Headgear does not harm the airway? A new trial
The relationship between orthodontic treatment and the airway is an area of controversy in orthodontics. This recently published trial may provide us with some answers to this question.
One of the newly discovered benefits of orthodontic treatment is to improve children’s breathing. I have written about this previously. The basic premise that is put forwards is the protractive forces on the maxilla result in an increase in airway volume. Paradoxically, retractive forces from headgear or retraction of upper incisors restrict the tongue and/or airway. This then causes sleep disordered breathing and other problems. While this area is clearly important. There have been no clinical trials into this “pathology” and most of the evidence is at the level of case report and personal opinion.
In many ways, we may have lost opportunities to study this question. For example, the investigators in the “classic” early Class II treatment studies did not evaluate the airway. When we designed our study, we did not even consider that treatment would influence the airway. This is probably because this problem had not been identified in orthodontic patients.
I was, therefore, very interested to see this new study. This looked at the effect of cervical pull headgear on the skeletal pattern and the airway.
A team from Oulu, Finland did this trial. The EJO published the paper.
Johanna Julku, Kirsi Pirilä-Parkkinen, and Pertti Pirttiniemi
European Journal of Orthodontics, doi:10.1093/ejo/cjx088
They asked whether
“The timing of cervical headgear treatment had an effect on pharyngeal airway dimensions”.
What did they do?
They did a parallel group controlled trial with a 1:1 allocation. The PICO was:
Participants: 7 year old children with Class II occlusion with overjets greater than 6mm and a deep bite. The investigators identified the children from a school screening programme.
Intervention: Standard cervical pull headgear when the patients were approximately 7 years old. This was the early treatment group.
Comparison: No active treatment. They observed this group for 18 months. After this time they treated them with cervical pull headgear. This was the later treatment group.
Outcome: Cephalometric analysis of hard tissues and airway dimensions. They collected this data at the start of treament (T0), after early headgear treatment/observation (T1) and when all the treatment was completed (T2).
The sample size calculation was fairly clear. Unfortunately, I was not clear on the effect size that they used.
They used a pre-prepared randomisation, allocation and concealment were done using sealed envelopes. They could not blind the operators and patients to the intervention. Nevertheless, the ceph analysis was blinded.
What did they find?
They randomised 67 children to the early and later treatment groups. Seven of the early treatment group and 4 of the later group did not complete the study. They did not do an Intention to Treat analysis.
They presented their data in two massive cephalometric tables and analysed many variables. We need to be careful when we interpret this data because of the risk of finding statistical significance by chance because of the testing of multiple related variables.
I do not have the space to go through all the variables that they measured. However, in summary, they found the following
1 There was greater posterior movement of the maxilla in the early treatment patients. The mean difference between the early and later treatment groups for SNA was 1.2 degrees. They reported similar effects for ANB. These are small differences and I am not sure that they are clinically significant.
2 When they looked at the pharyngeal measurements, they did not find an effect of the headgear treatment.
1 Cervical pull headgear effectively corrected Class II malocclusion
2 The headgear treatment did not have an effect on airway dimensions.
What did I think?
This was a well carried out and very ambitious trial. The authors reported it well and wrote a clear discussion on their findings.
As with all studies, there are problems. We need to look at these closely so that we can decide on how confident we are with the studies findings.
The first, and most important, issue is the choice of cephalometric measurement as an outcome measure. This, of course, means that they could only measure the airway in two dimensions. As a result, many clinicians may not accept these findings. However, when they started the study, I am sure that CBCT imaging would expose the children to high levels of radiation and I am not sure that this would be justified.
The other issue is that they did not measure nasopharyngeal airflow as this is the most relevant outcome measure. Again, I think that this would be too resource intensive for this study.
Another important point that we need to consider is that the amount of “retraction” of the maxilla was small. I cannot see how this would have an effect on the airway.
I have thought about this carefully and I think that we should accept that this study is the best that we can get. It is certainly better than the current “evidence” that is based on a few case reports and personal opinion.
In summary, I feel that this paper adds to our knowledge. It is interesting that the findings do not support the current opinions and perceptions of those who are suggesting that retractive mechanics compromises the airway. This study also provides a model for future studies that should be carried out. Perhaps the myofunctional practitioners and the orthodontic physicians should get on with doing a study? Until then this is the best that we have got.
Emeritus Professor of Orthodontics, University of Manchester, UK.