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 ∼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 ° 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° to 55°C), NaOCl solution immersion, or 10⁵ of pre-fatigue cycles did not decrease the strength. Conclusion: Thermal stress, exposure to NaOCL, or 10⁵ cycles of mechanical stress does not decrease bond strength of composite bonded to dentin as tested in four-point bending.