Treatment Planning and Management of Orthodontic Problems
Growth Modification Applied to Anteroposterior Problems
Class II Mandibular Deficiency
Class III Maxillary Deficiency
Growth Modification Applied to Transverse Problems
Potential Alignment and Space Problems
Anteroposterior Dental Problems
When considering treatment for problems during the mixed-dentition years, the precise problem and the goals of treatment must be clearly in mind. Few problems will receive definitive or complete treatment at this stage of development, although some simple and isolated dental problems may be resolved. As always, information regarding the patient’s problems is gathered through an interview of the patient and the parents and a clinical examination. First, a list of goals is created by the clinician. The goals should address functional and aesthetic concerns of the patient and the clinician. After the goals of treatment have been established, a list of orthodontic problems is generated from this database, and the problems are ranked in order from most to least severe.1 The order is determined by patient, functional, and aesthetic concerns. The clinician is specifically trained to identify functional and aesthetic problems. This problem list does not always match the concerns of the parent and child. These concerns should be listened to carefully and often dictate treatment direction and treatment satisfaction outcomes. Many times the motivation for treatment can be elicited from these concerns. If the child patient desires to have treatment, cooperation will usually be good during treatment, and little parental support will be necessary. This is called internal motivation. External motivation, motivation supplied by the parent for treatment, will require continuous parental support to successfully complete treatment. If the chief complaint or reason for seeking treatment ranks low on the treatment priority list or will be addressed later in the treatment plan, an explanation should be provided to the child and parent to justify this situation.
After the problem list has been generated and each problem has been ranked in order of severity, possible solutions to each problem should be listed. The solution list should be comprehensive; that is, all reasonable solutions should be considered for each specific problem without regard for the other problems. After the solution list has been constructed, the clinician should look for similar solutions that are listed for more than one problem. In some cases, the best solution for one problem is the best solution for all problems, and the treatment plan is easily derived. Unfortunately, in most cases, a solution for one problem is not the solution for the others, and, worse, may actually magnify the second problem. The treatment plan should meet the goals of treatment established by the clinician. Treatment planning is not entirely scientific, and clinical wisdom is needed to determine a plan in these cases.
Orthodontic problems in the preadolescent patient are generally thought of as either dental or skeletal in origin. The complexity of these problems varies tremendously. Many dental problems are well within the treatment domain of the general practitioner. Skeletal problems, as diagnosed from the facial profile analysis and confirmed by supplemental means, are best managed by a specialist. However, the general practitioner should have an understanding of how skeletal discrepancies are treated.
Three basic alternatives for treating skeletal discrepancies exist: growth modification, camouflage, and orthognathic surgery. Growth modification is a means to change skeletal relationships by using the patient’s remaining growth to alter the size or position of the jaws. Camouflage and orthognathic surgery usually are considered for adolescent patients with minimal or no growth remaining or nongrowing adult patients. Camouflage orthodontic treatment is aimed at hiding a mild skeletal discrepancy by moving teeth situated on the jaws so that they fit together. The skeletal discrepancy still exists, but it is disguised by a compensated occlusion and acceptable facial aesthetics. Orthognathic surgery places the jaws and teeth in a normal or near-normal position through the use of surgical procedures and presurgical and postsurgical orthodontic treatment.2 For the mixed-dentition patient, only growth modification or no treatment is a reasonable choice for skeletal intervention.
Growth modification during the early mixed-dentition years rests on several assumptions that are not as clear as many would presume. First, a child must be growing for the growth to be modified. Most normal children in the 6- to 12-year age group are actively growing, and their faces are also growing. Furthermore, clinicians have thought that it is easiest to correct skeletal problems if a child is undergoing maximal facial growth during treatment. Although the data to support this contention are not voluminous or clear,3 clinicians have long sought to predict maximum somatic growth and maximal facial growth from other indicators. There appears to be wide variation in the amount of facial growth occurring at one time and an equally wide variation in the correlation of facial growth with overall body growth and other indicators that have been chosen.4–6 Because of this state of inaccuracy, the clinician should use as many indicators as possible (personal growth history, skeletal growth maturation, and onset of menarche) to make an educated decision about whether the child is growing at an acceptable rate. Girls tend to enter the adolescent growth spurt as defined by obvious somatic growth at around 10 years and boys at around 12 years.
The data are not totally clear that one must treat children when they are at a certain rate of facial growth to be successful, and experience has shown that most skeletal and dental problems can be managed later in one phase during the transition from the mixed to permanent dentitions. For these reasons, a single stage of orthodontic treatment is most popular and adequately effective. This enables practitioners to successfully manage most problems and deal with a more mature patient who is both reasonably cooperative and compliant. Asynchrony between dental development and rapid facial growth may create a situation in which the patient may be ready for growth modification but not for orthodontic dental treatment, or vice versa. These patients must be handled individually by balancing the dental and skeletal interventions. Similarly, some patients have compelling problems that demand earlier treatment as described later.
The second assumption made when growth modification is undertaken is that the practitioner can accurately diagnose the source of the skeletal discrepancy and then design treatment that will apply the appropriate amount and direction of force to correct the discrepancy. Diagnosis is not an exact science and may be confusing even with the use of cephalometric measures,7 and the discrepancy may be due to a number of small skeletal problems rather than to one easily identified discrepancy. It is important to remember that not all class II or class III malocclusions are created equal or have only one skeletal feature at fault. Force delivery to dental and skeletal structures also is inexact, and the clinical impression and treatment response may dictate alteration in the amount and direction of force applied to modify growth. Certainly orthodontic treatment for skeletal problems is not just a “see it” and “fix it” situation.
Third, growth modification is usually only one portion of a treatment plan. Most appliances used to modify growth—headgears and functional appliances, for example—are designed to alter skeletal structures rather than precisely move teeth. Although the appliances are capable of causing tooth movement, they are not as precise as fixed orthodontic appliances and usually are used before or in conjunction with fixed appliances. Therefore most growth modification treatments are followed immediately or at a later time by traditional fixed orthodontic appliances to move the teeth into a final position.
There are several theories offered to explain how growth modification works to achieve the desired results. The first theory suggests that growth modification appliances change the absolute size of one or both jaws. For example, a class II skeletal profile may be treated by making a deficient mandible larger to fit a normal-sized maxilla or by limiting the size of an oversized maxilla. Some clinical data show dramatic size changes, but there appears to be large variability in patient response to growth-modifying appliances, with modest changes in various structures being the rule rather than the exception.
Alternatively, growth modification may work by accelerating the desired growth but not changing the ultimate size or shape of the jaw. A deficient mandible may not end up larger than it ultimately would have been, but it may achieve its final size sooner. This requires the clinician to make some final dentoalveolar changes or compensations to establish an ideal occlusion following growth modification. This type of growth modification response also shows large individual variability. There is support for this interpretation of growth modification based on recent randomized clinical trials that demonstrate little difference between an early- and a late-treatment group of patients with skeletal class II malocclusion.8
A third possibility is that growth modification may work by changing the spatial relationship of the two jaws. The ultimate size of the jaw and its rate of growth are not changed, but by modifying the orientation of the jaws to each other a more balanced profile may result. For example, a convex profile and an increased lower facial height could be made more proportional to each other if the vertical growth of the maxilla could be inhibited and the mandible allowed to rotate upward and forward. The profile would then become less convex and the vertical relations more ideal. Jaw reorientation would be successful in a concave class III patient with a short face if the mandible could be rotated downward and backward (more vertical) to create a more acceptable profile. Reorientation does not work well in class II short faces or class III long faces because correcting one problem (e.g., the vertical) makes the other problem (e.g., the anteroposterior) worse.
As you can see, growth modification is at best inexact. From the best available data, it appears that if a patient is growing, on average modest skeletal changes can be accomplished during the mixed-dentition years. These are reasonably comparable if attempted early or late in this period of development. It may be advisable to attempt these changes during the earlier mixed-dentition years if patients have aesthetic complaints or, in the case of class II patients, they are trauma prone. Otherwise, conventional late mixed-dentition treatment appears to be just as sensible.
Growth Modification Applied to Anteroposterior Problems
Anteroposterior skeletal problems are class II and class III in nature. These descriptions are not very informative, however, because the source of the discrepancy may be the maxilla, the mandible, or a combination of the two. Therefore the first step in patient evaluation is to identify the source of the problem and then design a treatment plan to resolve the problem. Although this approach appears to indicate that these problems are clearly identifiable and treatable with concise approaches, the previous discussion makes it clear that this is not the case. In many moderately severe cases of anteroposterior problems a number of approaches may work that rely more on patient compliance than clinical expertise.
Class II Maxillary Protrusion
Class II maxillary protrusion is best managed by headgear therapy to restrict or redirect maxillary growth on the basis of retrospective studies and randomized clinical trials.8,9 Headgear places a distal force on the maxillary dentition and the maxilla (Figure 35-1). Theoretically, the relative movement of dental and skeletal structures depends on the amount and time of force application. In actual practice, it is probably not possible to move selectively only teeth or bones.9 Generally, skeletal and tooth movement are greater with higher forces, but tooth movement can occur with either heavy or light forces. The best approach is probably to apply forces ranging from 12 to 16 ounces per side for 12 to 14 hours and then monitor the skeletal and dental changes and adjust accordingly. Certainly, the skeletal and dental response varies according to the type of headgear chosen and the resultant direction of force exerted by the headgear. The most common varieties, cervical and high pull, provide predominantly distal and occlusal and distal and apical forces, respectively. Traditionally, one avoids using a headgear that tends to extrude posterior teeth in a person with a long face or a limited overbite. On the other hand, a headgear that extrudes the molars is often useful in a patient with a short face and a deep bite.
FIGURE 35-1 The class II maxillary protrusive patient is best treated by headgear therapy to restrict or redirect maxillary growth. A, This patient is being treated with cervical headgear that places a distal and extrusive force on both maxillary skeletal and dental structures. The force is provided by a neck strap attached to the outer bows of the headgear. B, The molar relationship is beginning to approach a class III dental position. C, Space is beginning to open up between the second primary molar and the first permanent molar. This type of change is not apparent for every patient because the amount of growth and the amount of cooperation can vary from patient to patient.
Class II maxillary protrusion can also be managed with a removable functional appliance of the activator, bionator, or twin block type (Figure 35-2). Although a functional appliance is primarily designed to stimulate mandibular growth, studies have indicated that it has some secondary effects of restricting forward maxillary skeletal and dental movement.8,10,11 This happens because the mandible, which is postured forward, tends to return to a more distal position as a result of the distal muscle and soft tissue forces that are also transmitted through the appliance to the maxilla and the maxillary teeth. The maxillary teeth tend to tip lingually rather than to move bodily, and the mandibular teeth tip facially.
FIGURE 35-2 The class II mandibular deficient patient is usually treated with a functional appliance that positions the mandible forward in an attempt to stimulate, accelerate, or redirect mandibular growth. A, This patient has a class II mandibular deficient profile. B, The patient’s molar and canine relationships reflect the skeletal class II relationship. C, The profile is immediately improved when the functional appliance is in place because the mandible is pushed forward into a class I relationship. D, Because functional appliances (a twin block in this case) position the mandible forward using the upper and lower dental arches, there may be movement of the upper and lower teeth. Dental aspects of the malocclusion must be considered during treatment planning. E, In this case, the patient wore an appliance similar to that shown in D for approximately 1 year. In the overall superimposition, the blue lines show there was slightly more change in the anteroposterior position of the mandible than in the maxilla. The maxillary superimposition shows the vertical position of the teeth were well controlled. In the mandibular superimposition, it is evident the patient grew favorably. In addition, the mesial and vertical eruption of the lower molar helped change the dental relationship to class I.
Another functional appliance is the Herbst appliance, which is a fixed appliance used to reposition the mandible forward. It is held in place with bands, stainless steel crowns, bonding, or a cemented cast framework (Figure 35-3). A pin and tube apparatus forces the mandible forward and places constant force on the maxilla and maxillary and mandibular teeth as the mandible attempts to return to a normal and more distal posture. Maxillary teeth tend to move distally and mandibular anterior teeth move forward. This appliance has shown changes similar to those of functional appliances in randomized clinical trials.11
FIGURE 35-3 The Herbst appliance is a fixed appliance that uses a pin and tube apparatus to reposition the mandible into a more forward position. A, This class II patient demonstrates correction to a near class I occlusion. B, Used in conjunction with fixed appliances, some of the dental effects can be more readily controlled.
Class II Mandibular Deficiency
The mandibular-deficient patient is usually treated with a removable or fixed functional appliance that positions the mandible forward in an attempt to stimulate or accelerate mandibular growth. Retrospective clinical studies have shown that these appliances can produce a small average increase in mandibular projection (2 to 4 mm/year).12,13 This has been confirmed by randomized clinical trials.8,14 Patient response varies greatly, and in many cases the increased growth does not totally correct the class II skeletal problem for several reasons. First, the amount of growth is not enough to overcome the discrepancy. Second, all the available growth would have to be specifically directed to produce anteroposterior change. This is usually not the case because some dental eruption and vertical growth occurs. This interaction between anteroposterior and vertical dimensional changes decreases ultimate mandibular projection and class II correction because the mandible grows downward and forward and not straightforward. The rest of the anteroposterior discrepancy is managed by restricting maxillary growth, tipping the maxillary teeth back, and tipping the mandibular teeth forward. Different appliances can be designed that exaggerate the secondary responses of maxillary restriction and dental movement if desired. The Herbst appliance, mentioned previously, also has been used with mandibular-deficient patients. Some studies also indicate that headgear treatment may cause an increase in mandibular growth.14,15
Class III Maxillary Deficiency
True midface deficiency can be treated by using a reverse-pull headgear or facemask to exert anteriorly directed force on the maxilla (Figure 35-4).16 The facemask applies force to the maxilla through an appliance (either a removable splint or fixed appliance) attached to the teeth; tooth movement also occurs. Some clinicians also use the facemask with maxillary expansion (either rapid or slow) in an effort to enhance the transverse coordination of the arches or to facilitate anterior movement of the maxilla due to alteration of the bony interfaces with other skeletal structures. A comparison of clinical studies found that less maxillary incisor movement occurs when expansion accompanies protraction.17 One prospective study found no difference between the expansion and nonexpansion approaches.18
FIGURE 35-4 A, The class III maxillary deficient patient is treated by using a reverse pull headgear or facemask to exert anteriorly directed force on the maxilla. The force is provided by rubber bands extending from the facemask to intraoral hooks or wires. B, These superimpositions shows a successful case in treating a case of class III maxillary deficiency. The overall superimposition shows the maxilla has been moved forward to a greater extent than the mandible. The mandible was rotated down and backward somewhat, which helped with the anteroposterior change in the skeletal relations. There was little change in tooth position in both the maxillary and mandibular superimpositions, which suggests most of the change was skeletal in nature.
Another approach is to use a facemask with miniplates attached to the maxilla. This method can be used in the late mixed dentition, probably at about 10 to 11 years of age, and shows greater skeletal change and movement in the zygomatic area as well.19 Finally, miniplates can be attached to the maxilla and mandible, and intraoral elastics can be used at around the same age. This has the effect of substantial change and no need for an extraoral appliance, which means the elastic force can be used continuously.20
Timing of this treatment has been controversial. Some authors believe that the ideal time to attempt this treatment is soon after eruption of the permanent incisors, whereas others have waited a bit longer. Clearly, postpubertal treatment is not indicated for growth modification.21 Data indicate that there is little anteroposterior difference in treatment effect whether treatment is applied early or late, as long as the treatment is completed before 10 to 11 years of age.22,23 Unfortunately, the long-term success of maxillary protraction is not clear. One fact appears to be emerging: mistaken diagnosis or treatment in patients whose class III malocclusion is the result of mandibular protrusion will usually fail. But, even with those who are correctly diagnosed, one in four will require additional treatment to correct the skeletal malocclusion.24
Functional appliances designed to stimulate maxillary growth do not seem to be effective. The improvement in facial profile obtained by using these appliances in patients with very minor class III problems is usually the result of a downward and backward rotation of the mandible. The occlusion improves as a result of facial tipping of the maxillary incisors and lingual tipping of the lower incisors
Class III Mandibular Protrusion
Class III mandibular protrusion has been historically managed with chin cup therapy (Figure 35-5). The theory of chin cup therapy is to apply a distal and superior force through the chin that inhibits or redirects growth at the condyle. Again, studies in animals have shown some change in absolute mandibular size, but clinical application in humans routinely has been less successful.25,26 The typical short-term treatment response to chin cup therapy is a distal rotation of the mandible and lingual tipping of the lower incisors. Therefore chin cup therapy is well tolerated in patients with mild mandibular protrusion and short to normal vertical proportions. It is contraindicated, however, in a person with a long lower face because the anteroposterior correction would come at the expense of an increased vertical dimension. The long-term results of chin cup therapy indicate that although a transient positive change can occur, the long-term results are difficult to differentiate from those in untreated patients.26 It may be possible that the use of class III elastics to maxillary and mandibular miniplates will prove useful in treating mandibular protrusion, but the short- and long-term data are not clear at this point. Functional appliances designed for the management of class III mandibular excess show the same minor changes as those occurring in class III maxillary deficiency.
FIGURE 35-5 The class III mandibular protrusive patient has historically been treated with chin cup therapy. The chin cup was designed to apply a distal and superior force through the chin to inhibit growth at the condyle. In clinical practice, this device has not proved to be routinely successful, although chin cup therapy does cause a distal rotation of the mandible. Therefore the chin cup may be useful for managing mild mandibular protrusion in which the vertical proportions are short to normal.
Growth Modification Applied to Transverse Problems
The most common transverse problem in the preadolescent is maxillary constriction with a posterior crossbite. Management of maxillary constriction can begin as soon as the problem is discovered if the child is mature enough to accept treatment. Treatment has the potential to eliminate crossbites of the succedaneous teeth, increase arch length, and simplify future diagnostic decisions that can be complicated by functional shifts. Most clinicians agree with the philosophy of early correction if there is a mandibular shift. Generally, it is believed that long-term facial asymmetry attributable to soft tissue enlargement and in some cases mandibular asymmetry can result from untreated mandibular shifts.27 Regardless of philosophy, treatment before adolescence and midpalatal suture bridging is recommended.
Three appliances can be used to correct the constriction, but the appliances are not interchangeable. In Chapter 27, the quad helix and the W arch for management of maxillary constriction are described. The appliances provide both skeletal and dental movement in the 3- to 6-year-old child.28 As the patient gets older, more dental change and less skeletal change occur. This is true because the midpalatal suture, which was open at an early age, has developed bone interdigitation that makes it difficult to separate. More force is required to separate the suture after initial interdigitation of the suture to obtain true skeletal correction than a quad helix or W arch can deliver.
In the older preadolescent patient, in whom there is a chance that the midpalatal suture is closed, an appliance that can deliver large amounts of force is necessary to correct the skeletal constriction.29 Rapid palatal expansion is the term given to the procedure in which an appliance cemented or bonded to the teeth is opened 0.5 mm/day to deliver 2000 to 3000 g of force (Figure 35-6). In the active phase of treatment, there is little dental movement because the periodontal ligament has been hyalinized, which limits dental movement, and the force is transmitted almost entirely to the skeletal structures. During retention, however, the skeletal structures begin to relapse toward the midline. Because the teeth are held rigidly by the appliance, they move relative to the bones. Depending on the amount of expansion needed, active treatment normally takes 10 to 14 days. Another approach to skeletal expansion is slow rather than rapid palatal expansion.30 Essentially the same appliance is used as in rapid palatal expansion, although force levels are calibrated to provide only 900 to 1300 g of force. Coupled with a slower activation rate, slow palatal expansion widens the palate by dental and skeletal movement. Although the final position of the teeth and supporting structures is approximately the same in rapid and slow expansion, proponents of slow expansion maintain that slower expansion is more physiologic and stable. Transverse growth modification also can be accomplished by means of acrylic or wire buccal shields attached to functional appliances or lip bumpers. The buccal shields relieve the teeth and alveolar structures from the resting pressure of the cheek muscles and soft tissues. Transverse expansion of 3 to 5 mm can be achieved, although the changes vary considerably. Whether the movement is dental or skeletal and whether it will remain stable is still in question because there are no controlled experimental studies to provide answers.
FIGURE 35-6 Rapid palatal expansion is used to treat maxillary constriction and posterior crossbite when there is a chance that the midpalatal suture is partially closed. The jackscrew in the appliance provides approximately 2000 to 3000 g of force when it is opened 0.5 mm/day. Depending on the amount of expansion needed, the appliance is normally activated two times each day for 10 days to 2 weeks. The appliance can be either cemented on the teeth with orthodontic bands (A) or bonded to the teeth (B).
Growth Modification Applied to Vertical Problems
Vertical skeletal problems are manifested as long and short facial heights and usually are located below the palatal plane.31 The short-faced person has a reduced mandibular plane angle and undererupted teeth. In the long-faced patient, the mandibular plane angle, lower facial height, and amount of dental eruption are increased in comparison with the patient with a normal face. Vertical skeletal problems can be managed with growth modification techniques, and some can be managed successfully; however, even when the treatment has been successful, maintaining the correction is extremely difficult. The face grows vertically for a long time, and there is a tendency for the original growth pattern and problem to recur.
Vertical skeletal excess may be managed with extraoral force or intraoral force. Extraoral force is delivered by means of a high-pull headgear through the maxillary first molars. The force is applied in a superior and distal direction and is designed to inhibit vertical development of the maxilla and eruption of the posterior maxillary teeth32 (Figure 35-7). Because no force is applied to the mandibular teeth, they are free to erupt and compensate for the reduced vertical development in the maxilla. In some cases, this compensatory eruption can eliminate all the positive effects of the high-pull headgear and lead to downward and backward rotation of the mandible instead of forward mandibular projection.
FIGURE 35-7 The patient with vertical skeletal excess is often treated with high-pull headgear. The force, generated by the strap resting on the head, is applied in a superior and distal direction and is intended to inhibit vertical development of the maxilla and eruption of the maxillary posterior teeth.
An alternative method for controlling vertical development is to block the eruption of the maxillary and mandibular teeth. A functional appliance can be designed that will force the mandible open to an increased vertical rest position. The force of the mandible attempting to return to its original vertical rest position is transmitted to the maxilla and the teeth in both arches. This results in mandibular growth being directed forward because no dental eruption has occurred to increase the vertical dimension and less increase in lower and total face height33 (Figure 35-8). Temporary anchorage devices (TADs) may prove to be of value in restricting vertical facial development. TADs are small diameter titanium screws placed into cortical bone. They do not osseointegrate so they can be removed after use. TADs provide the clinician with an anchor to apply force to teeth without causing other teeth to move because the screw is located in bone. In theory, the screws should not move, although it appears they do move with force application. In cases of vertical excess, TADs are placed to provide an intrusive force to the maxillary posterior teeth.34 Placing TADs in the mixed dentition patient is more difficult, however, because there are unerupted teeth in the way of insertion and the cortical bone does not hold the implant as well before approximately 12 years of age. Regardless of the means used to manage vertical excess, excellent patient cooperation is necessary because treatment must be continued or retained as long as the patient is growing.
FIGURE 35-8 Vertical skeletal excess also can be managed with a functional appliance designed to inhibit eruption of the maxillary and mandibular teeth. The appliance is constructed so that the mandible is placed in an open posture at an increased vertical position. The force of the mandible attempting to return to its normal, more closed vertical position is transmitted to the maxilla and to the teeth in both arches.
Vertical skeletal deficiencies can be managed with either headgear or functional appliances, depending on the accompanying anteroposterior relationships. The force vector from the headgear should direct the maxilla distally and extrude the maxillary posterior teeth, which would require cervical pull headgear. Because functional appliances are typically designed to inhibit eruption of upper and lower anterior teeth and promote eruption of the posterior teeth, they can also increase vertical facial height (Figure 35-9). In addition, because there is a component of forward or mesial movement of teeth as they erupt, an astute clinician will encourage lower molar eruption in class II cases (lower molar moves forward into class I) and upper molar eruption in class III cases. As in vertical skeletal excess, the original growth pattern tends to recur until growth is complete, and retention should be designed to prevent this recurrence.
A philosophy for space maintenance and the appliances recommended for the primary dentition are discussed in Chapter 25. The same philosophy and appliances apply to space maintenance in the 6- to 12-year-old age group. However, treatment for early loss of primary teeth in the mixed dentition requires some additional thought and consideration. Loss of posterior teeth in the primary dentition is a nearly universal indication for space maintenance therapy. In the mixed dentition, the timing of permanent tooth eruption, timing of tooth loss, presence of succedaneous teeth, and extent of crowding must also be taken into account.
Premature loss of a primary molar at a very early age delays the eruption of the permanent tooth. On the other hand, premature loss of a primary molar at an age near the time of normal eruption of the succedaneous tooth may actually accelerate the eruption of the permanent tooth and make space maintenance unnecessary. In general, eruption of the permanent premolar will be delayed if the primary molar is lost before age 8 years, whereas the premolar will tend to erupt earlier than normal if the primary molar is lost after age 8 years. A more accurate method of determining delayed or accelerated eruption of permanent teeth is to examine the amount of root development and alveolar bone overlying the unerupted permanent tooth from panoramic or periapical films. The succedaneous tooth begins to actively erupt when root development is approximately one half to two thirds completed. In terms of alveolar bone coverage, roughly 6 months should be anticipated for every millimeter of bone that covers the permanent tooth. If it is apparent that the tooth will be delayed in erupting and the space is adequate, space maintenance is absolutely indicated. Because space loss usually occurs within the first 6 months after the premature loss of a primary molar, space maintenance should be undertaken unless the tooth is expected to erupt within 6 months or unless there is enough space in the arch that a 1- or 2-mm space reduction will not compromise eruption of the permanent tooth.
A second factor to consider is the amount of time that has elapsed since the primary tooth was lost. At one extreme is the case of a primary molar scheduled for extraction. At the other extreme is a primary molar already missing for 6 months or longer. In the first case, space maintenance is certainly indicated to prevent space loss when the tooth is extracted. In the second case, the majority of space loss has already occurred, and space maintenance may not be indicated. The clinician should complete space and profile analyses and make a decision based on those findings. If there is excess space in the arch or if so much space has been lost that extraction of permanent teeth is inevitable, space maintenance is contraindicated. A space maintainer is indicated to prevent any more space loss if the space remaining is only marginally adequate to allow the permanent tooth to erupt. As always, there is little if any rationale for maintaining inadequate space.
The absence of a permanent successor also complicates space maintenance in the mixed dentition. The second premolar is the most commonly missing posterior tooth in the permanent dentition, excluding the third molars. If the primary second molar is lost prematurely, the clinician must make a decision about the space that would have been occupied by the missing second premolar. Two choices can be made. One alternative is to maintain space in the arch and eventually construct a fixed prosthesis or have an implant placed and restored. This is most feasible if the skeletal and dental relationships are class I, there is no crowding, and there is good interarch occlusion. This is an even more inviting alternative if only one of the premolars is missing (i.e., a unilateral missing premolar). The advent of resin-bonded bridges and intraosseous implants has made this option more popular. Another alternative is to allow or encourage the space to close. Factors that favor this solution include crowding in the arch, protrusive incisors and lips, bilateral missing premolars, and possibly other missing teeth. This topic is addressed in more detail later in this chapter.
The amount of crowding in the arch is an important factor in the decision about space maintenance, and it is predicted from the space analysis and put in perspective by the facial form analysis. If the incisor position is normal and there is adequate space or minor crowding in the arch, space maintenance should be initiated. However, early loss of a primary molar in an arch with substantial crowding must be considered carefully. Space maintainers alone will not solve a problem of this magnitude. Either permanent teeth will have to be extracted or the arches will have to be expanded. Expansion is possible only if the incisor position is normal or retrusive and the periodontal health is good enough to allow the incisors to be moved facially. If expansion is contemplated, space maintainers should be placed. In some cases, however, crowding of this magnitude is managed by extracting two first premolars and closing the remaining space orthodontically.
If no space maintenance is implemented and tooth movement results from drifting before first premolar extractions, less space remains to be closed later. Consultation with a specialist is usually desirable before this type of decision is made. If the crowding approaches 10 mm/arch, space maintainers may be needed even though permanent tooth extraction is inevitably required. The average width of a premolar is approximately 7 mm; therefore the extraction of two premolars would effectively result in a gain of 14 mm of arch length. If more space is lost in an arch that is already severely crowded, a two-premolar extraction may not resolve all of the crowding. Space maintainers would ensure that no further decrease in arch length occurs. In some instances, timed extraction (called serial extraction) can alleviate the crowding and relieve the demands of subsequent orthodontic treatment.
Probably the most significant difference between space maintenance strategy in the mixed dentition and that in the primary dentition is bilateral loss of teeth in the mandibular arch. In the primary dentition, two band-and-loop appliances are indicated; in the mixed dentition, the lingual arch is preferred if all lower incisors have erupted. Primary second molars or permanent first molars may be used as abutment teeth. If oral hygiene is a problem, it is recommended that primary second molars be banded. This is done so that if decalcification under bands occurs as a result of poor oral hygiene, it occurs on teeth that will eventually exfoliate.
Space maintenance in the mixed dentition requires close supervision as permanent teeth erupt and primary teeth exfoliate. When primary abutment teeth exfoliate, an appliance may have to be remade, using permanent teeth as abutments. Space-maintaining appliances obviously should be removed when the permanent tooth erupts into its proper position.
Potential Alignment and Space Problems
Problems associated with ectopic eruption of the permanent first molar have been discussed previously in Chapter 30. A 3- to 6-month observation period usually is the best initial therapy if the resorption is not too severe, because there is a possibility that the molar will self-correct spontaneously or “jump” distally and erupt into its normal position (Figure 35-10). Intervention is necessary if the molar is still blocked from erupting at the end of the observation period or if the permanent molar is severely impacted.35 The goal of treatment is to move the ectopically erupting tooth away from the tooth it is resorbing, allow it to erupt, and retain the primary second molar.
FIGURE 35-10 This radiograph illustrates the ability of an ectopically erupting permanent first molar to self-correct spontaneously. Note that the distal root of the primary maxillary second molar has been resorbed. Usually this type of resorption is the result of an erupting permanent molar that is caught on the distal aspect of the primary molar. If the resorption does not progress too far, the permanent molar usually “jumps” past the resorptive defect in 3 to 6 months.
If a small amount of movement is needed and little or none of the permanent molar is clinically visible, a piece of 20- to 22-mil brass wire can be passed around the contact between the permanent molar and the primary second molar. The brass wire is tightened every 2 weeks. When the wire is tightened, the periodontal ligament space is compressed and the molar is forced distally until it can slip past the primary molar and erupt (Figure 35-11). In some cases, a steel spring clip separator may be used to dislodge the molar, but only in cases in which there is minimal resorption of the primary molar. It may be difficult to seat the spring if the contact point between the molars is below the cementoenamel junction of the primary molar. Some authors advocate elastomeric separators, but they must be carefully supervised because they may dislodge in an apical direction, causing a periodontal abscess. Some elastomeric separators are not radiopaque and can be difficult to locate in the gingival sulcus.
FIGURE 35-11 A, This radiograph shows an ectopically erupting permanent maxillary left first molar. B, Because only a small amount of movement is required to correct the ectopic eruption, a piece of 20-mil brass wire is slipped around the contact point between the permanent molar and the primary second molar and is tightened. C, After the wire has been tightened three times at 2-week intervals, the molar is dislodged and begins to erupt into a normal position. (From Fields HW, Proffit WR: Orthodontics in general practice. In Morris AL, Bohannan HM, Casullo DP, editors: The dental specialties in general practice, Philadelphia, 1983, Saunders.)
Another method of moving the permanent molar distally is to band the primary second molar and apply a distal force to the permanent molar through a helical spring or elastomer (Figure 35-12). In fact, a type of band-and-spring appliance can be constructed at chairside using the orthodontic archwire tube on a molar band; the appliance is easily activated intraorally at subsequent appointments. These methods require that the occlusal surface of the permanent molar be visible so that force can be applied to move the tooth distally. A small ledge of resin or a metal button can be bonded to the occlusal surface to serve as the point of force application, or the end of the spring can be bonded directly to the impacted tooth. However, salivary contamination of the occlusal surface sometimes makes bonding a frustrating and difficult procedure. An even more cost-effective technique is to bond a permanent first molar bracket on the primary second molar and a permanent second molar bracket on the permanent first molar; then a self-retained helical spring is constructed between the two teeth to move the permanent first molar distally. This can all be accomplished chairside in a few minutes by a proficient wire bender. Such a band-and-spring appliance should be evaluated every 2 weeks and can work effectively in a short time because of the minimal root development on the permanent molar.
FIGURE 35-12 A and B, A band and helical spring appliance is used to treat an ectopically erupting permanent molar that requires a large amount of movement. The primary second molar is banded, and a helical spring is soldered to the band. A small ledge of composite resin, a metal button bonded to the occlusal surface of the permanent molar, or a small preparation can serve as a point of force application. The spring is reactivated at monthly intervals until the permanent molar is dislodged. C, Another band-and-spring design with a metal button bonded to the occlusal surface of the erupting permanent molar. Elastomeric chain or thread is attached from the button to the distal hook on the wire and changed monthly to provide the distal force to dislodge the molar. (A and B from Fields HW, Proffit WR: Orthodontics in general practice. In Morris AL, Bohannan HM, Casullo DP, editors: The dental specialties in general practice, Philadelphia, 1983, Saunders.)
Occasionally, the primary second molar must be removed if the permanent molar has caused extensive resorption of the primary root structure. In these cases, loss of arch length is certain, and some plan of treatment for the impending space deficiency should be considered in advance (Figure 35-13). If there is a congenitally missing second premolar or premolar extraction followed by space closure is being considered because of the crowding, then reduction in arch length by mesial movement of the molars is advantageous. To manage the space after extraction of the primary molar, a distal shoe can be placed to guide eruption of the permanent molar. A distal shoe maintains space but does not regain much space that was lost before the primary molar extraction. An alternative plan is to allow the permanent molar to erupt and then u/>