What is better, The Twin Block or the Frankel 2: A RCT
When I was a specialist trainee our first choice functional appliance was the Frankel 2. We hated them because they were difficult to use and always seemed to be breaking. So, we switched to the Twin Block because most other orthodontists in the UK were using this appliance. Since then I have always used the Twin Block to treat Class II malocclusion. This decision was not evidence-based and it is interesting to now see a new trial that compares the Twin Block and the Frankel. The results are very interesting and not what I expected.
A team from Cork, Ireland did this study. The Angle Orthodontist published it. As usual from the Angle is it open access.
Ciara Campbell et al. Angle orthodontist: Advance access.
What did they ask?
They did the trial to answer the following primary question:
“Is there a difference in Phase I treatment duration between the Frankel 2 and the Twin Block appliance”?
What did they do?
They did a single centre randomised clinical trial with two parallel groups. The PICO was:
Participants: Orthodontic patients aged 11-14 years old with an overjet of at least 8mm.
Intervention: Frankel 2 appliance
Comparator: Twin Block appliance
Outcome: Primary outcome was treatment duration. Secondary outcomes were PAR scores and several quality of life measures.
They used a standardised design for both appliances. They asked the participants to wear the appliances full time. Data were collected at the start of treatment and when the operator felt that a Class I incisal relationship had been obtained.
They did a sample size calculation based upon treatment duration. They did pre-prepared block randomisation with an allocation ratio of 1:1, this was concealed using sealed envelopes. Neither the operators or the patients were blinded to the allocation. However, the data was recorded and analysed blind.
They carried out the relevant multivariate analysis. This enabled them to take the effect of any confounders, such as gender, start malocclusion etc. into account. I thought that it was good to see that they did an Intention to Treat analysis. This meant that all participants were included regardless of the outcome or whether they completed treatment.
What did they find?
60 participants entered the trial. They allocated 30 to each group. At the end of the trial period, 20 of the Frankel group and 22 of the TB group completed the trial.
There were no differences in the groups at the start of treatment. At the end of the functional appliance treatment, there were no differences in the drop out rates or the final overjet. They did not detect any harms.
When they compared the effects of treatment. The mean treatment duration was 376 days (SD=101) for the Frankel group and 340 days (SD=102) for the TB group. This was not statistically significant.
When they looked at breakages, the mean number were 4 for the Frankel and 5 for the TB. Again this was not statistically different.
Finally, there were no differences in the PAR scores or any of the quality of life measures.
In effect, the two appliances performed the same.
Their overall conclusion was:
“Phase I treatment duration, number of appliance breakages, occlusal outcome and patient and patient perspectives were similar for the FR2 and the TB appliances”.
What did I think?
I thought that this was a well-done and reported trial that answered a clinically relevant question. The trial methodology was sound in all aspects. Importantly, the sample size was large. Furthermore, they analysed all the data with an intention to treat analysis (ITT)
My only concern was with the drop out rate. Even though they did an ITT, I cannot help wondering if the results would have been different had all the patients completed the study. However, this was a “real world” study and not all our patients complete treatment. Importantly, the dropout rate that they reported was similar to other studies. As a result, I can conclude that this study has considerable validity.
The results of this study make me wonder about my decision to switch from the FR2 to the Twin Block. My main reason was that I was concerned with the breakages of the FR2. This research does suggest that this was not an evidence-based decision.
However, I soon became keen on the Twin Block because of its clinical simplicity. In effect, my preferences governed my treatment decisions.
What do our patients think?
Finally, we need to consider our patient’s preferences. I thought that it was interesting that there were no differences in oral health quality of life between the appliances. However, this questionnaire was not specific to the discomfort and hassle of the two appliances. I would have liked to see the investigators obtain data on this aspect of treatment. It would undoubtedly have given us useful information that may influence our decision on which appliance is preferred by our patients. But, overall, this was an exciting and clinically relevant study.
Emeritus Professor of Orthodontics, University of Manchester, UK.