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PubMed2006

Changes in optical properties of enamel porcelain after repeated external staining.

STATEMENT OF PROBLEM: After staining a porcelain restoration, increasing the lightness (value) and decreasing the chroma of a restoration is not practically easy to accomplish. PURPOSE: The purpose of this study was to determine the color change of enamel porcelain after repeated external staining procedures over the enamel porcelain surface. Changes in translucency and differences in surface roughness were also measured. MATERIAL AND METHODS: Enamel porcelain (VITA OMEGA 900 Metal Ceramics) disks (1 x 12 mm) of 1 shade (EN2) were prepared, and 1 of 4 types of external stains (VITA Akzent stains) was applied over the specimens and fired. Firing was repeated 3 times after application of the same stains. Color of the specimens before and after stainings was measured with a reflection spectrophotometer. Two-factor repeated-measures analysis of variance with the fixed factors of the stain type and number of staining cycles for the changes in CIE L(*), CIE a(*), CIE b(*), color (DeltaE(*)(ab)), and chroma (DeltaC(*)(ab)) after repeated staining was performed (alpha=.05). Chroma change was calculated as DeltaC(*)(a)=(Deltaa *(2) +Deltab *(2))(1/2). Changes in translucency (translucency parameter and masking effect) and difference in surface roughness (Ra) after the third staining cycle were also determined. RESULTS: Color change after the first staining cycle was perceptible (DeltaE(*)(ab) >2) for 2 of 4 types of stains and was perceptible for all 4 types of stains investigated after the third staining cycle (DeltaE(*)(ab) = 2.36-11.04). Lightness generally increased, and chroma also increased after staining but varied by the type of stains and number of staining cycles. Translucency generally decreased after repeated staining. Surface roughness varied by the type of stain (P < .001). CONCLUSION: Color difference and lightness increased significantly after repeated staining cycles, but chroma change was small after repeated staining cycles. Therefore, repeated staining may be a method to increase the lightness of enamel porcelain.

Color↗
PubMed1982

A critical evaluation of Bernhard's EDTA regressive staining technique for RNA.

The EDTA regressive staining procedure to detect RNA (Bernhard's technique) is based on the proposition that after staining ultrathin sections with uranyl the stain is preferentially removed from DNA rather than RNA by the action of the chelating agent EDTA. Whilst attempting to use the EDTA regressive staining procedure to detect the presence of RNA in the large granule complexes of chicken erythrocyte nuclei, certain anomalous staining patterns were observed in the chromatin of these nuclei. Essentially, these were that the edges of condensed chromatin bodies stained positively for RNA even though this molecule is known not to be present there in significant quantities. The staining patterns suggested that chromatin was retaining its stain in a manner expected of RNA but not DNA as a consequence of EDTA-containing species failing to pass freely through the section. This hypothesis was tested by carrying out the EDTA procedure on embedded specimens of a DNA-containing virus, simian virus 40 (SV40), small enough not to be exposed at the surface of the section. In this way it has been shown that virus particles completely surrounded by resin destain so much more slowly than chromatin, which is accessible at the surface of the section, that without any other information it would be concluded that the viruses contained RNA, not DNA. This apparently anomalous result arises because the difficulties encountered by stain or EDTA molecules in passing through a plastic section were not appreciated at the time of the initial publication of the technique. The observations are discussed in the light of recent knowledge that has been gained on the kinetics of staining by measuring the electron-scattering densities of stained sections, similar measurements having been made on sections stained by Bernhard's technique. A model for the mechanism of the EDTA regressive staining technique consistent with the experimental observations is proposed and the conditions under which Bernhard's staining procedure retains its specificity are defined. Briefly, these conditions are that: (a) the sections be stained for only a short period with uranyl before treating them with EDTA even though such brief staining is undesirable for quantitative measurements of stain uptake into biological material; and (b) that sections stained in lead only be compared as controls with sections stained by Bernhard's technique so that any specificity of lead for sub-cellular components is not confused with a positive indication of the presence of RNA. Unless these conditions are fulfilled, results obtained by the use of the regressive staining technique may be highly misleading.

Animals↗
PubMed1985

Standardization of dyes and stains for automated cell pattern recognition.

An extensive review is presented of the various factors involved in the standardization of dyes and stains for cytologic material, which is a crucial point in achieving objective and reproducible measurements of cells for recognition by automated microscopy (high-resolution cell image analysis; automated cell pattern recognition [ACPR]). Two principal methods of standardization are considered at length: (1) standardization based on the physical and chemical characterization of the dyes (physicochemical standardization), as adopted by the German Bureau of Standards, and (2) standardization based on direct visual assessment of stain performance (performance standardization), as adopted by the United States Biological Stain Commission. The procedures, achievements and problems of both methodologies are discussed, as are such related matters as staining time, solution pH, etc., especially with regard to the two most important stains in diagnostic cytology: the Papanicolaou stain and the Romanowsky-Giemsa stain. The standardization of these two stains is considered in detail, with an eye towards their suitability for ACPR. The mechanisms of the staining results produced by these stains are examined, as are the extant problems with each. The Papanicolaou stain, while neither standardized nor stoichiometric, has proven to be of use in cytophotometry. Similarly, the Romanowsky-Giemsa stain, while standardized, is also not a stoichiometric stain. Yet both have been successfully used in some aspects of ACPR; no "ideal" stain has yet been found that would make cell samples ideally suited for machine evaluation. It is concluded that the standardization of biologic dyes and stains, which can contribute to the success of ACPR, should be undertaken by multidisciplinary expert panels, in which the current concerned organizations could play a role. It is also concluded that ACPR may, in fact, contribute to the standardization of dyes and stains: that computer-directed morphometry and automated image analysis with sophisticated statistical analysis may become major tools in the validation of data on staining. For example, computer analysis could be used to pinpoint the particular variant of the Papanicolaou stain that leads to the best overall reproducibility of cell descriptors, in effect achieving "preliminary standardization by computer judgment of stain performance."

Adjuvants, Pharmaceutic↗