Influence Of Polyurethane-gel Prepolymer On Polymerization Shrinkage And Mechanical Properties Of Composite Resin

Objective:With the development of dental materials science,composite resin has replaced silver amalgam as the most widely used dental defect restoration material in dental clinical treatment due to its excellent comprehensive properties.However,the microleakage,secondary caries and restoration fractures caused by polymerization shrinkage of composite resin are important reasons for the failure of clinical repair treatment.Therefore,reducing the polymerization shrinkage of composite resin has always been a research hotspot in dental materials.Polyurethane is a polymer material widely used in the medical field with good biological and mechanical properties.It is mainly used in human body repair materials,intelligent drug slow-release materials,tissue engineering materials,and surgical materials.In this study,a light-curable polyurethane-gel prepolymer that can chemically react with resin matrix monomers is prepared,and polymerization shrinkage rate,elastic modulus,flexural strength,degree of conversion and Vickers hardness are tested to comprehensively evaluate its influence on resin’s polymerization shrinkage and mechanical properties,and in-vitro cytotoxicity experiments is used to study the biological safety of the prepolymer,which is hoped that it can provide an experimental basis for reducing composite resin polymerization shrinkage.Methods:1.By solution polymerization method,using isophorone diisocyanate,bisphenol-A and hydroxyethyl methacrylate as raw materials,and 1,4-butanediol and trihydroxymethylpropane as chain-extenders and crosslinkers,reactive polyurethane-gel prepolymer（IBGBMA）is synthesized,that can form a chemical bond with resin matrix monomers,and its structure is characterized by Fourier transform infrared spectroscopy（FTIR）.2.The Bis-GMA/TEGDMA（7:3）resin matrix without IBGBMA is configured as control group,and the matrix added with 5wt%,10wt%,15wt%,and 20wt%IBGBMA are used as experimental groups.3.The polymerization shrinkage rate of each group after curing is detected by the density bottle method.The three-point bending test of the universal testing machine is used to detect the elastic modulus and flexural strength.The peak area method of FTIR is used to detect degree of conversion.The Vickers hardness tester is used to detect the Vickers hardness of each group.And the in-vitro cytotoxicity experiment are used to detect related growth rate of cell（RGR）to evaluate the biological safety of the material.4.The experimental results were statistically analyzed using SPSS21.0 software.The polymerization shrinkage rate,elastic modulus,flexural strength,degree of conversion,Vickers hardness,and RGR were in accordance with the normal distribution.The result is expressed in the form of mean±standard deviation（±s）.The polymerization shrinkage rate,elastic modulus,flexural strength,degree of conversion and Vickers hardness between groups were analyzed by One-way ANOVA,and RGR between groups were analyzed by Two-way ANOVA.Comparisons between the two groups were performed using Tukey-test,and test significance level wasα=0.05.Research results:1.The FTIR results showed the characteristic absorption peaks of a photo-curable group（C=C）at 1638cm^-1as well as the group（-NHCOO-）at 3310cm^-1,indicating that the active target product IBGBMA was synthesized,which can polymerize with the resin matrix during light curing.2.With the increase of IBGBMA addition,the polymerization shrinkage rate in experimental groups was decreased,and it was all lower than control group（P﹤0.05）.3.The elasticity modulus in 20wt%IBGBMA group was significantly reduced（P﹤0.05）.The difference between the other experimental groups and control group was not statistically significant（P﹥0.05）.4.The flexural strength of 15wt%IBGBMA group was higher than the other groups（P﹤0.05）.The 20wt%IBGBMA group was lower than 5wt%IBGBMA group,10wt%IBGBMA group and 15wt%IBGBMA group（P﹤0.05）,which was not statistically different from control group（P﹥0.05）.5.The degree of conversion of 15wt%IBGBMA group and 20wt%IBGBMA group was gradually decreased（P﹤0.05）.There was no significant difference between control group,5wt%IBGBMA group and 10wt%IBGBMA group（P﹥0.05）.6.The Vickers hardness of 20wt%IBGBMA group was significantly increased（P﹤0.05）,and the difference between the other experimental groups was not statistically significant7.In vitro cytotoxicity experiment,RGR was affected by resin extraction time and IBGBMA content,when extraction time was prolonged and IBGBMA content was increased,RGR was decreased（P﹤0.05）,there was no interaction between the two factor（P﹥0.05）.The toxicity evaluation was graded as level-0 or level-1.Conclusion:The active polyurethane-gel prepolymer was successfully synthesized.The polymerization shrinkage rate of 15wt%IBGBMA group was significantly reduced after curing（Р﹤0.05）,and its flexural strength and Vickers hardness were enhanced（Р﹤0.05）,while its elastic modulus was not affected,and the comprehensive properties was improved.