EFFECTS OF DOPAMINERGIC DRUGS, OCCLUSAL DISHARMONIES, AND CHRONIC STRESS ON NONFUNCTIONAL MASTICATORY ACTIVITY IN THE RAT, ASSESSED BY INCISAL ATTRITION

Observational methods and the recording of nonspecific jaw movements o r masticatory muscle activity have been used to evaluate oral parafunc tional movements in animal models of bruxism. In this study, we have u sed a new approach in which the non-functional masticatory activity in the rat was assessed by the measurement of incisal attrition, with th e aim of investigating the role of diverse factors involved in the eti ology of bruxism. We quantified the attrition rate weekly by making su perficial notches in the lower incisors and measuring the distances to the incisor edges. Repeated stimulation of the dopaminergic system wi th apomorphine led to an enhancement of the non-functional masticatory activity (p < 0.0001). The severity of the apomorphine-induced oral b ehavior was positively correlated (r(s) = 0.69, p < 0.01) with an incr ease in the incisal attrition rate (20.9%, p < 0.0001). Apomorphine-in duced non-functional masticatory activity was strongly enhanced by the placement of an acrylic cap on both lower incisors (306%, p < 0.0001) , but not by the cutting of a lower incisor. Repeated cocaine administ ration also increased the attrition rate (22.5%, p < 0.0001). However, neither chronic blockade of dopaminergic receptors with haloperidol, nor its withdrawal, modified attrition. In addition, since emotional d isturbances are considered to be causal factors of bruxism, we tested whether experimental stress might accelerate tooth wear. Exposure to t wo different chronic stress regimes did not induce significant changes in incisal attrition. Moreover, exposure to chronic stress after the withdrawal of chronic haloperidol treatment did not alter attrition ei ther. These results partially support the role of the central dopamine rgic system in bruxism and suggest that stress, in general, may not be a relevant factor in tooth wear.