August 24, 2020

Do extractions influence the airway? A new study.

Despite the current lack of evidence, orthodontists are still promoting non-extraction treatment as part of “airway friendly orthodontics”.  The authors of this new paper looked at the relationship between extraction treatment and airway changes.

Over the past ten years, there has been increasing interest in the relationship between orthodontics and disordered breathing. I have posted a lot about this before. We have also included an excellent summary of the AAO meeting on airway and orthodontics.  In general, there is an absence of evidence to suggest that there is a relationship between orthodontics causing or treating breathing disorders.

A team from San Francisco did this new study. The Angle Orthodontist published their paper.

Airway and cephalometric changes in adult orthodontic patients after premolar extractions

Adrienne Joy et al.

Angle Orthodontist: Advanced Access:  DOI: 10.2319/021019-92.1

In their literature review, they mentioned that there is a belief that orthodontic extractions may result in a collapse of the airway. However, there is little evidence for this claim.  So they did this study.

What did they ask?

They did the study to answer the following question;

“Is there a relationship between the extraction of premolars and changes in the airway dimensions in a sample of non-growing patients”?

What did they do?

They did a retrospective study.

In the first stage of the study, they searched the records of the patients who had been treated in their orthodontic department from January 2007 to June 2018.  They used the following inclusion criteria to identify the patients in the study:

  • The patients had to be at least 18 years old.
  • They had pre and post-treatment CBCT images.
  • At least two premolars were extracted as part of their treatment (extraction group)
  • No extractions were done (non-extraction group).

At the end of this process, they had identified 42 patients in the extraction and the non-extraction groups.  Within the extraction group, 6 patients had only had upper premolars extracted.

They analysed the CBCT scans by dividing the airway into three areas. These were the nasopharynx, retropalatal region of the oropharynx and the retroglossal region. They then calculated the airway volume for each part (mm3) and the most constricted area (MCA) of the airway in mm2.  They also calculated a large number of other measurements.

Two judges made all the airway measurements. Finally, they did a large number of statistical tests across the variables. The extensive amount of data was presented in several complex tables.

What did they find?

I am sorry to be so honest here. But I do not know what they found.  This is because the data presentation and statistical analysis were so complicated that I could not decipher it.  I simply could not understand the statistical analysis and its description.  However, I have extracted the data on MCA, as this was the most relevant information that I could find.  I have put this in this table.

MCA (mm2)ExtractionNon-Extraction
Nasopharynx289.30 (72.1)266.7 (76.0)256.8 (77.9)256.8 (73.7)
Retropalatal182.5 (86.1)167.5 (110.9)149.6 (75.9)139.9 (83.0)
Retroglossal172.0 (98.3)174.4 (92.7)134.3 (66.2)126.0 (70.0)

I could not work out if these differences were statistically significant. However, I did wonder if the effect sizes were small.

In their summary, the authors pointed out that there was no change in these measurements over time, there was a slight tendency for extraction cases to have larger measurements at the start and end of treatment and there were no differential effects with extraction.

Their overall conclusions were:

“There was no evidence that extractions in non-growing patients had negative consequences on the airway dimensions.”

What did I think?

Regular readers of this blog know that I do not usually review retrospective studies. However, I make an exception to this practice when the retrospective study provides us with interesting information that may be used to plan a randomised trial.  I will also do this when a flawed retrospective study comes to firm conclusions that may add to the controversy. I do this to make sure that the flaws are understood and also to provide information for readers who are not sure how to interpret these papers.  This paper falls into this latter group. I shall carefully outline the problems with this study.

Problems with the study design

Firstly, I would like us to think about the ability of the study to answer the question that they post. An excellent place to start would be to consider the ideal study design.  This would be a trial in which we could take a group of patients and randomly allocate them to extraction or non-extraction treatment.  However, there is some doubt that patients would enrol in such a study. This is because most would express a preference for non-extraction treatment.

An alternative would be a prospective study with well-matched participants with similar levels of crowding and other occlusal features who have treatment with or without extraction. These participants could have standard baseline records taken, including three-dimensional imaging as well as patient-focused assessment to evaluate any symptoms related to possible breathing disorders. These tests could then be repeated after treatment and indeed, even sometime later to assess whether an extraction-based treatment has a meaningful long-term effect.

Another method is a well-done retrospective study that is designed to minimise selection bias. If this is successful, then the groups would have minimal differences at the start of treatment. Unfortunately, in this study, 24 of the extraction group and only 5 of the non-extraction group had crowding greater than 7mm. As a result, the groups were very different at the start of treatment.  This is why one group had extractions, and the other did not.  I feel that this is a significant flaw in this study. There were also the well-recognised problems of measuring the airway using static measurements, possible errors in patient positioning and changes in airway volume due to breathing.

Final thoughts

As a result, I am sorry to suggest that I disagree with the methodology that they used.  Unfortunately,  in my mind, this casts some doubt on the results of this study.


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Have your say!

  1. It is very complex to determine if extractions reduce airways and if they actually decrease it, it is difficult to say that it is bad.
    All those patients who may have extractions and reduced airways should undergo a study with the specialist in Otorhinolarygology to determine if the airways are really negatively affected, regardless of whether the images confirm such reduction.
    In addition, not always when extractions are made, all the teeth are retruded, the limit is set by the lower incisor and many cases require mesializations.
    I also believe that it is more important to eradicate chronic inflammation and obtain health of all tissues than the relative measures of airways.
    When the patient stabilizes in CR, the lower arch back off and the airways decrease, when the patient is stabilized, all tissues return to normal: muscles, joints, mucous membranes, etc.
    Perhaps it is more important to place the jaw where it belongs regardless of the airways, and for the same reason that should be valid for extractions.

  2. The paper is flawed in several ways. First, the measurements did not actually capture the anatomical upper airway completely (see Fig 2). Second, the initial airway size was different in the two groups at the outset. Instead of correcting for this, the authors used it to support their ‘findings’, ignoring the fact that size obfuscates shape-change and masks treatment effect. Third, the respiratory cycle was not controlled and the authors admit that in the last sentence of the Discussion, negating the results reported. Fourth, as noted by Dr Martinez, there is no indication of the spectrum of orthodontic mechanics utilized in the heterogeneous population studied.

    • Good response. O’Brien’s blog often seems to operate to defend the status quo, even if the status quo defies sense. We can design studies to show whatever we want. Most studies, like this one, are not very good. I had extractions as a teenager and I had what I posit are predictable negative sequelae. Reduced tongue space leads to snoring and sleep apnea, which can lead to chronic fatigue and other problems. Do we even need a study for this? What exactly do we expect to find? Are we really meant to believe that making the container for the tongue smaller is harmless? Why stop at taking out 4 teeth? Why not 12? If we can take out 4 premolars with no repercussions, why not 12? When does extraction become harmful? Orthodontists often take out 8 teeth. What about 16? Let’s take them all out — if anyone complains of problems afterwards, they’ve obviously drunk the Kool-Aid. There are an ever-increasing number of people who get treatment for their past extraction-retraction orthodontics, and many swear by their improvement. At what point do positive testimonials count as evidence in themselves? “Mainstream” orthodontists insist that they have better and above all more consistent results than functional therapists and other “quacks”. Well, bariatric surgeons probably have a 100% success rate in making people skinny. Should everyone skip dieting and exercise and go under the knife? After all, dieting and exercise are unpredictable. Bariatric surgery is guaranteed! “The evidence proves it.”

  3. In my view it was a gòod attempt but, there are alot of flaws in study.
    1 No skeletal classification mentioned. No growth pateron mentioned.
    2 didn’t mention crowding and spacing.
    3 Did not mentioned inclination of teeth.
    4 Didn’t include a controll group of normal occlusion both skeletal and dentaly to compare growth modification.
    5 no history of any ENT related diseases.

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