A massive systematic review on the speed of canine retraction!

We are all interested in the factors that influence the speed of tooth movement. This new systematic review provides a large amount of information that may impact our use of adjuncts in orthodontic treatment.

Over the past few years, many studies have looked at interventions that may speed up the rate of orthodontic tooth movement. Most have shown a limited effect of the many interventions that have been developed and marketed with little evidence. However, many of these studies have been small and potentially underpowered. As a result, I was interested to see this new systematic pooling of the data from these investigations.

What did they ask?

They did this review to answer two main questions:

“How long does it take to fully retract maxillary teeth after first premolar extraction”?

And

“What is the canine retraction rate”?

These were two straightforward, simple and clinically relevant questions.

What did they do?

They did a standard systematic review. The team carried out a literature search, identification of paper, assessment of Cochrane Risk of Bias, extracted data and identified the overall strength of evidence. They registered the review before they started and reported it according to the PRISMA 2020 statement.

The PICO was

Participants

Humans of any age needing maxillary canine retraction as part of orthodontic treatment.

Intervention

Retraction of maxillary canines using full arch fixed appliances.

Comparison

Any surgically assisted or non-surgical techniques or appliances.

Outcome

Duration of maxillary canine retraction in months from the start to the completion of retraction. The secondary outcome was the canine retraction rate.

They only included randomised trials in the review.

The team carried out the relevant data and meta-analysis.

What did they find?

At the end of the literature search and filtering, they included 50 trials. 6 of these were parallel designs, and 44 were split-mouth studies. The mean age of the participants was 19.9 years.

The 50 studies produced an amazing amount of information. As a result, I shall concentrate on the main findings in a few bullet points. These were

• The mean duration of complete canine retraction was 4.98 months (95% Cis -2.9 to 12.8 months).
• Surgically assisted orthodontics was associated with greater retraction at all time points. These were months 0-1 (mean difference 0.5mm, months 0-2 (MD=0.53), and months 0-3 (MD=0.67). At the end of treatment at months 0-4, the mean difference was 1.13mm (data from three trials).
• There was no influence of orthodontic vibrators, self-ligation, photobiomodulation, platelet-rich plasma or fibrin.

However, most of their meta-analyses showed high levels of heterogeneity.  This reduces our confidence in the findings.  Furthermore, when they looked at the total duration of retraction, this data was derived from only two small studies.

The authors concluded that

It takes 5 months to fully retract canines.

After three months of treatment, high-quality evidence suggests surgically assisted orthodontics speeds up canine retraction.

What did I think?

This was a massive work, and the authors should be congratulated on this comprehensive review. They produced a large amount of information and data. In fact, I needed a lie down after reading the paper!

As usual, I shall declare an interest. I know Martyn Cobourne well, he contributes to this blog, and we grew up in the same small village in Worcestershire, UK. However, I have not discussed this paper with him.

Some of you may remember that I have been critical of the onslaught of orthodontic systematic reviews that have included low-quality research. One major strength of this review is that it only included trials. The number of included studies was very high. However, only 16 of these trials were of low risk of bias. As a result, this reduces the certainty of the data.

They found strong evidence for the trials that evaluated surgically assisted orthodontics. The authors pointed out that this finding was similar to other reviews. Nevertheless, they stated that we should be cautious about this finding because they only included two studies in the final data synthesis.

I looked closely at their data and the very clear discussion. They pointed out that the effect of surgical assistance was strongly influenced by corticotomy, a very invasive procedure. Whereas laser-assisted flapless corticotomy,  piezocision, and MOPs are less invasive, there is limited evidence that these may accelerate tooth movement.

Final comments

We now have to consider how we interpret this information. To do this, we need to look at the strength of the evidence and the effect sizes. It appears we can have some confidence in the findings on surgically assisted orthodontics, which is reassuring. However, when we look at the effect sizes, they are still small. Therefore, we have to ask our patients whether they want a surgical procedure to reduce the length of canine retraction by only one month.

Most importantly, we need to consider that we do not know if the differences detected in canine retraction result in changes in overall treatment time. These studies are still lacking.

So, how does this leave us? It is up to you to decide. This is a complex problem. I still would not attempt surgically assisted orthodontists, but am I a simple old-fashioned orthodontist?

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