An investigation of cuspal deformation and delayed recovery after occlusalloading

Objective: The purpose of this study was to investigate the extent of progr essive cuspal displacement during prolonged occlusal loading (either contin uous or cyclic) and delayed cuspal recovery following removal of the load. Methods: Extracted maxillary premolars with extensive MOD cavity plus endod ontic access were subjected to an occlusal load applied to both cusps, foll owed by a recovery period. Two types of loading were applied: (a) continuou s 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 subseque nt 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 recover y from cuspal deformation was prolonged up to 20 min, also in a time- and l oad-dependent manner. Cyclic loading resulted in a cumulative increase in c usp displacement but to only a very small extent (approximately 1 mum after 1000 cycles). Conclusions: Progressive cuspal displacement and delayed rec overy 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). (C) 2001 Elsevier Science Ltd. All rights reserved.