Effect Of The Veneering Technique On The Bond Strength Of Veneering Porcelains With Zirconia

With the improvement of living level, all-ceramics materials have become to be the alternative restoration materials, because of the limited esthetics and allergist by metal ions. With the advancement of industry and technique, more and more all-ceramics with esthetics and biocompatibility were used in the clinical, specially in the anterior. But because of the brittleness of porcelains, these materials could not meet the posterior restorations, to restrict the development of all-ceramics. From the early1990s, zirconia were introduced into dental restorations as the core of the fixed restorations, and the high flexure strength and high fraction toughness were their remarkable advantages, besides good biocompatibility, high stability and esthetics. But because zirconia being consisted by crystals without glass matrix induced bad esthetics and great hardness, the veneering ceramics on the zirconia to simulate the natural teeth and to protect the opposite nature teeth are needed. With the technique CAD/CAM used to making the zirconia cores, bi-layered zirconia restorations had be used in the clinical. However, the clinical statistics showed, the failure rates were higher than the one of metal-ceramics. The mainly failure reasons were:veneering chipping and delamination, secondary caries and so on. In order to solve the problem of chipping and delamination, many investigations in the vitro were taken, from the advancement of material, the analysis of interface, and a finite element analysis of stress. With the increasing of technique, the idea whether the improvement of materials and technique skills or not to rise the bond strength, will become the one of methods to reduce failure rate in these years.Object:In this study, the object is to discuss the effects of the veneering technique on the bond strength and to analyze the difference of interfacial morphology of veneering porcelains with zirconia by the shear bond test and the interfacial micrology observation.Methods:In this study, two technical veneering ceramics were molded on two commercial zirconia surface as the experimental groups, IPS e.max ZirCAD/IPS e.max ZirPress (Group EP), IPS e.max ZirCAD/IPS e.max Ceram (Group EV), Incoris ZI/IPS e.max ZirPress (Group IP), Incoris ZI/IPS e.max Ceram (Group IV) respectively. As the control, two technical dentin ceramics were molded on one nickel-chromium alloy surface, Wiron99/IPS InLine POM (Group NP) and Wiron99/IPS InLine (Group NV). Half of each material groups was thermocycled20000cycles. Subsequently, specimens were subjected to shear force in a universal testing machine. The fracture surfaces and the cross sections were analyzed by the stereomicroscope and FE-SEM (field emission scanning electronic microscope).Results:1.Before thermocycling, the shear bond strengths of Group NP and Group NV were not significantly different from Group EP (P>0.05), and higher than Group EV, Group IP and Group IV (P<0.05), while the values of Group EP were higher than Group IV (P<0.05). After thermocycling, the shear bond strengths of Group NV were higher significantly than Group EP, Group EV, Group IP and Group IV (P<0.05), while the values of Group NP were higer significant than Group EV and Group IV(P<0.05). There are no significant difference among other groups (P>0.05), and between thermocycling and non-thermocycling in the every group (P>0.05). 2. The failure modes were adhesive mainly in the press-on groups, and veneering cohesive mainly in the veneer-on groups on the zirconia surface. On the NiCr surface, the failure modes were comination failure from dentin ceramic to the oxide layer.3. The FE-SEM figure showed that there are more pores and defects in the veneering ceramics and interface in the veneer-on groups than those in the press-on groups in the zirconia system. And the figure of Group NP showed that InLine POM and OP connected closely, and compact in the InLine POM, but a little of pores in the OP layer and the interface of OP and Ni-Cr.4. The energy disperature spectrum of interface displayed the diffusion of element:In the Group EP, from the side of ZirPress to the side of ZirCAD, the element Si was decreased, with the thickness of element transformation about2-3um. In the interface of NiCr and OP, from the side of OP to the side of NiCr, the element of Zr and Si was decreased, with the thickness was about2-3um.Conclusion:1. Compared to the other experimental groups in this study, the bond strengths of ZirCAD and ZirPress were the better to meet the clinical requirement, looking forwards to reduce the clinical failure rate.2. The technique of hot-pressed veneering ceramic was recommended to be used on the surfaces of zirconia and metal core crowns, to reduce the inner defects of veneering ceramics and to improve process efficiency.3. The shear bond strengths of zirconia-veneering ceramics were not affected by two years thermal fatigue treatment.