Chewing efficiency of pre-orthognathic surgery patients: selection and breakage of food particles

Comminution of food is the composite result of selection and breakage. Selection is characterised by the chance that a food particle will at least be damaged by the teeth during chewing. For any size, this chance equals the ratio between the weight of damaged or broken particles and that of all initial particles. The breakage process refers to fracturing of selected particles. The aim was to examine whether a reduced chewing performance of pre-orthognathic surgery patients is due to an impairment of selection, breakage or both. Eight cubes of 8.0 mm of the silicone-rubber Optosil " were used as a test food to determine chewing efficiency for 12 patients (skeletal Angle Class II and dental Angle Class II, subdivision 1) and 12 controls (class I molar relation). Selection and breakage were determined in one-chew experiments using various particle sizes. Chewing efficiency was significantly lower for the patients than for the controls. The selection chance was significantly smaller for the patients, in particular for smaller (< or = 4.8 mm) particles. The degree of breakage was lower for the patients, in particular for medium-sized particles of 4.8 mm. These findings suggest that the reduced chewing performance of pre-orthognathic surgery patients is due to an impairment of both selection and breakage.