Nitinol Type Alloys General Characteristics and Applications in Endodontics

A very extensive literature review presents the possibilities and needs of using, in endodontics, the alloys commonly known as nitinol. Nitinol, as the most modern group of engineering materials used to develop root canals, is equilibrium nickel and titanium alloys in terms of the elements’ atomic concentration, or very similar. The main audience of this paper is engineers, tool designers and manufacturers, PhD students, and students of materials and manufacturing engineering but this article can also certainly be used by dentists. The paper aims to present a full material science characterization of the structure and properties of nitinol alloys and to discuss all structural phenomena that determine the performance properties of these alloys, including those applied to manufacture the endodontic tools. The paper presents the selection of these alloys’ chemical composition and processing conditions and their importance in the endodontic treatment of teeth. The results of laboratory studies on the analysis of changes during the sterilization of endodontic instruments made of nitinol alloys are also included. The summary of all the literature analyses is an SWOT analysis of strengths, weaknesses, opportunities, and threats, and is a forecast of the development strategy of this material in a specific application such as endodontics.

SPECIFIC FEATURES OF INELASTIC PROCESSES IN MATERIALS WITH NANOSCALE DEFECTS

Теоретически проанализирована высокоскоростная деформация сплавов, содержащих зоны Гинье-Престона, в условиях высокоэнергетических внешних воздействий. Анализ выполнен в рамках теории динамического взаимодействия структурных дефектов. Исследуемый механизм диссипации заключается в необратимом переходе энергии внешних воздействий в энергию дислокационных колебаний. Получено аналитическое выражение динамического предела текучести с учетом всех структурных дефектов, содержащихся в сплаве. Показано, что в условиях высокоэнергетических внешних воздействий наноразмерные дефекты влияют на характер зависимости механических свойств от концентрации атомов второго компонента. Зависимость динамического предела текучести от концентрации атомов второго компонента становится немонотонной и имеет минимум. Выполнены численные оценки концентрации, при которой предел текучести становится минимальным. При таком значении концентрации происходит переход от доминирования торможения дислокации зонами Гинье-Престона к доминированию торможения атомами второго компонента. The high strain rate deformation of alloys containing Guinier-Preston zones under high-energy external influences has been theoretically analyzed. The analysis was carried out within the framework of the theory of dynamic interaction of structural defects. The investigated dissipation mechanism consists in the irreversible transfer of energy of an external impact into the energy of dislocation vibrations. An analytical expression for the dynamic yield stress taking into account all structural defects of the alloy has been obtained. It is shown that, under high-energy external influences, nanoscale defects affect the nature of the dependence of mechanical properties on the concentration of atoms of the second component. The dependence of the dynamic yield stress on the atomic concentration of the second component becomes nonmonotonic and has a minimum. Numerical estimates of the concentration corresponding to the minimum yield stress has been made. At this concentration value, a transition occurs from the dominance of the dislocation drag by the Guinier-Preston zones to the dominance of the drag by the atoms of the second component.

Hydrolysis Reaction and Amorphization of Ce–Ti Oxide Catalysts During Synthesis

The change in the crystallinity of Ce–Ti oxide nanocatalysts with different water contents was investigated in terms of the local atomic structure and the surface atomic concentration. The crystallization of TiO2, which was induced by the hydrolysis of the Ti precursor, was observed in the catalyst synthesized via a liquid phase reaction employing a mixture of ethanol and distilled water as the solvent. The hydrolysis reaction of the Ti precursor was impeded in the solvent mixture of ethanol and anhydrous ethanol. CeO2 nanocrystallization occurred due to the suppression of the TiO2 crystal growth. Low crystallinity of the catalyst synthesized in a single anhydrous ethanol solvent was observed through the broadened X-ray diffraction (XRD) peak and the diffused ring pattern in transmission electron microscopic (TEM) images. In addition, the Ce–O and Ce–Ce bond lengths of the catalyst synthesized using the single solvent decreased beyond those of the catalysts synthesized in the mixed solvent, indicating the amorphization of the catalyst. It was also verified that the inhibition of the precursor crystallization during the synthesis led to the enhanced dispersion of the nanocatalyst, compared to the stoichiometry of the surface atomic concentration.

Bandgap atomistic calculations on hydrogen-passivated GeSi nanocrystals

We present a detailed study regarding the bandgap dependence on diameter and composition of spherical Ge-rich GexSi1−x nanocrystals (NCs). For this, we conducted a series of atomistic density functional theory (DFT) calculations on H-passivated NCs of Ge-rich GeSi random alloys, with Ge atomic concentration varied from 50 to 100% and diameters ranging from 1 to 4 nm. As a result of the dominant confinement effect in the DFT computations, a composition invariance of the line shape of the bandgap diameter dependence was found for the entire computation range, the curves being shifted for different Ge concentrations by ΔE(eV) = 0.651(1 − x). The shape of the dependence of NCs bandgap on the diameter is well described by a power function 4.58/d1.25 for 2–4 nm diameter range, while for smaller diameters, there is a tendency to limit the bandgap to a finite value. By H-passivation of the NC surface, the effect of surface states near the band edges is excluded aiming to accurately determine the NC bandgap. The number of H atoms necessary to fully passivate the spherical GexSi1−x NC surface reaches the total number atoms of the Ge + Si core for smallest NCs and still remains about 25% from total number of atoms for bigger NC diameters of 4 nm. The findings are in line with existing theoretical and experimental published data on pure Ge NCs and allow the evaluation of the GeSi NCs behavior required by desired optical sensor applications for which there is a lack of DFT simulation data in literature.

Decontamination of Ti Oxide Surfaces by Using Ultraviolet Light: Hg-Vapor vs. LED-Based Irradiation

C-range Ultraviolet (UVC) mercury (Hg)-vapor lamps have shown the successful decontamination of hydrocarbons and antimicrobial effects from titanium surfaces. This study focused on surface chemistry modifications of titanium dental implants by using two different light sources, Hg-vapor lamps and Light Emitting Diodes (LEDs), so as to compare the effectivity of both photofunctionalization technologies. Two different devices, a small Hg-vapor lamp (λ = 254 nm) and a pair of closely placed LEDs (λ = 278 nm), were used to irradiate the implants for 12 min. X-ray Photoelectron Spectroscopy (XPS) was employed to characterize the chemical composition of the surfaces, analysing the samples before and after the lighting treatment, performing a wide and narrow scan around the energy peaks of carbon, oxygen and titanium. XPS analysis showed a reduction in the concentration of surface hydrocarbons in both UVC technologies from around 26 to 23.4 C at.% (carbon atomic concentration). Besides, simultaneously, an increase in concentration of oxygen and titanium was observed. LED-based UVC photofunctionalization has been suggested to be as effective a method as Hg-vapor lamps to remove the hydrocarbons from the surface of titanium dental implants. Therefore, due to the increase in worldwide mercury limitations, LED-based technology could be a good alternative decontamination source.

Rheological properties measurement of Mucuna solannie as cement slurry extender: characterization and verification using rheological models

Rheological properties of lead cement slurry with Mucuna solannie admixture as an extender was measured in accordance with API standard. Bentonite extender was used as a control. The elemental and oxide compositions of Mucuna solannie were determined using Scanning Electron Microscope and X-Ray Florescence (XRF) methods, and rheological properties were obtained using rheometer after conditioning. The rheological data from Mucuna solannie and bentonite lead slurries were validated using Bingham Plastic and Herschel-Bulkley models. The result showed that Mucuna solannie contains high carbon atomic concentration and is responsible for its high rheological properties values. Lead slurry prepared with Mucuna solannie gave higher plastic viscosity, yield point and gel strength than that of bentonite. Herschel-Bulkley model described the rheological properties better than Bingham Plastic model. Due to high rheological properties values of the slurry prepared with Mucuna solannie, dispersant is needed for the optimization of the yield point and gel strength.

D-Glucuronic Acid-Coated Ultrasmall Bi2O3 Nanoparticles for CT Imaging

Ultrasmall Bi2O3 nanoparticles (davg = 1.5 nm) coated with biocompatible and hydrophilic D-glucuronic acid were prepared for the first time through a simple one-step polyol process and their potential as CT contrast agents were investigated by measuring their X-ray attenuation properties. Their observed X-ray attenuation power was stronger than that of a commercial iodine CT contrast agent at the same atomic concentration, as consistent with the magnitudes of atomic X-ray attenuation coefficients (i.e., Bi > I), and much stronger at the same number density. The results indicate that the nanoparticle sample is a potential CT contrast agent.

Demonstration of a SiC Protective Coating for Titanium Implants

To mitigate the corrosion of titanium implants and improve implant longevity, we investigated the capability to coat titanium implants with SiC and determined if the coating could remain intact after simulated implant placement. Titanium disks and titanium implants were coated with SiC using plasma-enhanced chemical vapor deposition (PECVD) and were examined for interface quality, chemical composition, and coating robustness. SiC-coated titanium implants were torqued into a Poly(methyl methacrylate) (PMMA) block to simulate clinical implant placement followed by energy dispersive spectroscopy to determine if the coating remained intact. After torquing, the atomic concentration of the detectable elements (silicon, carbon, oxygen, titanium, and aluminum) remained relatively unchanged, with the variation staying within the detection limits of the Energy Dispersive Spectroscopy (EDS) tool. In conclusion, plasma-enhanced chemical vapor deposited SiC was shown to conformably coat titanium implant surfaces and remain intact after torquing the coated implants into a material with a similar hardness to human bone mass.