Nominal shear or fracture mechanics in the assessment of composite-dentin adhesion?

This study addresses the anticipated problem of discriminating among high-p erforming dentin adhesives. The simplicity of the nominal shear bond test, despite being heavily criticized, has made it a routine procedure for the d etermination of bonding efficacy. A fracture mechanics approach has been su ggested as a better assessment of bonding efficacy (Versluis ct nl., 1997). However, experimental complexity is a major limitation. It is hypothesized that a new, simplified interfacial fracture toughness test (Lin, 1994) wil l evaluate bonding agents differently if compared with the traditional shea r bond test. Therefore, the objective of this study was to compare the perf ormances of six dentin bonding agents subjected to the interfacial fracture toughness test (critical plane strain energy release rate) or to the nomin al shear bond test (shear bond strength). Their performances were also char acterized by scanning electron micrography of the fracture surfaces for evi dence of dentin cohesive failure. Statistical analyses showed only marginal differences between these determinants of the two tests. However, when the analysis was applied only to the materials that had 100% frequency of dent in cohesive failure in shear testing, which also had high bonding efficacy, the difference in adhesive strengths between the two tests became signific ant. The reliability of the nominal shear test is questioned when dentin co hesive failure occurs, which usually is associated with high bonding effica cy. Since it is expected that bonding efficacy will increase further, the i nterfacial fracture toughness test is the preferred methodology to distingu ish among high-performing dentin adhesives.