| Dental composites are polymeric materials mainly based on methyl methacrylate as resin matrix which is representative of Bis-GMA. They could be polymerized accompanied by volumetric shrinkage and stress, leading to a serial of clinic failures and becames focus of dental research in polymeric materials. Expanding monomers are a kind of functional compounds with expansion or little shrinkage in the polymerization, and have been applied to modify the polymeric materials in biological, chemical, and medical field for synthesis of non-shrinkage resin cements and composites. The research aimed to synthesize a spiroothorcarbonate expanding monomer and to study the application in modifying the dental resin matrix methyl methacrylate it for the purpose of reducing shrinkage, whose related properties were also evaluated. The paper was divided into three parts: the determination of expanding monomer modified resin system, biological evaluation of expanding monomer modified resin system, physico-mechanical evaluation of expanding monomer modified resin system, which was specifically described as below: In attempt of reducing polymerization shrinkage, We synthesized a kind of spiro orthocarbonate expanding monomer, 3,9-Diethyl-3,9-bis(allyloxymethyl)- 1,5,7,11-tetraoxastetraoxaspiro[5.5]undecane to copolymerize with epoxy 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate. The modified epoxy was mixed with methyl methacrylate resin Bis-GMA to compose a hybrid resin system. The initiation conditions and component ratio were determined by polymerization shrinkage and other physico-mechanical properties test, and the reactions were comfirmed by spectroscopic evidence. The mechanical and biological properties of hybrid systems were also investigated. The results were as following:1. The epoxy resin was photo-sensitive to the visible light of dental lamp in the presence of photo initiation system: iodonium diphenyl hexafluorophosphate, camphoroquinone and N, N- dimethylaminoethyl methacrylate. The contents of initiation system effected the resin curing degree in a certain extent and proved be appropriate in ratio of 5 % to fully curing;2. The spectroscopic evidence of NMR and FTIR showed that the copolymerization of epoxy and expanding monomer could occured in visible light at room temperature. The volumetric shrinkage decreased with the increase of DB-TOSU. 60 % DB-TOSU led to least shrinkage of 2.26 %;3. DSC curves showed that hybrid resin system was composed of expanding monomer modified epoxy and methyl methacrylate Bis-GMA in two different curing mechanisms, which were compatible with each other. Bis-GMA was cured in higher degree due to dual initiation, but the resin system was weakened in flexural strength when reduced in shrinkage in over addition of modified epoxy. Bis-GMA/(ECHM-ECHC+DB-TOSU) was proper at a ratio of 70/30, whose flexural strength is 80.03 MPa and shrinkage is 4.1 %;4. Results in biocompatibility demonstrated that the experimental hybrid resin system reacted negatively in mucous membrane irritation test,acute hemolysis test and short-term systemic toxicity, while positive in cytotoxity test atâ…¡degree with statistical differences with negative control, which suggested that the soluble minor molecules residua leaking from net structure of cured resin caused the negative effect on the cellular metabolism and needed further curing reaction;5. The evaluation of polymeric shrinkage,sorption and solution,mechanical properties suggested the experimental hybrid resin system had reduced polymerization shrinkage and stress, but less reactivity of the expanding monomer led to the deficiency of system as well as physico-mechanical properties loss, which limited the addition. When Bis-GMA/ (ECHM-ECHC+DB-TOSU) was at ratio of 70/30, the hybrid system got reduced volumetric shrinkage and stress with physico-mechanical properties in acceptable range.
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