Variables affecting measurements of vertical occlusal force.

Previous studies of occlusal force have provided conflicting results. The purpose of these studies was to determine whether the extent of vertical opening, contralateral occlusal support, or head posture influenced vertical occlusal forces during swallowing, simulated chewing, and maximum biting effort. Three samples of subjects with normal vertical facial proportions--one each of children, adolescents, and young adults--were evaluated to determine the effects of changes in small (2.5 vs. 6.0 mm) vertical separation of the first molars. A sample of young adults was used to evaluate changes in large (10-40 mm) vertical openings, and a sample of adolescents was used to investigate the effect of contralateral support and head posture. All between-group comparisons were evaluated using non-parametric statistics. For the small vertical openings, there was significantly more vertical occlusal force at 6.0 than 2.5 mm in children during swallowing and chewing but not during maximum biting effort. In adults, there was significantly more force during swallowing at 6.0 than at 2.5 mm separation, but no differences in chewing or maximum biting. Increasingly large vertical openings resulted in a progressive increase in maximum bite force to a maximum at about 20 mm, followed by a decrease and then a second increase to near-maximum force at about 40 mm for young adults. There were no significant differences in vertical force with or without contralateral support or between flexed, normal, and extended head postures at either of the small openings.