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ABSTRACT: Glass transition temperatures (Tg) determined at high rates of heating or cooling are essential for applications involving stress relief during cooling from firing of glass-to-metal seals and dental restorations. The measurement of Tg at heating rates as high as 600°C min−1 is reported. These high-rate data, when combined with previously reported low-rate (≤20°C min-1) values, indicate that the Arrhenius-type relation between Tg and heating or cooling rate is maintained into the high-rate regime.
Journal of the American Ceramic Society 06/2006; 68(2):C‐58 - C‐59. · 2.27 Impact Factor
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ABSTRACT: The effect on mechanical behavior of ZrO2 additions to a dental porcelain was investigated. The ZrO2 was introduced into the glassy matrix phase of the porcelain by refritting the all-glass porcelain constituent. X-ray diffraction indicated that a sizeable fraction of the ZrO2 was retained in the tetragonal form after the porcelain was fired. Zirconia additions to the porcelain produced substantial improvements in fracture toughness, strength, and thermal shock resistance.
Journal of the American Ceramic Society 03/2005; 69(4):C‐75 - C‐77. · 2.27 Impact Factor
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ABSTRACT: Fatigue in ceramics refers to the subcritical growth of cracks, aided by the combined influence of water and stress. The dynamic fatigue (constant stressing rate) method was used to obtain subcritical crack growth parameters for three dental ceramics: a feldspathic porcelain, an aluminous porcelain, and a fine-grain, polycrystalline core material. The constant stressing rate experiments were carried out at 37 degrees C for all three ceramics in distilled water, and, for the feldspathic porcelain, in artificial saliva as well. Considerable differences were found in the value of the crack growth exponent (n) among the three ceramics. The feldspathic porcelain was lowest in n-value, while the fine-grain ceramic had the highest n-value. No differences were found for the feldspathic porcelain with respect to n measured in water and in the artificial saliva. Lifetime prediction curves in 37 degrees C water, constructed from the n-values and inert strengths, showed that fatigue failure within five years is a good possibility for feldspathic porcelain specimens at stress levels which can reasonably be anticipated to occur in the oral environment. Little likelihood of failure was perceived for the fine-grain ceramic. The aluminous porcelain was intermediate between these two materials with respect to failure probability.
Journal of Dental Research 08/1986; 65(7):993-7. · 3.49 Impact Factor
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Dental Materials 05/1986; 2(2):58-62. · 3.13 Impact Factor
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ABSTRACT: The glass transition temperature (Tg) of a dental porcelain is a factor in determining the magnitude of residual stresses introduced in a dental porcelain during cooling of a porcelain-fused-to-metal prosthesis. Tg is known to vary with changes in heating or cooling rate. However, available commercial instrumentation does not permit Tg to be obtained at the very high cooling rates commensurate with actual dental laboratory practice. Tg values are reported here for a number of commercial dental porcelains and other materials. These data were obtained by the bending beam technique, employing a special low thermal-mass furnace to permit rapid heating and cooling rates. Measurements were made at rates as high as 600 degrees C/min. Coefficients of determination (r2) for 1/Tg vs. ln (heating rate) were excellent. This relation is consistent with previously reported low rate Tg data obtained by a different technique.
Journal of Biomedical Materials Research 04/1986; 20(3):293-300.
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ABSTRACT: Ceramic materials suffer from a number of limitations which restrict their use in dental restorations. Chief among these shortcomings is their extreme brittleness which is manifested as a low ability to absorb elastic strain energy during structural failure. This property is embodied in the material parameter, fracture toughness or KIC. The fracture toughness values of two types of dental porcelains, the feldspathic and aluminous porcelains, were determined by the indentation technique. The aluminous porcelains were significantly tougher than the feldspathic porcelains. These differences in KIC were attributed to differences in the nature of crack-microstructure interaction occurring in the two types of porcelain.
Dental Materials.
