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The palatally-impacted labial canine

Published: November 2012

Bulletin #16 November 2012

The palatally-impacted labial canine

In last month’s bulletin (Bulletin #15 October 2012) on this website, a case was presented in which the unerupted maxillary left canine had migrated mesially on the labial side of the root of the lateral incisor, to end up on the palatal side of the root of the central incisor, close to the mid-palatal suture. Because the plane film records had been misread, the surgical exposure of the tooth was made from the palatal side and orthodontic traction was applied from the palatal. The misdiagnosis and the treatment provided complicated the situation of the canine still further and the tooth was eventually extracted.

….. but how could that disappointing outcome have been avoided and was there a way in which the tooth could have been brought into its place in the arch?

A case with a similarly located canine impaction is presented here, in which the tooth was salvaged by adopting a more appropriate biomechanical strategy. The tooth was brought into alignment in a reasonable time frame, with an excellent periodontal prognosis. The tooth was difficult to recognize as having previously been impacted, with few tell-tale gingival signs, periodontal recessions and irregularities, although there was an increased crown height in comparison to its antimere. To all intents and purposes, the tooth was indistinguishable from any other normally-erupted tooth, even to the professional eye.

Two similar case reports have been published by the author, elsewhere.1 These cases are certainly unusual, but they are not rare. With my special interest in impacted teeth, it stands to reason that I am likely to have a much larger collection of cases of this type than most of my colleagues will see in a lifetime. I have records of 28 cases of palato-labial impacted maxillary canines. Many of these cases were referred to me prior to treatment or in various stages of uncompleted or failing treatment, while others were sent to me from abroad for advice on diagnosis and treatment planning, through the Clinical Consultation resource on this website.

The video clip on the Home page of this site, shows the CBCT of the present case. In the most graphic and convincing manner, this imaging modality has revealed two very obvious and serious anomalies of tooth position, each of which constitutes a major disturbance of the occlusion and a potential nightmare for the orthodontist:

  1. The unerupted left maxillary canine appears to be in an intractable location, straddling the alveolar ridge with an oblique bucco-lingual orientation. The root is labial and the crown palatal. The deciduous canine is in place and has a full length root. The root of the lateral incisor is displaced distally and palatally, to accommodate the physical presence of the impacted canine.
  2. The unerupted second premolar in the same quadrant of the mouth is very severely displaced, lying palatally impacted to the line of the arch, with a strong distal tip and a 90 degree rotation. Its apex is in close relation to the apex of the impacted canine. The reason for the impaction of the second premolar appears to be the total subgingival infraocclusion of the completely resorbed dentine substance of the second deciduous molar, leaving only the enamel shell of its crown.

But let’s see how this case was first seen and evaluated before the CBCT was considered necessary and how the spectacular imaging of this modality contributed to the success of the treatment.

Clinical Examination

_16._Fig._1

Fig. 1. Clinical intra-oral views of the patient’s dentition prior to treatment.

The patient was a young male aged 13.5 years, with good facial proportions and a pleasing but mildly class 2 profile. At the initial clinical examination in March 2009, it was noted that the occlusal relations of the molars on the right side were normal for this late mixed dentition stage of dental development. The overbite and overjet were moderately increased, the maxillary central incisors vertical and the lateral incisors proclined, typical of a class 2 division 2 arrangement and there was a minor degree of intercanine crowding of the teeth in the mandibular dentition. The principal clinically-visible anomaly was on the left side of the maxilla, characterized by the extreme mesial tipping of the first molar into a full class 2 relation, interproximally contacting the distally tipped and 45 degree mesio-buccally rotated first premolar (Fig 1).

Radiographic Examination
The patient had been seen elsewhere, monitored over a period of 6 years and had arrived for the initial consultation at the author’s private office, already in possession of several radiographs. These included a recent panoramic film and cephalogram taken 5 and 2 months earlier, respectively.

_16._Fig._2._Iniitial_pan_Nov

Fig. 2. The pre-treatment panoramic view shows the very late mixed dentition, with deciduous maxillary canines and right second molar retained and the resorbed empty enamel shell of the buried left second molar blocking the path of eruption of the severely displaced second premolar. The right permanent canine is in appears to be in a reasonable place for its normal eruption. The left canine is partially transposed with both the lateral incisor and the unerupted second premolar. The relative enlargement of the crown of the left canine suggests that it is palatally displaced in relation to the central incisor.2, 3

The panoramic view of the patient, taken in November 2008, showed the late mixed dentition stage, with maxillary deciduous canines and left second molar still present. All permanent teeth were present in various stages of development, approximating to a dental age of 11 years. Second and third molars were unerupted. The right maxillary unerupted canine and second premolar were in fairly normal positions. The left maxillary canine and lateral incisor overlapped and showed a degree of transposition, as did the first and second premolars of the left side. The over-retained enamel shell of the left second deciduous molar was impacted deep in the tissues between the molar and premolar teeth (Fig. 2).

_16._Fig._3

Fig. 3a. The anterior section of the lateral cephalogram shows both unerupted canines depicted against the background of the superimposed anterior teeth.

Fig. 3b. The same view as in Fig 3a, with the long axes of the central incisors (yellow line), lateral incisors (blue line) and canines (orange line) drawn in. The left canine is also mesially displaced and mesial to the root of the lateral incisor (see fig. 2). It is therefore palatal to the central and labial to the lateral incisors. It will be noted that the divergence of the apical extensions of the yellow and blue lines creates a wide space in the antero-posterior plane, in which the canines are situated. We call this the “window of opportunity”, since it represents the only possible path through which the canine may be successfully drawn, following a surgical approach from the labial side.

As with the case described in October’s bulletin on this website and using plane films only, the key to the bucco-lingual location of the canine in relation to the adjacent incisors lay with the cephalogram (Fig. 3a). Despite the superimposition of all the anterior teeth upon one another in this view, the orientation of these three teeth could be demarcated, when the film was examined with care. Together with the partial transposition of canine and lateral incisor seen on the panoramic view, it was determined that the canine was labial to the root of the lateral incisor and lingual to the central incisor (Fig. 3b).

_16._Fig._4

Fig. 4a, b. 3-D screen shots of the CBCT images. Please study the video clip on the Welcome page of this website to understand why a palatal approach to the surgery would be disastrous.*

Fig. 4c. An axial (horizontal) cut of the CBCT image to show the location of the canine between central and lateral incisors.*

This was subsequently confirmed very graphically in the 3-D views when a CBCT was commissioned, a fact which assisted enormously in the orthodontic planning of the directional traction and in the approach to the surgical exposure (Fig. 4a, b). The axial 2-D slices showed the labio-lingual relationship between the canine and the two adjacent incisors (Fig. 4c).

Treatment Planning

If it had been possible to ignore the dental configuration of the teeth in the left side of the maxilla and taking the overall features of the malocclusion into consideration, the case clearly called for a “non-extraction” approach to treatment.

Impacted premolar: If we consider the left side of the maxilla in isolation, 4 treatment options appear to be relevant, each of which includes the extraction of the infraoccluded deciduous second molar. In addition,extraction would be required of:-

  1. the impacted ectopic second premolar, with uprighting of first molar and first premolar
  2. the adjacent erupted first premolar, expecting spontaneous eruption or exposure of the second premolar and application of orthodontic traction to align it.
  3. the first permanent molar, expecting spontaneous eruption or exposure of the second premolar and application of orthodontic traction to align it.
  4. the second permanent molar, with tipping of the mesially tipped first molar distally and expecting spontaneous eruption or exposure of the second premolar and application of orthodontic traction to align it. It is expected that the third molar will erupt into the place of the extracted second molar.

The etiology and treatment of impaction of the second maxillary premolar in these special circumstances is not relevant to the aim of the present discussion and merits a report devoted to it alone. It will be the subject of a future bulletin and will include a description of the treatment provided in this case.

Impacted canine:- The present discussion refers solely to this displaced canine and how it was successfully resolved. The following treatment options are relevant:-

  1. Extract the permanent canine and build the patient’s dental future on the questionable longevity of the deciduous canine, particularly since it required to be moved out of its crossbite relation.
  2. Extract the deciduous canine, move the lateral incisor distally and align the canine in the lateral incisor transposed position.
  3. Expose the canine from the labial side and apply traction from high in the labial sulcus to take advantage of the divergence of the long axes of the two incisors. Then to take the tooth distally and into the place vacated by the deciduous canine.

Option #3 was chosen, since it was anticipated to produce a result with the least number of compromises and the closest to an ideal arrangement. No extractions were made in the right side of the maxilla, nor in the mandible.

The first part of the overall orthodontic treatment which was begun in June 2009, dealt solely with the premolar impaction anomaly in the left side of the maxilla, which involved the initial use of a simple removable plate appliance. This was followed in November 2009 by a fixed Tip-Edge** multibracketed appliance in the maxilla, which included a bracket on the left lateral incisor.

Why Tip Edge**, you ask? Well, it is true that this is my appliance of choice for my routine orthodontic cases but, in the present context, it has specific and important advantages. It should be clearly understood that the intention here was to exploit the widely divergent root orientation of the central and lateral incisors of the left side to provide the escape route for the crown of the canine to be moved high and labially between these two roots (Fig. 3b). It was, thus, essential that the root of the central incisor not be torqued lingually, nor the root of the lateral incisor mesially uprighted nor torqued labially, which is most often an essential part of the first leveling and alignment stage of the treatment. The canine had to be successfully drawn through the narrow conduit between the divergent roots of the central and lateral incisors and these movements would have closed down this “window of opportunity” for the canine. Despite full ligation into the lateral incisor bracket, uprighting and labial root torqueing movement were avoided, due to the exclusive use of round wires throughout the treatment and because of the special features of the Tip Edge bracket, with its wide and tip-angulated slot. Had any other form of horizontal channel bracket appliance been used, then the lateral incisor would remain unbracketed during this period and, of course, the use of rectangular archwires would need to be strenuously avoided.

_16._Fig._5

Fig. 5a. Given the small mesial overlap of the canine seen on the CBCT images, the auxiliary labial archwire was ligated into place with the horizontal loop sited between central and lateral incisor, immediately prior to the surgical exposure.

Fig. 5b. With the tooth exposed from the labial side, an eyelet attachment was bond to the mid labial aspect of the tooth. The tip of the canine remained unexposed and it was realized that the loop of the auxiliary labial archwire had been placed too far mesially.

Fig. 5c, d. The auxiliary archwire was moved more distally, to the distal of the lateral incisor before it was engaged in the twisted steel ligature such that, in its active position, it was flush with the re-sutured labial flap.

Once leveling had been achieved adequately, a heavy round 0.022” passive base arch was placed and, in piggy-back fashion, a 0.016” auxiliary steel archwire was prepared, which carried a horizontal long finger loop with a terminal helix in the lateral incisor/canine area, ready to be tied in at the time of surgery (Fig. 5).

In February 2010 at surgery, a labial approach to the canine was performed, with a full flap raised in the sulcus, from the gingival margin of the incisor teeth. Access to the canine was easy and entailed limited removal of the thin bone overlying the tooth. The exposed crown was very close to the root of the central incisor, on its distal and palatal aspects (Fig. 5b). Exposure was made of the distal and labial aspects of the canine, to provide a small area of crown surface which was large enough for the surgeon to maintain hemostasis while the orthodontist bonded a small eyelet attachment carrying a twisted soft stainless steel ligature to the acid etched surface of the tooth.

The twisted steel ligature was passed through the flap at the same height as the bonded eyelet attachment, so that it pierced the flap high in the sulcus after the flap was fully re-sutured. To have removed a part of the flap in an open surgical procedure would have left a large area of bone exposed, requiring a surgical pack to facilitate healing. This would additionally have exposed much of the root surface of the central incisor and threatened its vitality and its prognosis.

Once the flap had been sutured back into its original place, the horizontal loop of the auxiliary archwire, which had been tied in immediately prior to the surgery, was raised up until it was in close proximity to the replaced flap covering the alveolar process of the sulcus and ensnared in the twisted steel ligature (Fig. 5c, d). This effectively provided pure labial movement, with no downward vertical component that would have brought the canine on a collision course with the incisors. This was done in order to draw the canine between the roots of the two incisors at a height where their roots were the most divergent (Fig. 3b).

_16._Fig.6

Fig. 6a. The canine is now palpable immediately distal to the lateral incisor, although its twisted steel ligature has exited the tissue much further distally.

Fig. 6b. An apically repositioned flap has been raised incorporating attached gingiva from the crest of the ridge at its cut edge. The distally bonded eyelet attachment that was placed at the time of the initial exposure has been removed with its steel ligature.

Fig. 6c. A new eyelet was bonded in a vertical orientation in the mid-labial position and the tissues re-sutured further apically. Placement of a regular bracket would cause much gingival irritation in these sensitive circumstances. A fine 0.012” NiTi auxiliary wire has been threaded directly through the eyelet and into all the brackets of the upper arch, to produce a downward and distal component of force to erupt the tooth.

In the follow-up period, the patient was seen at 3-week intervals to re-approximate the loop to the sulcus mucosa, in line with the progress of the labial movement of the canine. When the canine became palpable labially above and mesial to the lateral incisor, a distal direction of traction drew the tooth around the lateral incisor root and towards the canine area, at which point the deciduous canine was extracted. The permanent canine was drawn further distally and occlusally, still subgingivally, until it became palpable low down on the distal side of the lateral incisor (Fig. 6a). The canine was then surgically re-exposed using an apically-repositioned procedure, in order to provide the tooth with labial attached gingival (Fig. 8b, c). At this visit, the original eyelet, placed at the time of the first surgical exposure, was detached and substituted by an eyelet in the mid-buccal position of the crown of the tooth in a vertical orientation, so that a fine NiTi auxiliary archwire could be threaded through it, and used to draw the canine into its place and to distance it from the root of the lateral incisor, which then could be uprighted with an auxiliary spring.

_16._Fig.7

Fig. 7a. Once the tooth has erupted sufficiently (10 days later), a regular bracket is substituted for the eyelet and an uprighting component of force augments the traction of the canine.

Fig. 7b. With full engagement of the heavy main arch in the canine bracket, a reciprocal torqueing spring was placed to labially torque the severely displaced lateral incisor root and to lingually torque the root of the canine.

When the patient returned 10 days post-operatively for removal of sutures, the canine had moved down sufficiently for a Tip Edge bracket to be placed and for the alignment of the canine to progress rapidly (Fig. 7a). With all the teeth in alignment, it was clear that the canine required considerable lingual root torque and the lateral incisor needed to be torqued labially. A simple reciprocal torqueing auxiliary was place under the 0.020” round main archwire, to complete the alignment (Fig. 7b).

_16._Fig._8._post_tx_pan

Fig. 8. The post-treatment panoramic view.

_16._Fig._9 _16._Fig._10

Fig. 9. Clinical intra-oral views of the patient’s dentition seen at the 1 year post-treatment evaluation, when the twistflex splints were placed.

Debonding was performed in October 2011, 28 months after commencement of treatment for the extreme abnormal configuration of the teeth in the left side of the maxilla, but just 18 months following the exposure of the impacted canine. The panoramic view (Fig. 9) was taken at debonding and the final photographs were recorded 12 months post treatment, in October 2012 (Fig. 10).

References:

  1. Becker A. The orthodontic treatment of impacted teeth. 3rd edition. Oxford: Wiley-Blackwell Publishers, 2012: Chapter 6 (Fig. 6.45) and Chapter 15 (Fig. 15.6)
  2. Chaushu S, Chaushu, G, Becker A..The use of panoramic radiographs to localize maxillary palatal canines. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endododontics 1999; 88:511-516.
  3. Chaushu S, Chaushu G, Becker A. Reliability of a method for the localization of displaced maxillary canines using a single panoramic radiograph. Clinical Orthodontics and Research 1999; 2:194-199

* Originally published in Becker A. The orthodontic treatment of impacted teeth. 3rd edition. Oxford: Wiley-Blackwell Publishers, 2012. Copyright by the author.

** Tip-Edge is a trademark of TP Orthodontics Inc. LaPorte, Indiana, USA. The author has no commercial interest in this product.