IMPACT VELOCITIES OF THE TEETH AFTER A SUDDEN UNLOADING AT VARIOUS INITIAL BITE FORCES, DEGREES OF MOUTH OPENING, AND DISTANCES OF TRAVEL

A potentially dangerous situation arises when an individual bites on h ard and brittle food which suddenly breaks, since the impact velocity of the lower teeth onto the upper teeth after the food is broken can b e high and may cause dental damage. The present experiments were desig ned to study the magnitude of the impact velocity after a sudden unloa ding at various initial bite forces, degrees of mouth opening, and dis tances of travel. Subjects were asked to perform a static biting task during which the resistance to the bite was suddenly removed. The upwa rd mandible movement was arrested after a certain distance. The veloci ty of the lower teeth at impact was calculated just before the mandibl e came to a standstill in combinations of 4 different bite forces (100 , 80, 60, and 40 N), 4 different initial degrees of mouth opening (33. 5, 30.5, 27.5, and 24.5 mm), and 3 different distances of travel of th e mandible (4.5, 3.0, and 1.5 mm). We found that the bite force rapidl y declined after the unloading, resulting in a small impact velocity o f the lower front teeth. This impact velocity largely depended on the magnitude of the initial bite force and the distance traveled; it was barely sensitive to variations in degree of initial mouth opening. The maximal velocity of the lower teeth was 0.43 m/s (at an initial bite force of 100 N). This maximum was reached after a distance of travel o f about 4 mm in 12 ms. The data suggest that the rapid decline in bite force coupled with a limitation of impact velocity is due to the forc e-velocity properties of the active jaw muscles and is not caused by n eural control.