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Fracture toughness of different adhesive/dentin interfaces analyzed by finite element stress analysis

Objectives: This study aimed to assess the fracture toughness of different dentin adhesive approaches and to evaluate the stress distribution at the bond interface during fracture toughness testing by finite element analysis. Materials and Methods: Specimens for chevron-notched beam fracture toughness (CNB) were prepared with dimensions of (3.0 mm × 4.0 mm × 20 mm) according to ISO 24370:2005 standard. Chevron notch was prepared at the adhesive–dentin interface using a highly polished stainless steel spacer. Four different dentin adhesives approaches were used total etch 3 and 2 step and self adhesives 2 and 1 step. A total of 60 specimens were prepared for each adhesive approach (n=15). Each specimen was loaded until failure in a 4-point bend test setup and the fracture toughness was calculated according to the ISO specifications. Finite element modeling of the specimens was carried out in order to analyze stress distribution during fracture toughness testing. Data were analyzed by one-way ANOVA followed by tukey‘s post hoc test with significant level at p < 0.001 level (p= 0.0001). Results: Solobond plus 3-step etch-and-rinse showed the highest mean fracture toughness (1.78 MPam1/2) Whereas, Futurabond M+ 1-step self-etch showed the lowest value (1.13 MPam1/2). These finding were supported by finite element analysis which showed stresses to concentrate at the adhesive–dentin interface during fracture toughness loading and crack propagation. Conclusion: The adhesive approach has a strong effect on the fracture toughness of the adhesive–dentin interface. the 3-step etch-and-rinse approach showed the highest mean fracture toughness while 1-step self-etch approach showed the lowest value.