Does anchoring a fixed functional appliance to the mandible have an effect?
Does anchoring a fixed functional appliance to the mandible work?
After all the excitement of last week’s post I’m going to return to a simple review of a recent randomised trial on the effects of anchoring a fixed functional appliance to the mandible. It was published in the Angle orthodontist; so it is open access.
Elkordy et al
Angle Orthodontist: Advanced access
I think that it is now well established that most of the changes that occur with fixed or removable functional are dento alveolar with some minor skeletal change. Furthermore, a large component of the overjet reduction is due to proclination of the lower incisors. This may be particularly marked with fixed functional appliances because they are tooth bourne. This type of tooth movement is unwanted, as it may be unstable and attempts have been made to minimise this effect. These investigators carried out a study to find out if fixing the mandibular component of the fixed function appliance to the mandible resulted in reduced lower incisor proclination and increased skeletal change.
What did they do?
They carried out a randomised clinical trial in which a total of 36 young people with Class II malocclusion were randomly allocated to receive treatment with either
- Forsus appliance
- Forsus appliance fixed to the mandible with mini screws
- Untreated control (Delayed treatment for 6 months)
They carried out a sample size calculation, randomisation and allocation concealment were good. The patients were bonded up with MBT brackets until levelling and alignment were complete. They the fitted the two variants of the Forsus appliances.
They took Cone Beam CT images at the start of treatment and when the overjet was fully reduced for the treatment groups. While for the control group they took CBCT at the start of the observation period and after 6 months. The study had full ethical committee approval.
The outcome measures were restricted to cephalometric measures derived from the cone beam CT images. Their statistics were very simple involving comparison of many cephalometric measurement with the high risk of false positive due the multiple comparisons of related measurements.
What did they find?
Their first finding was that the appliance corrected the incisor relationship for 88% of the patients. But then they went into a massive mind numbing cephalometric festival comparing many measurements at different time points. I also thought that it was strange that they did not really compare the treatment with the control group. I was really disappointed to see this because it was almost impossible to identify the effects of the treatment. After a lot of work, I managed to come up with these values to summarise the effects of treatment within the treatment/control groups.
|Difference (means, 95% CI)||-1.08 (-2.16, 0.00)||-0.52 (-0.73, -0.3)||1.45 (0.43, 2.47)||-4.82 (-5.83, -3.8)|
So to summarise.
- The upper incisors retroclined
- The lower incisors proclined but less in the Forsus with mini implant anchorage by 4 degrees.
- The upper molars were moved distally
- There was no effect on ANB or mandibular growth.
What did I think?
I thought this was a fair study. However, I was very disappointed to find that there were so many cephalometric measurements. This made the paper very difficult to read and I really wish investigators would limit the number of cephalometric variables that they are measuring. I am sure that no one looks at the massive tables of data. In fact, I even wonder if the journal editors and referees look at them! I have discussed this previously in this blog.
I was also confused on the discussion because the authors stated that there were skeletal changes with treatment but I think that they were comparing the before and after treatment values. When I looked at the data and tried to compare the treatment with the control, I could not find clinically significant differences.
In their discussion, they did not really discuss why they did not detect greater growth modification with the functional appliances compared to the control, particularly with the Forsus retained by mini-implants. However, I did spot that the implants were bonded to the mandibular canines ( see figure). This made me wonder whether some of the force was transmitted to the lower arch resulting in incisor proclination. Alternatively, this could also illustrate that no matter what you do you cannot increase mandibular growth?
In summary, this was an interesting trial. However, the authors fell into the trap of presenting a large amount of cephalometric data which made the paper very difficult to interpret. It certainly is not an “easy read”. Nevertheless, I think this still goes some way towards reinforcing other research that suggests we cannot really alter skeletal growth with our appliances.
Emeritus Professor of Orthodontics, University of Manchester, UK.