Do orthodontic extractions lead to posterior positioning of the condyle?

Over the past year I have written several times about the recent research on orthodontic extractions. This new study attempts to find if extractions influence the 3D position of the condyle.

The debate on the effects of orthodontic extractions appears to be never ending.  There are proponents on both sides of the discussion. Interestingly, scientific research does not support most of the claims made by the non-extractionists.   One of these claims is that extractions and retraction of the incisors displace the condyles posteriorly.  A team from Cairo, Yemen and  Saudi Arabia did this study to look at this interesting question.

Three-­dimensional­ assessment­ of ­condylar ­position­ and­ joint­ spaces­ after­ maxillary­ first­ premolar ­extraction­ in­ skeletal­ Class­ II malocclusion.

MS Alhammadi et al

Orthodontics and Craniofacial Research: Advance access DOI: 10.1111/ocr.12141

They pointed out that most of the research into this problem is based upon the analysis of two-dimensional images.  As a result, they wanted to improve the quality of the data by using CBCT to image the condyles.

They set out to:

“Evaluate the effect of premolar extraction and incisor retraction on the TMJ”.

vervolg: Do orthodontic extractions lead to posterior positioning of the condyle?


What did they do?

They did a prospective study and the PICO was:

Participants:  32 patients aged 18-25 years with a skeletal Class II malocclusion with a protruded maxilla and “normal’ mandible.

Intervention:  Orthodontic treatment with upper premolar extraction and retraction of the incisors.

Comparison:  This was a “before and after” study.  There was not a control group.

Outcome: Position of the condyle.

They did a sample size calculation based on a change of 30% in the position of the condyle.

They collected CBCT scans and measured TMD status at the start and end of treatment.

What did they find?

They found that there was a statistically significant posterior positioning of the condyle following treatment.  This change in position resulted in an increased anterior joint space and decreased posterior joint space.  However, no participant developed TMD.

I have included the relevant data in this table.

A-P condylar position   5.77 (4.47-7.06) 6.82 (5.42-8.22)
Anterior joint space   3.1 (2.39-3.81) 3.9 (3.12-4.68)
Posterior joint space   2.78 (2.4-3.09) 2.23 (1.96-2.5)

You may spot that the 95% CIs overlap. However, this does not always mean the differences are not statistically significant.

What did I think?

I have thought a lot about this study because of their conclusions.  I shall discuss this in terms of the design, analysis and interpretation.

When I looked at the design I thought that it was good to see that this was a prospective study that collected all the data on the participants.  However, the sample size was rather small.  I also had some concerns about the data analysis because this was simplistic.  Ideally, they should have done a regression analysis. This would have taken into account features, such as, starting overjet, gender and amount of retraction.  All these are important variables.

However, my greatest concern is the absence of a control sample.  This could be patients who had been treated without extractions.  In fact, the inclusion of this group would be the only way to answer the study question.

My other concern is about whether the differences that they found were clinically significant.  I cannot help feeling that the differences were rather small with wide confidence intervals.  This means that there is a high level of uncertainty in the data.

What can I conclude?

While is is easy to simply dismiss the results because of the issues I have raised. I think that it is important that they were close to finding interesting information.  This study is not sufficiently powered to change practice.  Nevertheless, they investigated an interesting question that should be researched with larger and more robust studies.


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