A new study shows that sandblasting decreases bonded retainer failure rate: an RCT

There have been many recent studies on the effectiveness of orthodontic retainers. As a result, we are getting a substantial body of good clinical evidence on their use. However, trials consistently show a high failure rate for bonded retainers. Consequently, researchers are conducting more research to find ways to address this issue. One approach involves considering sandblasting the enamel surface as part of the bonding protocol. This study examined the effectiveness of this method.

A team from Strasbourg, France, did the study. The AJO-DDO published the paper.

What did they ask?

They did this study to

“Compare the debonding rate of mandibular fixed retainers at 18 months after two different enamel preparations before enamel etching”

What did they do?

The team did a 2-arm parallel-sided randomised single-centre clinical trial with a 1:1 allocation.  The PICO was

Participants

Orthodontic patients aged greater than 11 years who had finished two arch fixed appliance treatment.

Intervention 1

Bonded 3/3 retainers constructed from 0.0215 multistrand wire. Prior to bonding the teeth were polished with pumice.

Intervention 2

The same design of wire retainer. The operator sandblasted the teeth before etching.

Outcomes

First time bonding failure during an 18-month follow-up. Secondary outcomes were wire fractures and unexpected tooth movement.

They followed up the patients every 3 months after bonding for 18 months.

The sample size calculation was based on detecting a 29% difference between the two interventions using data from another study. This required a sample size of 88 patients.

They used a pre-prepared remote randomisation, and the allocation was concealed from the operator during eligibility.

It was not possible to blind the operator or patient to the treatment allocation. However, the clinical outcome data collection was blinded.

They used Chi-squared and Kaplan-Meier survival analysis to evaluate the data. This was appropriate.

What did they find?

Eighty-eight patients were enrolled, with a median age of 16.5 years. 6  dropped out of the sandblasting group, and 2 in the pumice group were lost to follow-up.  As a result, they analysed 44 patients in the sandblasting and 38 in the pumice group.

At the 18-month data collection, the first-time failure rate was 7.9% in the sandblasting group and 25% in the pumice group. This was statistically and clinically significant.

There was no effect of gender on the failure rate.

When they looked at unwanted tooth movements, they found these in 9.8% of the sandblasting group and 4.7% of the pumice group. This was not statistically significant.

Their conclusion was

“After 18 months of follow-up, enamel preparation by sandblasting before acid etching showed a statistically and clinically significant threefold reduction in the failure rate of mandibular fixed retainers”.

What did I think?

This was a very good, simple trial that was conducted well. The paper was clear and well-written. 

It was encouraging to see a clear improvement in the success rate of the retainers placed in the sandblasting group. This indicates that we should consider incorporating this step into our bonding protocols. Importantly, the duration of follow-up was longer than most bonded retainer studies. As a result, this study does have generality. While we would like to see longer follow-up in this type of study, this is probably the longest we can get without a high number of dropouts.

It was also interesting that the failure rate for the pumiced group was high. This appears to be a common feature of retainer studies, as we all believe that our failure rates are much lower than the 25% reported here. Simon Littlewood addressed this in a post on this blog, and his comments are valuable.

If I were still working in the clinic, I would probably buy a sandblaster. However, I still think my failure rates were low!