Fixed retainers fail a lot! A new trial
Retention is one of the most important parts of orthodontic treatment. Surprisingly, we do not have a substantial body of evidence to help us decide our retention regimes. This new trial shows that there is a high level of failure of bonded retainers. It made me think about my retention regimes.
Retention is a “hot topic” in orthodontic treatment at the moment. We need more high-level research into methods of retention. Importantly, these studies need to report on long-term outcomes. The investigators in this new trial looked at important outcomes two years after placing retainers. A multinational team from Poland, Switzerland, and the Czech Republic wrote this paper. The AJO-DDO published it.
What did they ask?
They did this study to answer this question;
“Are there any differences in survival time and periodontal health when using a round or rectangular wire fixed mandibular retainers”?
What did they do?
They successfully did a randomised controlled trial with a parallel-group 1:1 allocation. The PICO was
Participants: Orthodontic patients who needed fixed mandibular retention from canine to canines. One private office did the treatment.
Intervention: Fixed retainer made from 0.0265X0.016 inch 8 strand rectangular braided wire.
Comparator: Fixed retainer constructed from 0.0215 inch round wire
Outcomes: First-time failure and periodontal health.
The retainers were all placed by one experienced operator. The investigators collected data when they placed the retainers at 3, 6, 12,18, and 24 months after placement. They recorded the time to failure and periodontal health with the Periodontal Index, Bleeding On Probing, and Plaque Index.
They used pre-prepared block randomisation and concealment in sealed envelopes. Then, the study coordinator opened the envelopes. This method is a high level of concealment from the operator.
They could not collect the data blind. This issue is important, and I shall return to this later.
What did they find?
They enrolled 133 participants in the study and analysed data from 132.
They found that there was a high failure of retainers in the two years of the study. For example, 37 (56.1%) of the round wire group and 32 (48%) of the rectangular wire had a retainer failure. However, there was no clinical or statistically significant difference between the two interventions.
When they looked at periodontal health, there were no differences between the groups for all the indices. But importantly, they found that periodontal health was good and not influenced by the retainers.
What did I think?
I thought that this was a very nicely done and written-up trial. The authors and the journal used the CONSORT guidelines, which made it easy for me to interpret the findings. If you can access the paper, it is well worth reading it.
The most surprising finding was the very high failure rate of the retainers. We also need to realize that the authors only looked at lower retainers. As a result, I wonder if the failure would be higher if they had included upper retainers? When I think about my clinical practice, I am sure that my retainer failure rate was not this high.
The authors discussed this finding in detail. Their most compelling reason for this finding was that they meticulously looked for any failures in this trial. Furthermore, other studies were retrospective and subject to selection bias. Finally, they felt that other trials reported similar failure rates. However, I could not find a reference for this statement?
I also thought that it was a shame that they did not record any harms from the retainers. For example, unwanted tooth movements. Nevertheless, it was great to see that they are doing this in a longer-term five-year follow-up of these patients.
The authors reassured me that the retainers did not affect the periodontal measurement, which adds to the evidence on this important possible effect of long-term retention.
The results of this trial certainly made me think about fixed retainers. When I was working, I tended to use VFRs because I was concerned about periodontal health and failures. However, this has a “trade-off” of relying on cooperation. Nevertheless, this trial provides us with very useful information on our retainers, and it is a valuable piece of research.
Emeritus Professor of Orthodontics, University of Manchester, UK.