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.
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 :
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’?
Professor of Orthodontics, Queen Mary University of London, UK