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PubMed1994

Isothermal anneal effect on microcrack density around leucite particles in dental porcelain.

Because of the large differential in thermal expansion coefficient between leucite and the surrounding glass matrix, microcracks form around the leucite crystallites during the manufacture of dental porcelain frits. These microcracks decouple leucite from the surrounding glass matrix and affect the bulk thermal expansion of the porcelain frit (Binns, 1983). The purpose of this study was to determine if the microcrack density in a dental porcelain decreased as a result of isothermal heat treatment. Ten specimens of a commercial dental porcelain that had previously exhibited an increase in thermal expansion as a function of isothermal heat treatment were prepared and divided into two groups. The experimental group was heated to 750 degrees C and held for 16 minutes at that temperature. The control group received no anneal. The mean microcrack densities were determined by quantitative stereology to be 575 cm2/cm3 +/- 75 cm2/cm3 (mean +/- SEM) for the control group (no anneal) and 231 cm2/cm3 +/- 25 cm2/cm3 for the experimental group (16-minute anneal at 750 degrees C). The specimens annealed at 750 degrees C had a significantly lower microcrack density (p < 0.001) than those that received no anneal. A model was developed to estimate the effect of microcracking on thermal expansion of the porcelain, and a 6% increase in the coefficient of thermal expansion of the porcelain was predicted from this model as a result of this decrease in microcrack density.

Aluminum Silicates↗
PubMed1989

A rapid heating and cooling rate dilatometer for measuring thermal expansion in dental porcelain.

Herein we describe a dilatometer that consists of a low-mass infrared furnace for rapid heating or cooling, an optical pyrometer, and a laser interferometer. The dilatometer facilitates observations of thermal expansion at rates comparable with those in dental laboratory practice over the temperature range necessary for comparison of thermal expansion of dental porcelain and alloy. Examples of thermal expansion data obtained at a 600 degrees C/min heating rate on NIST SRM 710 glass and dental porcelain are reported. To a limited extent, thermal expansion data above the glass-transition temperature range of dental porcelain were obtained. A shift of the glass-transition temperature range to higher temperatures was observed for both materials, compared with data obtained at 20 degrees C/min.

Chemical Phenomena↗
PubMed1990

Effects of zirconia addition on fracture toughness and bending strength of dental porcelains.

Zirconia dispersed composite porcelains with glass and aluminous porcelain as matrix were prepared as models of dental porcelains. The bending strength and fracture toughness of the composite porcelains were examined. The bending strength and fracture toughness of composite porcelains containing 50 wt% zirconia were 20 to 80% greater than in glass alone. However, bending strength and fracture toughness decreased upon the addition of zirconia at more than 50 wt%. Moreover, in the case of aluminous porcelain as matrix, fracture toughness increased to a maximum value of 2.6 M Pa.m1/2by addition of 23 wt% zirconia, twice the toughness of glass alone. On the other hand, no increase of bending strength was observed in this case. Deflection and bowing of cracks as well as microcracking effects were related to these increases of mechanical properties in zirconia dispersed composite porcelains.

Aluminum Oxide↗
PubMed1998

Depth-resolved Raman microprobe examination of a commercial dental porcelain exposed to a simulated oral environment.

OBJECTIVES: The specific aims were investigation of the chemical transformations into the interior of a commercial dental porcelain upon exposure to a simulated oral environment and identification of structural alterations that contribute to the strengthening of the porcelain. METHODS: Samples of a commercial dental porcelain, Duceram LFC, were exposed to refluxing dilute acetic acid for 0, 1, 5, 10, and 72 h to simulate exposure to the oral environment. The control and refluxed samples were examined using a depth-resolved Raman microprobe system covering the low (0-2550 cm-1) and high (2000-4000 cm-1) frequency ranges. Spectra were processed using exploratory factor analysis. Significant factors were retained, accounting for 99.999% of the variance. RESULTS: The porcelain was found to be significantly depolymerized prior to acid-refluxing. Exposure to water and to acid resulted in the formation of a better-ordered region near the surface. In that region, three intermingled zones of chainlike metaborate and pyroborate, of boroxol rings, and of a mixture of borate and silicate tetrahedra were identified. The borate/silicate factor was dependent on refluxing time. Hydroxyl groups were detected in all of the samples, but no changes to the hydroxyl environment were noted until after 10 or more hours of refluxing. Then, molecular water and isolated hydroxyls/SiOH were detected. After 72 h, an additional unassigned factor around 2800-2950 cm-1 was noted. SIGNIFICANCE: Acid refluxing causes generation of ordered boron-containing species near the surface of the porcelain.

Boron Compounds↗
PubMed2003

Relative wear of enamel opposing low-fusing dental porcelain.

PURPOSE: This study evaluated the wear of human enamel opposing 5 low-fusing dental porcelains and a traditional feldspathic control. In a second experiment, the repeatability of the test method and the effect of ceramic overfiring on enamel wear were also evaluated. MATERIALS AND METHODS: Five low-fusing dental porcelains--Finesse (FI), Rhapsody (RP), IPS d.Sign (DS), Omega 900 (OM), and Duceram LFC (LFC)--and 1 traditional feldspathic porcelain--VMK 68 (VMK)--were formed into disks (n = 10) and used as substrate for the wear test. Enamel was harvested from extracted human molars and machined into cusps with a 5-mm spherical radius (n = 60). The Oregon Health Sciences University oral wear simulator was used to simulate chewing and the size of the resulting enamel wear facets (in mm(2)) were evaluated after a specified number of chewing cycles. A portion of the experiment was duplicated to assess the repeatability of the data and determine the effects of overfiring on enamel wear. Data were subjected to analysis of variance and post hoc tests to determine significant differences. After wear testing, scanning electron micrographs were made using representative ceramic samples from each group. RESULTS: The results indicate that none of the low-fusing ceramics resulted in significantly less wear than the VMK control. In fact, 3 of the low-fusing porcelains (OM, RP, LFC) resulted in significantly greater enamel wear than VMK. Enamel wear was not significantly affected (p = 0.29) by the increased ceramic firing temperature. Wear data were repeatable, with no significant difference (p = 0.56) between the enamel wear from 2 separate experiments. The results from both experiments indicated that ceramic material significantly affected enamel wear (p <0.001). There was significantly less enamel wear opposite DS than LFC. CONCLUSIONS: This work suggests that variations in ceramic composition and microstructure may affect the opposing enamel wear, but that low-fusing temperatures do not necessarily guarantee low enamel wear. Although the clinical relevance of this testing apparatus may be questioned, the testing method was repeatable.

Aluminum Silicates↗
PubMed2004

Comparison of three systems for the polishing of an ultra-low fusing dental porcelain.

STATEMENT OF THE PROBLEM: With the introduction of newer dental porcelains, there exists the need to evaluate different porcelain polishing systems available on the market. PURPOSE: The purpose of this study was to compare the surface roughness produced by 3 different porcelain polishing systems on an ultra-low fusing porcelain. MATERIAL AND METHODS: Sixty-three ultra-low fusing porcelain (Finesse) discs (10 x 2 mm) were fabricated and randomly divided into 3 groups (n=21). Both sides of each disc were abraded with a medium-grit diamond bur. One side was autoglazed and was considered a control. The other side was polished until the surface appeared shiny to the naked eye using 1 of 3 porcelain polishing kits (Axis Dental, Jelenko, and Brasseler systems). The surface of each disc was evaluated quantitatively with surface profilometry and qualitatively using scanning electron microscopy (SEM). A mean roughness profile (Ra) value was determined for each side of each specimen to describe the overall roughness of the surface. The Ra mean difference for each specimen was determined by subtracting the mean experimental readings (polished surface) from the mean control readings (glazed surface) and was used for the statistical analysis. The data were analyzed using analysis of variance followed by a Tukey multiple comparison test (alpha=.05). Representative specimens from each group were evaluated by scanning electron microscopy. RESULTS: The Axis porcelain polishing system produced a smoother surface than the Brasseler or Jelenko systems (0.586 +/- 0.256, 0.306 +/- 0.238, and 0.277 +/- 0.230, respectively). No significant difference was found between the Jelenko and Brasseler porcelain polishing kits (F=10.6, P <.001). The images obtained through SEM were evaluated and found to be consistent with the profilometer readings. CONCLUSION: Within the limitations of this study, all 3 porcelain polishing systems produced a surface smoother than the autoglazed surface of Finesse. The Axis system provided a significantly smoother surface compared to the Brasseler and Jelenko polishing systems.

Air Abrasion, Dental↗
PubMedDate not supplied

Surface layer characterization after dual ion exchange of a leucite-reinforced dental porcelain.

The dual ion-exchange technique has been shown to improve the strength of feldspathic dental porcelains by first replacing constituent alkali ions with smaller ions above the strain point, and then exchanging the smaller ions for larger ions at temperatures below the strain point. The strength increase is directly related to the thickness of the surface-exchanged layer. This study evaluated the thickness of the exchanged layer after dual ion exchange of a leucite-reinforced dental porcelain. Optec HSP porcelain disks were fabricated, submitted to a dual ion-exchange treatment, and indented at various loads before determining the biaxial flexure strength. The mean flexural strength for the ion-exchanged groups was significantly higher than for control groups, except when the depth of the median crack exceeded 138 microns. Wavelength Dispersive Spectrometry analyses on cross sections showed that the mean potassium amount in the glassy matrix was significantly lower (P < .001) for the treated specimens than for the controls. The mean thickness of the exchanged layer after dual ion exchange was estimated at 140 microns.

Aluminum Silicates↗
PubMed1980

Translucency of dental porcelains.

The translucency of comparable shades of five dental porcelains was determined. Both direct transmittance and total transmittance were measured at wavelengths of 400-700 nm. For 1 mm of porcelain, the values for direct transmittance were low and averaged 0.13 percent, whereas the values for total transmittance averaged 26.8 percent. Transmittance increased with increasing incident wavelength. These results indicated a high degree of light scattering.

Color↗
PubMed1998

Estimation of residual stress in dental porcelain by laser-Raman spectroscopy.

Residual stress in the surface of dental porcelain was estimated using laser Raman spectroscopy. Sixteen different magnitudes of residual stress were generated in commercial porcelain disks by tempering, ion exchange, and slow cooling. The specimens were analyzed using a laser-Raman spectrometer with an Ar+ laser. The Raman shift of the largest peak near 500 cm-1 originating from silica was used as an indicator of the level of residual stress. For comparison, the residual stress in the specimen was estimated by the indentation micro-fracture method. The Raman shift of the porcelain increased with increasing residual stress at 3.7 x 10(-2) cm-1/MPa (R2 = 0.89). The increase in the Raman shift corresponded to the increase in compressive stress. In addition, the value of full width at half maximum on the peak corresponded to the residual stress (-1.57 x 10(-1) cm-1/MPa: R2 = 0.82). These results revealed that the increase of residual stress in porcelain clearly appears on the Raman spectrum as an increase in the Raman shift. It is thus feasible to estimate residual stress in porcelain by laser-Raman spectroscopy.

Aluminum Silicates↗
PubMed2003

Effect of surface topography on the color of dental porcelain.

The objectives of this study were to evaluate the color difference depending on the surface topography of roughness and glazing, and to determine the effects of color measuring geometry and the standard illuminant on the color of a dental porcelain. Disk specimens of A3 shade were fired with commercial dental porcelain for PFM. Specimens were divided into non-polished (ST 1), polished with 200, 400, 1000, 1500-grit SiC papers (ST 2, 3, 4, 5) and glazed (ST 6) groups. After measuring the average surface roughness (Ra), color was determined under the illuminant A and D65 on a spectrophotometer with the specular component excluded (SCE) and included (SCI) geometry. Ra values were significantly influenced by the surface topography. With the SCE, the CIE L* value after glazing was significantly lower than that after polishing. Color differences (DeltaE*) measured with the SCE were higher than those with the SCI (2.61-4.66 vs. 0.93-1.57). Therefore the SCE geometry seemed to more accurate protocol for the color measurement of dental porcelain.

Journal Article↗
PubMed2004

Indentation fracture toughness and dynamic elastic moduli for commercial feldspathic dental porcelain materials.

OBJECTIVE: The purpose of this study was to evaluate and compare the indentation fracture toughness, true hardness and dynamic elastic moduli for 14 commercial dental porcelain materials. METHODS: The specimens were fired according to manufacturer instructions. The density of the specimens (n=3) was measured by means of the water displacement technique. Dynamic Young's shear and bulk moduli and Poisson's ratio (n=3) were measured using a non-destructive ultrasonic technique using 10 MHz lithium niobate crystals. The true hardness (n=3) was measured using a Knoop indenter and the fracture toughness (n=3) was determined using a Vickers indenter and a Tukon hardness tester. Statistical analysis of the data was conducted using ANOVA and a Student-Newman-Keuls (SNK) rank order multiple comparative test. RESULTS: The SNK rank test analysis for the mean dynamic Young's modulus and fracture toughness was able to separate 14 dental porcelain materials into seven and nine groups, respectively, at p=0.05. The elastic moduli, true hardness and indentation fracture toughness for opaque porcelains were significantly higher than incisal; and body materials at p=0.05. SIGNIFICANCE: The indentation fracture toughness and the ultrasonic test methods exhibit lower coefficient of variation compared to conventional methods and have considerable advantage for ceramic dental materials in that only small specimens are required to produce an acceptable number of data for statistical analysis.

Aluminum Silicates↗
PubMed2001

[A study on the bond interface between low-fusing dental porcelain and pure titanium].

OBJECTIVE: To evaluate the bond interface between low fusing dental porcelain and pure titanium by observing the topography and detecting the ionic diffusion in the interface area. METHODS: The low fusing-porcelain La-porcelain produced by the authors or Vita Titankeramik porcelain was fused to the surfaces of pure titanium. The topography of the interface between pure titanium and porcelain, and the structure of experimental materials were observed with SEM. The state of ionic diffusion in the interface area was investigated with EPMA. RESULTS: Excellent permeation and diffusion of La-porcelain were observed on the surfaces of pure titanium. The diffusion of ions of stannum and silicon was discovered in the interface area. The microstructure of La-porcelain to pure titanium bond interface was finer than that of Vita Titankeramik porcelain. CONCLUSION: Excellent bond can be produced in the interface between La-porcelain and pure titanium. The bonding mechanism may involve mechanical bond and chemical bond. The ionic diffusion of stannum plays an important role in the bonding of porcelain to pure titanium.

Dental Alloys↗
PubMed2006

Difference in color and color parameters between dental porcelain and porcelain-repairing resin composite.

The objective of this study was to measure the differences in color and color parameters between dental porcelain and porcelain-repairing resin composites. The colors of three shades (A2, A3, A3.5) of one brand of dental porcelain, three original shades (A2, A3, A3.5), and three combinations (A2/A3, A3/3.5, A2/A3.5) of three brands of porcelain-repairing resin composites (ABT, FSP, TCR) were measured. The specimens were 2 mm thick, and 1 mm of each shade was layered to make combined shades. Differences in color (DeltaE(ab) (*)), lightness (DeltaL*), chroma (DeltaC(ab) (*)), and hue (DeltaH(*)) between porcelain and resin composite were calculated. Color difference was calculated as DeltaE(ab) (*) = (DeltaL*(2) + Deltaa*(2) + Deltab*(2))(1/2), chroma difference was calculated as DeltaC(ab) (*) = (Deltaa*(2) + Deltab*(2))(1/2), and hue difference was calculated as DeltaH(ab) (*) = (DeltaE(ab) (*2) - DeltaL*(2) - DeltaC(ab) (*2))(1/2). The influence of porcelain shade, brand of resin composites, and shade of resin composites were analyzed by three-way analyses of variance, and the differential influence of color parameters on color difference was analyzed with multiple regression analysis (alpha = 0.05). Differences in color and color parameters were influenced by the porcelain shade, brand and shade of resin composites. The DeltaE(ab) (*) value was in the range of 2.2-16.9. The DeltaE(ab) (*) value was correlated with DeltaC(ab) (*) (standardized correlation coefficient, beta = - 0.85), DeltaL* (beta = - 0.52), and DeltaH(ab) (*) (beta = 0.08). Between the same shade designated pairs of porcelain and repairing composite, color difference was perceptible. Therefore, studies to improve the color matching between porcelain and repairing resin are recommended.

Color↗
PubMed1980

The shear strength of dental porcelain.

The widespread use of porcelain in restorative dentistry is generally due to its esthetic appearance even though it is brittle. The transverse strength, or modulus rupture, averages around 108 MPa (16,000 psi) for aluminous porcelain and 88 MPa (13,000 psi) for feldspathic porcelain. The tensile strength, as determined by diametral compression, is approximately 29 MPa (4,200 psi) for opaque feldspathic porcelain and 40 MPa (5,800 psi) for gingival feldspathic porcelain. The compressive strength is reported to be 340 MPa (50,000 psi) for a feldspathic porcelain. These mechanical strength properties of dental porcelain confine its use to low stress-bearing restorations or to those restorations with a metal substrate.

Aluminum↗
PubMed1989

Effect of alumina concentration on the thermal diffusivity of dental porcelain.

The importance of the thermal diffusivity of restorative dental materials is well established. The laser flash method first described by Parker et al. (1961) is widely used to determine the diffusivity of industrial materials but has not hitherto been reported in the study of dental materials. The effect of the crystalline alumina content of dental porcelains has been investigated using this technique which permits rapid and accurate measurement. Values of 1.45 mm2/s and 0.66 mm2/s were determined for a commercial aluminous core porcelain and a dentine porcelain respectively. Mixtures of core and dentine powders exhibited intermediate levels. Increasing the alumina content resulted in increased diffusivity. The highest value was determined for a new high strength aluminous core porcelain which yielded a diffusivity of 1.74 mm2/s. This material was found to contain an increased concentration of alumina particles.

Aluminum↗