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Treatment planning an impacted canine with severe incisor root resorption

Published: January 2014

Bulletin #29 January 2014

Treatment planning an impacted canine with severe incisor root resorption

It should have come to your notice that I have made the treatment of impacted teeth a particular hobby of mine, which is why I encourage anyone (doctor or patient) seeking advice to contact me through the Clinical Consultation page on this website. In the preface to the first edition of my book which was published in 1998, I pointed out at the time that there were virtually no graduate/postgraduate orthodontic specialty programs that included tooth impaction in their curricula in any didactic or disciplined academic fashion. This situation has not changed in the 15 years since that time. The upshot is that there are few orthodontists out there in the big wide world who are proficient at treating them. In contrast with other areas of our profession, educators in this sphere are few. Following the lamented passing of Samir Bishara in October 2010, of Juri Kurol in October 2011, of Tiziano Baccetti in November 2011 and most recently, of Vince Kokich in July 2013, there remain even fewer of us who actually teach and research the broad subject of impacted teeth. If we add to that the fact that I live, teach and do my research in a dangerous neighborhood, it appears that I belong to an endangered species in a high risk branch of the orthodontic profession!

The orthodontic department of the Hebrew University-Hadassah School of Dental Medicine in Jerusalem is a notable exception to this educational vacuum and, as the direct result, a disproportionately large quantity of the clinical research that has been published in the peer-reviewed orthodontic literature on virtually every aspect related to impacted teeth, has emanated from Jerusalem.

Over the period of the last several years, I have had an ever-increasing flow of patients’ radiographic records sent to me, in which one or more impacted teeth figure prominently, requesting recommendations for treatment. Some of these referrals involve problems that might be fairly banal, while others are more difficult than may appear at first sight. There were those, too, which had become unnecessarily complicated during the treatment because of an erroneous initial radiographic assessment and this led to misdiagnosis of the position and orientation of the impacted tooth. From there it is but a short distance to surgical exposure in the wrong location or to inappropriate directional traction and abject failure.

There are points of consequence that are worth discussing in many of these cases, not just with the referring doctor or enquiring parent, but with my wider audience of respected colleagues-at-large, particularly those who have expressed an interest in this website and the issues debated in it. From time to time, therefore, I intend to present a case sent in by one of my contributors – always maintaining complete anonymity of the writer (except where expressly requested otherwise) and the patient ……. of course! Constructive comment or criticism of the views expressed or advice given are welcome and, where appropriate, may influence me to edit the specific bulletin accordingly.

The patient:

This month, we discuss the case of a 14 year old boy. He was examined by my correspondent who summarized the clinical features thus: class II division 1 malocclusion, involving a 6mm overjet and a reduced overbite on a skeletal class II base, due to mandibular retrognathia. The Frankfort mandibular plane angle (FMPA) was average, with moderate crowding in the mandibular dentition and severe crowding in the maxilla. The picture was complicated by the presence of a palatally impacted maxillary canine, associated with particularly severe root resorption of both permanent incisors on that side, which displayed very mild mobility.

In compromised clinical situations such as this, where the prognosis of individual teeth obfuscates judgments that are otherwise straightforward, the patient’s records tend to find their way to many experienced clinicians in an effort to find an optimal treatment plan, one which will provide an acceptable solution while minimizing the potential risks.

By inviting more “second opinions”, one will likely receive wildly diverse third and fourth treatment options, rather than confirmation of one favored approach. Furthermore, it must be remembered that teeth with shortened roots also have a fascination for practitioners of other branches of our profession. So, when endodontists, periodontists and implantologists are recruited to throw in their pennyworth, they may be seen to be gloomily crowing over the predicted imminent demise of a tooth by what appears to them to be progressive and unstoppable root resorption. Treatment decision-making then becomes an insurmountable undertaking!

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Fig. 1. The initial malocclusion. Note the canine is absent on the left side of the maxilla and its space is almost totally lost. Note also the slender incisor crown shapes and the marked maxillary midline deviation to the left.

My correspondent, a senior clinician, teacher and researcher, was not the person responsible for the treatment but was requested by a graduate student (trainee) in their institution’s orthodontic specialty program to offer an opinion regarding the best line of treatment for the patient.

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Fig. 2a-c. The initial plane film radiographic records which included (a) cephalogram, (b) partial panoramic view and (c) periapical film of the case, showing the severe horizontal root resorption of the two left incisors and the impacted canine with an enlarged follicle.

The clinical records comprised intra-oral clinical photographs (Fig. 1), a panoramic radiographic view and a lateral cephalogram (Fig. 2). There was also a single periapical view of the canine, taken with the x-ray cone directed towards the lateral incisor. Facial photographs were not offered, possibly to ensure patient anonymity. No other plane radiographic films nor CBCT were available.

When confronted with a patient and his/her initial radiographic records or, as in this case, the intra-oral clinical photographs and the radiographic records, it is logical to make an initial assessment of the immediate problem, i.e. the impacted tooth and the resorbed incisors, but to do so within the context of an overall assessment of the malocclusion, i.e. class II with crowding.

Pertinent questions then need to be asked. Are the existing radiographs of our 14 year old patient adequate for the present purposes? Is the problem clearly seen? Should we request a tube shift pair of periapical radiographs for bucco-lingual positional diagnosis? Is a cone beam CT essential? Should these be obtained before we make an initial tentative assessment from the intraoral clinical photographs and radiographs? Perhaps we should insist on all these aids being available and only then move straight on to a definitive and final treatment plan?

The patient may well have been taken by surprise by the sudden and worrying diagnosis and also has some basic questions, such as: “……. is treatment advised in order to promote my appearance because I am not interested in this?” or “…… what will happen if I do nothing and the canine remains impacted?” On the other hand he/she may be interested in exploiting the full potential of the appliances to achieve optimal treatment results in terms of health, appearance and long term prognosis. It is the duty of the practitioner to establish the objective level of treatment need and to advise the patient accordingly.

Overall Assessment

Looking at films of incisor root resorption associated with palatally displaced canines (PDC), one may be permitted to assume that a year or two earlier there was no resorption and that this has occurred because of the aggressive behavior of the canine in its attempts to erupt. Without any action on the part of the orthodontist, therefore, one may also be permitted to further assume that the resorption process will continue and that the prognosis of the incisor will become progressively worse. Ipso facto active intervention is crucial and urgent, if the resorption process is to be arrested. To achieve this, the canine must be distanced from its intimate relationship with the incisor roots and this may be achieved by orthodontic movement of the tooth away from the area, after surgical exposure and active orthodontic traction has been applied in an appropriate direction.1 A second alternative is to extract the canine, while a third option is to extract one or other of the severely resorption-afflicted incisors and the healthy canine drawn down into its place.

In the case at hand, there is a class II malocclusion which, although on a skeletal class II base, was not considered for jaw surgery but rather for a strictly dental compensation approach. This had already been decided by my correspondent, presumably on the basis of the facial appraisal and in subsequent discussion with the patient. The molar relation shows a full class II interdigitation on the right side and a marginally less class II occlusal relationship on the left. The overjet was 6mms and the proclined lower anterior teeth were crowded. Almost a full tooth width of space was lacking in the left side of the maxilla for the impacted canine and there appeared to be a Bolton discrepancy due to slender maxillary central and small maxillary lateral incisors (Fig. 1). In an identical dentition but unaffected by the root resorption, two maxillary premolars and a mandibular incisor may have been selected for extraction, in order to reach an acceptable result. However, the presence of this degree of root resorption of the incisors inserted new factors into the equation.

Radiographic assessment

The next question that needs to be discussed is in regard to the adequacy of the radiographic records. As noted above, these presently comprise a panoramic view, a lateral cephalogram and a single periapical film (Fig. 2). Should we request a second periapical film to be in a position to perform a tube-shift (parallax) bucco-lingual diagnosis of the canine location? Is it essential to perform a CBCT?

When there is severe horizontal resorption of the roots of the incisors, as appears to be the case with this patient, it is very likely that the canine is in the same bucco-lingual plane as the incisor roots. The view from the lateral cephalogram is highly instructive in these cases, yet few of us looks at this film as a means of contributing to canine positional diagnosis. The film shows the canine to be clearly on a collision course, deviating neither buccally nor lingually from the line of the arch, as depicted in this true lateral view. Referring back to the panoramic view, the canine can be seen to be approaching the midline and superimposed on the roots of both incisors on that side. The midline portion of the panoramic film is analogous to a standard p-a view of the canine, being imaged when the rotating cone is positioned at the back of the neck. Taking these two views together, localizes the canine in the line of the arch, obliquely bearing down on the roots of the incisors from a distal vantage point. This means that a labial surgical and orthodontic approach to the resolution of this impaction exists, as well as a palatal one. Both need to be taken into consideration in this decision, specifically regarding preservation of incisor vitality during surgery and, following that, orthodontic directional traction strategy, arrest of the resorption and addressing the periodontal outcome of the future aligned tooth.

From the existing plane film radiographs in the case presented here, therefore, it was determined that the crown tip was situated immediately over the resorbed apices with no bucco-lingual displacement, resulting in what appeared to be a strictly horizontal resorption. Because all the teeth are in the line of the arch, with no buccal or lingual displacement, their radiographic depiction was essentially two dimensional. Thus, the severity of the resorption was obvious and the information needed to determine a path for eruption of the canine appeared to be adequate, from these plane films alone. But this would be highly misleading. With the tip of the canine crown actually located in the open crater that was the resorbed end of the incisor root, a small vertically-prominent rim or spicule of unresorbed root may have been present on one side which would impede movement in that direction and would dictate the need for an alternative eruption path. This feature is unlikely to be seen in routine radiography and surgical exploration at the time of exposure is to be strongly discouraged, since it will inevitably devitalize the incisor roots.

Treatment options

Under the circumstances pertaining in this case, the choice of extraction of the maxillary first premolar of the opposite right side remained unchanged and was expected to permit closure of the overjet on that side and correction of the deviated dental midline.

On the left side of the maxilla, there are 4 possible extraction scenarios and each has its merits and its shortcomings:-

1. The first premolar is markedly rotated but otherwise completely healthy. Extracting it as part of the orthodontic strategy would leave the surgeon with the immensely difficult task of exposing the canine to permit attachment bonding while, at the same time, preserving the vitality of the two incisors. Nevertheless, with this option, an outcome comprising three anterior teeth aligned in their proper places would create the best appearance. However, the roots of both incisors are already extremely resorbed and the amount and scope of movement that the canine will be required to endure before it is finally aligned in its proper place, will require a high level of technical skill on the part of the orthodontist. This is an unnecessarily “macho” treatment plan which, even in the best circumstances, would further compromise the incisor roots and would almost certainly leave the canine with a poor periodontal condition and a reduced prognosis. In other words, the three anterior teeth of the left side would all have a very questionable future.

2. Extracting the canine itself is the approach which offers the shortest treatment time with the least amount of mechanotherapy - of particular significance in this case. However, the surgical task of extracting the canine, whose cusp tip is burrowing aggressively in the resorption crater it has created in the incisor root ends, is formidable, if vitality of the incisors is to be preserved. Nevertheless, by eliminating the need for resolving the canine impaction, it eliminates the most difficult part of treatment, which relies heavily on anchorage support from adjacent teeth. Thus, while actual incisor movement in each of these 4 treatment options is relatively minimal, in the case of canine extraction the resorbed incisors will not be used for anchorage and their chances of achieving long term viability might benefit, if they can survive the surgical episode. The first premolar would need to be over-rotated approximately 60 degrees mesio-lingually and its crown prosthodontically modified, to simulate the canine.

3. Extraction of the lateral incisor offers perhaps the best long term prognosis of the dentition. In substituting for the lateral incisor, it simplifies the resolution of the canine impaction by creating space for it in a more convenient location in the dental arch, thereby reducing the mechanotherapy needed to align it and improving its periodontal prognosis. Substituting the small lateral incisor with a relatively large and bulky canine, however, will adversely affect the appearance, particularly since the other incisors are small and slender. Nonetheless, replacing the lateral incisor with the healthy canine reduces the number of teeth with a poor prognosis. The premolar would need to be aligned as in option 2.

4. With resorption of the severity seen in this case, even the central incisor enters the scene as a candidate for extraction, which entails bringing the canine into its place and crowning it. It should be recognized that, in terms of appearance, prosthodontically converting the shape of the canine crown to a central incisor is a more satisfactory alternative than with the lateral incisor. For this option to be viable, it would be necessary to draw the canine mesially, which could endanger what remains of the resorbed root of the lateral incisor with which it is in close relation, in addition to requiring considerable uprighting of the canine root.

A cone beam CT will provide considerable 3-D additional information in most cases where the canine is either buccal or palatal to the incisor roots and where we wish to diagnose the existence and severity of incisor root resorption. In these cases, the resorption shortens the incisor roots in a progressive downward dynamic, but it is a rare case where shortening the root occurs on all sides to a similar degree. It is almost always oblique, affecting the side of the root facing the impacted tooth. Thus in a palatal impaction, the palatal side of the root of the incisor will likely be affected and, with plane film radiography alone, it will be impossible to see the lesion unless there is alteration of the mesio-distal profile of the root, as seen on the films. CBCT adds the third dimension to the imaging and can identify the earliest manifestation of resorption and it is capable of defining and depicting the 3-D location and relations of the tooth to the surrounding structures with great clarity, leaving little room for mistaken positional diagnosis. For all these reasons it is widely recommended in the treatment of impacted teeth, in general.

A late discovery

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Fig. 3a-c. The images taken from the CBCT scan included (a) panoramic view and two transaxial views through (b) the central incisor and (c) the lateral incisor showing the different angles of the resorption crater and the close proximity of the impacted tooth to the resorbed area, in each case.

Having studied the material on the assumption that the plane film records described above were the only ones available, I received a note from my correspondent in reply to my request to commission a CBCT. The note enclosed attachments with 3 frames from a CBCT that had been performed earlier and only very recently discovered (Fig. 3). These included a panoramic view and 2 transaxial slices. Although there were no axial slices nor 3-D views, these images offered new information that was not evident from the above-mentioned films.

The transaxial slice through the central incisor shows the canine crown situated on an obliquely resorbed incisor root, which offers a minor impediment to labial traction of the canine in the form of a raised edge to the resorption crater. Thus, although option 3 technically makes the canine resolution easier and offers the possibility of resolution with the least collateral damage, careful planning is needed to be sure to expose on the labial side, drawing the canine a little superiorly and labially to lift it over the raised crater edge. The tooth may then be moved distally to circumvent the root of the central incisor and on into the space of the extracted lateral incisor. n general, substituting a canine for a lateral incisor in the esthetic zone suffers the drawback of a high gingival level. By additionally drawing the canine labially will usually result in an exaggerated labial clinical crown length, in the final analysis.

On the other hand, the shape of the resorption crater lends itself better to drawing the canine palatally away from the central incisor root and distally to the lateral incisor location from the palatal side. Drawing the canine through the palatal mucosa is likely to invest the canine with an improved gingival level and a more acceptable appearance.

Whether option 1, 3 or 4 is chosen, this patient needs to be referred for surgery as early as possible, since the resorption process in these cases is rapid. The design for the surgical exposure must be determined by both the orthodontist and the surgeon, but the exposure itself must be a very limited, closed surgical procedure. The middle and cervical areas of the crown of the tooth only should be exposed. Extending the exposure coronally to the sensitive root area must be avoided. No attempt should be made to remove the entire dental follicle and an eyelet attachment should be bonded and ligated with a twisted ligature wire.

In the end, it is the orthodontist who bears responsibility for the treatment outcome in these cases and the surgeon acts only as a facilitator to provide access to the tooth. Experience has taught me always to be present at the surgery to bond the eyelet myself, but also to see that the surgery is done in accordance with my wishes and the pigtail ligature drawn in an appropriate direction through the flap. If a labial approach has been chosen, the flap should be fully replaced, but the twisted steel ligature from the eyelet should exit through the middle of the flap, horizontally opposite the attachment. Any attempt to leave the tooth exposed widely enough for the tissues not to heal over, in an open procedure, will inevitably result in the collateral exposure of the resorption front and the vital tissues of the incisor, which will devitalize. For a palatal approach, an open exposure can be considered if the site of a window excision is made high enough in the vault towards the cingulum area of the canine. A full flap closed exposure procedure is also available in this case, in which the twisted wire ligature from the eyelet attachment would be taken through the middle of the flap, as opposed to through the sutured edges.

There are many aspects to be taken into consideration in the planning of this patient and most of them are discussed here. Which line of treatment will be taken by the orthodontist responsible for the case is entirely dependent on a future discussion that will no doubt take place between the orthodontist, the surgeon and the patient and it may well involve other factors, including economic and social considerations that are beyond the scope of this column.

References

1. 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

2. 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