October 04, 2021

Maxillary Overexpansion: Too much of a good thing?

Maxillary expansion is becoming more popular.  But what happens when we over-expand?  This post by Padhraig Fleming looks at a new study that overexpanded children’s maxillas.

Not for the first time, expansion appears to be the zeitgeist in orthodontics. Orthodontists have spawned a range of novel approaches in recent years. Many of these are invasive, and most are directed at facilitating skeletal expansion in mature individuals. I have concerns that the development of these attractive ‘hammers’ may mean that milder forms of arch constriction are seen as a ‘nail’ with more invasive treatments normalised.

In younger patients with transverse maxillary constriction, we can achieve skeletal expansion readily with non-surgical means. However, the quest for more skeletal change prompted this study to argue that a greater amount of expansion might increase the relative contribution of skeletal change to any transverse increase. A team from Dallas did this study. The Angle Orthodontist published the paper.

Short-term skeletal and dentoalveolar effects of overexpansion: A pilot randomised controlled trial

Authors: Arun K. Bala; Phillip M. Campbell; Larry P. Tadlock; Emet D. Schneiderman; Peter H. Buschang

Angle Orthod. 2021. doi: 10.2319/032921-243.1

What did they do?

They conducted a pilot randomised controlled trial with 28 participants.

Participants: All participants were aged less than 16 years at the start of the trial. They were in the mixed dentition, required at least 4 mm of palatal expansion to treat transverse deficiencies. Their periodontal health was good.

Interventions: They fitted Rapid maxillary expanders with hyrax screws (10 or 12 mm) to bands on the maxillary first molars. Metal arms extended to the second and first premolars or deciduous molars. The clinicians expanded the conventional group until the palatal cusps of the posterior maxillary teeth were positioned along the lingual incline of the buccal cusps of the posterior mandibular teeth. In the over-expansion group, the participants activated the RME screws activated maximally (10 to 12 mm). Participants turned the expansion screw once (0.25 mm) daily. When the expansion was complete, they measured screw activation intra-orally using digital callipers.

Primary outcome: Skeletal versus dental change.

The investigators used pre-determined randomisation. However, they gave us no information on allocation concealment.

What did they find?

They presented a lot of data. I have tried to pick out the most relevant:

  • The screws were activated 1.8 times more in the experimental group (10.1 vs 5.6mm).
  • More molar flaring arose in the overexpansion group (2.8-fold)
  • Skeletal and dentoalveolar change as a proportion of molar expansion was similar in both groups. Skeletal expansion amounted to 57% and 47% of the change in the overexpansion and conventional expansion groups, respectively
  • The amount of skeletal expansion, as a proportion of overall transverse change reduced with increasing skeletal maturity
What did I think?

I thought that this was an innovative and interesting study. It appears that there may be some short term gain from over-expansion; however, the absolute differences were minor. Importantly, these were not statistically significant. It would therefore be intuitive that longer-term gain from over-expansion is unlikely.

From a methodological perspective, the sample size was small. The authors made several statements about possible differences between the approaches; however, statistically, significant differences were rarely observed. This might relate either to the fact that no significant difference exists or may be due to the low sample size, which reduces the statistical power.

Another consideration here is the long term effect of overexpansion. In particular, it does seem that greater expansion does translate into both larger increments of skeletal and dental change. One would have to question whether these more significant transverse increases are associated with a higher relapse potential and the risk of periodontal breakdown. We do know that both of these can take time to manifest. As such, while further research with larger samples may be warranted, it would also be helpful to undertake a more prolonged follow-up.

What can we conclude?

Overexpansion of rapid maxillary expanders may lead to a marginally higher proportion of skeletal relative to a dental change in the short term. Unfortunately, the impact of over-expansion in the longer term is not yet known… We still don’t appear to know how much expansion is enough.


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Have your say!

  1. Thanks for the summary, Pad. I would also like to note that 15 years ago, a review suggested that only 20% of the initial amount of maxillary skeletal expansion through RME was still measurable over the long-term. I am not aware of any update to that proportion. So, to the best of our knowledge, when using an expansion screw of 10mm, only 2mm of actual skeletal expansion will remain five years or more later. Hence, an additional increase of 4mm (measured as the screw turns – 16 turns) would provide 0.8mm more skeletal expansion years later.

  2. We over expand not to get better expansion but to account for possible loss of expansion in some kids not wearing retainers well and hopefully to a more ideal level but not back in a cross bite. It’s easy to strap a retainer to a rat with a screw…Ha Ha.

  3. Marco Rosa’s technique of Haas expander cemented to primary second molars with no direct force on upper 6’s has become our standard expansion protocol due to all dental expansion being lost with the exfoliation of primaries, and that U6’s can become a very acurate indicator in the clinic of how much skeletal expansion has occured. Less guesswork.

  4. Interesting……how long have orthodontists been using maxillary expanders? 50 years? 60 years? And we still have inadequate data on knowing how much to expand? Really?

  5. as an undergraduate in the 1980s we were told rapid expansion gets a lot of maxillary expansion initially and as it relapses it becomes a 50:50 skeletal:dental expansion if the molars are retained. So a longitudinal analysis is important. Lopex Gavito and Little estimated 1/3 relapse of expansion so over expand to this amount. Nobody seems to recommend a consensus of an expansion regime- one turn ? two turns per day? per week? also one doesn’t want the bite jacked open by palatal plunger cusps. so we are none the wiser. Also another factor is what the consumer wants, how wide do they want their smile , ie a smile design. I think a complete meta analysis of all of the studies might tell us what to do, even as a MSc project.

    • What is interesting is that orthodontics has conveniently “forgotten” that the teeth, palate, etc., are attached to the rest of the stomatagnathic system, and splitting the palatal suture has to have an effect on the other cranial sutures in some fashion. I have patients whom, as children, had rapid palatal expanders, and now experience mild to severe headaches, which started during orthodontic treatment. It is amazing that there has not been more research in cranial facial pain related to RPE. In fact, it is amazing that more research has not been involved in the ways tooth movement, or changes in the occlusion from restorations affects the rest of the body from a physics standpoint. Any clues to this?

  6. “Participants turned the expansion screw once (0.25 mm) daily.” However: A brief survey of the specifications for most standard expansion screws as illustrated in the manufacturers’ catalogs (Dentaurum, Scheu, Unitek, et al.) will reveal that 4X1/4 turn of the expansion screw yields 0.8mm of expansion.

  7. Here there is not only an expansive recurrence problem that can somehow be predicted or calculated, nor is it just a question of whether we can fit all sides of the teeth by expanding the arch, perhaps it is a more fundamental problem:
    We have to respect the biology and individuality of the patient, in dolichifacial patients with narrow faces and arches we cannot expect to arbitrarily have a broad, wide palate.
    We also have the neutral zone that we must respect, according to the theory of balance we cannot move the teeth beyond a limit and for the bones it must be the same consideration, when we face the bones against the muscles, the latter will always win.
    We must also take into account the lower arch, although supposedly in theory we can expand the upper arch by 10 mm at the expense of the mid-palatal suture, the lower arch can only verticalize the teeth or shape the arch, we cannot expand it at will, so Therefore, to have good arch coordination, the upper arch can only expand as far as the lower arch allows.
    The justification that expanding the upper arch improves the flow of the airways is also not very clear, with respect to health, in children the clearest and most important problems to take into account in this matter are the adenoids, tonsils, allergies, etc.
    Finally, we do not understand very well what is the effect of palatal expansion on the pterygoid plates, we can only speculate, we do not know if the stress thus caused is good for the circumcranial-maxillary suture systems …

  8. Dear Prof Fleming

    I found your critical review of this novel, but only marginally useful paper, to be excellent and was especially encouraged by your comment, ‘In younger patients with transverse maxillary constriction, we can achieve skeletal expansion readily with non-surgical means.’ In my pediatric dental practice Paddy, a 13+ year-old patient who might sometimes be referred to my office (by mostly pediatric healthcare professionals) per observable MTD-SDB co-morbidity, would be considered a ‘geriatric patient’ relative to when they might’ve been first indicated for intervention with palatal expansion.

    Within the introduction of reference # 6 in this paper’s bibliography it clearly states that the 4 most frequent indications for palatal expansion in the deciduous and early mixed dentitions, include ‘constricted upper dental arch related to oral breathing and a high palatal vault’, etc., yet this paper reviewed by you lists as inclusion criteria ‘….require at least 4mm of palatal expansion, and in non-growing adolescent patients, etc.. On what basis were they determining were the authors basing a precise need for at least 4 mm of maxillary expansion I wonder.

    I am now composing what will amount to becoming an annotated bibliography for the syllabus of a continuing education curriculum that one of the board certified Pediatric Sleep Medicine physicians with whom I collaborate in Chicago, had asked me to design for physicians, GDP’s, Pediatric Dentists and Orthodontists wishing to further their knowledge beyond what they’d been exposed to in their undergraduate and post-graduate medical and dental trainings; I’d be happy to share this with you Prof Fleming upon request after its completion. These articles, that span over a century of published medical and dental scientific literature, are supportive of our thesis which identifies specific malocclusion phenotypes, e.g., maxillo-mandibular transverse and/or sagittal hypoplasia, deep/narrow palatal vaults and/or excessive or insufficient vertical skeletal growth, as being initially detectable during the first 72 months of life, are usually reliably persistent beyond age 6, and are already, or will very likely become, also predictably associated with increased risk of developing SDB/OSA co-morbidity.

    As many clinicians are now becoming better informed about the intimate biological connection between the soft and hard tissues of the adjacent respiratory and masticatory biological complexes (i.e., the CFRC-Craniofacial Respiratory Complex), and how RPE intervention for non-syndromic transverse malocclusion, which again, is a frequent associated morbidity, it seems reasonable to suggest that, to ignore the importance of resolving transverse deficiency malocclusion upon their first recognition, is in my opinion, a medically- indefensible position.



    • Kevin,

      You’ve been talking about very early treatment and your collaborations in Chicago for many, many years now. You mention about your life changing results multiple times on this blog, in many youtube videos, podcasts etc etc.

      Have you considered publishing your outcomes so the rest of us can learn what we are doing wrong?

  9. Muscle always wins.

    This is why unexplainably some cases fly with a bit of expansion, and others the mandible refuses to advance and development starts to relapse, soon as the retainers are lost.
    Myofunctional tongue training needs to accompany maxillary expansion.

    Keep your tongue up in the roof of your mouth, tip body and root. Lips together, breath through your nose.
    Tonsils and adenoids out if required, nasal pet and food allegens removed.

  10. I really like to support the opinion of Carlos Flores-Mir and remind of two impressive publications, one of Garib D (https://doi.org/10.1043/0003-3219(2005)75%5B548:RMETVT%5D2.0.CO;2 ) and the other of Baratieri C (https://doi.org/10.1590/S2176-94512010000500011) which both proved, that only 30% of tooth borne expansion arrives in the median maxillary suture. This means with 7 mm of expansion we just achieve 2 mm of real skeletal suture opening. The next issue is to retain these results.
    Since eight years we are doing maxillary expansions in children and adolescents with pure bone borne expanders based on two mini screws in the anterior palate without contact to the adjacent teeth. These (MICRO2) expanders may stay in the mouth for several years – firstly as expanders and secondly as retention and can be reactivated if needed. The activation protocol is 0.17mm per week, which allows the lower buccal teeth to upright spontaneously without the need of a treatment device. This way the upper dentition is not involved in the expansion procedure and therefore shows no tendency to relapse.

  11. Someone signed off on 2 exposures of CBCT for these kids – before and after – to confirm the skeletal changes. Really?
    For a 4mm requirement? Were they going off the WALA ridge or some other landmark? The lower molars are subject to lingual tip in compensation for the narrow maxilla, so I don’t know if lining the cusps up is a definite way of knowing when to stop turning. On the other hand, I don’t know if there is a consensus for when you need to correct a crossbite – is the prevailing opinion in the UK that you don’t need to fix a buccal crossbite if there isn’t a displacement?

    Stephen Murray
    Swords Orthodontics

  12. As our manuscript will be submitted as a retrospective analysis, you would maybe not be impressed or influenced by the data. As for what it is Nicky that you might now be ‘doing wrong’, I’d say probably nothing.

    Given your apparent lack of interest, and thus also, your lack of experience, in validated risk assessment, definitive diagnosis, comprehensive and collaborative treatment planning/Tx execution, and managing behavior, expectations and age-appropriate anxiety in toddlers/pre-schoolers(under age 72 months old) who present with malocclusion and co-morbid SDB behavioral traits(on PSQ), you should probably not be doing anything to serve these kids, save maybe referring them to colleagues who might indeed be interested and experienced…..maybe Peter Doyle?

  13. Thanks Kevin,

    I’m not sure if any orthodontist/dentist in the UK is copying you in trying to resolve sleep disordered breathing in 2-5 year olds with expansion/functional appliances/headgear etc.

    I’d be interested to look at any research on the subject. Do you have any rough publication date in mind?

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