NEWSLETTERS

Treatment planning bilaterally impacted and transposed labial canines

Published: June 2015

Bulletin #45 June 2015

Treatment planning bilaterally impacted and transposed labial canines

In this month’s bulletin we discuss the case of an 11.6 year old girl in the late mixed dentition stage. Her chief complaint was the fact that she still had 3 deciduous anterior teeth and had been told that 2 of her permanent teeth were impacted in the maxilla.

Clinical examination

efg._Fig._1aefg._Fig._1b

Fig. 1. Intra-oral photographs of the initial malocclusion.

The intra-oral examination of the patient revealed several of the features associated with a very large section of the population affected by maxillary canine impaction. The erupted mandibular dentition included all the permanent teeth, including the second molars (Fig. 1). Only the second premolars were unerupted, with infraoccluded second deciduous molars still firmly in place. The erupted maxillary permanent dentition comprised only central incisors, first premolars and first molars. On the right side, deciduous lateral incisor, canine and second molar were present, while the deciduous canine and infraoccluded second molar were in place on the left side.

The antero-posterior molar relation was class 1 and the overbite and overjet were 3-4 mms. There was a minor degree of mandibular intercanine crowding. A small median maxillary diastema was present, but the central incisors did not display the typical distally angulated flaring of their crowns. Contrary to the expected convergence of the long axes of the roots of these teeth in the apical direction, they featured a slight apically-divergent orientation. There was a lateral open bite on the left side whose origin was undoubtedly due to the infraocclusion of the two deciduous second molars on that side, together with an associated under-eruption of the adjacent first premolars1. Clinically, the unerupted maxillary canines could be palpated high in the labial sulcus.

Radiographic examination

efg._Fig._2aefg._Fig._2b

Fig. 2a. Panoramic view of the dentition, showing retained deciduous teeth, infraoccluded second deciduous molars, congenitally absent maxillary lateral incisors and (probably) right maxillary third molar, late developing mandibular right second premolar, in addition to the very high and angulated impacted maxillary canines.

Fig. 2b. Periapical radiograph of the maxillary anterior teeth

From the panoramic radiograph (Fig. 2a), it was evident that the maxillary lateral incisors and the right maxillary third molar were congenitally absent and the maxillary canines mesially angulated and impacted high in the maxillary basal bone. Three of the four unerupted second premolars were marginally late in their development, with about half their expected root length completed and in good positions for a normal eruption within a few months. In contrast, the initiation of root development of the mandibular left second premolar had barely started, in line with a dental age of about 6 years for this specific tooth. The mandibular second molars were already erupted with a dental age assessment equivalent to the patient’s chronologic age. All four first premolars were erupted with 2/3 of their final root length, as expected at this age.

efg._Fig._2c

Fig. 2c. Anterior section of the lateral cephalogram shows the maxillary canines superimposed on one another, very high and labially displaced in the maxilla.

Since the two impacted canines were not close to the midline, as seen on the panoramic and periapical views (Fig. 2a, b), the forward location of their image on the lateral cephalogram indicates that they were both labial to the line of the arch (Fig. 2c).

CBCT examination

A well prepared CBCT reconstruction of the raw data has several elements and a very large number of photographic and video images.2, 3 Thus, “cuts” or “slices” of the images may be performed in the strictest conformity with the 3 planes of space, to provide true coronal views, cross-sectional views and axial views. They may also be performed obliquely in many different directions, to provide additional information. Three-dimensional screen shots may also be depicted at different angles and elevations and a composite 3D video clip (Fig. 3) prepared, to greatly benefit understanding of the inter-dental relationships in the three planes of space. 

Fig. 3. can be viewed by clicking on http://youtu.be/v-RsjTivmvQ.

This is a 3D video clip reconstruction from the raw data of a cone beam acquired CT. It is presented both in both transparent and solid format. Note the artistry of the technician in producing a beautiful rendition of the location of the tooth and the inter-relations between the teeth and surrounding structures. It will be easily understood why this modality eliminates the possibility for mistaken diagnosis.

It is obviously impossible to reproduce all of these in the context of this bulletin and we shall concentrate here on presenting just an essential few, in order to be in a position to offer a reasoned approach to the resolution of the impactions.

efg._Fig._4

Fig. 4a, b. 3D screen shots of the right and left sides, showing the abnormal angulation of the first premolars that has brought their developing apices mesially beneath the canine crowns, to block the descent of the canines. Note how the infraoccluded left deciduous molar has displaced the apex of its successor upwards into the area of the developing canine apex.

The lateral 3D screen shots (Fig. 4a, b) show the very considerable mesial displacement of the first premolar on each side, whose root ends are in close proximity with the inferior aspect of the canine crowns. The left lateral 3D screen shot (Fig. 4a) shows the developing apex of the second premolar to be displaced high into basal bone and close to the developing apex of the canine. In their turn, the canine crowns appear to be in contact with the apices of the erupted central incisors and their root apices are more distally located than is normal.

efg._Fig._5

Fig. 5a, b. The same views as in Fig. 3a, b, as seen on the longitudinal cuts. In these cuts, one may see the intimate inter-relation between the developing apices and crown follicles of the teeth in the immediate area.

Clearly then and although the crowns of the canine and premolar are in their correct order, the root apices of these teeth are markedly transposed. Looking at the longitudinal cuts (Fig. 5a, b), one may see that the apices of the two teeth have a mesio-distal transposition discrepancy of about 4-5mms on the right and about 7-8mms on the left.

efg._Fig._6

Fig. 6a, b. The cross-sectional cuts across the alveolar ridge in the area of the deciduous canine and first premolar shows the location of the canine crowns to be surgically accessible from the labial side of the alveolar ridge. The slice in Fig. 5b has cut through the two developing root apices of the left first premolar.

The cross-sectional cuts in the deciduous canine region of each side show the permanent canine crowns to be high above the deciduous canine apices and surgically approachable from the labial side (Fig. 6a, b).

Diagnosis

The diagnosis of the malocclusion is Angle’s class 1 with normal molar relations and a more or less normal incisor relation. There is mild mandibular intercanine crowding and congenitally absent maxillary lateral incisors and (at least so far) a missing maxillary third molar. If one were to rehabilitate the missing lateral incisors, a minor degree of maxillary crowding would probably be revealed, of the same order as seen in the mandible. The maxillary canines are impacted high in the maxilla with a forward and downward apex-to-crown orientation and are strongly transposed with the first premolars whose apices are mesially displaced while their crowns are well situated. On both sides, these incomplete and developing premolar root apices present an impediment to the resolution of the canine impaction.

Etiology

The unusual and almost identically bilateral and abnormal orientation of the long axes of the first premolars, strongly hint at a genetic cause for this unusual configuration of the premolars and canines. This impression is supported further by the bilateral distal displacement of the canine apices and the fact that the transposition is identical on each side. It is a moot point as to whether impaction of the canines is due to their obstruction by the premolar roots or because of the general orientation of the canines themselves or the genetically dictated orientation of the premolars or because there are no lateral incisors to provide eruption guidance. It seems likely that each of these factors may have combined to play a part in the etiology of this very special scenario.

Treatment plan

It is quite clear that the key to resolution of the impaction of the canines and their alignment rests with distancing the premolar roots from their proximity to the canines.

The suggested treatment plan is, therefore, as follows:-

1. Place a mandibular lingual arch soldered to molar bands to prevent loss of the leeway space, when the deciduous molars are lost

2. Extract the maxillary deciduous second molars

3. Place a multibracketed maxillary appliance. Brackets should be placed on the first premolars and central incisors, but also on the deciduous canines to provide support for the use of initial alignment archwires. Similarly, with the expected fairly rapid eruption of the second premolars, brackets should be placed on them as soon as is practical.

4. The bracket on the first premolars should be aimed at uprighting the root apices of these teeth distally, away from the canine crowns.

5. Check the degree of uprighting achieved, using periapical radiography of the premolars and re-set the premolar bracket to increase the distal uprighting to a temporarily excessive degree. This will move the roots into close proximity to the second premolars roots.

6. Consolidate the maxillary dentition as a composite anchor unit by placing a heavy passive round or rectangular stainless steel archwire.

7. Expose the two canines from the labial side, using a closed eruption procedure from a surgical flap raised in the attached gingiva of the crest of the ridge around the necks of the deciduous canines and right lateral incisor, which should be extracted at the same visit.

8. An eyelet attachment should be bonded to the canines and the flaps fully sutured back to their former place, drawing a twisted soft stainless steel ligature or gold chain from the eyelet downward to emerge through the re-sutured edge of the flap.

9. Extrusive forces should be applied to the ligature or chain until the two canines erupt into the dental arch, directly through the attached gingiva.

In the meantime, a mandibular fixed appliance should be placed after the deciduous second molars have shed or are extracted and the teeth may then be suitably aligned. Additional space may need to be provided in the upper jaw to accommodate an implant to replace the missing lateral incisors and this can probably best be achieved with slight proclination of the incisors and with width enhancement in the narrow form of the arch. Alternatively, the excessive space may be fully closed up by moving the canines, premolars and molars mesially into interproximal contact with the central incisors and with each other. The decision on whether to go for space opening or space closure should only be made after the canine impaction has been fully resolved and the teeth erupted.

There is another factor that may be considered here. Rather than extracting the deciduous canines, it may appear to be a good plan to move them mesially into contact with the incisors or distally into contact with the premolars. These teeth have excellent and long roots and it would seem a shame to extract them if they can be used to replace and simulate the missing incisors. The aim would be to then bring the canines down into the prepared space, which would require some prosthodontic additions and/or reshaping but, potentially, a more natural solution. Unfortunately, moving the deciduous canines may exact a heavy price, since it may serve as a trigger that initiates and/or exacerbates a rapid resorption of the roots of these deciduous teeth following the application of what would normally considered routine orthodontic forces. This would leave the patient with a short-term result only and the need for prosthodontic rehabilitation at an early date.

References:

1. Becker A, Karnei-R'em RM. The effects of infraocclusion: part 2 - the type of movement of the adjacent teeth and their vertical development. American Journal of Orthodontics 102:302-309,1992.

2. Chaushu S, Chaushu G, Becker A. The role of digital volume tomography in the imaging of impacted teeth. World Journal of Orthodontics, 2004; 5:120-132

3. Becker A, Chaushu S, Casap-Caspi N. CBCT and the Orthosurgical Management of Impacted Teeth. Journal of the American Dental Association 2010;141(10 suppl):14S-18S