Effect of bidirectional loading on contact and force characteristics under a newly developed masticatory simulator with a dual-direction loading system.

Mechanical responses of the test specimen under bidirectional and unidirectional loading were investigated using a newly developed masticatory simulator. The simulator adopted a four-bar linkage mechanism to create both loading patterns. Scratch/occlusal contact characteristics, contact force profiles and the fracture of restored tooth samples were investigated. With bidirectional loading, which imitates the nature of human chewing cycle closer than the unidirectional loading does, the occlusal contact was ovoid in shape whereas a small circular area was observed from the test with unidirectional loading. The contact force profiles were also noticeably dependent on the loading patterns. Measured contact forces from bidirectional loading were more uniform than those from unidirectional loading. Bidirectional loading also induced the cuspal fracture with similar characteristics of natural cuspal fractures in humans. The differences of force characteristics between those of bidirectional and unidirectional loadings emphasize the importance of employing bidirectional loading in dental material testing.