Study On The Application Of Urushiol And Its Derivative In Dentin Adhesive System

Dental caries is a common disease in dentistry,and the current clinical treatment method is the restoration of light curable composite resin.When the dentin is etched by etching gel,the exposed collagen fiber network and the infiltrated polymerized adhesive monomers form a"hybrid layer".The quality of the hybrid layer plays an important role in the bonding strength.The monomers penetrate into the dentin tubules form resin tags,which also affect the bonding strength.The polymerization shrinkage of the composite resin after light curing will cause not only a slight gap between the resin-dentin interface but also the microleakage.As the thermal expansion coefficient of the composite resin and the dentin are different,the gap will become larger during the temperature changes in oral,as a result,the saliva will enter into the gap and the bacteria in it will activate the endogenous matrix metalloproteinase and cysteine cathepsins in dentin after producing acid.These enzymes destroy the collagen network and cause the degradation of the hybrid layer.The occurrence of secondary caries has become the main reason for the failure of composite resin.By strengthening the dentin structure and exploring new adhesive systems to improve the bonding strength and durability has been a focus of research now.Increasing the cross-linking of demineralized collagen can enhance the combination of collagen and adhesive monomers.Although the cross-linking of the collagen matrix is a phenomenon that occurs naturally in dentin,exogenous collagen cross-linking agents can induce additional intermolecular and intra-molecular cross-linking.Improving the cross-linking of the demineralized collagen network attributes to the bonding durability and tolerance to enzymatic hydrolysis.In addition,the preservation of the collagen network is a barrier to acid diffusion and mineral release,contributing to the deposition of minerals during remineralization.At present,because of the high cytotoxicity of chemical cross-linking agents such as glutaraldehyde,natural collagen cross-linking agents have received more and more attention.The catechol group of the natural collagen cross-linking agent plays a role.The group interacts with proteins by the following four different mechanisms to induce cross-linking,including covalent interaction,ionic interaction,hydrogen bonding and hydrophobic interaction.And the catechol group of collagen cross-linking agent can also promote remineralization.Several natural plant monomers often have antibacterial,anti-oxidant and anti-cancer effects,with almost no drug resistance or side effects,and become medicinal materials.Raw lacquer sap is extracted from a common plant lacquer tree that mainly grows in Asia.The lacquer sap contains many components,and urushiol is its main component and the functional monomer.Lacquerware and Buddha statues painted with raw lacquer sap,despite being buried underground for thousands of years,their appearance is still intact.Researches found that urushiol has a strong hydrophobicity,due to its catechol functional group and a long saturated or unsaturated alkyl chain.As a consequence,it has been used as a coating until now.This study intends to explore the effect of urushiol on demineralized dentin collagen and its hydrophobicity,which has a long history in China.After applying it into the dentin bonding system,it will improve the dentin collagen cross-linking and preserve the integrity of the hybrid layer,thereby improving the bonding strength and durability.In the study of Chapter 2,the catechol group in urushiol was used to promote collagen cross-linking to detect the resistance of cross-linked collagen to collagenase degradation.Effects of different concentrations of urushiol on collagen cross-linking were observed by scanning electron microscope(SEM).The results showed that as the concentration of urushiol increased to 3wt%,the effect of promoting collagen cross-linking became more and more obvious.The folds formed from the wall of the dentin tubules,the gaps between the collagen fiber bundles became smaller and fused.After 48 hours of enzymatic hydrolysis of collagenase,the weight loss rate of collagen modified by urushiol after collagenase degradation decreased significantly,indicating that the resistance to enzymatic hydrolysis of collagen after urushiol treatment was improved.Scanning electron micrographs showed that the dentin collagen sheet modified by urushiol after enzymolysis basically retained the complete dentin structure,while the dentin collagen sheet without the action of urushiol could not distinguish the dentin structure,which also confirmed the lacquer The phenol-modified dentin collagen has improved resistance to enzymatic hydrolysis.In the study in Chapter 3,urushiol was dissolved in two different solvents,ethanol and DMSO,preparing primers with concentrations of 0.1wt%,0.5wt%,0.7wt%,and1wt%.By detecting the degree of conversion,contact angle,the micro-tensile strength immediately and after aging,and the scanning electron microscope(SEM)we evaluate the effect of the primer on the bonding strength.The results showed that DMSO-urushiol primer had higher bonding strength than ethanol-urushiol primer.Urushiol had an effect on the degree of conversion,but no significant bonding strength.The bonding strength after the primer treatment was significantly higher than that of the control group.After 5000 thermocycles,the bonding strength of each group decreased,but the aging process had no effect on the bonding strength of the samples treated with ethanol-0.7wt%urushiol and ethanol-1wt%urushiol primers.Cytotoxicity results also meet the requirements of clinical application.In the research of Chapter 4,a light curable urushiol derivative monomer was synthesized by the chemical synthesis,and completely replaced the Bis-GMA monomer in the adhesive,as a result,a new etch-and-rinse adhesive was prepared.The mass fractions of urushiol derivatives were 55wt%,60wt%,65wt%,and 70wt%respectively.Firstly,characterization of the derivative was determined by FTIR and NMR.The tests of the degree of conversion of the adhesive,contact angle,water sorption and solubility,micro-tensile bond strength immediately and after aging,nanoleakage and cytotoxicity were performed.The results showed that,compared with the control group,the noval adhesive had a higher polymerization rate and a higher water contact angle after curing,indicating that it has better hydrophobicity after curing.The water absorption and solubility were significantly lower than those of the commercial adhesive Single Bond 2,and the bonding strength increased with the increase of the derivative monomer mass fraction.Especially after thermocycles,the bonding strength of the U_70%group did not change significantly and with lower nanoleakage,indicating that the hydrolysis resistance of the bonding interface of novel adhesive significantly increased the aging resistance of the interface.The cytotoxicity also met the requirements of clinical application.In summary,this study firstly determined the effect of urushiol on the collagen cross-linking,providing a basis for its application in dentin bonding systems.Moreover,it was applied as primers with different concentrations to improve dentin bonding strength and durability.Finally a light-curable derivative monomer based on urushiol was designed and synthesized.After using it as the main monomer of the adhesive,the noval adhesive with hydrophobicity effectively improved the hydrolysis resistance of the bonding interface,thereby increasing its bonding strength and extending the service life of the restorations.It also provides an important reference for the clinical application of urushiol.