Effects of silane-modified fillers on properties of dental composite resin

Magnetic-Responsive Janus Nanosheets with Catalytic Properties

In this article, we describe a method to fabricate magnetic-responsive Janus nanosheets with catalytic properties via the surface protection method. Fe₃O₄ nanoparticles and PW₁₂O₄₀^3--based ionic liquid are located on the two opposite sides of the Janus nanosheets, respectively. The Janus nanosheets are characterized by Fourier transform infrared, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and ζ-potential analyses. They are used as recyclable catalysts to the esterification reaction of methanol and oleic acid for their magnetic-responsive and catalytic properties. The esterification ratio is up to 80% and there is nearly no change when Fe₃O₄ nanoparticles/PW₁₂O₄₀^3--based ionic liquid composite nanosheets were recycled four times.

Reinforcement of dental resin composite via zirconium hydroxide coating and phosphate ester monomer conditioning of nano-zirconia fillers

OBJECTIVES

The present study aimed to evaluate effects of conditioning with the phosphate ester monomer 10-methacryloyloxydecyl dihydrogen phosphate (MDP), with and without precoating with zirconium hydroxide for nano-size zirconia fillers, on mechanical properties of dental resin composites.

MATERIALS AND METHODS

Nano-zirconia fillers coated with or without zirconium hydroxide [Zr(OH)₄] were prepared. Transmission electron microscopy (TEM), Fourier infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) were used to observe the coating and to characterize Zr(OH)₄ coating on the zirconia filler surface. Zirconia fillers with or without Zr(OH)₄ coating were conditioned with MDP and were subsequently used to prepare experimental resin composites. XPS was used to analyze the Zr-O-P bonds on the filler surface after MDP conditioning. Moreover, three-point bending strength and elastic modulus of prepared resin composites were measured, and Weibull analysis was performed. Resin composites without addition of zirconia fillers and the ones with addition of untreated or silane conditioned-zirconia fillers were set as controls. Cell counting kit (CCK)-8 was used to test cell cytotoxicity of these zirconia fillers-containing experimental resin composites.

RESULTS

Nano-zirconia fillers were coated with Zr(OH)₄ through chemical deposition. FTIR and XPS analysis confirmed the increase of hydroxyl groups after Zr(OH)₄ coating. XPS detected the highest contents of Zr-O-P bonds on MDP-conditioned zirconia fillers with pre-Zr(OH)₄ coating, followed by MDP-conditioned zirconia fillers. Resin composite with added MDP-conditioned zirconia fillers with and without Zr(OH)₄ coating exhibited greater three-point bending strength, elastic modulus values, and Weibull moduli. According to the cytotoxicity classification, resin composites containing experimental zirconia fillers were considered to have no significant cell cytotoxicity.

CONCLUSION

Nano-zirconia fillers conditioned with MDP, with or without precoating with Zr(OH)₄, improve the mechanical properties of resin composites, and are potentially safe for clinical use.

Influence of Acid, Ethanol, and Anthocyanin Pigment on the Optical and Mechanical Properties of a Nanohybrid Dental Composite Resin

This study investigated the influences of acidity, ethanol, and pigment on the optical properties, microhardness, and surface roughness (R_a) of a nanohybrid dental composite resin. A total of 108 disc-shaped specimens were fabricated using a nanohybrid dental composite and allocated into 36 different storage solutions according to the levels of pH (2.0, 3.0, 4.0, and 5.5), ethanol (0%, 20%, and 40%), and anthocyanin pigment (0%, 2.5%, and 12.5%). Measurements of the colorimetric parameter and the amount of color change (ΔE), translucency parameter (TP), microhardness, and surface roughness (R_a) were performed at 24 h (baseline), 1-, 2-, 3-, and 4-weeks. Repeated measures of analysis of variance (ANOVA) with a Tukey honestly significant difference test and Pearson correlation analysis were carried out (α = 0.05). Pigment of 12.5% or 40% ethanol significantly increased the ΔE (P < 0.001, P = 0.048, respectively). Pigment of 2.5% or 12.5% significantly decreased the TP (P = 0.001, P < 0.001, respectively). Microhardness of composite resin stored in pH 2.0, 3.0, 4.0 solution was lower than that for pH 5.5 (P < 0.001). Pigment, ethanol, and pH did not influence the R_a. TP change and ΔE, and R_a and ΔE had a significant positive correlation (P < 0.05). In conclusion, pigment and ethanol levels influenced the optical properties and acidity affected the microhardness of composite resin.

Physicochemical and Microbiological Assessment of an Experimental Composite Doped with Triclosan-Loaded Halloysite Nanotubes

This study is aimed at evaluating the effects of triclosan-encapsulated halloysite nanotubes (HNT/TCN) on the physicochemical and microbiological properties of an experimental dental composite. A resin composite doped with HNT/TCN (8% w/w), a control resin composite without nanotubes (HNT/TCN-0%) and a commercial nanofilled resin (CN) were assessed for degree of conversion (DC), flexural strength (FS), flexural modulus (FM), polymerization stress (PS), dynamic thermomechanical (DMA) and thermogravimetric analysis (TGA). The antibacterial properties (M) were also evaluated using a 5-day biofilm assay (CFU/mL). Data was submitted to one-way ANOVA and Tukey tests. There was no significant statistical difference in DC, FM and RU between the tested composites (p > 0.05). The FS and CN values attained with the HNT/TCN composite were higher (p < 0.05) than those obtained with the HNT/TCN-0%. The DMA analysis showed significant differences in the TAN δ (p = 0.006) and Tg (p = 0) between the groups. TGA curves showed significant differences between the groups in terms of degradation (p = 0.046) and weight loss (p = 0.317). The addition of HNT/TCN induced higher PS, although no significant antimicrobial effect was observed (p = 0.977) between the groups for CFUs and (p = 0.557) dry weight. The incorporation of HNT/TCN showed improvements in physicochemical and mechanical properties of resin composites. Such material may represent an alternative choice for therapeutic restorative treatments, although no significance was found in terms of antibacterial properties. However, it is possible that current antibacterial tests, as the one used in this laboratory study, may not be totally appropriate for the evaluation of resin composites, unless accompanied with aging protocols (e.g., thermocycling and load cycling) that allow the release of therapeutic agents incorporated in such materials.

Effect of thiourethane filler surface functionalization on stress, conversion and mechanical properties of restorative dental composites

OBJECTIVES

This study evaluated the efficacy of a thiourethane(TU)-modified silane agent in improving properties in filled composites.

METHODS

The TU-silane agent was synthesized by combining 1,3-bis(1-isocyanato-1-methylethyl)benzene and 3-(triethoxysilyl)propyl isocyanate with trimethylol-tris-3-mercaptopropionate (TMP), at 1:2 isocyanate:thiol, leaving pendant thiol and alkoxy silane groups. Barium glass fillers (1μm average particle size) were functionalized with 5wt% TU-silane in an acidic ethanol solution. Commercially available 3-(trimethoxysilyl)propyl methacrylate (MA-silane) and (3-mercaptopropyl)trimethoxysilane (SH-silane), as well as no silane treatment (NO-silane), were used as controls. Composites were made with BisGMA-UDMA-TEGDMA (5:3:2), camphorquinone/ethyl-4-dimethylaminobenzoate (0.2/0.8wt%) and di-tert-butyl hydroxytoluene (0.3wt%) and 70wt% silanated inorganic fillers. Polymerization stress (PS) was measured using a cantilever beam apparatus (Bioman). Methacrylate conversion (DC) and rate of polymerization (RP) during photoactivation (800mW/cm²) were followed in real-time with near-IR. Flexural strength/modulus (FS/FM) were evaluated in three-point bending with 2×2×25 mm.

STATISTICAL ANALYSIS

2-way ANOVA/Tukey's test (α=5%).

RESULTS

DC, Rp_max and E were similar for all groups tested. FS was similar for the TU- and MA-silane, which were statistically higher than the untreated and SH-silane groups. Stress reductions in relation to the MA-silane were observed for all groups, but statistically more markedly for the TU-silane material. This is likely due to stress relaxation and/or toughening provided at the filler interface by the oligomeric TU structure.

SIGNIFICANCE

TU-silane oligomers favorably modified conventional dimethacrylate networks with minimal disruption to existing curing chemistry, in filled composites. For the same conversion values, stress reductions of up to 50% were observed, without compromise to mechanical properties or handling characteristics.

Chemical and Mechanical Properties of Experimental Dental Composites as a Function of Formulation and Postcuring Thermal Treatment

This study evaluated the influence of formulation and thermal treatment on the degree of conversion, fracture toughness, flexural strength, and elastic modulus of experimental composites. Six composites were analyzed at BisGMA : TEGDMA molar ratios of 1 : 1 and 7 : 3 with filler at 30, 50, and 70 wt%. The degree of conversion was analyzed by Fourier transform infrared spectroscopy, fracture toughness was measured using the single-edge notched beam, and flexural strength and elastic modulus were measured with the 3-point bend test. For all tests, one-half of the specimens received thermal treatment at 170°C for 10 min. Data were analyzed by the Kruskal-Wallis or ANOVA/Tukey's test (α = 5%). The 1 : 1 BisGMA : TEGDMA ratio showed higher properties than the 7 : 3 ratio. Although the material with 70% filler had a conversion lower than the one with 50%, it showed higher mechanical properties. The thermal treatment improved all properties in all materials. Therefore, the use of an equimolar ratio of BisGMA : TEGDMA can be paired with 70 wt% filler to design dental composites that possess increased advantageous physical and chemical properties. Furthermore, the simple and low-cost method of thermal treatment proposed for use in clinical dentistry has been shown to effectively improve the properties of all evaluated materials.