May 25, 2020

RME does not influence upper airway volume? A trial

One of the newer “developments” in orthodontics is the treatment of the airway. One method of increasing the airway that is being promoted is Rapid Maxillary Expansion.  Let’s see if this new trial shows this effect of RME.

RME is a well-established treatment to treat maxillary transverse discrepancies.  Traditionally, orthodontists anchored RME devices to the teeth. Recently, new skeletal anchorage devices have been developed.  This has resulted in several claims being made for their superiority over tooth-borne methods. These include more significant expansion and the improvement of the airway. This is particularly relevant to the new speciality of “Airway Friendly Orthodontics”.

This new trial looked at the effects of three different expansion devices on the airway.

A team from Sydney did the study. The EJO published the paper.

The upper airway volume effects produced by Hyrax, Hybrid-Hyrax, and Keles keyless expanders: a single-centre randomised controlled trial.

Gordon C. Cheung et al.

European Journal of Orthodontics, 2020, 1–11. doi:10.1093/ejo/cjaa031

What did they ask?

They did the study to answer this question;

“What are the short-term changes in upper airway volume after RME with a conventional tooth-borne (Hyrax), tooth-bone-borne (Hybrid Hyrax) and the Keles keyless expander measured by CBCT”?

What did they do?

They did a randomised controlled trial with a 1:1:1 allocation ratio.  The PICO was;

Participants: 66 healthy 10-16-year-old orthodontic patients with unilateral or bilateral crossbites and a maxillary transverse deficiency of more than 5mm measured from the cusp tips of the upper first molars.

Interventions: Hyrax expander

Comparators: Keles expander or Hybrid Hyrax expanders

Outcome: They chose a primary outcome of treatment-induced changes in overall airway volume. Secondary outcomes were other airway measurements, all derived from CBCT images.

They collected the data at the start of the expansion and at 6 months at appliance removal. They took the CBCT images using a standardised protocol and asked the participants to stay still during scanning. An experienced operator recorded the data from the scans. The threshold was set to between 50 and 70 for all the scans.

They did a sample size calculation based on detecting an effect size of 20% increase in airway volume. This showed that they needed a minimum of 15 patients per group to power the study.  They used pre-prepared randomisation and good allocation in sealed envelopes.  Finally, their statistical analysis was relevant.

What did they find?

They randomised 66 participants. Unfortunately, there were failures of the Keles device and they switched 8 participants to the Hyrax appliance.   As a result, at the end of the study, they were left with data from 51 patients. These were divided into 19 Hybrid-Hyrax and only 13 Keles expanders.  There were no differences between the groups at the start of treatment.

When they analysed the data they found that the Hybrid-Hyrax group had an increase in airway volume of 5903mm2 (+8.3%), the Hyrax increase was 2537 mm2 (+3.8%), and the Keles group had an increase of 3001.4 mm2(+4.5%). These differences were not statistically significant.

Their final conclusion was:

“All three RME devices produced relatively small increases in the total volume of the upper airway, and this casts doubts on their clinical relevance”.

They also stated:

“Any benefits in terms of increased airway volume obtained from RME are not necessarily translated into an improved function for breathing disordered patients”.

However, I could not find any data in this paper that underpinned this strong statement.

What did I think?

Firstly, I thought that this was a nicely set up and designed study.  Nevertheless, the investigators raised some limitations.  I believe that the most important of these was that there was no untreated control group. As a result, we cannot conclude that the treatment caused changes in the outcome measures. These could have arisen from average growth.  However, I wonder if they could have used a delayed treatment group as a control.  This has been the method used in other orthodontic studies.

It is also essential to consider that the failure rate of the Keles appliance was high.  Ideally, they should have used an Intention to Treat analysis. This would have included the data from all patients, even those whose appliance failed.

We also need to consider that the high drop out rate has resulted in a lack of power, and this may explain the absence of statistical significance. Nevertheless, the effect sizes are small, and they are unlikely to be clinically significant.

Finally, I am aware that there are difficulties in the accurate measurement of the airway from CBCT images, and this relies on the phase of inspiration/expiration of the participant.

So what can we make of the results of this paper? I think that the most important fact is that the treatment changes were small. This is an important finding and suggests that RME does not result in a meaningful change in airway dimensions.  It is important to consider that this study used RCT methodology. They, therefore,  addressed the authors criticism of other studies that relied on lower levels of evidence and reported on minuscule levels of change.

Final comments.

I think that it is imperative to remember that the investigators did not measure disordered breathing neither were the participants assessed by ear, nose and throat specialists for adenoids, tonsil size or any kind of airway obstruction.

However, this study does provide us with useful information on the effect of RME on airway volume and casts some doubt on the use of RME in airway focussed orthodontics to improve childhood breathing.  In many ways, this study reinforces the AAO paper on orthodontics and breathing disorders.


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Have your say!

  1. What about tongue position after RME.
    This is the determining factor in the study of airway. Not a static CBCT

  2. Hi Kevin:
    It’s an interesting study but your conclusions appear contradictory. On the one hand you say “the investigators did not measure disordered breathing” but then you contradict this by saying “In many ways, this study reinforces the AAO paper on orthodontics and breathing disorders”. The main deficiency of the study, which likely explains the current findings, is that the effects of normal growth and development of the upper airway during the period of study (which is significant during this time; Schendel et al; Gonzales et al) have not been taken into account; size-change has likely been masked by shape-change inter alia, as addressed by the spatial matrix hypothesis (Singh 2004).

    Disclosure: Dr Singh is Founder/Chief Medical Officer, Vivos Therapuetics, Inc.

  3. Thanks for sharing this review of Gordon’s work. Without having read the article and going solely by this review, it was a 4-8% increase in airway volume but we cannot say with any certainty whether this is meaningful or not. An assumption is made that this small increase is not meaningful but we do not know this as it was not measured based on this review. It would be useful to know; did this have any effect on any sleep disordered breathing, OSA, or quality of life scores and what sort of change/expansion is required to be able to achieve this (if it occurs) and in what type of patient (which would require a much larger study). Also, does any benefit hold up long-term (and compared with a control with normal growth). Personally, I feel research needs to look at what is the end-point of interest (e.g. disease) which will take longer but give us more direction as to what is useful treatment and what is not. Perhaps we need to reconsider the direction of research in Universities and other settings to a longer term goal carried on by a number of students rather than a ‘complete within a set period of time so I can graduate’ model? Should I duck for cover now? 😉

  4. 10-16 years old? I think most of us agree that RME is most effective in much younger ages, even without looking at sleep/airway issues. There is a proponderance of research out there supporting RME (usually with Adenotonsilectomy) is quite successful. Is it just the surgery aspect that is helpful? Maybe, but there is research supporting RME with the absence of surgery as well. Hand picking an article that in my opinion, is studying children older than most proponents of pediatric sleep intervention RME advise is misleading.

    • Dear Bill

      A 10-16 year old is considered a geriatric patient in my practice.

      We begin ENT evaluation, expansion-protraction and adjunctive myofunctional therapy when the problem initially avails itself, most often in the primary/early mixed dentition. Early Childhood Malocclusion(ECM), like Early Childhood Caries(ECC), is first detectable by age 71 months, never self corrects, persists and worsens beyond initial detection without appropriate intervention(McNamara, Bishara, EH Angle, EA Bogue et al), and is often comorbid with poor sleep hygiene.

      Not until ECM is considered a ‘disease of early childhood’….and also, not until Orthodontic post-graduate residents receive clinical and didactic learning opportunities in Child Development and Pediatric Behavior Guidance(as do Pediatric Dentists in their post-grad training programs), papers like this one recently reviewed by Prof O’Brien, will continue to excite his readers who are either unwilling/un-desirous of providing (at least) validated sleep and airway hygiene risk assessment and indicated ortho intervention, or referral for Tx intervention, and little kids will continue to be marginalized or ignored by these talented clinicians. Published medical a dental literature pre- and post-dating the WW II/Nuremberg Trials EBM-era, clearly describe ‘ECM-airway compromise(mouth-breathing) co-morbidity’ as a solvable problem when physicians and orthodontists closely collaborate.

      It’s inevitable I think that the good prof KO’B will I eventually emerge as a leader in this new era of ECM DxTx….I hope so anyway.

  5. The Hyrax and Keles appliances are tooth borne, depending on the first molars being driven into the buccal cortical plate to provide the resistance to pull the two halves of the maxilla apart. The hybrid hyrax appliance, like the Haas, the bonded Haas, and Marpe appliances push the two halves of the maxilla apart via tissue (boney) anchorage. More bone expansion, less tooth tipping. Interesting study design that needs more variables control in its next incarnation.

    • Dr Malerman:
      There doesn’t seem to be a biologic basis for “the first molars being driven into the buccal cortical plate”. Exerting forces on the bone will cause bone resorption, increasing the risk of in fenestration and/or dehiscence. It’s biologically difficult “to provide the resistance to pull the two halves of the maxilla apart” since the periodontia are subject to sutural homeostasis, and the maxilla articulates with the palatine bone posteriorly; so would it also need to be “pulled apart”. In any case, the ensuing hemorrhage/bone fracture would likely heal thru differentiation of localized mesenchymal stem cells, since the midpalatal suture is also subject to sutural homeostasis. This series of events would, presumably, change the maxillary bone morphology with concomitant effects on contiguous structures such as the nasal cavity and maxillary air sinuses.

  6. The Sydney paper, was there Myofunctional therapy involved?

  7. I think that kind of “flash titles” as “RME did not influence the upper airway volume” try to decrease the importance of this procedure highlighting what RME did not do.
    In this study the authors evaluated the overall upper airway volume change (volume changes in the nasal cavity, nasopharynx, oropharynx, and hypopharynx). Previous studies did not conclude that RME increased the total airway volume significantly. Many of these studies reported that its’ effect was limited with nasal cavity. Besides, this effect has synergic outcomes in primary school children by changing functional matrix, that results in treating sleeping disorders and OSAS problems. On the other hand, any study doesn’t claim that RME solves total upper airway problems and OSAS at older children or non-growers. Previously, some Authors were insisted on that RME procedure did not have any skeletal effects. These Authors refered to the study of Dr.Sarnas which was a case report. On the other hand, more than a thousand study reported that RME has skeletal effects. Many of these studies reported that RME increased the nasal volume, and had positive effects to the breathing by helping “normalization” of respiratuary system in many ways (mucousal, bacterial, sinovial etc.) I wonder one thing: Is it based on an evidence that RME did not influence the upper airway volume? Also, the Authors concluded that RME resulted in relatively small increases in total upper airway volume and its separate compartments.

  8. So the news is it improves airway , but only a little , and Its measurable , but not enought to matter.
    I’d be happy with a little improvemet on my own air way all day long. If it was 1% I would still take it.
    Also mandibular position often improves with age if the mandible has not been entrapped. Maxillary development encourages this .
    I will finish a class 2 case , sometimes slightly disapointed with the limited mandibular, sagittal A-P improvement, and quietly think well its better but not perfect ,(Maybe I should have been more traditional and extracted and retracted upper anteriors to reduce the over jet a little further, as traditionaly taught.)
    Nine times out of ten, at 5-10 year review , I am very please with the final mandibular position , facial appearance and reduction in overjet, and very pleased I did not extract and retract. The case often continues to improve after debond.
    The patient has been set up to be allowed to fully facially develop. To pretend you can fully correct facial disproportion in 18 months with orthodontic appliances is obviously folly. It takes much longer than that to achieve balance.
    Im a big fan of all things regarding maxillary expansion as it helps the patient avoid the premature aging that occurs with upper canine retraction following extractions.
    Facial growth and airway development is a marathon , not a sprint that finishes at age 16.

    Sorry to be slightly critical Kev , but whats an opinion if its not worth squabbling over.
    Good post , good subject. You are obviously flirting with the dark side!
    Keep them coming.
    Regards Peter

  9. It’s always interesting to see the purveyors of alternative facts contort and distort their imaginations, in an attempt to deny findings that contradict their unfounded opinions. Of course, several of these are KOLs, who either have a course to sell, or an appliance to promote (a popular class II corrector, for example).
    Perhaps this type of research is not favorable to one whose agenda is Airway-Friendly pseudo-science. Despite the decrying of the acolytes of the Pyramid of Denial, this was definitely a well-done study with important findings.

    Bottom-Line – Maxillary expansion, in the hope of increasing airway volume appears to be pointless. However, that doesn’t mean there are not other measures of improvement, such as decreased airway resistance etc.
    It’s now past time for the usual suspects to discard nonsensical verbiage like Airway-Friendly Orthodontics or 4D Morphotropic Orthodontics and stop making false claims such as “Airway-focused Preventative Techniques” etc.

  10. It is unfortunate that such a simple question is still deemed unanswered in our literature, while other healthcare professions are able to see the actual result and move forward. The important thing regarding expansion and nasal breathing is the improvement of function. This has been shown effective using higher level evidence base methods: Camacho M, Chang ET, Song SA, Abdullatif J, Zaghi S, Pirelli P, Certal V, Guilleminault C. Rapid maxillary expansion for pediatric obstructive sleep apnea: A systematic review and meta-analysis. Laryngoscope. 2017. So many questions about this current project. How can it be take serious with such a small sample size, no control group, and such a lack of comprehensive look of the existing literature such as the above systematic review and meta analysis? That the nasal dimensions will increase with expansion is logical, and we can actually see it anatomically. That the function improves, it has been proven in the higher level methodology we have. Expansion is not a one size fits all solution, but we know what it can do as a tool, if this is the job that is needed.

  11. Let’s repeat this study with TAD borne RME!

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