Purpose: The objective of this study was to determine whether elevator and depressor muscle activity during 5 minutes of mastication is affected by the presence of a prosthetic appliance in elderly patients. Materials and Methods: Thirty edentulous subjects (EG) and 30 age-matched dentate subjects (DG) were studied. Surface electromyographic (EMG) recordings were obtained from the anterior temporal muscle, masseter muscle, and the submandibular group in the region of the anterior belly of the digastric muscle on the left and right sides. Muscle activity was recorded during maximal voluntary contraction (MVC) in the intercuspal position, maximal opening (Omax), and during 5 minutes of mastication. Elevator muscle activity during mastication was expressed as a percentage of maximal muscle activity in the intercuspal position (%MVC), and depressor muscle activity was expressed as a percentage of maximal opening (%Omax). The effect of 3 factors was investigated using a mixed analysis of variance design: the factor of muscle, with 6 muscles involved; the factor of time (5 minutes of mastication); and the factor of dental status, where some participants had their own natural dentition and others had complete dentures. Results: The results revealed significant effects for the factors "muscle" and "time" (P .001 for the factor "muscle"; P .001 for the factor "time"). The time by group interaction was significant (P = .046). In the EG, muscle activity gradually decreased during the 5-minute interval of mastication, while in the DG it decreased more rapidly from the first to the third minute and then increased until the fifth minute. There was also a significant effect regarding the presence of natural teeth or complete dentures (P .034). Complete denture wearers had higher muscle activity relative to %MVC or %Omax than dentate subjects. Conclusions: Muscle activity during 5 minutes of mastication depended greatly on the presence of the prosthetic appliance, since edentulous subjects had to use higher potentials of muscle activity (%MVC or %Omax) than age-matched dentate subjects, and were unable to increase activity at the end of mastication. The difference in chewing patterns and activity between complete denture wearers and dentate subjects should be explained to patients prior to prosthetic treatment to help them adjust their expectations.