Bond strength of five dental adhesives using a fracture mechanics approach

Objectives  : The adhesion tests utilized in dentistry are unable to separate the effects of adhesive composition, substrate properties, joint geometry and type of loading on the measured bond strength. This makes it difficult for the clinician to identify the most suitable adhesive for a given procedure and for the adhesive manufacturer to optimize its composition. Thus, an adhesion test protocol based on the fracture mechanics has been proposed to generate data for which separation of the effect of composition from that of the joint geometry on the shear (τa)(τa) and tensile (σa)(σa) bond strengths was possible for five commercial dental adhesives.Methods: Planar 40×5×5 mm3 sections of bovine femur   were used as model adherends. The adhesive thickness (h)(h) was varied from 15 to 500 μm. Commercial adhesives with fracture toughness (KIC)(KIC) ranging from 0.3 to 1.6 MPa m1/2 were used. Double lap joint (DLJ) and modified compact tension (MCT) specimens were conditioned for 24 h in 37 °C distilled water, then dried in a vacuum oven at 37 °C for 24 h prior to testing. The thickness dependence of σaσa and τaτa was measured at constant strain rate and analyzed using the interface corner stress intensity factor model.Results  : Both τaτa and σaσa increased with increasing adhesive thickness, exhibiting a maximum bond strength at the optimum thickness (hopt)(hopt). For h