The three major factors associated with oral mastication are, according to the authors' opinion, the masticatory pressure, the occlusal surface and the action of carrying food into proper position by the tongue and other oral muscles. The effects of this carrying action by muscles on masticatory efficiency were examined by means of a grinding test machine, specially devised by Yokota, one of the authors. The particle size distribution obtained when the machine was allowed to grind equally sized food particles was compared with that obtained when the machine was provided with unequally sized particles, and the results were shown in Fig. 1. and Fig. 2. From these data it was revealed that the carrying action exerted unequal effect upon the particles so that the larger particles were preferencially carried and grinded. Hence in measuring masticatory efficiency, hitherto adopted method of calculating amount of over size of the larger sieves only, should be re-examined as to its validity.
