March 16, 2015

Can we predict eruption of palatally displaced canines? a RCT

Predictors of eruption of palatally displaced canines.

Several months ago I reviewed an excellent trial on the interceptive treatment of palatally displaced canines (PDC). This was a very popular post that generated many comments. In my discussion, I wondered if the authors had carried out any additional work on whether they could predict the effects of removing the primary canine. I am really pleased to see that they have done this in the second part of the paper that has been published behind the EJO paywall.

Extraction of the decidous canine as an interceptive treatment in children with palatally displaced canines. Part II. possible predictors of success and cut-off points for a spontaneous eruption.

Julia Naoumova et al

European Journal of Orthodontics, 2015 1-11 Advance

doi: 10.1093/ejo/cju102

In their introduction, they reminded us that their previous study showed that extraction of the primary canine increased the eruption rate of palatally displaced canines. They also pointed out that not all permanent canines erupted when the primary canine was removed and conversely some erupted when the primary canines were not extracted.  They, therefore, carried out this study to evaluate any predictors of PDC eruption. They also wanted to identify cut-off points to identify  those cases for which the interceptive removal of primary canines would not work. These are really useful clinical questions.

What did they do?

I have reviewed the methodology in detail in my earlier posting. In brief, they randomly allocated 67 patients with PDC to have their primary canines extracted or not. They took CBCT images at baseline, six months (T1) and at 12 months (T2). They carried out in intention-to-treat analysis.

The sample size reflected the aims of this part of the project. They evaluated the predictive effect of pre-treatment angular and linear measurements taken from the CBCTs, on whether the PDC erupted or not. They also used a technique called Receiver Operating Characteristic. This is a method of identifying cut-off points which would identify the effect of the predictors (CBC measurements) on the outcome. If you want to find out more on ROC analysis see this link is useful.

What did they find?

I am going to concentrate on the main findings of this study and concentrate on the initial displacement of the PDC from the midline. They found that:

  1. The probability of successful spontaneous eruption of a PDC is increased by 18 times if the primary canine is removed.
  2. Palatally displaced canines erupt spontaneously more readily in younger patients, when the canine was less displaced from the normal position.
  3. If a canine cusp tip is 11 mm or more from the midline then it is more likely to erupt, even if the primary canine is not removed.
  4. If it is 6 mm or less from the midline it is unlikely to erupt, even when the primary canine is removed.
  5. If the distance between the cusp tip and the midline is between 6 to 11 mm; there is likely to be benefit from the extraction of the primary canine.
  6. The greatest predictor on eruption was removal of the primary canine.

What did I think?

I thought that this was a very useful study with clinically relevant findings. I did find interpreting  the data was rather tricky; but the study is complicated.  In my interpretation I have concentrated on the distance of the PDC from the midline. I did this because I am trying to keep my blog posts simple.  However, I suggest that this may not be  this straightforward and you should read this paper in detail.

I also think that it is worth mentioning that these results are only applicable to the accurate measurements that are obtained from CBCT.  I am certain that we cannot be so confident from panoral images.

Will this change my practice? I feel that I will remove the primary canine unless the palatally displaced canine is very displaced (<6mm from the midline). In these cases I am more likely to consider surgical exposure rather than waiting for spontaneous eruption.  Let’s discuss this?

ResearchBlogging.orgNaoumova, J., Kurol, J., & Kjellberg, H. (2015). Extraction of the deciduous canine as an interceptive treatment in children with palatally displaced canines. Part II: possible predictors of success and cut-off points for a spontaneous eruption The European Journal of Orthodontics DOI: 10.1093/ejo/cju102

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Have your say!

  1. There is another RCT on the subject that I found easier to interpret by Bazargani et al. published last year in Angle Orthod (2014). In that study they used panoramic radiographs which is more applicable to the clinic.

    Best regards/Ann

  2. Thank you Kevin love the blog. Please can you tell us where you think this leaves the Royal College guidelines on the elective loss of primary canines?

    And how you feel about the production of guidelines for care in the absence of the highest level of evidence?

  3. Many years ago Dr. Jack Dale of Toronto, CD advised me that removing a deciduous canine early did little to encourage the eruption of a permanent canine if that permanent canine appeared to headed toward impaction because removal of the deciduous canine created no additional space. Dr. Dale’s recommendation was to remove both the deciduous canine and first deciduous molar. This allows the first bicuspid to drop down making some additional space for the canine to drop back and erupt normally. I found Dr. Dale’s protocol to be quite successful as long as the permanent canine was not more than 2mms behind the lateral incisor. I know of no studies to support this approach but it might make for some interesting discussion.

    • Hi Terry, yes I cannot help thinking that making the space may be a useful strategy. Jack Dale’s method is interesting but did he use a space maintainer to prevent mesial movement of the permanent molar?

      Best wishes: Kevin

  4. Hi Kevin

    Thanks for highlighting this paper, which could be very useful to us. When you mention the distance of the canine tip from the midline are they just drawing a direct line from the canine to the midline and measuring this? I presume canine angulation made no difference? I have been trying more and more with canines to just open the space more. I seem to be getting good results. What will be interesting now will be to look at the cases retrospectively and see how far the canines were positioned from the midline and then look at the rates of spontaneous eruption.


    • Hi Chris, I just concentrated on the distance from the cusp tip to the midline, because I wanted to keep the posting simple. In the paper they measured the height and the mesio angular angle. Making space and awaiting eruption was something tested by Baccetti and Leonardi. The trials were not well reported but they concluded that making space with distal movement or RME was also effective.

      best wishes: Kevin

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