Which are best? Fixed or removable functional appliances….
Over the past few months I have covered several interesting and clinically relevant systematic reviews. I was pleased to come across this new review on the effects of fixed versus removable function appliances published in the European Journal of Orthodontics. Our choice of functional appliances is important and I hope that this review blog post can provide us with some good clinical information.
It is now many years ago that we carried out a multicentre trial that compared the Herbst and the Twin Block appliance. This can be found here. I was also one of the operators in the study and I learnt a lot about using fixed functional appliances. My personal experience was that the Herbst appliance was very effective but the trade-off was that we had major problems with breakages. As a result, several years later, my preferred appliance is still the Twin Block. This is my personal opinion reinforced by the results of our trial, but what does this new review tell us?
EJO Advanced publication. DOI: 10.1093/ejo/cjv086
This is another publication from the team at Queen Mary University, Whitechapel, London, South of England. Unfortunately, it is behind the impenetrable paywall of the European Orthodontic Society…
This was a nicely written paper. I thought that the literature review was particularly good and I recommend that anyone on a training programme should read this as it provides a great outline of functional appliance treatment. In addition to outlining the various advantages and disadvantages of the types of functional appliances the authors also pointed out that we need to move away from purely morphological measurements and include patient perspectives. I have covered this subject previously another blog posts.
Their objective was to provide evidence on the efficacy of fixed and removable functional appliances in terms of both morphological and patient centred outcomes and I felt this was very important.
What did they do?
They carried out a systematic review to high standards and they clearly stated the PICO.
Participants: Children less than 16 years old with Class II malocclusion
Interventions: Any type of fixed functional appliance
Comparison: Any type of removable functional appliance
Outcome measures: The primary outcomes were measures of skeletal, dento alveolar and soft tissue correction.
This review was carried out to a high standard as they only included randomised or nonrandomised trials. All the studies had to be prospective. It is important to work to this high level of selection criteria because this reduces the chance of selection bias that is inherent in retrospective investigations.
After their screening and application of selection criteria they identified four studies. They evaluated these studies with the Cochrane Collaboration risk of bias tool and provided a large amount of information on potential bias. They concluded that three studies were at high risk of bias and one was unclear. The most common reason for this allocation was unclear randomisation and allocation concealment.
I find it interesting that one of the studies they classified as “high risk of bias” was the Herbst vs Twin Blocks study that I carried out. In this study we reported that we had a greater dropout rate in the Twin Block group than the Herbst group. As a result, the authors classified study as being at high risk of bias. This is the correct conclusion from applying the Cochrane tool. However, it is important that this does not diminish one conclusion from our study in which we found that there was better cooperation with the Herbst appliance than the Twin bBock. Putting this aside, I will never forgive the authors for this classification!
More seriously lets look at what they found.
What did they find?
Firstly, two of the studies compared with the Twin Block and the Herbst appliance while the other two compared the Activator with the Forsus and the TFBC appliance. It was not possible to combine the data into a meta analysis because of differences in measurement between the studies. They did provide a lot of detail of relevant cephalometric measures that showed the effect of the appliances on dento alveolar and skeletal measurements (which were small). They concluded that all the variations of functional appliance successfully reduced the overjet to normal limits. There were also minor skeletal changes but as these were not compared to an untreated control group. We cannot, therefore, make any conclusions on whether the appliances changed the skeletal pattern more than normal growth.
They also stated that they were disappointed at the limited use of patient centred measures. They drew attention to our study in which we measured breakages and patient acceptance of the appliance. They also pointed out that our findings would have been viewed very differently if we had drawn greater attention to them in our paper. I completely agree, if I had my time again I would have emphasised the patient centres measures more. For example we showed that the Twin Block had a greater negative affect on speech, sleep patterns and schoolwork and the length of the treatment was longer than with the Herbst. Yet there were greater breakages with the Herbst appliance and it was more expensive. This information should be very useful when we are deciding on potential treatments with our patients.
What did I think?
I feel that this review does add to our knowledge, despite the limitations of the number of papers. I can conclude the following.
- There is little difference in the dental and skeletal effects of fixed and removable functional appliances.
- Most of the correction of the overjet is by dento alveolar movement, but there is a small amount of skeletal change (1-2mm).
- There is greater co-operation with fixed functional appliances but this is not 100%. There is no such thing as non compliance orthodontic treatment!
- Only one study reported on patient centred outcome and these should be included in all trials in addition to some cephalometric and dental measurements.
I will still stick with the Twin Block because of the cost and the additional time that is needed to deal with breakages with a fixed functional appliance.
Pacha, M., Fleming, P., & Johal, A. (2015). A comparison of the efficacy of fixed versus removable functional appliances in children with Class II malocclusion: A systematic review The European Journal of Orthodontics DOI: 10.1093/ejo/cjv086