Four-point bending evaluation of dentin-composite interfaces with various stresses

Fracture properties of composite-dentin beams bonded with a self-etching adhesive were tested following short term pretreatments to simulate potential degradation mechanisms (thermal cycling, immersion in 5% NaOCl, or fatigue cycling). Beams of rectangular cross-section were shaped to a size of similar to 0.87 x 0.87 x 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. Testing was performed in Hanks' Balanced Salt Solution at 25 degrees C. Solid 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 56.3 MPa. Thermo-cycling (5 degrees to 55 degrees C), NaOCl solution immersion, or 10(5) of pre-fatigue cycles did not decrease the strength. Conclusion: Thermal stress, exposure to NaOCL, or 10(5) cycles of mechanical stress does not decrease bond strength of composite bonded to dentin as tested in four-point bending.