Meeting Abstract

P2.77  Jan. 5  An experimental model for quantifying the modulation of mastication to variation in food material properties in Cebus capucinus REED, D.A.*; ROSS, C.F.; Univ. of Chicago; Univ. of Chicago dreed@uchicago.edu

The masticatory system is ideal for evaluating hypotheses regarding the modulation of motor systems to the external environment during rhythmic behaviors. Food material properties are known to influence EMG activity and kinematics of mammalian mastication, but their precise effects are not well documented, in part because of the difficulty of precisely measuring jaw kinematics in three dimensions. To address these issues, three-dimensional kinematic, EMG, and mandibular bone strain data were collected from two Cebus capucinus using a Vicon motion analysis system. A novel bone screw mechanism eliminated error resulting from skin movement and enabled collection of three-dimensional kinematic data with a high degree of precision (+/-0.048 mm). The positions of the first molars were digitized relative to the position of each kinematic marker. The digitized coordinate system was then rotated into the kinematic coordinate system using Euler Angles and molar displacement was quantified throughout the chew cycle. The relative timing of a range of EMG, bone strain and jaw kinematic events were then calculated, including onset and offset of fast-strain (FST) loading, fast-close slow-close (FCSC) transition, and minimum gape. Preliminary analyses reveal a significant relationship between the closing angle of the jaw and the square root of the ratio of toughness to Young�s modulus [(R/E)^0.5] for 17 food types. Significant relationships were also found between (R/E)^0.5 and both the displacement of the first molar from FCSC transition to minimum gape and the time from minimum gape to the FST offset. These relationships suggest that foods with a high (R/E)^0.5 elicit a more vertical jaw angle prior to occlusion, experience a greater displacement of the molar from FCSC transition to minimum gape, and induce a more rapid unloading time relative to minimum gape.