The Influence of Initial Breakage on Size Reduction during Habitual Chewing of a Solid Test Food

Food comminution during chewing is due to intra-oral particle selection and subsequent breakage. Under conditions of habitual chewing and a nearly complete selection, the influence of initial breakage on particle size reduction was studied in trials with a first chewing cycle (N = 1) from a sequence of randomized trials with various cycle numbers. Furthermore, relationships were examined between degree of fragmentation from breakage (r-fr), molar maximal bite force (MBF) and chewing efficiency (the number of cycles needed to half the initial particle size, N(1/2-Xo)).

Thirty-one subjects with a natural dentition chewed samples of 2 half-cubes (9.6 × 9.6x4.8 mm) of Optosil®, using sequences with 1-7 cycles, in 2-10 randomized trials; 10 trials with one cycle. Particle size distributions by underweight, characterized by median particle size, X₅₀, were obtained using sieving. N(1/2-Xo) was derived from the log(X₅₀)-log(N) relationship. and r-fr from the cumulative distribution of underweight fractions of damaged particles for N = 1. MBF was determined on both sides of the jaw using a force transducer and averaged.

A strong, decreasing regression occurred in X₅₀ at N = 1 with r-fr (R² = 0.934, p < 0.001). The decreasing regression of N(1/2-Xo) with r-fr was moderately strong (R² = 0.454; p < 0.001). Thus, initial size reduction is strongly determined by breakage and overall reduction partly, when chewing small amounts of particles. N(1/2-Xo) vs. MBF and r-fr vs. MBF were weakly related (R²≤0.124, p = 0.052-0.127). The lack of a pronounced relationship between r-fr and MBF suggests that either MBF is not relevant but supra-threshold force, or that another factor, occlusion, may influence breakage.