March 17, 2022

Extraction of primary canines: Authors response.

There were many questions following our recent blog on extracting primary canines to encourage the eruption of impacted secondary canines. The authors of the paper have written this short blog post. They address my points and many of the comments on their systematic review. It is great that they have done this, and their response, written by Phil Benson,  is constructive.


Thanks very much for blogging about our recent review concerning interventions for promoting the eruption of palatally displaced permanent canine teeth (PDC). PDCs is a common clinical problem. As a result, it is of interest to all orthodontists and general dentists. We agree that there are several complicated issues related to the data. We have tried to explain, explicitly in the review, the decisions we have made about how to handle these. Furthermore, we have also undertaken sensitivity analyses with and without some of these data to determine the effect the decisions have on the results.

Risk of Bias

Regarding the risk of bias (RoB) assessment for the first (and currently only) sound RCT into whether extraction of the primary canine is an effective intervention (Naoumova 2015). We assessed it as a low risk of bias for all domains except Other (we used the Cochrane RoB1 tool). We also considered the decision by the investigators to extract all primary canines in control participants at 12 months if they were not showing signs of mobility. The investigators chose this period of 12 months based on Ericson and Kurol’s somewhat inferior study. In contrast, we found data to suggest that some PDCs may take up to 18 months to erupt, particularly in the younger age groups.

Therefore, it is possible that extraction of the primary canine speeds up the eruption of the PDC rather than improving its chances of erupting. This feature would put the experimental group at an advantage compared with the control at 12 months. Cochrane’s guidance with the RoB1 tool gives a study an overall Unclear RoB grading, even if just one category is judged to be at an Unclear RoB.

The effectiveness of primary canine extraction

Primary canine

If we now look at the effectiveness of extracting the primary canine as an intervention. It might be more revealing if we view the absolute numbers rather than the relative proportional difference. This shows that for 9 out of 23 participants, who had an extraction of the primary canine, the PDC successfully erupted at 12 months. Whereas the PDC successfully erupted when the primary canine was not extracted in 3 out of 22 participants.

We suggest that deciding the effectiveness of an intervention, based on the results from 12 individuals with ‘events’ of interest, in one study from one centre, leaves a considerable degree of uncertainty. Particularly as there were relatively high proportions of participants in the study still referred for surgical exposure in both groups (Extraction: 7/23; Control 11/22; RR 0.61, 95% CI 0.29 to 1.28). The current Grade Pro guidance is that when there are fewer than 100 ‘events’ and a relative risk reduction of less than 30%, it is not possible to meet the threshold for optimal information size (OIS) or review information size (RIS) and judgments for imprecision should be downgraded, whatever the ‘event’ rate in the control group of participants (Guyatt 2011

Exclusion of data

Regarding the decision to exclude some of the data from one of the three studies comparing the intervention single v double primary tooth extraction. This was due to the decision of the study investigators to include participants judged to have bilateral PDCs, then randomising the intervention to the two sides separately. We decided to exclude some of these data because of confounding. We undertook a sensitivity analysis with and without these study data, and the results were very similar.

Other points

Thanks to those who have left their insightful comments, which are always welcome. Regarding this comment:

‘there is a place for more formal clinical guidance and decision trees for interception rather than another “it doesn’t work” headline.’

We want to emphasise that we did not state that extraction of the primary canine “does not work”. Nevertheless,  the evidence is still uncertain (the absence of evidence is not the same as evidence of absence). We have outlined our suggested guidelines for the removal of primary canines in a paper. You can find this  here:

Concerning Dr. Attric’s comments, we have tried to answer some of your questions in our review. We agree that we need to do more well-designed clinical research into this problem. As a result, we tried to obtain funding for a large trial looking at this question. Unfortunately, this was not successful. This was because the UK funding agencies felt this was not a high priority. I would be happy to share the protocol with anyone interested. I think we all agree with Dr. Attric when he says that we should avoid ‘the indiscriminate extraction of more primary canines than is necessary.

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Have your say!

  1. Thank you Kevin.

    The suggested guidelines for the removal of primary canines in the paper cited, is an excellent start.

    Creating space at the canine, even by opening space between the lateral incisor and primary molars until the first premolar erupts, appears to be more successful that lateral expansion, perhaps because less space is opened in the A-P dimension with an RME. A good study would certainly be more useful that a few successful cases, but we need to start with a reasoned approach.

    The retention of primary canines can be important if the permanent canines fail to respond to treatment. They can always be extracted in treatment if they are hindering the eruption of their permanent successor. Or, could even be extracted if an exposure is necessary, avoiding one traumatic experience for the young patient.

    • root size of deciduos canine should be 3/4 th or any other rationale such as proximity of the erupting canine in relation the deciduos canine… Is there any rationale which is evidence based which citics are bound to say is conclysive… 🙏🏻

  2. It’s so refreshing to have a debate based on the best evidence and it’s interpretation. This Cochrane review and indeed the Naoumova RCT are both painstaking pieces of work that are a credit to our specialty.
    I appreciate the criticisms highlighted in the review and take the point that this is only one RCT – but this is a difficult subject area to investigate. I guess my worry is whether an RCT of this nature will ever be repeated? Anyway, my comment would be on harms – extracting the C seems to require space in the arch to work and in these circumstances with a local anaesthetic and compliant child – what are the potential harms? None that I can really think of, so even with very weak evidence this procedure would seem to me to be worth trying? Because you don’t really lose anything?
    Also – where is the data regarding 18 months for the canine to erupt? And, I’m not sure I appreciate the distinction between speeding up eruption of a PCC and increasing its chances of erupting?

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