Pulsed electromagnetic field (PEMF) reduces orthodontic treatment time.
Researchers continue to search for methods of increasing the rate of orthodontic tooth movement to reduce treatment time. While there have been several studies into these treatments. Most papers show that we cannot speed up tooth movement. This new study looked at Pulsed electromagnetic fields (PEMF). The investigators concluded that this new technology reduces orthodontic treatment duration.
PEMF is a treatment that involves pulsing electromagnetic fields in tissue. This promotes healing by increasing blood circulation. The PEM device is a coil that carries a current, and a pulsed magnetic field is generated. Unfortunately, investigators have not done any studies on PEMF and human orthodontic tooth movement. This paper outlines the first of these studies.
A team from Nagpur, India, did this study. The AJO-DDO published the paper.
Efficacy of pulsed electromagnetic field in reducing treatment time: A clinical investigation
Wasundhara Ashok Bhad
Am J Orthod Dentofacial Orthop 2022;161:652-8.
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
| Control | PEMF | Diff | 95% CI | p | |
| T1 | 0.71 | 0.82 | 0.5 | 0.3-0.7 | 0.0001 |
| T2 | 1.23 | 1.45 | 0.6 | 0.44-0.8 | 0.0001 |
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.
Final comments
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.
Emeritus Professor of Orthodontics, University of Manchester, UK.
I made some comments about this paper recently, which I include here for interest. I agree that it is important to investigate these types of adjuncts as robustly as possible but there are definitely some issues here
Just when we thought we had seen all the possible adjuncts to orthodontic treatment there appears to be a new kid on the block – zapping the patient with a pulsed electromagnetic field. This can apparently promote healing by increasing blood circulation around the teeth and potentially speed up tooth movement with a fixed appliance.
A new article in the American Journal of Orthodontics and Dentofacial Orthopedics has investigated the use of this technology with an experimental design commonly applied to this type of research: canine retraction in the maxillary arch of first premolar extraction cases using NiTi coil springs against fixed anchorage and a randomly assigned split-mouth protocol with and without the adjunct under investigation (in this case, application of a pulsed electromagnetic field via a URA worn overnight; with the control side shielded with aluminium foil).
In this study, average increases in canine retraction rates (mm/month) are seemingly huge: 41% and 31% reported on the experimental side compared to control after 3 months of retraction and at completion of retraction, respectively. This looks very impressive but reporting % changes can be misleading and they need to be qualified in terms of clinical effect (as Kevin O’Brien has previously pointed out – 80 or 90% of not much is still not much…..). Of far more interest is how far the canines were actually retracted and specifically, how long did it take? – the authors only tell us this for the 3 month observation period where the canines were retracted an average of 3.73 mm on the experimental side and 2.16 mm on the control side – a difference of 1.57 mm. Is 1.57 mm more canine retraction over 3 months really clinically significant? I am not so sure! It’s certainly not as impressive-sounding as a 41% increase in rate of tooth movement! We do not know how long it took to complete canine retraction in the two groups because it is not reported for some reason – we are only told that complete canine retraction was represented by an average movement of 6.76 mm on the experimental side; and at this point in time, the distance was an average of 4.81 mm on the control side. This is almost 2 mm difference, which might be clinically relevant, but it is difficult to say when you do not know the time-spans and also I worry that the time-point for taking these measurements was at the completion of canine retraction on the experimental side – if the canine retraction is already complete on the control side at this point then this will introduce bias. Indeed, the methodology seems to assume by default there would be a faster rate on the experimental
side, which also hints at bias.
I think the conclusions in the abstract that a pulsed electromagnetic field is a good option to reduce orthodontic treatment duration based upon 1.57 mm more canine retraction over 3 months is a little optimistic. It’s not clinically relevant in terms of canine retraction and certainly isn’t relevant in terms of the whole period of treatment with fixed appliances. Interesting study none-the-less!
Hi Kevin:
Happy Memorial Day. This is an interesting study which brings up two questions that appear to occur repeatedly in these types of studies. I have no real issues with this particular study but one has to ask;
Q1. If there was no attempt to modify bone physiology then would one expect a ‘clinical’ difference in tooth movement based on alteration of mechanical parameters alone? If so, what is the mechanism that these novel mechanical methods utilize as opposed to other physical techniques?
Q2. When does a change become clinically significant? If the tooth movement was 0.7mm not 0.6mm, would that be ‘clinically’ significant? What is the threshold or consensus for clinical significance, if it differs from statistical significance?
Split mouth designs as you point out have inherent flaws. Journals should be careful in publishing articles like this that look at a small segment of overall treatment (canine retraction) compared to the entire treatment duration for efficiency and effectiveness. Even if there was an effect, it could be followed by a lag phase. The real clinically important question is what is the effect on overall treatment duration?
Great and relevant comments!
Again, the companies will latch onto this as they seek the Holy Grail of faster tooth movements. Even Evidence Based statements need to be carefully examined. I am grateful and appreciative for our colleagues in Academia .