TMD is not associated with dental occlusion?
In this week’s popular post series, I will revisit a post I published in 2017. This was on the association between occlusion and TMD. I have changed the original version, given developments in how we currently interpret systematic reviews. I have left the original comments at the end of the post. You can see that things got heated!
One of dentistry’s longest-standing controversies is whether the occlusion is associated with TMD. This new systematic review may give us some answers?
Over many years we have discussed, argued, and debated whether occlusion is associated with TMD. People have organised conferences, run legal cases, written complete editions of journals, and developed multiple philosophies in attempting to address this question. In some cases, an almost religious approach had been taken towards analysing and achieving the perfect occlusion. Yet, even now, we are no nearer the truth. I thought that this systematic review might give us an answer to this question.
D Manfredini et al
J Oral Rehabil. doi:10.1111/joor.12531
A team based in the beautiful city of Ferrara in Italy did this study.
What did they ask?
They did this study to find out if:
“There was an association between features of dental occlusion and temporomandibular disorders”
What did they do?
They did a systematic review of the literature until January 2017. The PICO was
Participants: Adult populations
Intervention: Any treatment or association
Comparator: Description of the patient’s occlusal features
Outcome: Measure of association between occlusal features and TMD.
They included case-control and population-based studies.
They carried out an electronic search for the papers. Two authors reviewed the papers independently. Finally, they conducted a quality assessment of the papers using the Newcastle-Ottowa scale for case-control studies.
What did they find?
They screened a final sample of 822 citations, and following filtering, etc., they reduced this to 25. They classified 17 as case-control studies. In these, the authors compared a sample of TMD with non-TMD individuals in patient populations. While the other 8 papers compared the features of dental occlusion in individuals with TMD signs/symptoms and healthy subjects from non-patient populations.
When they carefully analysed the papers, they found;
- There was high variability in the occlusal features investigated and the TMD diagnosis.
- Only a few papers carried out a multivariate analysis of the data. This is necessary because of the multi-factorial nature of TMD.
- They found marked heterogeneity between the papers.
Importantly, when they looked at the quality of the papers, only two were of high quality, and most fell into the moderate range.
Their general finding was that there was a lack of a clinically relevant association between TMD and dental occlusion.
Overall, they felt that the studies provided some information on associations between occlusal factors and TMD. Unfortunately, these findings were not consistent, and this was important. They finally concluded:
“There are no grounds to hypothesise a major role for dental occlusion in the pathophysiology of TMD”.
“They encourage Dental clinicians to abandon the old-fashioned gnathological paradigm”.
What did I think?
Initially, I thought it brilliant; there is no link between occlusion and TMD. This means that we cannot “blame” orthodontic treatment for causing TMD, nor can we “cure” it. This avoids many of the problems that we have faced as a specialty in this area. However, we need to be cautious in our interpretation of this data.
I then had a careful look at the review. I thought that they did it well and reviewed a large number of studies. Importantly, they did not find any strong evidence relating occlusion to TMD. This is an important finding.
However, I could not help thinking that the authors reached this conclusion because the TMD research was not done well. This is not unusual in the dental literature. Furthermore, I would bet that if someone systematically reviewed the literature on the effect of extractions, the association between orthodontic treatment and breathing, and even the effects of orthodontic treatment, we would come to the same conclusions. This is a common finding in systematic reviews.
I am also certain that if there is higher level evidence, then the authors would have found it an used the data in the review.
As a result, after a careful read, I feel that this situation is similar to other areas of dentistry/orthodontics. We can only conclude that there is an “absence of evidence.” This is important because this does not mean there is evidence of the absence of an effect. In other words, we cannot conclude that there is no association between occlusion and TMD. We can only conclude that there may be an effect, but we have not found it. I have blogged about this before.
This fact is reflected in their cautious but correct and nicely stated conclusions.
In summary, my overall conclusion is that we do not have evidence to underpin treatment aimed at treating TMD by altering/correcting the occlusion. As a result, we either have to stop this type of treatment or explain to our patients that there is no evidence supporting the treatment we propose. They can then decide whether they wish to undergo care based solely on clinical experience or dogma?
I have concluded this before for other treatments, and while this may be depressing, it is our current state of knowledge. Again, this is a good area for research. It would be great if someone would conduct high-quality research in this area.
Emeritus Professor of Orthodontics, University of Manchester, UK.