| Dental caries is one of the most common oral diseases.It is the primary cause of tooth pain and loss.Without proper care,caries will progress until the tooth is destroyed.In the treatment of dental caries,high-quality organic-inorganic resin composite restoration materials are of great significance.The resin composite is composed of organic resin monomers and inorganic fillers.The type,particle size,structure,and dispersibility of inorganic fillers have significant effects on the performances of resin composites.The purpose of this paper is to design and construct high-performance nano-micro-structured fillers for dental restorations.Firstly,in view of the structural and functional requirements of dental inorganic fillers,the high-gravity technology was presented to prepare highly stable monodisperse nanodispersions.Then,the atomization molding"polymerization"technology was applied to efficiently build multifunctional nanoparticle clusters.Furthermore,these nanoparticles or/and nanoparticle clusters were well dispersed in dental polymer matrices,thereby realizing the preparation of high-performance dental resin composites.This project mainly focuses on the controllable preparation mechanism of monodisperse nanoparticles,and the interaction mechanism of nanoparticles and“polymerization”controlling rules in the atomization process,revealing the structure-function relationships of the preparation process,shape and structure,and application property to obtain multifunctional fillers and resin composites with great comprehensive performance.The main content and innovations of the thesis are as follows:1.Monodisperse SiO2 nanodispersions were prepared by a high-gravity sol-gel method.The influence of the rotating speed of rotating packed bed and reactant concentration on the morphology and particle size of products were explored.The results show that the increase of rotating speed can cause a decrease in particle size,but a high rotating speed may result in an irregularity of the products.In addition,as the concentration of NH3·H2O increases,the particle size of the product continues to increase.The sizes of SiO2 were controlled in the range of 20-330 nm.Compared to the stirred tank reactor,the reaction time of the high gravity method was shortened by 1/3,the particle size of the product was reduced by 1/2,and the size distribution was narrower.The freeze-drying technology was used to obtain SiO2 nanopowders as fillers to prepare resin composites.The results show that with the increase of filler loading from 40%to 70%,the flexural strength,flexural modulus,compressive strength,and hardness of composites increased by 43%,111%,29%,and 219%,respectively.As the size of nanoparticles increased,the mechanical properties of resin composites first increased and then decreased,reaching the maximum value when the size was 80 nm.Compared with the commercially available SiO2 nanoparticles,the filling amount of as-prepared monodisperse SiO2 was increased by nearly 30%.Meanwhile,the dispersibility of monodisperse nanoparticles in the resin composites was better,resulting in better mechanical properties.2.Based on the SiO2 nanodispersion,spray drying technology was further used to continuously and efficiently construct micron-scale SiO2 nanoparticle clusters.The effects of spray drying parameters and raw material conditions on the morphology and particle size of clusters were explored.The results show that the SiO2 clusters with the particle size of 1-3μm and regular morphology can be obtained when the inlet temperature,compressed gas flow rate,and solid content of SiO2 nanodispersion were 100°C,480 L/h,and 3 wt.%,respectively.The nanoparticle clusters with a relatively dense structure can be constructed by the SiO2 nanoparticles with an initial particle size of 20-60 nm.The composites prepared by filling SiO2 nanoparticle clusters with a mass fraction of 70 wt.%and an initial particle size of 60 nm have better filling performances.At the same filling amount,the filling performances of nanoparticle clusters were significantly better than that of the initial nanoparticles and micro-particles of similar size,demonstrating outstanding nano-micro structural effects.In addition,the discrete element method was applied to explore the strengthening mechanism of SiO2 nanoparticle clusters,showing that the ability of deformation and gradual breaking of SiO2 nanoparticle clusters helps the mechanical enhancement of dental resin composites.3.To further improve the filling properties of SiO2 nanoparticle clusters,a heat treatment process was used to enhance their structural stability.The influences of heat treatment temperature on the structure and filling performance of clusters were explored.Under the same filling amount of 70wt.%,the flexural strength,flexural modulus,and hardness of composites filling the heat-treated clusters（500°C）were significantly improved compared to those of the unheated clusters,but the compressive strength was reduced.To solve this problem,the monodisperse SiO2 nanoparticles or unheated SiO2nanoparticle clusters were as co-fillers of heat-treated SiO2 nanoparticle clusters.The results show that under the same filling amount,the strengthening effect of SiO2 nanoparticle clusters was better than that of nanoparticles.The composites filled with 60 wt.%heat-treated SiO2 nanoparticle clusters and 10 wt.%untreated SiO2 nanoparticle clusters had significantly improved in compressive strength,and the flexural strength,flexural modulus,and hardness of these composites were significantly higher（14%,23%,and 48%respectively）than composites filled with untreated SiO2 clusters.4.To impart antibacterial properties to the resin composites,SiO2-Zn O composite nanoparticle clusters（CNCs）were further constructed to enable the composites antibacterial activity while maintaining the mechanical properties and aesthetics of resin composites.The influence of the addition of nano-Zn O on the morphology and particle size of CNCs and the influence of the content of Zn O on the properties of composites were studied.The results show that the introduction of Zn O nanoparticles did not destroy the shape and compact structure of nanoparticle clusters.Compared to the resin composites filled with SiO2 nanoparticle clusters,the mechanical properties of resin composites filled with CNCs were further improved.The antibacterial activity of resin composites increases with the rise of Zn O content.The antibacterial rate of resin filled with 70 wt.%Si66Zn4（CNCs composed of 66/70 nano-SiO2 and 4/70nano-Zn O）can reach more than 99.9%.5.Different nanoparticles were aggregated during the mixing process due to opposite Zeta potential before they were spray-dried through the traditional two-fluid nozzle,which may adversely affect the CNC structure.To solve this problem,the three-fluid spray drying method was used to construct high-performance multifunctional CNC fillers.For the SiO2-Zr O2 binary composite system,despite the introduction of Zr O2 nanoparticles,the resin composites filled with CNCs constructed by the three-fluid nozzles kept good mechanical properties,while filling performances of the CNCs constructed by the two-fluid nozzles were significantly decreased.In addition,the mechanical properties and radio-opaque ability of resin composites filled with SiO2-Zr O2 CNCs were significantly improved by the heat treatment process of CNCs.The radio-opacity of composites can meet the ISO standard when the Zr O2 content reaches more than 10 wt.%.More importantly,this method can also be applied to ternary or quaternary composite systems.For example,the resin composites filled with SiO2-Zr O2-Zn O CNCs（the mass ratio of 56/10/4）had excellent antibacterial properties（antibacterial rate>99.9%）while maintaining good mechanical properties and radio-opaque capability. |
