Tensile fatigue of two composite cements bonding three base metal alloys to bovine enamel

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.