NEWSLETTERS

The Impacted Mandibular Canine

Published: May 2015

Bulletin #44 – May 2015

The Impacted Mandibular Canine

Impacted mandibular canines have been the subject of many published journal articles and, for the most part, the articles have described the condition for its oddity/curiosity/rarity/freaky/quirky value, rather than satisfying the patient’s hope that something constructive may be done about it.

In terms of etiology, very little is known about the mandibular canine that exhibits intraosseous migration in a more or less horizontal direction, but it seems largely agreed that the potential for an exaggerated degree of migration is an attribute of this tooth, to the virtual exclusion of all other teeth in the mandible, with the possible exception of the second premolar. The tooth will usually travel mesially and will transmigrate over the midline symphysis to the opposite side by as much as 30mms from its normal location, in the more extreme examples. Its occurrence is unilateral in the majority of reported cases. On the other hand there are cases where a potentially normal eruption path of the canine may have become deflected by the presence of a supernumerary tooth or odontoma or a soft tissue pathologic entity, such as an apical granuloma or dentigerous/radicular cyst related to a non-vital deciduous tooth (Fig. 1).

As one who sees many patients for treatment of the infinite array of incarnations that tooth impaction may display, I occasionally see patients with impacted or transposed or transmigrated mandibular canines who are seeking treatment. As with most of my colleagues, I turn some of these patients away with a referral for extraction to the oral and maxillofacial surgeon, but there are a few whom I accept for treatment, with the view to achieving an acceptable result, with the full complement of teeth. So, what are the special circumstances that will commit so many of them to the trash can and which are the few that deserve conservative orthodontic treatment?

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Fig. 1a. A panoramic view shows an incomplete root canal treatment in the left mandibular deciduous canine.

Fig. 1b. A panoramic film taken 3 years later shows the development of a dentigerous cyst displacing the permanent unerupted canine.


Prevention and interception:

Canines that are discovered moving past the root of the lateral incisor and on towards the midline, in the complete absence of any pathologic entity, appear to be the least likely to respond to interceptive measures, such as the extraction of the deciduous canine and deciduous first molar. However, follicular enlargement seems to be often associated with a migrating unerupted canine (Fig. 1). When the same deciduous teeth are extracted, without resolving the follicular enlargement, it again seems likely that the migrating canine will continue on this course undisturbed, probably because cystic change (a.k.a. follicular enlargement) is responsible for some extreme tooth displacements.


When the enlargement of the follicle can be related to the presence of a granuloma of a non-vital deciduous canine or first molar, these teeth should be extracted (Fig. 2). If, at the same time, surgically initiated rupture of the follicle by creating a window in the follicle and then maintaining the patency of the opening with a surgical pack, the pathologic entity will effectively be eliminated. This is because the epithelial lining of the opened follicle metaplases to become contiguous with the oral mucosa during its healing process1. In this situation, one may usually expect to see much spontaneous improvement in the orientation of the tooth in a very short time (Fig. 2).

Limiting technical factors:

A labially impacted canine is generally located in the sub-apical depression between the labially angulated anterior border of the alveolar ridge and the prominence of the chin (Fig. 3a, b). Although it lies on the labial side of the incisor roots, it is usually in a direct vertical line with the cervical margins of the incisor teeth or even lingual to that line. This means that erupting this tooth vertically can only be performed if space is made in the dental arch immediately above it. The roots of the adjacent incisors prohibit the tooth from being erupted mesial or distal to that directly vertical line without it simultaneously being drawn labially away from these roots and the ridge.


To move the tooth labially, it is necessary to position the arm of a custom-designed spring (Fig. 3c) on its labial side with its active position tightly held against the surgically exposed tooth. The deeper down the tooth, the greater will be the irritation that this spring causes to the oral mucosa of the inside of the lip and the depth of the labial sulcus (Fig. 3d, e)and this factor alone may create an intolerable situation for the patient. If box loops are used, then the double loop design will cause an even greater soft tissue impingement.

To reduce the degree of irritation, an eyelet placed on the distal aspect of the crown of the canine will fare much better, but it will only permit distal tipping of the canine. This is fine for a canine whose apex is in the correct location, but not so when there is a total transposition between the canine and the lateral incisor. Of course, irritation of the lip tissue will also be reduced if the canine is not moved labially to a sufficient degree, but if distal movement is performed under these circumstances, the incisor will lose its labial cover of bone.

It is therefore reasonable to conclude that apex location in the mesiodistal plane, depth of the tooth in relation to the depth of the sulcus and the distance that the tooth has migrated are all factors that need to be taken into consideration in deciding whether to attempt its resolution.

There are two major problems with viewing and diagnosing the 3-dimensional positions and relations between the roots of the canine and the lateral incisor, which are usually evaluated using a panoramic radiograph. This film is enormously valuable in general, but in the present situation it presents an over-simplified picture (Fig. 3a). By flattening out its depiction of the circular form of the anterior portion of the jaw into a 2D picture, a displaced canine may look alarmingly simple because the curve will be lost. Secondly, when a deeply impacted labial canine superimposes on the lateral incisor in the narrow width of the lower jaw, the root of the incisor will be markedly displaced lingually and, often distally, to create a partial or total transposition between the two.

Because the canine requires to be moved around the dental arch, labial to the roots of the incisors, it is highly likely that the tooth will lose much of its own labial alveolar bone and soft tissue cover, as it is drawn to its ideal location and will arrive there presenting a very long clinical and reduced bone support (Fig. 3g). Its long term prognosis will therefore be compromised. Simultaneously, it may cause resorption of the labial bony cover of the incisor roots, as it goes.

The following is a list of factors that need to be considered before attempting to attempt the orthodontic treatment of the labially impacted mandibular canine:-

1. Depth of labial sulcus and its relation to the depth of the canine

2. Position of apex of the canine

3. How far has the tooth traveled mesially?

4. How far lingually has the incisor root been displaced?

5. Curvature of the arch

6. How much bone will remain to cover the incisor roots following movement of the canine?

Case 1 – prevention is better than cure.cba._Fig._2

Fig. 2a. A panoramic view of a young boy with a large radicular cyst initiated by the periapical granuloma from the non-vital deciduous first molar. Note how the cyst has pushed the canine mesially and inferiorly and the first premolar horizontally and inferiorly.

Fig. 2b. Following extraction of the deciduous canine and first molar, together with drainage of the cyst, the canine and premolar have erupted and spontaneously uprighted, with space maintenance only.

A 9 year old boy was referred to me by his pediatric dentist and an orthodontist because of swelling of lower left side of the face. He had a history of much dental caries of the deciduous dentition and several restorations had been performed, including the root canal treatment of the deciduous left mandibular canine. The panoramic radiograph (Fig. 2) revealed the presence of a large radiolucent area under the deciduous left first molar, which enveloped the early developing and unerupted first premolar, which was tipped mesially 90 degrees in the horizontal a-p plane. The neighboring unerupted permanent canine was strongly mesially tipped, apparent

ly being “pushed” by the body occupying the large radiolucent area.

The working diagnosis of the radiolucent area was a dentigerous cyst, caused by irritation of the dental follicle of the canine or, alternatively, a radicular cyst arising from the rests of Malassez in the apical granuloma from the non-vital deciduous first molar. In either case, the enlarging cyst would undoubtedly be the prime suspect in the alteration of eruption path of the permanent canine. The deciduous canine and the deciduous molar were extracted and the cyst itself was opened to the oral environment (marsupialization). A small pack was placed over the area and sutured into place, in order to prevent the wound from healing over and left for only a week. A simple lingual arch space maintainer was then placed.

When the patient was seen 2½ months later, the formerly horizontal premolar was seen to be erupting mesially. A periapical radiograph showed considerable improvement in the orientation of their long axes. At a subsequent visit, 8 months later and 10 months after the surgical episode, both teeth had erupted. The premolar had uprighted a full 90 degrees and the canine had over-uprighted by 50 degrees and now stood at a 5 degree tip to the distal!

What was the key here?

1. Seeing the condition early, with a relatively modest degree of displacement

2. Recognizing the lesion as a cyst

3. Knowing that marsupialization causes contraction of the dislocated teeth towards the middle of the former void and regeneration of bone behind the former cyst lining.

Could success have been predicted? Yes, to a fair degree of certainty.

Case 2 – This is what the macho orthodontist might do. Would you call this success?

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Fig. 3a. A panoramic view of the transmigrated left permanent canine, beyond the mandibular midline and below the level of the incisor apices.

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Fig. 3b. A true occlusal view of the incisors shows the canine to be labially impacted, with its root apex in the normal location.

The patient was a 14 year old male with a class 2 division 1 malocclusion. The teeth in the maxilla were treated using a headgear and routine alignment. In the mandible, there was an over-retained deciduous left canine, with reduced space to accommodate the permanent canine. The initial panoramic radiograph (Fig. 3a) showed the deciduous canine to have lost virtually all its root to resorption, but with the presence of a supernumerary tooth apical to it. The height of the crown of the permanent canine was seen to be slightly apical to the roots of the incisors and at an orientation 30 degrees to the horizontal plane. Its crown tip had already transmigrated across the midline suture, to the distal edge of the right central incisor root. Its root apex was situated in its ideal antero-posterior location, but very close to the lower border of the mandible.

It was a long time ago and I was that macho orthodontist. This was my case and I was going to show ‘em!

From a naïve glance at the panoramic view, I reasoned that the orientation of the tooth in the antero-posterior plane and the fact that its apex was in the desired location, provided an excellent opportunity to simply push the crown back over the midline and distally in a wide tipping movement towards its place in the arch, with the root apex as the fulcrum of this planned arc of circle movement. Its very depth in the mandibular bone, below the incisor apices would be an advantage in facilitating the movement. Space needed to be made for the tooth and this was achieved using class 3 intermaxillary elastics and a coil spring in the immediate area.cba._Fig._3c

Fig. 3c. Following space regaining, an auxiliary light stainless steel overlay archwire is placed in its passive mode, immediately prior to exposure surgery. Note the loop lies horizontally.

Before I started, I recognized that the tooth was below the depth of the labial sulcus and that it had to be brought labially away from the incisor roots before the distal swing could begin. It was clear to me at the outset that I would need an active mechanism that would not ulcerate the very mobile oral mucosa that invested the labial surface of the alveolus and its opposing oral mucosa covering the inside of the lip – not to mention the connecting oral mucosa in the depth of the sulcus trough. It had to be very delicate, applying a light force with a good range of movement to obviate the necessity for frequent visits and adjustments (Fig. 3c, f).cba._Fig._3dcba._Fig._3e

Fig. 3d. A full flap exposure is performed to reveal the crown of the canine in the depth of the sulcus. Not the relative lack of labial bone over the incisor roots.

Fig. 3e. An eyelet attachment is bonded to the canine crown and the surgical flap is fully replaced. Activation of the auxiliary spring is made by ensnaring the horizontal loop of the auxiliary archwire in the twisted steel ligature from the eyelet immediately following the re-suturing of the flap (not shown).

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Fig. 3f. Seen 3 weeks later and following much healing, the vertical and active mode of the auxiliary spring can be seen.

Surgery was performed under local anesthetic by the then head of surgery in the OMFS department, Prof. Arye Steyer, who opened a full flap down into the chin area, before we saw the tooth (Fig. 3d). Access was in fact very easy for him and, while he retracted the flap and maintained a dry field, I bonded the eyelet attachment with a twisted 0.012” steel ligature as the connector (Fig. 3e). He then re-sutured the flap to its original place – given the deep location of the tooth vis-à-vis the sulcus depth, there was no way that this exposure could have been performed as an open procedure. Had a non-flap window technique been used to expose the tooth, control of bleeding would not have been adequate to permit successful attachment bonding. Only the long twisted ligature protruding through the base of the replaced oral mucosa flap was visible when he had finished.

Prior to the commencement of the surgical procedure, I had already placed the prepared full arch auxiliary archwire in piggy-back style over the heavy base arch (Fig. 3c). The auxiliary was held in place with elastic modules, with the active loop which had been prepared for the canine lying horizontally unattached, in its passive position. This did not interfere with the surgical field and its presence permitted me to ensnare its terminal helix with the shortened and hooked end of the twisted ligature in just a few seconds at the end of the surgical procedure (Fig. 3f).

A glance at the photographs taken during the surgery will reveal how little bone covered the roots of the incisors on the labial side, even before traction had been initiated.

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Fig. 3g. In the final stages of alignment, an auxiliary torqueing arch is placed over the main arch top correct the position of the canine and premolar roots.

The canine was erupted and drawn labially and distally as planned, towards the assigned canine location. The labial movement had to be very limited to avoid erupting the tooth into the body of the lip tissue but, nevertheless, the tooth arrived to its destination well outside the bony envelope and required considerable lingual root torque, in the final stages. This resulted in a very long clinical crown and a periodontal attachment of oral mucosa, rather than of attached gingiva (Fig. 3g). Additionally, periapical and panoramic films taken in the final days of active treatment showed a very significant degree of apical root resorption of many of the teeth in that jaw (Fig. 3h, i) In the 1 year follow-up photographs, a degree of labial relapse of the tooth was obvious.cba._Fig._3hcba._Fig._3i

Fig. 3h. Periapical views of the incisors, canine and premolars show the considerable degree of apical root resorption, following the long period of treatment and associated root movements.

Fig. 3i. A panoramic view at the end of treatment shows the achieved root parallelism, but also resorption in several other teeth.

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Fig. 3j. Seen a year post-treatment, note the long clinical crown of the canine and the degree of positional relapse of the canine.

Surgically, the attempt was successful, orthodontically it was partially successful, but periodontically it was a failure. All-in-all a pyrrhic victory because “the strength of a chain is measured only in its weakest link”.

Case #3 – turning adverse (pathologic) conditions to advantage

This case is still in the treatment planning stage and orthodontic treatment has not yet commenced. Initially, on the basis of the panoramic radiograph, the case appeared similar to case #2 in this presentation. The patient was 12 years of age male with a spaced dentition and with all four second molars erupted. The maxillary second deciduous molars were still present, but about to be shed and the second premolars and permanent canines in the maxilla were clearly about to erupt.

The right mandibular canine was impacted labially and had transmigrated about 3mm over the midline, superimposing on the apex of the left central incisor. Its own root apex was vertically below its ideal mesio-distal location, in the compact bone of the lower border of the mandible and its apex-crown long axis was at a 30 degree angle to the horizontal plane. The crown was enveloped by an enlarged follicle (a.k.a. small dentigerous cyst).

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Fig. 4a. This patient was seen at an early stage and the abnormal orientation of the canine, with its follicular (dentigerous) cyst, was diagnosed. The deciduous canine and first molar were extracted in the hope that the tooth would self-correct. However, nothing was done regarding treatment for the follicular cyst.

Fig. 4b. Seen 16 months later, the canine has continued in its former direction and has transmigrated over the midline.

The referring orthodontist informed me that the deciduous first molar and canine teeth had been extracted in the immediate area 16 months earlier, in the hope that this would encourage the tooth to alter its eruption path(Fig. 4a, b). The earlier panoramic view was produced and it showed that there were potential developmental problems related to all four canines. The left mandibular canine and both maxillary canines were unerupted at the time and each had a moderately enlarged follicle. These teeth erupted spontaneously during the period of observation, despite the potential for eruption disturbance. The right mandibular canine follicle was larger than the others at this time and the tooth was the only one with an abnormal eruption path. However, its apex-crown long axis was about 50 degrees to the horizontal and it was barely overlapping the distal side of the right incisor root and still some way from the midline.

It is arguable that this tooth would not have transmigrated over the midline nor would the orientation of its long axis have become more horizontal, had the follicle had been opened (marsupialized), drainage established and its patency maintained to prevent recurrence. On the contrary, it may be justifiable to go so far as to suggest that there would probably have been some spontaneous improvement in its orientation and, perhaps, even a small chance of autonomous eruption of the tooth into the mouth, as we have seen in case 1 above.

In consultation with the patient and his parent, it was recommended that the tooth be extracted, because of the considerable likelihood that a periodontal failure would accompany an orthodontic and surgical success, as in case #2. Nevertheless, it was decided to perform a cone beam CT of the immediate area, to complete the imaging process and to provide the case with a full 3D basis upon which to justify the decision.

cba._Fig._4c cba._Fig._4d

Fig. 4c, d. The CBCT axial and 3D screen shot views of the tooth show it to be enclosed in a large follicular (dentigerous) cyst, which has displaced it labially away from the alveolar ridge and improved its access to biomechanical means of orthodontic correction.

The CBCT views showed that the tooth was enclosed within a large dentigerous cyst, which had additionally displaced it labially, away from the roots of the incisors (Fig. 4c, d). Superimposition of the canine over the roots only involved the last millimeter of root apex, due to the depth of the canine crown. At that level, it can be seen that the apical third of the root was covered on its labial side only by the external surface of the sac lining of the cyst, with no bone intervening. Moreover, these roots were situated within a crater carved into the labial alveolus by the presence of the expanded cyst. Thus, from this labial location, 2-4mms labial to the alveolar bone, tipping the tooth distally around the arch would appear to be a justified approach that appears to have a better prognosis than was first thought, from viewing only the panoramic view. Additionally, with resolution of the cyst, it can be reasonably expected that the lack of bone over the incisor apices will be compensated by new bone filling in the resorption crater, on their labial aspect1.

Case 4- ….. with the best intentions in the world!

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Fig. 5a. Periapical views of the transposed order of the lateral incisor and canine teeth. Note that the root apices of the two involved teeth are also completely transposed. It is impossible to correct the order of these teeth within the narrow alveolar rim of bone, without creating serious periodontal problems, including long clinical crowns, gingival inflammation and recession and loss of bone support.

The case involved a 15 year old female who had been in orthodontic treatment by a general dentist for several years for the correction of a severe mandibular left canine-lateral incisor (Md2C) transposition (Fig. 5a). cba._Fig._5b

Fig. 5b. The orthodontist attempted to reverse the abnormal order. The illustration shows different views of the condition when first seen for re-evaluation of treatment. It was considered that extraction would be the most appropriate line of treatment at this point. Note the extreme labial ectopy and uncontrolled mesio-labial rotation that has occurred due to elastic traction direct to a labial bracket and the degree of gingival inflammation and gingival recession present.

The lateral incisor had been moved into interproximal contact with the central incisor and the canine had been surgically exposed and attachment bonded. The canine was then extruded occlusally and tipped distally to circumnavigate the lateral incisor on its labial side. Neither the canine nor the incisor had been moved bodily and their apices remained in the original transposed relation. As the result of traction to the ideally-placed bracket of the canine in a distal direction, labial to the dental arch, the canine had become rotated 90 degrees and its labial side palpably devoid of alveolar bony plate. The gingivae were swollen and hemorrhagic and the head of the clinic where the child was treated referred her to me with the expectation that the canine was no longer viable and would need to be extracted (Fig. 5b). Orthodontic treatment had not been performed in the maxilla.

cba._Fig._5c

Fig. 5c. The treatment direction was changed and the lateral incisor was moved distally, to create space for the canine in the transposed order between the lateral and central incisors.

It was clear at that point that correcting the transposed order was only possible at extreme periodontal cost and the early extraction of the canine. The only possible line of treatment that could be designed to save the tooth would be to bring it into the alveolar bone as soon as possible. The canine was freed from the existing distal traction elastic and its bracket removed, to simplify oral hygiene, which had been largely ignored up to that point. In order to achieve this without requiring the extraction of other permanent teeth, the deciduous canine was extracted. The lateral incisor was then pushed back distally into the healing socket area of the extracted deciduous canine, to create space between it and the central incisor. The canine was then realigned into the transposed order (Fig. 5c). At the same time, orthodontic alignment and occlusal relations were corrected with the use of a fixed multibracketed orthodontic appliance in the maxilla (Fig. 5d, e).

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Fig. 5d. Occlusal and anterior views of the achieved alignment at the completion of treatment shows considerable improvement in the gingival condition of the canine, good alignment, but a long clinical crown in comparison with the unaffected right canine.

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Fig. 5e. Clinical views of the completed treatment on the day appliances were removed.

So, what is the bottom line?

Whenever the labially impacted mandibular canine is impacted on the mesial side of the lateral incisor, we are forced to move it “round the corner in the outside lane” and its periodontal prognosis is poor. The orthodontist who plans the treatment using the flat panoramic view alone, will fail to grasp the hidden 3D factors that are at play in a curved archform and will likely cause the treatment to fail. Impacted teeth within an expanding dentigerous cyst or being pushed by a radicular cyst probably have greater powers of resolution when the causative pathology has been eliminated, provided the treatment is done early enough1. Extraction of deciduous canines and premolars alone will probably not be useful preventive measures in the presence of an enlarged follicle/dentigerous cyst, unless the cyst itself is also evacuated.

Reference

1. Becker, A and 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.