“Real-World” Evidence on Bonded Mandibular Retainers: Survival & Clinical Implications

The number of bonded retainer trials is increasing, and we are gaining evidence on this important aspect of orthodontic care. However, most of these trials are conducted in dental schools with inexperienced operators, which limits the generalisability of their findings. This new study was carried out in a specialist orthodontic practice and provides us with valuable, clinically relevant information on different retainers.

The study team evaluated several retainer materials and bonding methods.

A team based in London and Dublin, Ireland, did this study.  The AJO-DDO published the paper.

What did they ask?

They wanted to find out.

“What was the 2-year survival rate of bonded mandibular retainers using three different fabrication methods”?

What did they do?

They did a single-centre parallel-designed randomised clinical trial. The PICO was.

Participants

The team recruited three hundred orthodontic patients from a single specialist orthodontic practice from November 2017 to December 2021. All participants had had comprehensive orthodontic treatment with a pre-adjusted edge Rice system

Intervention one

A chair side made and directly bonded 0.03 x 0.01 Ortho Flex retainer.

 Intervention two

Laboratory-fabricated and indirectly bonded multi-strand retainer.

Intervention three

A laboratory made and directly bonded Blu-Elgiloy fixed retainer.

Outcomes

The primary outcome was time to bonded wire failure. Secondary outcomes were patient-reported outcome measures.

They used a pre-prepared randomisation. They concealed the allocation using sealed envelopes. It was not possible to blind the operator or participant to the type of bonded retainer. However, they assessed the outcomes blind.

They collected data when the bonded retainers were fitted, and reviewed the patients at six weeks, six months, 12 months, and 24 months. An independent operator measured incisor irregularity at the start of retention and after 12 months.

They did a clear sample size calculation based on previous research. They also used relevant statistical analysis, including the Kaplan-Meier calculation, to determine survival curves for the various interventions.

What did they find?

The study involved 300 participants and they randomised them into three groups. 88% of the participants returned after 24 months.

They found that the 24-month survival rates were 68% for the multistrand wire, 96% for the Ortho Flex, and 92% for the Blu-Elgiloy.

There was no statistically significant difference between the Ortho Flex and the Blu-Elgiloy.  Both performed better than the multistrand wire, and the difference was statistically significant. It was clear that this difference was clinically important. 

When they looked at Little’s index, they found that there was a minor relapse in all three groups in the region of less than a millimetre. None of these were statistically significant.

The overall conclusion was

“The Ortho Flex and the Blu- Elgiloy performed better than the multistrand retainer in terms of retainer survival time. There were no other significant differences for the patient-reported outcomes and incisor relapse”.

What did I think?

This was a well-done and clearly reported study in a high-quality journal. It was very interesting that the referral rates were different between the three interventions. The results of the study certainly emphasised that the multistrand retainer was not as effective as the other two retainers that they tested.

The authors drew attention to the fact that the failure rates of the retainers were similar to those of other studies. However, for the Ortho Flex and Blu-Elgiloy, their performance was superior to other trials. This may be because an experienced operator fitted the retainers. This is in contrast to other studies in which inexperienced operators working in dental schools carried out the bonding. Other differences may be due to the physical properties of the retainers.

As with all studies in orthodontics, there was a dropout rate that may be considered high. Nevertheless, this is the best that we can do, and the authors should be congratulated on completing this study.

Final comments

There is no doubt that this study provides us with valuable clinical information. Importantly, this was done in a specialist practice, so the findings are relevant to the setting in which most orthodontic care is delivered. I cannot help thinking that all orthodontic trials should be done in this setting. But this adds yet another challenge to orthodontic researchers!