Effects Of Air-blowing Pressure On The Bonding Performance Of Self-etch Adhesives

Preserving tooth tissue and protecting dental pulp to the greatest extent is one of the principles in restoration of tooth. Minimally Invasive Dentistry(MID) which benefits from the development of material and technology of adhesive dentistry, has moved the principle a big step forward.In clinical practice, the offending teeth usually become enamel subsurface lesion and dentin exposure, which due to dental caries, trauma, chronic injury, etc. In addition, the offending teeth need preparation before the restoration, so most resin bonding restorations occur on dentin. The structure of dentin is quite different from that of enamel, it has the following characteristics: high organic matter content, dentinal tubules which filled with liquid, and dentin reactive change. Consequently, the research on dentin bonding is the hotspot and difficulty in dental bonding field, while the problem of dentin bonding performance especially bonding durability has been the choke point in the development of dental bonding restoration technology. Incomplete infiltration of resin monomers into demineralized dentin and residual solvent of adhesives are important factors which affect the bonding performance of resin-dentin.1. Purpose:This study was to evaluate the effect of air-blowing pressure on bonding performance of self-etch adhesive system by investigating immediate and aging microtensile bonding strength(μTBS), and observating bonding interfacial nanoleakage and micromorphology. And it also investigated whether high pressure air-blowing technique can remove residual solvent on bonding interface, facilitate infiltration of resin monomers into the demineralized dentin,and improve the hybrid layer quality, thus to develop bonding strength and durability, in order to provide a new strategy to improve bonding performance of resin-dentin.2. MethodsThis study compared the effects of pressure of air-blowing with 0.1MPa(gentle) and 0.3MPa(strong) on dentin bonding of self-etch adhesives, the distance of blowing is 1cm, the time of blowing is 5s.For two-step self-etch adhesive system(SE bond), the specimens were divided into 5 groups based on different bonding procedures.For one-step self-etch adhesive system(S3 bond), the specimens were divided into 3 groups based on different bonding procedures.Bonding performance investigated in this study involves bonding strength, bonding durability, bonding interfacial nanoleakage and micromorphology.2.1. Bonding strength study: μTBS was used to compare immediate bonding strength achieved with different air-blowing pressure on SE bond and S3 bond.2.2. Bonding durability study: μTBS was used to compare aging bonding strength achieved with different air-blowing pressure on SE bond and S3 bond after thermal cycling.2.3. Bonding interfacial nanoleakage study: Both FESEM and TEM were used to evaluate bonding interfacial nanoleakage achieved with different air-blowing pressure on SE bond and S3 bond respectively.2.4. Bonding interfacial micromorphology study: FESEM was used to compare bonding interfacial micromorphology achieved with different air-blowing pressure on SE bond and S3 bond.3. Results3.1. Two-step self-etch adhesive system3.1.1 Bonding strength: Gentle air-blowing primer + gentle air-blowing bond shows the highest immediate μTBS(P < 0.05). The μTBS of gentle air-blowing primer + strong air-blowing bond and strong air-blowing primer + strong air-blowing bond +gentle air-blowing bond show no significant difference(P > 0.05), those of rest groups have statistically significant differences(P < 0.05).3.1.2. Bonding durability: After 5000 times thermal cycling, strong air-blowing primer + gentle air-blowing bond shows the highest μTBS(P < 0.05). The μTBS of gentle air-blowing primer + gentle air-blowing bond and gentle air-blowing primer + strong air-blowing bond show no significant difference(P > 0.05), those of strong air-blowing primer + strong air-blowing bond and strong air-blowing primer + strong air-blowing bond + gentle air-blowing bond show no significant difference(P > 0.05), those of rest groups have statistically significant differences(P < 0.05). The aging μTBS of gentle air-blowing primer + gentle air-blowing bond and strong air-blowing primer + strong air-blowing bond + gentle air-blowing bond are significantly lower than immediate μTBS(P < 0.05), while those of strong air-blowing primer + gentle air-blowing bond and gentle air-blowing primer + strong air-blowing bond are sifnificantly higher(P < 0.05).3.1.3. Bonding interfacial nanoleakage: The nanoleakage of strong air-blowing primer + gentle air-blowing bond is least, shows significant differences with gentle air-blowing primer + gentle air-blowing bond, gentle air-blowing primer + strong air-blowing bond, and strong air-blowing primer + strong air-blowing bond + gentle air-blowing bond(P < 0.05). Those of rest groups have no statistically significant difference(P > 0.05).3.1.4. Bonding interfacial micromorphology: Comparing gentle air-blowing, strong air-blowing makes solvent evaporate more completely, adhesive penetrate deeper, and the formed resin tags more longer, dense and evenly.3.2. One-step self-etch adhesive system3.2.1 Bonding strength: The immediate μTBS of gentle air-blowing is highest, but that of each group shows no significant difference(P > 0.05).3.2.2. Bonding durabilityAfter 5000 times thermal cycling, the μTBS of strong air-blowing + gentle air-blowing is highest, but that of each group shows no significant difference(P > 0.05). The aging μTBS of gentle air-blowing is significantly lower than immediate μTBS(P < 0.05), while those of other groups are not(P > 0.05).3.2.3. Bonding interfacial nanoleakage: The nanoleakage of strong air-blowing + gentle air-blowing is least, but that of each group shows no significant difference(P > 0.05).3.2.4. Bonding interfacial micromorphology: Comparing gentle air-blowing, strong air-blowing makes solvent evaporate more completely, adhesive penetrate deeper, and the formed resin tags more longer, dense and evenly.4. Conclusions4.1. For two-step self-etch SE bond system, the primer blown with higher pressure air, and the bond blown with lower presussre air can significantly improve the bonding durability.4.2. For one-step self-etch S3 bond system, air-blowing pressure has no significant effect on the bonding strength.