Effect of impact velocity and specimen stiffness on contact forces in a weight-controlled chewing simulator

Chewing simulators are used for preclinical evaluation of newly developed dental restorative materials. To guarantee the independence of test conditions, contact forces during chewing simulation should be independent of the specimen. Because of its mode of operation, i.e., impact of an antagonist, this requirement is not met for a widely used chewing simulator (Willytec/SD Mechatronik, Feldkirchen-Westerham, Germany). This study was therefore intended to clarify the extent to which specimen stiffness affects maximum contact force at different impact velocities. Possible differences between the forces in the eight test chambers were also of interest.

From each of five dental materials differing in Young's modulus, eight cylindrical disks were manufactured and embedded in specimen holders. Alumina spheres were used as antagonists. During chewing simulations with different impact velocities and dental materials, vertical acceleration was recorded and contact forces were estimated on the basis of these measurements.

Specimen stiffness and impact velocity had a substantial effect on maximum contact force. The force overshoot relative to the static load ranged from 4% for small specimen stiffness and low impact velocity to values greater than 200% for high specimen stiffness and high impact velocity. Large differences between the chambers were also detected.

Weight-controlled chewing simulations should be performed either with a low impact velocity or with a spring-damper system (placed between mass and specimen) which efficiently reduces the effects of contact force variation. Influence of specimen stiffness on contact forces must be considered at data interpretation.