FRACTURE-TOUGHNESS OF DENTIN RESIN-COMPOSITE ADHESIVE INTERFACES

The reliability and validity of tensile and shear bond strength determ inations of dentin-bonded interfaces have been questioned. The fractur e toughness value (K(IC)) reflects the ability of a material to resist crack initiation and unstable propagation. When applied to an adhesiv e interface, it should account for both interfacial bond strength and inherent defects at or near the interface, and should therefore be mor e appropriate for characterization of interface fracture resistance. T his study introduced a fracture toughness test for the assessment of d entin/resin-composite bonded interfaces. The miniature short-rod speci men geometry was used for fracture toughness testing. Each specimen co ntained a tooth slice, sectioned from a bovine incisor, to form the bo nded interface. The fracture toughness of an enamel-bonded interface w as assessed in addition to the dentin-bonded interfaces. Tensile bond strength specimens were also prepared from the dentin surfaces of the cut bovine incisors. A minimum of ten specimens was fabricated for eac h group of materials tested. After the specimens were aged for 24 h in distilled water at 37-degrees-C, the specimens were loaded to failure in an Instron universal testing machine. There were significant diffe rences (p < 0.05) between the dental adhesives tested. Generally, both the fracture toughness and tensile bond strength measurements were hi ghest for AllBond 2, intermediate for 3M MultiPurpose, and lowest for Scotchbond 2. Scanning electron microscopy of the fractured specimen h alves confirmed that crack propagation occurred along the bond interfa ce during the fracture toughness test. It was therefore concluded that the mini-short-rod fracture toughness test provided a valid method fo r characterization of the fracture resistance of the dentin-resin comp osite interface.