March 15, 2021

A closer look at Maxillary Skeletal Expansion (MSE).

Some time ago, I did a post on Maxillary Skeletal Expansion (MSE). I wrote this as an introduction to the technique. Since then, I have obtained updated information on the evidence that underpins this treatment. I hope that you find it useful.

In my  earlier post, I outlined this relatively new technique. I pointed out that the evidence supporting its effectiveness was somewhat limited. As a result, I contacted the developer of MSE, Professor Won Moon and asked him for his best sources of information. He recommended another three papers. He was the supervising (last) author for each article. This is my interpretation of this research. I will, briefly, look at each paper separately.

These were all retrospective analyses of morphological changes measured with CBCT.

What did they ask?

“How much palatal sutural opening and pterygopalatine disarticulation occurs after ME”?


The pre and post-treatment records of 50 patients with an average age of 18 years old. The main inclusion criteria were that they had a maxillary deficiency.

What did they find?

The mean palatal opening was 0.57 degrees. 84 out of 100 pterygopalatine sutures split between the medial and lateral plates.

What did they ask?

“What are the midface changes represented by the magnitude and pattern of lateral movement of the zygomaticomaxillary complex”?


15 consecutively treated patients aged 17 years old.


Upper infra zygomatic distance increased by 0.52mm, and the lower increased by 4.62mm. The authors presented multiple measurements that were not clinically significant.

What did they ask?

“What is the quantity, magnitude, parallelism and asymmetry of this type of expansion in growing patients”?


31 non-growing patients who were 20.4 years old treated by MSE.

What did they find?

The maxillary expansion at ANS was 4.98mm, and at PNS, it was 4.77mm.

What did I think?

I still think that there may be something to this technique. However, before we widely accept it, I would like to see more research on the patient burden, risks, pain, harms, influence on the airway, success/failure rate, and effectiveness compared to other techniques.  There is absolutely no reason why this cannot be studied in a randomised trial. In fact, I cannot really understand why this has not been done by now.

All we have as the best evidence is these papers.  Unfortunately, I have some concerns about the research methodology.  The authors state that the patients, in all the articles, were treated at UCLA and covered by the same IRB approval. As a result, the authors are reporting different outcomes for the same sample in separate papers.

Furthermore, each paper has different numbers of patients.  I raised this with Professor Moon and he explained that the patients in the paper were all from the same retrospective cohort that grew over time as more patients were treated by MSE.   The differences in sample size is due to delays in the peer review process and enrolment of completed patients.  I looked at the dates the papers were submitted and the number of patients in the studies and included this information in this table.

Paper Date submitted Number of cases
Paredes Jan 2020 39
Colak Feb 2020 50
Elkenaway May 2020 31

This means that the studies are at risk of considerable selection bias.

Importantly, as they are essentially the same sample, this is a thin slicing of data with multiple analysis. We also need to remember that the measurements made on the CBCTs are interrelated.  There is, therefore, a risk that the overall treatment effects are not apparent.  This may also represent a statistical “fishing expedition” where the same cases are over analysed in a search for statistical significance.

Final thoughts

In many ways, these papers are very similar to the work of Hans Pancherz on the Herbst appliance in the 1980s onwards. He had a sample of well documented patients that he analysed in several papers.  At that time, this was a logical approach and the papers were a very valuable first step in understanding the treatment effects of the Herbst appliance. These were then followed by trials that showed the treatment effects were less and that there were issues with breakages and overall co-operation.

Similarly, these current papers do provide us with some early information on MSE.  Importantly, they have showed sutural splitting and some clinically significant movements in a non-growing population. As a result, they are of some value, providing we acknowledge their retrospective nature and high selection bias.  However, we also need to consider what we do not know about MSE.  We have no strong evidence on the success/failure rate, any harms, stability, patient perceptions and influence on the airway. These factors are all very important.

Unfortunately, MSE is also being promoted as a method of expansion in children, in the complete absence of evidence.  We need to remember that there is no evidence that this treatment is better than more traditional and less invasive methods of expansion. Furthermore, there is also no evidence that in children MSE improves the airway, cures sleep disordered breathing, improves school grades and changes the position of the eyes!  There is certainly more than a whiff of snake oil with the use of MSE in children.

Finally, there is clearly a need for randomised trials into this interesting clinical development. These will not be difficult to do.  Hopefully, someone will be keen to carry out this prospective research in the future. Until then our knowledge of this technique is very limited.



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Have your say!

  1. I just saw a patient in my office a few weeks ago. She was over 30 and had ended up in the hospital after a local doctor placed an RPE and had her turn it every other day. I don’t normally comment on these things but as someone who has seen the ramifications of a version of this technique I caution others to stay away from it. She can barely open her mouth. She started having seizures. She has numbing and facial pain on her right side. The doctor is definitely looking at a lawsuit.

  2. Tomonori Iwasaki et al. Nasal ventilation and rapid maxillary expansion (RME): a randomized trial. European Journal of Orthodontics 2021, 1–10

    This was an interesting RCT comparing traditional RME, Hybrid-RME (TAD assisted) and Keles expander showing promising effects on nasal ventilation in all devices and also that hybrid-RME performed better in skeletal parameters. It would be interesting to read your thoughts on this.

  3. Dear Prof. O‘Brian,

    Thank you for your interesting comments and thoughts on skeletal anchorage for maxillary expansion.

    You mentioned that there are no high level papers about MSE. Please let my mention some RCT studies proving the benefits of skeletal anchorage for maxillary expansion using the hybrid hyrax expander (Won Moon‘s MSE expander is more or less a copy with non-recommendable insertion sites for the TADs):

    Iwasaki et al. Nasal ventilation and rapid maxillary expansion
    (RME): a randomized trial. EJO 2021

    Garib et al. Orthopedic outcomes of hybrid and conventional Hyrax expanders:
    Secondary data analysis from a randomized clinical trial. Angle 2021

    Bazargani et al. Effects on nasal airflow and resistance using
    two different RME appliances: a randomized
    controlled trial. EJO 2017

    Additionally, there are numerous studies showing the benefit of skeletal anchorage for maxillary protraction.

    Kind regards,

    Benedict Wilmes

    • Hi Benedict, thanks and I have reviewed some of these papers previously. My comments in the post today were directed at MSE which people are suggesting is different from the skeletal anchorage that you have described. As a result, I made my post very specific to MSE. I am under the impression that MSE is being held up as a miracle new technique and this is another reason for my comments. The paper by Iwasaki, is in the line for discussion in my blog and I am going to try to address the difference between MSE and hybrid hyrax expander then. However, as much as I have read the techniques I am not sure there is a big difference? Am I right?

      Best wishes: Kevin

      • Dear Kevin,

        Thank you for your reply! You are absolutely right, we need some good studies now! Especially regarding the promised effect that we can open every/most of the sutures in adults.

        The biggest difference between hybrid hyrax and MSE is from my point of view:
        – MSE is pre-fabricated, which facilitates an easy use (this is the reason for the popularity): „Appliance first“
        – Hybrid Hyrax expander is individually designed with the focus on maximum available bone and stability for the TADs: „Bone first“.

        So everything in life had pros and cons 😉

        There are numerous studies about the availability of bone in the palate. Practitioners should briefly check these studies or a CBCT before „screwing“ their patients.

        Hope you are doing fine!


  4. Hi Dr. O’Brien, there is a blogger who compiled an impressive list of resources on MSE, including a lot of research articles. Here it is in case you are interested.

  5. Dear Dr O’Brien
    I would like to thank you for this post. It is food for thoughts for anyone who tried or adopted MARPE approach or any of its variant (2 screws hybrid hyrax).
    It reminds me a few things.
    Twenty five years ago, the “goût du jour” to widen the maxilla was Surgically Assisted Rapid Palatal Expansion (SARPE). This was heavily promoted by Vanarsdall and Fonseca. In my area, it became the standard of care among the orthodontist community.
    In 2001, I attended a miniresidency at UNC. During a lecture about the hierarchy of stability, I raised the hand an said to Dr Proffit that SARPE was more stable than segmented Le Fort 1. With a little smile “au coin de sa bouche” Dr Proffit asked me if I can prove that.
    He told me that he can help me to publish it. Too late for me, I was hooked… It was the carott and stick technic of Proff.
    8 years later, a Master degree in my right pocket, one publish paper and a follow uppaper in press, I came to the conclusion that SARPE is not more stable than 2-3 piece Le Fort 1.
    Vanarsdall was yelling at me at the 2008 Angle East meeting…
    Nowaday, the “goût du jour” for widening the maxilla is MARPE.
    I adopted this technic in 2017 and since then, did only 2 or 3 SARPE… for the “failed” MARPE.
    I agree that it is not that simple to expand a maxilla in non growing patient.
    Yes, one will encounter difficulty and failure. I did. Hence I got frustrated.
    Why? Because, it is hard to predict which one will NOT split.
    I can say that 30 y old men and above are the more prone to fail. Surprisingly, female in their late 30s do well. A firefighter of 55y, forget it. It went into SARPE.
    You ask very good questions about the research about this technic.
    However, what choice do we have when a non-growing patient need palatal expansion. I mean real expansion, 8-10-12 mm.
    Segmented Le Fort 1: Data show it is the least stable surgical procedure.
    SAPRE: Data show that dental expansion stability is not better than Le Fort 1, but Skeletal stability is good.
    MARPE/MSE: Did not see data on stability, but the capacity to provide skeletal expansion is promising.

    What choice the clinician have?
    I have a fair success rate with MARPE. I would not return to SARPE as a standard of care, but I always say to the patient there is a possibility that it could be necessary.
    MARPE, although invasive, is much less invasive than SARPE (and segmented Le Fort 1). Morbidity of MARPE is nothing to compare with SARPE. (Except fo the failed one…)
    Does MARPE help nasal breathing? This is something I ask to all my patients. Most of them say yes, they see a change. Is it a proof? No, it is not. But I find it funny to hear.

    This is my 2 cents. I do not pretend that the Truth has been revealed with MARPE. I think it is an evolution of a technic to expand the maxilla that was introduce by HAAS some 50-60 years ago.

  6. Hi Kevin, very timely review of a popular technique these days. I am curious about the stability for: 1. Maxillary Expansion, 2. Manibular inter-canine change, and, 3. Maxillary protraction, using this techgniue to loosen the sutures. All previous surgical (and non-surgical) techniques for expansion have resulted in similar dental relapse over time while maintaining the cross-bite correction.
    How is this technique going to be different? One can only speculate given the results of studies on different surgical and non-surgical expansion techniques. However, it is likely that results may be similar.

  7. “84 out of 100 pterygopalatine sutures split between the medial and lateral plates.” Did someone leave the back door open? Any ideas on how to close it?

    • If these structures are sites of mechanical resistance opposing separation of the maxillary halves,, then to achieve sutural widening they have to,by necessity, become disarticulated.

      I am unsure why you would wish to “close the back door”

      I would appreciate your insight on this

  8. Previously, expansion / disjunction was used in patients with triangular, arthritic palate, due to posterior crossbite, however today it is used for everything, as a “miracle device”, to breathe better, to sleep better, to learn better, to be more attractive…
    None of this is proven and I doubt that these statements are true, we also have to take into account recurrence and muscle balance.
    Furthermore, we do not know what long-term health repercussions the pressures and tensions on the pterygopalatine plates and the cranial suture system have.
    We must start to think if we are doing the right thing, if we are only overtreating, is it logical to expand the arches in a Dolichofacial patient? In a patient who has a thin, narrow facial phenotype?

  9. “Unfortunately, MSE is also being promoted as a method of expansion in children, in the complete absence of evidence. We need to remember that there is no evidence that this treatment is better than more traditional and less invasive methods of expansion”

    This relatively new RCT showed MARPE gets twice as much skeletal expansion compared to Hyrax in teenagers

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