May 13, 2024

Extracting premolars does not influence the airway?

The debate on whether orthodontic treatment impacts the airway is ongoing. A vocal group claims that amputating teeth during orthodontic treatment can lead to airway problems. However, this claim has yet to be backed up by high-quality research. It is crucial to remain open-minded about the relationship between orthodontic treatment and airways until conclusive evidence exists. This new paper represents a positive step towards understanding this issue better.

The theory suggests that extracting teeth for orthodontic purposes may cause airway issues. This is because retracting dental arches to close spaces could impede tongue function, which may hinder the growth of the airway.

A team from Adelaide, Australia, looked at this in this paper. The AJO-DDO published the paper.


The orthodontic extraction of second premolars: The influence on airway volume.

Miodrag Mladenovic, Simon Freezer, Craig Dreyer, and Maurice J. MeadeAJO-DDO Advance access.

What did they ask?

They asked the following question.

“What are the volumetric changes of the airway in a sample of patients who underwent the extraction of second premolars as part of their orthodontic treatment compared to a non-extraction control group”?

What did they do?

They tried to answer this question by doing a retrospective study of case records collected from one orthodontic practice in Adelaide.

They did a sample size calculation that showed they needed to collect the records of 52 per group.

The team used the following inclusion criteria for the study.

  • Single-phase fixed appliance treatment
  • Complete records, including pre and post-treatment CBCT images.
  • The patients in the study group had extractions of second premolars in the maxilla or all second premolars.

They then categorised the experimental group according to the amount of crowding. Mild crowding was <3mm; if the crowding was greater than 3mm, this was classified as moderate/severe.

Finally, they measured airway volume and other linear measurements from the CBCTs. The primary outcome was the airway volume proper (OCP).

They analysed the data with the relevant univariate and multivariate statistics.

What did they find?

They collected the records of 54 experimental and 59 control patients. There was no difference in the age and initial level of crowding between the groups.

These were the main findings.

Both groups experienced an increase in airway volume. However, the change in airway volume was not different between the study groups.  I have put this data in this table.

 Pre-treatmentPost treatment

I wanted to know what the unit of measurement was. I presume that it was mm3.

The correlation analysis showed that seven variables could influence the change in airway volume. These were the volume of the Oral Cavity Proper (OCP), age, growing/non-growing, airway length, maxillary arch length, mandible arch length, and area of the minimum constriction. They used these variables in a regression analysis, which explained 70% of the variation. This is a good fit for an orthodontic model.

This model showed that the only variables with a statistically significant effect were the area of minimum constriction and changes in airway length.

Their conclusion was.

“The volume of the airway increased in both groups; this is likely to be the effect of normal growth. The orthodontic extractions did not have an effect”.

What did I think?

It is good to see that investigators are now seriously investigating the association between various forms of orthodontic treatment and the airway. This work is important as it deals with what may or may not be an important problem for providing orthodontic care in children.

Although the findings of this study may seem convincing and comforting to those of us who believe that there is no correlation between orthodontics and the airway, we must exercise caution when assessing this paper. This is because it is a retrospective analysis of a particular group of patients, and as a result, it has certain limitations that we must consider.

When examining a retrospective study, it’s crucial to consider the size of the sample that was screened to obtain the final sample. In this study, the authors screened the records of patients treated between 2015 and 2022 in one orthodontic practice. However, the total number of patients treated during this time was not provided, making it difficult to assess the sample’s representativeness. This lack of information raises questions about the generalizability of the findings to a larger population.

The study authors noted that they took care to match the groups in terms of crowding, but they were unable to completely eliminate susceptibility bias. This is because they did not consider the skeletal classification, which may be linked to the airway. However, I believe that if the sample size were large enough, any differences between the groups would be negligible.

I’m unsure why the patients underwent pre- and post-treatment CBCT imaging. This is not typically required as a routine pre-treatment diagnostic image, and there doesn’t seem to be any reason for routine post-treatment CBCT views either. It makes me wonder if this sample differed from typical orthodontic patients.

I was also concerned that the extraction group appeared to have smaller airway volume at the start of treatment than those who were treated non-extraction. It was not clear whether this difference was statistically or clinically significant. However, this was not one of the variables that an initial association revealed that could have had an explanatory effect. As a result, I assume that these pre treatment variables were not fitted in the regression. I would have liked to see a comment from the authors on this.

Finally, it is no surprise to anyone that patients needing second premolar extractions treated by a specialist do not have reduced airway volume because it is doubtful that the incisors would be retracted. 

You may think I have been overly critical in interpreting this paper. However, I have applied the same criteria to papers that make positive claims about orthodontics and the airway.

Final comments

We need to evaluate the value of this paper. In my opinion, it is a useful first step in exploring the question. Although the sample is retrospective, it provides some information. The findings indicate that orthodontic extractions did not significantly impact airway volume. This could have implications for clinical practice, but it is ultimately up to individual clinicians to decide if it warrants a change in their practice. This paper also provides valuable data for future research, including sample size calculations for prospective studies.

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Have your say!

  1. My immediate thought was ‘ why would they have even have pre and post on CBCT’s’?

  2. Do you have any opinion on the findings that the extraction group had a smaller airway both pre and post-treatment even though it grew? It makes some sense to me that we are more likely to extract teeth in patients who just have a smaller anatomy including jaw structure.

  3. It would be interesting to find out if extraction of FIRST premolars had a similar effect? Prof Mills..”Four 4’s, if not why not”! I am fairly sure that most orthodontists in the 21st Century don’t blindly follow that concept!

  4. I am surprised to see this study published. I was under the impression that CBCT is not a good tool to measure the dynamic nature of the airway, which is a partially soft tissue tube that changes form during function. The question then really is, is this a good representation of reality for the samples under review? Also, now that this has been published in AJO- DDO, it is citable material for all to perpetuate this unproven bias in use of the tool.

  5. FYI we wrote an article on this subject in 2022
    Effect of premolar extraction on upper airway volume and hyoid position in hyperdivergent adults with different mandibular length
    Ruoyu Ning, Jing Guo, and Domingo Martin
    Changsha and Jinan, China and Barcelona, Spain

    Am J Orthod Dentofacial Orthop 2022;

  6. A little over 10 years ago, I saw some young patients in one family who had seen another dentist and transferred over to the clinic I was working at. All children were under 10 years old and all of them had CBCTs as a matter of routine imaging during their initial visit. There were no pathologies suspected nor noted prior to taking these images.

    I suspect there are very large differences in the way many clinicians operate around the world and that pre and post orthodontic treatment CBCTs are probably more routine than some may think. I’m an Australian dentist and I never understood the point of the whole mouth series of PAs that American dentists appeared to be trained to do. I’d like to think dental schools around the world train dentists to take as few radiographic images as possible but I know that the interpretation of “as little as possible” varies.

  7. Hi Kevin, thanks for the summary. This paper is a good start to further research. I would be interested to know if any difference in airway could be detected in the bi-dental protrusive patients that had 4x second premolars removed where the treatment plan was to alleviate crowding and/or retract incisors. I wonder if the patients with non-extraction lower arches should be excluded from the data set, as upper incisor retraction would presumably not go beyond the lower incisor position.

    • Thanks for the comments. I agree with your points. But if they wanted to looked at bi-dental protrusive patients they would nee to increase the sample size or even carry out a study that only includes these patients. this would certainly answer the question about retraction causing breathing disorders. you are correct on the amount of retraction needed for single arch treatments. I agree that they should be excluded but I am not certain if this study team took this step.

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