[Effect of different surface treatments on the crystal structure and properties of zirconia]

To investigate the effects of 3 surface different treatments on the crystal structure, shear bond strength,roughness value and flexural strength of zirconia.

The zirconia specimens were prepared and randomly divided into 4 groups and received the following treatments: (1) blank control group,the specimens without treatments; (2)sandblasting with alumina group, sandblasting the specimens with 110 μm alumina particles for 21 s as working pressure 0.25 MPa and working distance 10 mm; (3)laser etching group, coating the surface of the specimens with graphite powder and using Er:Yttrium Aluminum Garnet (Er:YAG) laser to irradiate the surface 30 s; (4) hot-etching group, putting the specimens in a closed reactor within a 1:1 mixture of 40% (mass traction) nitric acid and 68%(mass traction) hydrofluoric acid liquid, the reaction of 30 min in a water bath at 100 degrees centigrade. The changes of crystal structure, shear bond strength(SBS) and flexural strength of zirconia after different surface treatments were tested.

The X-ray diffractometer (XRD) patterns showed that the volume percentage of monoclinic phase of the 4 groups was 0.91%, 12.50%, 6.64% and 17.81% respectively. The roughness value for the four groups were as follows: blank control group,(0.29±0.01) μm; sandblasting with alumina group, (1.05±0.11) μ m; laser etching group, (0.73±0.04) μm; hot-etching group, (1.31±0.06) μm, respectively(P<0.05). Mean SBS was (7.09±0.46) MPa in blank control group, (12.14±1.51) MPa in sandblasting with alumina group, (8.82±0.74) MPa in laser etching group and (11.97±0.99) MPa in hot-etching group. There was no statistically significant difference between sandblasting with alumina group and hot-etching group (P>0.05), but the difference between the other groups were statistically significant(P<0.05). Mean three-point bending was (933.70±44.13) MPa in blank control group, (850.95±60.66) MPa in sandblasting with alumina group, (771.53±68.08) MPa in laser etching group and (766.27±57.49) MPa in hot-etching group. There was no statistically significant difference between sandblasting with alumina group and hot-etching group (P>0.05), but the difference between the other groups were statistically significant (P<0.05).

After different surface treatments, the surface of zirconia has changed from tetrago-nal to monoclinic phases in varying degrees. In addition, surface treatments could improve the bond strength of zirconia to resin cement, and also lead to a decrease in the flexural strength of zirconia.