Variations in human masseter and temporalis muscle activity related to food texture during free and side-imposed mastication

Adjustments of mastication to food texture have been examined in various st udies, but the notion of food texture is often ill defined and usually asse ssed in terms of hardness. The goal of this study was to examine the patter n of activity in masseter and temporalis muscles during mastication of diff erent food samples with known textural properties and to determine the inte rindividual variability. Electromyograms were recorded from the right and l eft masseter and temporalis muscles in 36 young adults during 'free-style' and side-imposed mastication. Five different typos of food with known rheol ogical properties were used. Both temporalis and masseter activity increase d with increased stress at maximum str ain of the chewed samples. A power f unction optimally described the relation between muscle work per chew and t he mechanical measurements of food; this confirmed that the masticatory pro cess is adjusted to accommodate to food texture. Temporalis muscle activity was more influenced by food texture than was masseter muscle activity. Les s muscle work was needed to prepare the food bolus for swallowing during fr ee-style mastication. However, 25% of the participants showed no difference s between unilateral side imposed mastication and 'free-style', suggesting that they might have greater chewing efficiency on one side. (C) 1999 Elsev ier Science Ltd. All rights reserved.