Effect of surface reaction layer on three-point flexure bond strength of resin composite to cast Ti and Ti-6Al-7Nb

This study investigated the effect of the cc-case on the three-point flexure bond strength of resin composite to different thicknesses of cast CP Ti and Ti-6Al-7Nb. Cast plates (0.3, 0.5, and 0.7 mm thick) were prepared for each metal. Plates without alpha-case were also prepared for the 0.5 and 0.7 mm thick CP Ti and Ti-6Al-7Nb. After resin composite was polymerized on the plates, the resin/metal specimens were subjected to three-point bending testing. The fracture force (N) and deflection (mm) at fracture were recorded. The fracture force of the specimens increased with increasing specimen thickness. Specimens without a-case withstood greater fracture force than specimens of either metal with alpha-case. CP Ti and Ti-6Al-7Nb without a-case deflected more than with alpha-case. The results suggested that the bonding between the veneer composite and thin cast structures (< 0.5 mm) is likely to fail and that the surface reaction layer (alpha-case) should ideally be removed.