Although masticatory performance is most closely related to occlusal factors, it is difficult to determine precisely the interrelationships and their contributions to masticatory function. The research project of Lepley et al, reported in the May 2011 issue, was well designed and provided a general demonstration of masticatory performance and the influencing factors. But I want to draw attention to 3 aspects of the report.
First, the area, number, and locations of occlusal contacts are influenced by different levels of bite force. Previous studies have indicated that bite force and occlusal contact area of the entire dental arch increase in parallel with clenching intensity. The locations of the occlusal contacts also change with different levels of clenching intensity. This is mainly because of physiologic tooth mobility and dental arch deformation during clenching. Nonrigidity and deformation of the bone and periodontal ligament allow minor tooth movement during masticatory function. The higher the level of clenching intensity applied between antagonistic teeth, the more tooth displacements would occur in the periodontal socket. This results in a decrease of space between antagonistic teeth and an increase in occlusal contact area.
Second, the bite force in chewing food is lower than the maximum bite force. It is only 30% to 50% of the value of the maximum bite force. From this point of view, control of the occlusal force is important in evaluating occlusal contacts. It is better to study the relationship between the actual force on a tooth and the resulting occlusal contact patterns. That is, the contact pattern in the intercuspal occlusion should be evaluated in relation to the level of clenching intensity. The different levels of clenching intensity can be monitored by the activity of the masseter with electromyography and visual biofeedback.
Third, the accuracy and precision of evaluating maximum bite force are affected by the mechanical properties of the bite-force measuring equipment. Bite-force measuring methods with pressure-sensitive detectors (<0.1 mm in thickness) are superior to those with a strain-gauge transducer, in which the maximum bite forces are recorded by measuring heads placed on the tooth with 3 to 7 mm of bite opening. Bite opening produces changes in vertical dimensions, which can affect myofunction and result in bite-force value changes. Previous studies have stated that whether jaw separation was increased or decreased from the optimum opening (14-20 mm), the strength of the maximum bite force would decrease.
On the whole, to determine the relationship between bite force and occlusal contact, bite force should be evaluated under natural conditions and with minimal disturbance to the occlusion. Moreover, the area and location of occlusal contacts should be recorded at the same time as the bite force is evaluated.