EFFECTS OF FOOD TEXTURE AND SAMPLE THICKNESS ON MANDIBULAR MOVEMENT AND HARDNESS ASSESSMENT DURING BITING IN MAN

This study was designed to investigate the relationship among jaw move ments, physical characteristics of food, and sensory perception of har dness in man. Vertical movements of the mandible were recorded with an infrared tracking device in humans during biting on two test foods, c arrot and cheese. Samples of standard length (2 cm) and width (2 cm) w ere prepared in three different thicknesses (0.5, 1.0, and 1.5 cm). Ni ne subjects were asked to perform two types of bite with their incisor teeth. In the first, they cut through the food, then stopped and spat out the pieces (bite alone); in the second, biting was followed by ma stication and swallowing (bite+chew). The 12 conditions (thickness x3, food x2, and bite x2) were presented in a random order within each bl ock, and blocks were repeated five times (60 trials per subject). Subj ects also estimated the hardness of the samples twice for each conditi on on visual analogue scales (VAS) 100 mm long. The duration, vertical amplitude, and maximum vertical velocity of the mandible during bitin g were calculated by computer for the three phases of the movements (o pening, and fast and slow closing). Multilevel statistical models were used for data analysis. The estimated hardness scores associated with the first bite of thin carrot (59.0 VAS units) was significantly grea ter than for cheese (16.8 VAS units). The type of bite had no signific ant effect on these scores, but the estimate of hardness was significa ntly greater for the thickest sample (+13.3 VAS units). Food type had its strongest effect on the slow-closing phase. In particular, the pea k velocity that followed the fracturing of the food sample was much gr eater for carrot than for cheese (thin, 34.1 mm.s(-1) vs. 26.6 mm.s(-1 )), and the difference between foods increased with thickness. The amp litude of opening was significantly greater for the thickest sample th an for the other two. There were no significant relationships between VAS scores and the movement parameters. These results suggest that, wh en humans bite food: (1) changing the thickness of food has a greater effect on movement parameters than changing from soft to hard food, (2 ) the parameters of biting change little if biting is followed by mast ication, (3) hardness perception is dependent on the thickness of food , (4) hardness perception is not different when food is removed from t he mouth than when it is chewed and swallowed, and (5) there is no rel ationship between any of the parameters of movement that change with f ood type and the perceived hardness of food.