Study On The Light-cured Composite Resin Of Oral Dental Caries Reparation And Dentin Adhesive

Light–cured composite resin has been widely used to repair dental defects, prepare dental caries and other aspects of oral beauty because it is easy for clinical operation, beautiful and practical. Scientists have devoted lots of time and efforts to discover new resins and new fillers aiming to reduce the polymerization shrinkage, water sorption and enhance the mechanical properties of the cured resin composites. Methylacrylate monomers such as Bis-GMA(2,2-bis-[4-(2-hydroxy-3-methacryloyloxypropoxy) phenyl]propane) and UDMA(1,6-bis-(2-methacryloyloxyethoxycarbonylamino) are widely used in this field depending on its excellent performances. Nanoscale fillers also have been introduced into composite resins with the rapid development of nano-technology. The introduction of new resins and fillers have improved the combination property of composite resin, however, problems still exist and have been troubled those people who have applied this technology, such as secondary caries and fracture.The service life of composite resin is mainly depended on the mechanical property of resin matrix and filler, the water absorptivity of composite resin and the properties of dental adhesives. As a result, reducing the polymerization shrinkage and water sorption, enhancing the mechanical properties of the cured resin composites and exploiting perdurable dental adhesive become the research focus of this field.Resins containing epoxy ring-opening orthocarbonate expandable and based on olefin radical transfer mechanism are introduced to overcome the large polymerization shrinkage which exists in methylacrylate composite resin in recent years. However, the low polymerization rate and cure depth have limited their widely application in the oral caries restoration field.In chapter 1, we reviewed the development and classification of composite resin(include monomers and fillers) and dental adhesives. Then, the designing ideas and research contents were presented.In chapter 2, glass flake filler was introduced into composite resin in the aim of reducing the water absorption for its perfect performance in the anti-corrosion coating field. Big size filler(~50 μm) was grinded and extruded into smaller filler(~20 μm) and was etched by HF to make the surface of filler roughening. Then, the rough filler was treated by the silane coupling agent(KH570, C=C bond is grafted onto the filler), making the filler to be easily dispersed into the resin matrix and enhancing the interaction forces between the resin and filler. 9 types of composite resins were prepared depending on the proportion of filler and monomers. The mechanical properties, water absorption, polymerization shrinkage were tested separately. The results showed that with the increase of sheet glass fillers, the mechanical properties of composite resin nearly increased twice. At the same time, the water absorption(the water absorption of 35 day result was reduced to 0.7%, which decreased by 50% compared to the commodity’s 1.5%) and polymerization shrinkage showed a downward trend.In chapter 3, an elastic layer of polyurethane composite is firstly introduced to composite restoration. The elastic layer is applied to the gap between the composite resin and the adhesive layer. The applied elastic layer can eliminate the stress which comes from polymerization shrinkage and the expansion and contraction stress(mainly caused by the different thermal expansion coefficients of the composite resin and dentin) generated by alternating hot and cold in daily life. The results of resin composite restoration tests show that the microleakage depth of samples with elastic layer were about 300 μm while the control group had permeated to the bottom(about 2 mm). The experiment revealed that the elastic layer could satisfy the clinical biosafety requirement just as other products already used and successfully prevent the occurrence of microleakage. By analyzing the results of the experimental group, we believe that the experimental group had a slight leakage after 7 days because of the hydrophilic component in the adhesive absorbing water, then this result leads to the study of the next chapter.In chapter 4, a kind of moisture curable and hydrophobic dental adhesive was prepared. The cytotoxicity of this new adhesive was just as other commercial products already used in clinical. The contact angle of new adhesive was about 96 o while all the commercial products’ contact angle was below 51 o, which proved the new adhesive own better hydrophobic property. The results of microtensile test showed the initial microtensile strength of the new adhesive was similar with the self-etching merchandise adhesive’s bond strength, but after they had been soaked in a thermostatic artificial saliva environment for 30 days, the microtensile strength of commodity adhesive declined sharply(37% at most), on the contrary our new adhesive’s microtensile strength showed an ascending trend(21% at most). The result microleakage test showed the new adhesive could efficiently prevent the occurrence of microleakage. We could also observe the resin tags clearly from the scanning electron microscope(SEM) figure.