Antonio Shigueaki Takimi

Niobium pentoxide as a novel filler for dental adhesive resin.

OBJECTIVES The purpose of this study was to develop an adhesive resin with incorporation of niobium pentoxide and evaluate its properties. METHODS Niobium pentoxide was characterised by X-ray diffraction, surface area, particle size, micro-Raman, scanning electron microscopy and the effectiveness of silanisation process by Fourier Transform Infrared (FTIR). An experimental adhesive resin was formulated with 0, 5, 10 and 20wt% Nb(2)O(5). The formulated adhesive resins were evaluated based on microhardness, degree of conversion, radiopacity and interface (resin/dentine) characterisation by micro-Raman. RESULTS The particles used in this study presented a monoclinic crystalline phase with typical chemical groups and micrometre mean size. Microhardness and radiopacity increased with higher amounts of Nb(2)O(5), and the particles were able to penetrate into the hybrid layers. CONCLUSIONS Therefore, Nb(2)O(5) may be an alternative for polymer-based biomaterials. CLINICAL SIGNIFICANCE Niobium pentoxide could be used to produce adhesive resins with enhanced properties.

Physicochemical and bioactive properties of innovative resin-based materials containing functional halloysite-nanotubes fillers

OBJECTIVE This study aimed to assess the degree of conversion, microhardness, solvent degradation, contact angle, surface free energy and bioactivity (e.g., mineral precipitation) of experimental resin-based materials containing, pure or triclosan-encapsulated, aluminosilicate-(halloysite) nanotubes. METHODS An experimental resin blend was prepared using bis-GMA/TEGDMA, 75/25wt% (control). Halloysite nanotubes (HNT) doped with or without triclosan (TCN) were first analyzed using transmission electron microscopy (TEM). HNT or HNT/TCN fillers were incorporated into the resin blend at different concentrations (5, 10, and 20wt%). Seven experimental resins were created and the degree of conversion, microhardness, solvent degradation and contact angle were assessed. Bioactive mineral precipitation induced by the experimental resins was evaluated through Raman spectroscopy and SEM-EDX. RESULTS TEM showed a clear presence of TCN particles inside the tubular lumen and along the outer surfaces of the halloysite nanotubes. The degree of conversion, surface free energy, microhardness, and mineral deposition of polymers increased with higher amount of HNTs. Conversely, the higher the amount (20wt%) of TCN-loaded HNTs the lower the microhardness of the experimental resins. SIGNIFICANCE The incorporation of pure or TCN-loaded aluminosilicate-(halloysite) nanotubes into resin-based materials increase the bioactivity of such experimental restorative materials and promotes mineral deposition. Therefore, innovative resin-based materials containing functional halloysite-nanotube fillers may represent a valuable alternative for therapeutic minimally invasive treatments.

Quantum Dots as Nonagglomerated Nanofillers for Adhesive Resins

Nanoparticles used in adhesive resins are prone to agglomeration, turning the material susceptible to physical failure. Quantum dots are nonagglomerated inorganic nanoparticles (1 to 10 nm) when in equilibrium. The aim of the present study was to synthesize and characterize zinc oxide quantum dots (ZnOQDs) and to develop and evaluate an adhesive resin with the addition of ZnOQDs. ZnOQDs were formulated by self-organization in chemical reaction with isopropanol and added to 2-hydroxyethyl methacrylate (HEMA). HEMA containing ZnOQDs was used for the experimental group and neat HEMA for the control group. Mean ZnOQD diameter was evaluated in isopropanol and in HEMA by ultraviolet-visible spectroscopy. The adhesives were evaluated for degree of conversion (n = 5), softening in solvent (n = 5), ultimate tensile strength (n = 5), microtensile bond strength (n = 20) at 24 h and after 6 mo, SEM-EDS (scanning electron microscopy–energy-dispersive x-ray spectroscopy; n = 3), and superresolution confocal microscopy (n = 3). Data of microtensile bond strength after 6 mo and Knoop hardness after solvent immersion were evaluated by paired t test with a 0.05 level of significance. The other data were evaluated by independent t test with a 0.05 level of significance. Ultraviolet-visible spectroscopy indicated that the mean ZnOQD diameter remained stable in isopropanol and in HEMA (1.19 to 1.24 nm). Fourier transform infrared spectroscopy analysis showed the peak corresponding to zinc and oxygen bond (440 cm-1). The experimental group achieved a higher degree of conversion as compared with the control group and presented dentin/adhesive interface stability after 6 mo without altering other properties tested. SEM-EDS indicated 1.54 ± 0.46 wt% of zinc, and the superresolution confocal microscopy indicated nonagglomerated nanoparticles with fluorescence blinking in the polymerized adhesive. The findings of this study showed a possible and reliable method to formulate composites with nonagglomerated nanoscale fillers, shedding light on the nanoparticle agglomeration concern.

Niobium pentoxide phosphate invert glass as a mineralizing agent in an experimental orthodontic adhesive

OBJECTIVE The aim of this study was to develop an experimental orthodontic adhesive and evaluate how adding phosphate invert glass containing niobium pentoxide (PIG-Nb) affected the adhesives properties. MATERIAL AND METHODS PIG-Nb was added at 1, 2.5, and 5 wt% to experimental adhesive (75 wt% bisphenol A methacrylate [BisGMA], 25 wt% triethylene glycol dimethacrylate [TEGDMA], 5 wt% colloidal silica and photoinitiator system). The adhesives were evaluated for mineral deposition, degree of conversion (DC), softening solvent by Knoop microhardness (KNH) variation, pH changes, and shear bond strength (SBS). One-way analysis of variance (ANOVA) (DC and ΔKHN%), two-way ANOVA (SBS), repeated measures ANOVA (pH), and paired test (KNH1 and KNH2) were used at a significance level of P < .05. RESULTS Adding PIG-Nb to orthodontic adhesives induced deposition on its surface associated with a constant neutral pH. The SBS increased after immersion in artificial saliva, and the PIG-Nb5 exhibited less softening. CONCLUSION The addition of PIG-Nb into orthodontic adhesives induced mineral deposition. Experimental orthodontic adhesive containing 5% wt of PIG-Nb exhibited increased mineral deposition and suitable properties for orthodontic applications.

Use of Natural and Modified Natural Nanostructured Materials

The use of natural nanomaterials is environmentally friendly, socially responsible and cost effective. Hence, several industries are investing in cheap ways to explore and process natural resources to make natural nanomaterials available. Natural nanomaterials are abundant; however, certain drawbacks such as incompatibility and extraction are a challenge to make their use more advantageous. Montmorillonite is the most common natural nanomineral used in industry and nanocellulose could be extracted from the most important skeletal component in plants, cellulose. In this chapter a brief overview is given of natural and modified natural nanostructured materials, with emphasis on layered silicates (clays) and cellulose-based materials, followed by some industrial examples.

SYNTHESIS OF WC-12wt%Co NANOCOMPOSITES BY HIGH ENERGY BALL MILLING AND THEIR MORPHOLOGICAL CHARACTERIZATION

In this work micrometric particles of WC and Co were processed by high energy ball milling in a planetary ball mill. We evaluated the phase formation and changes in microstructure of WC-12wt%Co as a result of the following milling parameters: ball-to-powder weight ratio, milling time and speed. The material was characterized by X-ray diffraction (crystalline phases and crystallite size), particle size analysis (average grain diameter), the BET method (surface area), and scanning electron microscopy (powder morphology). The average particle size (D50) and crystallite size were respectively 1.63μm and 13.8nm, for a surface area of 4.709 m2/g, using a ball-to-powder weight ratio of 1:20, a milling time of 5h and a milling speed of 500 rpm.

Evaluation of Flame-Sprayed Alumina Powders Produced Using Different Ethanol/Water Ratios in the Starting Solutions

Alumina powders were synthesized using a cost-effective process that used a Bunsen–Meker flame as the source of energy for the chemical reactions. With the aim of evaluating the influence of solvents on the morphology of powders, three starting solutions with different ethanol/water volume ratios were prepared. Ethanol/water ratios of 50:50; 20:80, and 1:100 were studied. X-ray diffraction analyses showed amorphous powders in the as-synthesized condition. After calcination at 1150°C, the powders became crystalline, and a major crystalline phase, α-alumina, was identified in all the powders. Using scanning electron microscopy, the typical morphology of the flame-sprayed powders, composed of aggregated spherical and unshaped particles, was observed. The specific surface area of the as-synthesized powder was greater than that of the calcined powder, with a maximum value of 36.75 m2/g, which corresponded to the powder obtained with the starting solution prepared only with water. Thermogravimetric analyses showed that the powder produced from a precursor solution composed only of water also had the highest loss (34.72%). Transmission electronic microscopy was used to observe the nanostructures of alumina powders. A maximum crystallite size of 24.6 nm, corresponding to the starting solution prepared only with water, was obtained.

Influence of Inorganic Sealant in Hot and Cold Erosive Wear in Plasma Sprayed Alumina Coating

Plasma sprayed alumina coating is applied in many industrial applications in order to promote wear and corrosion resistance. Nonetheless, high porosity remained after deposition is a critical factor because it decreases the wear resistance. Some inorganic sealants can be used to reduce the open pores and superficial micro-cracks effect, improving the wear and corrosion resistance of alumina coatings. In this work, plasma sprayed alumina coating samples were divided into two groups: i) impregnated with inorganic sealant (AlPO4) and heat treated; ii) as deposited. Erosive wear tests were carried out in an erosion rig according to ASTM G76. The samples were subjected to an erodent flux, with impact angles of 30º up to 90º, at a velocity of 50m/s and temperatures of 25°C up to 400°C. The samples were characterized by SEM, Vickers microhardness, potentiodynamic anodic polarization and erosive wear rate. Results showed that erosive wear rate of alumina impregnated coating is lower than without the sealant. The sealed alumina coating presented higher mechanical properties; improved microstructural characteristics and the sealant promoted better lamellae contact, as can be observed by less sharpness in pits formation of microstructure.

Radiopaque dental adhesive with addition of niobium pentoxide nanoparticles

Radiopacity is an important property of dental adhesives, because it allows the adhesive resin to be in contrast with the tooth structure and other restorative materials. This study aimed to develop a radiopaque experimental adhesive resin through the addition of niobium pentoxide (Nb2O5) particles. The effects of adding different concentrations of Nb2O5 nanoparticles synthesized by microwave-assisted hydrothermal synthesis (MHS) were compared to the commercial Nb2O5 microparticles. The experimental adhesive resin was formulated by mixing bisphenol A glycidyl methacrylate (Bis-GMA), 2-hydroxyethyl methacrylate (HEMA), camphorquinone (CQ) and ethyl 4-(dimethylamino)benzoate (EDAB). Experimental adhesive resins were evaluated by the radiopacity, degree of conversion, Knoop microhardness, translucency parameter, depth of cure, viscosity, and sedimentation rate. Synthesized Nb2O5 showed hexagonal structure and nanoneedles aggregates in form of nanoflowers. The incorporation of Nb2O5 nanoparticles into the dental adhesive resin showed high dispersion stability and improved the radiopaque properties.

Electrical and Microstructural Properties of Varistors Based on Nanostructured Tetra-Needle Like Zinc Oxide Powders

t is well known that nanostructured materials have relevant influences in properties behavior that can be achieved when compared with conventional materials. In this study is proposed an investigation of the electrical and microstructural properties of zinc oxide based varistors prepared with nanostructured zinc oxide powder obtained by a thermal evaporation process. Zinc oxide powder morphology was investigated by scanning and transmission electron microscopy (SEM and TEM, respectively) and the specific surface area evaluated by adsorption of N2. The varistors were prepared by the mixture of typical dopants with zinc oxide powders in a ball mill. The surface area of zinc oxide powder used was 17.4 m2/g with tetra-needle like morphology. After powder mixture process it was observed by TEM micrographs that most of the tetrapod shaped zinc oxide broke into needles well mixed with dopant particles. The compressed powders were sintering at 1050, 1150 and 1250°C for 1.5 h and densification over 94% were achieved in all tested temperatures. Preliminary electrical characterization reveals that nanostructured zinc oxide compositions have interesting varistor properties.