A new trial shows that retention may not be needed?
Retention is one of the areas of orthodontic care that is somewhat controversial. While we may know the best retention regimes. We do not know what happens if we do not retain our patients. This new trial looks at this question.
Several researchers have carried out good studies on orthodontic retention. These have looked at different types of retainers and/or the effects of full or part-time wear. These studies have provided us with evidence that we can share with our patients. However, the big question about retention is whether we need to retain our treatment? To answer this, we need to carry out studies that look at the effects of not providing retention. I was, therefore, really interested to see this trial that had a control group of patients who did not have any retention.
A team from Malmo, Sweden, did this trial. The EJO published it.
Sasan Naraghi et al. EJO advanced access. doi:10.1093/ejo/cjaa010
What did they ask?
They asked this simple question;
“Is orthodontic retention needed after orthodontic treatment for impacted maxillary canines and moderate crowding in the maxilla”?
What did they do?
They did a single centre randomised trial with two parallel arms and a 1:1 allocation ratio. The PICO was:
Patients who had at least one impacted or unerupted maxillary canine and moderate irregularity of the maxillary six anterior teeth of 4-6mm (measured by Little’s Index).
Upper removable vacuum formed retainer. They asked the patients to wear this for 22-24 hours per day for the first 4 weeks and then 10-12 hours per day.
No retention. They removed the archwires and left the brackets in place. Then after 10 weeks if there had been an increase in LI of higher than 3mm, they replaced the wires. If there had been no relapse, they removed the brackets.
The primary outcomes were change in a single contact point displacement and the sum of LI for the six anterior maxillary teeth. Secondary outcomes were changes in arch length, dimensions and rotation of teeth.
They collected data at the end of active treatment (T1) and 12 months later (T2). Impressions were taken at these points and converted to 3D scans.
They did an explicit sample size calculation, used a pre-prepared randomisation process and concealed the allocation with sealed envelopes. They did not register the trial before it started. Blinding of the operator and patient to the treatment allocation was not possible. However, the study casts were anonymised.
What did they find?
The study enrolment started in June 2013 and ended in April 2018. They randomised 32 participants to retention and 31 to no retention. Surgical exposure was carried out for 15 participants in the retention and for 19 in the no retention group.
In the no retention group, one patient had a contact point displacement of >2mm during the 10 weeks “interim” period. They discontinued the observation period and replaced the archwire to align the teeth.
When they looked at the amount of relapse after 12 months. The mean change in Little’s Index for the retention group was 0.4mm (95% CI=0.2-0.6), and for the no retention group, this was 1.3mm (95% CI=0.9-1.7). This was statistically significant.
They did not find any other significant differences between the groups for the other outcome measures.
Importantly, most of the changes occurred during the first 10 weeks of observation.
Their overall conclusion was;
“The changes in Little’s Index between the retention and no retention groups were statistically but not clinically significant. Since satisfactory clinical results 1-year post-treatment in the no retention group, retention does not appear to be needed”.
What did I think?
I thought that this was an excellent trial. I was particularly impressed with the way that they introduced and managed a no retention group. The concept of leaving the appliance in place and then replacing the archwires if relapse occurred dealt with the ethical issues that may be associated with no retention.
They did the trial well in terms of randomisation, concealment of allocation and blinding. Initially, I was a little concerned that the trial was not registered before it started. However, they started this study in 2013, and trial registration was not widely recognised at this point. This is important because registering a trial before it starts ensures that the investigators do not change the outcomes as the trial progresses. This is a definite source of bias.
I thought that the findings were interesting. They were also important because they showed that retention may not be necessary. However, we need to consider that these results may only be relevant to upper incisor/canine relapse. I am not sure whether we can extrapolate these findings and conclusions to lower incisor crowding.
This is an excellent study that certainly provides us with useful clinical information. Its design may also be used to inform future investigations into retention. I hope that this great team carries on their excellent work, and they continue to provide information that leads to changes in clinical practice.
Emeritus Professor of Orthodontics, University of Manchester, UK.