Study On The Effects Of The Multicomponent Nano-coating On The Bond Strength Of Titanium-porcelain

With the excellent biocompatibility, corrosion resistance and otheradvantages, titanium has been widely used in oral clinical. Due to the lowmelting point, low thermal expansion coefficient of titanium porcelain powderwas successfully placed on the market, titanium-ceramic technology has alsobeen considerable development. But the titanium-porcelain bond strength wasstill significantly lower than the bond strength of Ni-Cr alloy and porcelain. Thereasons was that the titanium surface can easily form a porous and nonadherentoxide under the high temperature environment. With small particle size, highsurface tension and surface binding energy, nano-materials displays a strongchemical activity and can take place chemical reaction with the oxygen of theporcelain and metal surfaces. In order to limit the excessive oxidation oftitanium in the porcelain sintering process and improve the bond strength oftitanium-porcelain, the surface of titanium was coated with nano-coatings by thesol-gel technology and then impose the appropriate heat treatment in this study. Otherwise, with the purpose of obtaining a theoretical basis for the furtherclinical applications of titanium porcelain restorations, we simulated the oralenvironment and studied the variational rule of titanium-porcelain bondstrength in acidic artificial saliva with the F-and the corrosion mechanism. Theresults are as follows:1. Compared with the titanium-porcelain system without any intermediatecoatings, the bond strength of the same system coated with TiO₂-SiO₂nano-coatings, being produced by the sol-gel technology and fired at750°C wassignificantly increased by21.77%. While the titanium-porcelain bond strengthwas significantly reduced by13.28%under the heat treatment conditions of300°C; Little effect of heat treatment duration on the bond strength of titaniumporcelain was found; Though the effects of the molar ratio of nano-coatingscomposition to the titanium-porcelain bond strength was also not obvious, butthere was still the variational rule of the lower Ti content and the higher Sicontent, the lower bond strength of titanium-porcelain.2. The X-ray diffraction patterns （XRD） patterns of the TiO₂-SiO₂nano-coatings fired at different temperatures was shown that although the XRDpattern of the specimen fired at750°C was significantly different from thespecimen fired at300°C and500°C, but the rutile phase was not found in allspecimens, which proved the TiO₂-SiO₂nano-coatings can be used as oxygenseparation barrier and effectively prevent oxidation of titanium in the process ofporcelain being fused to the titanium. With the different heat treatment durationand the molar ratio of the composition, no significant change of the crystal ofTiO₂-SiO₂nano-coatings was happened.3. The scanning electron microscope （SEM） photomicrographs of titanium-porcelain interface morphology of the specimens before porcelain fused with different heat treatment temperature、heat treatment duration and the molar ratioof the composition were observed that the TiO₂-SiO₂nano-coatings fired at300°C or500°C was loose and messy with larger cracks while the same coatingfired at750°C was compact and homogeneous without any obvious cracksexisting. The cross-sectional SEM microphotograph of the specimen fired at750°C after three-point bending test revealed that the location of thetitanium-porcelain fracture had been changed, which not existed between theoxide film of the titanium surface and titanium substrate, but within theTiO₂-SiO₂nano-coatings.4. With the basis of the above study, the Sn element was added into theTiO₂-SiO2nano-coatings to study the effects of the composite nano-coatings tothe bond strength of titanium-porcelain. The experimental results shown that thetemperature of the TiO₂-SiO₂-SnO_xnano-coatings fired which can significantlyincrease the bond strength of titanium-porcelain was opposite to the TiO₂-SiO₂nano-coatings. The bond strength of the titanium-porcelain system coated withTiO₂-SiO₂-SnO_xnano-coatings, being produced by the sol-gel technology andfired at300°C, was significantly increased by21.32%. With the more of heattreatment duration, the bond strength of titanium-porcelain was higher; Themolar ratio of nano-coatings composition can also effect the titanium-porcelainbond strength. When the molar ratio of Ti: Si: Sn was5:4:1and2:2:1, the bondstrength of titanium-porcelain was significantly increased, which was no notablychange under the three ratios for4:5.5:0.5.5. The X-ray diffraction patterns （XRD） patterns of the TiO₂-SiO2-SnOxnano-coatings fired at different temperatures was shown that compared with theXRD patterns of the specimens fired at300°C and500°C, no SnO phase wasfound in the XRD pattern of the specimen fired at750°C, which was replaced by the SnO2phase. The results shown that SnO maybe oxidized to SnO2with thefiring temperature elevated. The rutile phase was not found in all specimens,which indicated the TiO₂-SiO₂-SnO_xnano-coatings can be used as oxygenseparation barrier and effectively prevent oxidation of titanium in the process ofporcelain being fused to the titanium. No significant change of the crystal wasobserved under different heat treatment duration and the molar ratio of thecomposition.6. The scanning electron microscope （SEM） photomicrographs of titanium-porcelain interface morphology of the specimens before porcelain fused underdifferent processing conditions shown that compared with the disorderly andloose surface morphology of the TiO₂-SiO₂-SnO_xnano-coatings fired at500°Cor750°C, the same nano-coatings fired at300°C was compact andhomogeneous without any obvious cracks existing. The cross-sectional SEMmicrophotograph of the specimen fired at300°C after three-point bending testrevealed that the location of the titanium-porcelain fracture had been changed,which not existed between the oxide film of the titanium surface and titaniumsubstrate, but within the TiO₂-SiO₂nano-coatings.7. The bond strength between the TiO₂-SiO₂or TiO₂-SiO₂-SnO_xnano-coatingsfired at different temperatures and titanium substrate was respectively tested bythe scarification. When the heat treatment temperature was300°C、500°C and750°C, the bond strength of the TiO₂-SiO₂nano-coatings to the titaniumsubstrate was15.3N、22N and28.5N respectively, which shown that with theincreasing heat treatment temperature the bond strength of the nano-coatings tothe titanium substrate was also increased; while the bond strength of theTiO₂-SiO₂-SnO_xnano-coatings to the titanium substrate was18.5N、24.5N and22.8N respectively, which shown that with the increasing heat treatment temperature the bond strength of the nano-coatings to the titanium substrate wasincreased and then gradually decreased.8. The titanium-porcelain bond strength of the specimens immersed in the acidicartificial saliva containing F-was compared in this study, which wassignificantly decreased after1day. With the longer immersion time, the bondstrength of titanium-porcelain gradually reduced and finally stabilized. Therewas no obvious relationship between the bond strength of titanium-porcelainand the acid species. The location and manner of titanium-porcelain fracturecan’t changed with different pH values, F-concentration and acid species, thefracture still occurred mainly between the oxide film of the titanium surface andtitanium substrate.