September 14, 2020

Skeletal effects of expansion treatment: A RCT.

I wonder if maxillary skeletal expansion is becoming more popular?  This new trial provides us with some great information on this form of care.

Maxillary expansion is the standard treatment for maxillary constriction.  The most common form of therapy is Rapid Maxillary Expansion.  Importantly, when we consider this treatment, we need to maximise the skeletal and minimise the dental components of any expansion.  As a result, clinicians have developed methods of directly fixing the expansion devices to the bone using mini-screws or mini-implants.  Several reports have suggested that these tooth-bone-borne RME appliances are useful.  This new trials reports on a one year follow up of this form of treatment.

A team from Sweden did this study. The EJO published the paper.

What did they ask?

They did the study to

“Assess and compare the influence of conventional tooth-borne RME (TB RME) and tooth-bone-borne RME (TBB RME) on dental and skeletal structures in growing children”.

What did they do?

They did a two-arm parallel-group randomised clinical trial.  I have posted about this study before.  The PICO was

Participants: 54 8-13-year-old children with a unilateral or bilateral crossbite with constricted maxilla.

Intervention: Tooth-bone-borne RME with two 1.7x8mm mini-screw implants.

Control: Tooth-borne RME

Outcomes: The primary outcome was the amount of expansion in the mid-palatal suture measured from CBCT images. Secondary outcomes were skeletal expansion at the nasal base, dental tipping of molars, tipping of alveolar bone and cost of treatment.

They collected the data at pre-treatment (T0), directly after expansion (T1), and 1 year post-expansion (T2).

They used pre-prepared stratified randomisation, concealment was via contact with a remote team member who provided details of the intervention. Their sample size calculation was based on detecting a difference of 1.5mm in expansion between the interventions. The outcome assessors were blinded.

What did they find?

They included 52 participants in the trial. They followed all the patient to the one-year post-expansion point. Notably, they reported that there were no harms.

I have extracted the relevant data for the amount of expansion for the appliances into this table.

After expansion (mm)One year post-expansion (mm)
Dental Effects
Tooth-borne RME5.2 (4.8-5.6)3.8 (3.3-4.2)
Tooth-bone-borne RME5.8 (5.4-6.3)4.1 (3.6-4.5)
Difference0.6 (0.1-1.2)0.3 (-0.3-0.9)
Skeletal Effects
Tooth-borne RME2.3 (1.9-2.8)0.1 (-0.2, -0.3)
Tooth-bone-borne RME3.4 (2-3.8)0.1 (-0.2-0.3)
Difference1.1 (0.5-1.7)-0.2 (-0.6, -0.3)

They also stated that the expansion of the nasal width for the TBB group was twice that for the TB RME (3.5mm compared to 1.8mm).  But I could not find these values in the large amount of data contained in the complex tables.

When they looked at cost, they found that the TBB appliance was around €130.00 more expensive than the conventional TB RME.

They also referred back to their other paper in which they measured nasal airflow and suggested that this difference explained their previous finding that the TBB RME treatment resulted in higher airflow than the TB RME.

Their overall conclusions were

“TBB RME results in greater expansion than TB RME. However, this difference was about 1 mm and may not be clinically significant”.

Skeletal expansion at the level of the nasal cavity was significantly higher in the TBB group.

They also stated:

“If a patient showed no signs of upper airway obstruction, it seems that conventional TB RME does the job with good stability after one-year post-expansion”.

“The TB RME is the most cost-effective of the two interventions”.

“If patients show signs of airway obstruction, then the TBB RME is indicated’.

What did I think?

I thought that this was an excellent well-done trial that was clearly reported.  However, I did not have the time to work through all the highly detailed tables, and I hope that I have distilled the necessary information.

I want to acknowledge the large amount of work that the authors did for this trial.  Trials take a great deal of effort, and I feel that they did well to carry out and complete this study.

I felt that their conclusions were very interesting and relevant. We need to consider whether the treatment effects were clinically significant. I cannot help feeling that they were not, and it may be difficult to justify the more expensive and invasive procedures for the TBB RME.

What about the airway?

Unfortunately, I have difficulty in agreeing with their conclusions about airway obstruction. In their previous paper, they showed that the airway was improved with TBB RME, and this conclusion looked robust to me. However, I am not sure whether they can extrapolate their current findings on the morphological change to these results.  Nevertheless, they can do this by revisiting their data and test if there was a direct causal effect between the dimensional and the airway changes that they have reported in these two papers. Perhaps, this is going to the subject of a third paper that ties everything together?

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Have your say!

  1. Given the near-obsession with maxillary expansion (when in doubt, expand and always be in doubt) this article along with your unbiased review and commentary is timely and very useful, thanks. As research has indicated (Stumbling on Happiness, 2006), belief systems and emotions have more influence than legitimate factual publications…..expand, enjoy, breathe, repeat.

  2. What about the turbinate increase in size during and following RME? Did they consider this?

  3. Their paper on nasal resistance was also only measure immediately post expansion.

    The 12 month follow up of the rhinomanometric measurements would also be interesting to see.

  4. Thanks for posting this, Kevin. My concern is that these types of studies are fundamentally flawed; not in their execution, but in the interpretation of results. For example, the term ‘growing children’ is redundant. I personally and professionally have never met a child aged 8-13 yrs who was not actively growing. The reason for being pedantic is because the effects of childhood growth were, yet again, completely ignored (Disclaimer: I only read the Abstract). It is well established [1] that the effects of growth have thwarted orthodontic interpretation since tools that took these changes into account were not readily available in the past. However, even tho’ they are available today, their utility has been overlooked. In addition, the associated biologic phenomena have also been ignored. For example, the authors claim that the expansion in the midpalatal suture was approx. 1 mm. This is reductionism at its best, and working under the conditions of parsimony leads to erroneous conclusions. The effects of sutural homeostasis are disregarded. The researchers were unable to explain how the palate got wider without the width of the mid-palatal suture showing much change; a phenomenon which has been known for years [2]. Furthermore, the application of linear analysis to a non-linear system might easily explain why the nasal cavity findings were so disparate in two groups. The lack of rigor in determining shape-change is perhaps best illustrated by the authors interpretation of “dental expansion”. Dental tissue behavior differs distinctly since the crowns of the teeth cannot undergo shape-change or size-change. In effect, “dental expansion” is simply a change in location secondary to tissues capable of remodeling, such as bone. However, the authors describe this as alveolar “bending” without providing any evidence of the same, even tho’ techniques that quantify deformational allometry have been available for decades.

    1. Singh GD. On Growth and Treatment: The spatial matrix hypothesis. In: Growth and treatment: A meeting of the minds. McNamara JA Jr (ed.) Vol 41, Craniofacial Growth Series, Ann Arbor, USA, 2004, 197-239.
    2. Vizzotto MB, de Araújo FB, da Silveira HE, Boza AA, Closs LQ. The quad-helix appliance in the primary dentition–orthodontic and orthopedic measurements. J Clin Pediatr Dent. 2008;32(2):165-170.

  5. Interesting article. However the periodontal effects of expanding, tooth borne only frequently result in the facial aspect of the molar roots being’pushed’ out of the usually already thin facial bony housing! At this time, we need CBCT analyses both pre-treatment and at the 1 year evaluation. Sagittal slices will give one a clear picture of the above issue.

    Colin Richman DMD

  6. This seems to be a significant article. I am going to withhold comment until I have a chance to read the whole article. I requested a copy today. For AAO members, getting copies of articles like this is very simple and a great member benefit. There is a simple form online at and it is easy to copy and paste from Kevin’s review into the relevant fields. Thank you Kevin for bringing it to my attention, and as always, for your review.

  7. After reading the article, I have these concerns from a clinical applicability standpoint:
    1) There was no measure of any correlation between the number of activation of the expanders and the dental and skeletal measurements. They just said all expanders were activated to the same occlusal relationship. The patients were a mix of unilateral and bi lateral x bites. What I really want to know is how much of the expansion put into the expander is translates to suture opening.
    2) Location of TAD’s was not ideal and the design of the TAD expander not ideal. The area of greatest resistance in expansion is at the zygomatic buttresses, or roughly the first molar area. The tooth borne expander had a wire lingual to the teeth soldered to both arms of the expander, very rigid. TAD expander had the two arms of the expander splayed a long ways apart and not connected, much less rigid. The fact that the amount of molar tipping was similar in both groups seems to indicate that they were both functioning similarly in the molar region
    3) No discussion of age or comparison of ages of two groups. Range was 8-13 with a randomized distribution with only gender considered. There is a big enough difference between expansion ina an 8 yr old and a 13 yr old that it should have been shown that the samples were age matched.
    –My take home from reading the article is that even a bone borne expander with TAD’s very far anterior out preforms a tooth borne expander across all measurements in this study. Cost benefit ratio in children with this type of expander are questionable.

    • Hi John, thanks for the question and comments. In answer to your points 1 and 3. Any varation between the samples and activation etc will be taken into account by the randomisation. If the sample is large enough.

      With regard to your point number 2. This is concerned with the clinical protocol. This was a very experienced team and while there are variations in technique between orthodontists, I cannot really criticise their techniques. Perhaps, you could take this up with them?

      Best wishes: Kevin

  8. Thank you for this precise revision, Dr. O’Brien!
    I add this:
    If the mean age were higher, (13 yrs) the results would be different?

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