Association of Masticatory Ability with Functional Tooth Units Composition Categories

Objectives: It is reported that the masticatory ability is influenced by the number of natural teeth and functional tooth units (FTUs). The aim of this study was to examine the relationship of masticatory ability with FTUs composition categories in Japanese adults with and without 20 and more natural teeth. Methods: Subjects were 2,164 people (Male: 916; 61.7±8.8 years old, Female: 1248, 59.8±9.2 years old) who lived in Akita Prefecture. The number of FTUs was defined as pairs of posterior opposing natural and artificial teeth on implant-supported, fixed (pontics) and removable prostheses, in which one FTU was defined as two opposing premolars and two FTUs as two opposing molars. Subjects were divided into 2 groups based on whether they had 20 and more natural teeth or not. Subjects in each group were further divided into two groups according to a self-reported chewing-ability test: subjects who reported they could chew all 15 test foods and those who reported they could not chew some test foods. FTUs composition categories were compared at opposing tooth pair level. Results: Among subjects with 20 and more natural teeth, the total proportion of FTUs at every tooth pair was higher in those who could chew all foods compared to those who could not. The subjects without chewing difficulties had higher proportion of FTUs with natural teeth, especially in molars, compared to their counterparts. Among subjects with 19 and less natural teeth, there was no apparent difference in the total proportion of FTUs at each tooth pair. The subjects who could chew all foods had higher proportion of FTUs with natural teeth and lower proportion of FTUs based on removable prosthetic teeth. Conclusion: The composition category of FTUs, particularly the number of FTUs based on natural teeth, was considered a key factor affecting the self-reported masticatory ability.