Heterogeneity of temporomandibular disorders: cluster and case-control analyses.

Cluster analysis has been applied to the classification of temporomandibular disorders (TMD). The factors most often used in these classification systems are psychological and psychosocial. The aim of this study is to classify individuals diagnosed with TMD, by using cluster analysis based on their clinical condition and the global severity of the disease. In this study, one investigator selected the patients at the dental clinics located at the Jewish General and Montreal General hospitals, Montreal, Canada, from September 1994 to December 1997. The study population included 162 outpatients. The results of this study indicated the existence of four TMD subgroups: three TMD pain groups with localized or generalized disorder related to different levels of interferences in their life and a non-pain, but disabled group. External validation of the cluster solution support the replication of the four groups and allow for further interpretation of the patients' profiles. Clenching-grinding and depression were related to the groups presenting generalized TMD. Orthodontic treatment and female sex, however, were the factors associated with a more localized condition. This classification system may provide a better understanding of the TMD subgroups and clues for the treatment and prognosis of TMD patients.