The effect of bolus size on the chewing cycle in humans.

No general agreement exists regarding the effect that bolus size has on masticatory movement, probably because both the size and texture of food change during mastication. In this experiment, in order to clarify the effect of bolus size on masticatory movement, a food that does not change in size and texture--chewing gum--was chosen, and the relationship between bolus size and the chewing cycle was analyzed. Ten healthy subjects in their twenties were asked to chew pieces of softened chewing gum of four different sizes. For ten cycles, beginning with the fifth cycle of mastication, gape and masticatory width were calculated for the spatial parameter of the chewing cycle, and cycle time was calculated as the temporal parameter. The relationship between these parameters and the bolus size was investigated. As the bolus size increased, the spatial and temporal parameters increased. In addition, there was a positive correlation between the bolus size and each parameter. The influence of the bolus size was as follows: gape, r = 0.91; masticatory width, r = 0.79; and cycle time, r = 0.74 (all, P < 0.001). From these results it was concluded that the shape of the chewing cycle was altered by the size of the food bolus, and that the changes in sensory input from the peripheries greatly affected the masticatory movement.