Forces applied by the incisors and roles of periodontal afferents during food-holding and -biting tasks.

The force exerted by the central incisors while holding and splitting a food morsel was analyzed to characterize human biting behavior. The force was continuously sampled by a transducer-equipped plate upon which a small piece of dry biscuit or half a peanut rested. Subjects were instructed to position the plate between the incisor teeth and to split the morsel either immediately ("split task") or after holding it for a brief period ("hold-and-split task"). While holding either food substance between the incisors, subjects automatically exerted light contact forces of less than 1 N (0.36-0.76N range among subjects). Considering that the subjects had no instructions about what force levels to employ, the hold force was remarkably stable during individual trials and highly similar among trials. Even during the split task, subjects opted to "hold" the morsel momentarily on ca. 50% of the trials with a similar, low contact force. For both tasks, subjects split the morsel by exerting a distinct, rapidly executed ramp increase in force. The split occurred at 7.8-10.3 N (range among subjects) bite force for the biscuit and 16.0-19.0 N for the peanut. The magnitude of the forces used during the hold phase were within the range over which most periodontal afferents are optimally sensitive to changes in force, i.e., forces below about 1 N. This observation suggested that the subjects automatically adjusted the force to maximize the availability of information from periodontal afferents and avoided higher forces at which the sensitivity of most afferents was not optimal. We further confirmed that the periodontal receptors serve a role in controlling the hold force by anesthetizing the periodontal tissues: subjects employed considerably higher and more variable hold forces, but there was no effect on the split phase. In addition, the morsel frequently escaped from the incisal edges of the teeth while the subject attempted to maintain it in position. It was concluded that subjects rely on signals from periodontal afferents to regulate the jaw muscles, particularly when they first contact, manipulate, and hold food substances between the teeth.