Total failure energy of a composite resin bonded to human enamel

Total failure energy is defined as the energy required to stress a bond to the point of fracture. This study was designed to assess and compare the total failure energy of a resin-enamel bond with conventional tensile and shear bond strengths. A commercially available composite resin was bonded to human enamel surface. During testing, the applied load versus displacement of the load fixture was recorded and analyzed by a data acquisition system. The tensile and shear bond strengths as well as the total failure energies were calculated. The mean tensile bond strength (21.2 MPa) was higher than the mean shear bond strength (11.6 MPa). The mean total energy applied for tensile failure of the bond (2.1 kg.mm) was also higher than that for the shear failure (1.5 kg.mm). There were statistically significant correlations between bond strength and total failure energy. The failure modes of the shear bond test revealed a higher frequency of adhesive failures compared to the tensile bond test. Further, a dramatic difference existed in the cohesive failure mode between tensile (cohesive composite failure) and shear (cohesive enamel failure) tests. The total failure energy, which represents the fracture strength as well as the failure process of a bond, may be considered an appropriate criterion for characterizing the failure of a bond.