What did they ask?
They did this study to ask:
“What is the effect of PEMF on the rate of orthodontic tooth movement”?
What did they do?
The investigators carried out a split-mouth randomised controlled trial. The PICO was
Participants: 19 orthodontic patients, 2 male, and 17 female. This group were 18-24 years old. All treatments involved extraction of upper first premolars.
Intervention: Pulsed electromagnetic field (PEMF) applied to one side of the mouth. This was randomly allocated
Control: Treatment as usual
Outcome: Rate of retraction of permanent canine teeth (mm/month)
They carried out a sample size calculation. However, the authors did not state the clinically significant difference they hoped to detect. This revealed that they needed a sample size of 19.
The PEMF device was embedded in a removable appliance that they asked the patients to wear 8 hours a day. They constructed the device to provide PEMF to one side of the mouth. The side was randomly allocated. They concealed the allocation using sealed envelopes.
They removed the upper premolars before appliances were fitted. Then they bonded MBT brackets and worked through archwires to 19X25 ss wire. Next, TADs were placed mesial to the first molars, and Ni-Ti coil springs were used to provide a force of 150g to the canines.
They measured the rate of tooth movement from study casts by measuring the distance from the cusp tip of the canine to the mesiobuccal cusp of the first molar. The investigator measured these distances at T0 (after leveling and alignment), T2 (3 months of retraction) and T3 (completion of retraction on the experimental side).
From this data, they calculated the rate of tooth movement at T1 and T2. Finally, they did simple t tests to evaluate the differences between groups.
What did they find?
I extracted the data on the rate of tooth movement at T1(3 months) and T2 (end of space closure on the experimental side). I also calculated the 95% confidence intervals. Here is the data in mm/month
Their overall conclusions were:
“Using PEMF resulted in an increase of 31% in the rate of tooth movement and reduced orthodontic treatment time”.
What did I think?
Firstly, these investigators are to be congratulated on carrying out this study. I have said before that these interventions should be tested before widespread commercial promotion. I thought this was a complex study, and the results were interesting. However, I have a different interpretation of the data from the investigators. This is simply because the effect size is minimal and is not clinically significant. While the authors make a claim that there is a 30% difference in the rate of tooth movement. We need to remember that 30% of a small number is not very much.
There are other issues with the split mouth nature of the study and cross-over effects due to the continuous archwire.
I may be being harsh here, but in my courses on critical appraisal, I often suggested that we look at the data tables before looking at the paper. If the effect size is small, we need to consider if this will change or reinforce our clinical treatment. I am sure that it is not worth the effort and cost of this intervention to increase the rate of tooth movement by 0.6mm per month? I really hope that the promoters of this treatment do not start claiming an up to 30% increase in the rate of tooth movement.