Agenesis of One or Both Maxillary Lateral Permanent Incisors
The failure of one or both maxillary lateral permanent incisors to form usually comes to light after an examination instituted because there are problems in the transition of the maxillary incisors (see Chapter 8). The child and the parents are usually not prepared for it.
In this chapter the symptoms are given that can point to agenesis of maxillary lateral permanent incisors. The space conditions in the dental arch that are important in treatment are dealt with. Advantages and disadvantages of orthodontic and prosthodontic space closure are explained. Special consideration is given to the esthetic aspects of placing the permanent canine alongside the central incisor. The different possibilities for prosthodontic closure are discussed. The role played by the dental arch relations in deciding on the treatment mode is clarified. Possibilities for influencing the development of the dentition in good time are indicated. Unilateral agenesis is treated separately. Retention and postretention problems are brought up.
Agenesis may not come as a surprise in families with members whose maxillary lateral permanent incisors never formed or formed in miniature. In history taking, one should remember to enquire about the occurrence of agenesis in the family. Further, one should be alert to agenesis of maxillary lateral permanent incisors when:
1. Lateral deciduous incisors are missing
2. Lateral deciduous incisors are still present and exhibit only little mobility 1 year after emergence of the central permanent incisors
3. Eighteen months after the emergence of the central incisors (and exfoliation of the lateral deciduous incisors) the mucous membrane has not yet been penetrated by the lateral permanent incisors
4. An unusually large central diastema exists
5. The size of the central diastema does not reduce or reduces only a little
6. Palpation of the alveolar process does not reveal the presence of lateral permanent incisors
Certainty about the presence or otherwise of unerupted teeth is only obtained radiographically. This means should only be used when there is no other clear sign of formation.
The long-term planning of the case determines when it is essential to know if teeth are present or not. This is enlarged upon in section 10.8. In general one must have positive information 1 year before the second transitional period is due.
In cases of missing lateral incisors where a marked crowding in the maxillary dental arch would exist if all permanent teeth were present, the most obvious treatment objective is to achieve contact between the central incisors and the canines.
Maxillary permanent canines are formed with a mesial angulation, certainly in instances of a small anterior section of the apical area. Their path of eruption conforms with this. In the absence of the maxillary lateral permanent incisors, the canines can emerge particularly far mesially and contact the central incisors. In such instances the lateral deciduous incisors exfoliate as their roots resorb at the approach of the permanent canines. When the anterior section of the apical area is large, a more mesial emergence of the permanent canine can be encouraged by early removal of the lateral deciduous incisors and persistence of the deciduous canines. The latter can be extracted later, unless long-term retaining is aimed for. Indeed, in situations of crowding, retaining the deciduous canines is not indicated.
In imminent cases one can artificially reduce the available arch length in the involved quadrants by removing the maxillary second deciduous molars early. Their extraction should preferably be executed a good 6 months before the adjacent first deciduous molar is due to exfoliate. Subsequently, the first permanent molar migrates and rotates mesially.
It is better to extract the first deciduous molar at an earlier moment, when rotation of the maxillary first permanent molar should be prevented and only a limited reduction of arch length is needed.189
If no crowding exists, and particularly if excess space prevails, achieving contact between canines and central incisors (with or without retention of the deciduous canines) is not the only solution. Closing the space through prosthodontics should also be considered. In arriving at the best solution the relation between the dental arches is an essential variable (see 10.7).
On the basis of purely dental arguments it is preferable to avoid prosthodontic appliances as much as possible.150, 214 One should realise that the dentition of the patient involved must function for many years yet. Hence, the long-term planning should strive to keep a substantial part of the natural dentition intact during the patient’s entire lifetime. In that light, it makes a considerable difference if an initial prosthesis is provided at the age of 18 years as compared with 48 years.
As a standard solution it is best to aim for closing the anterior spaces with contact between permanent central incisors and canines. Contraindications for such a decision are:
1. An extreme surplus of space in the maxillary arch
2. A Class I anomaly with no crowding in the mandible
3. A dished-in profile
4. Esthetic problems (see 10.5)
5. A Class III anomaly
When there is much room in the maxillary dental arch and a contraindication to arrive at a continuous arch of permanent teeth without diastemata, it is reasonable to attempt to retain the deciduous canines as long as possible. As has already been pointed out, the permanent canines can emerge in the place where the lateral permanent incisors should have emerged, especially when there is a great deal of space. Often in such circumstances the deciduous canines do not resorb and exfoliate. Certainly, when the resorption of the deciduous canine roots is limited, these teeth can last many years. If they are lost at a later stage, at least the period during which a prosthodontic appliance has to be provided is correspondingly reduced. Moreover, a better prosthodontic restoration is possible in this situation than where the space to be filled is between the central incisor and canine.
The possibilities for prosthodontic restoration are broadened by the use of bonded composite resins. Bridges made using this method, particularly if employing a cast palatal splint fixed to the abuttments, can remain in place over a long period.