Opto-electronic analyses of masticatory mandibular movements and velocities in the rat

Abstract

High-speed, high-resolution data (frontal plane) were collected from 6 Sprague-Dawley rats by opto-electronic mandibular tracking (OMT), followed by microcomputer analysis of individual chew cycles. Mastication comprised rapidly alternating, unilateral cycles with variable degrees of lateral translation. There was no evidence of bilateral mastication (simultaneous chewing on both left and right sides). Analysis revealed significant ( p ⩽ 0.01) differences between whole-cycle, slow-open (SO) phase, fast-open (FO) phase, fast-close (FC) phase, and slow-close (SC) phase duration, height, width, and velocity during mastication of standardized foods (pellets and slurry). Regression analysis between millimetres of vertical/horizontal movement ( Y) and vertical/horizontal velocity ( X) revealed differences during these mastications. Whole-cycle and SO-phase regression equations had the greatest disparity between pellet and slurry chewing for both vertical and horizontal movements. Correlation coefficient analysis between movement and velocity data indicated that (1) vertical correlations were smaller than horizontal ones, (2) slurry correlations were greater than pellet ones except for whole cycles, (3) FO phase had the largest movement/velocity correlation during both pellet and slurry mastication, and, that (4) SC phase had the smallest movement/velocity correlation. Vertical and horizontal movements during pellet FC phase were significantly ( p ⩽ 0.01) greater than slurry ones; both vertical and horizontal movements during pellet SC phase were significantly ( p ⩽ 0.01) less than slurry ones. This phase-isostasy was also detected during vertical movements in SO and FO phases. These findings, when combined with information concerning muscle-spindle activity, suggest that vertical masticatory movements of the mandible are under less neuromuscular control than horizontal ones.