Variables related to masseter muscle function: a maximum R2 improvement analysis.

A multiple linear regression analysis, with stepwise maximum R2 improvement technique by forward selection and pair switching, was used to select the occlusal, morphologic, and histologic variables which explained most of the variation in bite force and electric masseter muscle activity. The variables comprised tooth contact and facial morphology together with thickness and fiber characteristics of the masseter muscle. The study included 13 healthy women, 21-28 yr of age, with a minimum of 24 teeth and no serious malocclusion. Significant exploratory models (R2: 0.55-0.85) were shown concerning bite force, and electromyographic amplitude during resting posture, maximal voluntary contraction (ICP), and unilateral chewing, as well as contraction time (chewing side). Muscle thickness and molar contact had a significant, positive effect on the level of forceful muscle contraction. The explorative model both demonstrated explicable relations, and offered better insight into interrelations than did univariate analysis.