Lets talk about micro-osteoperforation….
Let’s talk about micro-osteoperforation….
At a recent conference, I was discussing “ways to make teeth move faster”. After my presentation, a delegate asked me about the evidence that underpinned micro-osteoperforation or MOPS. So, let’s talk about MOPS/Propel…
The leaders in MOPS are Propel. I will start by looking at their website. It is small, compact and does not contain much information. It shows that Propel has two main products. One is the VPro5 this is an intra-oral vibrator that appears to be similar to AcceleDent but you only need to use if for five minutes a day. They market this device as an “aligner seater”. They do not provide any research that supports its use.
Their other product is called the Excellerator. This is a method of micro-osteoperforation and involves making small holes in the alveolar bone and speeding up tooth movement. The only supporting evidence they provided was a paper published in the AJO-DDO in 2013. I have posted about this paper before, but I am going to have another close look at it….
The papers that provide us with evidence
Mani Alikhani et al
Am J Orthod Dentofacial Orthop 2013;144:639-48
In the introduction to the paper, the study team point out that while the skill of the clinician and co-operation of the patient influence treatment duration, the main factor controlling the rate of tooth movement is bone biology. They then put forward a theory that causing localised trauma to bone stimulates chemokines. This then leads to an increase in osteoclastic activity and rate of tooth movement. They quote some animal studies in support of this claim.
A study on some rats that died….
I then had a look at the paper they quoted. This was published in the Journal of Dental Research and you can find it here.
They took 48 rats and fitted an orthodontic spring from the molar to the incisor. They then applied one of four interventions to the rats
- Orthodontic force applied with no activation
- Orthodontic force applied to spring
- Orthodontic force applied and they raised a soft tissue flap
- Orthodontic force applied, flap raised and they made several perforations of the alveolar bone
They evaluated the levels of various markers and chemicals. But I was more interested in tooth movement. They only wrote one paragraph on this part of the study and they did not describe how they measured tooth movement, apart from writing that this was done after 28 days. They reported that the mean tooth movement for the orthodontic force group was 0.29mm and for the orthodontic force plus perforation it was 0.62mm.
Unfortunately, they did not provide any data on standard deviations or confidence intervals, they simply stated that they were significantly different. We need to note that the effect size of the interventions is about 0.3mm/month. Importantly, they calculated this from a sample of only 12 rats in each group.
My feeling is that from this sparse amount of data they could not conclude with confidence that the rate of tooth movement was increased. So, not a great deal of evidence here. Let’s get back to the AJO paper…
What did they do?
They did a parallel-group RCT with 1:1 allocation. They powered the study to detect a 50% difference in the rate of tooth movement. I could not check this calculation because they did not give sufficient information.
The PICO was
Participants: Orthodontic patients 18-45 years old
Control: No intervention
Outcome: Rate of canine retraction measured from study casts.
They did not provide any details of randomisation, sequence generation and allocation concealment. This is a major deficiency in the paper and it results in the study being of a high risk of bias.
I was also really confused about how they allocated the interventions and I had to work really hard to find out what they did. I think that this is what happened…
They randomly assigned the patients to
- An experimental group who got MOPS on either the left or right side. They randomised the sides, but they did not give any details on how they did this.
- The control group did not have MOPS.
They then compared the rate of tooth movement for the experimental group with the control group. They also carried out a comparison between the MOPS side and the non-MOPS side in the MOPS group. In effect, they introduced a split-mouth component into the study. I have no idea why they took this step because it adds to the confusion and the difficulty of interpreting the data.
The residents providing the treatment were not blinded to the allocation. This is reasonable and understandable.
They took study casts at the start of canine retraction and 4 weeks later. The operator drew vertical lines on the palatal surface of the canines and measured the distance from these lines to the lateral incisor using digital callipers. They carried out simple comparisons with the relevant univariate statistics.
What did they find?
20 patients completed the study. They illustrated the differences between the groups using clinical photographs. They presented the tooth movement data using graphs and not as figures. As a result, I found it very difficult to interpret. I am not sure why they took this approach. I have estimated this data (means and 95% CIs) from their graphs.
|No MOPS||0.5 (0.28-0.7)||0.6 (0.52-0.76)|
We now need to look at this data carefully. I worked out the following
The mean difference (effect size) is 0.6mm/month, when we look at the confidence intervals this shows that this difference could easily be from 0.5 to 0.7mm/month. This means that there is high uncertainty in the data. In spite of this uncertainty, the authors concluded that this intervention significantly increased the rate of tooth movement. They also state that MOPS could reduce treatment time by 62%. I have no idea how they reached this conclusion.
What did I think?
I really had problems understanding this study. I found their methods confusing because they used a combination of a 1:1 parallel trial and a split-mouth study. Furthermore, I felt that the lack of clarity in the methods meant that this study is at high risk of bias.
I could also not understand why they used graphs and clinical pictures to present their data. We really need to see some numbers here.
I also thought about the effect size with respect to the normal rate of tooth movement. It appears from the literature that the average rate of canine retraction is approx 1.1mm/month. This is similar to the rate that they detected in the MOP group in this study. In other words, the MOPS do not appear to speed up canine retraction when compared to the average rate.
Secondly, the effect size was only 0.6mm/month. This is not large and I cannot help wondering if this is worth the additional cost and hassle of MOPS.
Finally, I thought that their overall conclusion that MOPS could reduce treatment time by 62% was not supported by their data.
In summary, there are many issues with this paper that are not clear and I really wonder if it does provide evidence that Propel increases the speed of tooth movement. It would be great to see larger-scale studies into this treatment, as this technique may have potential.
Currently, we only have one small study of 20 patients (at high risk of bias) and a study on some rats with no detail of how tooth movement was measured. This should not be sufficient to adopt a new treatment.
As things stand, we have to conclude that there is an absence of evidence that MOPS is effective….but let’s continue promoting this form of untested treatment.
Emeritus Professor of Orthodontics, University of Manchester, UK.