Effects of Luting Cements and Surface Conditioning on Composite Bonding Performance to Zirconia

Purpose: This study compared bond strength, durability, and mechanical properties of luting cements for bonding zirconia: a resin-modified glass ionomer cement (RMGIC), a conventional composite cement, and two self-adhesive composite cements. Materials and Methods: The air-abraded zirconia specimens were assigned to 12 groups (n = 30) to prepare bonded specimens. Classification was based on the pre-conditioning selection: none; primers containing 10-methacryloyloxydecyl dihydrogen phosphate (MDP); universal adhesives containing MDP. Further classification was done according to the type of luting cement: RMGIC; conventional composite cement; MDP-free self-adhesive composite cement; MDP-containing self-adhesive composite cement. The shear bond strength (SBS) was measured after 24 h of water storage or aging with 20,000 thermocycles plus an additional 60 days of water storage at 37°C. The elastic modulus and three-point bending strength were determined, and a related Weibull analysis of the four luting cements was performed. Results: The choice of luting cement and aging significantly affected the SBS. Aging decreased the SBS in most groups, except for those that used MDP-containing primers plus conventional composite cements. RMGIC had SBS (before and after aging) that were similar to the MDP-free self-adhesive composite cement. Use of MDP-containing products prior to conventional composite cements provided the highest initial SBS. However, pre-conditioning with MDP-containing products failed to increase the SBS of RMGIC. RMGIC showed lower elastic modulus and three-point bending strength than did the three composite cements. Conclusions: RMGIC is an alternative to composite cements for luting zirconia restorations. Conditioning with a primer containing MDP combined with conventional composite cement is more reliable. Keywords: yttria-stabilized tetragonal zirconia, phosphate ester monomer, resin-modified glass-ionomer cement, composite cement, surface treatment, bonding