Bonding of universal adhesives to Y-TZP

Objectives: To evaluate the bonding capacity of a composite to polished and alumina-blasted Y-TZP, as mediated by 5 universal adhesives.
Methods: The adhesives tested were All-Bond Universal (AB), Adhese Universal (AD), Clearfil Universal Bond (CU), Prelude One (PR) and Scotchbond Universal Bond (SB). Y-TZP disks (n=20/product) were prepared, half were wet-polished (up to 1000grit-size) and the rest were blasted with 50μm alumina powder using an intraoral etcher (2.3bar/5s). All surfaces were treated with the adhesives and a resin composite (Tetric EvoCeram, Ø=3.5mm, h=2mm) was bonded onto them. After 1w storage (water/37^oC), the composite specimens were debonded under shear loading (SBS). The Y-TZP surfaces were examined under a stereomicroscope to characterize the failure mode. Statistical analysis was performed by 2-way ANOVA and Tukey test (a=0.05). Polished Y-TZP surfaces were further primed with each adhesive, kept intact for 20min (dark/dry storage/37^oC), rinsed with ethanol, air-dried and analyzed by reflection FTIR microscopy.
Results: Statistically significant differences were found in the adhesive parameter, but not in the surface-finish parameter. On polished surfaces (SBS range: 34.6/CU-29.0/PR MPa) PR,SB showed significantly lower values than AD,CU. AB showed no differences from all adhesives. On sandblasted surfaces (SBS range: 34.0/AD,CU-29.8/SB MPa) no statistically significant differences were found among the materials. No differences were found between the two surfaces treatments for any adhesive used. In most cases mixed failures of the composite were observed with residual material covering less than 50% of the bonding surface. FTIR microscopy demonstrated evidence of adsorbed species (C=O, P=O, Si-O-) possibly associated with primary bonding.
Conclusions: Differences were found among universal adhesive materials in SBS on polished surfaces. Alumina sandblasting diminished these material differences, but failed to increase the SBS in comparison with the polished substrate. The SBS along with the FTIR data may indicate formation of primary bonding.