Comparison of resin bonding improvements to zirconia between one-bottle universal adhesives and tribochemical silica coating, which is better?

Objectives To evaluate the bonding of resin-cement to yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) via silica coating followed by silanization, and three one-bottle universal adhesives, with or without prior conditioning using a zirconia primer. Methods Y-TZP specimens (n = 160) were conditioned by tribochemical silica coating and silanization (CS), or alumina sandblasting with one of the following MDP containing adhesives or primers: Z-Prime Plus™ (zirconia primer, ZP), Single Bond Universal™ (SU), Clearfil Universal Bond™ (CU) or All-Bond Universal™ (AU). Additionally, some specimens (ZPSU, ZPCU and ZPAU) received Z-Prime Plus™ followed by one of the three adhesives. After 24 h water storage and "aging" (20,000 thermocycles plus additional 40-day water storage), shear bond strength (SBS) was measured. Fourier-transform infrared spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) were employed for characterization of the chemical bonds between the primer/adhesives and the zirconia. Thermodynamic calculations were used to examine the hydrolytic stability between the MDP-zirconia chemical bonds and the SiO₂-silane chemical bonds. Results The CS and ZPCU groups showed higher SBS than the other six groups. There were no significant pairwise differences amongst ZP, SU and ZPSU, or amongst ZP, AU and ZPAU. Aging led to significantly decreased SBS for all groups except CS and ZPCU. There was no statistically significant interaction between surface treatment and aging. XPS determined the chemical bonds between MDP and zirconia. FTIR showed similar shifts in characteristic phosphate peaks for all the primer and/or adhesive groups. Result of thermodynamic calculation showed that equilibrium constant of SiO₂-silane system is much larger than the one of MDP-tetragonal phase zirconia system. Significance The application of one-bottle universal adhesives after alumina sandblasting is an alternative to tribochemical silica coating with silanization for bonding to zirconia, while bonding between resin and Y-TZP is more susceptible to hydrolysis when zirconia primer or one-bottle universal adhesive is used.