Treatment Planning for Class I Anomalies
In this chapter the subjects to be dealt with include crowding and spacing, proposition/eversion and retroposition/inversion of incisors, deviations in vertical and transverse occlusion, and double proposition and “dished-in” profiles as they occur in neutro-occlusion.
In this and Chapters 12 to 15 the following general subjects are treated: anatomical aspects, guidance of the development of the dentition (and facial growth), when and how to treat. The final subject matter is retention and relapse.
By definition, a Class I case has a normal sagittal occlusion of the dental arches. When the sizes of the mandible and maxilla do not correspond with each other, an abnormal disposition of teeth can result. For example, in cases with a small anteroposterior dimension of the maxilla, the anterior section of the apical area of the maxilla may lie too far dorsally to that of the mandible. In otherwise normal circumstances the maxillary incisors will then be tipped far labially.
If the crowns of the teeth are large and the tooth-bearing parts of the mandible and maxilla are well-developed, a double proposition usually results. Abnormally small crowns may lead to a double retroposition, usually resulting in a fallen-in mouth—a “dished-in” profile. This picture can also be present in a normal dental situation when there has been much growth of nose and chin to ventral.
Dominance of the dentition in the face can also be the result of marked eversion of the mandibular and maxillary incisors without there being any anomaly in the size of the jaws.
Crowding and spacing are generally expressions of discrepancies between size of apical areas and dental arches on the one hand, and the sum of the mesiodistal crown diameters on the other.
As a way of increasing understanding in diagnosis and treatment planning, the different anomalies are described in relation to the concept of “apical area”. The apical area is subdivided into anterior, middle and posterior sections (see Fig. 5-7). This subdivision of the apical area however involves a risk that the apical area may not be considered as a whole. Further, there is a disadvantage that points that are of importance for different sections are repeated in the text. Intervention in one section often influences the situation in the adjacent section. Furthermore, the borders of the sections are arbitrary and can move; they can be shifted spontaneously, or under the influence of orthodontic treatment. For example, the size of the posterior section of the apical area in the mandible can increase if the mandibular second premolar is missing and the first permanent molar drifts mesially after loss of the second deciduous molar. In this case, the middle section of the apical area naturally becomes smaller. When after extraction of both first premolars, the canines go distally, the anterior section of the apical area is increased and the middle section is decreased in size.
The attractiveness of a face is determined partly by its form and composition and partly by liveliness and expressiveness (facial animation). The fullness of the orofacial region plays an important part in that respect. The facial form and expressiveness depend on harmoniously formed underlying bony and dental structures and on a well-functioning musculature.
Extraction of teeth and retruding of incisors are associated with resorption of bone and reduction in the prominence of the soft tissues draped over them. As a result the fullness of the face can be reduced to such an extent that it becomes less attractive. Reduction of the canine prominence not only exaggerates the nasolabial fold but, as a rule, also reduces facial animation. Extraction therapy also has a tendency to make the maxillary arch too narrow. When the canines assume the positions of the first premolars, the lateral incisors come too close to the corners and the normal appearance of the front teeth is lost. When smiling, dark corners on each side between teeth and cheek can be seen. Retrusion of mandibular and maxillary incisors can make chin and nose relatively and undesirably more prominent. Danger for this occurrence prevails particularly when the chin and nose are abnormal in size or position, or are still growing. The region between them—the area of the mouth—can come to lie disfiguringly far back.
Despite the fact that the development of orthodontic anomalies cannot—or at least only exceptionally can—be prevented, there is certain room for interceptive procedures (8.3). The development of the dentition can be guided by simple measures, particularly when applied in the first and second transitional periods. Again, there are some examples: removal of persisting deciduous teeth or root fragments that impede the successors in achieving good positions, grinding away the mesial surfaces of deciduous molar crowns so that crowding mesial to them can decrease; occlusal grinding of a deciduous molar so that an emerging antagonist may be guided in the proper direction.397
The best period to begin treatment of a neutro-occlusion is principally determined by factors that have to do with the development of the dentition, unless functional abnormalities exist. Disregarding interceptive measures, it is preferable usually to begin active treatment during the second transitional period. The difference in mesiodistal crown diameters between deciduous molars and their successors can then still be used to combat threatening crowding. The second permanent molar has not yet emerged, so the first molar can if necessary be moved a little distally. Also the mesial migration of the first permanent molar can be resisted. Moreover, emerging premolars and canines can go directly to a correct position or be guided into them. Further, since treatment cannot be considered complete until all permanent teeth have reached occlusion (with the exception of the third molars), beginning early can unduly prolong the treatment time.
In cases where it has been decided to remove one or more permanent teeth, maximum advantage can be taken of any spontaneous correction by performing the extractions some time before placing appliances. This may only be done if mesial migration of teeth distal to the extraction space is not a disadvantage. If this migration has to be prevented, then either the extraction should be postponed till just before fitting the appliance (or even after), or an appliance be fitted immediately for the express purpose of holding the teeth that are not to move, but which will allow movement of those teeth that may spontaneously correct themselves. It is in the first 2 or 3 months after extraction that spontaneous movement of adjacent teeth is greatest.356
It is naturally preferable to seek the desired result by the simplest effective means. Complex techniques, which of course are sometimes essential, generally have more disadvantages for the patient and his dentition than do the simpler ones. It is also important to assess how much time is involved in the treatment. Treatment over a long period tests both the cooperation of the patient and the endurance of the practitioner. Therefore, a short complex treatment may be preferred to a long simple one.
The possibilities and limitations of some techniques have already generally been discussed (8.6) but a few remarks can be added.
Removable appliances can deliver fine results in capable hands, unless bodily movement, torquing, and/or vertical movements are required. By fixing attachments and auxiliary springs to particular teeth, it is possible to extend the action of such appliances. It is even possible by placing composite on vestibular surfaces to increase the retention of a plate and sometimes to secure vertical movement.
Lingual and palatal arches serve to expand or compress arches transversely, to upright molars, and to move incisors labially. Buccal arches (lip bumpers), which are inserted only into buccal tubes on permanent molars, work principally by holding the vestibular musculature away from the teeth. In that way they can secure an increase in arch perimeter and have the advantage that the necessary space develops, not by applying force but due to a “spontaneous” development of the dental arch. It is suggested that such changes are less likely to relapse than those obtained by other methods. However, such appliances are not always easily tolerated by patients. Lingual, palatal and buccal arches can be used to rotate the molars to which they are fitted. Rotation of molars is principally necessary in the maxilla, where the palatal root induces rotation if the molar moves mesially. The remaining teeth can only be moved to a limited extent using lingual or palatal arches.
If one strives for as good and stable a result as is possible, then perfect contact points are necessary. It is therefore often necessary to use fixed appliances because rotations and bad interproximal contacts, especially in the mandible, could otherwise not be corrected adequately. Certainly, whenever crowding in the mandible is such that extraction is indicated, it will almost always be necessary to employ a full fixed appliance. With other techniques it is simply not possible to obtain the necessary movements of the teeth and their roots so as to leave the roots parallel and the crowns at the right heights and in proper contact.
In treatments without extractions a good result can sometimes be achieved with fixed appliances that only involve a part of the dental arches. For example, brackets and tubes might be fitted only to molars and canines and incisors. Occasionally, maxillary premolars (and canines) need not be involved if they are in satisfactory positions and are not required for purposes of anchorage.
Functional appliances or headgears are generally not indicated in Class I anomalies. However, in cases where teeth are missing through agenesis, trauma, or caries, it can be desirable to move a dental arch or a segment of it in a mesial direction.397 In such cases extra-oral traction (Delaire’s facial mask) for the ventral movement of teeth is a useful aid.
A deciduous dentition without ample spaces between the incisors in both jaws is usually followed by a permanent dentition with considerable crowding. This crowding can be corrected by increasing arch length, reducing the sum of the mesiodistal diameters of the crowns of the teeth by extraction (or proximal stripping), or sometimes by a combination of both.
In theory, the dental arch length can be increased by expanding the arch transversely, by moving the incisors labially and by moving the molars distally. All three movements are more restricted in the mandible than in the maxilla. In the maxilla the midpalatal suture retains its potential for bone formation through which the transverse dimensions of the maxilla can be increased. Moreover, apposition and resorption of the alveolar processes of the maxilla in the posterior regions can contribute to widening. The maxillary sinus is adaptable; the surrounding bony structures conform to changes. One should be quite certain that the crowding is due to a transverse abnormality before attempting to correct it by arch expansion. If crowding is due to a sagittal abnormality it can hardly ever be relieved by transverse movements.
Intrusion brings the apices of maxillary incisors into the region of the maxilla where the labiolingual dimensions are gradually larger the more cranially they move. So, with intrusion, one increases the possibility of root movement over a greater labiolingual distance. Moreover, intrusion of the maxillary incisors leads to a reduction of the overjet and overbite.367 Whether actual intrusion occurs, or whether eruption is prevented while the lower face height increases, depends on the amount of vertical growth taking place.
Furthermore, in the maxilla the first and second molars can be moved distally, through which or course the space available for the second and third molars is reduced.
The possibility of expanding the mandibular dental arch is limited to what buccal displacement and uprighting of teeth can be obtained within the cortical plates. The basal bone of the jaw and the location of the apical area in the mandible cannot be influenced by therapeutic measures.
In the mandible the limitations in the incisor region correspond with those in the posterior parts. The lingual and labial cortical plates are close together. Tooth movement is limited labiolingually to tipping. The room for the roots does not increase significantly with intrusion.
The limited possibility of increasing the arch length in the mandible also provides a limitation for the alterations that can be achieved in the maxilla. For the best possible chance of stability in the final result, it is essential to secure a solid interdigitation of the posterior teeth and a good contact between the incisors. The arch width that is attainable in the premolar/molar region of the mandible determines that of the maxilla; the disposition of the mandibular incisors determines that of the maxillary incisors. The mandibular arch dictates the confines of the maxillary arch. Many practitioners first have the provision of a good mandibular arch as their objective, after which the maxillary arch is adapted to coordinate with it.
The development from deciduous to permanent dentition is characterized by a great variation in width changes in the dental arches. Sometimes the increase in width is marked, sometimes minimal, and exceptionally even negative.264 Predicting the changes in width is difficult so generally it is wise to adopt a wait and see policy.
The most important parameter in the treatment plan for crowding is the Arch Length Discrepancy (ALD). If there are still deciduous teeth present one can use the Mixed Dentition Analysis (MDA). Sometimes it turns out subsequently that the premolars, especially the canines, are smaller than was estimated, which enhances the chance of success in treatment without extraction. Extraction is irrevocable, it can always be done later; it is seldom too late.57
It is not realistic to give guidelines for and against extraction based only on the calculated ALD because too many other factors are involved. For example, there is the conformation of the facial skeleton, the potential facial growth and development of musculature, the changes in dental arch measurements, the possibilities for expanding the arches, and the effect of extraction on facial form.
In the field of orthodontic treatment, extraction of permanent teeth must never be proceeded with until it has been definitely confirmed that there are no agenetic teeth and, as far as it is possible to see on radiographs, that all teeth are normally formed. Further, in a case with an ALD, it should be borne in mind that it may also have a TSD which calls for reduction of some mesiodistal crown diameters and this could also reduce to some extent the ALD.
If it is decided that with increase of arch length, no good, or stable, result can be secured, this is not to say that extractions are inevitable. Rather, one can do without treatment at all, or one can accept that dentally no “ideal” result is attainable.
In neutro-occlusion and neutrorelation extraction in one jaw must be coupled with extraction in the other jaw, unless teeth are already missing, or it is intended to change the sagittal occlusion in the posterior segments. Often, however, crowding in the mandible compels extraction. If the crowding is confined to one side, it is tempting to only extract in that quadrant. Usually this is not a good solution because the existing asymmetry is increased and, above all, will increase further as time goes on. This does not always apply to the maxillary arch, where sometimes space is almost entirely eliminated by mesial movement of the teeth distal to the space, so that the midline is little affected. Moreover, with unilateral extractions, it is difficult (even with fixed appliances) to reach a symmetrical arrangement of both maxillary and mandibular incisors.
The influence of extractions on the face is again emphasized. In connection with this one must also take into account the nose and chin growth that may occur, especially in boys at their later phase of growth. This can alter facial appearance considerably.24 122 328
It is generally irresponsible to decide at an early age that four first premolars must be removed. This also applies to removing deciduous canines with which, following the concept of serial extraction*, this therapy can be initiated. One then loses not only the development in width of the arch that otherwise would occur, but also the decision about extraction of permanent teeth is made at the time when the face has yet to grow a great deal. Extractions can severely disadvantage the facial development in a way that cannot be foreseen. Further, it sometimes subsequently happens that so much space develops, despite the extraction of the deciduous canines, that extract of premolars is seen to be unnecessary.45 Fortunately, the situation can still be rectified in such cases, but it is stressed that extra caution is necessary.
Proponents of serial extractions have not compared their results with corresponding cases that were treated without extractions of permanent teeth. It is only on the basis of such comparative investigations that a secure judgement can be made of the effect of serial extraction therapy. It is recommended then that this type of therapy only be employed after very serious assessment of the consequences in each case. If in doubt, it is always best to wait. Extraction can always be done and, even if all premolars and canines have emerged, it is still possible to obtain an acceptable result by extraction of the four first premolars, followed by proper use of the appropriate techniques.
Many cases in which serial extraction is performed must subsequently have full fixed appliances for correction. This naturally reduces the value of the advantages originally said to be forthcoming when the intention was to eliminate use of appliances. It would appear that serial extraction can only be suggested to the patient and his parents with many provisos and as a plan of treatment that might only with very great good fortune be a short cut.
Particularly in the mandible, crowding of the permanent dentition is the rule rather than the exception. Adolescents with good occlusions—also without orthodontic treatment—will often develop crowding (tertiary) on maturing.348 Maturing of the perioral musculature and the fact that mandibular growth proceeds longer than does that of the maxillary complex are probably the most important causes of tertiary crowding. It is more than likely that the relationship is temporal and not causal, but it is still remotely possible that third molars are a factor in crowding of incisors, despite there being no supporting scientific evidence available.32 314 Further, mandibular incisors also crowd in the absence of third molars. The crowding in the mandibular arch can also increase much later.324
The degree of crowding can differ greatly. In extreme conditions extraction of teeth will be the first approach to be considered. When there is little crowding, foregoing treatment is always the first choice.
For the stability of the mandibular arch, good contacts are essential; particularly those between lateral incisors, canines and first premolars.131 Correction of crowding in the mandibular arch which does not achieve good mutual support between the teeth concerned will usually relapse severely.
During the second transitional period the first permanent molars migrate more mesially than in the developmental phases, before or after (Fig. 8-2), and in so doing occupy most of the extra space (leeway) made available by the smaller premolars supplanting the deciduous molars. In cases with crowding in the incisor region, and also when there is too little space for an emerging canine, one can try to utilize the leeway space to secure a better disposition of the anterior teeth. This can happen if the deciduous molars are grinded away (sliced) mesially, and is especially beneficial when the mesial convexity of the second deciduous molar is removed.397 To prevent the arch length reducing, one can also use a lingual arch fixed to the first permanent molars and resting against the mandibular incisors lingually. There is some question as to whether more is gained by the lingual arch than by proper use of slicing. Lip bumpers are also used with this objective in mind.
In discussing crowding in the incisor region of the mandible, a number of features emerge that apply similarly (sometimes to a high degree) to crowding in the canine/premolar region and/or in the molar region. Also, in a later discussion of crowding in the maxilla, points are mentioned in dealing with the incisor region which apply to the whole arch. Although this approach, specifically due to the repetitions, may become confusing, for didactic reasons it has been chosen. One should also bear in mind the previous remarks made about crowding in the different sections of the apical area, when the disadvantage of looking at parts instead of the whole was pointed out. Crowding is seldom restricted to one part. In treatment planning one naturally has to integrate the parts and the apical area has to be considered in its entirety.
With a small anterior section of the apical area in the mandible both permanent canines are laid down a smaller distance apart than normal. The space for the developing permanent incisors is then limited and the laterals are found far lingually. The incisors can also be laid down rotated and seriously overlapping (or fanned out).396
During emergence of permanent mandibular incisors, an adjacent deciduous tooth, (mostly a deciduous canine) can prematurely resorb and be lost. Unilateral premature loss is associated with a displacement of the midline of the incisors towards the side of the loss, something that can occur in the mandible even before emergence.395 Guidance of the development of the dentition by extraction of the corresponding deciduous tooth on the other side is often desirable. The active therapy that would later be needed is then simpler. However, the situation in the maxilla must then be considered since the overjet and overbite will increase if the deciduous canines there are not also removed. Premature loss due to resorption, certainly bilaterally, is a sign of primary crowding. Furthermore, after premature loss of the deciduous canines there will be less increase in arch width than would otherwise have been the case. This is also the situation when deciduous canines are extracted prematurely, something seldom indicated.408
It is normal that soon after emergence the lateral incisors lie lingually and that there is little space for them in the arch.265 Even in cases with marked lack of space, the arch length can increase spontaneously to a considerable extent, and the lingually placed lateral incisor can still fit into the arch.217 One should guard against extracting lingually placed mandibular incisors.
As previously indicated, there is a limit to the possibility of increasing mandibular arch length. Expansion of the intercanine width to correct crowding is usually unstable. After removing the appliance (or the retainer) there is almost always a return to the original intercanine distance. 166 230 324 Moreover, in most cases, it appears that in nontreated individuals with good occlusions, the intercanine distance in the mandible actually decreases between the ages of 13 and 20 years.348 There is a little more scope for expanding and uprighting the first and second premolars,131 317 but this provides little increase in arch length. The possibilities for expanding the arches are probably related to facial types; in wide faces the prognosis is better.
The movement of the mandibular incisors to the labial can provide extra space, especially when premature loss of deciduous teeth, abnormal posture of the lower lip, or thumb sucking has tipped them lingually. Susceptible periodontal conditions and eversion of the incisors can make labial movement undesirable.
Correction of crowding in the mandibular incisors is a part of forming a harmonious mandibular arch with good contact points and, better still, contact areas. The objective can usually only be reached with full fixed appliances. An 0.045″ arch or a lip bumper can be used prior to that. The desired goal can in certain cases also be achieved with a lingual arch.
If the crowding is so great that the above measures are not sufficient, then extraction is inevitable and it is necessary to determine which teeth are the best to remove. In extreme mandibular incisor crowding, one can consider removing one incisor and one premolar from the other quadrant. In exceptional cases, two incisors may be the best choice, particularly if there is agenesis of two maxillary lateral incisors. When one, but particularly two, mandibular incisors have been extracted, there is in relation to the maxillary anteriors usually such a deficiency in tooth material in the mandibular anteriors that with a solid posterior interdigitation good contact cannot be obtained in the anterior region. There is then a risk of a deep bite developing with upright maxillary and mandibular incisors. It is particularly desirable to utilize a diagnostic set-up when contemplating extraction of incisors. This applies in fact for all situations where extraction of teeth other than corresponding premolars (molars), particularly asymmetric extractions, might offer a good solution to the problem.
The mandibular incisors are important in stabilizing the occlusion and should be kept intact as far as possible.18 In most cases with serious mandibular incisor crowding where a decision has been made to extract, first premolars are the best teeth to sacrifice. Through distal movement of the canines, sufficient room can be found for the incisors. Extraction of first premolars is an especially good solution when canines slope severely to the mesial. An advantage of this approach, compared with removal of incisors, is that a better occlusion can be obtained. The premolar crowns of both jaws have approximately the same mesiodistal width, so that equal amounts of tooth material will have been removed. (If mandibular extractions are performed in a case of neutro-occlusion, compensating maxillary extractions are essential.) If one removed two relatively narrow mandibular incisors in such a case, then there is a good chance that a tooth size discrepancy would be introduced, resulting in a less good occlusion.
It is worth noting that extraction of first premolars does not always lead to stable results and permanent relief of mandibular anterior crowding. Investigations into many cases out of retention over ten years have shown that two-thirds of them had developed an unsatisfactory disposition of the mandibular incisors.230 Alongside this it can also be seen (as mentioned) that between the ages of 13 and 20 years, untreated good occlusions will often lose some of their intercanine width and the mandibular incisors will become irregular.348
Sometimes it is preferable to extract mandibular second premolars, for example when one wishes to limit the effect of the extractions on the profile, or when the mandibular second premolar has an abnormal crown form. It is also when there is agenesis of one second premolar that extraction of the second premolar on the other side is called for.
Extraction of the first permanent molar can be a solution worth attention when there is incisor crowding and the first molars are in poor condition (e.g., hypoplastic, severely carious, large restorations, root filled, periapical lesions).
For that matter, in choosing which tooth to extract, the quality of all teeth concerned is very relevant. Sometimes the choice must fall on a defective tooth that one would really rather have retained.
Extraction during the second transitional period of second permanent molars in the mandible may give a spontaneous reduction in later crowding
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