Influence Of Different Surface Treatments On The Shear Bond Strength Of Zirconia-veneering Ceramic Systems

Objective: The aim of this study was to assess the influence of different surface treatments on the shear bond strength of the zirconia-veneering ceramic systems,in order to provide theoretical basis for the clinical application of surface treatments.Methods:Zirconia coreswere cut into 28 specimens with low speed saw and then dense sintered into 12mm×8mm×4mm according to the manufacturer’s instructions.The specimens from each zirconia core material were groundby diamond bur on one surface（12mm×8mm）only.Then,the specimens weredivided into four groups according to the different surface treatments as follows: Group A（control group）: the specimens were exposed only to grinding;Group B（sandblasting group）: the specimens were abraded with Al₂O₃ particles（100 mesh）at a pressure of 0.3MPa with a distance of 10 mmfor 15 s.Group C（hot-etching group）: the zirconia specimens were immersed in a solution which include 80 mL of methanol,20 mL of 37% HCl,and 0.2 g FeCl₃ then heated up to 100 ℃in a water bath for 30 min.Group D（sandblasting+hot-etching group）: the zirconia specimens were sandblasted as group B first and then treated as group C.All the specimens were rinsed with running water and then cleaned ultrasonically in a distilled water bath for 3 min,then cleaned ultrasonically twice in ethanol bath for 3 min,and gently air-dried lastly.Four specimensrandomlyselected from each groupwere examined under a scanning electron microscope to observe the features of the treated surfaces.Another four specimens randomlyselected from each group were analyzed by x-ray diffraction,to determine the crystal phases of the sintered zirconia grains to quantify the monoclinic and tetragonal phases.The veneering porcelain was layered on the remaining specimens and controlled thedimensions（5mmx5mmx3mm）.Then the specimens were embedded intothe custom-made mold withautopolymerizing acrylic resin as standard shear bond test specimen.All the specimens were mounted in a universal testing machine,at a crosshead speed of 0.5 mm/min,until separation of the veneer from the zirconia-based ceramic occurred,to recorded the maximum force（N）and then calculated the shear bond strength（MPa）.SPSS13.0 statistical software was performed to determine whether there were significant differences in shear bond strength among the 4 groups.Results:1 The microstructure of treated zirconia surface under scanning electron microscope:Group A: The zirconia surface showed the regular scale-like structure;Group B: The zirconia surface showed many uniform size of rugged mountain-like structure,and there distribution of some tiny cracks;Group C: The zirconia surface showed many ball-like structure arranged in irregular;Group D: The zirconia surface showed many high mountain-structure,between the mountain-structure are many deep fracture.2 The results of treated zirconia surface analysis by x-ray diffraction:The four groups’ x-ray diffraction graph showed that the peaks of every group are roughly same,the main peak is T（101）,and all have emerged M（111）peak,but the peak intensity are relatively small.The relative amounts of the monoclinic phaseof the groups are as follows: 12.40%,16.28,12.99%,15.16%.3 The mean and SD values forthe shear bond strengthof the four groups are as follows: A group（15.96±3.44）MPa;B group（20.58±2.21）MPa;C group（26.28±2.86）MPa;D group（22.51±1.94）MPa.The ANOVA analysis showed a significant difference in the shear bond strengths between groups（P<0.001）.And the SNK test showed that the shear bond strength of group A is lower than other groups（P < 0.05）,and the shear bond strength of group C is higher than other groups（P < 0.05）,and there is no significant difference between group B and group D（P > 0.05）.Conclusions:1 The hot-etching method can significantly improve the shear bond strength of the zirconia-veneeringceramic systems,and the change of the zirconia crystal phase structure and the formation of micro cracks are very few.It is considered that the hot-etching method is an ideal method for treating the zirconia surface.2 The methods of sandblasting and sandblasting+hot-etching can also improve the shear bond strength of the zirconia-veneeringceramic systems,but the effect is not as significant as hot etching,and emerged more change of the zirconia crystal phase structure and the formation of micro cracks.It is suggested that the hot-etching method can replace of sandblasting method in clinic in order to obtain better bonding effect.