| Porcelain-fused-to-metal restoration is currently widely used in crown and fixed bridge prosthesis. Titanium has been widely used in basal material due to its good resistance to corrosion, excellent biocompatibility, ideal physical and mechanical properties and relatively low price. However, porcelain fracture occurs often in titanium- fused-to-metal restoration in clinical observation because the bonding strength of titanium-porcelain is low. Therefore the success rate of titanium- fused-to-metal restoration can be improved by enhancing the bonding strength of titanium-porcelain. Titanium has very strong reduction capability at high temperature, which readily forms on titanium surface a layer of oxide film that is thick and loose and lacks of adhesive force in the course of porcelain sintering. This is the reason why the bonding strength of titanium-porcelain still tends to be low even when titanium porcelain is used. Many studies have shown that the bond strength of titanium-porcelain can be improved by creating a Titanium surface coating which will prevent excessive oxidation of titanium at high temperature. In this study middle layer was made by Electro-spark Deposition(ESD) technology and effect of this approach on bonding strength of titanium and porcelain was investigated. Optimal selection of process parameters was made to improve the bonding strength of titanium-porcelain. The study will provide references to clinical applications. Specific methods and results are as follows:1.Surface treatments of pure titanium specimens by ESD using electrodes of silicon, zirconium, cobalt-chromium alloy were made respectively and no treatment was made to the control group. Sintering Ti-22 porcelain system onto the middle parts of the specimen after conventional sandblasting according to IS0 9693(1999)Amd.1 2005(E) Standard. Then an analysis based mainly on the three-point flexural bonding strength of titanium-porcelain was conducted. The results show that there were no significant differences of the surface roughness among the four groups after sandblasting(P>0.05). The three-point flexural bonding strength of titanium-porcelain was highest in the silicon electrode group(30.08±1.55MPa)and it was significantly higher than that of three other groups(P<0.05). There were no significant differences among other three groups (P>0.05) in terms of the three-point flexural bonding strength of titanium-porcelain. No obvious oxide layer was observed at the titanium-porcelain interfaces in the four groups with scanning electron microscope. A 15-20 m transition layer was observed between the middle layer and the titanium base in the silicon electrode group.2.Based on the foregoing experiments, pure titanium specimens by ESD were divided into three groups by different types of sandblasting using silicon electrodes: general sandblasting, intensive sandblasting 1 and intensive sandblasting 2. The results show that there were no significant differences of the surface roughness between the three groups after sandblasting(P>0.05). The three-point flexural bonding strength of titanium-porcelain of the intensive sandblasting group 1 was(30.08±1.55MPa), which was significantly higher than the general sandblasting group(29.95±1.49MPa)(P<0.05) and the intensive sandblasting 2(26.30±1.31)(P<0.05). Cracks were in the middle layer in the general sandblasting group with scanning electron microscope. Cracks were not observed in the middle layer in the intensive sandblasting group 1. The middle layer in the intensive sandblasting group 2 was completely removed by sandblasting. No obvious oxide layer was observed at the titanium-porcelain interfaces in the three groups. A transition layer could still be observed between the middle layer and the titanium base in the intensive sandblasting group 1. The results of X-ray diffraction analysis indicated that in the general sandblasting group TiN, Ti5Si3 and TiSi2 were produced and in the intensive sandblasting group 1 Ti5Si3 and TiSi2 were produced.3.Based on the previous experiments, the operating voltage of ESD was adjusted. Suitable operating voltage was selected by comparison of the three-point flexural bonding strength of titanium-porcelain in different groups. The results showed that there were no significant differences of the surface roughness among the four groups after intensive sandblasting (P>0.05). The bonding strength of the gradient voltage group was the highes(t35.55±2.00MPa), which was significantly higher than that of three other groups(P<0.05). No obvious oxide layer was observed at the titanium-porcelain interfaces in the four groups with scanning electron microscope. According to the results of Energy Dispersive Spectrometer, the content quality ratio of silicon in the middle layer is 1.24%, 4.12% and13.03% in the 50V,70V and gradient voltage group respectively. Conclusion:1. Using silicon electrode, with air as media and electrical parameters as follows: 300 F, 50Hz, 70V-60V-50V (gradient voltage) and 100% coverage, the bonding strength of titanium-porcelain can be significantly improved(35.33±2.00MPa)by ESD with intensive sandblasting.2. Preparing the middle layer on pure cast titanium surface using ESD can improve the bonding strength of porcelain-titanium. This technology has fine potential in application. |
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