The Comparison Of Three Kinds Of Veneering Ceramic Produced By Different Processes

Objectives:With this in vitro study the shear strength of zirconea-base being veneered with CAD/CAM gennerated high-strength ceramic,the traditional layering ceramic and the overpressing ceramic,to explore whether the binding ability of CAD/CAM sintering ceramic is better than the overpressed ceramic or the layering technique ceramic.Methods: The fabrication process of the specimen will imitate the fabrication process zirconia-based crowns in framework structues.30 disc-shape zirconia specimens were produced by CAD/CAM system,which were with thickness of 5mm and a rounded flat surface with diameter of 10 mm,and divided into three groups(Group A,Group B,Group C).In the Group A zirconia specimens received conventional veneering in layering technique,in Group B the veneering porcelain was pressed over the zirconia specimens,and for ghe Group C a CAD/CAM-fabricated high-strength veneering ceramic was sintered onto the zirconia specimens.The shape of all ceramic is cylinders withth the diameter of4 mm and the height of 3mm.Subsequently,specimens were subjected to shear strength in a universal testing machine.The fracture surfaces were analyzed by the stereomicroscope.Results:1,Specimens from Group C showed a mean shear strength of23.337(6.664)Mpa,Group B 25.137(5.472)Mpa and Group C 32.600(8.170)Mpa.2,The sheor bond strengths of Group A were not significantly different from Group B(P > 0.05).3.The difference between Group C and Group A,B were statistically significant(P < 0.05).3,In Group A,the failure modes were comination failure.In Group B and Group C,the failure modes were adhesive failure.Conclusion:The new CAD/CAM-fabricated bilayered restoration were superior to the present techniques(layering veneering technique and overpressed technique)in terms of shear strength.