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A locked out canine: implications for treatment planning

Published: September 2017

Bulletin #69 September 2017

A locked out canine: implications for treatment planning

Have you wondered why it is that the immediate close relatives of many of our dental colleagues show a high incidence of some of the more bizarre dental anomalies, rarely seen among members of a random general population? In this month’s bulletin I describe the skeletal and dental features that make up the malocclusion of a girl aged 13.6 years, who happens to be (wouldn’t you know it?) the niece of one of Israel’s senior oral and maxillofacial surgeons. We call this phenomenon “personnelitis”.69.Fig._1

Fig. 1. The patient at age 13.6 years in profile and en face.

The patient exhibited a mild skeletal II profile due to a degree of mandibular retrognathism, relative to a lesser retrognathism of the maxilla (Fig. 1). There was marked lip incompetence, with the lips fairly wide apart at rest, due largely to a short upper lip. The maxillary gingivae were visible at rest with an accompanying minor chronic inflammation of the labial gingivae. The permanent dentition was erupted to the second molars in both jaws, with the exception of an over-retained deciduous maxillary left canine.

69.Fig._2a

Fig. 2a. Intraoral photographs of the teeth in occlusion. The over-retained deciduous canine is seen on the left side of the maxilla.

69.Fig._2b

Fig. 2b. the occlusal views of the two jaws.

The molar relation was slightly in excess of a half cusp class II. The incisor overjet was 5mms and the overbite 4mms, with contact high on the cingulum of the maxillary incisors. The lower anterior canine-canine segment was over-erupted by about 2mms above the molar/premolar occlusal plane, while the maxillary incisors were similarly elongated, due to the A-P discrepancy and the poor lip control. The mandibular dental arch was generally in excellent mesiodistal alignment, with 2 very slightly slipped contacts at the left central incisor. The maxillary dentition was similarly well ordered, with tiny space interproximally on each side of the over-retained deciduous left canine (Fig. 2a, b).

69.Fig._3

Fig. 3a. The panoramic radiograph illustrates the full complement of teeth, including unerupted third molars. The maxillary left canine is impacted high in the maxilla, surrounded by an enlarged dental follicle, the root of the left deciduous canine is only partially resorbed. A root of the first left maxillary premolar appears shortened and curved to the mesial.

Fig. 3b, c. periapical views of the canine area taken for diagnosis with Clark’s tube shift method, indicates labial displacement of the canine in relation to the lateral incisor. The curved root of the premolar appears shortened.

The panoramic and periapical radiographs (Fig. 3a-c) showed that all the permanent teeth were present, with the crowns of the unerupted third molars at about the completion of calcification and no root development yet. The maxillary left deciduous canine still had most of its root intact and the permanent canine unerupted and located high in apparent contact with the mildly shortened root apex of the adjacent lateral incisor. The permanent canine was encompassed by an enlarged follicle/dentigerous cyst. Additionally, a root of the adjacent first premolar showed a small mesial curvature in its long axis. For the sake of completeness, the cephalometric analysis of the patient is presented here and it confirms the clinical impressions described above, although its further discussion is largely irrelevant to the spirit of this bulletin.

Essentially, the case may be presented as a mild dental class II on a skeletal class II base with little to no crowding in either jaw and a vertical excess of the anterior segments of both arches. The lip cover was poor. All this was complicated by the presence of an impacted maxillary left canine.

If we were to ignore the impacted tooth, the remaining malocclusion would need to be treated by normalizing the antero-posterior relationship between the two dental arches in one of the following ways:-

1. With a non-extraction approach, to correct the class II dental relationship with an en bloc movement of the teeth in one jaw vis-à-vis or versus the teeth in the other, taking care to level the occlusal plane before or during this process. This could be achieved using one of a number of methods including the so-called functional appliances, such as twin blocks, bionators, Fraenkels etc. It could probably be equally well served with the use of fixed multibracketed appliances with the addition of extra-oral and/or intermaxillary traction – fixed (Carriere, Herbst, Forsus etc) or removable (class II elastics and headgears).

2. Extracting a tooth on either side of the maxillary arch, usually a premolar and normalizing the incisor relation by retracting the anterior teeth into the space, while calculating to “burn” intra-arch anchorage by drawing the molars mesially and into a class II dental relation.

3. There is probably a minority of practitioners who would consider parallel extractions in the mandibular dentition to achieve both a normal incisor relation and a normal molar occlusion.

However, there is a problem with the impacted canine!

The following is a list of concerns that an orthodontist might have in relation to the canine:-

1. The canine is surrounded by an enlarged follicle/dentigerous cyst, which must be considered as a possible contributory cause of the lack of eruptive progress of the canine. Is this a reason to prefer an extraction protocol that includes the canine, in preference to a premolar?

2. The tip of the canine crown is in close proximity to the apex of the lateral incisor, which has a shorter root than its antimere. Could this be due to root resorption related to the futile eruptive efforts of the canine? Will resorption continue after aligning the canine, thereby to undermine the longevity of the incisor? Is this a reason to prefer an extraction protocol to include the canine, rather than a premolar?

3. The canine is located high in the maxillary alveolus, far from its place in the arch and, perhaps, the orthodontic treatment would be unnecessarily long or its prognosis poor. Is this a reason to prefer an extraction protocol to include the canine, rather than a premolar?

4. The first premolar has a strange dilaceration of one of its roots which also appears shorter on the panoramic film. For preference, perhaps, that should be extracted rather than the canine.

Extracting the permanent canine itself because there is the suspicion of its having caused a minor degree of resorption of the lateral incisor root, or because it is involved with pathology (the dentigerous cyst), is a harsh and unfounded operative decision. In earlier studies, our clinical research group in Jerusalem has provided strong evidence that root resorption which is associated with an unerupted canine will arrest when the canine is distanced from the area.1, 2 Similarly, teeth impacted within dentigerous cysts have been shown to be eminently orthodontically/surgically salvageable with an excellent post-treatment prognosis.3

Perhaps, too, the root curvature and the root’s length of the premolar tooth may have been a determining etiologic factor in the canine impaction and its continued presence may effectively obstruct its resolution.

Accurate positional diagnosis

It becomes clear that the initial radiographic examination, which included 2 periapical views, a panoramic view and a cephalogram, is far from adequate for our present purposes because we lack information regarding the existence, extent and location of the assumed incisor root resorption. We also need to know the length and proximity of the dilacerate root of the premolar to the canine and whether it is on the buccal or lingual side. This information has a bearing on operative decisions that are about to be made.

69.Fig._4

Fig. 4. An axial cut from the CBCT reconstruction shows the canine crown surrounded by the enlarged follicle and locked between the roots of the lateral incisor and first premolar. The premolar clearly has a much elongated root, not obvious from the planar radiographs.

69.Fig._5

Fig. 5a. A coronal slice shows the restricting influence of the roots of the incisor and premolar on the canine crown, in the bucco-lingual view.

Fig. 5b. A cross-sectional slice shows the mesial extention of the elongated root of the premolar labial to the canine crown.

Fig. 5c. A more anterior cross-sectional view slice the canine crown in direct contact with the lateral incisor root.

Accordingly, a CBCT was ordered and the relevant sections of the secondary constructions are presented herewith (Fig. 4, 5).

From these comprehensive views, particularly the 3D video clips (see URL’s https://vimeo.com/231505687 and https://vimeo.com/231505198), which have been expertly animated by the CBCT technician, it can be seen that the palatal root apex is curled around and in contact with the labial side of the premolar, while the palatal root is on the palatal side. The mesial surface of the canine is in contact with the disto-labial surface of the apical portion of the incisor root, where it has resulted in some resorption of the canine root apex. The canine is thus trapped on all sides and unable to be moved in any direction.

Treatment Options

1. Non-extraction treatment to normalize the dental arch relations, while ignoring the impaction, will likely result in further resorption of the lateral incisor. The final dental alignment would have to include the continued presence of the deciduous canine, with no possibility of its later replacement with an implant, without extraction of both permanent canine and the premolar.

2. “Prophylactic extraction” of the deciduous canine will not resolve the impaction.

3. Extracting the canine will be extremely difficult and will undoubtedly result in loss of vitality for the premolar and, probably, also for the lateral incisor and the deciduous canine.

The treatment plan adopted for the left side involved the extraction of both the deciduous canine and the first premolar, with its convoluted root pattern. On the right side, the first premolar was tagged for extraction. No mandibular extractions were ordered.

69.Fig._6

Fig. 6a-c. The reflected flap surgical flap, the exposure of a minimal surface of the canine crown with extraction of the deciduous canine and first premolar and the bonded eyelet attachment with twisted stainless steel 0.012” ligature, respectively.

With this in mind and prior to the extractions being performed, orthodontic brackets were placed on all the maxillary teeth, from second premolar to second premolar, including the first premolars and the deciduous canine which were scheduled for extraction. This was done to provide retention and stability to enable the use of fine NiTi archwires in the initial stages of the treatment, by avoiding long spans of unsupported wire. Once leveling and alignment had been achieved, the patient was brought to the oral and maxillofacial surgeon (the aunt of the child) and the teeth were extracted (Fig. 6a, b) as directed although there was considerable difficulty in freeing the canine of the premolar roots. At the same time, the canine was exposed and the orthodontist bonded an eyelet attachment with a light cure composite (Fig. 6c), while the surgeon maintained the area free from blood and saliva which would otherwise cause the eyelet to detach.

69.Fig._7

Fig. 7a. The lower archwire is an 0.020” stainless steel base arch and the upper is an auxiliary 0.016” stainless steel wire with a horizontal loop formed in the canine area, terminating in a small helix.

Fig. 7b. An occlusal view of the archwires in place, following replaced and sutured surgical flap . The horizontal loop of the auxiliary archwire is in its passive state. The twisted ligature emanating from the eyelet can be seen lying freely behind the horizontal loop.

Fig. 7c. A view from the left side toshow the horizontal loop having been raised and ensnared by the twisted ligature into a vertical, active state. There is now easily measurable and light traction applying a labially-directed force to the canine.

At the same surgical visit, the orthodontist replaced the main 0.020” base arch, together with a full arch, piggy-back auxiliary archwire carrying the active horizontal loop for drawing the impacted canine (Fig. 7a), in an initial labial and distal direction (Fig. 7b, c).

Orthodontic treatment was only commenced a few months ago and the surgery undertaken only just 6 weeks ago, in July of this year. This unfinished case is presented here only to demonstrate how planar radiography of many cases with impacted teeth may not be adequate to the task of permitting the execution of successful treatment and how the advent of CBCT imaging may be of great value in appropriate cases. The remainder of the treatment is expected to be quite routine, once the canine has been drawn into its place.

References:

1. Chaushu S, Kaczor-Urbanowicz K, Zadurska M, Becker A. Predisposing factors for severe incisor root resorption associated with impacted maxillary canines. American Journal of Orthodontics and Dentofacial Orthopedics, 2015;147:52-60

2. Becker A, Chaushu S. Long-term follow-up of severely resorbed maxillary incisors following resolution of etiologically-associated canine impaction. American Journal of Orthodontics and Dentofacial Orthopedics 2005, 127: 650-654

3. Becker A, Chaushu S. Healthy periodontium with bone and soft tissue regeneration following orthodontic-surgical retrieval of teeth impacted within cysts. A chapter in: Biological Mechanisms of Tooth Movement and Craniofacial Adaptation, edited by Z. Davidovitch and J. Mah. Boston, Mass: Harvard Society for the Advancement of Orthodontics, 2004; pages 155-162.