Penetrativity of sealants: I.
Penetration coefficients of sealants were measured. It was found that the time required for a sealant to penetrate a specific distance is highly dependent on the penetration coefficient of the sealant.
Capillary Action↗
Biomedical subjects
W J O'Brien
Publications and source records attributed to W J O'Brien.
Fracture-surface analysis of a glaze-strengthened magnesia core material.
The purpose of this research was to study fracture initiation in a glaze-strengthened magnesia ceramic substance used as a core material for all-ceramic crowns. The fracture surfaces of modulus of rupture bars were studied to locate the fracture initiation point. These points were located at the center of hackles that are oriented parallel to the direction of the crack advance. The distance from the fracture initiation point to the surface of the test bars was measured. A direct relationship was found between the flexure strength and the depth of the fracture initiation point. This is consistent with the theory that residual compressive stresses at the glaze-body interface inhibit the spread of flaws and are responsible for the increases in strengths observed.
Crowns↗
Differences in color between fired porcelain and shade guides.
The inaccuracy of premixed porcelain shades may cause errors when color matching porcelain crowns. Most brands of porcelain are labeled to match shades of the Vita shade guide, but produce slightly different colors from this guide upon firing. The purpose of this study was to quantify in CIE delta E* units the color differences between the Vita shade guide colors and four commercial porcelains for metal ceramic crowns. Two operators prepared shade-guide teeth from six shades of four brands of porcelain. Opaque, body, and incisal layers were fired in the form of shade-guide teeth on Vita ceramic carriers used for making custom shade-guide teeth. The colors of these teeth were measured with a Beckman spectrophotometer with an integrating sphere. The average delta E* values for the differences between the colors of the Vita shade guide and the fired porcelains for each of the brands were 3.1, 2.9, 4.1, and 2.0, respectively, for the first operator and 4.1, 2.6, 2.8, and 1.6, respectively, for the second operator. The color difference between the custom shade-guide teeth and the Vita master shade guide were significantly affected by both brands and shades. The overall average error resulting from the differences in colors between the Vita shade guide and fired porcelains was 3.0 for the first operator and 2.8 for the second operator. The mean delta E* between the teeth prepared by the two operators was 3.6. The color difference between the teeth made by the two operators was not significantly affected by brands or shades.
Analysis of Variance↗
Coverage errors of two shade guides.
Dental shade guides contain a limited selection of colors compared to those found in human teeth. An error in shade selection is thus introduced, since many tooth colors must be defined by approximation to the nearest shade of the guide. The Bioform and Vita Lumin guides, and a combination of the two, were spectrophotometrically compared to the published colors of 335 human teeth. The minimum CIE L*a*b* color difference was calculated for each tooth using each shade guide. The average of these color differences was defined as the coverage error. The Bioform and Vita shade guide coverage errors were not significantly different, but the coverage error was significantly lower when the combination was used. The use of both guides in shade selection is recommended to reduce the coverage error.
Color↗
The strength of alumina and magnesia core crowns.
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Aluminum↗
Penetrativity and wetting of topical fluoride preparations: an in vitro study.
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Dental Enamel↗
Use of a dual filter-mirror device with a fluorescent plaque disclosant.
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Dental Devices, Home Care↗
Color differences coefficients of body-opaque double layers.
Porcelain restorations have double-layer color effects resulting from the presence of body and opaque layers. The purpose of this study was to quantify the color differences resulting when a defined thickness of body porcelain is fired on an opaque porcelain of the same shade designation and from the same porcelain brand. A color difference coefficient was defined as the color change resulting from a 1-mm-thick layer of body porcelain on an opaque porcelain of the same shade and brand. Six shades and four porcelain brands were evaluated in this study. The range of color difference coefficients for all shades and brands was 6.76 to 14.32. There was no significant difference between shades or between brands. The use of color difference coefficients is a practical method of evaluating porcelain shades and brands and should provide guidance in the choice of porcelains and the fabrication of porcelain restorations to better achieve the desired esthetics.
Color↗
Strength of magnesia-core crown with different body porcelains.
The diametral strengths of magnesia-core crowns made with different body porcelains, Will-Ceram, Crystar, Ceramco II, and Vita VMK 68, were measured. The results were compared to the diametral strengths of aluminous-core crowns and Renaissance crowns. A one-way analysis of variance showed that there were no significant differences in the strengths of magnesia-core crowns or the aluminous-core crowns, but the Renaissance crown strengths were significantly lower.
Aluminum Oxide↗