The effect of particle size reduction on the jaw gape in human mastication

Eight subjects participated in chewing experiments to examine how the jaw gape in consecutive chewing cycles depends on the dimensions and the volume of the food bolus. Different volumes of chewing-gum and a silicone rubber (Optosil) were used. The initial particle size of Optosil was also varied. With the aid of a sieving procedure, the size distribution of Optosil particles was determined after different numbers of chewing cycles. The maximum size of a chewing-gum bolus along three orthogonal axes was determined after a random number of chewing cycles for all the volumes of chewing-gum offered. The jaw gape was measured by means of an optical motion analysis system and calibrated at the level of the first molars. The maximum jaw gape and the gape at the first fall in mandibular velocity after the onset of jaw-closing were determined for different chewing cycles from the position signal and its time derivative. For each volume of chewing gum offered to the subject, the average of the maximum gapes attained in the subsequent cycles of jaw movement was related to the characteristic height of a bolus of that volume; maximum velocity of closing appeared to occur while the antagonistic teeth were already penetrating the gum bolus. The increase in the maximum jaw gape, the gape at the velocity maximum, and the height of the gum bolus, as a function of the volume of chewing-gum, could be well-described by a power function of the volume. The exponent of the power function for both jaw gapes was only slightly smaller than the exponent obtained for the bolus height.(ABSTRACT TRUNCATED AT 250 WORDS)     

Visual evoked potentials and visual acuity after transurethral resection of the prostate

Changes in visual evoked potentials, visual acuity, blood ammonia levels and serum electrolytes (Na+ and K+) after transurethral resection of the prostate using glycine as an irrigating fluid performed under subarachnoid block were studied in 12 patients, in the pre-operative and immediate postoperative periods. Visual evoked potentials (p100 latency), recorded by shift of a checkerboard pattern, increased significantly from a pre-operative value of mean (SEM) 101.18 (1.63) msec in the right eye, and 102.5 (1.47) msec in the left eye to 108.91 (1.8) msec (p less than 0.01) and 108.08 (2.53) msec (p less than 0.01) respectively in the postoperative phase. There were no changes in visual acuity as assessed by a Snellen's chart, blood ammonia levels and serum electrolyte concentrations. The amount of glycine used intra-operatively for irrigation ranged from 3 to 31 litres.