How long should patients wear their retainers?
It is great to see an increasing amount of research into retention. This new study looked at the effect of different wear times of retainers on the amount of relapse. It reinforces clinical opinion and provides us with practical, clinically relevant information.
We know that part-time wear is as effective as full-time retainer wear. But we do not accurately know how long our patients wear their retainers. Therefore, the investigators used thermal timing devices to answer this question in this study.
A team from Denizil, Turkey, did this interesting study. The Angle Orthodontist published the paper, and it is open access!
What did they ask?
They did the study to
“Find out whether long or short wear times of removable retainers are effective for the maintenance of stability”.
What did they do?
The team did a prospective cohort study by enrolling 47 patients aged between 15 and 25 years.
The inclusion criteria for the participants were:
- They completed fixed appliance treatment with four premolar extractions.
- The final occlusion was good.
All the patients received upper and lower vacuum-formed retainers. In addition, they fitted a Theramon timer into the lower retainer.
The operator asked all the patients to wear their retainers for 20-22 hours per day. The patients attended the clinic every 8 weeks, and the team collected data from the Theramon sensors.
They calculated the mean daily wear time at the end of the study period.
Finally, the investigators collected Irregularity Index data, arch widths, arch length, overjet and overbite from 3D models. This data was collected before treatment (T0), at debonding (T1), 6 months later (T2), and 12 months after debonding (T3).
What did they find?
The mean daily wear time was only 9.24hrs/day for all the patients. They then divided the patients into two groups according to their wear time. The short wear time group wore their retainer less than 9 hours per day, and the long wear time group (>9hours wear per day).
Five patients dropped out of the study. The reasons were 2 requested leaving, 2 lost their retainers, and 1 had no data. This left 20 in the SWT and 22 in the LWT groups.
There were no statistically or significant differences between the groups. However, they found a more significant irregularity in the SWT (LII = 2.37) than the LWT (LII= 1.0) group in the mandible. However, the effect size was only 1, which may not be clinically significant.
Their overall conclusions were:
“There were no significant differences between the wear time groups for maxillary irregularity, transvers measurement, overjet, overbite and arch length after 1 year of retention”.
“There were differences in mandibular irregularity between the groups. However, the effect size was small”.
What did I think?
This cohort study revealed some interesting and clinically relevant findings. Firstly, I was surprised to see that the patient’s co-operation was very poor. This was far below the hours that the operators recommended. Other investigators have found similar problems with the wear time of Twin Block appliances. This does make me wonder whether any of our patients comply with our instructions? It also raises issues about the effectiveness of part-time wear of appliances.
When I looked at the relapse data, I wondered about the wear time of the retainers. This was that even part-time wear of vacuum-formed retainers seemed to be effective. This is reinforced by studies that have looked at night-only retention and shown that this is effective. So perhaps we are concluding that retainer wear of only 9-10 hours at night is sufficient to retain in the short term. This is certainly supported by the results of some randomised trials.
We do need to consider the shortcomings of this study. The sample size was small, the retention period was short at 12 months, and I would have liked to see a regression analysis that treated wear time as a continuous variable.
Nevertheless, I feel that this study does add to our knowledge about the wear time needed for retainers. It is up to you to decide if this influences your recommendations to your patients.
Emeritus Professor of Orthodontics, University of Manchester, UK.