Abstract
This study analyzed the reaction layer and measured the marginal crown fit of cast titanium applied to different phosphate-bonded investments, prepared under the following conditions (liquid concentration/casting temperature): Rema Exakt (RE) - 100%/237 degrees C, 75%/287 degrees C, Castorit Super C (CS)-100%/70 degrees C, 75%/141 degrees C and Rematitan Plus (RP)- 100%/430 degrees C (special to titanium cast, as the control group). The reaction layer was studied using the Vickers hardness test, and analyzed by two way ANOVA and Tukey's HSD tests (alpha = 0.05). Digital photographs were taken of the crowns seated on the die, the misfit was measured using an image analysis system and One-way ANOVA, and Tukey's test was applied (alpha = 0.05). The hardness decreased from the surface (601.17 VHN) to 150 microm (204.03 VHN). The group CS 75%/141 degrees C presented higher hardness than the other groups, revealing higher surface contamination, but there were no differences among the groups at measurements deeper than 150 mum. The castings made with CS - 100%/70 degrees C presented the lowest levels of marginal misfit, followed by RE -100%/237 degrees C. The conventional investments CS (100%) and RE (100%) showed better marginal fit than RP, but the CS (75%) had higher surface contamination.
Highlights
Silica-based phosphate-bonded investments exhibit a thermal expansion compatible with titanium casting shrinkage,7 but the silica is highly reactive at high temperatures
Other thermally more stable refractory oxide materials have been developed, but they have shown thermal expansion unable to compensate for the casting shrinkage of molten titanium
The heating temperature necessary to achieve an expansion equivalent to that of the Rematitan Plus at the temperature recommended by the manufacturer (430°C) was determined for these investments
Summary
Titanium has been used for dental prosthesis frameworks because of its excellent biocompatibility, high corrosion resistance, low density, adequate mechanical properties and low cost. titanium has a high melting point (1,720°C) and high chemical reactivity with oxygen and nitrogen (atmospheric air) as well as with other elements of the investment materials. Its extreme reactivity at high temperatures results in a contaminated surface layer that leads to a nonhomogeneous microstructure with consequent increase in hardness, brittleness, and susceptibility to corrosion.5,6Silica-based phosphate-bonded investments exhibit a thermal expansion compatible with titanium casting shrinkage, but the silica is highly reactive at high temperatures. Other thermally more stable refractory oxide materials (calcium oxide, magnesium oxide and aluminum oxide) have been developed, but they have shown thermal expansion unable to compensate for the casting shrinkage of molten titanium.7In 2007 Ferreira et al. measured the setting and thermal expansion of 3 phosphate-bonded investments: Rematitan Plus ( for titanium), Rema Exakt and Castorit Super C, using different special liquid concentrations. Silica-based phosphate-bonded investments exhibit a thermal expansion compatible with titanium casting shrinkage, but the silica is highly reactive at high temperatures.. Other thermally more stable refractory oxide materials (calcium oxide, magnesium oxide and aluminum oxide) have been developed, but they have shown thermal expansion unable to compensate for the casting shrinkage of molten titanium.. In 2007 Ferreira et al. measured the setting and thermal expansion of 3 phosphate-bonded investments: Rematitan Plus ( for titanium), Rema Exakt and Castorit Super C, using different special liquid concentrations. The heating temperature necessary to achieve an expansion equivalent to that of the Rematitan Plus (control group) at the temperature recommended by the manufacturer (430°C) was determined for these investments. The Rema Exakt and Castorit Super C investments achieved expansion equivalent to that of Rematitan Plus (430°C) at significantly lower temperatures
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