What did they ask?
They did the study to;
“Evaluate and compare the five year post treatment changes in the maxilla and mandible with two different retention protocols”.
What did they do?
They did a single centre two-arm randomised controlled trial with a 1:1 allocation.
The PICO was:
Participants:
Adolescents treated with upper and lower fixed appliances (MBT 0.022)
Intervention:
Upper VFR and lower fixed retainers.
Control;
Upper and lower VFRs
Outcome:
The primary outcome was Little’s Irregularity index. Secondary outcomes were other dental measurements and participants’ perceptions of their retainers.
They collected study casts at debonding (T1), after 6 months of retention (T2), after 18 months (T3), and after 5 years of retention (T4).
The clinicians asked the participants to wear their retainers full time for one week, then nightly only for a year. After one year, they reduced wear to every other night, and two years after debonding, they wore their retainers for 1-2 nights per week.
The fixed retainers were made from 0.8 hard ss wires bonded to the canines.
They carried out a sophisticated and relevant multivariate analysis. This included imputation of data for participants who did not complete the trial.
What did they find?
The authors reported a large amount of data. Therefore, I have decided to concentrate on what I felt were the most clinically relevant outcomes.
Firstly, the team randomised 104 patients into two groups of 52 participants. At the end of the study, 74 completed the trial. This was a dropout rate of 28%. Equal numbers of patients dropped out of each group. When they analysed the data, they used imputation techniques to obtain meaningful data for the dropouts. As a result, they did an intention to treat analysis for all the participants who started the trial.
These were the main findings:
- There was a significant difference in the LII between the fixed retainers and the VFR group in the mandible at the end of the study. This was a median difference of 0.6mm.
- Arch length decreased, intercanine width remained stable, but there was a significant decrease in the maxillary arch width of a median of 0.2mm.
- The participants were satisfied with their retention regimes. However, when they looked at self-reported compliance, they found that 72% of all patients were not wearing their removable retainers at 5 years.
- Finally, 7% of the fixed retainers failed.
The authors concluded.
“Anterior alignment in the mandible was more stable with a bonded retainer compared to a removable VFR after 5 years of retention”.
What did I think?
This was a nicely done RCT. Randomisation was well done in advance, and concealment was good. The team analysed and recorded the data blindly. They did a relevant statistical analysis, and the paper was clearly written. I thought it was nice to see such a well-done and reported trial.
This was another trial that suggested the advantages of bonded retainers. However, as I have discussed before, the main problem with bonded retainers is that we need to monitor them. When we consider the results of this trial, we have to appreciate that the amount of relapse is small. Importantly, we need to think about whether this was clinically significant. Only you can make this decision.
Final comments
My decision on the best retainer is still influenced by my clinical impression, and I will stick with VFRs. Nevertheless, the evidence of the superiority fixed retainers is mounting. I may change my mind as further trials are published.
There have been several good trials over the last couple of years and our evidence base is building nicely. Perhaps, Simon Littlewood (the Lord of retention) could take some time out from touring the World and update his team’s excellent Cochrane review on retainers? I would really look forward to this update.
