July 31, 2017

TMD is not associated with dental occlusion?

One of the longest standing controversies in dentistry is about 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 the 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. This new systematic review may give us an answer to this question.

Temporomandibular disorders and dental occlusion. A systematic review of association studies: end of an era?

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.  They set out to answer whether

“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 patients 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 carried out 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 multi-variate 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 brilliant, there is no link between occlusion and TMD. This means that we cannot “blame” orthodontic treatment for causing TMD and neither 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 jumping to conclusions.

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 evidence relating occlusion to TMD.

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.

As a result, after a careful review I feel that this situation is similar to other areas of dentistry/orthodontics. This is that there is an absence of evidence.  This is important, because we need to understand that this does not mean  there is evidence of 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.

Where does this leave us?

In summary, my overall conclusion is that that we do not have evidence to underpin treatment aimed to treat TMD by altering/correcting the occlusion. As a result, we either have to stop this type of treatment or we need to explain to our patients that there is no evidence that supports the treatment we propose.

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 and it would be great if someone would carry out some high quality research in this area.

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Have your say!

  1. Interesting as usual! I totally agree we need to stop treating patient occlusion to fix TMD problems but a question that arise to my mind is: could we perform orthodontic treatment for esthetic or hygienic reason in TMD patients safely without the risk of worsening initial condition ?

  2. No surprise here

  3. retrospective systematic reviews are proving disappointing at proving anything. The fact that out of 822 papers, only 2 were of good enough quality speaks volume about TMD research. As a clinician, I wish systematic reviews would be of greater use. Not sure they are worth reading as their main conclusion is almost always: More research is needed. I think we should concentrate on prospective clinical trials if we want orthodontic research to gain any credibility….

    • Although I think almost all the systematic reviews do conclude that there is no strong evidence of “xxx”; completely discard them is also dangerous. They simply summarize what is known only through the lenses of published research. Which by the way can itself be really biased. I do not necessarily see a position of do not even waste your time reading research. At least personally some limited evidence, although limited, is better that nothing and just practice based on biased beliefs.

      I believe a such summary provides busy clinicians with a glimpse of what is know so that they can act accordingly. Most clinicians will not read published papers as they are not written in a reader friendly matter. Most will read title and conclusions and go from there. The key obviously is that the reviews present a broad common sense perspective of what they found and not make categorical conclusions when they should not.

      Better clinical research is certainly needed!

  4. I applaud Professor O’Brien for maintaining a highly objective perspective on this paper. There is always an intuitive leap between a paper’s data and its conclusions. It would appear that the authors of the paper have chosen to dismiss any association between occlusion and TMD rather than draw Professor O’Brien’s more cautious (and I would say) more ‘truthful’ conclusions.
    In my opinion, a major part of the problem with research around TMD and occlusion is the lack of a coherent model to test against. For instance, when splint studies are compared, what exactly is a ‘splint’ and is it designed to create the same changes to occlusion? There is evidence from a Loughborough University study that changing dental occlusion alters oral muscle function in healthy adults *. I believe it to be high quality evidence (but, as one of the authors, I would say that wouldn’t I!). It was conducted at a highly-regarded Institution with very experienced post-doc Health and Sports Science researchers and published in a pretty respectable journal, though.
    As clinical dentists we all see patients who appear to suffer some form of discomfort or dysfunction as a result of changing their dental occlusion. Thankfully, the VAST majority of them appear to get better over time. The Loughborough researchers conclude this is probably a result of Wolff’s Law and the Moss Functional Matrix. Essentially, joints modify their form in response to alterations in function. Anthropological evidence backs this up, too.
    Personally, I don’t think the Gnathological view of occlusion is very close to reality, either. As a GDP I have monitored thousands of patients over many years with healthy, functional jaw joints and no reported head and neck pain. Most of them were nowhere near class I dental occlusion and many did not possess canine guidance either. But that’s not the same as believing that there is no connection between the way the teeth function together and the health and function of the TMJ and associated musculature.
    So, in my clinical work with patients requesting treatment of TMD I make sure any occlusal alterations are made in a reversible manner (i.e. with some from splint) and the patient is aware that there is little hard evidence behind the approach. And I’m certainly not proposing orthodontics as a first -line ‘cure’ or, indeed, a cause of TMD.
    Thank you Professor O’Brien for helping to keep the air so clear in the evidence-based dentistry environment.
    *Neuromuscular function in healthy occlusion.
    Forrester SE, Allen SJ, Presswood RG, Toy AC, Pain MT.
    J Oral Rehabil. 2010 Sep;37(9):663-9.

  5. After 40 years of practice I must state that I feel, based on my experience and training, that there is a correlation to occlusion and TMJ complaints IN SOME PATIENTS!!!! We have all, or rather many of us have, applied a splint and made occlusal adjustment to our TMD patients and found that they do better. Sometimes more than other. I reject the claim that that those results are merely a placebo effect; “you may as well place a sock in the mouth, you would get the same result.” If that were the case I would have a stock of socks in my cupboards. I think the issue is that TMJ problems are very difficult to diagnose and treat. They are multi-factorial conditions, with occlusion being one, and in my belief a major one, factor. There are also stress, personality, trauma, genetics, and the individual adaptive capacity of the patient. The ART of the practice of dentistry comes into a play to huge degree in treating these cases. There is way too much variability in our individual patients and in the manner of practice to easily perform meaningful studies. I think the studies are flawed, rather than the concept. Indeed, much more attention needs to be made to more exacting and research methods that take into account all of these TMD conditions. In the meantime, let’s not throw the baby out with the bath water and just throw up our arms and say, “Well, there’s the evidence!!! Nothing works.” We would be doing a great disservice to our patients and the profession if we did so. A better approach is to proceed eyes wide opened with informed consent in treating our patients about what we do know, what we believe and why we believe it, and the options they have…and of course, always putting the patients’s best interest above anything else.

  6. Does this lead to the conclusion if Occlusion has no deleterious effect upon TMD one way or another, then Orthodontics having arbitrary rules of occlusion is similarly invalid and arbitrary to the rules of occlusion???

    If it doesn’t matter how the teeth meet or function wrt TMD or symptoms, then surely it’s just cosmetic if no symptoms ie: not being Class 1 isn’t a disease and there are NO oral health grounds for treatment, just cosmetic then ???

    Yours curiously,


    • No not at all. It means that there is an absence of evidence and this does not mean that there is evidence of absence…There are some clear indications for orthodontic treatment for example, severe crowding, impactions, large overjets leading to trauma. You need to obtain class I occlusion to correct all these features.

      • So we have to tell our patients there is an absence of credible evidence in the scientific literature, especially for much of Ortho, so using best practice Evidence Based Medicine triple-criteria, that published-evidence tennet scores zero leaving Clinical Experience and Patient Wishes to dominate the discussion/decision, basically?

        Yours logically,


        ps – evidence only moderate wet reduced trauma for large overjets of say 9+mm, so class2 with 5mm OJ shouldn’t be made Cl1 for ‘health’ reasons?!?

        • We have to use clinical experience and patients wishes to inform all decisions. this is particularly relevant when we do not have strong evidence. There is actually more evidence in orthodontics than you realise. However, I do agree there are several areas where it is lacking.

          Your comment on correction of OJ is correct. This is why OJ less than 6mm are in Grade 3 of the Dental Health Component of IOTN.

      • With due respect to the author and his professional integrity, doesn’t it sound like juggling with phrases?
        wrt to “absence of evidence does not mean that there is evidence of absence”. More so, after decades of experimentation and observation and publication of hundreds of researches.


  7. Are there not people in this world who naturally have perfect occlusion? All 32 permeant teeth perfectly straight with jaws beautifully balanced. Why not find this 5% and see if they have TMD? Then we would know if there was a link.

    Every other “control” is a farce in disguise, no?

  8. Hi Kevin thanks for the article.

    1. Would it not also be prudent and ethical to inform the patient that you don’t know if orthodontics will worsen or improve or not affect TMD if the patient already indicates symptoms before treatment?

    2. And if the patient complains either of developing TMD symptoms during orthodontics (however unlikely) or worsening of underlying symptoms present pre-treat : that as practitioners, you have, as yet not conducted sufficient research to conclude how the two pathologies may be related so don’t know how one affects the other?

    In order to allow the patient to make the most informed and objective decision possible about his/her treatment and health.

    Thanks F

    • Yes, this is correct. I think that this information is already given by practitioners. I certainly do this.

      • I have never received this information of the several consultations with orthodontists I have had. It was never mentioned unless I made specific comment of it.
        A general enquiry of my colleagues and friends who have undergone orthodontic treatment reveals the same. F

  9. Statistically, it may be that dental occlusion isn’t associated with TMD, but dental malocclusion certainly causes TMD in some cases. I’m not a dental professional, but I hope that my input as a patient is also welcome in this forum. Until a dentist removed one of my wisdom teeth and thereby all stability in my jaw (four teeth had been extracted during adolescence) and causing severe malocclusion, I had no TMD issues whatsoever. The malocclusion forced me to keep my mandible in a posterior position to have more than just a millimeter of contact between the teeth in the maxilla and the mandible, thereby causing an extreme overbite and TMD. The pain, clicking and fatigue kept increasing in severity until 10 years later, when I made myself a bite plane which I wore even in daytime. My mandible moved forward to its natural position and the issues went away almost instantaneously. I should add that it was a dental professional who had successfully treated tinnitus in numerous patients who pointed out that my TMD was due to the acquired overbite (which in turn was due to the malocclusion).

  10. Kevin, your 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” are probably accurate considering the current state of scientific understanding of TMD.

    The clinical reality, though, especially among those who have spent time in Craniomandibular practice, is that there most definitely IS a relationship.

    If one alters the occlusion (the mandibular/maxillary relationship) in any direction, vertically, antero-posteriorly or laterally, there MUST be a concomitant alteration in each condyle/fossa relationship. If one alters the maxilla to the extent that there is an effect on the mandible, the same principle applies. It is not a matter for science; it is a matter of simple bio-mechanics. There is no doubt that a group of Year 10 biology students in school, studying the human skull, would come to the same conclusion.

    It is also a matter of degree; it is generally understood that the TM joint is the most adaptable joint in the body, so that if the occlusal changes are minimal there will be little or no effect on joint function. If the individual’s cranial status is good, then a considerable degree of adaptability is available and TM joint symptoms may not appear.

    However, this does not apply to all individuals; some are set up or susceptible to TM problems and the slightest occlusal change can become immediately problematic. These are the ones encountered so frequently in craniomandibular practice who have a history extraction/retraction orthodontics along with their current TM issues.

    These are the cases that confuse the scientists, who seem to imagine we are claiming that there is a 100% mathematical relationship between retraction orthodontics and TMD. This misunderstanding also explains why the orthodontic establishment is so defensive about this issue.

    So should extraction/retraction orthodontics be avoided for temporomandibular reasons? Most certainly. But there are many other reasons too. All of which point to the importance a thorough TMJ examination before the final orthodontic treatment plan is decided. To commence orthodontic treatment in the presence of frank TM dysfunction will simply ‘fix’ the TM issues in place and in our view would amount to gross professional incompetence. Sadly, the establishment denial of the connection makes this disaster more likely to occur, which is why we are grateful for your comment “we cannot conclude there is no association . . .”

  11. The fundamental problem with this discussion about occlusion, and in fact many discussion about “evidence”, is that several essential words after the word “evidence” are frequently missing.
    The missing words are “in the literature”
    There is plenty of evidence clinically that altering occlusions can help patients with jaw joint problems If there is no “evidence” in the literature then this shows the inadequacy of the literature
    Discouraging dentists from adjusting occlusion is a disservice to patients

    • I totally agree with you. This study is useful to show the inadequacy of the sperimental designs. The conclusions are arbitrary and source of the misunderstanding.

  12. This is absolutely disgraceful.

    The ‘bite’ is physically linked to jaw function in terms of the position of the jaw and in terms of the reciprocal forces on it.

    Do you have any understanding of Newton’s third Law? it applies to the teeth as much as anything else. When you close your mouth there are reciprocal forces on the jaw muscles dependent on the geometry of the contact surface, the bite.

    These papers are deceitful. the reasoning underlying them is totally inappropriate for the physics at hand. you can’t look at teeth and know the positioning and forces on the jaw joint.

    personally, my life has been destroyed by a dysfunctional bite. It is a living hell and I have to face these disgusting trick statistics denying my problem exists.

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