August 23, 2021

Does airway volume increase after RME?

There is a lot of interest in the role of orthodontic treatment and the airway.  When we expand the maxilla, we hope that we develop various nasal parameters. However, this is not completely clear. This new study shows that RME increases airway volume. So, let’s have a good look at it.

The definitive source of information on airway issues and orthodontics is the AAO white paper on the airway.  We have gone into a great degree of detail on this previously. However, when they considered the effect of RME on nasal volume and OSA, the authors concluded.

“Improvement of the OSA should be highlighted as a “possible,” or  “anticipated,” outcome of treatment. But, no guarantees of OSA resolution can be implied or stated emphatically by the treating orthodontist”.

This paper investigated the concept of changing airways.  The AJO-DDO published the article. A team from Boston, Saudi Arabia and New Jersey did the study.

Analysis of nasal airway symmetry and upper airway changes after rapid maxillary expansion

Di Cosimo et al. AJO-DDO advanced access:  Doi:

What did they ask?

They did this study to:

“Evaluate the effect of RME on the dimensions of the airway”.


“Evaluate any changes in the longterm”.

What did they do?

They did a retrospective study of existing records and screened their records for pre and post orthodontic treatment CBCT images.

They used the following inclusion criteria for the study.

  • Pre and post-treatment CBCT images
  • No history of adenotonsillectomy
  • The patients had non-surgical expansion.
  • The expansion treatment was successful.

All subjects had completed RME with a banded hyrax appliance.

They then used the same repository for images that they included in a control group.  These were age and sex-matched patients who did not present with a maxillary deficiency. Importantly, this group did not have maxillary expansion.

The study sample included 28 patients with a mean age of 9.86 years. The matched control was a group of 20 subjects with a mean age of 10.41 years. There was no difference in the groups concerning age and gender.

They measured the volume of the nasal cavity, nasopharynx and oropharynx.  These were the primary outcomes.

What did they find?

The study sample included 28 patients with a mean age of 9.86 years. The matched control was a group of 20 subjects with a mean age of 10.41 years. There was no difference in the groups concerning age and gender. 

The authors presented a large amount of data. Therefore, I decided to look at the main feature of airway volume change. I have included this in the table below.

GroupTotal nasal cavityNasopharynxOropharynx
RME2249 (2102)1000.6 (917)2349.2 (2520)
Control372 (1456)191.4 (855)2244.0 (4345)

This data showed that the changes for total nasal cavity and Nasopharynx dimension were statistically different. Notably, there was no effect of RME on the oropharynx.

It was also evident in their data that the percentage change in the airway volume for the RME group was much more significant than for the control group.

Their overall conclusions were

“Maxillary expansion shows a significant increase in the nasal and nasopharyngeal volumes two years post treatment”.

What did I think?

This paper outlined an interesting study that the authors wrote up well. I suggest that you should read it.

I have carefully considered the methods that they used. There are several factors that I looked at closely.  The first factor was that this was a retrospective study. Notably, one of the selection criteria was that the treatments were successful.  This step meant that the findings are only valid for successful treatment. Ideally, the authors should have included all treatments, which would give us a realistic evaluation of the effects of an intervention.  In effect, this study is subject to considerable selection bias, and we need to remember this when we look at the results.

Nevertheless, the authors showed considerable differences changes in airway volume between RME and the control groups.  These were very compelling. I thought it was important to see that the authors did not claim that these effects had an influence on the airway, etc. Nevertheless, I would like to see whether these changes resulted in any change in patient-reported outcomes, such as reduction in disordered breathing, etc.  Unfortunately, this data was not available due to the retrospective nature of the study. As a result, I am not sure if reporting morphological change is sufficient in airway research.

The airway volume?

Furthermore, while I am not an expert on airways etc. But, as the airway is a tube, any problems are probably caused by the narrowest part of the tube. Importantly, this study did not detect any effects on oropharyngeal volume. As a result, any amount of maxillary expansion may make no difference to the patient.  I have probably looked at this too simplistically, and I hope some airway experts can provide input here.

We also need to remember that the airway is dynamic. As a result, the dimensions differ according to whether it is breathing in or out.  As a result, CBCT measurement may be unreliable.

Final comments

Finally, we need to consider whether this study reduces the current uncertainty that we face in the role of orthodontics and breathing. Again, it is up to you to decide when you interpret the paper.

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Have your say!

  1. Bravo!

  2. Vindification for Dr Timms !

  3. Thank you Dr.O’Brien for sharing this study .

    There are important point that needs to be addressed whenever we study the relation between orthodontics and airway , especially when it’s evaluated using CBCT or claimed to have an effect on breathing disorders.

    First : whatever you see in a CBCT represents an airway for (Awake) person .. not (asleep) ..
    this is important because the airway tube changes between awake and asleep patients .. that’s why our fellow ENTs use DISE: Drug induced SLEEP endoscopy because they want to see the airway during sleep .. this is a major limitation to any claim from studies that relate orthodontics to sleep apnea using CBCT ..

    Second : airway changes as you change your position .. the CBCT we take at our offices is taken while your patient is sitting or standing .. and the airway changes when you lay down ..

    This is another major limitation.. we can’t evaluate the airway on CBCT and link it to sleep disorders when the time and position are not valid ..

    I also want to highlight a study by Zimmerman EJO 2017 that found reliability issues between orthodontists in evaluating airway dimensions on CBCT .. sometimes it’s not easy to find the appropriate points to measure airway dimensions ..

    Thank you again for sharing this study ..

    Dr.Suliman A. Alsaeed BDS, MSc, FRCD(C)
    Diplomate, American Board of Orthodontics
    Diplomate, American Board of Dental Sleep Medicine
    Assistant Professor 
    College of Dentistry 
    King Saud Bin Abdulaziz University for Health Sciences 
    Riyadh , Saudi Arabia 

    • Contrato for your imput

    • I agree with your thoughts here Prof. Taking CBCT to measure volume doesn’t help us when we should be looking at patient centred metrics such as breathing function changes and reported changes in subjective symptoms from the patient. Volume is only one part of the entire equation therefore these papers don’t have ground to make sweeping claims that one intervention cures the issue, but it certainly can help the issue.

  4. Thank you for posting this paper Prof O’Brien. What you stated about how interpretation of these data should be framed for parents is spot on- “Improvement of the OSA should be highlighted as a “possible,” or “anticipated,” outcome of treatment. But, no guarantees of OSA resolution can be implied or stated emphatically by the treating orthodontist”. Also from this paper I interpreted from these results that had been obtained from an experimental cohort 10+/- year-olds that, if correcting MTD with RPE protocols will often, but no promises, yield mitigation of airway-associated co-morbidities, why not consider treating MTD at earlier stages of development, say within the primary or early mixed dentitions?

    As a Dental Sleep Medicine consultant at two tertiary care children’s hospitals, I have been expanding kids with MTD-SDB co-morbidities for over a decade; we are now conducting a retrospective analysis, similar to this posted AJODO paper, of over 50 children who’d begun RPE Tx before the age of 71 months old…..stay tuned Prof, I know you will have a field day picking it apart, and I will appreciate it sir.

    Kevin Boyd

  5. Alteration of the structure is but one part in the equation. Similarly, an orthopaedic surgeon rarely operates without pre and post physical therapy to ensure the return to adequate function of the patient. An intervention is rarely curative in and of itself, but just one part of the equation.

    If you’re doing Orthodontics for the airway, you must accompany the structural development with assessment and treatment of any nasopharyngeal pathologies, retraining of the oral musculature and patterns of breathing. Food for thought.

  6. I do agree with the previous comments that measuring nasal cavity volume and drawing conclusion on these is very much pseudo research. Volume and area measurements on the respiratory components was quite popular many years ago in connection with adenoids and the impact on craniofacial growth. An interesting small research was performed by one investigator in the US who merely put some small elastic expanders om the opening of the nostrils and this created a tremendous effect on the respiratory capacity and much more that all other measures. The respiratory tube from nostrils to lungs is a complex organ and involves many parts. It is a bit naïve to think that expanding the maxilla a couple of millimetres would have any impact on air flow. Spirometry measurements or other measurements that could measure changes in air flow is probably the only way to evaluate true impact of any intervention on the respiratory organ. The narrowest part of the respiratory tube is probably note related to the width of the maxilla except in few cases with extreme maxillary constriction. The effect in these cases should, however, also be evaluated with air-flow capacity rather than arbitrary measures on radiographs of hard tissues.

  7. A great acknowledgement Emad of Orofacial Myofunctional Therapy and (p.r.n.) adenoidectomy, as either or both might be appropriate as effective adjunctive interventions with RPE for kids with MTD and SDB/OSA co-morbidity….from ages 3-10+/-.

    Might some agree that the compelling results of this featured trial alone, might render a future prospective RCT on this topic, virtually l impossible to pass ethics standards if investigators were to propose withholding RPE Tx from a comparative control cohort of young children afflicted with MTD-SDB/OSA co-morbidity?

  8. Might anyone agree that, per the positive therapeutic results published in this featured retrospective analysis, it would now be unethical to approve a proposed prospective RCT with similar inclusion criteria (Tx:RPE for Dx:MTD on an experimental cohort of 10+/- year olds) by virtue of also requiring an untreated control group of similar age and need for RPE?

  9. Ok, I’ll admit I haven’t read the original paper but….

    ….if it’s a retrospective study, why did all these 10 year olds have CBCTs?

    Stephen Murray
    Swords Ortho

  10. I think if you look at the severe end of expansion with SARPE there definitely is a positive transverse airway change.
    Liu P, Jiao D et al (2019). Oral surgery, Oral Pathology, and Oral Radiology, 127(5),381-386.

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