NEWSLETTERS

A fatal mistake with a transposed canine

Published: March 2017

Bulletin #64 March 2017.

A fatal mistake with a transposed canine

One occasionally comes across an impacted maxillary canine which has become partially or completely transposed with the lateral incisor and, from the literature,1, 2 we read that its prevalence is between 0.1-0.4%. While the presentation is mainly unilateral, the canine of the opposite side may also be impacted but usually in a more favourable location and more amenable to treatment. The likelihood of identical bilateral transposition appears to be very low.

Typically, this type of transposition is seen and diagnosed in a routine 2D panoramic film. The canine crown is most frequently mesial to the crown of the lateral incisor, although its long root is often oriented at an angle to the vertical and crosses over the root of the incisor, with its apex distal to that of the incisor. Because of its angle to the vertical, further eruptive movement is expressed in the mesial direction and, in its more severe form, the canine crown may then come to lie on the lingual side of the central incisor. Thus, the canine ends up with the orientation of its long axis mesio-distally inclined, descending apico-coronally but with a strong horizontal component, having crossed the line of the arch from the labial side of the lateral incisor root. Since it is a space-occupying body in a bucco-lingually narrow alveolus, it secondarily displaces the lateral incisor root lingually and the central incisor root labially, to create a very wide distance between their root apices. The roots of these teeth can often be palpated as they bulge the labial or palatal bony plate. This is reflected in the angulation of the crowns of these teeth but, more importantly, it creates a wide angle between the long axes of their displaced roots, when seen in cross-sectional CT cuts. The crown of the canine is firmly locked within this V-shaped root configuration and its root proceeds distally on the labial side of the lateral incisor!

Should the surgical exposure and orthodontic traction be from the labial or lingual sides?

Once the orthodontist can build a mental picture of this complex scenario in the 3 planes of space, he/she will realize that this impasse has only one conservative solution. The canine needs to be exposed on the labial side of the alveolar ridge and drawn labially, as high as possible, between the widely apically-diverging roots of the two incisors. A case of this type is presented in the 3D video clip on the Home Page of this website and its treatment is described in Bulletin #16 November 2012, entitled: The palatally-impacted labial canine.

Orthodontists and surgeons still remain loyal to the time-honored, but somewhat primitive, tube shift method of bucco-lingual positional diagnosis of the crown of the canine vis-à-vis the incisor roots, using two periapical views taken at different angles. In the present situation, this radiographic tool will only correctly define the canine crown as being located lingual to the root of the central incisor. However, the complex inter-relations between canines and incisors, in the context of this type of transposition, demands more sophisticated diagnostic modalities, i.e. cone beam computerized tomography (CBCT). Attempting to draw the tooth lingually will cause the canine root to generate further lingual root torque of the lateral incisor, with the likelihood of lingual dehiscence of its root. At the same time, such a plan will only be successful if the canine were to be subjected to an exaggerated degree of apical root movement which will exact a huge price by compromising the prognosis of the treated outcome.3

Case report

64_Fig._1a

Fig. 1a. Plaster casts of the teeth in occlusion.

64_Fig._1b

Fig. 1b. Occlusal views of the two dental arches.

64_Fig._2


Fig. 2. Lateral cephalogram and panoramic view taken in February 2008. These films show the mesially-displaced and palatally-impacted left canine (arrow) reaching the mid-palatal suture. It is in a transposed relation with the lateral incisor, the root of which appears distally displaced.

The records of the case discussed this month were sent to me for an opinion in January 2009. The orthodontist was a young colleague working somewhere in Europe who had already begun treatment to open anterior space with an extra-oral headgear inserted into molar tubes. The plaster casts (Fig. 1a-c) and radiographs (Fig. 2) of her 12 years old female patient had been taken a year earlier, in February of 2008.

They showed a severe class II division 2Fig_3 malocclusion with strongly retroclined maxillary central incisors and marginally less retroclined mandibular incisors, that had resulted in a 90% overbite. The left maxillary lateral incisor was proclined into a 300 angulation to the horizontal. The panoramic view showed transposition of the unerupted left maxillary canine and lateral incisor, with the crown of the canine reaching the midline suture. On the anterior portion of the lateral cephalogram, the very vertical orientation and over-eruption of the central incisors was clearly seen, as was the degree of lingual root tip of the lateral incisor. The canine crown was lodged between the two, as an apparently obvious factor in the severity of buccolingual displacement of these two incisors, in opposite directions (Fig. 3).

64_Fig._3

Fig. 3. Close-up of the anterior maxilla to show the orientation of the central incisor (yellow broken line), the lateral incisor (green broken line) and the canine (red broken line) in the antero-posterior plane.

The advice given to the orthodontist, in February 2009, was to perform cone beam CT imaging. It was explained that it would confirm the location and orientation of the three involved teeth and whether a complete resolution of the impaction was possible, or if it would be necessary to compromise by aligning the teeth in their transposed order. It would further reveal whether there was resorption of the roots of these teeth that may dictate extraction rather than alignment. It was pointed out that the only way to resolve the transposition to the ideal order, without extraction, was to expose the canine on the labial side and to draw the tooth labially and distally, between the roots of the central and lateral incisors, as emphasized above.

64_Fig._4

Fig. 4. Intra-oral views showing the initial condition when an extra-oral headgear was first prescribed, in March 2008.

I did not hear from the orthodontist for several years thereafter so, when my curiosity overcame me in September 2015, I wrote to her again to find out how the case had panned out. In very recent e-mail correspondence, I learned that space had eventually been provided with the extraoral, distal-driving, headgear forces (Fig. 4), although it spread over several long years, due to limited patient compliance. The parents had steadfastly refused the recommended extraction of teeth. The orthodontist’s reply saddened me on several counts.

So, what happens if the exposure and traction are made from the lingual side?

The patient had been referred to an oral and maxillofacial surgeon with the request to expose the canine and place an attachment on it. The surgeon had clearly studied the radiographs and erroneously decided that, since the crown of the canine was lingual to the central incisor, the tooth needed to be approached from the lingual side. This meant that orthodontic traction could now only be applied from that side!

64_Fig._5

Figs. 5a, b. Clinical and radiographic occlusal views of the patient following active orthodontic traction of the canine into the palatal area in July 2008. The root of the lateral incisor and the palatal root of the first premolar lie in the path preventing the canine from being moved buccally into the line of the arch.

The orthodontist had then proceeded to extrude the canine downward and posteriorly, erupting it into the palate (Fig. 5a, b). It was only in March 2011 that the parents overcame their resistance to permitting the orthodontist to prescribe the much needed CBCT examination (Fig. 6). Thus it became obvious that the root of the lateral incisor required to be labially torqued, in order to remove the root impediment from the path of the canine.

64_Fig._6

Figs. 6a-d. CBCT 3-dimensional views of the left side of the maxilla from the palatal side, the front, the buccal side and the occlusal, respectively, imaged in March 2011. The entanglement of the newly erupted left canine can be clearly seen (yellow arrows). The interfering root end of the almost horizontal lateral incisor is indicated by the small green arrows. The green asterisks identify the mandibular anterior teeth in their deep overbite relation.

All the other teeth in the maxillary dental arch were brought into their ideal locations, leveled and aligned, until it was possible to place a heavy main archwire ligated into their brackets. This created the compound anchor unit from which to apply traction to the canine. The canine was then tipped towards the labial archwire (Fig. 7a, b) until it, too, could be ligated in the main arch and then individual rotation and torqueing spring auxiliaries were used over an extended period to achieve the appropriate torque values needed (Fig. 7c,d).

64_Fig._7a

Fig. 7a. was photographed in February 2015, Fig. 7b in August 2015, Fig. 7c in December 2015 and Fig. 7d in November 2016.Following labial root torque of the lateral incisor, the canine was tipped towards its place in the arch, causing gingival recession and exposure of lingual root surface of the canine (arrow), which remained even after very considerable buccal root torque had been performed. A marked periodontal defect remains at the end of treatment.

The maxillary dentition was debonded in November 2016 (Fig. 8), having been in treatment continuously since 2008. The orthodontist pointed out that she had been “ ……. forced to finish because of massive bone resorption on teeth 22 and 23. I am very frustrated because I managed to bring the canine in a relative good position but didn't see the resorption coming at that extent. It is less than a year that I am dealing only with the torque of the tooth. As I could see the root palatally I expected some bone buccally. The CBCT shows a very thin buccal plate in the upper jaw in general.”

64_Fig._8

Fig. 8. Following removal of the maxillary appliance, the achieved alignment is excellent, with surprisingly mild gingival recession and increased crown height of the canine.

At the completion of the treatment, she reported that the canine and lateral incisor were mobile and are bereft of a long term prognosis. So, the resolution of this difficult impaction and the alignment of the teeth can be registered as a remarkable surgical and orthodontic success, but an outright failure of significant consequence from the periodontal point of view - the dental equivalent of the medical saying “....the treatment succeeded, but the patient died!” (Fig. 9).

64_Fig._9a 64_Fig

Fig. 9a. Adjacent cross-sectional CBCT cuts through the canine show the tooth to be almost completely lacking of alveolar bone support, immediately prior to debonding the appliance.

Fig. 9b. The cone beam 3D view of the lateral incisor and canine, to show the extreme loss of supporting alveolar bone.

In fact, the orthodontist is now chastising herself harshly, although the picture may not be quite as black as she has painted. In the first place, we know that during tooth movement there is a widening of the socket due to resorption and the new bone that is apposed is sparsely calcified initially, which results in a significant degree of mobility. Furthermore, the uncalcified bone is not visible on radiographs in general and, because of the contrasting effect of CBCT imaging, the degree of apparent bone loss may often be very much exaggerated. It is only in the months following cessation of orthodontic movement that reparative calcification and maturation will mitigate these alarming clinical and radiographic features.

Could this outcome have been avoided?

A fatal mistake was introduced into the treatment of this case, because the surgeon had not been apprised of the direction that traction needed to be applied. Direct communication between orthodontist and surgeon was not established, resulting in each specialist being ignorant of the requirements of the other! The treatment provided was multidisciplinary rather than inter-disciplinary.

It must be accepted that a labial approach to this impacted canine would have offered a far shorter treatment duration and a far better prognosis. This is because the root apex of the canine was close to its desired location, at the start. Therefore the biomechanics needed to resolve the impaction largely entailed tipping movements. In the treatment of the present case, while noting the enormous amount of crown tip that had been performed, it is essential to appreciate that the root apex of the canine had travelled an even greater distance. This apex had been drawn from its initial location on the labial side of the arch mesially and lingually around the mesial side of the lateral incisor, to the middle of the palate, during which time it had further displaced the lateral incisor root lingually. During the period of time that the tooth was on the palatal side, it was tipped towards the labial archwire (no doubt accompanied by a degree of reversed apical movement), and then torqued labially to a point immediately opposite its original location in the line of the arch. A truly remarkable distance by any standards but one which exacted a fateful price.

The orthodontist had not been present at the surgical exposure. In her e-mailed reply to me, she wrote "…….. I send all my impacted cases to a very experienced maxillofacial surgeon and I let him decide (my emphasis) each time where is he going to expose the tooth." She then added" sincethen I control this also myself." I am very careful now with my cases and I always have the chance to go during the operation and place the button etc.

My reply to her was ‘…….. It is a very serious mistake to have the surgeon decide, regardless of how senior and experienced he/she is. No surgeon can put himself/herself into the place of the orthodontist, to know which way we want to move the tooth. These cases are 100% orthodontic cases requiring orthodontic decisions. The surgeon's only task is to provide the orthodontist with access to a tooth that he/she cannot otherwise control. Unfortunately, it is often very difficult for a surgeon to recognize this fact and to accept playing a subordinate role – the second fiddle. In the end, it is the orthodontist who is responsible for the result - not the surgeon. 

In my early days as an orthodontist I had the same problem as you did. For many years now I have instructed the surgeon to do what I want and I am always present at the exposure to make sure he does what I want. I bond the attachment, I place the de-impaction auxiliary, tie the elastic thread, decide the direction and the many other important things that will make my life easier post-surgery. There were 2 or 3 very senior surgeons who would not accept this and I simply stopped working with them. I took a couple of the younger guys, explained what I needed and I trained them into doing things my way. In Israel today, many of the younger surgeons will not undertake the exposure if the orthodontist is not present.’

In a subsequent e-mail, I noted "……On the one hand, I am amazed at your obvious orthodontic skill and ability in being able to move this canine and its adjacent lateral incisor in the way that you have and to achieve the beautiful orthodontic result. On the other hand, the exaggerated movements of crown and, in particular, roots have taken their inevitable toll on the periodontal prognosis of the result. One only has to imagine where the root apex of the canine started and where it is now, to realize how far it has been moved... there is a limit to the amount of crown and root movement that a tooth can tolerate and you have exceeded this limit.’"

Postscript

For obvious reasons, the orthodontist concerned must remain anonymous. However, this does not detract from my thanks to her for having agreed to share with me the lessons that may be drawn from the case and for her having so freely and generously granted permission for it to be published on this website.

I strongly recommend an article that I recently authored together with Prof. Stella Chaushu, entitled: “Surgical treatment of impacted canines: what the orthodontist would like the surgeon to know.” The article specifically defines the role of the oral and maxillofacial surgeon in the surgical exposure of impacted teeth and offers a rationale and modus operandi for its implementation. It is highly relevant to the discussion in this bulletin.4

References

1. Yilmaz HH, Türkkahraman HH, Sayin MÖ. Prevalence of tooth transpositions and associated dental anomalies in a Turkish population. Dento-Maxillo-Facial Radiology 2005;34:32-35.

2. Papadopoulos MA, Chatzoudi M, Eleftherios M, Kaklamanos G.Prevalence of Tooth Transpositio:n A Meta-Analysis. Angle Orthodontist 2010;80:275–285.

3. Kohavi D, Becker A, Zilberman Y. Surgical exposure, orthodontic movement and final tooth position as factors in periodontal breakdown of treated palatally impacted canines. American Journal of Orthodontics 1984;85:72-77.

4. Becker A, Chaushu S. Surgical treatment of impacted canines: what the orthodontist would like the surgeon to know. Editor Michael Kleiman, in: Oral and Maxillofacial Surgery Clinics of North America. New York: Elsevier Inc. 2015;27:449-458.