Fatigue of dentin–composite interfaces with four-point bend

Objectives The objective was to determine the fracture and cyclic fatigue properties of composite–dentin beams bonded with a self-etching adhesive in four-point bend. Methods Beams of rectangular cross-section were shaped to a size of ∼0.87mm×0.87mm×10mm and placed in a four-point bending apparatus, with the loading points 1.8 and 7.2mm apart, with the interface centered between the inner rollers. Cyclical loading was performed in Hanks’ Balanced Salt Solution at 25°C, with forces between 54% and 99% of the bending strength of the bonded beams. Results Solid dentin and solid composite beams [n =6] had bending strengths of 164.4 and 164.6MPa, respectively, under monotonically increasing loads. Bonded beams [n =6] had strengths of 90.6MPa. No significant difference was found between solid composite and solid dentin beams, the bonded beams were different (ANOVA, p <0.0001) With long-term cycling, stresses below 49MPa were tolerated for 106 cycles, but with increasing stress up to 90MPa, beams failed earlier, demonstrating that subcritical fatigue cycling will eventually cause failure. Significance Fatigue may be a significant mechanism of dentin–composite bond degradation.