June 03, 2024

What is better? Quad helix or RME for maxillary expansion.

Many researchers are doing trials to determine the effectiveness of expansion appliances for correcting crossbites. This research is timely as expansion seems to be becoming a popular treatment method. Furthermore, many methods of expanding arches now carry different levels of risk and treatment burden.  

With this explosion of interest in expansion, we must base our treatment decisions on high-quality data. It is reassuring that investigators have done several trials into expansion.  This new study adds to our knowledge.

A team based in Sweden did this study. The Angle Orthodontist published the paper.


Skeletal effects of posterior crossbite treatment with either quad helix or

rapid maxillary expansion: a randomized controlled trial with 1-year follow-up.

Stina Hansson; Eva Josefsson; Henrik Lundc; Silvia Miranda-Bazargani; Anders Magnuson; Rune Lindsten; Farhan Bazargani

Angle Orthodontist: On line: DOI: 10.2319/010424-9.1

What did they ask?

They did this study to answer this question.

“What are the effects of RME or Quad Helix treatment on the midpalatal suture, the teeth and adverse effects when correcting unilateral posterior crossbites”?

What did they do?

They did a two centre two arm parallel group RCT. A team based in Orebro and Jonkoping, Sweden did this trial.

The PICO was


Children in the mixed dentition with unilateral posterior crossbite with the maxillary first molars erupted.


RME with Hyrax screw attached with bands on the deciduous second molar and bonded to the deciduous canine 


This was a quadhelix  attached with bands on the first permanent molars


The primary outcome was the midpalatal suture expansion in a coronal and axial view.  Secondary outcomes were marginal bone levels on the permanent first molars, Bone thickness and fenestration, dehiscence and root resorption of the first permanent molars.

The team carried out a sample size calculation that was based on the ability to detect a difference of 2mm of the midpalatal suture expansion between the groups.

They did a remote  pre prepared randomisation with the allocation done by a staff member who was not associated with the trial.

All the patients had a 8cmx8cm CBCT scan at baseline (T0), at the end of expansion (T2) and one year after treatment was completed (T3).

The endpoint of treatment for both groups was when the palatal cusp of the maxillary first molar was in contact with the buccal cusp of the mandibular first molars.

Finally, the team carried out the relevant uni and multivariate statistics.

What did they find?

They randomised 42 patients with a mean age of 9.5 years (SD=0.9) into two groups. They analysed the data from all the patients.

Primary outcomes

In the RME group the palatal suture opened 4.1mm inferiorly and 3.0mm superiorly in the coronal view. Whereas, In an axial view it opened 4.1mm anteriorly and 1.1mm posteriorly.

In the quad helix patients in the coronal view the suture opened 0.1mm superiorly and 0.3mm inferiorly.  In the axial view it opened 0.3mm anteriorly and0.0 mm posteriorly. All these differences were statistically significant.

At follow up there were no differences between the groups due to new bone formation.

Secondary outcomes

The buccal marginal bone level was significantly decreased by 0.4 mm greater in the quad group than the RME. There were minimal differences in the palatal bone thickness. The authors found 7 more fenestrations in the quad helix group after treatment. This was clinically and statistically significant. 

The study team concluded.

“The quad helix did not open the midpalatal suture in mixed dentition treatment.The opening of the suture with RME was more anterior and inferior. Importantly, more buccal bone loss and and fenestrations were found with the Quad Helix than the RME”.

What did I think?

This was a nicely done small trial directed at a simple and clinically relevant question. There are an increasing number of methods for upper arch expansion. It seems almost daily that various orthodontic groups are promoting a new innovation with a low evidence base. It is a great shame that the do not do trials of this nature before they make their claims.

The results of this trial show that most of the movement obtained with the quad helix is dentoaveolar with very little skeletal change.   From this we can conclude that RME is the most effective method of skeletal expansion at this stage of development.  

Some questions?

I had two main questions about this study. Firstly, I was unsure why they did not fit the RME to the first permanent molars, even when they were erupted. This meant significant differences between the interventions.  However, this may be the main reason there was less buccal bone loss on the first molars for the RME group.

I also looked at the clinical trials registry entry for the study and found that the original sample size was 72 and in this paper it was 42. 

I contacted the authors about these issues, and they kindly responded. They explained that the difference in sample size was because they initially calculated a sample size for the outcomes of pain and discomfort. They reported this part of the study in another paper. To minimize CBCT exposure, they performed an additional calculation to assess dento-alveolar effects, as detailed in this paper.

The main author provided information about the RME design. They selected this design because it was being promoted as a new technique to minimize the risk of bone loss around the permanent molars. The researcher also noted that the traditional RME design was typically used in regular clinical practice.

Final comments

I realise that I have written a longer discussion than usual.  I hope that I covered this paper satisfactorily. After looking at this is in detail. I can conclude that this small trial showed that RME was a better method for maxillary expansion than the quad helix for children in the transitional dentition.  I wonder if it is now time for a team to carry out a high-quality systematic review into expansion. We certainly, have enough studies and questions about this treatment.

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Have your say!

  1. Thank you Kevin for this post. One of my significant concerns in the mixed dentition is that banding primary teeth often leads to tears (or worse) at de-band ( or indeed unintentional extraction).
    I regularly use quads banded to 6’s and regularly observe significant median diastema opening. Perhaps I activate these more or less aggressively than in the study. In a unilateral crossbite I will expand the quad by a molar width and by at least 2 widths in a bilateral case. I like to achieve a t least a unilateral scissor bite before removal and will often then retain with a TPA.
    I have used this general procedure for years because it seems to work and I almost never need further expansion in the adult dentition if/when we transition to full fixed. Nor do I artificially enlarge the natural dental arch width.
    How much true sutures change I get is unknown because I don’t take occlusal or similar radiography due to ALARA considerations.

  2. There is much here beyond the very excellent comparison between the quad helix and classic hyrax.

    What can be logically derived from this research is the importance of a sufficient moment-to-force ratio for meaningful sutural separation and transverse maxillary expansion to take place. That is, in order to counteract the tipping from a facial force applied to the posteriors, there needs to be sufficient detorque force, a moment that is facial apex and lingual crown.

    This research would seem to show that there is too much flex in the quad helix to be able to apply sufficient detorque to the molars, relative to the facial force applied, to achieve transverse maxillary expansion. Even though it is a fixed appliance, a quad helix would seem to be shown to have too much flex in the wire to be able to apply the moment-to-force ratios necessary to achieve sutural separation and transverse palatal expansion.

    Of important note in this is that a quad helix is a fixed appliance with a theoretically rigid attachment to the posterior dentition. The resulting relevant concern that can be derived from this is, if even certain designs of fixed appliances cannot achieve the moment-to-force ratio necessary to split the palate and transversely expand the maxilla in a clinically successful manner, how might this same issue apply to removable appliances being marketed and sold for this same purpose?

    Specifically of concern is Invisalign’s controversial claim to be able to separate the suture and expand the maxilla with its new removable appliances. To date, other removable appliances have been unable to generate and sustain the moment-to-force ratios necessary to accomplish much beyond tipping the maxillary posteriors to the facial. The above-listed study, shows that even some fixed appliance designs cannot achieve this.

    However, despite insufficient scientific evidence, ideally, a PRCT published in a peer-reviewed journal, we are asked to accept that Invisalign’s removable appliance can do this. Moreover, we are asked to purchase and use this unproven appliance on our patients.

    It would seem of importance that the research which was submitted by Align to a peer-reviewed journal for publication was rejected. Currently, whatever unpublished data is available is listed as being on file with Align. It seems like they are saying as evidence “trust us”.

    This practice of marketing a product before valid scientific research, while one of the banes of our profession, is hardly unprecedented. We have seen this with many other products marketed with much fanfare, supported by all of the “cool kids”, and later shown to be ineffectual.

    For Align, despite its longevity as a corporation and its unique product, I cannot think of an instance of their sponsoring PRCT research by independent unbiased researchers that found itself published in a peer reviewed journal. Perhaps someone else can think of an instance. None comes to mind for me. Now, as independent research is coming out on treatment with Invisalign, nearly all seem to show that certain movements are not predictable, not fully achieved, or not changed in a clinically sufficient manner. One does wonder if they knew this long ago, and if this was the motivation for not sponsoring independent valid research.

    So, we are back at a quad helix not achieving sutural separation and transverse palatal expansion to any degree comparable to classic Hyrax. Is there sufficient analogy here to at least start to wonder if we should not use a removable Invisalign expander on our patients until there is unbiased independent PRCT research published in a peer-reviewed journal in support of Invisalign’s expander? Could we needlessly be harming our patients if we bypass this step?

  3. Dear Prof. O’Brien

    Might you agree that each of these 9.5+/- year old patients with obvious maxillary skeletal transverse deficiency (MSTD) at T-0 could have been diagnosed with MSTD, and treated (p.r.n.) much earlier in their lives when the transverse hypoplasia was maybe less obvious, but still non self-correcting, say when in their full deciduous or early mixed dentitions? Also, would you agree that obtaining pre-Tx data regarding the presence of possible Orofacial Myofunctional Disorder (OMD) traits and/or Sleep-Related Breathing Disorder (SRBD) behavior co-morbidities would have made this study a bit more in line with current standards of prudent care for children?

    Thanks for considering my questions.

    Kevin Boyd, DDS, MSc

    • Thanks for the comments.Sorry for the delay I have been on holiday. Currently, there is a lock of evidence supporting the concept of early orthodontic treatment and sleep disordered breathing. I agree that there should be studies into this area, but I imagine that this study was planned before the current interest in this area.

  4. My treatment for crossbites with narrow maxilla was expansion with RME and after overexpansion I removed the RME after 6 weeks and used a palatalbar with arms to the canines. the gap between the central incisors after about 4 to 5 days of activation indicated the opening of the midpalatal sutur and with the canineextensions of the palatalbar I could achive more asymmetric expansion of canines which was in many cases nessesary for the correction of crossbites. in addition I used biteplates in the lower arch . In class3 cases the caninearm could be used with extensions to the incisors to correct anterior crossbites. I think .that removing the RME early gives the tongue the room to find the normal restingplace in the palatal area which ist prevented by the RME.

  5. Was it really necessary to CBCT all of these children 3 times to find an outcome that is already well established from previous studies? That RME gives greater skeletal change than quad helix

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