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Bulletin #65 April 2017

Impacted Canines, Adjacent Roots and Directional Traction

It is well known that retroclined incisors, as seen in class II division 2 malocclusions, occur in association with a high lower lip line – meaning that in its resting posture, the lower lip covers much of the labial surface of the upper incisors. The teeth are thus controlled by the vertical inner surface of the lip, which accounts for their vertical/retroclined angulation. It will be remembered that in the normal situation, only the incisal millimeter or less of the incisors lies in contact with the oblique inner surface of the crest of the lip.

In a short correspondence that I had many years ago with Dr. Glyn Wreakes, a well-known consultant orthodontist in the UK, he had observed that palatally impacted maxillary canines seemed to be common to an exaggerated degree in class II division 2 malocclusions. Whether or not there is any evidence in support of this observation has not, to my knowledge, ever been established. However, the roots of retroclined incisors are labially displaced and their profiled outline is often palpable and visible on the labial side of the alveolar ridge.

It is reasonable to hypothesize that the labial displacement of the roots offers a “vacant” lingual area for the developing permanent canines to move into and to become impacted there. In other words, the high lower lip line is the primary cause of the retroclination and the canine impaction is secondary to it.

There is another way of looking at it, which is equally tenable. One may theorize that the palatal impaction of developing canines behind the incisors physically displaces the incisor roots labially, simply by their space-occupying presence within the narrow alveolar ridge. In this scenario, the forward and medial eruptive movements of the canines are primary and this secondarily contributes to retroclination of the axial orientation of the incisors.

On the other hand, there is a considerable volume of literature indicating a strong genetic influence both in regard to canine impaction and also in regard to the occurrence of class II division 2 malocclusions. Thus, heredity offers a third plausible explanation for the association between the two phenomena.

Fig. 1. Intraoral views of the initial condition.

The case illustrated in this month’s bulletin is a typical example of this phenomenon (Fig 1). The records of the 15 year old male patient were sent to me for an opinion, by a regular reader of these website bulletins. The occlusion was classified as class II division 2 subdivision right hand side, where the molar relation discrepancy was 2/3 of a cusp width. The left side was normal. The 4 maxillary incisors were markedly retroclined and the mandibular incisors less so, while the vertical overbite was 70%. The deciduous maxillary canines were the only deciduous teeth present and both unerupted permanent canines were palpable in the palate.

Fig. 2a. Pre-treatment panoramic view, showing the images of the impacted canines, reaching almost to the midline. The images of the canines are significantly enlarged indicating their palatal location. The roots of the deciduous canines are seen to be entirely unresorbed

.

Fig. 2b. A view of the anterior section of the lateral skull radiograph confirms the palatal location of the fully superimposed impacted canines (arrow).

The panoramic view showed the crowns of the two canines close to the midline, while their root apices extended posteriorly and superiorly almost to the second premolars (Fig. 2a). The apex-crown orientation of their long axes was downwards (in the vertical plane), mesially (in the a-p plane) and medially towards the midline (in the coronal plane). The standardized lateral skull view (cephalogram) shows the two canines almost identically superimposed on one another (Fig. 2b).

Fig. 3. A 3-D axial view of the maxilla showing the location of the impacted canines in relation to the erupted teeth (arrows).

The two deciduous canines exhibited long and unresorbed roots and there was no apparent incisor root resorption that could be associated with the proximity of the canines. The root apices of both impacted canines were seen on the CBCT to be located between the roots of the second premolars and first permanent molars, lingual to the line of the arch (Fig. 3).

Orthodontic treatment began with the express aim of increasing the space in the canine region to accommodate the permanent canines, using full maxillary and mandibular orthodontic appliances. Once achieved, the patient was sent to the oral surgeon with the request to expose the canine and to bond an attachment with a gold chain drawn to the labial archwire at the intended final destination of the canine, in the dental arch (Fig. 4).

Fig. 4. A panoramic view of the case after surgical exposure, attachment placement and the application of traction directly to the labial archwire.

At the next and subsequent visits to the orthodontist, the chain was ligated and re-ligated to the light nickel-titanium archwire. The traction force was effected by elastic resistance to the lateral and vertical displacement of the archwire.

I am sure that those of my readers who are familiar with these bulletins will recognize this treatment approach for this specific patient, to be a recipe for potential failure!^{2, 3} It is the result of 2-dimensional thinking of a 3-dimensional problem. We become so dependent on the panoramic view (the 2-D aspect) of the dentition that we find it difficult to relate to the additional information that is available on a comprehensive CBCT work-up (the 3-D aspect).

Fig. 5. The same 3-D axial view of the maxilla as in Fig. 3, showing the location of the root apices of the canines (arrows) and the sites at which there is a clash between the canines and the roots of the adjacent teeth when traction is applied direct from the labial archwire (red stars).

The late, lamented and sorely missed Vince Kokich recognized the need for circumventing incisor roots when applying traction to impacted canine and he railed against dragging the palatal canine across the root of the lateral incisors, thereby causing “…..root resorption, bone loss and disadvantageous periodontal consequences” (Fig. 5).

In the present case, the crowns and the roots of both canines were located on the palatal side of all the maxillary teeth, from incisors to second premolars, as is seen on the CBCT axial 3D screen shot (Fig. 3). As such, the incisor roots were preventing labial movement of the crown of the canines, while the premolar roots were directly in the path of any attempted corrective buccal movement of the canine roots. The orthodontist here had nevertheless applied traction from the labial archwire direct to the two canines and had experienced considerable resistance. Notwithstanding Kokich’s warning, these teeth were being drawn labially, regardless of the incisor roots anteriorly and the palatal roots of the first premolars, which was seriously undermining the anchorage. The contact with the premolar roots is particularly damaging, since it creates a fulcrum around which the canine crown may be moved labially but, as the root apex is moved in the direction of the mid-palate. In the event, the left canine did succeed in reaching the labial archwire, despite the obstructive premolar root, but the right canine did not.

Fig. 6.  A panoramic view taken after failure to retrieve the right canine. Note the log jam between the roots of canine and premolar, at one end and between canine crown and the lateral incisor, on the other.  Note also the development of an open bite on the right side, with mesial tipping of the molars, both of which being characteristics of anchorage loss.

The clash between the right canine and its immediate neighbors can be seen on the panoramic film taken at this stage. It shows the fruits of poor planning of anchorage and the blind application of traction (Fig. 6). Anchorage loss is well illustrated by the mesial tipping of the anchor molars and by the iatrogenically driven open bite. In the event, the right canine failed to resolve due to a log jam with the adjacent teeth. While the left canine was successfully aligned, there is cause to wonder whether the roots of the adjacent teeth were resorbed in the process, as Kokich had warned.

In cases of this nature, a sound approach is to free the impacted tooth from its ligation to the archwire and treat the unfortunate side-effects – close down the open bite, upright the molars and ensure adequate space, before proceeding to reconsider how to circumvent the cause of the debacle.

For most cases of this type, the best way to resolve the impactions here is to first apply extrusive force to these two teeth in a vertically downward direction, aimed at erupting them into the mid-palate.^4-6 Once there, they would have a direct and uninterrupted path to their places in the arch, free of the premolar roots.

Fig. 7. Buccal, lingual and axial views of the right side depict the transposition of the roots of canine and premolar (arrows). Note that more-than-adequate space had been prepared to accommodate the canine, but the direction of its long axis (the path of its eruption) in relation to the erupted teeth, demands an even greater space opening.

However, there is one added tip that most orthodontists do not consider, which relates to the premolar roots and, more specifically, to the palatal root of the first premolar. As seen here, the first premolar root is upright and yet it blocks the movement of the canine. In other cases the tooth is often to be seen with a mesially tipped root orientation and this is sometimes aggravated by an additional mesio-buccal rotation, which brings the palatal root further mesially, to block a potential eruption path of the canine.⁶ After space opening, therefore, these cases may often benefit from distal uprighting or intentional over-uprighting of the root and mesio-palatal rotation, to clear an unobstructed path for the canine (Fig. 7).

References

1. Kokich VG. Preorthodontic uncovering and autonomous eruption of palatally impacted maxillary canines. Seminars in Orthodontics, 2010;16:205-211.

2. Bulletin #6, December 2011 on this website. Salvaging a failing case. http://dr-adrianbecker.com/page.php?pageId=281&nlid=22

3. Bulletin #7 January 2012 on this website. Opening space for the canine – it’s not as simple as it seems!

http://dr-adrianbecker.com/page.php?pageId=281&nlid=21

4. Becker A, Zilberman Y. A combined fixed-removable approach to the treatment of impacted maxillary canines. Journal of Clinical Orthodontics, 9:162-169, 1975.

5. Becker A, Zilberman Y. The palatally impacted canine: a new approach to its treatment. American Journal of Orthodontics, 74:422-429,1978.

6. Kornhauser S, Abed Y, Harari D, Becker A. The resolution of palatally-impacted canines using palatal-occlusal force from a buccal auxiliary. American Journal of Orthodontics and Dentofacial Orthopedics 110:528-534,1996.