Tensile fatigue endurance limits were determined for three base metals (NiCr, NiCrBe, and CoCr) bonded to bovine enamel using two composite cements: a BisGMA/phosphate ester composite cement which relies on a sand-blasted metal surface, and a BisGMA composite luting cement which relies on electrolytically etched metal surfaces. Samples were tested to failure or to 106 cycles at 5 hz in Ringer's solution at 37°C, and endurance limits were determined using a two-point test strategy. SEM evaluation was performed on fractured samples to determine failure mode. Statistical analysis of the results showed no difference between cements when using NiCrBe; however when using CoCr, the Bis-GMA/phosphate ester cement produced greater values than the Bis-GMA cement that relied on electrolytical etching. The opposite result occurred when a NiCr alloy was tested with both cements. Evaluation of the results for each cement with the three different alloys showed statistical significant differences. SEM fracture analysis revealed a mixed failure pattern with apparent adhesive fracture from both the composite-enamel and composite-metal interfaces and cohesive failure throughout the cement. © 1993.
