Removal of two primary teeth per side: A new direction for ectopic canines?

A wise man once told me ‘If in doubt, don’t extract’. I was therefore interested in reading this new clinical trial. This looked at whether we should remove two primary teeth (canine and first molar) to improve the eruption of ectopic palatally-displaced canines (PDCs).

We have seen a welcome improvement in our evidence base relating to interceptive management of ectopic canines in recent years. Much of this research has emerged from Scandinavia. This interesting paper builds on this work. A relatively recent trial using a contemporary methodology and three-dimensional imaging by Nauomova and colleagues has helped to re-affirm the earlier work of Ericsson and Kurol. This suggested that the removal of primary canines may improve the position of ectopic permanent canines.

Currently, clinicians propose a wide array of more invasive alternatives to improve the position (and indeed produce ‘independent’ eruption) of ectopic canines. These interventions include adjunctive use of transverse expansion, arch lengthening with cervical-pull headgears and re-opening of an excess of space with fixed appliance. In addition to the removal of first primary molars primary canines. They base these techniques on the potential benefit of space creation in encouraging favourable movement of the canine. By and large, these more invasive approaches have demonstrated equivocal benefit.

A team based in northern Norway did this study.  The Angle Orthodontist published the paper. I have yet to visit northern Norway; however, my children continue to suggest that we go there some time!

What did they ask?

They asked this question;

“Is extracting the primary canine and first molar more beneficial than extracting the primary canines alone in improving the position and eruption rate of palatally-displaced canines (PDCs)”?

What did they do?

They did a two-group randomised controlled trial with a 1:1 allocation (32 participants overall with 48 PDCs) over a 24-month observation period as follows:

Participants: 

• Aged 9.5 to 13.5 years
• With one or two PDCs and presence of primary canines and first molars, and permanent lateral incisors
• Displaced canines in sectors 2-4 based on an accepted classification (Lindauer et al., 1992)
• With aligned, spaced and mildly crowded arches

Intervention Groups:

Double-extraction group (DEG): With the extraction of both the primary canine and the primary first molar

Single-extraction group (SEG): Involving extraction of the primary canine only.

Primary outcome(s):

The eruption of the canine; and eruption of canine into the correct position

Secondary outcomes:

Positional change of unerupted canine

A panoramic radiograph was available before the study, They took another radiograph every six months until the canine erupted into the mouth. Importantly, if the canine position worsened or did not improve improvement within 12 months, they provided alternative treatment  (surgical exposure and fixed orthodontic appliances).

What did they find?

The groups were relatively well-matched in terms of canine position at baseline. Notably, a significant proportion of the ectopic canines erupted over the 12 months. However, there was no difference between the groups with 16/25 (64%) in the DEG erupting while 18/23 (78%) canines erupted in the SEG (P= 0.283). In total, 64% of the canines emerged favourably in the DEG vs 57% in the SEG. Again, this difference was not significant (P= 0.600).

In terms of the secondary outcomes (positional change based on radiographic analysis), they did not find any significant difference between the two groups for changes in canine angle or sector. Unfortunately, six of the canines deteriorated in position. Four of these were in the DEG and two in the SEG. They also found that the start angulation of the canine and the space conditions at baseline were predictors of positive response to interceptive extractions.

What did I think?

Firstly, I think that this was an interesting study. I am not sure how common the recommendation of loss of two primary teeth per side is; however, this study suggests that this approach is unwise.

From a methodological perspective, the study is very well-executed. Recruitment took place over a prolonged period reflecting the narrow selection criteria. These strict criteria helped to limit the potential for confounding related to the stage of dental development, the position of the canine, and the potential absence of maxillary lateral incisors. Overall, therefore, the authors made a monumental effort and are to be congratulated for seeing this study through.

The percentage of teeth erupting over the observation period (which I believe was two years) was significant (71%). This is mainly in keeping with similar studies.

Limitations

I note that other studies considered whether removal of the primary canine is of benefit and included an untreated control. These investigators could have included a third group. Nevertheless, because of the consistent findings from previous studies, this is probably unnecessary and would have made the research hard to complete.

A further limitation relates to the use of two-dimensional imaging. However, the authors do focus on the clinically-relevant finding of the eruption (or otherwise) of the canine. They, therefore, provide us with crucial information that is relevant to clinical practice.

What can we conclude?

There does not appear to be an added benefit in recommending extraction of the primary first molar (in addition to the primary canine) in improving the rate of eruption or the position of PDCs.