Funcionalização e incorporação de partículas inorgânicas em compósitos nanohíbridos experimentais

Abstract

The aim of this study was to coat and to functionalize the surface of zirconia and alumina ceramic nanoparticles, coating them with a layer of silica and to incorporate them into experimental bimodal nanohybrid resin composites and to characterize in vitro physical-mechanical performance. For comparison, nanosilica composite of similar size (Aerosil 150 and OX50) and a commercial nanoparticulated resin (Filtek Z350, 3M Oral Care) were evaluated. Methodology: 1) Functionalization of the nanoparticles using TEOS as a precursor of silica, getting particles that we called AlSi and ZrSi, and subsequent silanization of these nanoparticles. 2) Formulation and incorporation in co-monomeric blends: Bis-GMA, Bis-EMA6, UDMA and TEGDMA, in the ratio 7: 7: 5: 1 (wt/wt) and a photoinitiator system (CQ and EDAB). The filler hybrid system was completed by adding 0,7µm barium borosilicate glass. In total, 4 experimental groups were obtained: ZrSi, AlSi, Aerosil 150 and Aerosil OX50. The ZrSi composite was compared to Aerosil OX50 and AlSi compared to Aerosil 150. 3) Physico-mechanical characterization: viscosity, surface topography analysis by scanning electron microscopy (SEM), the degree of C=C conversion (DC), Knoop hardness, flexural strength and flexural modulus, fracture toughness (KIC), edge chipping resistance (ReA), polymerization depth and optical characteristics: opacity and radiopacity. For flexural strength and KIC, the specimens were evaluated after 24h or aging for 15.000 thermal cycles (5 - 55°C). The data were statistically analyzed using One Way Analysis of Variance (ANOVA) followed by Tukey’s post hoc (α = 0.05). When there was the aging factor, the data were analyzed by two-way ANOVA. The composites containing AlSi and ZrSi had higher apparent viscosity than those containing only silica. In the SEM it was possible to observe the presence of ZrSi and AlSi agglomerates, of varied size and irregular shape, while the silica particles had a more homogeneous distribution. The experimental composites reached higher values of DC> 50%. The polymerization depth for the OX50, AlSi and Aerosil 150 was higher (around 2.8mm) and for the ZrSi less than 2 mm, which correlated with the higher opacity of this material. The composites with nanosilicas showed lower values of hardness, ZrSi presented similar values than the control Z350. For flexural strength, at 24 hours, the highest values were obtained for nanosilica composites, being similar to each other. After aging by thermocycling, AlSi and ZrSi showed no reduction in flexural strength. All groups reached the requirements proposed by the ISO 4049 standard for radiopacity, with the ZrSi composite being the opaquest. For the KIC results, at 24h, the AlSi composite obtained the highest values, while the ZrSi composite were similar to Aerosil 150 and OX50 groups. After aging, all materials reduced the KIC, but the AlSi and ZrSi nanoparticles composites showed a smaller reduction than the others, indicating greater stability of their mechanical properties. The material containing AlSi presented the highest ReA, while the composites containing ZrSi and OX50 presented similar behavior. In conclusion, the silica coating of zirconia and alumina nanoparticles allows effective silanization and incorporation of these in nanohybrid composites. The materials presented promising mechanical properties compared to experimental composites prepared with silica nanoparticles and the commercial nanoparticulate composite, especially considering the greater stability of the flexural strength and fracture toughness. The use of ceramic nanoparticles of a composition different from those currently used in resinous composites can lead to the development of materials with improved properties and fewer clinical flaws related to chips and fractures.