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)
Evaluation of a reproduction technique for the study of the enamel composite/bracket base area.
The objective of the study was to evaluate a reproduction method that would enable the study of the enamel/ bracket/composite interface in vivo, and consisted of in vitro assessment of two different impression materials to compare reproduction of brackets bonded to extracted teeth followed by in vivo assessment of the superior material. In vitro standard edgewise brackets were bonded to two extracted teeth and impressions were taken using two different types of low viscosity silicone-based impression materials. A medium viscosity silicone impression material was used to support the original impression. Three impressions of both the gingival and occlusal aspect of the bracket base region were obtained using each of the impression materials. Replicas were then prepared for SEM viewing and these compared to SEMs of the real teeth for reproduction of detail. A 3-point Reproducibility Index was used to compare the SEM photographs of the comparable replicas. One impression material was clearly superior to the other and produced an acceptably accurate representation of the true clinical situation in three out of four samples. This material also performed well in the in vivo situation. The technique described is satisfactory for the production and analysis of SEM pictures of the enamel/composite/ bracket base interface in vivo. (+info)
Study of resin-bonded calcia investment: Part 1. Setting time and compressive strength.
This study was carried out to develop a new titanium casting investment consisting of calcia as the refractory material and a cold-curing resin system as the binder. The setting time of the investment was investigated under different N,N-dimethyl-p-toluidine (DMPT) contents in methyl methacrylate monomer (MMA) and benzoyl peroxide (BPO) contents in calcia without any sintering agent. The effects of the sintering agents, which were calcium fluoride (CaF2) and calcium chloride (CaCl2), on the compressive strength of the investments were investigated at room temperature before and after heating to two different temperatures. The shortest setting time (68 minutes) of the investment was obtained at 0.37 DMPT/BPO (1.5 vol% /1.0 mass%) ratio by mass. The highest strength (16.5 MPa) was obtained from the investment which contained 2 mass% CaF2 and was heated to 1,100 degrees C. It was found that the developed calcia investment containing 2 mass% CaF2 has a possibility for use in titanium castings. (+info)
Fit and dimensional changes of cast CP titanium crowns fabricated using sintered molds.
The present study was undertaken to evaluate the clinical applicability of cast CP titanium crowns fabricated with sintered molds. To this end, the dimensional changes and accuracy of fit of cast CP titanium crowns, manufactured under varying mold firing temperatures, were examined. Molds were fired at 7 temperatures. The outer height of the crown and outer width of the occlusal surface decreased under all sets of firing conditions. The outer width of the cervical part tended to increase at firing temperatures of 1,200, 1,300 and 1,400 degrees C. The inner widths of the occlusal surface and cervical part tended to increase under all sets of firing conditions. In the analysis of the fit of crowns, floating (gained latitude) was observed under all sets of conditions. However, the amount of floating was significantly smaller when the firing temperature was 1,200, 1,300 or 1,400 degrees C than when it was 800, 900, 1,000 or 1,100 degrees C. (+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)
Labor reduction for mold preparation of a commercial titanium cast denture system using a heat-shock method.
The purpose of this study was to investigate the application of a heat-shock method to fabricate titanium cast plates. Duplications of a maxillary model were prepared using DM under different firing schedules. Molds with patterns on the duplications were made by an outer investment (D), followed by heat shock at 850 degrees C. Duplications heat shocked at 850 degrees C after 30 min from mixing exploded within a few minutes. This explosion was successfully avoided by a drying procedure prior to the heat-shock. The molds were available for the heat shock at 850 degrees C when the duplicate models were prepared by firing either using the conventional method and the heat shock above method described. Therefore, we could reduce the preparation time from about 16 hr with the conventional method to about 10 hr at the longest with the heat-shock method. These results suggested that the heat-shock method was labor-saving for fabricating titanium cast denture plates when controlling preliminary conditions prior to use. (+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)
Study of resin-bonded calcia investment: part 2. Effect of titanium content on the dimensional change of the investment.
In the present study, titanium powder was chosen as an expanding agent of an experimentally prepared resin-bonded calcia investment. The effect of Ti content on the dimensional change was investigated. In addition, the effects of the heating rate and heating temperature on the dimensional change of the investment were investigated during setting and after heating. The expansion increased with Ti content and the highest expansion (1.57%+/-0.58) was obtained at 10 mass% Ti. The highest expansion was obtained at 900 degrees C for 30 min heating and was independent of the heating rate. These findings mean that the titanium powder in the calcia investment oxidized sufficiently at that heating condition. It was found that the developed resin-bonded calcia investment was able to compensate for casting shrinkage of pure titanium by adding some Ti powder to the investment. (+info)