September 18, 2017

Extracting primary canines intercepts permanent canine impaction!

The impaction of permanent canine teeth is a real problem. We frequently try to intercept this by extracting primary canines. But is this effective?

There have been surprisingly few trials that have looked at this treatment.  In this blog I have previously discussed a Cochrane review that was published in 2012. These authors concluded that there was no evidence that the removal of the primary canines was effective. Then in 2015 Julia Naoumova published a really nice trial. She concluded that the removal of the primary canine was of benefit.  As a result, I feel that there is still some confusion about this treatment. Therefore, I was interested to see two new systematic reviews into this problem. It is worth having a look at them.

Firstly, I will look at the one done by Naif Almasoud. The Angle Orthodontist published this paper. It is open access so you can have a look at it.

Extraction of primary canines for interceptive orthodontic treatment of palatally displaced permanent canines: A systematic review

Naif N. Almasoud a

Angle Orthod. On line DOI: 10.2319/021417-105.1

He set out to discover if removing the primary canines intercepted the palatal impaction of permanent canines.  He did a standard systematic review. The PICO was

Participants: Children with at least one palatally displaced permanent canine

Intervention: Removal of the primary canine

Control: Non extraction of the primary canine

Outcome: Eruption of the permanent canine.

What did he find?

He only included randomised trials and identified four studies.  Two had been recently carried out. One was by Naoumova (2015) ( I have posted about this one) and the other was by Bazargani et al (2014). I must have missed this one!  The other two studies were by Baccetti and Leonardi.

At this point, I would like to mention that the studies by Baccetti and Leonardi were reviewed in the Cochrane review.  The authors of this review did not include the data from these studies because they were at high risk of bias and the interpretation of the data was not clear.  Dr Almasoud also felt that these studies were at high risk of bias.  As a result, I am not going to include this data in my interpretation.

I would now like to look at the other new review.

Effectiveness of extraction of primary canines for interceptive management of palatally displaced permanent canines: a systematic review and meta-analysis

Ameirah Saeed Alyammahi et al

European Journal of Orthodontics, 2017, 1–8 DOI:10.1093/ejo/cjx042

The European Journal of Orthodontics published this paper. Unfortunately, it is behind a paywall, so unless you are a member of the EOS or have access through a library, you cannot read it…

A team from Dubai did this review.  They set out to answer the same question and used the same PICO.  They assessed bias using the Cochrane Risk of Bias tool.

What did they find?

This time they found five RCTs.  These were the same studies that Dr Almasoud found, but they included another study by Baccetti. As with other reviews, they found high risk of bias in the studies by Baccetti and Leonardi.  As a result, they analysed the studies with high and low risk of bias separately. In effect, the Naoumova and Bazargani were the  only studies that provided good evidence.

What can I conclude?

I will only include the data from the recent high quality studies. I have put the relevant data into this table.

StudyEruption after extraction (%)Eruption after non-extraction (%)Risk Ratio (95% CI)
Naoumova69391.6 (0.9-2.7)
Bazargani67421.7 (1.1-2.7)

The results clearly show that removing the primary canines increases the chance of eruption of palatally places permanent canines.

Interpretation of this type of data can be tricky. I have discussed this in a previous post. We can conclude the following:

  • If we extract the primary canines when we see a palatally displaced canine there is a 25-30% increase in eruption of the permanent canine, when compared to no treatment.
  • The risk ratio means that the patients who had primary canines removed had 1.6/1.7 times the chance that their permanent canines would erupt, when compared to no treatment.
What did I think?

I feel that we can conclude that there is clear evidence that the extraction of primary canines leads to an increase in the eruption of palatally displaced permanent canines. Nevertheless, we need to appreciate that success is not guaranteed.  The data from these studies is very helpful to our patients when we explain the treatment to them.

Finally, I would like to make a comment on the reviews.  In a previous post I concluded that we may have too many systematic reviews.  I cannot help thinking that these reviews are a good example of this problem.

We now have a Cochrane review and two other reviews into the same clinical issue.  I am not surprised that the recent reviews have come to the same conclusions.  I am also sure that when the Cochrane review is updated, this will reinforce these findings.  (It would be great to see this one updated soon…). This must represent a waste in research resource and perhaps we should stop duplicating reviews?

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Have your say!

  1. Dear Friend, I published 2 articles about how to prevent canine impaction by extracting primary canine. If you ar interesting I can send it to you. It s in Franche but who knows. Sincerely
    Dr LE GALL Michel
    Spécialiste qualifié en ODF, MCU-PH, HdR
    Doctorat en Mécaniques Energétiques
    Coordonnateur interrégion Sud du DES d’ODF
    Responsable hospitalo-universitaire de l’UF d’orthopédie dento-faciale
    Hôpital de la Timone Marseille

    Villa Gabrielle 314 bd M. Pagnol 13400 Aubagne
    00 33 4 42 03 18 52
    00 33 6 10 02 60 72

  2. Naoumova’s study was really wonderful and (in my opinion) can be considered as a definitive proof of this issue.
    I want to tell you very interesting story happened in the Angle Society Biennial Meeting this year.
    Dr. McNamara said that now he does not believe that we can increase mandibular growth significantly (in the long term).
    One of our long-standing controversial stories is about to end.

  3. Clearly if the crypt of the canine contacts the root of the deciduous tooth there might be a benefit but if the canine is so far away how would it sense that the deciduous tooth had been removed

  4. Wasn’t there also a study involving removal of primary cuspid AND primary 1s molar which showed better results due to accelerating eruption of 1st bicuspid clearing path for cuspid?

    • Double vs Single Primary Teeth Extraction Approach as Prevention of Permanent Maxillary Canines Ectopic Eruption
      Alessandri Bonetti Giulio, MD , DDS. et. al.
      pediatric dentistry v 32 / # 5 SEP / OCT 2010

  5. Hello Kevin,
    As a wet finger pediatric dentist I appreciate your continued interest in the “impacted canine” controversy. It’s something we see in practice all day long. The difference in diagnosing and normalizing a canine in sectors I & II vs sectors III & IV may only be a mere 2 to 3 mms as the canine transverses the root of the lateral incisor. Once it crosses the mid-line of the lateral incisor the chances of normalization decrease substantially! As in the Bazargani article of bilateral impactions the extraction side had 100% (14 of 14) of canines normalize if found in sectors I & II and only 20% (2 for 10) normalized if found in Sectors III or IV. If viewed in totality that equates to only 67% (16 of 24) but broken down into sectors tells another story. The point is in everyday practice early detection through knowledge of the characteristics of canine impactions and diligence can make all the difference in the outcome of these type of cases. Keep up the good work as always.

  6. Thanks for the article, very interesting.

    These comments are in rhetoric, while they’re still fresh in my mind and I completely forget.

    Surely early detection of the characteristics of adult malocclusion and early intervention by way of oral myology or growth modification in growing children is worth considering as a viable research method as it could prevent any unnecessary orthodontic treatment and extraction.

    Im no expert but if there is insufficient space for the permanent canines to erupt correctly, surely extracting the primaries and forcing them to drop into an position where there may be insufficient bone support could de-stabilise the two halves of the palate and cause shifts in growth of the maxilla a kin to two tectonic plates colliding, causing crowding as each teeth fights one another for space or worse significant asymmetrical shifts in the two halves of the maxilla. Of course you could then provide braces but the lack of bone support remains unchanged, thus permanent retention into adult life.

    The bone support for the canines also marks the outer edge of the pyriform aperture, the volume available for nasal breathing, so it would be interesting to study nasal cavity volumes in patients with impacted permanent canines who’ve undergone orthodontic intervention in comparison to a series of other controls.

    It would be interesting to evaluate the long term stability of this form of intervention treatment into adult life without permanent retention.

    • Apples and oranges. Buccal vs palatal. As in this article and others that have been reviewed by Kevin they are almost exclusively pertaining to palatally impacted canines and not buccally impacted canines. In short, palatally impacted canines have a genetic component to their development and a local component due to small lateral incisors and most are in non-crowded dentitions with roughly 85% of cases having sufficient space for the permenant canines.
      Buccally ectopic canines on the other hand do not have a genetic component and are seen almost exclusively with crowded dentitions and large size teeth. Therefore in the case of palatally impacted canines (as reviewed by Kevin) we are not worried about thin bone support but how can we get the canine to erupt and positioned into the arch with hopefully the right angulation and torque to the tooth. I have seen a lot of cases with palatal impactions where the primary canine was extracted in a timely manor and the permanent canine erupt without any additional orthodontic treatment needed. This would be the best scenario for long term stability wouldn’t you say. Since palatally impacted canines have a genetic component oral myology in my opinion would not tend to prevent these impactions.
      In the future Kevin may look to review articles describing the different characteristics of buccally impacted canines vs palatally impacted canines like: “Dentoskeletal characteristics in patients with palatally and buccally displaced maxillary permanent canines.” Cernochova & Izskovicova-Holla, Euro Journal of Ortho (2012) 34: 754-761 or Mucedero & Baccetti 2013 article “Prevalence rate and dentoskeletal features associated with buccally displaced maxillary canines. Euro Journal of Ortho (2013) 35: 305-309.

  7. The timing of the primary canine extraction would be crucial in order to have enough a positive outcome. Clinically I have seen many situations where early extraction of primary canines leads to the incisors occupying their space ( in arches prone to crowding) and that could increase the chance of permanent canine impaction.

  8. What about the extraction of upper E before the ectraction of primary canines?

  9. We agree with David and John that the amount of displacement of the unerupted permanent canine towards the midline is an important factor when deciding whether or not to ask for the primary canine to be removed, as an interceptive procedure. We like David Spary’s theory about tooth contact, whereby if the primary canine isn’t in contact with its successor and bone exists between the root surfaces, how does the successor tooth know where to move after extraction?

    Our simple rules (supported by the current literature and outlined in Cobourne MT, Orthodontic management of the developing dentition – an evidence-based guide. Springer 2017) are based upon diagnosing, from a standard midline occlusal radiograph, in which sector (described in Ericson and Kurol’s articles) the crown of the unerupted permanent canine lies:

    Sector 1 (no overlap of the canine crown with the lateral incisor root); angle less than 21 degrees to midline – unlikely to be displaced, of little concern, should erupt in time, provided that space is available;

    Sectors 2 and 3 (canine crown overlapping the root of the lateral incisor); angle of less than 21 degrees to the midline – consider interceptive treatment by creating space or extracting the primary canine (or both). There is probably little to lose if the root of the primary canine is already resorbing and the patient is willing; however we are still not sure, from existing research, if extracting the primary canine actually causes change in direction in the path of eruption or whether it just speeds up the eruptive process.

    Sectors 4 and 5 (canine crown overlapping the root of the central incisor) – we think that these will require surgical exposure and orthodontic alignment; therefore, there is little advantage to extracting the primary canine and risking the patient not being suitable for fixed appliances, when the eruption of the permanent canine fails to normalise. It is better to leave the patient with a primary canine, than an unsightly gap. In these cases, where the canine is considerably displaced, the primary canine root is often of a reasonable length and has a good medium-to-long term prognosis.

    Julia did a very nice piece of work; however there a few aspects about the study we would highlight. Those participants in the control group, whose permanent canines had not erupted within 12 months, were considered unsuccessful and had their primary canine extracted anyway, even though 60%, were still quite young, at 12 years or under, when there might still be time for the permanent tooth to erupt. Also, Julia was privileged to have Dr Kurol as a co-supervisor for her PhD. He obviously co-authored the original, highly-cited article, advocating the extraction of the primary canine, nearly 30 years ago. Although her work largely supports the original findings, she found that the intervention was not quite as successful as originally suggested.

    We also agree with Kevin about the proliferation of systematic reviews. Just to let you know that the Cochrane review is currently being updated to include all interventions to promote the eruption of palatally displaced permanent canine teeth without the need for surgical exposure.

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