Surface Modification Of Dental Aluminum Oxide Based Ceramic Via Sol-gel Silica Coating

The increasing popularity of full ceramic restoration is due tosuperior optical properties and high biocompatibility. Because ofbrittleness and low tensile strength, a high long-term success rate fullceramic restoration relies on adequate resin bonding, which helps toincrease the fracture resistance of tooth and restoration, and minimizesmicroleakage.Aluminum based ceramic contains only a small amount of silica,silane application do not significantly enhance the resin-to-ceramic bondstrength, and etching with hydrofluoric acid do not create amicroretentive surface compared with conventional ceramics. A durableresin bond strength to Aluminum based ceramic was achieved by thecombined use of a silica coating system and sandblasting with aluminum oxide powder. The classical method for silica coating is Silicoaterdeveloped in 1984 based on pyrolytical method. One of the recentmethods is based on tribochemical silica coating of the metal surface(Rocatec system). Although effective, both of these methods needexclusive apparatus and complicated and skilled procedure. A simple andeffective surface silica coating treatment of aluminum oxide basedceramic is needed to obtain durable bond strength of resin luting cement.In recent years, solution-gelatin (sol-gel) synthesis of nano-composites containing ultrafine particles of silicon in oxide matrices hasbeen rapidly developed. Sol-gel process is becoming one of the mostuseful and versatile methods of oxide film fabrication due to thefollowing advantages: low-processing temperature, homogeneity ofcoatings, easy control of coating thickness, as well as the possibility toadd reducing and oxidizing agents in small concentrations.In this study, nano-silica coating was prepared on the surface ofglass-infiltrated aluminum oxide ceramic and was characterized, its effecton the bond strength between Bis-GMA resin and glass-infiltratedaluminum oxide ceramic was verify by using the microtensile test. Also,the effects of different surface pre-treatments including nano-silicacoating on color stability of underlying resin materials were examined. ◆PartⅠSurface modification of dental aluminum oxide ceramic with nano-silica coatingObjectives: The aim of this study was to make nano-silica coatingthrough sol-gel process, and to evaluate the wettability of dentalaluminum oxide based ceramic with and without nano-silica coating.Methods: Nano-silica coating was prepared with colloidal silica sol onglass-infiltrated aluminum oxide ceramic surface which had been treatedwith air particle abrasion. Atomic Force Microscope (AFM) and FourierTransmission Infrared spectrum (FTIR) and Energy Dispersive X-raySpectroscopy (EDS) were used for coating characterization. Contactangles of oleic acid to finished, sandblasted and coated ceramic surfaceof were measured.Results: AFM pictures showed that some parts of nano-particles incoating gel conglomerated after heat treatment. It can be seen from the IRpicture that bending vibration absorption kurtosis of Si-OH also vanishedafter heat treatment. As showed in EDS, content of silicon elementincreased much after sandblasting ceramic surface was coated bynanostructure silica. Among contact angles of three treated surface, theones on polished surface were the biggest (P=0.000, P=0.000), andsandblasting combined nano-silica coating surface the smallest (P=0.000,P=0.003). Conclusions: Nano-silica coating can be made with sol-gel processsuccessfully, which increased content of silicon element of dentalaluminum oxide ceramic. Heat treatment may reinforce Si-O-Si netstructure of coating gel. Wettability of dental aluminum oxide ceramicwith silica coating is higher than with sandblasting and polishing.◆PartⅡEffects of nano-silica coating on microtensilebond strength of glass-infiltrated aluminumoxide ceramicObjective: Aim of this study was to evaluate the effect of nano-silicacoating with sol-gel process on bonding strength between glass-infiltratedaluminum oxide ceramic and resin luting cement.Methods: Three glass-infiltrated aluminum oxide ceramic groups werefabricated to receive different surface treatments as sandblasting (P),sandblasting and application of silane couple agent (PO), sandblastingand silica coating and application of silane couple agent (PTO). Eachceramic block was bonded to composite resin with light curing resincement, and the samples were cut for micro tensile bonding strength test after 24 hour storage in room temperature distill water.Result: There existed no difference between Group P and PO (P=0.797),and Group had the highest micro tensile bonding strength (P＜0.05).Conclusion: A higher bonding strength could be acquired though preparednano-silica coating with sol-gel process on glass-infiltrated aluminumoxide ceramic surface followed by application of silane.◆PartⅢEffects of ceramic covering on color stability of light-cured composite resinPurpose: This study investigated the color stability of composite resinusing ceramic discs to be as light transmission inter-medias.Materials and Methods: A IPS-Empress 2 ceramic disc in 1.0mmthickness was fabricated, twenty composite resin test pieces (five for eachgroup) were irradiated directly (Group A) and indirectly with a LED lightsource for 40s through the ceramic disc after being treated with differentsurface treatment including sandblasting (Group B), sandblasting+hydrofluoric acid etching (Group C) and sandblasting+hydrofluoric acidetching+nano-silica coating with sol-gel process (Group D). Changes in color of test samples were determined after storage in red wine for 1day,5 days, 10 days and 15 days using the CIE-Lab system by a colorimeter.The results were analyzed by one-way analysis of variance and LSDmulti-compare.Results: The color change of resin disks immersed for different days wassignificantly different among four groups (P＜0.05). For the sameimmersed time,△E was no different among each group (P＞0.05).Conclusion: Surface treatment to ceramic with thickness less than 1mmwould not change color stability of light-ouring composite resin beneath.