Synthesis of Al2O3-0.5B2O3-SiO2 fillers by sol-gel method for dental resin composites

The purpose of this study was to evaluate the formation of aluminoborosilicate obtained by the sol-gel method, characterize the microstructure, morphology and texture of the synthesized glass powder, and use them as filler in dental resin composites. The sol-gel method was employed for the synthesis of glass particles with composition Al2O3-0.5B2O3-SiO2, using the solutions of aluminum acetate, boric acid, nitric acid and TEOS alcoholic solution. Glass particles were obtained by calcination of xerogel at 400°C, 500°C, 600°C and 700°C, and were characterized by Differential Thermal Analysis (DTA), Thermogravimetric analysis (TGA), X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) Surface Area Analysis, field emission gun scanning electron microscope (FEG-SEM), particle sizing analyzer by laser diffraction, Fourier transform infrared spectroscopy analysis (FTIR-AT). The glass particles calcinated at 500 and 600°C were silanated using a concentration of 10% (wt%) of 3-methacryloxypropyl-trimethoxysilane (MPTS) in acetone medium. The dental resin composite comprises of a mixture of bis-phenol-A bis-(2-hydroxypropyl)-methacrylate (Bis-GMA), tri(ethylene-glycol)-dimethacrylate (TEGDMA), bis-phenol-A ethoxylate-dimethacrylate (BisEMA), urethane-dimethacrylate (UDMA), 2-(Dimethylamino)-ethyl-methacrylate (DMAEMA) and camphorquinone with the silanated glass particles. DTA analysis reveals a glass transition temperature (Tg) ranging from 735 to 820°C. BET analysis showed the surface area of the glass powders between 6.4 and 20.6m2/g, and no porosity was detected by BET measurements. XRD analyses reveal the formation of amorphous glass systems for powders calcined at 400°C, 500°C, 600°C and 700°C. SEM-FEG observation revealed irregular morphology of the agglomerates, no surface porosity and particle size ranging between 56 to 740nm. Particle size increases slightly with increase of the calcination temperature. XRD and DTA analyses reveal that the synthesized powders are amorphous independently of the calcination temperature. The position and intensity of the bands in the FTIR spectra were influenced by the temperature of calcination, showing structural changes of the glass with the heating, mainly the hydroxyl groups that are removed from the calcination at 600°C. The silanization with MPTS reduces the surface area indicating that the silane promotes the formation of strong agglomerates, since even using a high-energy planetary ball mill after silanization, the powders were not properly desaglomerated, increasing the surface area of the powders after silanization. The flexural strength (FS) and compressive strength (CS) for the dental composite employing the synthesized Al2O3-0.5B2O3-SiO2 silanated glass particles are compatible with commercial dental composites (Charisma, Heraeus Kulzer, Germany; and Llis, FGM, Brazil).