The Effect And Mechanism Of Silane Coupling Agent On The Bonding Performance Of Ceramic And Fiber Post

Bonding techniques today are widely used in every branches of dentistry. It has not only facilitated the clinical procedures, but also produced more conservative restorative techniques and met in some extent the growing cosmetic needs of patients. Some tooth-colored restorations, such as all ceramic crown, porcelain laminate veneer and translucent fiber post, are warmly welcomed by the patients and dentists. These bonded restorations are usually cemented onto the tooth structure by resin cement. However, the deficient bond strength between restorations and resin cement may result in clinical failure.Surface treatment is the key factor that would influence the bonding performance between restorations and resin composites. The frequently used surface treatments include abrading, sandblasting, etching and silanization.The silanols in the silane coupling agent can react with the hydroxy groups on the surface of restorations, forming covalent bond or hydrogen bond. Therefore, silanization is an effective way for improving the bond strength between restorations and resin composite. The efficiency of silane coupling agent may be affected by the composition of silane, temperature, catalyst, composition of restorations, type of resin cement and mechanical surface treatments.Most of the existing researches about silane coupling agent are focused on the effect of silanization on the bonding or improving the application methods of silane coupling agent. There are not so many studies that systematically evaluated the effect of relevant factors, such as mechanical treatments and temperature, on the performance of silanization. The mechanisms of silane coupling agent, especially for two-component silanes, have not been clearly discovered.The purpose of the present study is to investigate the mechanism of silane coupling agent, and evaluate the different relevant factors on the effect of silane treatment. Therefore, the bonding performance of ceramic restorations and fiber post could be improved. It may be helpful to the further researches and clinical practices about silane coupling agent.The total study was divided into two parts.Part 1: The effect of silane coupling agent on the bonding between ceramic and resin composite.In experiment 1, four different silane coupling agents (Porcelain Primer, Ceramic Primer, Porcelain Bond Activator and Porcelain Liner M) were applied onto the HF etched or phosphoric acid etched ceramic, respectively. The shear bond strengths between treated ceramic and resin composite were evaluated. Results showed that: the efficiency of two-component silanes were better than one-component ones; HF etching further improved the ceramic bond strength; the two-component silane combined with HF etching generated the best bond strength, while the one-component silane combined with phosphoric acid etching showed the lowest bond strength; the effect of two-component silane combined with phosphoric acid etching was comparable with that of one-component silane combined with HF etching.In experiment 2, four different silanes were applied onto the HF etched or phosphoric acid etched ceramic, respectively. The interfacial integrities between ceramic and resin composite were evaluated by SEM observation. Results showed that: the efficiency of two-component silanes were better than one-component ones; HF etching on ceramic surface further improved the interfacial integrity between ceramic and resin composite; the two-component silane combined with HF etching generated the best bonded interface, while the one-component silane combined with phosphoric acid etching showed poor interfacial integrity; the effect of two-component silane combined with phosphoric acid etching was comparable with that of one-component silane combined with HF etching.In experiment 3, an one-component silane coupling agent (Ceramic Primer) and a two-component one (Porcelain Liner M) were applied onto the ceramic surface respectively, then heated at different temperature (20-100℃). The bond strengths between ceramic and resin composite were evaluated. Results showed that: about 60℃heating during silanization generated the best bond strength for both of the two kind of silanes; from 20 to 60℃, the bond strengths were improved as temperature increased; further increasing the temperature, the bond strengths would decrease; it may speculated that the heat treatment during silanization should be no more than the boiling point of silanes.In experiment 4, two components of Porcelain Liner M were mixed and subjected to the in-situ FTIR analysis for 48 hr after mixing, including a dynamic analysis for 3 hr. The shear bond strengths between composite and ceramic treated with the silane mixture that had been kept for 0, 0.5, 1, 2, 3, 6, 12, 24 and 48 hr were also measured, respectively. The results showed that: after mixing the two components, the rate of silanes hydrolysis was faster than silanol condensation during the early period, then the condensation would be dominant during the later period; at 37 min after mixing, the concentration of silanols reached the peak value, while the silanes hydrolyzed completely at 85min; the concentration of silanol had a great influence on the bond improving efficiency, while a mass of oligomers or polymers in the mixture may weaken the coupling efficiency of silanol; the tested two-component silane mixture can keep best activity for 6 hr, and significantly improved the bond strength; after being kept for 48 hr, the silane mixture had no effect on the ceramic bonding.Part 2: The effect of silanization and related factors on the bonding between fiber post and resin composite.In experiment 1, DT quartz fiber posts were treated by Rocatec sandblasting, Calibra silane coupling agent, or sandblasting combined with silanization, respectively. The bonding between fiber post and Calibra resin cement were measured by micro-tensile bond strength test and SEM observation. The results showed that: both sandblasting and silanization significantly improved the bond strength; while the effect of sandblasting was better than silanization; SEM observation confirmed the sandblasting roughed the surface of fiber post;all specimens showed good integrities at the bonded interface.In experiment 2, a mould made of resin cement to simulate the root canal was designed. Zircon-silicium fiber posts (Easy post) were divided into different groups according to different resin cements (Calibra, FluoroCore 2, Multilink and VariolinkⅡ), with or without silanization on the post surface, light-irradiating the adhesive and Calibra resin cement or not. The results showed that: specimens luted with Calibra or FluoroCore 2 resin cements were better than those with Multilink or VariolinkⅡ, both in bond strength and interfacial integrity; the silanization could not improve the bonding of zircon-silicium fiber post; using XP Bond/SCA adhesive significantly improved the bonding performance of zircon-silicium fiber post; when the XP Bond/SCA adhesive was used, neither light irradiating the adhesive, nor light irradiating resin cement did significantly increase the bond strength further.In experiment 3, the bond strength between fiber post and resin composite was measured when the mould was used or not, respectively. Emphasis was given to the C factors in different cementing methods. The results showed that: high C factor value decreased the bond strength between fiber post and resin composite; the bond strengths of specimens with mould were lower than those without mould. Therefore, the C factor must be taken into consideration for the fiber post bond strength test, and the mould designed in the present study could reflect the real condition of fiber post cementing into root canal.Basing on the results above, it can be briefly concluded that: the efficiency of two-component silane coupling agents are better than one-component ones, both for bond strength and interfacial integrity; proper heating can significantly improve the efficiency of different silanes; the hydrolysis/condensation reactions occurred in two-component silane mixture have a great influence on the bonding efficiency, the tested two-component silane mixture can keep best activity for 6 hr after mixing; both silane treatment and Rocatec sandblasting can improve the bonding performance of quartz fiber post; silane treatment can not improve the zircon-silicium fiber post bonding; the C factor must be taken into consideration for the in vitro fiber post bond strength test.