Object: Few studies quantify reactions of masticatory muscles during clenching at different occlusal positions in individuals with different anterior and posterior guidance relationship and different number of working-side occlusal contacts. The hypothesis that altered incisal guidance (IG) and a different number of working-side occlusal contacts in complete denture wearers (CDW) change a pattern of temporal muscle activity and loadings to the mandible during clenching in incisal and lateral positions was tested.
Design: EMG activity during clenching in incisal (IP) and left (LOP) and right lateral occlusal (ROP) positions was compared between dentate subjects (DS) with steeper IG than condylar guidance (PG) and canine or canine+first premolar guidance in laterotrusive movements with CDWs who had steeper PG than IG and group function. EMG values were expressed as percentages of maximum voluntary clenching in maximum intercuspation (ICP) in each individual.
Results: The CDWs exhibited significantly higher posterior temporal muscle (TP) activity in IP and during lateral biting on mediotrusive side than DSs. Their coronoid process had to be pulled backward by TP fibers to rotate condyle in a counter-clockwise direction (PG>IG); contrary DSs had to rotate condyle in a clockwise direction to compensate for vertical overlap (IG>PG). Group function allowed more working-side contacts in CDWs and significantly higher anterior temporalis (TA) activity.
Conclusion: Alteration of IG-PG ratio and a number of occlusal contacts during lateral clenching change a pattern of TA and TP activity in CDWs and a direction of mandibular loadings, although age related changes might also be responsible.