Effect of biting speed and jaw separation on force used to incise food.

Biting food too quickly might affect the control of jaw-closing muscles and the estimation of bite force. The objectives of this study were to compare the incisal bite forces used to cut food and the activity of masseter (MA) and anterior temporalis (AT) muscles between slow, habitual and fast biting speeds and also between small and large jaw openings. Twenty subjects were asked to use their incisors to cut through a 5 mm thick of chewing gum. In the first experiment, subjects bit at 10-mm incisal separation with slow, habitual and fast biting speeds, and in the second experiment, subjects bit with their habitual speed at 10- and 30-mm incisal separations. The activities in the MA and AT muscles were assessed with surface electromyography, and the bite force was recorded by a force sensor placed beneath the chewing gum. Peak bite forces and associated MA amplitudes were increased significantly as biting speed was increased (P's < .05). Anterior temporalis amplitude was significantly increased during fast biting compared to slow and habitual biting (P's < .001). At 30-mm incisal separation, both peak bite force and AT amplitude were significantly increased, whereas MA amplitude was significantly decreased, compared to those at 10-mm separation (P's < .05). Biting off food quickly with incisor teeth results in larger activities in both MA and AT muscles. In addition, biting a large piece of food resulted in increased activity of AT muscle. Both conditions could be injury stimulator for jaw muscles.