Headgear influences dental arch dimensions. Or does it?
I am under the impression that less headgear is being used as orthodontic treatment techniques evolve. But are we discarding an effective treatment? This trial provides us with useful information.
I have not used headgear for ages. This is mostly because the children of inner-city Manchester were not “keen” on it. Nevertheless, some operators in the UK and other countries use headgear as an essential part of their treatment. This is particularly true of the Scandinavian countries (I think?). This is relevant in interceptive treatment. A team from Finland did this study. The EJO published their paper.
Johanna Julku et al
European Journal of Orthodontics, Advanced access. DOI 10.1093/ejo/cjy083
They have published several papers on this study and I have written about them previously when they reported on the effect of HG on the airway.
What did they ask?
They did the study to find out whether the timing of cervical pull headgear had an effect on dental arch dimensions. They also wanted to look at any influence of the gender of the participants.
What did they do?
They did an interesting randomised trial. They screened healthy 7-year-old children in school. To be included in the study the children had to have a Class II malocclusion based on molar relationship and an overjet of 6mm or more. They found that 67 children were eligible for the study and they all agreed to take part.
The PICO for the study was:
Participants: 7-year-old children with Class II malocclusion
Intervention: Cervical pull headgear with 500g force used for 8-10 hours per day.
Control: No treatment and then Headgear when they were older.
Outcome: Upper and lower arch measurements.
In effect, this study was similar to the other Class II studies where an intervention (HG) was either provided early or at a later age. They randomly allocated the children to early headgear treatment at aged 7 or HG 18 months later.
They collected data from study casts at the following stages of treatment.
T0: At the start of the study
T1: After 18 months of HG treatment or observation
T2: After 24 months of treatment for the later treatment group.
I was not sure if the “earlier” treatment group had any treatment between T1 and T2?
They made several measures of dental dimensions on the dental casts.
Their power calculation was not too explicit as they did not state what outcome measure that they based this on. This suggested that the sample size should be 11 in each group. However, they enrolled three times this number of participants. This could result in a study being overpowered and lead to statistically significant findings when the effect size is small (see later).
What did they find?
67 participants started the study. After five years, 56 completed the study. The groups remained balanced, and this should not lead to bias.
So that I can be brief, I have decided only to report and discuss two of the measures that they made from the casts. These are the distance from the canine tip to the distobuccal cusp of the first molar and the distance between the lingual/palatal surfaces of the first molars. If you want to look at the paper, there are many more measurements for you to look at.
This table contains the relevant data at the end of the study for the dental measurements in mm with 95% confidence intervals.
|Canine to Molar||Intermolar||Canine to Molar||Intermolar|
|Early Group||27.7 (27.2-28.2)||53.6 (52.5-54.7)||27.8 (27.2-28.3)||33.1 (32.2-33.9)|
|Change from start||1.3||2.4||-1.2||1.1|
|Later Group||27.5 (26.8-28.2)||52.3 (51.2-53.3)||25.9 (25.1-28.3)||31.5 (30.4-32.5)|
|Change from start||0.7||1.8||-1.7||0.3|
This data is tricky to interpret. But the best way is to look at the effect sizes and decide if you feel that they are clinically significant. Then look at the 95% confidence intervals. There are two things to look for here. Firstly, if they overlap there is unlikely to be a statistically significant difference. Then look at the range of values if these are wide then there is a degree of uncertainty in the data. I did this, and I felt that the effect of the treatment was small and not clinically significant. The CIs were tight, and so there is some certainty in the data.
When I looked at all the data, there were several instances of small effect sizes being statistically significant and this may be a result of the high power in this study.
Their overall conclusions were:
- Cervical Headgear treatment was effective in widening the maxillary dental arch
- There was a natural expansion of the lower arch.
What did I think?
This is an excellent trial that and was carried out well. However, when I look at the effect sizes, I am concerned that these are rather small. As a result, I am not sure about their conclusions. But I will leave this for you to decide.
I have reviewed this trial before, and it was difficult to build a total picture of the effects of the headgear treatment because they have reported this study the in several papers. I have looked back at these. The most comprehensive report they published was on the impact of the headgear on the skeletal pattern and the airway. I felt that this showed that there were minimal effects of the headgear on the skeletal pattern, with an effect size of 1.2 degrees on SNA. Furthermore, they also showed that there was no effect on the airway.
I cannot help thinking that when we consider all the results of this study, then we can conclude that cervical headgear therapy does not do too much? This is the real value of this study.
However, this may be the cynic in me and my bias against headgear? Maybe the inner city children of Manchester are right?
Emeritus Professor of Orthodontics, University of Manchester, UK.