As one of the most time-consuming steps, canine retraction takes up a majority of orthodontic treatment with fixed appliance therapy. For years, investigators and clinicians have tried to devise methods and techniques to reduce the time taken for canine retraction.

There are several factors that influence the time that is taken for canine retraction, including, the type of mechanics used, the material used for retraction, the type of spring used in friction mechanics, the type of tooth movement and anchorage.


Another important factor that has not been explored enough is the time that has elapsed between premolar extraction and the start of retraction.


There are a few studies, with contradictory results that do not give us clarity on whether retraction must be done right after extraction or only once the socket is healed in order to save time.


In today’s blog, we will discuss the following randomized controlled trial, where the authors set out to compare the mean canine retraction rate between healed and recently extracted site.



Comparison of mean canine retraction between healed and recently extracted site: A single centre, randomized control trial


Nazneen Rabia Zubair, Ambreen Afzal Ehsan, Hasnain Sakrani

APOS Trends in Orthodontics, 2021


What they did?


Designed a randomized controlled trial , and active-controlled trial with a 1:1 allocation ratio.


Patients who required first premolar extractions were selected.  The exclusion criteria comprised of smokers, patients above 30 years or below 15 years, patients with active local (oral) or systemic diseases and long-term medications and those who did not wish to participate.


The patients were divided into two groups. In the first group, premolar was extracted. This group was the ‘healed socket group’. One month later, the premolar on the alternate quadrant was extracted and this was the ‘recent extraction group’. One week after the extraction in the ‘recent extraction group’ was carried out, retraction was started. The type of mechanics employed was sliding mechanics using NiTi closed coil springs.


The duration for which the rate of canine retraction was assessed was one month.


They recorded the distance in millimetres from the distal surface of canine to the mesial surface of second premolar at the contact point.


What did they find?


The mean canine retraction rate (mm/month) was higher in the recent extraction socket. The difference was 0.45mm/ month, which was statistically significant. They also found that the mean canine retraction was higher for males when compared to females for both extraction sites. Similarly, in a younger age group the mean rate of extraction was greater for both groups.


Positive attributes to the study.


This is an important study, the results of which could change the way we, as orthodontists plan treatment for faster results. While the rate of canine retraction is known to be altered by a number of factors, there is still inconclusive evidence regarding the role played by the timing of extraction.


Previous histological studies show that there is a simultaneous, independent activation of teeth that are to be retracted, irrespective of the type of socket. In a histological study by Murphey, 1970 (10.1016/0002-9416(70)90086-2) it was found that retraction could not bend the distal inter septal bone and that osteoclastic resorption in compression areas was necessary to initiate significant tooth movement.


Clinically, however, the results of the current study prove that there was a statistically significant difference between the rate in two groups, which was 0.45 mm/month.  While the clinical significance of this is questionable, previous clinical studies (10.1093/ejo/19.6.711) have shown a significant difference in the rate of canine retraction between healed and recent extraction sites.


This was a randomized controlled trial, where allocation concealment and blinding were carried out.

This was also a split mouth and therefore, the selection bias was significantly low.

There was uniformity in the delivery of retraction force and distal tipping was minimized by using a full sized arch wire.


The sample size for the study was adequate. The authors had calculated sample size using a previous study.


While this study showed that there was a significant difference in the rate of canine retraction between recent and healed extraction sockets, there were some concerns regarding duration for which the retraction rate was assessed. The authors assessed the rate for a period of 1 month, which may have been inadequate, but the authors justify that this was done to avoid potential breakage.


The short duration does not tell us, whether the rate of retraction was consistent throughout the entire period of space closure.


Another limitation was that the difference in time between the healed and recent extraction socket was only a month, whereas it takes 100 days approximately for the formation of mature bone. (10.14219/jada.archive.1960.0152).

Despite this, there was a significant difference in the canine retraction rates between the two groups. Whether it is the regional acceleratory phenomenon (RAP) or distal bone bending that contributes to faster retraction is debatable. This could have been identified by evaluating the consistency of the rate of space closure.


Another aspect of retracting into a recent extraction socket that was not evaluated was the potential discomfort felt by the patient. Pain and other patient centered outcomes could have been evaluated.


The type of tooth movement, whether it was tipping, or bodily movement, the angulation of the root and anchorage loss were not evaluated. The measurements taken were from a dental cast alone.



While the results of this study indicate that retracting into a recent extraction socket can save treatment time – further evidence regarding the type of tooth movement, and the time taken for overall orthodontic treatment and the rate of space closure at the end of every appointment during the course of retraction is needed in order to bring about changes in clinical practice!