Interfacial fracture toughness of aged adhesive–dentin interfaces

• Interfacial chevron-notched beam fracture toughness of aged adhesive–dentin interfaces was measured.
• Interfacial fracture toughness is a more consistent method to assess mechanical properties of the interaction between adhesive and dentin.
• Multi-step adhesives showed higher fracture toughness upon water storage than one-step self-etch adhesives, but these performed considerably better than a self-adhesive composite.
• Ranking of adhesives upon water storage using interfacial chevron-notched beam fracture toughness and micro-tensile bond strength testing correlated well.

ObjectiveTo assess interfacial fracture toughness of different adhesive approaches and compare to a standard micro-tensile bond-strength (μTBS) test after 6 months water storage.MethodsChevron-notched beam fracture toughness (CNB) was determined using a modified ISO 24370:2005 standard. Adhesive–dentin micro-specimens (1.0 mm × 1.0 mm × 8–10 mm) were stressed in tensile until failure to determine the micro-tensile bond strength (μTBS).ResultsThe highest mean μTBS and interfacial fracture toughness were measured for the multi-step adhesives Clearfil SE Bond (Kuraray Noritake) and OptiBond FL (Kerr). While large differences were observed in the bond strength values (from 7.4 to 27.2 MPa) of the one-step self-etch adhesives tested, interfacial fracture toughness was less different (from 0.7 to 1.0 MPa m1/2). The adhesive with the lowest mean toughness (All-bond Universal, Bisco) had however the highest Weibull reliability, which might be a better parameter in regard to more consistent clinical performance. The self-adhesive composite Vertise Flow (Kerr) scored significantly lower at all levels.SignificanceAlthough the ranking of the adhesives tested using CNB and μTBS corresponded well, the outcome of CNB appeared more reliable and less variable.