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At least 19 recordsLinked to original sources
PubMed2000

Strengthening mechanisms of current dental porcelains.

Dental porcelains have a high glass content, which provides the translucency necessary for esthetic restorations. Because glasses are brittle, they fail under tension or bending by the propagation of preexisting flaws (e.g., scratches, porosities). Several approaches that are based on impeding the propagation of flaws have been used to strengthen dental porcelains, including bonding to metals, adding microcrystalline phases, and surface treatments (i.e., polishing, ion exchange, hydration). Through these methods, porcelain systems are used routinely for all-ceramic anterior restorations; however, porcelain-fused-to-metal restorations remain the most reliable for posterior applications.

Crystallization↗
PubMed1983

Gel route preparation of low fusing dental porcelain frit.

Dental porcelain frits have been prepared by the gel route, a procedure involving solubilization of alkalies, boron, rare earth, and other compounds in an alumina-silica sol. Using this procedure, porcelain frits suitable for metal-ceramic application have been prepared that fire to maturity at temperatures lower than current commercial porcelains. Solubilities, translucencies, thermal expansion coefficients, dilatometric softening temperatures, and flexure strengths are within the ranges of current commercial porcelains. The high degree of dispersion of pigments and phosphors made possible by gel route technology and the technology's ability to disperse crystalline phases to strengthen porcelain offers many processing advantages. Gel route technology also offers a great degree of freedom in modifying porcelain properties.

Aluminum Oxide↗
PubMed2004

Study on the effect of Y2O3 addition to the fluorescent property of dental porcelain.

The appearance of dental porcelains is comparable to natural teeth. This study discusses the effect of Y2O3 addition to the fluorescent property of dental porcelains. The composition of dental porcelains contained Y2O3 as the fluorescent agent and base frit. The combinations of Y2O3 added consist of a series with 0.5, 1.0, 1.5, 2.0 and 2.5 wt% respectively, based on the total composition. In the extreme condition, fluorescent agents are added from 5.0 up to 10.0 wt%. In order to enhance the fluorescent property of dental porcelains, an opacifiying agent, cerium oxide (CeO2) was also added to dental porcelains composition. The fluorescent property was determined using Spectroline EF-1400C/F that emits 240 nm wavelength ultraviolet light. The microstructure was examined by Scanning Electron Microscope (SEM). The result shows that, the fluorescent properties displayed are similar to natural teeth when subjected to ultraviolet light. SEM micrograph was able to show the fluorescent agent dispersed in glass phase. Increasing additions of Y2O3 gave the fluorescent properties near to natural teeth.

Biocompatible Materials↗
PubMed2001

Evidence of a critical leucite particle size for microcracking in dental porcelains.

The leucite particles in dental porcelains are often partially encircled by microcracks that are the result of the thermal expansion mismatch between leucite and the surrounding glass matrix. Although the magnitude of the stress at the particle-matrix interface is independent of the particle size (Selsing, 1961), Davidge and Green (1968) showed experimentally that there is a critical particle size below which microcracking is absent. The critical particle size is explained by a Griffith-type energy balance criterion: Below the critical size, the stress magnitude may be sufficient to cause cracking, but there is insufficient strain energy for the creation of the new surfaces of the microcrack. The purpose of the present study was to determine whether the mean leucite particle size of a dental porcelain influences the degree of microcracking in the porcelain. Microcrack density, leucite particle surface area per unit volume, and leucite mean volume-surface diameter, D3,2, were determined by quantitative stereology on 10 specimens each of 6 dental porcelains and Component No. 1 of the Weinstein et al. patent (US Patent 3,052,982, 1962). The fraction of leucite particles with microcracks around them, f(mc), was estimated for each porcelain from the microcrack density and the leucite surface area. Using the equations of Selsing (1961) and Davidge and Green (1968), we calculated the critical particle diameter, Dc, for leucite to be 4 microm. The porcelains were partitioned according to whether their mean leucite particle diameters, D3,2, fell above or below Dc, and their values of f(mc) were analyzed by a permutation test with random re-sampling. The porcelains with mean leucite particle diameters below Dc had a significantly lower fraction of cracked particles compared with the porcelains with mean leucite particle diameters above Dc (p < 0.05). This study provides evidence that microcracking in dental porcelain can be minimized by a reduction of the mean leucite particle diameter to less than 4 microm.

Aluminum Silicates↗
PubMed2004

Influence of powder/liquid mixing ratio on porosity and translucency of dental porcelains.

STATEMENT OF PROBLEM: Dental technicians use a variety of techniques when condensing dental porcelains. It is unclear whether these techniques affect the total porosity and translucency of dental porcelains. PURPOSE: The objective of this study was to determine whether varying the powder/liquid ratio during condensation affects porosity and translucency of porcelains. Material and methods Duceram LFC dentin, Duceram LFC incisal, IPS Eris dentin, and IPS Eris incisal porcelains were studied. For each specimen, 1.0 g of porcelain powder was mixed with 1 of 3 different volumes of deionized water to form a slurry with a thin, medium, or thick consistency. The slurries were condensed in a plastic syringe mold, fired, and polished to a 3-microm finish to form 12 groups of 4 specimens each (14-mm diameter, 1.10-mm thickness). The apparent density (g/mL) of each specimen was measured using Archimedes method, and the porosity (%) calculated. Each specimen was coupled to standard ceramic tiles using an immersion liquid, and the color shade was measured in CIE Yxy coordinates using a tristimulus colorimeter. Translucency was assessed by calculating the contrast ratio of shade value (Y) in front of black versus white backgrounds. Two-way analysis of variance and Tukey's multiple comparison tests (alpha = .05) were used to test for significant effects of factors. RESULTS: Porcelain type and powder/liquid ratio had a significant interactive effect on the apparent density (P < .001) and on total porosity (P = .003); however, there was no consistent trend. The powder/liquid ratio did not significantly affect translucency (P = .28), but porcelain type had a significant effect on translucency (P < .001). CONCLUSION: In this in vitro study, total porosity of specimens prepared using 4 porcelains was found to be sensitive to powder/liquid ratio; whereas translucency was found to be insensitive to powder/liquid ratio.

Analysis of Variance↗
PubMed1998

Glazing and finishing dental porcelain: a literature review.

BACKGROUND: Dental porcelain has found an increased number of applications in recent years with the development of new methods for the construction of porcelain veneers and intracoronal restorations. In addition, it is used in metal-ceramic and all-porcelain crowns and bridges for the restoration of anterior and posterior teeth. METHODS: This paper presents a review of a number of studies that have examined the visual and microscopic appearance and roughness of glazed, unglazed and polished porcelain surfaces using techniques such as, scanning electron microscopy and surface profilometry. FINDINGS: All have agreed that glazed porcelain provides a smooth and dense surface. Many have shown that polishing can produce an equally smooth surface, which may even be esthetically better. Some studies supported the use of polishing as an alternative to glazing. However, reports have shown that unglazed porcelain is more abrasive than glazed. CLINICAL SIGNIFICANCE: This paper aims to guide general practitioners in the proper polishing of adjusted porcelain in the dental office. The recommendations of various authors are summarized in Table I.

Crowns↗
PubMed2004

Study on changing the coefficient of thermal expansion (CTE) of dental porcelain.

Raising the thermal expansion coefficient (CTE) of dental porcelains is important to match the CTE of the ceramic material with the higher CTE of the metal inlay in dental restorations. The higher thermal expansion of the leucite phase increases the overall thermal expansion coefficient of the dental porcelain. Potassium nitrate (KNO3) additions in controlled percentages to the base dental porcelain formulation help in the formation of a leucite phase. The percentage added was 5,10 and 20 weight percent of leucite, respectively, to the total base frit composition. The change in CTE values was then investigated using a Linseis Dilatometer. A 20wt% KNO3 addition resulted in a CTE of 9.0 microm/m-K compared to the 7.7 microm/m-K CTE of the base composition. The microstructures observed under the scanning electron microscope (SEM) show a multiphase material with the leucite phases dispersed within a glassy matrix. The results suggest that higher CTEs in the dental porcelain are possible by increasing the KNO3- additions within the limits tested.

Ceramics↗
PubMed1990

[Fluorescence of dental porcelain: material and methods].

Dental porcelain emits some fluorescence under the action of ultra-violet rays. This emission may be at the origin of errors in the choice of the colour of a crown. In order to study this fluorescence phenomenon, the following experimental protocol has been developed: 363.8 nm exciting radiation isolated from the emission by an Argon laser; Fluorescence emitted by the sample and dispersed via a spectrometer, protected by a stop-U.V. filter; Influx collected by a photomultiplier, then directed, after passage in a picoamperemeter, toward a mini-computer programmed to print the spectra; Correction of the spectra by a tungsten lamp used at the 2,600 K colour temperature; Use of reference spectra. On the same graph, the sample spectra are represented in solid lines, while the spectrum of the enamel used as a reference is shown as a dotted line. The results show that: Enamel has a fluorescence spectrum which has the shape of a wide band, with a maximum of 450 nm (characteristic of a blue-green shade) and a slow decrease up to 680 nm. The enamel fluorescence does not depend on the colour of the tooth; Dentine has a distribution spectrum which is similar to that of enamel but is three times fuller; The spectra of the ceramic samples reveal: a wide band due to transition metals, fine lines due to rare earth (terbium and europium). When the saturation degree of the ceramic increases, its fluorescence colour varies due to the relative increase in the amplitude of the lines in relation to the bands. Thus, when the sample colour progresses from B1 to B4, its fluorescence colour becomes greener.(ABSTRACT TRUNCATED AT 250 WORDS)

Color↗
PubMed1994

Leucite content of selected dental porcelains.

Leucite is a major crystalline component of dental porcelains. The presence of tetragonal leucite in dental porcelains increases their coefficients of thermal expansion due to its high coefficient of thermal expansion (20-25 x 10(-6)/degrees C). This is particularly useful for those porcelains designed for bonding to precious metals and nickel alloys. The purpose of this study was to determine the leucite content of selected commercial dental porcelains in relation to their coefficient of thermal expansion values. The weight fraction of leucite was determined with quantitative x-ray diffraction using copper as an internal standard. Coefficient of thermal expansion values were determined using a thermal dilatometric analyzer. Five commercial body porcelains were studied. Leucite was not detected in samples of Vitadur N and Duceram LFC. An ANOVA showed that there was a significant difference in the weight fraction of leucite for Silhouette, Ceramco II, and Optec HSP porcelains. Linear regression revealed a correlation (R = 0.91) between weight fraction of leucite and the coefficient of thermal expansion for those samples containing leucite. Duceram LFC, which is recommended by the manufacturer for use with metals and leucite-containing porcelains, had no detectable leucite although the coefficient of thermal expansion was found to be 13.2 +/- 0.4 x 10(-6)/degrees C at 25-472 degrees C. A low glass transition temperature contributed to the high average coefficient of thermal expansion value.

Aluminum Silicates↗
PubMed1991

[Positive identification of dental porcelain in a case of murder].

Dental prostheses can provide important evidence for use in personal identification. In recent years, the variety of materials used in prostheses has increased with the diversification of dental treatment. The detailed analysis of these materials can provide significant information to assist in personal identification. This paper reports a case when identification was achieved by the comparative analysis of fragment of fused dental porcelain. In April, 1990, a woman aged 24 years was found murdered in her apartment in Hamamatsu City, Shizuoka Prefecture. Near her body a small mass of fused porcelain was recovered. Subsequently, a 48 year old male suspect was arrested. An examination of his teeth revealed a small fragment of dental porcelain adhering to an abutment tooth. This was removed for testing. The suspect denied the charge of murder. A comparative analysis of the porcelain found in the apartment and the porcelain that was removed from the suspect's abutment tooth, was carried out by scanning electron microscopy (SEM) and electron probe X-ray microanalysis (EPMA). The SEM examination demonstrated remarkable similarity in respect of the structure of the porcelain and the nature and distribution of the air bubbles produced during the baking process in both samples. The EPMA showed the elemental composition of each sample to be identical. This case demonstrated that detailed analysis of dental materials may affords a useful aid for personal identification.

Adult↗
PubMed2000

'Fluxes' and chemical solubility in dental porcelains.

Materials such as sodium, potassium, magnesium, and calcium oxides are routinely added to glasses commonly called "fluxes." These materials act as modifiers that disrupt the network arrangement of atoms in glasses and are used to optimize their fusion, expansion, or chemical properties. Dental porcelains are made of glasses and ceramic components such as leucite. The international standards ISO 6872 and ISO 9693 mandate a chemical solubility test, in which a solubility limit (< 100 g/cm2 for the test) is set for dental porcelains. Dental porcelains that have passed this test are very stable in the oral environment and lose very small amounts of porcelain to dissolution by saliva. The oxides that leach from these porcelains are relatively benign, and are usually absorbed through the average diet in much larger quantities. In addition to these factors, the long and successful clinical history of restorations made out of dental porcelains is a strong argument for their safety and efficacy, when used in accordance to indications and recommended techniques.

Aluminum Silicates↗
PubMed1998

Cerium oxide as a silver decolorizer in dental porcelains.

OBJECTIVES: Silver-base alloys are known to produce an esthetically unpleasant yellow-green tint in the dental porcelain when making PFM restorations. Cerium oxide is used in dental porcelains to simulate the natural fluorescence found in human dental enamel, and has also been used in the glass industry as a decolorizer. The purpose of this study was to determine the effect of CeO2 additions on the resistance of dental porcelain to staining from silver contamination. METHODS: Five batches of porcelain were prepared according to Weinstein et al. (1962) with 0.00, 0.05, 0.10, 0.15 and 0.20 wt% additions of CeO2. To determine the resistance of these porcelains to silver staining, 0.10 wt% additions of the silver oxides were triturated into the prepared CeO2 porcelains prior to sample fabrication. This procedure provided a more quantitative method of staining than firing directly on silver alloys. Silver oxide was added in two valence states as Ag2O and AgO to test for any possible effects on staining. Samples were pressed into a 17 mm diameter mold, and fired to 960 degrees C under vacuum. Three additional samples were prepared from the non-cerium porcelain frit to produce a non-stained control group. Color measurements were made with a spectrophotometer on the ten experimental groups and the control group. The CIE L*a*b* color difference, delta E*, was calculated between the control and the experimental groups. RESULTS: There was a significant decrease in the silver staining of dental porcelains when CeO2 additions of 0.10 wt% or greater were used. SIGNIFICANCE: Cerium oxide additions in the range of 0.10 to 0.20 wt% caused a three-fold reduction in the staining of dental porcelain samples which had been doped with 0.10 wt% of AgO or Ag2O.

Analysis of Variance↗
PubMed1995

The effect of the dissolution process of hydroxyapatite added to conventional dental porcelain on its mechanical strength.

The use of phosphates in dental glasses and ceramics for the application as biomaterial is merging. Hydroxy apatite is characterized by its solubility in the oral fluids. Studying the effect of the dissolution process of hydroxy apatite added to conventional dental porcelain on its mechanical strength was our aim in this work. Five formulations were prepared from Egyptian raw materials and the mechanical strength of each investigated formulation was measured. It is found that addition of bone ash in amounts not exceeding 10% raised the tensile strength of the investigated dental porcelain. The rate of dissolution of dental porcelain containing bone ash increases with percentage of bone ash added, as the values of mechanical strength were lowered. The pH of the solution was affected by time of immersion. Calcium ions released from the dissolution of tricalcium phosphate readily react with silicon ions giving calcium silicate which render the solution alkaline.

Biocompatible Materials↗
PubMed1999

Wear of low-fusing dental porcelains.

STATEMENT OF PROBLEM: The resistance of wear of dental porcelains is of concern when selecting a material for metal-ceramic and all-ceramic restorations. PURPOSE: An in vitro investigation was performed to rank a number of dental porcelains with respect to their wear-resistance properties. Material and methods. The wear test of 9 dentin porcelains was carried out on a wear test machine and the amount of wear was measured as the reduction of height of the specimens. The surface hardness and surface roughness were also considered. RESULTS: Resistance of wear was lowest for Finesse porcelain, and highest for Creation porcelain. Surface hardness values of the porcelain were quite similar for all porcelains but could be classified into 3 groups with Finesses and Vita Alpha porcelains as the softest and Creation porcelain as the hardest material. CONCLUSIONS: The low-fusing porcelain Finesse showed less abrasion resistance in comparison with Ducera Gold and Ti-Ceram porcelains. Among the high-fusing types, Vita Alpha porcelain was more wear-disposed than the others.

Analysis of Variance↗
PubMed1996

Effect of cubic leucite stabilization on the flexural strength of feldspathic dental porcelain.

Previous studies (Mackert and Evans, 1993) have shown that, when feldspathic dental porcelain is cooled, leucite undergoes a transformation from cubic to tetragonal, associated with a 1.2% volume contraction. This contraction leads to the formation of microcracks in and around the crystals and the development of tangential compressive stresses around the crystals. Our aim was to stabilize increasing amounts of the cubic form of leucite in a leucitereinforced dental porcelain, evaluate its effect on the flexural strength, and characterize its microstructure. The hypothesis was that in the absence of crystallographic transformation, the contraction of the leucite crystals would be lower, thereby limiting the formation of microcracks and minimizing the development of tangential compressive stresses around the leucite particles. We prepared 8 porcelain compositions by mixing increasing amounts of either leucite (KAlSi2O6) or pollucite (CsAlSi2O6) with Optec HSP porcelain (Jeneric/Pentron Inc., Wallingford, CT). Porcelain disks were made from each composition (n = 10 per group). X-ray diffraction analyses showed that the amount of stabilized leucite increased with the amount of pollucite added. The microstructure of the specimens containing tetragonal leucite was characterized by twinned leucite crystals, whereas no twinning was observed in the specimens containing cubic leucite. The evaluation of crack deflection showed that significantly less deflection occurred in the specimens containing cubic leucite. The mean biaxial flexural strength for the group corresponding to 22.2 wt% added pollucite, fired at 1038 degrees C, was significantly lower than that for the control group. The group corresponding to 22.2 wt% added leucite fired at 1150 degrees C exhibited a mean biaxial flexural strength significantly higher than that of all other groups that were not significantly different from the control group. Overall, the stabilization of cubic leucite reduced the flexural strength and the number of crack deflections in leucite-reinforced porcelain. Apparently, the development of tangential compressive stresses around the leucite crystals when cooled is responsible for a significant amount of strengthening of feldspathic dental porcelain.

Aluminum Silicates↗
PubMed1986

Glass transition temperatures of dental porcelains at high heating rates.

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.

Dental Porcelain↗