Fatigue of dentin–composite interfaces with four-point bend

Abstract 

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.

Keywords: Dentin, Composite, Adhesion, Four-point bending, Fracture, Fatigue