Proanthocyanidins Incorporation Improves Bonding Performance Of A Two Step Self-etching Adhesive

Adhesive systems have gained satisfactory short-term effectiveness, while theirlong-term stability is still questionable. One of the main causes for restoration failure isthe breakdown of resin-dentin interface. This interface is known as hybrid layer affordingthe main bonding strength. And the formation of interface owing to the course that resininfiltrates into the dentin matrix and form an interlocked. The collagen exposed zone, dueto the mismatching of dentin demineralization depth and adhesive resin penetration depth,rendering them susceptible to hydrolysis and enzymatic, etc. degradation, and eventuallylead to the failure of the adhesive.So the enhancement of collagen’s stability within the hybrid layer has been the mainresearch target to improve dentine bonding. Currently, the application of matrixmetalloproteinase inhibitors, antimicrobial adhesive agent, ethanol-wetting bondingtechniques, etc. can reinforce resin-dentin bonding restorations to some extent. However, the above mentioned methods were to reduce external influence, and the collagen in theinterface has not been enhanced. It is confirmed that cross-linking agents can enhance themechanical and biological properties of dentin matrix. Among them, the naturalcrosslinking agent of proanthocyanidins (PA),attracted much more concern due to goodbiocompatibility, anti-bacteria and protease inhibitory activity. Previous studies havedemonstrated that the modification of demineralized dentin using PA can improve thecollagen crosslinking degree and enhance the ultimate tensile strength of demineralizeddentin, protect the resin-dentin bonding interface, slow down the degeneration of theinterface caused by thermocycling. However, PA was only applied to etch-and-rinseadhesive system in these studies, and it has not been used in self-etching adhesive system.So this study was aimed to investigate the effect of different PA incorporation manners inclinically relevant time periods on the bonding performance of Clearfil SE Bond.1. Objectives1.1To compare the effect of different PA application manners in a two step self-etchingadhesive (PA pretreatment or incorporation into primer) with different concentrationson the degree of conversion, the immediate microtensile bond strength and theinterface morphology.1.2To investigate the effect of different PA incorporation manners with the optimalconcentration of PA on the durability of a two step self-etching adhesive system afterthermocycling.2. Methods2.1PA was incorporated into either ethanol to prepare a preconditioner, or into Clearfil SEprimer, at different concentrations (0%,1%,3%and5%). The effect of different PAincorporation manners on the degree of conversion (DC) by FTIR was evaluated.Preconditioning was conducted after the application of self-etching primer andtreatment duration for20s,40s and60s. Non-treated specimens were used as negative controls (NC).2.2Teeth were collected and exposed their occlusal dentin surface. They were then furthercut into4equal blocks and randomly assigned to one of the above-mentioned PApreconditioner groups（5groups） or PA-incorporated primer groups (4groups).Bonded specimens were prepared. Microtensile testing was conducted by a universaltesting machine. Debonded surface and bonding interface were observed under a feldemission scanning electron microscopy (FESEM).2.3According to the optimal concentration of PA, bonded specimens were prepared withdifferent PA incorporation manners and then thermocycling was done (5000or10000cycles). After thermocycling, the microtensile bond strength was determined, and thenthe fracture mode and morphology of bonding interface were observed by FESEM.3. Results and conclusions3.1When1%~3%PA-ethanol preconditioners was used for40s, there were no adverseinfluence on the DC of Clearfil SE bond and can improved the immediate bondstrength of the tested two-step self-etching bonding system.3%PA specimenspresented the highest bond strength among all groups. PA preconditioner manner canformed dense hybrid layer.3.21%~3%PA incorporated primer has no adverse influence on DC and can improved theimmediate bond strength of the tested two-step self-etching bonding system.Furthermore,3%PA pretreated specimens presented the highest bond strength amongall groups. But the DC and bond strength was lower than NC when PA concentrationincreased to5%. A more compact hybrid layer can be formed in the bondingspecimens, which prepared using PA incorporation manner.3.3The DC, immediate bond strength and the morphology of the hybrid layer were nosignificant differences between the two manners. And as immediate adhesiveproperties were concerned, the method of PA incorporated primer was superior to themanner of PA precondition.- 3.4The bond durability of3%PA incorporated primer after5000and10000times ofthermal cycling was significantly increased compared to NC group and3%PApreconditioner group.