Nobuya Shinozaki

Optical properties of base dentin ceramics for all-ceramic restorations

OBJECTIVES The study was conducted to compare the optical parameters of VM7(®) M-shade base dentin ceramics (VITA, Germany) for all ceramic restorations to the chemical composition across the 3D-MASTER(®) shade system. METHODS Three disc samples, 13 mm diameter and 1.4 mm thickness, were produced for each M-shade following the manufacturers instructions. Each disc was ground and polished to a thickness of 1.0 mm. Spectral light transmittance and reflectance data were recorded in the visible spectrum under the standard illuminant D65 and 2° observer at 10 nm intervals by using a computer-controlled spectrophotometer. Opacity, translucency and opalescence parameters were determined for each sample. RESULTS (1) Spectral transmittance and reflectance in the short-wavelength range systematically decreased with increasing chroma number (M1, M2, M3) when compared within the same value (lightness) group. (2) Spectral transmittance and reflectance decreased systematically across the whole visible spectrum with increasing value group number when compared within the same chroma group. (3) Analysis of relationship between chemical composition and various optical parameters for all the samples showed the significant contribution of ZrO₂ and Y₂O₃ substances to optical properties of the present material. SIGNIFICANCE Systematic variations in optical properties of VM7(®) M-shade base dentin ceramics were observed throughout the 3D-MASTER(®) shade system and were suggested to be caused by the fine structure of the sample which can interfere with shorter wavelengths in the visible spectrum.

Wettability, surface tension, and reactivity of the molten manganese/zirconia-yttria ceramic system

A basic research study for improvement of plasma-sprayed zirconia coatings has been conducted. The contact angle and surface tension of the molten manganese/zirconia-yttria ceramic system were measured at 1573 K by the sessile drop method, suggesting that molten manganese would spontaneously infiltrate open pores in zirconia coatings. Structure and elementary composition development of zirconia ceramics caused by reaction with manganese were examined by using scanning electron microscopy (SEM), an electron probe microanalyzer (EPMA), and an X-ray diffractometer (XRD). Manganese not only stabilized cubic zirconia but also contributed to the growth and volume increase of zirconia particles. In this article, the mechanism of making zirconia coatings dense with manganese is discussed based on the results of experiments.

Spectral reflectance and color of dentin ceramics for all-ceramic restorations

OBJECTIVE The study was conducted to observe the spectral reflectance curves, and evaluate the color coordinates (CIELAB) of VM7 dentin ceramics (VITA, Germany) across the whole 3D-MASTER shade system. METHODS Three disc samples, 13 mm in diameter and 1.4mm in thickness, were produced for each shade by firing following the manufacturers instructions. Each fired disc was ground to a thickness of 1.0 mm and both faces were polished. Spectral reflectance data in the visible spectrum under the standard illuminant D65 were collected at 1 nm intervals by using a computer-controlled spectrophotometer. Color coordinates, L*, a*, b*, C*, h, in the three-dimensional CIELAB color space were obtained. RESULTS (1) Spectral reflectance in the short-wavelength range systematically decreased with increasing chroma number (M1, M2, and M3) when compared within the same value (lightness) group (1M, 2M, 3M, 4M, and 5M). (2) Spectral reflectance decreased systematically across the whole visible spectrum with increasing value group when compared within the same chroma group. (3) A negative relationship was recognized between lightness (L*) and chromaticity index a* (red-green direction). That is, a* coordinate increases from approximately 1 for the 1M1 sample to approximately 13 for the 5M3 sample, the corresponding lightness systematically decreased from 87 to 69. (4) With increasing a* coordinate, hue angle (h) significantly decreased from 85 degrees for the 1M1 sample to 69 degrees for the 5M3 sample. (5) Lightness apparently increased with increasing hue angle (h) throughout the whole range of the 3D-MASTER shade system. (6) A strong positive relationship between chroma (C*) and chromaticity index b* (yellow-blue direction) was found, demonstrating that the chroma of the present ceramic is mainly controlled by the b* coordinate. SIGNIFICANCE Systematic variations in spectral reflectance and color coordinates of VM7 dentin were observed throughout the 3D-MASTER shade system and were suggested to be caused by the fine structure of the sample which can interfere with shorter wavelengths in the visible spectrum.

Development of hafnium metal and titanium-hafnium alloys having apatite-forming ability by chemical surface modification: DEVELOPMENT OF HAFNIUM METAL AND TITANIUM-HAFNIUM ALLOYS

Hafnium (Hf) has attracted considerable attention as a component of biomedical titanium (Ti) alloys with low Youngs moduli and/or shape-memory functionalities, because its cytotoxicity is as low as that of Ti. The drawback of metals is that their bone-bonding ability is generally low. It is known that apatite formation in the body is a prerequisite for bone-bonding. Although several chemical treatments have been proposed for preparing Ti for bone-bonding, there have been no similar investigations for Hf. In the present study, NaOH- and heat-treatments were applied to pure Hf and Ti-Hf alloys and their bone-bonding ability was assessed in vitro with the use of simulated body fluid (SBF). After NaOH- and heat-treatments, anatase formed on alloys with low Hf content (20-40% (atom%) Hf); mixtures of sodium titanate and hafnium titanate formed on alloys with similar Ti and Hf content (60% Hf); and hafnium oxide formed on alloys with high Hf content (80% Hf and pure Hf). Precipitates of apatite were observed on all the metals in SBF, except for the alloy with 60% Hf. We speculated that the hafnium titanate formed on this alloy had a low apatite-forming ability owing to its high negative surface charge, which inhibited P adsorption. The apatite-forming abilities of the Ti-Hf alloys strongly depended on their Hf content. The present results indicate that Hf-based materials have good potential for bone-bonding.

Thermodynamic Study on Interfacial Reaction between Molten Iron and Spinel

The effect of the oxygen concentration in the molten iron on the formation of the FeO-MgO phase at the interface between the MgAl2O4 spinel substrate and the molten iron was investigated at 1833 K on the basis of thermodynamics. The results showed that the FeO-MgO phase was formed at the interface between the molten iron and the substrate, if the oxygen concentration in the molten iron was larger than 0.04 mass% for the 50mol%Al2O3-50mol%MgO substrate and 0.08 mass% for the 61mol%Al2O3-39mol%MgO substrate, respectively. For both the substrates, with increasing the oxygen concentration in the molten iron, the activity coefficient of FeO in the spinel substrate increased, and when this value reached above 1.5, a part of MgO was discharged from the spinel and reacted with Fe and oxygen in the molten iron to form the FeO-MgO phase.

Thermodynamic Study on Interfacial Reaction between Blast Furnace Slag and Silicon Carbide

Silicon carbide(SiC) is used as a raw material contained in the refractory that is in contact with molten iron or slag during steel-making processes. In present work, the interfacial reactions between the SiC ceramic substrate and the blast furnace slag were investigated and the thermodynamic study on the reaction products was carried out. The results showed that the Ti component contained in the slag became TiC, and gathered at the whole interface between the SiC substrate and the slag after experiments.

Characteristic X-ray Spectrum Analysis of Micro-Sized SiC

It is general to use plural analysis methods to elucidate the structure and the composition of micro-sized materials. However, the following problems will arise during the use of these analysis methods: (1) It may be diffi cult to pinpoint the analysis area in some analysis methods, such as the X-ray diffraction (XRD) analysis. (2) Since an electron beam and X-rays are irradiated many times onto the same area, the sample surface gets damage such as carbon contamination. (3) It takes a long time to analyze. Therefore, electron probe micro-analyzer (EPMA) that can be used to elucidate the compound state of the micro-sized material by only once measurement has been discussed here. Generally, the EPMA can not only obtain the information of simple substances or elements, but also know the variation of the spectrum as changing the bonding state (Kinouchi, 2001; The Surface Science Society of Japan, 1998). However, since the spectrum cannot change regularly for each element in different bonding states, data such as peak shift, peak intensity ratio and half-value width must be one by one analyzed. As it is very diffi cult to prove the change of the characteristic X-ray spectrum theoretically from the viewpoint of the instrumental analysis according to many previous studies, a number of the analysis techniques of the characteristic X-ray have been established based on the experimental data (Abe et al., 2001; Honma et al., 1974; Murakami et al., 1991; Nishimura, 2007; Ohtsuka, 1982; Soejima, 1987; Uchikawa & Numata, 1973; Watanabe et al., 1970). In this study, EPMA that is suitable for micro area analysis was used and we tried to distinguish the kind of compound of the Si series material. At the same time, it was also discussed

Investigations of Wetting Properties of Stainless Steel by Molten Multi-Component Oxides

The wettability between molten impregnating materials and thermal spray coatings is an important factor in post-treatment process of porous coatings. Here, we present the study of wetting behavior of stainless steel substrates by multi-component oxides, using the sessile drop method. The multi-component oxides was mainly composed by SiO2 and Al2O3 and also with a little K2O, Na2O etc. At 1273K and 1353K, we found that the contact angles stabilized at around 45° and 75° respectively. The micro-observation confirmed that the evaporation of alkali metal oxides become a leading position in molten multi-component oxides evaporation at 1353K. As a result, the rupture of NaO and KO bonds will occur and lattice network structure of multi-component oxides reconstruct at excessively high temperature, leading the molten oxides to a higher viscosity and poorer wettability. As the basic researches, this paper also provide a theoretical basis for the deeply study on the post penetration treatment.