NEWSLETTERS

A maxillary canine impacted in all directions: thinking outside the box

Published: May 2014

Bulletin #33- May 2014

A maxillary canine impacted in all directions: thinking outside the box

The patient whose diagnosis and treatment options are the subject of discussion in this month’s bulletin was first seen in the private practice of a trained and experienced orthodontist who discovered the existence of an impacted maxillary canine from the radiographic examination. He commissioned a cone beam CT, saw that the situation was complex and, rather than treat the problem himself, referred the child to a University postgraduate orthodontic clinic. Here he would be treated by a young and inexperienced student, who is learning (albeit under appropriate qualified supervision) to be an orthodontist (sic).

The postgraduate student is presently undergoing specialist training in Orthodontics at a European University. He examined the patient, took impressions and performed a lateral cephalogram to supplement the existing imaging records for overall diagnosis and treatment planning. In discussions with his professor, a way to resolve the impaction of the very difficult maxillary canine could not be found. Clearly, the question as to whether the tooth could be brought into the dental arch with a good prognosis was considered critical in planning the treatment of the otherwise minimal malocclusion. Since the case was not an extraction case, it was hoped that the impaction could be satisfactorily resolved so that the tooth would become an integral element in the treated outcome. The professor recommended that the student send the case for troubleshooting advice, with the aim of finding a strategy that would resolve the impaction and ultimately align the tooth in the arch.

In his letter of referral and in his own words, the student correctly pointed out that “ …..the canine is lying horizontally. In the bucco-lingual direction (it) is lying over the dental arch. The crown of #13 (the canine) is oriented palatally in relation to the apex of #12 (the lateral incisor)”. He noted that the apex of the canine was very distally located, over the apex of the second premolar and, as such, he was concerned that extrusive movement of the canine would resorb the root of the premolar #14. His overall strategy was to expose the canine and to draw it into the arch, with the use of skeletal anchorage.

His specific questions to me were as follows:-

1. Would I recommend attempting to align the canine?

2. Would I prefer to use an extraction regimen, sacrificing the first premolar #14, alignment of the canine and closing the excessive space with orthodontic movement?

3. Would I recommend a labial or palatal approach to the surgery?

4. In which direction would I first apply traction and how?

5. Is resorption of the roots of #14 a likely consequence?

These questions show a clear understanding of the many aspects of the problem and the 3-D implications involved in the case.

Diagnosing the location of the impacted canine

We must begin by defining the location of the tooth in the 3 planes of space and relations to other teeth, which is based on the CBCT imaging “slices” and the 3-D screen shots that were sent to me, on which I based my recommendations.1, 2

Fig.1_2

Fig. 1, 2. Lateral and anterior 3-D screenshots of the dentition showing the high canine and its relationship to the adjacent incisor and premolar. The apical third root dilacerations of the premolar appears significantly distant from the canine. Note the distal position of the root apex of the canine.

From the anterior and sagittal 3-D screen shots seen in Figs. 1 and 2, we may describe the canine as being situated high above the apices of the two premolars, with its apex almost in the same sagittal plane as the mesio-buccal root of the first molar. Its apex-crown orientation tips 250 downwards and forwards to bring the crown tip to lie almost in contact with the root apex of the lateral incisor. Its crown is medially displaced, fully overlapping the root of the lateral incisor in the horizontal plane, with minimal vertical overlap of the apex. A clinically significant and often overlooked feature of this case is the mesially-directed dilaceration of the apical third of the buccal root of the first premolar.

Fig._3__4

Fig. 3, 4. Transaxial (vertical) slices from the CBCT imaging. The canine can be seen to be lying palatal to the lateral incisor and the premolar. Resorption is evident at the apex of the incisor and the dilacerated apical extension of the root of the premolar is clearly in contact with the canine.

The vertical (transaxial) slices are very revealing in terms of the relation of this tooth to its immediate neighbors. A radially-oriented cut (Fig. 3) shows the sagittal relationship of the crown tip of the canine to the root apex of the lateral incisor. The canine is located palatally to the lateral incisor root apex, which is shortened partly due to uncompleted root apexification, but also partly due to some early, canine-related, root resorption. While the screen shots in Figs. 1 and 2 did not appear to show any involvement of the premolar root apex with the crown of the canine, a coronally-oriented cut (Fig. 4) shows obvious contact between the two, which is manifestly deflecting the mesially-directed eruptive vector further palatally. To arrive at this diagnosis from any of the 3 CBCT-generated panoramic views (Fig. 5-7) taken in different vertical planes would be inconclusive.

Fig._5._6__7

Fig. 5-7. Serial 2-D panoramic slices taken from palatal to line-of-the-arch, respectively, from the CBCT, which give no indication neither of the incisor root resorption nor the severity of the root dilaceration of the premolar.

Limitations

The canine is prevented from being moved labially/buccally by its relationship to the lingual side of the lateral incisor and first premolar roots. Its apex is very distally located, which means that it cannot be moved downwards because of its close-to-horizontal angulation and location immediately above the premolar roots. Neither can it be moved mesially because of its relation to the lateral incisor root.

The crown of the tooth can be moved horizontally in a postero- palatal direction but, in order for this to be of practical disimpaction value, it must be moved away from the premolar roots and close to the midline raphe before it may be drawn vertically downwards. This would create the need for an inordinate degree of buccal root torque because the apex will be drawn palatally with the exaggerated movement of the crown. Furthermore, since it would still be mesially angulated with its apex too far distal, it would need to be uprighted in its palatally displaced position. Only then could it be drawn to the dental arch, but the mesial apical root dilacerations of the premolar would prevent its achieving an adequately torqued root.

In the language of the billiard halls – snookered!

Treatment options

Option #1 – from the labial side

For most of us, drawing a tooth buccally means ligating it to the labial archwire. To do this in the present context and with the canine so high, would introduce a vertical (downward) component into the force, which would immediately meet with the resistance of the root apices of the incisor and the premolar. To overcome this, it would be necessary to apply traction from a point high in the buccal sulcus and above the height of the premolar apex, in order to jump the canine over it. Just in case you could still be considering this, the surgical exposure would be very difficult and would need to be aimed towards the middle-to-CEJ area of the crown in order to distance if from the incisor root apex. A closed exposure technique would be mandatory.3, 4 Mechanically, this would mean placing a spring or fixed point of force application too high in the sulcus for the patient to tolerate.

Option #2 – from the palatal side

For the surgeon, gaining access to this tooth would be very difficult because of its height and access for bonding an attachment very restricted. An open surgical procedure in this case would leave the patient with a wide open field which, because of the depth of the canine, would almost certainly close over with healing soft tissue of the palatal mucosa, even if a surgical pack was left in place for several weeks – not to mention the post-operative pain and discomfort for the patient.5 Widening the exposure with the intention of eliminating this snag would risk the danger of devitalization of the premolar andor incisor. A closed exposure using a wide palatal flap skirting the gingivae of the upper teeth would be the procedure of choice, although bonding will be extremely challenging.

Traction would need to be made from a palatal cleat on the first molar of the opposite side, in order for the tooth to clear the root apex of the premolar by drawing it in the direction of the palatal midline raphe. The tooth would need to be re-exposed when it arrived at the midline, in a very minor surgical episode, but it would leave the canine with a very long distance to travel before it reached the archwire on the buccal side. It would then need mesial root uprighting and very considerable buccal root torque, much of which will have been generated iatrogenically by the movement towards the midline.

Option #3 – changing the immediate environment of the canine – thinking outside the box

A much more original approach is to change the immediate locale of the impacted canine by altering the orientation of one or more of the adjacent teeth. In the present situation, my preferred approach would be to rotate the premolar by turning is buccal aspect towards the mesial by 80-900 or rotation. This would divert the mesially-dilacerated apical third of its single root towards the palatal. At the same time, the root of the lateral incisor should be “over-uprighted” mesially, thereby distancing it from the crown tip of the canine.

At this point, surgical access will be much simplified and more conservatively performed with a labial approach to the canine. Orthodontic traction will also be simplified by a labial approach and traction in a labial direction using a labial auxiliary archwire placed piggy-back style over the base arch, as I have described elsewhere. The length of the vertical loop in this auxiliary archwire would need to be about half the height of the labial sulcus in its actively ligated mode and easily tolerated by the patient.

In the final stages, the over-uprighted lateral incisor and over-rotated premolar will need to be reversed once the canine has been brought to its place in the arch. The over-uprighting of the lateral incisor will have had a halting effect on the incipient root resorption that is occurring, notwithstanding the fact of the orthodontic movement itself. 6 I do not expect resorption of the root of the premolar, although I would welcome losing its root apex!

Postscript

It is interesting to note that the dental alignment of both jaws and the interarch dental relations appear to be close to the ideal, with good intercuspation of the posterior teeth and a normal overbite and overjet. There is a generalized mild degree of spacing and also note the maxillary lateral incisor anomaly and its late root closure. These are characteristics of the dentitions of many patients with palatally impacted canines.

This case is a prime example of the enormous advantage that CBCT has to offer in relation to plane film radiography in the diagnosis and treatment planning of impacted teeth. As little as 15 years ago, this case would have been a momentous failure because reliance for its positional diagnosis would have been placed on plane film radiography only. It could still fail but, given the diagnostic imaging available today, an accurate and planned strategy may be evolved and the chances of failure reduced very significantly.

Acknowledgement

I wish to thank the postgraduate student and his professor for granting me permission to publish this case on my website and for providing the appropriate records.

References

1. Chaushu S, Chaushu G, Becker. The role of digital volume tomography in the imaging of impacted teeth. World Journal of Orthodontics, 2004; 5:120-132

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

3. Becker A, Chaushu S. Palatally impacted canines: The case for closed surgical exposure and immediate orthodontic traction. American Journal of Orthodontics and Dentofacial Orthopedics 2013;143:451-459.

4. Chaushu S, Dykstein N, Ben-Bassat Y, Becker A. Periodontal status of impacted maxillary incisors uncovered by two different surgical techniques
Journal of Oral and Maxillofacial Surgery, 2009; 67:120-124.

5. Chaushu S, Becker A, Zeltser R, Branski S, Vasker N, Chaushu G. Patients' Perception of Recovery After Exposure of Impacted Teeth: A comparison of Closed versus Open-Eruption Techniques.
Journal of Oral and Maxillofacial Surgery 2005;63:323-329.

6. 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