Effects Of Air-abrasion Pressures On The Mechanical And Bonding Properties Of Translucent Zirconia

Objective.The purpose of this in vitro study was to investigate the effects of different air-abrasion pressures on flexural strength and shear bond strength of a translucent zirconia.Materials and Methods.Pre-sintered zirconia blanks(TT,UPCERA)were sectioned into plates(N=162)and beams(N=36,used for flexural strength test),followed by sintering according to manufacturer’s recommendations.The final dimensions of zirconia specimens were 8 mm x 8 mm x 2 mm for plates and 12 mm x 5 mm x 1.5 mm for beams.The surface of translucent zirconia ceramic was treated with 50 μm abrasive alumina particles at different pressure:0.1 MPa;0.2 MPa;0.3 MPa;0.4 MPa;0.5 MPa;nonabraded specimens were used as control group.For each group,three-point bending test was used to evaluate the flexural strength(n=6).Surface phase characterization(n=2),surface topography(n=2),and roughness(n=3)of specimens were analyzed.Following adhesive bonding and water storage(37℃)for 24 hours,specimens were subdivided into groups baseline and aged(5000 thermocycles between 5℃ and 55℃)(n=10).Then shear bond strength was measured and failure mode was recorded.Statistical analysis was performed with one-way analysis of variance(ANOVA)and Tukey honest significant difference test(a=0.05)Results.Increasing the air-abrasion pressure(0.3 MPa,0.4 MPa,and 0.5 MPa)decreased the flexural strength.Approximately 0.72%to 0.81%of monoclinic phase was induced by air-abrasion procedure.Varying the air pressure had a significant effect on the surface microstructure and roughness.Higher air pressure resulted in relatively rougher zirconia surfaces(p<0.05),and caused more flaws,debris and microcracks.The highest shear bond strength was obtained for zirconia surfaces abraded at 0.2 MPa(15.88±2.70 MPa)and 0.3 MPa(14.32±1.12 MPa).Aging with 5000 thermocycles did not decrease the strength for all groups except control group(p<0.05)Conclusions.Air-abrasion at a moderate pressure(0.2 MPa)could achieve good strength for TT zirconia ceramics while maintaining adequate and durable bonding with resin cement.