Glass-ceramic powders with the oxide batch formulation 54wt%SiO2, 20wt%P2O5 and 30wt%CaO were prepared by the sol-gel process using tetraethoxysilane, calcium nitrate and phosphoric acid as raw materials. The obtained gels and powders were characterized by TG-DTA thermal analysis, FTIR analyses and XRD measurements. The results indicated that (1) heating to more than 600°C brought about elimination of -OC2H5 side chains from gels, and formation of a SiO2-based glass network, (2) crystallization such as Ca3(PO4)2 notably occurred in the SiO2-based glass matrix when heated to more than 900°C, (3) -OH groups existed on SiO2-based glass-ceramic surfaces in the temperature region less than 900°C, and (4) the melting point of this composition was more than 1400°C. This study suggests that sol-gel-derived SiO2-based glass-ceramic powder containing P and Ca might be useful as bioactive implant materials.
The differential scanning calorimetry (DSC) curves for three commercial dentin and incisal porcelains fused-to metal were measured using high-temperature DSC. The glass transition temperatures (Tg) were determined from the DSC curves at heating rates of 7-20°C/min, and the activation energy was derived from an Arrhenius plot of negative reciprocal Tg vs. logarithm of heating rate. The Tg of the dental porcelains depended on the content of aluminum oxide, whereas the activation energy depended on the content of sodium oxide. The ultra-low fusing type porcelains had a low activation energy due to the higher content of sodium oxide than the other porcelains.
The desirable thermal properties of matrix glass to the strength of feldspar porcelain with leucite crystal were investigated. Five kinds of feldspar glasses, each with different a content of Na2O, were prepared for the matrix glasses of the leucite-containing porcelains. The specimens were arranged by mixing each glass powder with high-purity natural leucite crystals (0, 20 and 40%) followed by firing. The thermal properties of the glass and the transformation temperature of the leucite were measured. A three-point bending test was performed to measure the flexural strength of the porcelains. The glass transition temperature and deformation temperature of the glass-only porcelains were decreased as the Na2O content increased. The Na2O-modified glasses were substantially strengthened by the leucite dispersion. However, the strength of the porcelains was affected by the relation between the transformation temperature of the leucite and the thermal properties of the glass matrix. It was concluded that control of the residual stress in the composite porcelain is an important factor in developing high strength porcelain containing leucite.
In order to determine a coherent phase diagram of the [(AuCu)0.86Ag0.14]1-XPtX pseudobinary system, phase identifications and analyses of the microstructural configurations were performed by means of transmission electron microscopy. Various phase regions were detected in the coherent phase diagram as follows; (1) α0 (fcc) single phase region, (2) two-phase region (α1+α2), (3) AuCu I (L10)+α0, (4) AuCu I+α2, (5) AuCu II (L10-S)+α2, (6) AuCu I+AuCu II+α2, (7) AuCu I single phase region. Microstructural features of these regions relating to the phase transformations were described.
The effects of aging on the tensile fatigue strength of bovine dentin were investigated. Tensile tests and tensile fatigue tests were performed in 37°C water with the bovine dentin specimens of two different age groups. The tensile strengths of the young group and the adult group were 74.0MPa and 72.7MPa, respectively; there was no significant difference between the young and the adult group. However, the tensile fatigue strength of the adult group, 46.9MPa, was significantly weaker than that of the young group, 51.0MPa. There was a obvious difference between the tensile fracture surface and the tensile fatigue fracture surface; a smooth surface of the peritubular dentin and an uneven surface of the intertubular dentin were clearly distinct in the fatigue fracture surface. Plugged dentinal tubules and narrower dentin tubules were commonly observed in the adult group. These morphological changes were suggested to be the reason for the decrease in the tensile fatigue strength with aging.
The aim of this study was to clarify the erosion behavior of light-cured glass ionomer cement. One light-cured glass ionomer cement and two conventional chemically-cured glass ionomer cements were immersed in citric acid buffer solutions of pH 4 and pH 6. Fluoride release was almost the same in both types of cements, irrespective of pH. The amounts of other species eluted, such as Al, Sr, Si and P2O5 were smaller in the light-cured glass ionomer cement than in the conventional ones at pH 4. The amounts of species eluted at pH 6 were almost the same in both types of cement. Dissolution of the light-cured cement in pH 4 solution was controlled by the diffusion of the eluted species in the cement matrix. On the other hand, dissolution of the conventional cements was controlled by both diffusion and surface reaction. The surface features of the cements after erosion corresponded well to the dissolution mechanism. In pH 6 solution, dissolution of the cements was mainly controlled by diffusion of the species in the cement.
To analyze the functional and morphological harmonies of the tooth and dental arch, a computerized system to measure a dental cast and to detect the apex of dental cusps and angle points of incisors was developed. Detailed morphology in the measured dental cast could be displayed distinctively by computer graphics (CG) with a surface model. Accuracy in determining the position of the apex of the dental cusp was examined by increasing the measuring pitch from 50μm to 400μm, the error increased gradually with increased measuring pitch. Taking the measuring error, the time for measurement and the memory size for analysis into account, a measuring pitch of 200μm was determined to be reasonable. Three-dimensional data measurements from the apex of the dental cusp in molar, and the mesial and distal angles in canine and incisor were fitted to a polynomial formula. In the present measured model, the 4th order polynomial formula was used for the dental arch, and the 2nd order polynomial formula was used for the anteroposterior and lateral occlusal curves. These formulae could be simultaneously superimposed on the surface model of the dental cast, and displayed using CG.
The amount of Hg vapor released from “synthesized” γ1 with 1% (wt) Pd was reported to be less than 30% of that from γ1 with no Pd. This study tested the hypothesis that Hg evaporation from Pd-containing amalgams decreases with Pd concentration and that In also reduces Hg vapor. Specimens (4mm dia, 8mm long) were prepared by triturating Ag-Sn(25%)-Cu(12%) alloy powder containing 0.5-9.0% Pd with pure Hg and by triturating 3% Pd alloy powder with Hg containing 1-5% In (all residual Hg≅62%). The total amount (ng/mm2) of Hg vapor released at 37°C from freshly prepared amalgams was measured. Pd (3-9%) in the powder significantly (p<0.05) decreased Hg vapor release from amalgams during setting. Use of In-containing Hg also reduced Hg vapor release (5% In, p<0.05). The reduction in the Hg vapor pressure by adding Pd and the rapid oxide film formation on the In-containing amalgam appear to work together to reduce Hg vaporization from these amalgams.
This study investigated the chemical stability of pure gallium in water and saline solutions in order to obtain fundamental knowledge about the corrosion mechanism of gallium-based alloys. A pure gallium plate (99.999%) was suspended in 50mL of deionized water, 0.01%, 0.1% or 1% NaCl solution at 24±2°C for 1, 7, or 28 days. The amounts of gallium released into the solutions were determined by atomic absorption spectrophotometry. The surfaces of the specimens were examined after immersion by x-ray diffractometry (XRD) and x-ray photoelectron spectroscopy (XPS). In the solutions containing 0.1% or more NaCl, the release of gallium ions into the solution was lowered when compared to deionized water after 28-day immersion. Gallium oxide monohydroxide was found by XRD on the specimens immersed in deionized water after 28-day immersion. XPS indicated the formation of gallium oxide hydroxide on the specimens immersed in water or 0.01% NaCl solution. The chemical stability of pure solid gallium was strongly affected by the presence of Cl- ions in the aqueous solution.