Do premolar extractions influence the airway? A new systematic review.

The airway controversy in orthodontics is still ongoing. This is fuelled by claims made by airway-friendly orthodontists who are increasingly preying on the vulnerable. Lies, mistakes, or ignorance may drive their stance. One potential myth they propagate is that “the crime” of premolar extractions causes a restriction in the airway, leading to many problems. But what evidence do we have regarding the effect of extractions on the airway? This new systematic review may help.

This relationship between the airway and orthodontics is important. As a result, we urgently need to gather information. The authors of this new review suggest that they provide us with new information because they analysed data based on CBCT imaging.

I had a close look at this systematic review.

A team based in Switzerland and Australia did the research. The EJO published the paper. 

What did they ask?

They did this review to ask.

“Is there an effect on upper airway volume and the minimum cross-sectional area between those patients treated with and without bilateral premolar extractions as part of a course of orthodontic treatment”?

What did they do?

The team conducted a systematic review of the literature. This was registered before they started, and they followed the standard methodology.

I could not find a clear PICO in the methods, and so this is my interpretation.

Participants

Orthodontic patients who required fixed appliance treatment.

Intervention

Extraction of premolars as part of treatment.

Control

Non-extraction orthodontic treatment

Outcomes

Airway volumes and minimal cross-sectional area from CBCT images

The team did a literature search to identify randomised controlled trials, controlled clinical trials and retrospective studies.

They identified a final sample of papers and carried out data extraction, assessment of bias with the ROBINS-I tool and relevant meta-analyses.

What did they find?

After final filtering, they identified a final sample of 11 papers. All of these were non randomised retrospective studies conducted in university clinics and private practice. Regular readers will know the direction this post is heading!

Seven of the papers were in refereed journals, and four were dissertations.  Oh no, the level of evidence is falling like a stone!

The papers included data on 891 patients with an average age of 19.9 years with all types of malocclusion. In the extraction group, either two maxillary or four premolars were extracted.

The study team analysed the data with several meta-analyses and presented a large amount of data. I had a good look at this, including their detailed description of the data, and their extensive discussion. This suggested that extractions had no effect on any aspect of the airway dimensions. Except patients with extractions had an increased cross-sectional area of the oro-pharynx compared to those treated without extractions!

The strength of the evidence was moderate. This was mostly due to the inclusion of retrospective studies in the review.

Their conclusions were

“Limited evidence of moderate strength indicates that premolar extractions have little or no effect on the airway volume and minimum cross-section”.

What did I think?

Regular readers of my blog know that I have chosen to stop discussing systematic reviews unless they are of very high quality or cover significant clinical topics. However, I decided to discuss this particular paper because it addresses a controversial clinical area. Additionally, this research team has produced numerous systematic reviews.

It is disappointing that this review was limited to retrospective studies, which carry a high risk of bias. The team acknowledged this limitation. Furthermore, the main outcome measure was based on CBCT measurements and we know that these are not a good outcome measure for breathing disorders. We need to consider this when evaluating the usefulness of their findings.

It’s important to recognize that randomized controlled trials (RCTs) comparing extraction and non-extraction orthodontic treatments are unlikely due to ethical and consent issues. For instance, if we were to conduct such a trial, we would have to inform patients that we do not know whether extraction or non-extraction is the better treatment option. Consequently, patients may conclude that if we are uncertain about which approach is more effective, they would prefer non-extraction treatment and may not agree to participate in randomization.

This means that we can conclude that this review, even though the level of evidence is low, is the best that we can get.

Final comments

I have considered this review, and I am less certain than the authors about their conclusion. I lean more towards the idea that there is insufficient evidence to determine whether extraction impacts the airway or not.

This does not give “airway-friendly” orthodontists a “free pass” on their claims. It indicates that anyone advocating for non-extraction treatment or orthodontic extraction reversal treatment for airway-related reasons lacks the evidence to support their assertions. Consequently, their actions can be considered unethical.