Ectopic Maxillary Canines: Ten ways to minimise failure.

Padhraig Fleming outlines possible methods to reduce treatment failure for ectopic maxillary canines in this post.  This post is a nice mix of research findings and clinical experience.  

Introduction

Although we are loathe to admit it, failure is common in orthodontics. Few of us would be overly comfortable presenting ‘our worst 5%’. Fortunately, the effects of failure (at least in the short-term) might appear to be relatively mild and even incidental. For example, a small residual overjet, imperfect torque on a lateral incisor, a minor open bite or imperfect interdigitation. However, failure in the management of ectopic canines can be more problematic with possible complications including:

• Failure to erupt the tooth
• Iatrogenic resorption of adjacent teeth
• Occlusal canting

Failure to successfully align a canine is quite common, with Becker et al. suggesting a failure rate of as high as 30% in subjects over 30 years. My reading of this study is that it may exaggerate the likelihood of failure (even in this age cohort) with this group of clinicians being referred the most complex of canine cases. Nevertheless, failure is a real risk, particularly in older patients, and we ought to do our best to mitigate this. How can we do so?

Case selection: 

I know it’s a predictable one, but case selection (as always) is key. So, how do we decide which canines to align? Numerous studies have considered this question, but my main criteria are age, associated malocclusion, and canine position. 

Specifically, we should be less cavalier with older patients. We should always consider the dictates of the associated malocclusion. Put simply, if there is a significant space requirement in a quadrant with an ectopic canine (particularly if the patient is older and the canine is grossly ectopic), we should exercise caution in attempting to align the canine. 

Finally, gross displacement of the canine is a key consideration with plentiful research on this topic. However, if we are ‘compromising’ by removing a canine, there should be a clear benefit to this – either by reducing treatment time, obviating the need for orthodontics completely (perhaps in a less suited patient) or improving our predictability.

Surgical aspects: 

There has been lots of research concerning the effect of exposure type with little evidence to suggest a difference between open or closed exposures. My ‘rule of thumb’ is to request open exposure when the palatal canine is palpable. Deeper impactions may risk re-covering of the tooth (and Covid may have heightened the risk of this eventuality). 

Open exposures may permit autonomous eruption, which makes our lives easier. All too often, I have seen closed exposures with attachments close to the CEJ, leading to slower eruption and unwanted rotations. However, with open exposures, we can control the position of the attachment and therefore reduce the risk of this happening. 

Glass ionomer open exposures (GOPEX) are, I think, an excellent means of permitting open exposure while minimising the risk of re-coverage. We can also control our positioning of attachments with open exposures. We are able, therefore, to ensure that the attachment is on the surface facing the direction of tooth movement – typically palatal first and buccal later.

Don’t condemn the primary canine: 

Adults in particular may respond unfavourably to unaesthetic spacing and appliances. As such, the treatment process may have a bearing on the treatment outcome. Keeping the primary canine until it impedes alignment may therefore be sensible. Similarly, just occasionally the primary canine can be used as a point of force application.

Do what you can from the palatal aspect: 

With palatal canines, we often require an initial distal vector to negotiate the canine away from the root of the lateral incisor. The use of palatal auxiliaries or TADs are a subtle way of applying the needed directional force without placing visible appliances (See previous point). And don’t underestimate the effect of this initial posterior movement of a large and impacted tooth on the anterior-posterior anchorage demand.

 

Lateral incisor (and occasionally first premolar) position: 

Canines can fail to erupt due to interaction with adjacent roots. We should be mindful to avoid root interference with the lateral incisor the most common culprit. Artistic positioning of the bracket or local variations (e.g. by transposing the lateral incisor bracket) may be helpful in positioning the root mesially. 

Consolidate local spacing early: 

We know that canines often respond favourably to local space. Therefore, it makes sense to consolidate anterior spacing early in treatment to create space where it is required and avoid the need for reversing steps later in treatment.

Base wire: 

If we use fixed appliances, I rarely see the need to progress beyond a round SS base wire when applying active mechanics to the canine. Why? Eruption of the canine is the rate-limiting step. To me it makes sense to progress to this point early in treatment. Deferring active mechanics until, for example, a 0.019 x 0.025-inch SS wire is in place, therefore, strikes me as ‘sitting idly by’.

Respond to local intrusion/canting early: 

This consideration relates to the previous point. Adverse effects can, of course, happen as we apply vertical (as well as often horizontal and antero-posterior) forces to a canine. The canine has a large anchorage value- reciprocal effects can be marked. 

I often see the ‘finger of blame’ pointed at the base wire, with a larger base wire being touted as the solution to local intrusion or canting. Typically, however, I think the problem is ineffective force delivery, with the vector of force or local impediments (e.g., adjacent roots) being the issue. As always, the key is to review the presentation carefully and to adapt mechanics rather than continuing with a force system that is not working (and indeed is causing problems).

Be flexible around extrusive mechanics: 

The application of elastomeric traction is relatively simple and requires minimal effort. We may be tempted to reactivate elastomeric repeatedly to align ectopic canines. We know, however, that elastomeric forces decay, and eruption can be sluggish as a result. 

Moreover, we may reach a point where vertical activation from the base wire is impossible. Again, the ability to recognise this and respond efficiently is essential. Stainless steel auxiliaries (e.g., ballista springs) can be very helpful in this situation.

10. Attachment selection: 

Once we can place a bracket on the canine, the risk of outright failure will probably be mitigated. Nevertheless, torque delivery can be very slow and may well be aesthetically important. 

It is, therefore, wise to give the choice of bracket thought with local variation, including inversion, use of maxillary central incisor and mandibular premolar brackets, all possibilities to impart torque control. For this to have an effect, progression into large-dimension rectangular wires is a prerequisite.

I hope that you find this summary useful and I welcome any comments.