Durability of resin bonding to translucent zirconia materials: An in vitro study.

STATEMENT OF PROBLEM

How the yttria content (3Y-PSZ, 4Y-PSZ and 5Y-PSZ) affects the tensile bond strength of luting resin to translucent zirconia ceramics is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate whether the bond strength of resin to translucent zirconia ceramics and its durability are influenced by the yttria content (3Y-PSZ, 4Y-PSZ and 5Y-PSZ).

MATERIAL AND METHODS

Sixty-four disk-shaped specimens of zirconia ceramics were randomly allocated to 4 groups (n=16) with respect to the yttria concentration: GHT: 3 mol% yttria-partially stabilized zirconia 3Y-PSZ; GHTML: 3 mol% yttria-partially stabilized multilayered zirconia 3Y-PSZ; GSTML: 4 mol% yttria-partially stabilized zirconia 4Y-PSZ; and GUTML: 5 mol% yttria-partially stabilized zirconia 5Y-PSZ. For bonding, acrylic resin tubes were filled with composite resin and bonded to the zirconia disks using adhesive luting resin by following manufacturer's instructions. Half of each main group (n=8) was stored in water for 3 days at 37 °C. The other half was stored in water for 150 days with 37 500 thermocycles (5 to 55 °C). The tensile bond strength test was determined with a universal testing machine at a crosshead speed of 2 mm/minute using a chain loop for alignment.

RESULTS

The tensile bond strength was not significantly affected by the yttria concentration of different zirconia materials (3Y-PSZ, 4Y-PSZ, and 5Y-PSZ, P=.17). The mean ±standard deviation failure loads for groups ranged from 24.1 ±2.6 MPa for the ultratranslucent multilayered zirconia (with thermocycling) to 52.7 ±5.4 MPa for the high translucent multilayered zirconia (without thermocycling). However, artificial aging adversely affected the tensile bond strength values for all tested zirconia systems (P<.001). Scanning electron microscope evaluation showed that cohesive fracture was the predominant failure mode, while few specimens exhibited adhesive failure at the interface.

CONCLUSIONS

The yttria concentration (3Y-PSZ, 4Y-PSZ, and 5Y-PSZ) had no significant effect on the bond strength of different zirconia ceramics (P=.17), whereas the artificial aging procedures led to a statistically significant decrease in tensile bond strength (P<.001).