Transverse force across the maxilla in children and adolescents can open the midpalatal suture. A, The expansion force is usually delivered with a jackscrew mechanism fixed to maxillary teeth, as in this Hyrax expander with metal framework and jackscrew, seen at the end of rapid expansion (0.5 mm/day). The maxilla opens as if on a hinge, with its apex at the bridge of the nose. B, The suture also opens on a hinge anteroposteriorly, separating more anteriorly than posteriorly, as shown in this radiograph of a patient after rapid expansion.
It is important to realize that heavy force and rapid expansion should not be used in preschool children because of the risk of producing undesirable changes in the nose at that age (Figure 7-8). After adolescence, there is an increasing chance with advancing age that bone spicules will have interlocked the suture to such an extent that it cannot be forced open, and at that point surgery to reduce the resistance to expansion is the only way to widen the palate (see Chapter 18).
FIGURE 7-8 Rapid palatal expansion in young children can lead to undesirable changes in the nose, as in this 5-year-old who had expansion at the rate of mm/day (2 turns/day of the jackscrew). A, Nasal contours before treatment. B, Jackscrew appliance after activation over a 10-day period. C and D, Nasal hump and paranasal swelling, which developed after the child complained of discomfort related to the expansion. (Courtesy Dr. D. Patti.)
In adolescents, expansion across the suture can be done in three ways: (1) rapid expansion with a jackscrew device attached to the maxillary posterior teeth, the original (1960s) method, typically at the rate of 0.5 to 1 mm/day; (2) slow expansion with the same device at the rate of approximately 1mm per week, the method advocated more recently; or (3) expansion with a device attached to bone screws or implants, so that the force is directly applied to the bone and there is no pressure against the teeth.
Rapid Palatal Expansion: A major goal of growth modification always is to maximize the skeletal changes and minimize the dental changes produced by treatment. The object of maxillary expansion is to widen the maxilla, not just expand the dental arch by moving the teeth relative to the bone. Originally, rapid expansion of the midpalatal suture (rapid palatal expansion [RPE]) was recommended to help meet this goal. The theory was that with rapid force application to the posterior teeth, there would not be enough time for tooth movement, the force would be transferred to the suture, and the suture would open up while the teeth moved only minimally relative to their supporting bone.
With RPE at a rate of 0.5 to 1 mm/day, a centimeter or more of expansion is obtained in 2 to 3 weeks, with most of the movement being separation of the two halves of the maxilla. A space appears between the central incisors. The space created at the midpalatal suture is filled initially by tissue fluids and hemorrhage, and at this point the expansion is highly unstable. The expansion device must be stabilized so that it cannot screw itself back shut and is left in place for 3 to 4 months. By then, new bone has filled in the space at the suture, and the skeletal expansion is stable. The midline diastema decreases and may disappear during this time.
The aspect of rapid expansion that was not appreciated initially was that orthodontic tooth movement continues after the expansion is completed, until bone stability is achieved. In most orthodontic treatment, the teeth move relative to a stable bony base. It is possible, of course, for tooth movement to allow bony segments to reposition themselves while the teeth are held in the same relationship to each other, and this is what occurs during the approximately 3 months required for bony fill-in at the suture after rapid expansion. During this time, the dental expansion is maintained, but the two halves of the maxilla move back toward each other, which is possible because at the same time the teeth move laterally on their supporting bone.
If the changes were represented graphically, the plot for rapid expansion would look like Figure 7-9, A. Note that when the expansion was completed, 10 mm of total expansion would have been produced by 8 mm of skeletal expansion and only 2 mm of tooth movement. At 4 months, the same 10 mm of dental expansion would still be present, but at that point there would be only 5 mm of skeletal expansion, and tooth movement would account for the other 5 mm of the total expansion. Rapid activation of the jackscrew, therefore, is not an effective way to minimize tooth movement.
FIGURE 7-9 Diagrammatic representation of the typical skeletal and dental response to rapid (A) versus slow (B) palatal expansion. Rapid expansion was recommended when the technique was reintroduced in the 1960s because it was thought that this produced more skeletal than dental change. As the graph indicates, this is true initially: the teeth cannot respond, and the suture is opened. With 10 mm of expansion in 2 weeks, there might be 8 mm of skeletal change and only 2 mm of tooth movement at the time the expansion is completed. It was not appreciated at first that during the next 8 weeks, while bone is filling in, orthodontic tooth movement continues and allows skeletal relapse, so that although the total expansion is maintained, the percentage due to tooth movement increases and the skeletal expansion decreases. With slow expansion at the rate of 1 mm per week, the total expansion is about half skeletal/half dental from the beginning. The outcome of rapid versus slow expansion looks very different at 2 weeks but quite similar at 10 weeks.
Slow Palatal Expansion: Approximately 0.5 mm per week is the maximum rate at which the tissues of the midpalatal suture can adapt. If a jackscrew device attached to the teeth is activated at the rate of one-quarter turn of the screw (0.25 mm) every other day, the ratio of dental to skeletal expansion is about 1 to 1, tissue damage and hemorrhage at the suture are minimized, and a large midline diastema never appears. Ten mm of expansion over a 10-week period, at the rate of 1 mm per week, would consist of 5 mm of dental and 5 mm of skeletal expansion (Figure 7-9, B). The situation at the completion of active expansion is approximately analogous to RPE 2 to 3 months after expansion is completed, when bone fill-in has occurred. Thus the overall result of rapid versus slow expansion is similar,5 but with slower expansion a more physiologic response is obtained.
Implant-Supported Expansion: Now that bone screws can be placed in the maxilla to serve as temporary skeletal attachments, force can be applied directly to the maxilla instead of using the teeth to transfer force to the bone. This provides a way to expand the maxilla even if no teeth are present (Figure 7-10) and would avoid tooth movement and should produce almost total skeletal change in patients with lingual crossbite. With a jackscrew attached to skeletal anchors, minimum disruption of the suture would be desired, so slow rather than rapid expansion would be indicated.
FIGURE 7-10 A, Narrow maxillary arch with palatal screws for delivery of expansion force directly to the bone. The expansion device has a wire framework that clips over the exposed head of the bone screws. B, Expansion device in place with initial activation of the jackscrew. Note that although the molars are attached to the expansion device, the attachment is to a bar along which the attachment can slide, so the expansion force will be only against the screws. C, Progress, as expansion continues and the molar attachment slides along the bar.
Following expansion by any means, a retainer is needed even after bone fill-in seems complete. The expansion appliance should remain in place for 3 to 4 months and then can be replaced with a removable retainer or other retention device.
Changing Views of Class II Treatment: In the early years of the twentieth century, it was all but taken for granted that pressure against the growing face could change the way it grew. Extraoral force to the maxilla (headgear) was utilized by the pioneer American orthodontists of the late 1800s (Figure 7-11), who found it reasonably effective. This method of treatment was later abandoned, not because it did not work, but because Angle and his contemporaries thought that Class II elastics (from the lower molars to the upper incisors) would cause the mandible to grow forward and that this would produce an easier and better correction. At a later stage in the United States, guide planes consisting of a wire framework extending down from an upper lingual arch were used to force patients to advance the mandible upon closure, also with the idea of stimulating mandibular growth.
FIGURE 7-11 Extraoral force to the maxilla was used for Class II correction in the late 1800s and then abandoned, not because it was ineffective, but because the pioneer orthodontists thought that intraoral elastics produced the same effect. (From Angle EH. Treatment of Malocclusion of the Teeth. 7th ed. Philadelphia: SS White Manufacturing Co; 1907.)
With the advent of cephalometric analysis, it became clear that both elastics and guide planes corrected Class II malocclusion much more by displacing the mandibular teeth mesially than by stimulating mandibular growth. Even if the lack of desired change in jaw relationships is overlooked, correcting a skeletal Class II problem in this way is undesirable because the protruding lower incisors tend to upright after treatment and then lower incisor crowding and overjet return. Because of this, these methods and with them the idea of mandibular growth stimulation fell into disrepute in the United States, but growth modification with “functional appliances” that hold the mandible forward remained the mainstay of European orthodontics.
Although headgear was reintroduced into American orthodontics in the 1940s and came to be widely used in Class II treatment, it was seen primarily as a tooth-moving device until cephalometric studies in the late 1950s clearly demonstrated not only retraction of upper teeth but also effects on maxillary growth (Figure 7-12). By the 1980s, clinical success with functional appliances, including impressive amounts of mandibular growth in some cases, had been clearly demonstrated on both sides of the Atlantic, but questions remained as to whether these appliances could really stimulate mandibular growth.
FIGURE 7-12 Cephalometric superimposition showing growth modification produced by extraoral force to the maxilla (straight-pull initially, then high-pull). In the cranial base superimposition (A), note that the maxilla has moved downward and backward, not in the downward and forward direction that would have been expected during growth (and that was shown by the mandible). From the maxillary superimposition (B), it can be seen that the protruding and spaced upper incisors were retracted, but there was very little posterior movement of the upper molars. In the mandibular superimposition (C), note that the lower molars erupted more than the upper molars (i.e., good vertical control of the upper molars was maintained).
This depends on how you look at it. Growth stimulation can be defined in two ways: (1) as the attainment of a final size larger than would have occurred without treatment or (2) as the occurrence of more growth during a given period than would have been expected without treatment. Figure 7-13 is a hypothetical plot of the response to functional appliance treatment, illustrating the difference between (1) absolute stimulation (larger as an adult) and (2) temporal stimulation (acceleration of growth). As the figure suggests, an acceleration of growth often occurs when a functional appliance is used to treat mandibular deficiency, but the final size of the mandible is little if any larger than it would have been without the treatment.6 Cephalometric superimposition often shows more mandibular growth in the first months of functional appliance treatment than would have been expected (Figure 7-14). This is likely to be followed by a decrease in growth later, so that although the mandible grew faster than normal for a while, later growth was slower than would have been expected and the ultimate size of the mandible in treated and untreated patients is similar.
FIGURE 7-13 The difference between growth acceleration in response to a functional appliance and true growth stimulation can be represented using a growth chart. If growth occurs at a faster-than-expected rate while a functional appliance is being worn and then continues at the expected rate thereafter so that the ultimate size of the jaw is larger, true stimulation has occurred. If faster growth occurs while the appliance is being worn, but slower growth thereafter ultimately brings the patient back to the line of expected growth, there has been an acceleration not a true stimulation. Although there is a great deal of individual variation, the response to a functional appliance most often is similar to the solid line in this graph.
FIGURE 7-14 A, Cephalometric superimposition during treatment with a functional appliance (activator), showing excellent downward and forward mandibular growth between ages 11 and 13. B, Cephalometric superimpositions for same patient between ages 13 and 15, during fixed appliance therapy for final positioning of teeth. For this patient, the growth response to the activator was much more an acceleration than a true stimulation, as revealed by more growth than expected at first, and less growth later; yet the activator phase of treatment was quite successful in improving the jaw relationship.
If that view of their effect on mandibular growth is correct, functional appliances must do something else besides accelerate mandibular growth. Otherwise, the Class II malocclusion would never be corrected or would not stay corrected. In fact, these appliances also can affect the maxilla and the teeth in both arches. When the mandible is held forward, the elastic stretch of soft tissues produces a reactive effect on the structures that hold it forward. If the appliance contacts the teeth, this reactive force produces an effect like Class II elastics, moving the lower teeth forward and the upper teeth back, and rotating the occlusal plane. In addition, even if contact with the teeth is minimized, soft tissue elasticity can create a restraining force on forward growth of the maxilla, so that a “headgear effect” is observed (see Figure 7-14). Any combination of these effects can be observed after functional appliance treatment.
Randomized Clinical Trials of Early versus Later Class II Treatment: In the 1990s, two major projects using randomized clinical trial methodology and supported by the National Institute of Dental and Craniofacial Research were carried out at the University of North Carolina and University of Florida.7,8 More recently, an important trial at the University of Manchester that was supported by the Medical Research Council of the United Kingdom has been reported.9 The results provide by far the best data that ever have been available for the response to Class II growth modification treatment.
The data from all the trials show three important things: (1) on average, children treated prior to adolescence with either headgear or a functional appliance had a small but statistically significant improvement in their jaw relationship, while the untreated control children did not; (2) changes in skeletal relationships created during early treatment were at least partially reversed by later compensatory growth, in both the headgear and functional appliance groups; and (3) at the end of comprehensive treatment during adolescence, there were no significant differences between the early treatment patients and the previously untreated controls. In short, it seems to make remarkably little difference whether growth modification is done with headgear or a functional appliance, and it is equally effective and more efficient to do it during the adolescent growth spurt rather than prior to adolescence. Further data from the trials and data from well-designed and controlled retrospective studies are discussed in more detail in Chapter 13.
Camouflage by Tooth Movement: Tooth movement alone cannot correct a skeletal malocclusion, but if the malocclusion is corrected and the facial appearance is acceptable, the overall treatment outcome can be quite satisfactory. This is called orthodontic camouflage for the simplest of reasons: camouflage means that the jaw discrepancy is no longer apparent. Of course, treatment with tooth movement is successful only if both the facial appearance and dental occlusion are satisfactory.
Nonextraction treatment with Class II elastics: If forward movement of the lower arch can be accepted, a Class II malocclusion can be corrected just with the use of Class II elastics (or their equivalent in the form of fixed connectors). The correction is achieved, however, much more by forward movement of the lower arch than by moving the upper teeth back. Rarely, excess overjet and Class II buccal segments are due to a lower arch that is distally positioned on the mandible, and then moving the lower teeth forward is exactly what is needed. Almost always, however, Class II patients have the lower teeth normally positioned on the mandible or proclined to some extent. For these patients, the result of Class II elastics or their equivalent in the form of a fixed functional appliance is likely to be a convex profile with protrusive lower incisors and a prominent lower lip. This is best described as relapse waiting to occur (Figure 7-15). After treatment, lip pressure that moves the lower incisors lingually leads to incisor crowding, return of overjet, and return of overbite as the incisors tend to erupt back into occlusal contact from their lingual position.
FIGURE 7-15 It is possible with Class II elastics to correct a Class II malocclusion largely by moving the mandibular teeth forward relative to the mandible, but in a patient with a skeletal Class II due to mandibular deficiency, the result is both unesthetic and unstable. This girl, treated in this way, sought retreatment 5 years after treatment of that type. A and B, Frontal and profile facial photos, showing the prominence of the lower lip relative to the chin. C to E, Intraoral photos. Note that although the molar relationship is still almost Class I on the right side and ½ cusp Class II on the left, there has been a major return of overjet because the lower incisors have tipped lingually and become crowded. Vertically, relapse toward open or deep bite, whichever was present initially, is likely, so this patient almost surely had an open bite tendency before her initial treatment.
Retraction of the upper incisors into a premolar extraction space: A straightforward way to correct excessive overjet is to retract the protruding incisors into space created by extracting the maxillary first premolars. Without lower extractions, the patient would have a Class II molar relationship but normal overjet and canine relationships at the end of treatment. Temporary skeletal anchorage is very useful when maximum incisor retraction is desired or if the maxillary molars have little anchorage value because of bone loss. If mandibular first or second premolars also are extracted, Class II elastics can be used to bring the lower molars forward and retract the upper incisors, correcting both the molar relationship and the overjet.
Although premolar extraction for Class II correction can produce excellent occlusion and an acceptable dentofacial appearance,10 there are potential problems with this approach. If the patient’s Class II malocclusion is primarily due to mandibular deficiency, retracting the maxillary incisors would create a maxillary deformity to go with the mandibular one, which is difficult to justify as correct treatment (see the discussion of Class II camouflage in adults in Chapter 18). Extractions in the lower arch allow the molars to come forward into a Class I relationship, but it would be important to close the lower space without retracting the lower incisors. If Class II elastics are used, the upper incisors are elongated as well as retracted, which can produce an undesirable “gummy smile.”
Maxillary premolar extraction for Class II correction has been criticized as a risk factor for future TM dysfunction (TMD). No relationships between symptoms of TMD and the type of orthodontic treatment were noted in any of a considerable series of reports in the early 1990s. The best data come from a study in which a careful compilation of retrospective data was used to create two groups of patients whose “borderline” Class II malocclusions could have been treated equally plausibly with or without premolar extraction. One group had extractions, the other did not. Both groups had low scores for signs or symptoms of dysfunction, and there was no difference between them in any aspect of TM joint function.11 There is simply no evidence to support the allegation that maxillary premolar extraction causes TMD.
Distal movement of the upper teeth: If the upper molars could be moved posteriorly, this would correct a Class II molar relationship and provide space into which the other maxillary teeth could be retracted. If the maxillary first molars are rotated mesiolingually, as they often are when a Class II molar relationship exists, correcting the rotation moves the buccal cusps posteriorly and provides at least a small space mesial to the molar (Figure 7-16). Tipping the crowns distally to gain space is more difficult, and bodily distal movement is more difficult still. There are two problems: (1) it is difficult to maintain the first molar in a distal position while the premolars and anterior teeth are moved back, so it must be moved back a considerable distance, especially if it is tipped distally; and (2) the farther it must be moved, the more the second and third molars are in the way.
FIGURE 7-16 In a patient with Class II malocclusion, the upper first molar usually is rotated mesiolingually. Correcting this rotation, which is necessary to obtain proper occlusion with the lower first molar, usually moves the buccal cusps distally (but also tends to move the lingual cusps mesially). This improves the buccal occlusal relationship and, if the patient wears headgear as this is done, creates at least a modest amount of space for retraction of other maxillary teeth.
From this perspective, it is easy to understand that the most successful way to move a maxillary first molar distally is to extract the second molar, which creates space for the tooth movement. Until quite recently, the anchorage created by a transpalatal lingual arch was accepted as the best way to undertake distalization of the maxillary dentition. Although it is at least theoretically possible to do this with headgear, this type of treatment is time-consuming and requires excellent patient cooperation. Palatal anchorage for the molar movement can be created by splinting the maxillary premolars and including an acrylic pad in the splint so that it contacts the palatal mucosa. In theory, the palatal mucosa resists displacement; in clinical use, tissue irritation is likely. Even with the more elaborate appliances of this type (Figure 7-17), only about two-thirds of the space that opens between the molars and premolars is from distal movement of the molars, even when the molars are tipped distally. They tend to come forward again when the other maxillary teeth are retracted (see Chapter 15 for more details), so more than a half-cusp molar correction cannot be expected. The ideal patient for treatment with this approach, therefore, is one with minimal growth potential, a reasonably good jaw relationship (not severely mandibular deficient) and a half-cusp Class II molar relationship.
FIGURE 7-17 Molar distalization can be carried out with a variety of appliances that depend on the anterior teeth and the palate for anchorage. A, Combination distalization-expansion appliance (Pendex) at initial application. B, Appearance at appliance removal. Note the successful opening of space, but the tissue irritation caused by contact with the palatal mucosa. C, Nance holding arch with palatal button later in the same patient to maintain the molar position while alignment of the other teeth is completed. Appliances of this type now are rapidly being replaced by bone anchors (temporary anchorage devices [TADs]).
Using temporary skeletal anchorage greatly improves the amount of true distal movement of the maxillary dentition that can be achieved, and makes it possible to distalize both the second and first molars. It still is necessary to create some space in the tuberosity region, so removal of third molars is likely to be required later if it is not done immediately. In typical treatment, bone anchors are placed bilaterally in the vicinity of the base of the zygomatic arch (Edward Angle’s “key ridge”) or in the palate, and a nickel-titanium spring generates the force needed for distalization (Figure 7-18). For this purpose, bone screws between the teeth prevent the necessary distal movement of roots mesial to the screw. Although good data for typical treatment outcomes still do not exist, in some patients it has been possible to produce up to 6 mm of distal movement of first and second molars.12 In addition, the premolars migrate distally as the molars are moved back (which is due to the supercrestal fiber network). This makes the premolar retraction less complicated, and there also is no reaction force against the incisors to move them facially.
FIGURE 7-18 A, Bone anchor (miniplate attached to the base of the zygomatic arch with three screws, with only the tube for attachment of springs or screws extending into the mouth) for retraction of severely protrusive maxillary incisors in a young adult with bone loss from periodontal disease (so that the maxillary posterior teeth had little anchorage value). B, Retraction completed. Note that the Class II molar relationship has been maintained. Without skeletal anchorage the maxillary molars would have moved farther anteriorly into a super-Class II relationship. C, Cephalometric superimpositions on cranial base and maxilla, showing the extent of maxillary incisor retraction without any forward movement of the posterior teeth. For this amount of tooth movement in an adult, a single screw in the alveolar process on each side might not be stable.
The caveat, of course, is that moving the upper arch back that far may not be compatible with an acceptable facial appearance. If a Class II malocclusion is due to maxillary dental protrusion, moving the upper teeth back is a logical treatment approach. But if there is a significant component of mandibular deficiency, retraction of the maxillary incisors after distal movement of the molars and premolars has the same potential problem that can arise with first premolar extraction to allow retraction of the incisors: correcting the malocclusion in that way may detract from rather than enhance facial appearance.
Summary: In the absence of favorable growth, treating a Class II relationship in adolescents is difficult. Compromises may have to be accepted in order to correct the occlusion. Fortunately, even though growth modification cannot be expected to totally correct an adolescent Class II problem, some forward movement of the mandible relative to the maxilla does contribute to successful treatment of the average patient. The rest of the correction must occur from some combination of retraction of the upper incisors and forward movement of the lower arch. When little or no growth can be expected, orthognathic surgery to advance the mandible may be necessary to achieve a satisfactory result (see Chapter 19).
Growth modification for Class III patients is just the reverse of Class II: what is needed is differential growth of the maxilla relative to the mandible. Edward Angle’s concept was that Class III malocclusion was due exclusively to excessive mandibular growth. In fact, almost any combination of deficient maxillary growth and excessive mandibular growth can be found in Class III patients, and maxillary deficiency and mandibular excess are about equally likely. The realization that maxillary deficiency is so frequently a component of skeletal Class III and the development of new possibilities for correcting it have led recently to a great increase in treatment aimed at promoting maxillary growth. Unfortunately, data from randomized clinical trials are not available, and treatment recommendations must be based on reports from small and often poorly controlled studies.
Horizontal-Vertical Maxillary Deficiency: If headgear force compressing the maxillary sutures can inhibit forward growth of the maxilla, reverse (forward-pull) headgear separating the sutures should stimulate growth. Until Delaire and coworkers in France showed that forward positioning of the maxilla could be achieved with reverse headgear, if treatment was begun at an early age, reverse pull headgear (Figure 7-19) was remarkably unsuccessful in producing anything but movement of the upper teeth. The French results suggested that successful forward repositioning of the maxilla can be accomplished before age 8, but after that, orthodontic tooth movement began to overwhelm skeletal change, and more recent studies comparing untreated Class III children to those treated with maxillary protrusion have confirmed greater skeletal change at earlier ages.13 Long-term follow-up suggests that for a good chance of success, treatment should begin by age 10 at the latest.14 The chance of successful forward movement is essentially zero by the time sexual maturity is achieved.