The aim of this study was to evaluate the longitudinal clinical and physiological changes in jaw elevator muscle activity of partially edentulous patients, for approximately 3.5 years after treatment by removable partial dentures with free-end saddles. Seven patients (4 males and 3 females, aged 38-68 years) who visited a university dental hospital, and were found to have no signs and symptoms of TMJ disorders, participated in the follow-up study. The functional impression method with wax was used in the treatment process of these patients. At the follow-up times of 0.5, 1, 2, 3, and 3.5 years after denture deriverly, EMG activities using bipolar surface electrodes were recorded from masseter and anterior temporal muscle on both sides during maximal voluntary clenching and tapping, and at the same time the maximal bite force was also recorded using the Dental Prescale System. The integrated EMG, the correlation coefficient between muscle activities of both sides, bite force, and the location of the occlusal load center, were analyzed using repeated measured ANOVA. A comparison between each measuring session was carried out using Bonferroni's method.
Results were as follows : i) The muscle function of partially edentulous patients was clearly activated by wearing a removable partial denture, and the activation was kept at the same level until 3.5 years after denture deriverly. ii) The activation of jaw elevator muscles by wearing a denture was greater in masseter muscle than in anterior temporal muscle. This finding reflected the effect of the recovered occlusal contact. iii) The occlusal load center of the recovered dentition by a removable partial denture shifted anteroposteriorly close to the end abutment teeth.