New evidence on the treatment of palatally displaced canines!
Should we extract primary canines to prevent palatal canine impactions?
This post is on the most recent evidence on the effectiveness of removing primary canines in the hope that this encourages the eruption of palatally displaced permanent canines (PDC). As we all know, this is an established procedure that is practiced widely. However, a recent Cochrane review highlighted that there is limited evidence underpinning this practice. I have reviewed this previously. In the review they pointed out that previous studies have not included control groups or were not clear in their design and reporting. As a result, they concluded that there was no evidence to support the removal of primary canines to intercept palatal impaction of the permanent canine.
In my recent presentation to the British Orthodontic Conference, I discussed the effect of clinical uncertainty on treatment decisions. This was an interactive presentation and I asked the delegates to vote on whether they would remove primary canines in cases of PDC, in the absence of scientific evidence. It was really interesting to find that 78% stated that they would remove the primary canine and 81% were very certain about their decision! There is no doubt that this is a controversial area!
I was then very interested to see that a new trial has been published on this question in the European Journal of Orthodontics. I am going to review this in the same way that I would for a Cochrane review and concentrate on issues concerned with design and the risk of bias.
Julia Naoumova, Juri Kurol and Heidrun Kjellberg
European Journal of Orthodontics: Epub in advance of print.
This study was done by a well known research team and they aimed to evaluate the effect of interceptive extraction of the primary canine in children with palatally displaced canines.
They also wanted to analyse radiographic changes in the PDC and measure any root resorption. These were secondary outcomes and I was more interested in whether the permanent canines erupted or not, so I will not discuss these outcomes.
I felt that this was a well carried out trial. They randomised Children with PDC to either have the extraction of primary canines or no extractions. The inclusion criteria were clearly set out. I thought that it was interesting that one exclusion criteria was maxillary crowding greater than 2mm. I could not understand the rationale for this step, as it must have excluded a fairly large number of children. It also means that the results of this study are only relevant to children with minimal incisor crowding.
They included 67 patients in the trial with a total number of 89 PDCs. because some of the patients had bilateral impactions.
Randomisation was clearly outlined and concealment was by previously prepared sealed envelopes. All the participants had CBCT radiographs taken at the start, 6 months and 12 months. The last two radiographs were not taken if the permanent canine had erupted.
The primary outcome was the eruption of the permanent canine. But the sample size calculation was not based on this outcome, the authors based it on change in angulation of the PDC. I thought that this could result in the study being at risk of not having a large enough sample size to detect differences in the primary outcome.
What did they find?
They found that 69% of the PDCs erupted in the extraction group compared with 38% in the non-extraction. This was statistically significant and I would say that this was a clinically significant finding.
I felt that it would have been useful if they had presented other relevant data, for example, the odds ratio, risk ratio and numbers needed to treat. I have outlined this in a previous blog. So I reached for my odds ratio calculator and worked these out myself.
This revealed the following
|Variable||Mean Change/Year(Degrees)||Confidence Interval|
What does this all mean?
From this interesting paper, I can conclude that following the extraction of the primary canine when the permanent canine is palatally displaced.
- There is a 40% reduction in permanent canine impaction
- The risk ratio suggests that the chance of eruption of the permanent canine was 1.7 times greater than in the extraction group.
- Numbers needed to treat reveals that we need to extract 4 primary canines to prevent the impaction of one permanent canine.
These figures are encouraging. But we must take care in interpreting them and we must also look at the 95% confidence intervals. These are all wide and this suggests that there is still a degree of uncertainty in the data.
What will I do?
So, we have to consider that we have one trial that provides a moderate level of evidence with a degree of uncertainty in the data. We also need to evaluate the risks of removing the primary canine and these are low. As a result, in terms of risk benefit considerations, I have decided to start extracting primary canines.
I have also had an afterthought and I wondered whether there were any predictors for the success of treatment. Unfortunately, I could not find any. However, this is part I of a publication, so maybe this was addressed in the second part?
In summary this was a good study that provided useful clinical information on an established practice that up until now had no evidence base!
Naoumova, J., Kurol, J., & Kjellberg, H. (2014). Extraction of the deciduous canine as an interceptive treatment in children with palatal displaced canines–part I: shall we extract the deciduous canine or not? The European Journal of Orthodontics DOI: 10.1093/ejo/cju040
Emeritus Professor of Orthodontics, University of Manchester, UK.