Computational Studies Of The Mechanical Properties Of Silica/Dental Restorative Resin Composites

In recent years,dental restorative resin materials have a long service life and convenient clinical operation.By changing the type and content of dental restoration resin matrix,the comprehensive properties can be improved to meet different needs.However,dental restorative resin as dental defect filling material has some disadvantages,such as low wear resistance and insufficient toughness.Therefore,it is necessary to add inorganic fillers to improve the mechanical properties of resin materials.It is worth noting that nano inorganic fillers are prone to aggregation and uneven dispersion in the addition process,which can not give full play to their excellent physical and mechanical properties.Therefore,nano inorganic fillers need to be modified.At present,the research on the properties of dental restorative resin materials is mostly through experimental measurement and clinical use feedback.It is difficult to explain the change law of material properties from intermolecular force and microstructure.Computer simulation technology can predict the structure of materials by constructing models,explain the mechanism of material performance enhancement from a microscopic point of view,and supplement the deficiency of experiments.Therefore,we explore the effects of different content of resin matrix,Si O₂nanoparticles and polymer brush grafting density on the mechanical properties of dental repair resin composites,and to reveal its reinforcement from the micro scale,To provide theoretical basis and support for the experiment of strengthening and toughening dental resin composites.In order to explore the effect of resin matrix content on the mechanical properties of dental restoration resin materials,the models of UDMA/TEGDMA pure polymer resin system was constructed in this paper.Through molecular dynamics simulation,it is found that the free volume space of UDMA/TEGDMA polymeric resin system changes little with the increase of TEGDMA content in resin matrix.The hydrogen bond interaction decreased with the increase of TEGDMA content,that is,the intermolecular force decreased and the mechanical properties decreased.In order to explore the enhancement effect of nano inorganic filler on the mechanical properties of dental restoration resin materials,Si O₂/UDMA/TEGDMA composite resin system model was constructed in this paper.Compared with pure polymeric resin（E=3.54 GPa,G=1.35 GPa）,when the content of Si O₂ nanoparticles is 11 wt%,the elastic modulus and shear modulus of the composite resin are increased by 14.4%and 14.1%.This is because the addition of Si O₂ nanoparticles reduces the free volume fraction of the composite resin system,the"effective"free space of molecular chain movement decreases,the compactness of the dental restorative resin system gradually increases,and there are hydroxyl groups in the composite resin system,the number of hydrogen bonds formed between resin matrix and filler increases,the binding ability between molecules increases.Compared with the micromechanical model,it is found that it shows high consistency with Counto model,indicating that after the addition of nanoparticles,the rigidity of the composite resin system increases,and there is a strong interaction between the resin matrix and Si O₂ nanoparticles.We suspect that the properties of dental resin composites will change due to the surface properties of nanoparticles.We grafted epoxy oligomer（Epoxy Oligomers,shortened to EO）on the surface of Si O₂ nanoparticles,and the elastic modulus of dental restorative resin materials was studied by changing the chain length of epoxy oligomer.The results show that the intermolecular hydrogen bonding and binding energy can be significantly improved with the increase of grafting density.At the same grafting density,the longer the chain of epoxy oligomer,the stronger the hydrogen bonding and intermolecular binding ability.The radius of gyration of resin polymer chain does not increase or decrease linearly,the radius of gyration of resin polymer chain does not increase or decrease linearly,but decreases first and then increases.This is because the polymer chain shrinks after the addition of Si O₂-EO.With the build up of grafting density,the radius of gyration gradually improve However,the more the number of repeating groups,the smaller the radius of gyration of polymer chain,This is because the more the number of repeating groups and the longer the oligomer chain,the larger the occupied volume of Si O₂-EO filler in the model,and finally the movable"effective"free volume of polymer chain is reduced.Therefore,the extension of polymer chain is more difficult,so the radius of gyration is smaller.The mechanical properties of the composites are significantly enhanced with the increase of grafting density.At the same grafting density,the longer the chain of epoxy oligomer,the better the mechanical properties.The reason is that the structure of epoxy oligomer contains benzene ring and hydroxyl group.When the grafting density is higher and there are more repeating groups of oligomer,the rigidity of the system increases,the number of hydrogen bonds increases and the intermolecular force increases,Thus,the mechanical properties of the composites are improved.To sum up,this paper carried out the calculation and Simulation Research on the mechanical properties of dental restoration resin composites by molecular dynamics simulation,explored the mechanical properties of UDMA/TEGDMA polymeric resin system,Si O₂/UDMA/TEGDMA composite resin system and Si O₂-EO/UDMA/TEGDMA composite resin system respectively,and revealed its reinforcement effect from the microstructure of the material.