September 29, 2022

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.

 

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.

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.

Final comments

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.

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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,

    Tony.

    • 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,

        Tony.

        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.

        Thanks

  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).

    • Allow me to express my despair over some of the phraseology being used here. Starting with the title – – TMD is – – as if there is only one Temporomandibular Disorder. According to the classification that I developed many years ago, there are at least 27 definable Temporomandibular Disorders. It would be better if we would use the phraseology – – TMD‘s are –
      – and continue from there. Crossbites with significant lateral shifts are totally different creatures than condylar subluxations. The first is amenable to Orthodontic therapy, and the latter isn’t. I have long stated that there is absolutely no indication that the Temporomandibular Joints, which are a pair of synovial joints, are in any way exempt from the pathologies that afflict other synovial joints. Nobody speaks of a knee disorder in the singular, and it is time we stop referring to TMD as a diagnostic finding. It isn’t.

  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.

  13. I thought Jeff Okeson buried this argument at least 15 years ago. That said, he was looking at static occlusal features and evidence mostly from the prosthodontic literature. For me, I’m always looking at CO:CR discrepancies where there is a lateral component. I’d rather not leave those untreated in growing patients purely from their tendency to promote continuing asymmetrical faces, irrespective of their contribution or otherwise to future TMD.

  14. Is it possible that we are addressing the problem from a distorted perspective?
    The authors (like many others) are looking for an occlusion-tmd relation.
    TMD is a mandibular pathology.
    Maybe they should look at mandibular positioning in space, compared to the cranium, rather than occlusion. Occlusion could be perfect but with a distorted mandibular positioning in space.
    Just the humble opinion of a young orthodontist.
    I think that sometimes we ask wrong questions.

  15. If you ask the wrong questions when you design a study, you won’t get the answers that are needed. If you decide what you want the answer to be in any study before you conduct the study, then you will reach that answer one way or another because the data will be interpreted accordingly to reach the desired conclusion. Many are aware of some of the most eminent culprits who do this in the area of TMJ problems.

  16. The only question in my dental/orthodontic career where my clinical experience illustrates a diametrically opposed view to the literature.
    Very confusing !!

  17. Once there was a legal judgement that results of orthodontic treatment in a 12-year-old manifested the same patient aged 30 expressing TMD problems. Then “research” to show there was no correlation between ortho and TMJ NEEDED to be created. Yes I said it. Can you imagine the panic in the orthodontic specialty if a patient could come back and sue later for poor orthodontic treatment? It’s really a disgrace to the profession in a magnitude perhaps worse than the KOL bashing endemic to this site….and yes most are hucksters. But is orthodontic research really making any contribution to the quality of clinical treatment outcomes? My opinion is not at all.
    I know plenty of clinicians that anecdotally have observed improvement in TMD from well done orthodontic tx. For many, there is little hesitation to claim ortho done properly can ameliorate TMD. Isn’t it obvious that ortho NOT done properly might exacerbate or even cause TMD.
    If one believes research is so amazing in orthodontics you celebrate a false religion. Sadly, and all too often, university research proves to either produce conclusions so obvious one wonders why the study was even done. Or, even worse, the conclusions are simply wrong and violate common sense. We need good science but orthodontic research continues to fail us.

  18. I have not read the original paper, but based on Dr O’Brien’s summary, I am skeptical of its clinical relevance. Only adults were “participants”. As TMD is multifactorial what are the papers included in the review looking at? Are the symptoms due to masticatory muscle spasms and/or internal joint derangements and other arthritides (which may be more prevalent in adults). Combining all types of malocclusions in a study dilutes those malocclusions which in my experience are associated in some cases with TMD and when treated symptoms subside. Such as Cl II div 2 with deep overbites, and molar balancing interferences. In my opinion systematic reviews are not useful – its like lumping apples and oranges together.
    Regarding the comment about CR-CO discrepancies :
    Melvin Moss – Dent Clin N Amer 19:3, July 1975: “Despite its theoretical clinical utility, the search for an immutable condylar position, defined as centric relation….unfortunately is an ephemeral undertaking”.
    Keim R – J Clin Ortho 37:7,349, 2003 : “…the term centric relation has become obsolete. Like the mystical Shangri-La, it is a wonderful place where all problems are solved – but it does not exist in physical reality.

  19. I’m surprised that there are not more comments on this topic. There are so many thoughts this can lead to.

    First, this was such a big deal to us all when that orthodontist lost the million-dollar lawsuit for extracting upper 4s, and Witzig was admitted as an expert orthodontic witness even though he was not an orthodontist. Essentially, in hind sight, this orthodontist lost a million-dollar case for a problem they did not cause.

    Second, if occlusion really has no relationship to TMD, think of the very well-known and respected people who advocated for the equilibration of TMD patients. Many textbooks were written by very respected experts on this. Many dentists and orthodontists paid $10,000 or more for in-office courses on this. Many more patients paid thousands to have this done. Yet, there is currently no evidence that much of anything was ever accomplished, beyond the removal of enamel.

    Third and last, though the list could go on. For those of us treating TMD at any level, we have to wonder, if occlusion has no relationship to TMD, why are some patients’ symptoms reduced or resolved with splint therapy? Yes, I know that a Splint has effects outside of the occlusion. However, it is interesting to ponder.

    Last, yes that is a cheater 4th, I have enjoyed the tenuous research conclusions that the good news is that orthodontics is not causing TMD, and the bad news is that we are not preventing it. Thanks for posting!

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