Relationship between Mandibular Asymmetry and Temporomandibular Disorders

Abstract

Purpose: This study was performed to investigate the relationship between temporomandibular disorders (TMDs) and the asymmetry of the mandibular height. Methods: We compared 100 randomly selected TMD patients diagnosed by the research diagnostic criteria for TMD (RDC/TMD) Axis I with 100 non-TMD control subjects matched with the TMD patients in age and gender. The mandibular heights were measured on an orthopantomo-gram and the asymmetry index (AI) was calculated as previously described. Results: The absolute AI value of 4.37% turned out to be the least cutoff value defining asymmetry , which showed a significant difference in asymmetry incidence (p<0.01) between the TMD and control groups. The risk of TMD increased in the asymmetry group by 4.57 (odds ratio). The incidence of asymmetry was not related to age and gender in both of the TMD and control groups. When dividing the TMD group according to the RDC/TMD Axis I diagnosis, neither the incidence of muscle disorder nor disk displacement was related to the incidence of asymmetry. However, a higher incidence of asymmetry was observed in the subjects classified into the arthrosis/arthritis groups (p<0.01). Conclusions: Although it does not imply a direct cause-and-effect relationship, asymmetry resulting in more than 4.37% difference between mandibular heights may increase the risk of TMD and correlates positively to the incidence of arthritic change in the temporomandibular joint of TMD patients. a bilateral view for measuring vertical differences between both sides of the joints. From the results of such previous studies, mandibular asymmetry was observed to relate to the juvenile chronic arthritis, 11) TMD and para-function, 8) and articular disc displacement. 2,14-16) On the other hand, some limitations have been raised over those observations as well. It was pointed out that the cause of TMD is multifactorial and the criteria for diagnosis is unclear. 17) To clarify the relationship between TMD and asymmetry, gender, age and the influence of other factors should be considered and the diagnostic criteria for TMD should be clear. 4)