Effects of magnesia and potassium sulfate on gypsum-bonded alumina dental investment for high-fusing casting.
The purpose of this study was to improve the characteristics of gypsum-bonded alumina investments using magnesia and potassium sulfate as chemical additives. Magnesia content improved fluidity, delayed setting reaction, increased green strength, and decreased setting expansion, when mixed with distilled water. When the investment was mixed with potassium sulfate, the setting time and setting expansion were reduced, and the thermal expansion increased, however, the green strength decreased. Therefore, the investment with a small amount of magnesia mixed with potassium sulfate was considered a suitable composition, having adequate setting behavior, enough green strength and sufficient compensate expansion for casting. (+info)
Primary hypomagnesemia caused by isolated magnesium malabsorption: atypical case in adult.
Isolated magnesium malabsorption is a rare disorder, which bas been described in no more than 30 patients worldwide. Patients with this disorder typically present with convulsion and diarrhea in early infancy. Hypomagnesemia and hypocalcemia were found in a 35-year-old man with muscle cramps, who bad been diagnosed as primary hypoparathyroidism. Oral magnesium therapy corrected the low serum calcium, magnesium and parathyroid hormone levels. We report an atypical case of isolated magnesium malabsorption in an adult. (+info)
Structure of bioactive glass and its application to glass ionomer cement.
We prepared a new glass ionomer cement using bioactive CaO-P2O5-SiO2(-MgO) glass and investigated its setting process using FT-IR and MAS NMR analyses. The compressive strengths of the cements depended on the glass composition and a maximum strength of 33.3 +/- 4.7 MPa was obtained using cement with the glass composition of MgO:4.6, CaO:44.9, SiO2:34.2 and P2O5:16.3% in weight. FT-IR analysis showed that the COOH group in the polyacrylic acid decreased and carboxylate ion (COO-Ca2+) increased after the setting reaction. A broad signal appeared around -82 ppm in 29Si MAS-NMR spectra of the glass and a new signal corresponding to hydrated silica gel formation appeared around -102 and -111 ppm after setting. This suggests that Ca2+ was released from the glass powder to form carboxylate salt and that a degree of polymerization in the silicate network increased. The setting mechanism of the cement was found to be essentially the same as in conventional glass ionomer cement. (+info)
Interfacial oxidations of pure titanium and titanium alloys with investments.
External oxides of a commercially pure titanium (cpTi), Ti6Al4V alloy, and an experimental beta-type titanium alloy (Ti 53.4 wt%, Nb 29 wt%, Ta 13 wt%, and Zr 4.6 wt%) were characterized after heating to 600, 900, 1150, and 1400 degrees C in contact with three types of investments (alumina cement, magnesia cement, and phosphate-bonded) in air. XRD studies demonstrated that MgO, Li2TiO3 and/or Li2Ti3O7 were formed through reactions with the metal and the constituents in the magnesia cement-investment after heating to 900, 1150, and 1400 degrees C. Except for these conditions, TiO2 (rutile) was only formed on cpTi. For titanium alloys, the other components apart from Ti also formed simple and complex oxides such as Al2O3 and Al2TiO5 on Ti6Al4V, and Zr0.25Ti0.75Nb2O7 on the beta-type titanium alloy. However, no oxides containing V or Ta were formed. These results suggest that the constituents of titanium alloys reacted with the investment oxides and atmospheric oxygen to form external oxides due to the free energy of oxide formation and the concentration of each element on the metal surface. (+info)
Experimental ammonia-free phosphate-bonded investments using Mg(H2PO4)2.
In previous study, we found that Mg(H2PO4)2 instead of NH4H2PO4 was available as a binder material for phosphate-bonded investments and possibly could be used to develop the phosphate-bonded investment without ammonia gas release. The purpose of the present study was to develop the experimental ammonia-free phosphate-bonded investments by investigating suitable refractories. Mg(H2PO4)2.nH2O and MgO were prepared as a binder. Cristobalite and quartz were selected as refractories. The power ratio of MgO/Mg(H2PO4)2.nH2O was set constant at 1.2 according to our previous findings. Fundamental properties of dental investment such as strength, manipulation and expansion were evaluated. Using cristobalite as the refractory material, further investigations were performed. The refractory/binder ratio was definitely effective. The increase of this ratio led to low mold strength and large mold expansion. The present findings suggested that C5 was desirable for dental investment. (+info)
Experimental ammonia-free phosphate-bonded investments using Mg(H2PO4)2 solution.
In our previous study, we investigated ammonia-free phosphate-bonded investments using Mg (H2PO4)2 powder. The purpose of the present study was to attempt usage of 50 wt% Mg (H2PO4)2 solution instead of powder. Magnesium oxide (MgO) was prepared as a binder and cristobalite was selected as a refractory. After arranging six kinds of experimental investments (A-F) with different cristobalite/MgO ratios, the fundamental properties of the dental investments were examined. The properties of the molds were influenced by the amount of MgO. Decreases in MgO showed lower mold strengths, longer setting time and larger setting expansion. According to XRD analysis, the peaks of MgH(PO4)3 x 3H2O newly formed, cristobalite and MgO were detected in the A set, but MgO peaks in F set were reduced. On the other hand, the surface of F was entirely covered by phosphorus. From these results, it was found that the usage of Mg(H2PO4)2 solution was possible for ammonia-free investments. (+info)
An in vivo and ex vivo study to evaluate the use of a glass polyphosphonate cement in orthodontic banding.
The purpose of this study was to examine the effectiveness of a new glass polyphosphonate cement (Diamond) for orthodontic banding. Thirty-one subjects underwent in vivo testing to compare the failure rate of bands cemented using the test cement and bands cemented using a conventional glass polyalkenoate cement (Ketac-Cem) over a 6-month period at the beginning of active appliance therapy. In an ex vivo experiment 60 extracted teeth were banded using either the test cement or a glass polyalkenoate cement, and subjected to a debanding force using a Lloyd universal testing machine until failure. In the in vivo study the overall proportion of failure of the bands cemented with each cement was identical at 0.048. However, in the ex vivo study the probability of failure for the glass polyphosphonate cement was significantly higher than for the glass polyalkenoate cement, and the force to deband the glass polyalkenoate cement was greater than that of the glass polyphosphonate cement. In the clinical setting the new glass polyphosphonate cement performed as well as a conventional glass polyalkenoate cement, and these results suggest that it could be used as an alternative cement for orthodontic banding. The results of the ex vivo test bring into question the usefulness of this laboratory test as an indicator of clinical performance. (+info)
Development of a new investment for high-frequency induction soldering.
This study developed a new investment for induction soldering using high frequency induction heating. Ninety-five mass% magnesia clinker and 5 mass% dental stone were selected for the main constituents. The magnesia investment itself was scarcely affected by induction heating, so the addition of metal powders such as Fe, Ni, Co were investigated. Among these three powders, the addition of 10 mass% cobalt powder was most effective. This investment needed only 40 seconds of high frequency induction heating to go from room temperature to 900 degrees C without preheating. Thermal expansion of this investment in a vacuum atmosphere was 1.25% at 1000 degrees C. Dimensional changes during induction soldering were measured using German-silver and silver solder. When the new magnesia investment containing 10 mass% Co powder was used, the dimensional change was -0.2%. This contraction was less than when a magnesia investment without metal additives was used. (+info)