Methodological problems in studies on the etiology of temporomandibular disorders: Are the current opinions based on evidence?

The opinion that occlusal factors do not have a significant role in the etiology of temporomandibular disorders (TMD) is common among researchers. However, most epidemiological and experimental studies drawing conclusions on the causal role of occlusion in TMD suffer from methodological problems. The comparisons have not been informative because the compared groups have not differed sufficiently with regard to suspected occlusal risk factors. In particular, subjects unexposed to the risk factors are underrepresented or missing altogether. Studies applying design and methods recommended by experts of epidemiology have been unable to exclude occlusal factors from the etiology of TMD. The currently dominating opinion does not appear to be based on evidence. Keywords: etiological epidemiology, evidence-based dentistry, inclusion criteria, occlusion, representation