In Vivo And In Vitro Studies On The Preservative Effect Of Chlorhexidine On The Stability Of Resin-dentin Bonds

With the rapid development of dental bonding technology and adhesive materials, thedentin adhesives have showed the satisfied instantly adhesive properties. However, thestability and durability of the resin-dentin bonds remain a limit to long-term life ofadhesive restorations the. Dentin proteolytic enzymes include matrix metalloproteinases(MMPs) and cysteine cathepsins, etc. These proteases may be activated by the bondingprocess and degradation of the hybrid layer. The collagen fibers within the hybrid layerthat exposed during the process of dentin bonding and bonding degradation might bedegraded by these activated proteases, resulting in the destruction of the hybrid layer,decrease of bonding strength, and directly affecting the stability and durability of dentin bonding interface. Therefore, the degradation of dentin collagen caused by proteolyticenzymes is considered to be an important endogenous factor which leads the degradationof dentin bonding interface. Therefore, the application of MMPs inhibitors in the dentininterfaces can protect the collagen within hybrid layer from degradation.Chlorhexidine is an unspecific inhibitor of MMPs, also showing promising inhibitioneffect on the activity of cysteine cathepsins. It has already been used to protect the hybridlayer and demonstrated good prospects. Although chlorhexidine has been used for decadesas an antibacterial agent in Dentistry and showed good bio-security and molecular stability,the role and possible mechanism of chlorhexidine on the stability of the dentin interfaceare still uncertain. Especially the reactivity of pulp-dentin complex in vital teeth under thestimulate of both bonding procedure and chlorhexidine retreatment is unknown and needto be further studied.This study consisted of two parts: in vitro adhesive experiments and in vivo animalexperiments. In the laboratorial experiments, thermal and mechanical load cycling wereused to simulate fatigue aging process. Micro-tensile bonding strength testing was used toevaluate the bonding strength and interfacial nanoleakages were evaluated by fieldemission scanning electron microscope (Field Emission Scanning Electron Microscopy,FE-SEM) observation and energy dispersive X-ray spectrometer analysis (EDX); In theanimal experiments, Hematoxylin-eosin staining and immunohistochemistry chemicalanalysis techniques were used to evaluate the effect of chlorhexidine pretreatment on andthe re-secretion of MMPs from pulp-dentin complex. The purpose of this study is toevaluate the effect of chlorhexidine pretreatment on the stability of resin-dentin bondinginterface and further study the probable endogenous and exogenous factors on the stabilityof dentin interface, providing a scientific basis for the use of chlorhexidine to stabilizedentin bonding interfaces. The main findings of this study are as the followings:1. Bonding degradation occurred in adhesive restorations when using both the total-etchand self-etch systems under the fatigue aging challenge, representing as the decrease ofbonding strength and the increasing degrees of nanoleakages in bonding interfaces.2. For the total-etch adhesive Adper Single Bond2, chlorhexidine pretreatment could not affect the immediate bonding strength, and inhibit the decrease of bonding strength afteraging. For the self-etching adhesive Clearfil SE Bond, chlorhexidine treatment could notaffect its immediate adhesive strength and showed no significant effect on bondingstrength after aging.3. For both total-etch and self-etch adhesive systems, chlorhexidine treatment can reducethe degree of nanoleakage after the aging treatment.4. The use of Adper Single Bond2would stimulate the re-secretion of MMPs byodontoblasts in vital pulp-dentin complex, presenting as the high levels of MMP-2,MMP-8and MMP-9in the layer of odontoblasts.5. The use of2%chlorhexidine pretreatment on dentin might inhibit the expression andactivity of MMP-2, MMP-8and MMP-9in pulp-dentin complex.6. The treatment with both Adper Single Bond2and2%chlorhexidine on dentin surfacesin vital teeth may lead to the separation of pre-dentin layer and odontoblast layer. It didnot cause significant pathological reaction of pulp-dentin complex.