February 28, 2022

Does extracting primary canines help palatally displaced canines erupt? A surprising Cochrane Review!

We are on a real run of orthodontic Cochrane Reviews. This one is on the effects of removing primary canines on palatally displaced canines.  I thought that the results were surprising and certainly worth discussing.

Traditionally when we see a palatally displaced we consider removing the primary canines.  The theory underpinning our decision is that by creating space we can encourage normal eruption of the impacted tooth.  This treatment became increasingly popular following the publication of the landmark paper by Ericson and Kurol in 1988. However, as we have become more critical of research methods, we recognise that this paper does not provide a high level of evidence, because they did not include an untreated control group.  As a result, this new systematic review is necessary and timely.  It is an update of a Cochrane review.

Interventions for promoting the eruption of palatally displaced permanent canine teeth, without the need for surgical exposure, in children aged 9 to 14 years

Philip E Benson, Amarpreet Atwal, Farhan Bazargani, Nicola Parkin, Bikram Thind.

Cochrane Database of Systematic Reviews 2021, Issue 12. Art. No.: CD012851.

DOI: 10.1002/14651858.CD012851.pub2.

What did they ask?

They did this review to;

“To assess the efficacy, safety and cost‐effectiveness of any interceptive procedure to promote the eruption of a PDC compared to no treatment or other interceptive procedures in young people aged 9 to 14 years old”.

What did they do?

They followed standard Cochrane methodology in this review. This was hand and electronic searching for publications, filtering relevant papers, extracting data, carrying out a meta-analysis, assessing the risk of bias, and identifying the strength of evidence. The team did this in combination with the Cochrane Editorial team. As a result, this is a high-quality review.

The PICO was


Children between 9 and 14 years diagnosed with palatally displaced canines (PDC).


Any method of intervention intended to encourage the eruption of the PDC


Untreated control or another intervention.


Eruption of the canine into the mouth. The team also reported several secondary outcomes, but I will not address these in this post.

What did they find?

At the end of their searches, the authors identified four studies. Three of these were reported in three articles, and one was described in five papers. The studies included data on 199 randomised participants. Of these, 82 had unilateral PDC, and 117 had bilateral PDCs.

When they looked at the interventions. One study (67 participants) compared extraction of the primary canine with non-extraction of the primary canine. This study included participants with unilateral suspected PDCs (45) and 22 participants with bilateral PDCs. For the unilateral PDC group, the patient was allocated to extraction or non-extraction of the primary canine. If the participant had bilateral PDCs, the authors used a split-mouth design to have the primary removed or retained on either the right or left side.

The review authors had concerns with this approach because this would introduce confounders such as the severity of the impaction. As a result, they only included data from the intervention site for this group of patients.

In the other three studies, the investigators compared single upper primary canine extraction with double upper primary canine and first molar extraction. Consequently, the review authors decided to exclude data for the eruption of the PDC for one of the studies because of potential confounders.   This process was somewhat complicated, and I struggled to follow this part of the review. As a result, I decided to confine this post to the extraction of single primary canines. Julia Naoumova did this trial, and I have posted about it before.

Did the intervention work?

The systematic review authors analysed data from this study. This showed that without the extraction of the primary canine, 13.6% of the PDCs erupted. When the primary canine was removed, 39.1% of the PDCs erupted. The difference was 25% eruptions when the primary canine was removed. The CIs were very large from 1.4 fewer to 112.3 more. Furthermore, the authors concluded that the certainty of the evidence was low.

What did I think?

This was a highly detailed well, done systematic review. It was very complex, and the authors presented the data and conclusions well. However, the interpretation of the data was rather tricky. This is because of differences in interventions, outcomes, and even the age that a palatally displaced canine could be impacted.

I decided to look closely at their comments on the Naoumova study. The review authors raised several points that influenced their confidence in the results. These were:

The study was not registered before it started, and the primary outcome did not match the outcome used in the sample size calculation. However, the review team contacted the study author, and she provided information to the review team. They stated that this reassured them, and they judged the study to be at low risk of bias in the selective reporting domain.

Then later in the review, they stated that the study was at unclear risk of bias because of the same issues with the outcome measure and the sample size. So again, I was confused about this decision. As a result, I am not sure of their overall conclusion about this study.

Final comments.

This is a well-done review of a complex set of data. I have decided to interpret the findings by considering the risk/benefit balance. When we consider the risks of removing a primary canine. As this should be done under local anaesthesia, I assume that the risks are minimal. The data also shows that this procedure may lead to 25% more eruptions than doing nothing, but the CIs are wide.

My thoughts are that I would suggest the removal of the primary canines when I see a palatally impacted upper secondary canine. However, I would warn the patient and their parents that this may not be successful.

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Have your say!

  1. Previous studies have suggested extraction of primary canines, primary canines and first primary molars, cervical headgears, maxillary expansion, and various combinations. Although the quality of these studies were highly variable, pretty much all showed “doing something” resulted in better outcomes than “doing nothing “.

  2. I too have read Julia Naoumova’s papers with interest and was impressed by the level of clinical guidance they offer in selecting cases for interception and giving clinicians, patients and parents balanced and realistic expectations of the potential benefits. I was therefore surprised by the findings of the Cochrane review and found your blog helpful in understanding this, thank you.
    I was at the BOC in 2011 after the previous Cochrane Review was published and was among the 80% plus of the straw poll audience who said they would continue to intercept canines, just to fully declare my professional bias!!

    Whilst I understand that the level of evidence is low and know that canine interception can be unpredictable, if we consider the low cost and low risk of interception against the higher cost and risks associated with surgical exposure and alignment ( and within the current climate of treatment waiting lists,) I still believe that patients, clinicians and service providers can benefit from the appropriate selection of cases for interception with informed consent and that there is a place for more formal clinical guidance and decision trees for interception rather than another “it doesn’t work” headline.

  3. The extraction of primary canines encourages the eruption of their permanent successor in 25% more cases than not extracting?

    What is the timeframe for this successful outcome? How long should we monitor the intervention? Is there a relationship between canine eruption and the severity of the displacement or should all primary canines be extracted regardless of the severity? Does this intervention result in 25% fewer surgical exposures? What intervention is required in the 61% of cases where the canines did not erupt after extraction? Was the prognosis for the permanent canine worsened as a result of delaying any other intervention? Is orthodontic treatment necessary in some of those “successful” cases where the canine erupts? There are too many unanswered questions.

    Would a better approach not involve opening space for the permanent canine as soon as feasibly possible, as an intervention will be required in the vast majority of cases especially those that are severely displaced? The primary canines could be extracted where they are judged to be impeding the eruption of the permanent canine, as a result of their proximity, after space is opened.

    I fear that this review will result in the indiscriminate extraction of more primary canines than is necessary and will be judged as a success when the permanent canines erupt, as they do in the vast majority of cases without extraction. The message will be interpreted by our colleagues that extraction of primary canines will result in the eruption of the permanent canines. I have seen promises like that made to patients and by the time I have seen them significant damage has been done.

  4. One important caveat is that when primary canines are extracted early, the anterior teeth may drift distally and the space for the permanent one is lost. I have seen this happen numerous times. When I recommend extracting primary canines early I often deliver a removable retainer to maintain space.
    Also, all the research is for PDC, I have not seen research regarding Labially displaced canines and yet have seen many primary canines extracted, often by general dentists to “help” labially displaced canines erupt. Is anyone aware of any studies to back up this practice?

  5. I totally agree with all Dr Attrics comments . I personally am very uncertain if extracting primary canines helps , it may speed up eruption but in my mind, highly unlikely to change the course of eruption.
    I am hoping the review isn’t going to be interpreted the way Dr Attric thinks it may .
    I do quite a lot of clinical practice, seeing new patients in tertiary care. When I see patients with canines in sectors 2 and 3 ( these are the ones we are interested in) one often finds there is plenty of space in the arch but not between the premolar and lateral incisor. I always therefore create space first and when the primary canine becomes mobile I may ask for it to be extracted to speed things up . I personally never extract c’s in the hope an ectopic canine may change it’s direction

  6. Kevin I was surprised your blog post of this Cochran Systemic Review article did not elicit more comments or questions. We can debate whether there are to many systemic review articles and depending on the criteria each author uses can come to different conclusions. I want to spend more time discussing the conclusions of this article and it’s implications rather than their methodology. A direct quote from this article’s conclusions is “The evidence that extraction of the primary canine in a young person aged between 9 and 14 years diagnosed with a PDC may increase the proportion of erupted PDC’s without surgical intervention, is very uncertain”. My fear Kevin is that this article will perpetuate a notion that since there is no “good” evidence there is thus no good reason for extracting primary canines to facilitate the eruption of a palatally displaced canine. I say “there is no reason” to extract primary canine is because the authors have stated in previous blog post on your site and in their most recent response to your blog their own suggested guidelines for the “Management of the Palatally Displaced Canine” and it doesn’t involve extraction of primary canines. (Benson,Graham,Parkin 2018) They suggest a wait and see approach. Wait until the permanent first bicuspids have erupted and do orthodontic space opening in hopes the permanent canine will erupt. This technique with its own inherit risks have almost zero studies in the literature and could hardly be considered an interceptive procedure. Dr. Mary Short’s editorial response in the BDJ to earlier suggestions by Dr. Parkin on waiting and space opening procedures is “Many parents and orthodontist would prefer a short interceptive procedure undertaken under local anesthesia, where the favorable features for the improvement is preferable to supervised inactivity leading to an established palatally impacted canine.”
    I have heard other clinicians suggest orthodontic space opening in this context and I alway have to question the reasoning for such action. First from my own experience and clinical studies it is rare to see crowded cases with PDC’s. Normally just the opposite is seen. In Sigurd Hadler-Olsen’s study of 48 patients with PDC’s they found 94% had absolutely zero crowding of their arches. Other studies have suggested PDC patients have well developed wide arches . So to suggest orthodontic space opening in these cases seems inappropriate but in a select few cases for which I would agree if needed. This approach would suggest the treatment would start when the patient is older which is not advised by many investigators.
    On the flip side, Professor O’Brian in your 2014 blog post you stated that the extraction of primary canines to help facilitate the eruption of permanent PDC’s “is an established procedure that is practiced widely”. You went on to say in a lecture you gave to the British Orthodontic Conference you asked the delegation of orthodontist to vote on whether they would remove primary canines in cases of PDC, in the absence of scientific evidence? Your response stated that 78% of the delegates would recommend the extraction of the primary canines and 81% of them felt strongly about their decision. For which I agree.
    If I could supply some thoughts and suggestions about this complex subject and why our office strives to have a Zero-Tolerance Canine Impaction practice. I am a pediatic dentist in private practice for 38 years and also practice orthodontics, however not university trained.
    In dentistry we should follow our patients on a continuum of care and not a “spot check” approach to canine impactions. First and foremost any maxillary canine in Sector III or IV was in Sector II at some point. It is important to know that canines in Sector I & II have similar and favorable prognosis to treatment and canines in Sector III & IV have similar and unfavorable prognosis to treatment as it relates to extractions. I would want every pediatric dental resident coming out of a program to understand that in their busy practice 1 in 50 patients between the ages of 10 and 14 has the potential for an impacted canine and for every palatally displaced canine CBCT studies show 50% of those cases have some signs of root resorption (Ericson & Karol 2000). Also 25% of those cases the resorption could be severe in nature involving the pulp. I would also want them to know that most cases of root resorption happens in children over the age of 11 and from canines found in Sectors III & IV (Ericson & Kurol 1987 /Schindel & Sheinis 2013). Also 70% of cases with severe root resorption have alpha angles of at least 30º (Chaushu & Becker 2015) . Thus our goal is simple for achieving a Zero-Tolerance Caine Impaction practice and that would be to stay diligent in diagnosing and treating palatally displaced canines before they cross over the mid root of the lateral incisor into Sector III, preferably before age 11 to help prevent root resorption. Every patient from age 10 on should be palpated at every recall appointment for a buccal bulge and investigated if not found. In our practice most of the patients that receive interceptive extractions are between the ages of 10 1/2 and 11 1/2. Extractions in 12 to 14 year olds tend not to be successful. It would also benefit the clinician to know the relationship between PDC’s and the genetic components of Dental Anomaly Pattern (DAP).
    These genetic markers can easily be diagnosed at a first panorex screening around seven years of age. The five conditions we look for in our practice are missing teeth especially mandibular second bicuspids, distally inclined mandibular second bicuspids, small size teeth especially maxillary lateral incisors, ankylosis primary molars, and delayed dental development. It would be good to know that 60% of PDC cases have both delayed dental development and dental deep bites. If any of these conditions exists then these children can be monitored closely.
    Concerning the alpha angle of the permanent canine it would be good for clinicians to know that 90% of ten year olds have an alpha angle less that 21º from a study of 1000 panorex’s (Bonetti 2009). Knowing this you can understand the concern when we find a canine with an angle greater than 25º to 30º at any age. Both Dr. Naoumova and Drs. Short and Power have suggested that any canine with an alpha angle of 30º or more should be considered for an Ortho/Surgical Traction treatment approach. We have had success in intercepting cases with angles greater then 30º when diagnosed younger than 12 and found in Sectors II or just crossing over into Sector III with extraction of the primary canine. What is amazing is most of these cases the permanent canine erupt with limited to no orthodontic needs. Orthodontic and Pediatric Dentist must be aware that Ortho/Surgical gold chain traction of a permanent canine is not without it’s risk. Not only is this usually done under general anesthesia but studies show that more than 20% result in canines becoming ankylosed (Garcia 2013 and Motamedi 2009). These risk are not to be taken lightly. At the end of the day the proponents of a wait and see approach most likely believe I could potentially extract in cases that would naturally self correct where I believe that the wait and see approach ends up having more cases with a Ortho/Surgical treatment plan with its inherent risk that would otherwise have corrected nicely with a simpler extraction approach. Knowing this I also agree more research is needed for this complex subject. Kevin thank you for your excellent blog post and the wide subject matter you cover.

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