Structural Equation Modelling of the Relationship Between Parafunctions and Pain

Objectives: Human studies show that tooth contact/clenching produces increased pain and may lead to a diagnosis of temporomandibular muscle and joint disorder (TMJD). Animal studies show that evocation of pain leads to leads to clenching/activation of masseter muscles as a potential coping mechanism. In this study, pain and behavior data obtained from humans were subjected to structural equation modeling to examine causal pathways between tooth contact/clenching and pain.

Methods: Research Diagnostic Criteria for TMD were used to identify individuals with myofascial pain (with/without arthralgia), disc displacement, and non-TMD controls. Experience sampling methods were used to obtain information on pain. Subjects (N=86) were paged approximately every 120 minutes during waking hours and instructed to complete a pre-printed questionnaire form when paged. Subjects were paged for one week. Two structural equation models were specified, both containing two latent variables: (1) parafunction (represented by three observed variables), and (2) pain (represented by two observed variables). One model examined the path from parafunction to pain, and the other examined the path pain to parafunction (Figure 1). AMOS software (v. 7) was used to perform the analysis.

Results: The mean number of pager questionnaire cards completed by subjects was 47.7 (±9.7). Means were generated for each subject from the cards. Both models were identified (p < .001). The coefficient for the path from parafunction to pain was 0.78, and the coefficient for the path from pain to parafunction was 0.41.

Conclusions: The results indicate that the path from parafunction to pain is stronger in humans than the path from pain to parafunction. The findings are consistent with studies showing that experimental clenching produces pain in humans. Reduction of oral parafunctions may result in diminished pain in TMJD sufferers. Supported in part by grant DE13563 from the National Institute of Dental and Craniofacial Research.