| In restorative dental materials,dental composite resin has gradually replaced silver amalgam and other restorative materials due to its adequate adhesive strength,easy operation and aesthetic,and has become one of the most widely used dental restorative materials.The ideal dental composite resin should have favorable physical and chemical properties and biocompatibility,afford to support sufficient chewing pressure and friction,maintain satisfactory chemical stability,while try to do no harm to the doctors and patients.The traditional dental composite resin monomer is not only too viscous to operate,but also possesses excessive polymerization shrinkage,which will lead to the gap between the filling restoration material and the tooth tissue,resulting in the tooth fracture,and then also cause the secondary caries.More importantly,Bis-GMA,as one of the most used monomers of commercial dental composite resin,is synthesized from petrochemicals,a non-renewable resource with extremely limited reserves.Secondly,Bis-GMA is at risk of being hydrolyzed to BPA in humans,which seriously affects human health.Therefore,the development of high-performance bio-based dimethacrylates to replace Bis-GMA is the focus of research in the field of resin-based dental restoration materials,while possessing some practical significance and application value.In this work,the main chain structure and side chain structure of dimethacrylate were designed from the perspective of molecular design to prepare dental composite resins with less toxicity to humans and better performance.The bio-based dimethacrylate monomers were synthesized by using methoxyl alkylphenol as raw material and used in the preparation of dental composite resins.In order to develop bio-based dental composite resins with excellent comprehensive properties,the structure and properties of dimethacrylate monomer were gradually explored through the introduction of methoxyalkyl phenols,different alkyl side chains and rigid main chains.In the first part of the work,eugenol-based biphenol(BEF)was synthesized by aldol reaction using eugenol as the raw material,and the estrogenic activities of BEF and commercial biphenols(BPA and BPF)were compared.Eugenol-based epoxy intermediate(BEF-EP)was synthesized from BEF,then eugenol-based(meth)acrylates(BEF-GA and BEF-GMA)were further synthesized.Their structures were characterized by NMR and FT-IR.The resin matrices(5EA5T and 5EMA5T)and composite resins(5EA5TC and 5EMA5TC)were prepared from BEF-GA and BEF-GMA,respectively.The Bis-GMA-based resin matrix(5B5T)and composite resin(5B5TC)were used as control groups.The physical and chemical properties and toxicity of the resin matrix and composite resin before and after curing were evaluated according to ISO 4049 and ISO 10993-5,including viscosity,polymerization kinetics,polymerization shrinkage,water absorption,solubility,flexural strength,flexural modulus,fracture energy,and Vickers hardness.According to test results,compared with the control group,the eugenol-based dimethacrylate monomers possessed a lower viscosity value of 270 Pa·s and 240 Pa·s,about 32%and 28%of the viscosity value of the commercial Bis-GMA;5EA5T and 5EMA5T had passable polymerization kinetics,and the double bond conversions of 55.68±1.45%and 57.14±0.05%,respectively;The volumetric polymerization shrinkage of 5EA5T and 5EMA5T were 8.53%and8.76%,respectively;the solubility were 1.28±0.14?g mm-3 and 1.05±0.13?g mm-3,respectively;and the cytotoxicity grades were all low toxicity level.Their composite resins had good performance.However,the mechanical properties including flexural strength,flexural modulus and hardness of 5EA5T and 5EMA5T were slightly lower than those of 5B5T.So further improvement of the molecular structure of the dimethacrylate is needed to improve the performance.In the first part of this work,the potential of eugenol-based dimethacrylates for use in dental composite resins was showed.In order to improve the mechanical properties of the bio-based dimethacrylates,the second part of the work,4-methylguaiacol,derived from lignin,was used as a raw material for the synthesis of low estrogenic activity 4-methylguaiacol-based biphenol(BCF).4-Methylguaiacol-based(BCF-EP)was synthesized from BCF,then 4-methylguaiacol-based(meth)acrylates(BCF-GA and BCF-GMA)were further synthesized.Their structures were characterized by NMR and FT-IR.BCF-GA and BCF-GMA were used to prepare resin matrices(5CA5T and 5CMA5T)and composite resins(5CA5TC and 5CMA5TC).Flexural strength of 5CA5T was 114.99±1.53 MPa and the flexural modulus was 3.15±0.02 GPa,which exceeded 5B5T by 21%and 32%,respectively;the flexural strength of 5CMA5T was 100.49±1.70 MPa and the flexural modulus was 2.56±0.09 GPa,which exceeded 5B5T by 6%and 7%;besides,the double bond conversion of 5CA5T and 5CMA5T could reach 51.51±1.09%and 49.05±1.55%after 120 s irradiation,respectively.In the cytotoxicity test,both 5CA5T and 5CMA5T exhibited acceptable cell viability and low toxicity cytotoxicity grade.Their composite resins also showed excellent performance.However,compared to 5B5T,5CA5T and 5CMA5T had higher water absorption,and the adverse effects caused by water absorption on flexural strength,flexural modulus and hardness,which limited the use of the materials in wet oral environments to a certain extent.To address the weakness of high water absorption of bio-based dimethacrylate resin matrix,in the third part of this work,we proposed to reduce the content of diluent(TEGDMA),which greatly increases water absorption.By reducing the content of TEGDMA,the goal of reducing the water absorption of the resin matrix can be achieved.In addition,TEGDMA,a small lipophilic molecule,can penetrate cell membranes and react with intracellular molecules,leading to severe cytotoxicity.Therefore,reducing the content of TEGDMA will also decrease the cytotoxicity of the materials.This requires the use of lower viscosity dimethacrylate monomers to meet the rheological performance of the resin matrix with easy operation after reducing the diluent content.Therefore,from the perspective of molecular design,4-propylguaiacol derived from lignin was used as a raw material for the synthesis of 4-propylguaiacol-based biphenol(BDEF)with low estrogenic activity using the condensation reaction of phenols with aldehydes.BDEF was used as a raw material to synthesize 4-propylguaiacol-based epoxy intermediate(BDEF-EP),and then 4-propylguaiacol-based methacrylate(BDEF-GMA).BDEF-GMA was mixed with different ratios of TEGDMA to prepare resin matrices with different diluent contents.The effect of different TEGDMA contents in resin matrix on the performance was investigated,and the optimal formulation of resin matrix was explored.Compared with the previously synthesized bio-based di(meth)acrylates,the viscosity value of BDEF-GMA was the lowest at the same shear rate,about 195 Pa·s,which was about 23%of the viscosity value of commercial Bis-GMA;the viscosity of each group of resin matrix was greatly influenced by the TEGDMA content,and the viscosity value of the resin matrix was inversely proportional to the TEGDMA content.When the viscosity is too high,the polymerization kinetics of the resin matrix will be affected to a certain extent.Moreover,the polymerization shrinkage,water absorption and solubility of the resin matrix are also significantly influenced by the TEGDMA content,and the polymerization shrinkage,water absorption and solubility of the resin matrix decrease significantly as the TEGDMA content decreases.By weighting the performance results,when TEGDMA content was 30 wt.%,the resin matrix has preferable performance.The viscosity of 7G3T was about 0.96 Pa·s;the double bond conversion was 54.56±0.40%,the maximum polymerization rate was 8.21±0.95 s-1;the volume polymerization shrinkage was 6.26%,the polymerization shrinkage stress was 0.99 MPa;the water absorption and solubility were 40.13±0.11?g mm-3 and 0.38±0.09?g mm-3,respectively;the flexural strength and flexural modulus were 98.75±1.69 MPa and2.55±0.03 GPa,respectively;the cytotoxicity grade was non-toxic.Combining the above studies,we found that different side chain groups in the dimethacrylate monomer have crucial effects on the properties of the dimethacrylate monomer.In the fourth part of the work,the water absorption and mechanical properties of the bio-based dimethacrylate resin matrix were further improved by changing the main chain structure via introducing fluorenyl cardo ring structure main chain.From molecular design,guaiacol and 9-fluorenone were used as raw materials to prepare fluorenyl cardo ring structure guaiacol-based biphenol(BMHF)with low estrogenic effects.The fluorenyl cardo ring structure guaiacol-containing epoxy intermediate(BMHF-EP)and dimethacrylate(BMHF-GMA)were further synthesized.The resin matrix(5MHMA5T)and the composite resin(5MHMA5TC)were prepared by BMHF-GMA.Double bond conversion of 5MHMA5T and 5MHMA5TC were 54.25±2.77%and 51.52±2.51%,respectively,the polymerization rates were 9.68±0.21 s-1 and 8.87±0.18 s-1,respectively;the volumetric polymerization shrinkage of 5MHMA5T and5MHMA5TC were 7.19%and 4.45%,respectively.The polymerization shrinkage stress of 5MHMA5T and 5MHMA5TC were 0.92 MPa and 0.66 MPa,respectively;5MHMA5T and 5MHMA5TC had the lowest water absorption of 39.91±0.52?g mm-3 and 22.25±0.90?g mm-3,respectively.And the lowest solubility of 0.99±0.04?g mm-3 and 0.45±0.20?g mm-3,respectively;5MHMA5T and 5MHMA5TC had the lowest cytotoxicity and the toxicity grade were non-toxicity;5MHMA5T had the highest flexural strength and flexural modulus of 122.30±5.00 MPa and 3.49±0.02GPa,respectively.Compared with the commercial 5B5T,they were improved by 29%and 46%,respectively.And after sufficient soaking,the mechanical properties of5MHMA5T decreased insignificantly,which were higher than 5B5T.In summary,we prepared a series of bio-based di(meth)acrylate monomers through molecular structure design,from biomass monomers that are widely available in nature.The relationship between their molecular structures and properties were studied and explored.The goal in this study was to reduce the toxicity of dental composite resins and improve their properties.It is hoped that our research can draw attention to bio-based dental composite resins and provide new research ideas for the development of dental composite resins and bring safety to people's health. |
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