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

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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).

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