October 26, 2020

Interceptive extraction of primary mandibular canines for incisal irregularity: Marginal Gains?

This is a follow up post about  the interceptive loss of primary canines.  In my last summary, I cautioned ‘If in doubt, don’t extract’. As orthodontists, we manage the developing occlusion and consider interventions. Occasionally patients ask us if we should remove baby teeth to improve the alignment of teeth and simplify or indeed obviate the need for later treatment.  This new systematic review summarises this problem.

While international practice concerning the timing of orthodontic treatment is hugely variable, most of us feel that correction of crowding is often best performed in the late mixed or early permanent dentition. However, crowding can become apparent earlier. Does the removal of primary canines help to improve the appearance of crowded incisors? More importantly, perhaps, does interceptive removal of primary canines have long-term benefit?

My view on this is informed by one excellent clinical trial (Kau et al., 2004) carried out in Wales. Based on this study, I think that removal of primary canines may help to improve incisal alignment in the short-term. However, we may only be transferring the site of crowding from the lateral incisor region to the canine region as the permanent dentition becomes established. This effect comes at the expense of increasing the underlying crowding marginally, as well as requiring an additional dental procedure.

A research team in Brazil carried this systematic review. The  International Journal of Paediatric Dentistry published the paper.

The authors aimed to assess the impact of the removal of primary canines on intra- and inter-arch features.

The effect of extraction of lower primary canines in the morphology of dental arch: a systematic review and meta-analysis.

Authors: Daybelis González Espinosa, Crislyne Mendes da Vera Cruz, David Normando.

International Journal of Paediatric Dentistry. Sep 18. doi: 10.1111/ipd.12726.

What did they do?

They conducted a systematic review to assess the effect of extraction of mandibular primary canines on the mandibular arch and some inter-arch relationships.

The PICO framing was :

Participants: Children

Intervention: Extraction of primary canines. The title refers to mandibular canines only; however, it appears that participants having interceptive loss of all four canines were also included.

Control: No intervention.

Outcomes: Little’s irregularity Index and model-based assessment.

The authors intended to include both randomised and non-randomised studies. It is unclear whether they were going to include all possible study designs.  The authors used the ROBINS-I tool to assess the risk of bias for non-randomised studies and the updated Cochrane Risk of Bias tool to assess the bias within randomised controlled trials.

What did they find?

They identified three potentially eligible studies. One of these was a non-randomised. As a result,  they did not include this in the meta-analysis. As such, they were able to include only two primary studies in the quantitative analysis. These studies were carried out in Wales (Kau et al., 2004) and Sweden (Sjogren et al., 2011).

They decided that both studies had a low risk of bias.  It is important to note, however, that the first study examined the loss of lower canines alone, while the more recent study considered loss of all four primary canines. I am, therefore, not convinced that it is appropriate to compare these studies concerning the inter-arch effects (e.g. on overbite and overjet), in particular.

The authors present five forest plots based on the two studies with what they term as ‘crowding’ (More correctly, this is ‘incisal irregularity’), lower arch length, lower intermolar width, overbite and overjet.

What did they conclude?

The authors concluded that:

  • Extraction of primary canines relieves dental crowding in the mixed dentition,
  • There is also a decrease in the dimensions of the dental arch.  This may be critical in the development of the permanent dentition.
  • There is a slight reduction in overjet and a small increase in overbite.
  • When they are not part of the treatment goal,  We can prevent these changes by fitting a lingual arch.
  • We recommend that investigators carry out RCTs addressing the efficiency of primary canine extractions associated with a lingual arch.
What did I think?

I thought that this was an interesting review of an important topic. Children rarely enjoy having extractions. Dentists can also find the experience unpleasant (The prospect of removing teeth from children used to keep me awake at night!). There are also associated costs and burdens. It is therefore critical that we have good evidence to support interceptive extractions.

I thought that the search strategy and reporting were clear. The quality assessment was appropriate. It is important to consider that the authors were only able to identify two primary studies for inclusion in the analysis. While this may seem disappointing, both of these were excellent clinical trials. Nevertheless, I can’t help feeling that this review adds very little to this original work. This problem is not the authors’ fault as the lack of trials constrained them. However, I do wonder whether meta-analysis (certainly concerning the inter-arch outcomes) was appropriate.

When I considered the authors’ conclusions.  I think that the key message is that the removal of the primary canines improves alignment temporarily but amplifies any underlying crowding by reducing the arch length.

Furthermore, any conclusions based on overjet and overbite are tenuous as lower arch extractions only were performed in one study. Intuitively, we might expect a slight increase in both parameters in this trial, while extraction in both arches might have less effect on overjet, in particular. Finally, while the authors may believe that a lingual arch may be of benefit, they did not assess this as part of this review.

What can we conclude?

Based on primary data from two high-quality clinical trials, removal of primary canines does appear to improve the alignment of the incisors in the mixed dentition. This improvement is likely to be temporary and is offset by an aggravation of underlying crowding. So perhaps it is a case of ‘marginal short-term gain for marginal long-term pain’?

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Have your say!

  1. Mild to moderate lower incisor crowding may help the attainment of mandibular growth? By prematurely extracting lower primary canines, aren’t we causing a discontinuity of the dental arch to impede growth?- Easy and quick-fix methods are not always effective in the total, long term picture? Lower crowding is not affecting the aesthetics either. Tongue pressure will help decrowding by labial tipping also?
    As KOB has rightly put it, ‘An untimely stitch for a short time gain may need nine later’?

    • I have done early arch expansion for 20 years and for the next 20 I did extraction of the LC’s. I have found no effect on growth and I still treat non extraction. I was fortunate to figure this out because I had a pedodontist who always extracted LC’s in crowding cases. I expanded some early and others I would watch. The extraction of the LC’s let me kick the can later and take care of the whole problem in one phase instead of two phase. I obviously would use a LA if needed. This saved the kid from two phase treatment and I have not seen any difference in results . I was very good a two phase but if I can deliver excellent care at lower cost and time to patient. Thus it is either extractions of LC’s or early tx with 2 phase treatment. I just wanted to share my experience and observations. Also one of my thoughts is that it is better to have the L12 aligned early for better stability but again this is only an opinion but has worked very well for me over 40 years.

  2. A good reason to remove lower primary canines is when one of the central incisors is significantly labially displaced and is experiencing recession or reduced attached gingival. It would be nice to know if the authors of the underlying studies in the meta-analysis looked at gingival health as part of their studies. Short term improvement of crowding may not be enough reason to extract lower primary canines but prevention of additional gingival recession might be.

    • I agree with you and my thought is if I can align the L12 early in the absence of gingival issues without phase 1 tx then I can get started with regaining space if I desire near the loss of the LE’s and thus only treat in one phase.

  3. I never remove lower deciduous canines without placement of a lower lingual arch soon after extraction. I have never understood why this is not a much more common practice. Extraction of the lower deciduous canines and placement of a lower lingual arch provides the benefit of both the alignment and the gain (vs the loss) of the additional space gained from preservation of the “E space”. This study seems to validate the theoretical basis of that treatment approach. I think a comparison of extraction of lower deciduous canines plus lingual arch vs with out lingual arch would be interesting.

  4. I concur with the observation of Bill Gierie. Definitely gingival health would be an issue to consider. Another thing that comes to mind is the occasion when the midline is compromised due to the crowding, even if we know that comprehensive treatment later is needed, would it not be prudent to extract the canines and allow self correction of the midline.
    As and when the child develops extraction line of treatment can be carried out without having an additional aspect of non matching midline to correct.

    • Monir Zaki, I have heard this midline correction argument all my career (since 1986). As I dual trained individual, I have looked and looked for supporting studies. I have yet found to find a single piece of evidence that shows extraction of the contralateral canine results in midline correction. If you have any studies, please let me know. I do know my son published a study looking at the lower midline deviation when one primary canine is lost early or both are lost at normal time in the Iowa and Toronto Growth Studies (Robert Christensen, Pediatric Dentistry is the journal). There was very little difference in the two. Their conclusion was to rethink early removal of the contralateral canine. I doubt there is significant midline correction other than the correction of the irregularity index. However, as the two studies suggest, there is a price to pay in 2 and 1/2 to nearly 3 mm of arch length loss. Other than the soft tissue issues pointed out by Dr. Gierie, one should be very cautious in removing primary canines. As Dr. Preston Hicks, another dual trained person and wonderful educator once said, “the fastest way to create an extraction case is to remove the lower primary canines”.

  5. Its interesting that they could only find 2 pertinent research articles on this. This used to be a very popular technique. It is a modification of the serial extraction sequence.

    One thought advantage was that it would decrease the time needed to later close extraction spaces. Yes you were “robbing Peter to pay Paul” by stealing the C space and giving it to the incisors. However, if you were certain it was going to be a bicuspid extraction situation, it was thought to save time.

    I wonder if they just didn’t go far enough back in the literature as there is much written on this. Of course, those articles were for a slightly different purpose. So maybe they didn’t meet the criteria.

  6. Most here seem to agree that extracting primary canines is simply ‘kicking the problem down the road’ into buccal crowding in a few years. The reason is that it is a dental solution attempting (and failing) to deal with a skeletal problem – shortage of arch length/size. Much better to recognise the problem and address it correctly, hopefully avoiding any extractions.

  7. Just to add a little pepper to the discussion an old timer taught me years ago to take out lower D’s instead of the lower C’s and optional placement of a lingual arch when the lower anteriors aligned. The advantages of taking out the D’s were 1 the bite did not deepen because the C’s were removed 2 the occlusal forces drove the lower C’s distally allowing passive alignment of the lower anteriors in 3 to 6 months and 3 many times the lingual arch was not necessary .must have treated 500 plus cases like this with fantastic results rarely did I have to consider bicuspid extraction

  8. Could You please explain me what is the difference between incisor crowding and incisor irregularity?

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