A new trial shows us how functional appliances work.
We all know that functional appliances are great at treating Class II malocclusion. This new study provides us with further information on how they “work”.
Many researchers have looked at the effects of functional appliances on Class II malocclusion. The results of the trials have been consistent in their findings. In short, they report that the main effects of this form of treatment are dento-alveolar with some small skeletal change. These findings have been incorporated into systematic reviews, and the evidence for these treatment effects is becoming stronger.
This recently published trial adds to this evidence. It is concerned with the treatment effects of carrying out a 15-month course of functional appliance treatment. A team from the beautiful South of England did this trial. The EJO published the paper.
What did they ask?
They did this trial to answer this question.
“What are the treatment and post-treatment changes of Twin Block or Dynamax treatment over an extended period of appliance wear”?
What did they do?
They did a parallel-group two-arm randomised trial. The PICO was
Participants: Caucasians aged 11-13 years old with overjets of greater than 7mm.
Intervention: Dynamax functional appliance
Control: Twin Block functional appliance
Outcome: Skeletal differences between the groups measured by cephalometric analysis.
They did pre-prepared randomisation that they concealed in sealed envelopes. The sample size was based on changes in lower facial height. They recorded and analysed the data blind.
I thought that their treatment protocol was interesting, and I am going to describe it in detail.
- At the start of treatment, they took a cephalogram (T1)
- They asked the patients to wear their appliance full time for 15 months. This is longer than the “normal” functional phase of 9-12 months. At the end of this period, they took another cephalogram (T2). Importantly, they then stopped functional appliance treatment, and after three months, they reassessed the participants.
- They then treated the participants according to standard protocols.
- They took final stage records after another 12 months. This equated to 30 months from the original records and 15 months from the completion of the functional phase of treatment.
At this final stage of record collection, all the treatment had not been completed. However, the authors argue that at this point, there is unlikely to be any additional skeletal change.
What did they find?
They asked 150 patients to take part in the study and 78 were allocated to Twin Block and 72 to the Dynamax groups.
68 (87%) Twin Block and 61 (84%) of the Dynamax patients completed the 15-month functional phase of treatment.
At the end of the study, there were 52 (66%) Twin Block and 48 (66%) Dynamax patients with full records.
I extracted relevant data from the start of the study to 15 months into this table.
|OJ reduction (mm)||7.0 (6.-7.7)||5.8 (5.2-6.5)||0.0|
|Retroclination upper incisors (deg)||5.8 (2.9-8.6)||5.7 (2.4-8.9)||0.97|
|Proclination lower incisors (deg)||5.3 (4.0-6.7)||5.4 (3.6-7.1)||0.96|
|A point (mm)||0.8 (0.3-1.2)||0.2 (-0.3-0.6)||0.06|
|Pogonion (mm)||3.5 (2.8-4.2)||1.7 (1.1-2.3)||0.001|
When they looked at the changes from 15 to 30 months, there were some small differences in upper incisor angulation. The lower incisor retroclination for the Twin Block group relapsed by 2.9 degrees for the Twin Block and 3.4 degrees in the Dynamax. Finally, when they looked at mandibular length, the Twin Block group had less mandibular growth (0.7mm) than the Dynamax group (1.8mm).
In summary, they concluded.
“During the first 15 months, the patients treated with the Twin Block showed greater reduction in overjet and skeletal change for all measurements apart from A point. However, at the final record collection, most differences disappeared except for a difference of 0.6mm in mandibular length”.
What did I think?
I thought that this was an ambitious and complex study. They carried out the trial well. As with all trials, there are some areas that we can criticise. I will only mention the major ones. Firstly, the drop out rate at the end of the study is rather high. This means that a fair amount of data has been lost. However, there are no differences in the number of participants between the groups, and this reduces risk of bias. Furthermore, we must also appreciate that this final response rate is good for an orthodontic trial with difficulties caused by the long term nature of the study.
I was also a little unclear why the final data collection was done at 30 months and not at the end of all treatment. I wonder if the records had been collected at the end of treatment, whether this would have given us better information on the effects of the complete course of treatment?
However, if we bear these concerns in mind. This trial does add to the evidence. Importantly, this is another trial that illustrates that most of the effects of functional appliances are dentoalveolar with minimal skeletal change. When there are skeletal changes, these then “wash out” with growth. This reinforces the concept of a “mortgage” on skeletal growth, and at the end of treatment, minimal growth change has occurred.
In general, I thought that this was an excellent trial that added to our knowledge about the effects of functional appliances.
Emeritus Professor of Orthodontics, University of Manchester, UK.