I want to make a few observations about the recent discussion on malocclusions and temporomandibular disorders (TMDs) (Point/Counterpoint. Am J Orthod Dentofacial Orthop 2011;139:10-6). I agree that trying to improve the outcome of patients with orofacial pain, associated with centrally mediated nocturnal bruxism, by modifying minor slides or interferences is passé. However, there are many other types of malocclusions and TMDs with scant evidence about how treating one disorder might influence the outcome of the other disorder. Whether it would be warranted, or wise, to use a randomized controlled trial (RCT) to address the relative paucity of evidence in these circumstances is the subject for another discussion.
With respect to whether one disorder might be a risk factor for the occurrence of another disorder, such as whether malocclusions are risk factors for TMDs, investigators often face difficult obstacles in obtaining valid data. In general, an RCT cannot be used to study this question because randomization by malocclusion is not possible. Investigators have to resort to nonrandomized cohort or case-control studies that provide weaker evidence than an RCT and are often more difficult to interpret. Also, it is often difficult to limit a study to a specific type of malocclusion and TMD, which can weaken a study. Furthermore, in cohort studies, it can be difficult to recruit an adequate sample because of the low prevalence of some malocclusions and the low incidence of some TMDs. Thus, the discussion about whether malocclusions might be risk factors for the occurrence of TMDs (or the reverse, whether various TMDs might be risk factors for malocclusions) is likely to continue into the foreseeable future.