Which is better a bonded or a vacuum formed retainer? Here is a new trial.
One of the many controversial areas in orthodontic is our choice of orthodontic retainer. This new study gives us useful information.
I have posted on retention several times. I have concluded that there are disadvantages and advantages of the main types of retainer. However, in general the type of retainer we use depends upon our own and our patients choices. Nevertheless, there is not much information to inform these choices. I thought that this study goes some way to providing us with clinically useful information. A team based in the North of England did this new trial.
Incidentally, the North of England seems to be a hotbed of clinical trials in orthodontics. This may be a result of the weather.
The EJO published this new study.
Bonded versus vacuum-formed retainers: a randomized controlled trial. outcomes after 12 months
As usual, these very useful papers are behind the EJO paywall. The authors have also published this study in two parts. I have decided to incorporate them into one concise post. This makes it easier to read and reduces duplication.
The study team set out to answer the following question
“Is there any difference in the effectiveness, patient perception and periodontal outcomes of lower vacuum formed retainers (VFR) and lower bonded retainers (BRs)”.
What did they do?
They did a two arm parallel group RCT with a 1:1 allocation. Their PICO was
Participants: Patients completing fixed appliance therapy
Intervention: Upper and lower VFR worn at night only.
Comparison: Upper and lower BRs
Outcomes: Retainer survival, patient satisfaction measured by questionnaire, relapse measured by Little’s Irregularity Index and periodontal health
They carried out a good sequence generation, concealment and allocation via sealed envelopes. It was not possible to blind the patient or operator. Importantly, it was not possible to blind the person who was recorded the relapse from the dental models.
They recorded the data at the start of treatment and several time points. I am only going to discuss the data at the start and after 12 months.
I thought that it was great to see that they did an Intention to Treat analysis. This meant that they collected and analysed data for the participants who dropped out or failed to wear their retainers. They did the relevant statistical analysis.
What did they find?
They enrolled 60 participants. 30 were treated with BRs and 30 received VFRs. The groups were similar at baseline.
When they looked at stability, they provided a great deal of data. I have concentrated on the main findings. This table includes the amount of relapse measured by Little’s Index. They found that the data was not normally distributed so they presented this as the median and inter quartile range.
|Number of visits
|Chair time (mins)
They found that there was no difference in survival of the retainers in the maxilla. 63% of the BRs and 73% of the VFRs survived 12 months. However, in the mandible 50% of the BRs and 80% of the VFRs survived 12 months. This difference was statistically and clinically significant.
The data on patient satisfaction showed that more patients reported difficulty speaking and eating from VFRs and greater discomfort from BRs.
Finally, they showed that the presence of BRs increased levels of plaque, gingival inflammation and calculus when compared to VFRs. However, at 12 months the data suggested that there were no real implications for periodontal health.
The authors conclusions
Their overall conclusions were that when they compared BRs with VFRs:
- There was no difference in periodontal health
- No difference in relapse in the maxilla
- In the mandible the BR is more effective thant VFRs in preventing relapse
- No difference in the survival rate of the maxillary retainers. However, in the mandible the BRs had a higher failure rate.
- VR is easier to clean than the BR
- BR causes less speech and mastication difficulties
What did I think?
In summary, I thought that this was a nicely done study. They used good methodology and the findings were interesting. However, we need to be a little cautious in our interpretation because the sample size was based upon arch alignment changes. As a result, it may not have been sufficiently powered to detect any differences in the other outcome measures. This is particularly relevant when “no difference” between the interventions was detected.
Some may criticise the investigators for not measuring compliance with the VFRs. I feel that this step was not necessary as the intervention was the prescription of the retainer. If the participant did not wear the appliance this reflects the real world situation.
The study provided a lot of useful information. My feeling is that the BR has some disadvantages, for example, the high failure rate and the plaque and calculus retention. However, the VFR also has problems, for example, the patients reported that they had mastication and speech difficulties. Nevertheless, as they were asked to wear these at night, I wonder if this is a big issue. I also was not sure the difference in the relapse was clinically significant.
My favoured retention regime is VFRs at night only and this study reinforces my practice. But you can interpret this data to inform your retention protocols.
Emeritus Professor of Orthodontics, University of Manchester, UK.