Ruili Wang

Polymer grafted hydroxyapatite whisker as a filler for dental composite resin with enhanced physical and mechanical properties

The objective of this study was to investigate the effect of surface graft polymerization of hydroxyapatite whisker (HW) on physical and mechanical properties of dental composite resin. Poly bisphenol A glycidyl methacrylate (Poly(Bis-GMA)) was grafted onto silanized hydroxyapatite whisker (SHW) via solution polymerization and the amount of the Poly(Bis-GMA) on the surface was effectively controlled by polymerization time. The obtained poly(Bis-GMA) grafted hydroxyapatite whisker (PGHW) with different polymer contents was filled into a resin matrix respectively, meanwhile the composites with HW and with SHW served as controls. Monomer conversion was characterized by Fourier transform infrared spectroscopy (FTIR) and volume shrinkage of the composite resin was measured with a density tester. Mechanical properties were tested with a universal testing machine. The results indicated that the composite filled with PGHW-1h (graft ratio of poly(Bis-GMA): 8.5 wt.%) showed lower shrinkage and better mechanical properties, improving flexural strength by 6.5% and 11.9% compared with SHW filled composite and HW filled composite, respectively. However, PGHW with higher graft ratios aggregated seriously and formed defects in the composite, leading to deterioration of mechanical properties. It was revealed that the poly(Bis-GMA) on the surface of PGHW acted as a functional transition layer and enhanced interfacial compatibility and interaction between whisker and resin matrix, which facilitated the dispersion of PGHW in the composite and decreased the composite shrinkage. Thus, the graft polymerization of Bis-GMA on the surface of filler might be a promising modification method for the fabrication of dental materials.

Investigation on the physical-mechanical properties of dental resin composites reinforced with novel bimodal silica nanostructures.

The aim of this study was to investigate the influence of bimodal silica nanostructures comprising of SiO2 nanoparticles (SiO2 NPs, ~70 nm) and SiO2 nanoclusters (SiO2 NCs, 0.07-2.70 μm) on physical-mechanical properties of resin-based composites (RBCs). SiO2 NPs and SiO2 NCs were prepared with the Stöber method and the coupling reaction, respectively, then silanized and employed as fillers to construct RBCs using a mixture of bisphenol A glycerolate dimethacrylate (Bis-GMA) and tri(ethylene glycol) dimethacrylate (TEGDMA) as the organic matrix. Results showed that the properties of RBCs were influenced by the filler ratios of bimodal silica nanostructures, and the appropriate amount of SiO2 NPs could effectively increase the activating light efficiency and filler packing density of RBCs. Among all experimental RBCs, RBC 50-20 (SiO2 NPs:SiO2 NCs=50:20, wt/wt) presented the highest degree of conversion (71.6±1.1%), the lowest polymerization shrinkage (2.6±0.1%), and the enhanced flexural strength (104.8±4.4 MPa), flexural modulus (6.2±0.3 GPa), and compressive strength (205.8±14.3 MPa), which were improved by 44%, 19%, 28%, 48%, and 42% in comparison with those of RBC 0-60 (SiO2 NPs:SiO2 NCs=0:60, wt/wt), respectively. Besides, in vitro cytotoxicity evaluation of RBC 50-20 indicated its acceptable cytotoxicity. Although the best performance was achieved by commercial Z350 XT, the introduction of bimodal silica nanostructures might provide the enhanced physical-mechanical properties of RBCs, compared with those of RBC 0-60 reinforced with unimodal SiO2 NCs.

Wear behavior of light-cured resin composites with bimodal silica nanostructures as fillers.

To enhance wear behavior of resin composites, bimodal silica nanostructures including silica nanoparticles and silica nanoclusters were prepared and proposed as fillers. The silica nanoclusters, a combination of individually dispersed silica nanoparticles and their agglomerations, with size distribution of 0.07-2.70 μm, were fabricated by the coupling reaction between amino and epoxy functionalized silica nanoparticles, which were obtained by the surface modification of silica nanoparticles (~70 nm) using 3-aminopropyl triethoxysilane (APTES) and 3-glycidoxypropyl trimethoxysilane (GPS) as coupling agents, respectively. Silica nanoparticles and nanoclusters were then silanized with 3-methacryloxypropyl trimethoxysilane (γ-MPS) to prepare composites by mixing with bisphenol A glycerolate dimethacrylate (Bis-GMA) and tri (ethylene glycol) dimethacrylate (TEGDMA). Experimental composites with various filler compositions were prepared and their wear behaviors were assessed in this work. The results suggested that composites with increasing addition of silica nanoparticles in co-fillers possessed lower wear volume and smoother worn surface. Particularly, the composite 53:17 with the optimum weight ratio of silica nanoparticles and silica nanoclusters presented the excellent wear behavior with respect to that of the commercial Esthet-X, although the smallest wear volume was achieved by Z350 XT. The introduction of bimodal silica nanostructures as fillers might provide a new sight for the design of resin composites with significantly improved wear resistance.

Effect of hydroxyapatite whisker surface graft polymerization on water sorption, solubility and bioactivity of the dental resin composite

The aim of this study was to investigate the effect of poly bisphenol A glycidyl methacrylate (poly(Bis-GMA)) grafted hydroxyapatite whisker (PGHW) on water sorption, solubility and bioactivity of the dental resin composite. PGHW with different graft ratios was synthesized, by controlling grafting time, and filled into a dental resin matrix respectively. Fracture surface of the resin composites showed that PGHW-matrix interfacial compatibility and bonding were enhanced, and lower amounts of poly(Bis-GMA) on PGHW-1h (graft ratio: 8.5 wt.%) could facilitate the dispersion of PGHW-1 h in the composite. The PGHW-1h filled resin composite absorbed the lowest amount of water (27.16 μg/mm(3), 7 d), whereas the untreated hydroxyapatite whisker (HW) filled resin composite absorbed the highest. PGHW with higher graft ratios induced the decrease of the monomer conversion in the resulting composite, therefore, the PGHW-18 h (graft ratio: 32.8 wt.%) filled resin composite had the highest solubility. In vitro bioactivity of the studied resin composites in simulated body fluid (SBF) showed that a dense and continuous apatite layer was formed on the surface of the resin composite, and the surface graft polymerization on the whisker did not significantly affect the apatite forming ability of the resin composite. It was revealed that graft polymerization of an appropriate amount of Bis-GMA onto HW could be an effective method to improve the interfacial properties and stability in water of the dental resin composite without compromising the bioactivity.

A Facile Approach to Fabrication of Novel Magnetic Hydrogels Crosslinked by Multi-Functional Pomegranate-Like Nanospheres

A facile approach was explored to fabricate a novel magnetic hydrogel using pomegranate-like functional magnetic nanospheres (FMNs) as photoactive crosslinker and polyacrylamide as polymer matrix by photoinitiated free radical polymerization. These novel pomegranate-like FMNs were prepared by embedding Fe3O4 nanoparticles into polystyrene by miniemulsion polymerization. The effect of FMN concentration, acrylamide monomer molar concentration, polymerization time on the magnetic properties, morphology, swelling behaviour, and dynamic mechanical properties of magnetic hydrogels were systematically investigated. Our synthetic route expands the application of these materials in the fields of smart magnetic switches, targeted drug release, biomimetic sensors, and chemical devices.

Effect of Filler Ratio on Properties of Nanohydroxyapatite/SiO2 Based Bioactive Dental Resin Composites

Hydroxyapatite (HAP), as an essential component of bone and tooth, is one of the promising bioactive materials. The purpose of this study was to investigate the effects of incorporation of nanoHAP and SiO2 particles on the properties of bioactive dental composite. Silanized HAP and SiO2 were mixed with BisGMA/TEGDMA (1/1 wt/wt) monomers at various HAP/SiO2 mass ratios of 0:7 (no HAP), 5.25/1.75, 3.5/3.5, 1.75/5.25, 7:0 (no SiO2) to yield a series of pastes all containing 70 wt% filler loading. The results showed that flexural strength, elastic modulus and compressive strength gradually decreased with increasing amount of HAP particles, as well as curing depth and polymerization shrinkage, which resulted from the nature of HAP particle material. Water sorption and solubility in water increased slightly with addition of HAP particles. Degree of conversion test could support results above well. Remineralization test in SBF demonstrated dental composite with HAP particles had a good apatite-forming ability. Consequently, dental composite filled with lower amount of nanoHAP (HAP/SiO2 around 0.25) particles would possess better comprehensive performances.

Synthesis and Characteristics of Dental Composites with Novel Bis-GMA Derivate as a Resin Base

2,2-bis [4-(2-hydroxy-3-methacryloyloxypropoxy) pheny propane (Bis-GMA) and triethylene glycol dimethacrylate (TEGDMA) have been commonly used as a viscous monomer and a reactive diluent in the organic phase of dental restorative composites, respectively. The purpose of addition of TEGDMA is mainly to decrease the high viscosity of Bis-GMA caused by hydrogen bonding between hydroxyl groups. However, some adverse effects will accompany with increased amounts of the TEGDMA, such as higher values of polymerization shrinkage, which is not undesirable for the clinical application. Therefore, substituting hydroxyl groups of Bis-GMA might be an appropriate and effective way to reduce the amount of diluents and weaken the accompanied adverse effects. This work focuses on the synthesis of a novel Bis-GMA derivate, substituting acetyl groups for hydroxyl groups in Bis-GMA. The viscosity of Bis-GMA characterized with rotational rheometer was significantly decreased from 820 Pa.s to 11 Pa.s by substitution of acetyl group, leading to the low amount of TEGDMA in resin matrix. Differential Scanning Calorimeter (DSC) was used for investigating the reaction kinetics of this novel monomer with different mass ratios of TEGDMA. The results suggested that the maximum conversion of the Ac-Bis-GMA can reach 88% while the corresponding value for Bis-GMA is 75%. Dental composites were prepared from 2,2-bis [4-(2-acetyl-3-methacryloyloxypropoxy) pheny propane (Ac-Bis-GMA) or Bis-GMA resin mixtures with TEGDMA filled with 70 wt% silica co-fillers. The results presented that dental composites prepared from new resin matrixes exhibited adequate mechanical properties.

Dental Resin Composites with Enhanced Properties Bycommercial Silica Particles as Fillers

To explore the preparation of novel dental resin composites with enhanced properties, two commercial silica particles with sizes of around 1μm and 40 nm were chosen as inorganic fillers, and firstly surface functionalized by 3-methacryloxypropyltrimethoxysilane (γ-MPS) to incorporate cross-linkable vinyl groups onto the surface of fillers. Then the modified fillers were blended with organic monomers, bisphenolAdiglycidyldimethacrylate (Bis-GMA) and triethylene glycol dimethacrylate (TEGDMA), to fabricate the resin compositeswith a three-roll mixer.Resin composites with various weight percentage of fillers and component ratio of microparticle and nanoparticle were prepared. Surface functionalization of silica particles was characterized by fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA), and mechanical properties degree of conversion, and depth of cure of the resultant resin composites were investigated byuniversal testing machineand FTIR. The results indicated that surface modification of silica particles was successful and the surface organic contents were 3.29% and 4.34%, respectively. Among the studied resin composites, the resin composite with 75 wt.% silica particles (59 wt.% microparticles and 16 wt.% nanoparticles) presented the highest value of depth of cure (5.52 ± 0.07 mm), and optimum mechanical properties such as flexural strength (149.8 ± 3.3 MPa), flexural modulus (13.8 ± 0.06 GPa), compressive strength (340.6 ± 8.3 MPa) and Vicker’smicrohardness (78.26 ± 2.45 HV). The study of dental resin composites fabricated from commercial silica particles with excellent properties might provide a new sight for realizing the preparation of this kind of dental resin composites in an industrial scale.