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Results for “DENTAL PORCELAIN”

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At least 109 records · Page 6Linked to original sources
PubMed1992

A common origin for dental porcelain derived from an accused's hand and the decreased victim of an assault.

A small, solid fragment removed from a wound on a hand of a murder suspect was submitted to electron microprobe analysis and found to have the properties of dental porcelain. A sample of porcelain removed from the dental bridge of the deceased had an essentially similar elemental profile. This investigation assisted the Court by providing valuable objective evidence of a physical contact between the accused and the victim.

Adult↗
PubMed1981

[Studies on sintering of dental porcelain. (Part 1) Binary system sintering of alumina and low fusing frit (author's transl)].

Dental porcelains were made from frit and glass powder with electro fused alumina powder addition in the range from 20 to 60 wt% using sintering method at the temperature from 500 degree C to 1 000 degree C, and the effects of alumina content and firing temperature on firing processes of sintered composite were investigated. Shrinkage curves of the powder compacts varied with kind of frit and content of alumina. Particulary, powder compact with alumina addition in the range from 50 to 55% was found to have a remarkable influence for extention of firing temperature range. The densification of the powder compacts was considered to be accelerated by the dissolution of a small a mount of alumina particle into the frit and glass above 900 degree C. Expansion coefficient value of sintered composite of alumina and Pyrex glass powder gradually increased with increase of alumina content. Inversely, expansion coefficient of soda-lime-silica glass showed the minimum value at 40 wt% alumina content and then had a tendency of slight increases with increase of alumina content.

Aluminum Oxide↗
PubMedDate not supplied

Compositional influence on the strength of dental porcelain.

This work compared the tensile strength of two glass compositions with published values of currently available dental porcelains. The influence of several variables, such as air and vacuum firing, firing temperature, surface roughness, immersion in water, and the inclusion of filler particles, on the inherent strength of the glass compositions is also discussed. The authors developed a glass frit having a tensile strength of 102.4 MPa as determined by the biaxial flexure technique. This value compares favorably with the reported strength of commercial brands of feldspathic porcelains. The strength of this glass was not significantly reduced as a result of surface abrasion or immersion in distilled water.

Aluminum Oxide↗
PubMed2002

Variation in color between intended matched shade and fabricated shade of dental porcelain.

STATEMENT OF PROBLEM: The total quantifiable color difference between shade matching and shade duplication has not been investigated formally. PURPOSE: The purpose of this in vitro study was to evaluate and compare the color difference of the total color replication process and the direction of the individual color parameters for 3 dental porcelain shade-matching systems. MATERIAL AND METHODS: The shade of 11 porcelain master disks was determined visually and instrumentally using 3 porcelain shade-matching systems: (1) Vita Lumin/Vita VMK 68, (2) Vitapan 3D-Master/Vita Omega 900, and (3) Shofu ShadeEye-EX/Vintage Halo. Corresponding porcelain disks made of 4.5 mm opaque and 1 mm dentin porcelain were fabricated with each of the porcelain systems. The colors of the master disks and fabricated disks (CIE L* a* b* coordinates) were measured with a spectroradiometer with a 45 degrees /0 degrees configuration. Repeated-measures analysis of variance was used to evaluate within-group differences among the porcelain systems for the total color difference (Delta E) and direction of the color parameters (Delta L, Delta a, and Delta b). The Ryan-Einot-Gabriel-Welsch multiple range test was used for post-hoc analysis (alpha=.05). RESULTS: The largest mean Delta E was recorded for the Vitapan 3D-Master system, which was significantly different from the other systems (P=.0024). A significant difference was found between the interaction of the different systems and the direction of color (P=.0024). The amount of change within each color parameter was dependent on the porcelain system, as well as the amount of change among the color parameters. CONCLUSION: Within the limitations of this study, the results suggest that reliable delivery of a properly matched restoration to existing porcelain restorations cannot be ensured regardless of the shade assessment method used (visual or computer-generated).

Algorithms↗
PubMed1999

Elimination, via high-rate laser dilatometry, of structural relaxation during thermal expansion measurement of dental porcelains.

OBJECTIVES: Thermal expansion measurement of glassy materials is complicated by thermal history effects. Excess volume--trapped in quenched dental porcelains after firing--collapses via structural relaxation on first slow heating during conventional dilatometry, making the thermal expansion coefficient (alpha) obtained on first heating unreliable. The purpose of this study was to determine whether porcelain thermal expansion measurement at high thermal rates could minimize the influence of thermal history. METHODS: Eight thermal expansion specimens each of six body porcelains and the Component No. 1 (leucite-containing) frit prepared according to the patent by Weinstein et al. (US Patent No. 3,052,982) were subjected to three heat-cool conventional dilatometry runs at 3 degrees C/min, while eight thermal expansion specimens of each porcelain were reserved as untreated controls. Eight hollow, cylindrical specimens of the same brands were subjected to three heat-cool laser dilatometer thermal expansion runs at 600 degrees C/min, while eight cylindrical specimens of each porcelain were reserved as untreated controls. Thermal expansion data (25-500 degrees C) of all specimens were subjected to repeated measures analysis of variance. RESULTS: The alpha obtained on first slow heating was significantly lower than values for succeeding slow heat and cool runs in all porcelains (P < 0.001). High-rate alpha obtained on first heating was not significantly different from values of succeeding heat and cool runs in all porcelains (P > 0.05). SIGNIFICANCE: Conventional dilatometer measurements demonstrated occurrence of structural relaxation, as evidenced by the significant difference in the first heating and subsequent runs. High-rate laser dilatometry eliminated structural relaxation, thereby providing a thermal expansion measurement that is free of interference from thermal history effects.

Analysis of Variance↗
PubMedDate not supplied

An investigation of an ion strengthening paste for dental porcelains.

The effect of a commercial ion exchange paste on the tensile strength of high- and low-expansion dental porcelains was investigated. Strength measurements were correlated with changes in surface chemistry. The paste was found to be more effective for aluminous porcelains than for an inlay ceramic, although only when applied to the surface placed in tension. Surface finish also influenced the effectiveness of the paste. The depth of ion exchange was assessed by energy dispersive x-ray analysis and was found to extend to at least 100 microns, although the most marked change occurred within a 10-microns layer below the surface.

Aluminum Oxide↗
PubMedDate not supplied

The structure and microstructure of dental porcelain in relationship to the firing conditions.

A scanning electron microscope and heating microscope are used to visualize the microstructure of dental porcelain during fabrication and demonstrate the relationships of the porcelain firing conditions to the translucency and hue of the completed restoration. The firing cycle, temperature, rate of temperature rise, holding time, and cooling time influence the distribution of the sintering, glass, and crystal phases in the microstructure of the porcelain. Observing the changes of fritted porcelain and opacifiers as they progress through the firing cycle demonstrates how the quality of the final ceramic restoration is largely dependent on the firing conditions chosen.

Color↗
PubMed1986

An analytical model to predict the effects of heating rate and applied load on glass transition temperatures of dental porcelain.

An analytical model was developed to predict the effects of heating rate and load on the glass transition temperature (Tg) of dental porcelain. An equation similar to the Moynihan equation relating heating rate to Tg was found for midspan load. The validity of the analytical model was demonstrated by using viscosity data from one published study to predict Tg behavior in an independent study. Values of Tg calculated with the analytical model for a dilatometer specimen were found to be higher than Tg values calculated for a bending beam viscometer.

Chemical Phenomena↗
PubMed1994

Bonding of low-fusing dental porcelain to commercially pure titanium.

The objective of the investigation was to study the basic problems related to the firing of dental porcelain to commercially pure titanium. The firing of a low-fusing porcelain to sandblasted or electrolytically polished titanium was carried out in an ordinary dental furnace. The interfacial regions between the ceramic coatings and titanium were analyzed using scanning acoustic microscopy (C-SAM) and scanning electron microscopy (SEM) techniques. Thermal stresses in the joints were evaluated by means of a finite element model based on multilayer elastic strain analysis. The chemical reactions and their formation sequence at 750 degrees C was predicted thermodynamically and observed experimentally both at 750 and 800 degrees C. The C-SAM results gave evidence that the integrity of the porcelain-titanium joints are better in the sandblasted samples than in the electropolished ones, where defects were larger. SEM analyses of the same samples confirmed the C-SAM findings. Because the reaction layers are more continuous in the electropolished samples, cracks propagated more readily in these samples during the cooling procedure. Both thermodynamic calculations and experimental chemical analyses strongly indicate that the cause for the cracking of the reaction zone is thin layer of Ti (oxo)silicide and/or a relatively thick solid solution layer of Ti and oxygen.

Dental Bonding↗
PubMed1990

Effects of instrument-measuring geometry on colorimetric assessments of dental porcelains.

Recent developments in optical electronic instrumentation for color control have made the potential use of clinical photometric analysis a future possibility for dental materials selection and custom restoration design. The development of such instrumentation will require a more complete understanding of the performance of current technologies on translucent materials. This study was designed to evaluate the effects of instrument-measuring geometry on color-difference assessments made on dental porcelains. The results indicate that a high degree of correlation can exist between color-difference measurements regardless of the design of the instrument-measuring geometry. This work suggests that the development of clinically useful devices need not be restricted to more traditional integrating-sphere-type designs and that more photometrically efficient alternative designs should be explored.

Colorimetry↗
PubMed2002

Quantitative analysis of dental porcelain surfaces following different treatments: correlation between parameters obtained by a surface profiling instrument.

This investigation compared, by quantitative analysis, the surface roughness of dental porcelain submitted to three different treatments (glaze, trimming and polishing), utilizing a surface profiling instrument. The parameters Ra (median roughness), Rz (median of the maximum profile heights of five sample lengths), Rpm (median of the maximum profile heights related to the median line of five sample lengths), Pc (peak count per centimeter) and Rpm/Rz (proportional parameter) were evaluated. In addition, the correlation between Ra and the other parameters was analyzed. Based on the results obtained, it was seen that the Ra parameter did not present any correlation with the other parameters in some of the situations evaluated. This demonstrates that complementation of the measurement with other parameters is always necessary, providing a better evaluation of the functional properties of a surface.

Analysis of Variance↗
PubMed1983

The three-point beam test for the evaluation of dental porcelain.

The three-point beam test is simple and extremely sensitive to surface conditions. It appears to be ideally suited to the evaluation of dental porcelain, but specimen fabrication is difficult. In this study, specimens of porcelain fired on platinum foil have been constructed using an alumina former. The results showed excellent specimen consistency and reproducibility. Of the surfaces investigated, the use of tin-oxide-coated platinum foil did not result in an increase in transverse strength.

Dental Porcelain↗
PubMed1975

[Elastic modulus of dental porcelains by dynamic method (author's transl)].

Using an equipment with sensitive vibretor-controller oscillater of elactrostatic drive system, we sought for the difference between elastic modulus of various kinds of dental porcelain and elastic modulus by firing method. We examined the relation between temperature of firing and elastic modulus as well. The obtained results are as follows: 1). Elastic modulus of low fusing porcelain of enamel color was 4.32 times 10(11) dyn/cm2 by air firing 3.95 approximately 4.63 times 10(11) dyn/cm2 by vacuum firing. Low fusing of porcelain of dentin color and the one of enamel color had the same elastic modulus. 2). Elastic modulas of high fusing porcelain of enamel color was 3.58 times 10(11) dyn/cm2 by air firing, 3.41 approximately 3.64 times 10(11) dyn/cm2 by vacuum firing. High fusing porcelain of dentin color and the one of enamel color were of the same elastic modulus. 3). Porcelain of opaque color for metal bond was 3.22 times 10(11) dyn/cm2 by air firing 3.97 approximately 4.22 times 10(11) dyn/cm2 by vacuum firing. When dentin color was added to opaque color elastic modulus was low (3.90 times 10(11) dyn/cm2). 4). Alumina porcelain of opaque color was 5.42 times 10(11) dyn/cm2 by air firing, 6.50 approximately 6.80 times 10(11) dyn/cm2 by vacuum firing. When dentin color was added to opaque color elastic modulus was very low (3.90 times 10(11) dyn/cm2). 5). Elastic modulus to various kinds porcelain changes according to temprature of fusing. And the highest elastic modulus is at the temperature which is 50 approximately 100 degrees C lower than final firing temperature.

Dental Porcelain↗