An investigation of cuspal deformation and delayed recovery after occlusal loading

Objective: The purpose of this study was to investigate the extent of progressive cuspal displacement during prolonged occlusal loading (either continuous or cyclic) and delayed cuspal recovery following removal of the load. Methods: Extracted maxillary premolars with extensive MOD cavity plus endodontic access were subjected to an occlusal load applied to both cusps, followed by a recovery period. Two types of loading were applied: (a) continuous load of 100, 200 and 300 N for 0.1–1000 s; (b) cyclic loading of 300 N at 0.83 Hz for 1–1000 cycles. Cuspal displacement during loading and subsequent recovery were measured with an extensometer attached to both cusps. Results: Continuous loading led to progressive cuspal displacement that was both time- and load-dependent. After removal of the load, complete recovery from cuspal deformation was prolonged up to 20 min, also in a time- and load-dependent manner. Cyclic loading resulted in a cumulative increase in cusp displacement but to only a very small extent (approximately 1 μm after 1000 cycles). Conclusions: Progressive cuspal displacement and delayed recovery occur with prolonged continuous or cyclic occlusal loading. Continuous loading (e.g. as in clenching) is potentially more damaging than cyclic loading (as in chewing).