Micro-implant expansion again: A new trial.

What did they ask?

They did this study to ask this straightforward question about micro implant assisted rapid palatal expansion:

“Are there any differences between Micro-implant RPE  and tooth-borne expanders to treat maxillary deficiency during the post-pubertal growth stage”?

What did they do?

They did a prospective randomised controlled trial with a 1:1 allocation.  The PICO was:

Participants:

60 orthodontic patients with a skeletal maxillary deficiency needing more than 5mm dental expansion, a negative buccal corridor, and during the post-pubertal growth spurt.

Intervention:

Micro implant Rapid Palatal Expansion device

Control:

Hyrax RME device

Outcomes:

The primary outcome was the ratio of skeletal to dental expansion at the level of the maxillary first molar. There were many secondary outcomes derived from CBCT images.

They used pre-prepared randomisation and concealed the allocation in sealed envelopes.  Patients and orthodontists were not blinded to the treatment allocation.  I could not find any information on whether they used a blinded data collection.

They carried out a sample size calculation before the study started. This showed that they needed a sample of 28 patients in each group to detect a difference of 15% in the ratio of skeletal to dental expansion.

They took CBCT scans and dental casts one week before and one week after active expansion. They evaluated the scans mainly on two coronal sections and one axial slice.

Finally, they used univariate analysis to compare the interventions.  This meant that they carried out 23 tests and ran the risk of false positives amongst the many variables that they evaluated.

What did they find?

Unfortunately, they produced a mass of data and I cannot go into all of this in the space that we have.  As a result, I am going to concentrate on their primary outcome and some of the many secondary outcomes.

These main findings were:

• There were no differences between the two groups at the start of treatment.
• 30 participants in each group completed the trial.
• The ratio of skeletal to dental expansion was approximately two times higher in the Micro Implant RPE group (61.4%) compared to the Hyrax group (32.2%).
• The success rate of opening the midpalatal suture was higher in the MARPE group (100%) than in the Hyrax group (86.7%).
• The centre of rotation of the zygomatico-maxillary complex was located in the same position for each group.

In order to simplify my interpretation, I looked at several of the outcomes that they measured from the CBCT images more closely. These were the intermolar width at the level of the molars, the amount of sutural expansion, and the alveolar bone height at the molars.

They presented this as before and after values and changes in the variables. We need to remember that there are problems in looking at the change in orthodontic variables because this tends to mask small effect sizes. As a result, I concentrated on the post-expansion variables. I think that this is a reasonable decision. This is because if you take a sample of patients and randomly allocate a treatment. Then it is logical to assume that any post-treatment differences between the groups are due to the treatment. Importantly, taking this step clearly shows effect sizes.  This table includes this data (in mm) at the end of the expansion.

Their overall conclusions were:

“MARPE was more predictable and resulted in greater skeletal expansion compared to the Hyrax expander”.

What did I think?

This was an interesting and good study of a clinically relevant problem.  Interestingly, it appears that expansion can be achieved by most methods in patients who are past the pubertal growth spurt.  The mean age of the MARPE group was 15.1 years and the Hyrax was 14.8 years.

I was a little concerned that they did not provide any information on whether the data was recorded blind. This is important and puts the trial at a reasonable risk of bias.

I think that it is also important to consider the effect size. I am always cautious when I see data presented as percentages, as this tends to “mask” the effect size.  We need to remember to look to see if the effect size is clinically significant.  As a result, I looked closely at the post-treatment values. This showed that the effect sizes were rather small with wide confidence intervals.  From this simplified evaluation of the data, I think that I can conclude.

• Both MARPE and Hyrax expanded the maxilla.
• There was a greater sutural expansion with the MARPE than the Hyrax with an effect size of 1.6mm (it could just as easily range between 1.1mm or 2.1mm).
• The amount of dental expansion was similar.
• There was little effect of either appliance on alveolar bone height.

Final comments

This was an interesting paper that gave us some useful information on the effects of the most commonly used rapid expansion appliances.  However, I had some concerns about bias with respect to the recording of the cone-beam data.  This does mean that the trial is at risk of bias.

Finally, The most important factor to review in the appraisal of this paper is to consider the effect size. What you need to do as a reader of this blog and the paper, is to decide whether gaining an additional 1.6mm sutural expansion is worth the more invasive approach of micro-implant assisted expansion.  I would stick with RME because this is simpler, but I may be old-fashioned and cautious?