Fengwei Liu

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.

Novel bionic dental resin composite reinforced by hydroxyapatite whisker

Abstract Hydroxyapatite whisker (HW) was synthesised and used as a bioactive filler to reinforce dental resin composite. The effect of HW mass fraction on physical and mechanical properties of the composite was investigated by universal testing machine, microhardness tester and field emission scanning electron microscope (FE-SEM). HW had a superior reinforcing efficacy. Flexural modulus and Vickers microhardness of the resin composite were continuously improved with the increase of whisker fraction. Impregnation of 20 wt-% silanised HW into the resin dramatically improved flexural strength and compressive strength by 33·4 and 11·3% respectively. However, higher whisker fraction would not further enhance the strength of the composite, which might result from poor whisker dispersion. At higher filler loading, whisker tended to form agglomerations which were similar to the microstructure of enamel. It was revealed that HW could be a promising filler to fabricate bionic dental restoration with reliability.

Design and characterisation of dental resin restorative composites with Ac-Bis-GMA and bimodal silica nanostructures

Abstract To solve the high viscosity of bisphenol A glycerolate dimethacrylate (Bis-GMA), its derivate Ac-Bis-GMA substituting acetyl groups for hydroxyl groups was synthesised by the esterification reaction and mixed with tri(ethylene glycol) dimethacrylate (TEGDMA) as polymer matrix to fabricate dental resin restorative composites. To improve the degree of conversion (DC), polymerization shrinkage (PS) and wear resistance of resin-based composite (RBC) 58–12 filled with commercial microsize and nanosize (M/N) SiO2 particles, bimodal silica nanostructures consisting of SiO2 nanoparticles (NPs) and SiO2 nanoclusters (NCs) were introduced as inorganic fillers. Resin composites with different mass ratios of silanized SiO2 NPs and SiO2 NCs were fabricated under the light polymerisation, and the effect of filler compositions on these two properties, wear resistance (wear volume and worn surface morphology), and cytotoxicity assay of resin composites was investigated in this work. The results suggested that resin composites reinforced with bimodal silica nanostructures at the optimum ratio presented the improved performance, especially for RBC 35–35 (SiO2 NPs:SiO2 NCs = 35:35, wt/wt), which resulted in 16% enhancement in DC and 19% reduction of PS, the smoother and flatter worn surface after 10 000 wear cycles, as well as the excellent cytocompatibility, compared with those of RBC 58–12.This effective and facile way might provide a new sight to develop dental resin restorative composites for clinical application.

Surface modification of quartz fibre and its reinforced bis-GMA/MMA composites for dental post

Abstract A kind of bis-phenol-A-glycidyl dimethacrylate (bis-GMA)/methyl methacrylate (MMA) composite based dental post reinforced by quartz fibres (QFs) was prepared in this paper. Different factors were investigated to observe their influences on the mechanical properties of quartz fibre reinforced composite (QFRC) dental post, including the surface etching, silanisation grafting to QFs and the volume fraction of QFs. 3-methacryloxypropyl trimethoxysilane (γ-MPS) and 3-aminopropyl triethoxysilane (APTES) were used to graft to QFs to enhance compatibility of fibres and resins, and they were grafted to QFs successfully with different grafting ratios, which were confirmed by results of Fourier transform infrared spectroscopy (FTIR), Thermal gravimetric analysis (TGA) and contact angle measurements. The sorption and solubility in artificial saliva (AS) of QFRC post was also studied by soaking in AS for 4 weeks to compare weight changes and mechanical properties. Mechanical testing results suggested that QFRC posts with QFs grafted by APTES presented better properties and the optimal flexural strength and modulus were up to 620·3 MPa and 21·6 GPa respectively, which is outstanding in similar materials and suitable for the clinical application.

Design of resin composites with enhanced physical–mechanical properties

Abstract Novel dental resin composites reinforced with hydroxyapatite (HAP) nanofibres and silica nanoclusters were prepared and the influence of filler compositions on physical–mechanical properties were investigated in this work. HAP nanofibres and silica nanoclusters were fabricated by wet chemical method and the coupling reaction respectively, and then silanised to fabricate resin materials by mixing with dimethacrylate based matrix. The results of XRD pattern, FE-SEM images and FT-TR spectra all confirmed the successful synthesis of HAP nanofibres. Resin composites reinforced with HAP nanofibres and silica nanoclusters as co-fillers showed the reduced polymerisation shrinkage and the enhanced mechanical properties. Among all composites, composite 60∶10 (HAP nanofibres/silica nanoclusters = 60∶10, wt/wt) presented the superior performance, leading to 21% decrease in polymerisation shrinkage, and 13, 55 and 15% enhancement of flexural strength, flexural modulus, and compressive strength respectively, compared with those of composite 0∶60 without HAP nanofibres.