Shear bond strength of composite veneers and acrylic veneer bonded to ni-cr alloy: a laboratory study

A growing number of composite materials are being used as an alternative for veneering cast restorations. The objective of this investigation was to evaluate and compare the shear bond strength of UDMA based composite, restorative composite, and heat cure acrylic when veneered to Ni-Cr alloy and to evaluate the type of bond failure. Three different veneering materials were used: heat cure acrylic, UDMA based composite and a restorative composite. 10 samples were fabricated, each with heat cure acrylic and restorative composite and 20 samples were fabricated with UDMA based composite; thus, the total number of samples amounted to 40. All the samples were subject to shear bond stress fracture tests and observed for the type of bond failure. The greatest mean shear bond strength was recorded in relation to the UDMA based composite material when thermal conducting paste was used during the curing (10.51 MPa). The mean bond strength values of UDMA based composite without thermal conducting paste (8.92 MPa), heat cured acrylic veneering material (4.24 MPa) and restorative composite material (5.03 MPa) were significantly different from each other (p > 0.05). Samples veneered with heat cure acrylic veneering material and restorative composite material showed adhesive failure. Samples prepared with UDMA based composite veneering composite showed cohesive or predominantly cohesive failure. UDMA based composite veneering material when used with heat protection paste exceeds the shear bond strength requirement as suggested by Matsumura et al. (>10 MPa). A statistically significant association between the test groups and the type of failure was observed.