THE ASSOCIATION AMONG OCCLUSAL CONTACTS, CLENCHING EFFORT, AND BITE FORCE DISTRIBUTION IN MAN

The contact area during habitual biting can vary according to the acti vity of the jaw musculature. Forceful masticatory muscle activity may also induce deformations of the dento-alveolar tissues and the support ing skeleton, yielding various tooth loads despite an apparently even distribution of tooth contacts. To investigate this variability, we me asured bite forces simultaneously at multiple dental sites during maxi mum-effort clenching tasks. In each of four healthy adults with comple te natural dentitions, four strain-gauge transducers in the right side of an acrylic maxillary appliance occluded with the lower canine, sec ond premolar, and first and second molars. These, and matching contral ateral contacts, were balanced by means of articulating paper and a fo rce monitor (type F appliance). Bite forces were recorded when the sub jects, without visual feedback, clenched maximally on the appliance. S imilar recordings were made when contralateral molar and all contralat eral contacts were removed (type R and type U appliances, respectively ). Although the relation between individual forces often changed durin g the initial increase in force, it was generally constant around the maximum. The maximum forces at the four dental locations varied in dis tribution between subjects, but were characterized by posteriorly incr easing forces. Forces in the anterior region (especially at the canine ) significantly increased (up to 10 times) when clenching took place o n unilateral contacts only (type U) as compared with fully balanced on es (type F). Bite force distribution thus changed with biting strength and the location of occlusal contacts. Increased force in the canine region during unilateral clenching seems related to the pattern of jaw muscle co-activation and the physical properties of the craniomandibu lar and dental supporting tissues which induce complex deformations of the lower jaw.