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.
Farhan Bazargani et al.
European Journal of Orthodontics, 2020, 1–9 doi:10.1093/ejo/cjaa040
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)|
|Tooth-borne RME||5.2 (4.8-5.6)||3.8 (3.3-4.2)|
|Tooth-bone-borne RME||5.8 (5.4-6.3)||4.1 (3.6-4.5)|
|Difference||0.6 (0.1-1.2)||0.3 (-0.3-0.9)|
|Tooth-borne RME||2.3 (1.9-2.8)||0.1 (-0.2, -0.3)|
|Tooth-bone-borne RME||3.4 (2-3.8)||0.1 (-0.2-0.3)|
|Difference||1.1 (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?
Emeritus Professor of Orthodontics, University of Manchester, UK.