Hang on to what you have got: A new trial on orthodontic retention.
We do not know the best method of orthodontic retention. This ambitious trial may help give us the answer.
Orthodontic retention is one of the most controversial areas in orthodontics. As a result, there are many methods of retention. However, we do not really know which is the best method of orthodontic retention.
This new study provides us with very useful information. A team from London, South of England did this study. The AJO-DDO published it.
Dalya Al-Moghrabi et al
Am J Orthod Dentofacial Orthop 2018;154:167-74
In their introduction, the authors mentioned that while there have been several trials looking at orthodontic retention, none of these had followed the patients for longer than two years. As a result, they set out to do a trial that looked at retainer performance over at least four years. This is very ambitious. Let’s see how they got on.
“What is the stability of treatment with fixed and removable retainers over 4 years”?
The secondary outcomes were gingival health and plaque accumulation.
What did they do?
This was a long term follow up of a previous study in which they looked at stability after 18 months. I have posted about this before. I thought that this was a good study.
The PICO was
Participants: 82 orthodontic patients who had completed treatment.
Intervention: Bonded retainer made from 0175 co-ax wire
Comparator: Vacuum formed retainer (VFR). They wore the VFR retainer for 6 months full time, nights only for another 6 months and alternate nights for a further 12-18 months.
Outcome: Little’s Index and various measures of periodontal health.
They did a good randomisation, sequence generation, allocation concealment, sample size calculation and relevant statistical analysis.
What did they find?
They enrolled 82 patients into the study. After 4 years, 42 of these remained in the study. This represents a 50% drop out.
The median increase in irregularity for the VFR group was 2.37mm and for the fixed group this was 0.85mm. The median difference was 1.64mm. They did not find any other effects.
When they looked at the periodontal outcomes. They did not find any differences between the retainers. However, they found that there was significant plaque accumulation and gingival inflammation for both types of retainers.
They also reported that the non compliance rate for the VFRs after four years was 67%.
Their conclusions were;
- Fixed retainers were more effective than VFRs.
- Both types of retainer were associated with gingival inflammation and plaque accumulation.
What did I think?
This was an interesting and ambitious trial. It was interesting to see that in their earlier report on these patients that there were no differences between the retainers. This suggests that as the retention period becomes longer, fixed retainers are more effective. This may be related to the high levels of non-compliance for the VFR group.
While this study was good. I am concerned with the high drop out rate. It was good to see that there was no difference in the drop out rate between the groups. Importantly, the study still had sufficient power.
Unfortunately, we do not know if the participants who dropped out were different from those who remained in the study. This is likely to lead to bias. For example, those who returned may have been concerned with their relapse. Alternatively, those who dropped out may have been very poor compliers with their retention. As a result, while there is bias, we do not know its direction.
Finally, we all know that long term follow up of our patients is very difficult. I feel that the authors should be congratulated on this study. Their findings are clinically relevant. Nevertheless, you should make your own interpretation of this study in light of the high drop outs that they reported.
Emeritus Professor of Orthodontics, University of Manchester, UK.