Is Occlusion A Primary Cause to TMD?

A Multiple Logistic Regression Analysis of the Risk and Relative Odds of Temporomandibular Disorders as a Function of Common Occlusal Features

A.G. Pullinger (Section of Orofacial Pain and Occlusion, UCLA, School of Dentistry, 10833 Le Conte Avenue, Los Angeles, California 90024-1668), D.A. Seligman (Section of Orofacial Pain and Occlusion, UCLA, School of Dentistry, 10833 Le Conte Avenue, Los Angeles, California 90024-1668), J.A. Gornbein (UCLA Department of Biomathematics, Los Angeles, California 90024). Journal of Dental Research.

A multiple logistic regression analysis was used to compute the odds ratios for 11 common occlusal features for asymptomatic controls (n = 147) us. five temporomandibular disorder groups: Disc Displacement with Reduction (n = 81), Disc Displacement without Reduction (n = 48), Osteoarthrosis with Disc Displacement History (n = 75), Primary Osteoarthrosis (n = 85), and Myalgia Only (n = 124). Features that did not contribute included: retruded contact position (RCP) to intercuspal position (ICP) occlusal slides < 2 mm, slide asymmetry, unilateral RCP contacts, deep overbite, minimal overjet, dental midline discrepancies, ≤ 4 missing teeth, and maxillo-mandibular first molar relationship or cross-arch asymmetry. Groupings of a minimum of two to at most five occlusal variables contributed to the TMD patient groups. Significant increases in risk occurred selectively with anterior open bite (p < 0.01), unilateral maxillary lingual crossbite (p < 0.05 to p < 0.01), overjets > 6-7 mm (p < 0.05 to p < 0.01), ≥5-6 missing posterior teeth (p < 0.05 to p < 0.01), and RCP-ICP slides > 2 mm (p < 0.05 to p < 0.01). While the contribution of occlusion to the disease groups was not zero, most of the variation in each disease population was not explained by occlusal parameters. Thus, occlusion cannot be considered the unique or dominant factor in defining TMD populations. Certain features such as anterior open bite in osteoarthrosis patients were considered to be a consequence of rather than etiological factors for the disorder.

By Karen McCloy, DDS
Discussion:

Definitions

Occlusion is the act of the teeth coming together.

A primary cause is a factor that if present will reliably initiate the pathological changes that lead to tmd in a patient that did not previously have tmd.

TMD is a state of chronic pain in the tmj and the soft tissues supporting it. Chronic pain implies the presence of neural plasticity, so we are talking about a state of central sensitization involving the trigeminal nerve. There is no rule that says that tmd patients may not have similar changes in other areas of the central nervous system. Saying that someone has chronic pain does not address it's etiology, and someone with a clicking joint does not have tmd unless they have pain.

If you ask me is occlusion an important pain producing factor in patients with tmd the answer is a definite yes. In normal patients, without plastic changes, occclusal dsiharmony may be nociceptive, but that means it is not pain. Once there are neural changes it becomes pain, a form of allodynia where a nonpainful stimulus causes pain, like when you have a headache and touching your skin or brushing your hair hurts, and controlling it is key to calming down that nervous system.

But our treatment has multiple modes of action, besides occlusion.

It has a placebo effect, becasue we believe, and because of that our patients believe they will improve. Plus the decision to seek treatment also changes someones mindset and makes them more in control.

Our orthotics are a form of CBT.. cognitive behavioral therapy. We inserrt them and say lips together teeth apart, and the plastic reminds the patient what the correct oral posture is.

Orthotics provide an occlusal effect, because they provide stable and even point occlusion around the arch.

Orthotics have an orthopedic effect because the realign the mandible to the cranial base and cervical structures.

So we are back to Larry's the chicken or the egg. We only see the pain patients, and in them pain is correlated with occlusion, but that is not the same thing as causation. Our 1st study on nonpain patients showed that most of them had some form of occlusal issue, but they did not have pain. So I think something else has to happen.