| Adhesive dentistry has been progressing at a rapid rate over the past decades. A largepart of this success is attributed to the significant advances in dentin bonding technology.So far, the enamel adhesive technique has been quite well, but adhesion to dentin has beenvery challenging and unpredictable because of the heterogeneous nature of dentin matrix.The stability of dentin bonding interface is a key factor to affect the restorationsuccess. Incomplete infiltration of resin, poor qulitity hybride layer, hydrolytic of lowpolymerization monomer and degradation of exposed collagen were supposed toaccelerate the aging of bonding interface. Many strategies have been proposed byresearchers to prolong the bonding durability, including improving the conversion rate ofbonding agent, inhibiting of collagenolytic enzymes, promoting crosslink of collagen, andbiomimetic remineralization. Even though several studies revealed excellent immediatebonding effectiveness, the durability and stability of resin bonded interfaces on dentin created remain questionable.In recent decades, dentin noncollagen protein (NCP) has been found to involve indentin bonding process. Dentin proteoglycans (PGs), as the major components of NCP,also received extensive attention, but the mechanism of which is unknown. Therefore, thepurpose of this study was to assess the role of GAGs/PGs in dentin bonding process andbonding durability. Glycosaminoglycan (GAG) chains and PGs were removed from dentinrespectively to evaluate the effect of GAGs and PGs on durability of resin-dentin bonds.Also, the interaction mechanism between GAGs/PGs and dentin bonding was explored, inexpectation of providing a new thinking for the improvement of dentin bonding stability.Methods1) Two commercial dental adhesive systems, AdperTMSingle Bond2(SB) and Prime&Bond NT (NT) were used in the present study. Dentin GAGs and PGs were removedby chondroitinase ABC (C-ABC group) and trypsin (TRY) before application of thebonding agent. Then, microtensile bond strength (μTBS), fracture mode and bondinginterface morphology were evaluated via microtensile testing, stereo microscope andFESEM respectively.2) Using long-term soak in artificial saliva and in matrix metalloproteinases (MMPs) tosimulate aging conditions. The μTBS values, failure modes, bonding interfacemorphology and the amount of nanoleakage were evaluated to investigate thepotential effect of GAGs/PGs on the stability of resin-dentin bonds against artificialsaliva storage aging and MMPs degradation.3) After remove of dentin GAGs and PGs, morphology of collagen fiber and thethickness change of demineralized dentin in different dentin wetting conditions wereevaluated via field emission scanning electron microscopy, laser confocal scanningmicroscopy and FV10-ASW3.1Viewer analysis software, in order to analysis theeffects of GAGs and PGs on maintaining the micro-morphology of collagen fiber andthe hydration properties of demineralized dentin. 4) Contact angle tester and field emission scanning electron microscopy combined withEDX element analysis software were used to examine the wettability and permeabilityof dentin with/without GAGs/PGs, in order to explore the mechanism of GAGs andPGs in dentin bonding process and bonding durability.Results1) Dentin PGs participate in the dentin bonding process. Removal of GAGs decreasedthe immediate μTBS of dentin and total etching adhesives, while removal of PGsincreased the immediate μTBS.2) After saliva storage and MMPs aging, no significant difference in μTBS was foundbetween C-ABC group and control group (p>0.05). While the decreased rate of μTBSof C-ABC group was significantly lower than control group. Remove of dentin GAGsmaintained the integrity of the bonding interface and hybride layer, and slowed downthe aging process to a certain extent.3) The μTBS of TRY group was significantly higher than control group after salivastorage and MMPs aging (p<0.05). Also, the degree of nanoleakage of TRY groupwas significantly reduced, suggesting that the removal of PGs also maintains thestability of bonding interface, and improves the anti-aging ability of dentin bondinginterface.4) After remove of PGs, dentin collagen network collapsed and when dentin was in wetcondition, collagen interface enlarged. While after remove of GAGs, dentin collagennetwork also collapsed, but the core protein of PGs still filled within the collagenmesh and there was no significant change in collagen interface. It was suggested thatthe presence of GAGs and PGs maintains the spatial structure of dentin and it couldbe speculated that there was a relationship between the decreased μTBS of C-ABCgroup and the structure changes of collagen fibers/the presence of core protein of PGs.5) GAGs and PGs may modify the hydration status and influence the adhesive propertiesof the demineralized dentin. The hydration properties of demineralized dentin collagen would drop after the remove of GAGs and PGs. Removal of PGs cansignificantly improve the wettability and permeability of dentin surface tototal-etching adhesives, while the removal of GAGs only increased the wettability andhad no significant effect on its permeability. It was speculated that GAGs and PGscould improve the stability of dentin bonding interface by reducing the hydrationproperties of collagen and increasing the wettability and permeability of the dentinsurface. |
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