Fatigue of dentin–composite interfaces with four-point bend

ObjectivesThe objective was to determine the fracture and cyclic fatigue properties of composite–dentin beams bonded with a self-etching adhesive in four-point bend.MethodsBeams of rectangular cross-section were shaped to a size of ∼0.87 mm × 0.87 mm × 10 mm and placed in a four-point bending apparatus, with the loading points 1.8 and 7.2 mm 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.ResultsSolid dentin and solid composite beams [n = 6] had bending strengths of 164.4 and 164.6 MPa, respectively, under monotonically increasing loads. Bonded beams [n = 6] had strengths of 90.6 MPa. 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 49 MPa were tolerated for 106 cycles, but with increasing stress up to 90 MPa, beams failed earlier, demonstrating that subcritical fatigue cycling will eventually cause failure.SignificanceFatigue may be a significant mechanism of dentin–composite bond degradation.