FORCES APPLIED BY THE INCISORS AND ROLES OF PERIODONTAL AFFERENTS DURING FOOD-HOLDING AND FOOD-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 whi ch a small piece of dry biscuit or half a peanut rested. Subjects were instructed to position the plate between the incisor teeth and to spl it the morsel either immediately (''split task'') or after holding it for a brief period (''hold-and-split task''). While holding either foo d substance between the incisors, subjects automatically exerted light contact forces of less than 1 N (0.36-0.76N range among subjects). Co nsidering that the subjects had no instructions about what force level s to employ, the hold force was remarkably stable during individual tr ials and highly similar among trials. Even during the split task, subj ects 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 forc e. 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 f orces 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 subjec ts automatically adjusted the force to maximize the availability of in formation from periodontal afferents and avoided higher forces at whic h the sensitivity of most afferents was not optimal. We further confir med that the periodontal receptors serve a role in controlling the hol d force by anesthetizing the periodontal tissues: subjects employed co nsiderably higher and more variable hold forces, but there was no effe ct on the split phase. In addition, the morsel frequently escaped from the incisal edges of the teeth while the subject attempted to maintai n it in position. It was concluded that subjects rely on signals from periodontal afferents to regulate the jaw muscles, particularly when t hey first contact, manipulate, and hold food substances between the te eth.