Treatment Planning for Anomalous Teeth
Orthodontic anomalies can be caused or complicated by abnormalities of one or more teeth. This concerns agenesis, supernumerary teeth, abnormalities of size and form, consequences of trauma, ankylosis, ectopic formation, and impaction. These anomalies are discussed as they occur in cases with normal occlusion and jaw relation, without other abnormalities present.
In considering treatment planning in this chapter and the following ones, appliances which are considered appropriate for the treatment are only briefly mentioned, and treatment methods are only dealt with superficially and incidentally. Moreover, how a correction can be achieved is not stated every time, partly because this is often self evident and partly to avoid repetition.
Most subjects in this chapter come up again later chapters, which is another reason why only the main features are considered.
Agenesis occurs most often with third molars, after which come the maxillary lateral incisors, mandibular second premolars and maxillary second premolars. The remaining teeth are seldom agenetic (less than 0.5%). It is also worth mentioning that agenesis of mandibular incisors does occur, but is often not noticed. This agenesis can lead to a TSD, with consequences for the occlusion and one should make a habit of actually counting mandibular front teeth so as to avoid overlooking this phenomenon, as well as a supernumerary mandibular incisor.
In considering the solutions of a problem of agenesis of one or more teeth, one should weigh up the advantages and disadvantages of orthodontic and prosthetic alternatives. Factors involved are, among others, the duration of treatment, the quality of the dentition, possible other anomalies and the long-term value of the solution.
When orthodontic treatment is employed to close diastemata by mesial movement of a quadrant, or of premolars or molars, thought has to be given to the need for the most distal teeth to have an antagonist. If that is not the case, overerupting of the unopposed tooth can occur. Watching for this should continue till the third molars are in place.
Finally, the possibility of transplantation of tooth germs is mentioned but it is sufficient here to just offer a short discussion.
In a number of cases, particularly multiple agenesis, consideration can be given to enucleating unemerged teeth and replanting them in more useful locations. Examples are the transplantation of a premolar into the place of a maxillary incisor, and of a third molar into the premolar region. Naturally, if a tooth is a candidate for transplantation, it must be less useful in its old place than in the new one.
The maxillary lateral permanent incisor fails to develops in about 2% of the population. One of the possibilities for treatment in a neutro-occlusion is to move mesially all the teeth that are distal to the site of agenesis and make them occlude one premolar crown width more mesially. Removing a maxillary second deciduous molar about a year before it is due to exfoliate, can simplify later treatment because the first permanent molar will have by then drifted mesially. Further, one can try to encourage the maxillary canine to emerge in contact with the central incisor, something which in certain patients can be achieved by retaining the deciduous canine for the time being.397 It is important not to forget to remove the deciduous canine once it has deflected the permanent canine as required, otherwise the premolars will not be able to drift mesially.
With bilateral agenesis the posterior teeth on both sides can be moved mesially. One can also apply ventral traction at an early age by using a facial mask according to Delaire84 and bringing the whole maxillary arch forward. Afterwards, the closing of the diastemata in the maxillary incisor region is then achieved by tooth movement involving only the centrals and canines.
With agenesis of one or two maxillary lateral incisors, a compensating extraction of one or two mandibular incisors can be considered. One has to take into account the inclination of the maxillary and mandibular incisors which may be excessively steep and lead thus to a deep bite and a “dished-in” profile. In cases of unilateral agenesis, the midpoint of the dental arch in relation to the median plane is usually displaced. In unilateral agenesis, extraction of the lateral incisor on the other side should be considered, especially if it is deviating in size and shape.
The situation of a canine adjacent to the central incisor is not always esthetically the best solution, but it is a permanent one. In most cases, esthetics can be improved considerably by carefully grinding the canine and adding composite.
Further, a prosthesis can be used to provide a solution to agenesis of one or two maxillary incisors, first performing whatever minor tooth movements are necessary. It is not always possible to avoid diastemata. Moreover, account should be taken of a later appearance of diastemata, or increase in size of existing ones. In weighing up the pro’s and con’s for orthodontic or fixed prosthetic solutions of a problem of agenesis one should also consider that prosthetic replacement—with the exception of a direct-bonded bridge—is generally only acceptable after the age of 18 or 19 years. Until that time, a temporary replacement must be supplied (usually a partial denture) which also has its drawbacks.
Finally, one should always realize that the durability of a prosthetic solution is more limited than that of a successful orthodontic correction.
Failure of the maxillary second premolar to develop occurs about as often (in about 2%) as that of the maxillary lateral incisor.17 In cases without other abnormalities, and in which the second deciduous molar has a crown of good quality and limited root resorption (compared with the other side), the deciduous tooth can be preserved and further treatment is not required. If later the deciduous molar is lost, one can still decide whether or not prosthetic replacement is indicated.
If it is clear that the deciduous molar concerned is not likely to last long, then extraction during the intertransitional period is advised. The first permanent molar can then drift mesially. Orthodontic treatment may be required eventually to secure good alignment and occlusion of the posterior teeth.
If, in addition to the agenesis, other indications for orthodontic treatment exist, the result of the agenesis has to be considered in relation to the whole situation. Whether one shall extract other teeth in addition, and which approach is to be preferred, depends on many factors that are not appropriate to discuss at this point.
The second premolar in the mandible is not laid down in about 4% of the population. Most of the remarks made about agenesis of the maxillary second premolar apply also to this tooth. The later loss of a mandibular second deciduous molar without a successor has more unfortunate effects than the same situation in the maxilla. The adjacent teeth will tip more severely, the perimeter of the lower dental arch becomes smaller and overjet and overbite increase. Moreover, an antagonist is more likely to overerupt into the space left there.
If it is clear that the second deciduous molar cannot be retained, then early extraction is desirable. The subsequent changes will generally result in a better sequel than if the tooth is lost relatively late. In a neutro-occlusion with both mandibular second premolars agenetic and the deciduous teeth having a poor prognosis, extraction in the maxilla must be seriously considered. Usually premolars will be concerned.
One can also close the space due to the agenesis by moving the mandibular molars mesially. This creates a mesio-occlusion, which has certain disadvantages: the second maxillary premolar will occlude only with the mandibular first permanent molar, which provides an unsatisfactory interdigitation. Furthermore, the maxillary third molar will have a very limited occlusion with the mandibular one.
The mesial migration of the mandibular first permanent molar and the limiting of the distal migration of the teeth “mesial to the agenesis” can be secured by hemisection of the second deciduous molar. After endodontic treatment the distal half of the deciduous molar is removed. The braking effect of the remaining mesial part of the distal drifting of the teeth mesial to it is greatest when the mesial root is ankylosed. The mesial part is removed later, and the remaining space closed.
Extra teeth are met in every area of the dental arches, and the advised treatment is extraction. However, when a supernumerary tooth is properly formed, the removal of another tooth can be considered instead.
Supernumerary teeth are seen most in the maxillary anterior region in the form of a mesiodens (8.3).
Supernumerary mandibular incisors bear mention here. When five mandibular incisors are found, it can be difficult to identify the supernumerary tooth. It can be advantageous to retain a supernumerary tooth and extract another one instead. Sometimes no extraction is indicated (e.g., to avoid spacing or to compensate an extreme TSD).
Abnormalities in the form of the crowns of teeth can cause functional disturbances in the posterior teeth, though anteriorly, appearance is the primary concern. Solutions to this can be restorative or />