Dentin Porcelain Research Articles

The influence of alumina abrasion and cement lute on the strength of a porcelain laminate veneering material

The purpose of the current study was to examine whether alumina abrasion regime influenced the necessary surface roughness conducive to mechanical interlocking prior to composite resin bonding. The impact of alumina abrasion and cement lute on the bi-axial flexure strength and associated Weibull Moduli (m) on the cemented surfaces of disc specimens of porcelain laminate veneer (PLV) materials was therefore investigated. Sets of 20 Vitadur-alpha dentine porcelain discs (15 mm diameter, 1.7 mm thickness) were condensed and prepared by abrading with 25, 50 or 110 microm alumina. Further specimen groups were stored wet or coated with a resin cement. Mean fracture strengths, standard deviations and associated m were determined using a ball-on-ring assembly. The surface roughness was assessed using profilometry and scanning electron microscopy. The one-way ANOVA revealed a significant reduction (P<0.05) between the means of the dry control and alumina abraded specimens. A significant increase in m was identified for 50 and 110 microm alumina abraded cemented specimens (6.1+/-1.4 and 6.0+/-1.3, respectively) compared with the 25 microm alumina abraded cemented and non-alumina abraded cemented controls (3.9+/-0.9 and 3.5+/-0.8, respectively). Increasing the alumina particle size utilised for the abrasion resulted in a decrease in the surface roughness (R(a) value) which is the arithmetic mean of the absolute departures of the roughness profile from the mean line. Alumina abrasion acted to replace surface defects with a narrower distribution of defects. Composite resin polymerisation shrinkage may prevent surface flaws from being extended by healing the key surface defects and would appear to suggest that the use of a resin-based luting material may reduce the potential for crack propagation. Given the arrangement of ions across crack tips it is more likely that the resin composite cement enhanced strength by acting to heal key defects rather than imposing a compressive stress on the porcelain surface as suggested previously.

Comparison of the load at failure of soldered and nonsoldered porcelain- fused-to-metal crowns

Statement of problem The application of solder material to metal frameworks could affect the porcelain-to-metal failure load and possibly compromise the longevity of porcelain-fused-to-metal crowns. Purpose This in vitro study assessed the influence of solder on the porcelain failure load between metal and porcelain, using crown-shaped specimens. Material and methods Forty standardized crown patterns were fabricated on a metal die and cast with noble alloy (Protocol). The specimens were divided into test (soldered, n=20) and control (nonsoldered, n=20) groups. A 2-mm–diameter perforation was produced on the buccal surface of the test specimens, 1.5 mm apical to the junction between occlusal and buccal surfaces. The perforation was repaired with high-fusing white ceramic solder material. All castings were finished with aluminum oxide stones and airborne-particle abraded with 50-μm aluminum oxide at 75 psi of pressure. Two layers each of opaque and dentin porcelain were applied on all specimens. All crowns were subjected to a vertical compressive load with a universal testing machine at a crosshead speed of 0.5 mm/min until fracture. The loading apparatus of the device contacted the buccal cusp only. In both control and test groups, 10 crowns were loaded with a stainless steel pin (phase I) whereas the remaining 10 in each group were loaded with a carbon steel pin (phase II). Means of loads at failure were recorded in each group for each pin type and compared (soldered vs nonsoldered) by use of a t test (α=.05). Results Mean failure load for nonsoldered crowns was 349 ± 63 kgf in phase I and 228 ± 49 kgf in phase II. Soldered crowns showed a significantly lower failure load (265 ± 82 kgf [phase I; P<.02] and 154 ± 108 kgf [phase II; P<.04]) and a greater standard deviation. Conclusion Soldered metal-porcelain crown specimens demonstrated a significantly lower load at failure. Within the limits of this study, it was concluded that solder material might negatively affect porcelain-metal crowns.

The influence of cement lute, thermocycling and surface preparation on the strength of a porcelain laminate veneering material

Objectives. The purpose of the current study was to examine the impact of thermocycling on the development of surface flaws on the cemented surfaces of PLV restorations prepared by acid-etching or alumina (Al 2O 3) abrasion. Methods. Sets of 30 Vitadur-alpha dentin porcelain discs (15 mm diameter, 0.9 mm thickness) were prepared by either abrading with 50 μm Al 2O 3 or hydrofluoric (HF) acid-etching. Further specimen series were coated with a resin luting cement prior to thermocycling to simulate the conditions encountered ‘in service’. Mean fracture strengths, standard deviations and associated Weibull moduli ( m) were determined using bi-axial fracture (ball-on-ring). Results. The two-way ANOVA revealed significant differences between the mean strength values of the porcelain specimens abraded with 50 μm Al 2O 3 compared with the higher strength HF acid-etched specimens. Significant differences were also identified in the mean fracture strength data for the abraded cemented and acid-etched cemented groups with the abraded groups recording the highest strength levels. Significance. Composite resin polymerisation shrinkage may help to strengthen porcelain surfaces by imposing a compressive stress on the porcelain surface. However, the strength of the HF etched cemented groups when bonded to composite resin were weaker than abraded specimens. Etching the porcelain does not only provide the necessary surface roughness conducive to mechanical interlocking but would appear to have a weakening effect on the porcelain surfaces.

The influence of interfacial surface roughness on bilayered ceramic specimen performance

Objectives. The aim of the current study was to assess the influence of interfacial surface roughness on the performance of bilayered ceramic composite disc-shaped specimens. Methods. Specific surface flaw distributions were introduced to a series of standard aluminous core porcelain disc specimens (12 mm diameter, 1.7 mm thickness) prior to bilayering with dentin porcelain. Mean flexure strengths, standard deviations and associated Weibull moduli ( m) were determined using bi-axial flexure (ball-on-ring) for each series of 30 bilayered specimens. Results. The mean bi-axial fracture strengths of bilayered specimens resulted in significant differences between specimen groups with the smoothest interfacial roughness recording the highest strength and fracture strength reliability. Specimen delamination was identified in five of the bilayered group with the smoothest interfacial roughness compared with no specimen delaminations in the rougher interface groups. However, fracture occurred in the weaker dentin layer rather than along the interface between the dentin and core porcelain for specimens in these rougher interface groups. Conclusions. A smoother interfacial surface roughness resulted in increased performance, namely increased strength and reliability amongst the bilayered dental ceramic composite specimens examined in the current investigation. The incidence of complete or partial delamination of the reinforcing core and aesthetic dentin was increased for these specimens since the reduced tortuosity of the interface between porcelain layers fails to restrict propagation of a crack front along the interface.

Effects of acid hydrolysis and mechanical polishing on surface residual stresses of low-fusing dental ceramics

Statement of problem Cracks may arise in a ceramic restorative material over time, resulting in sudden fractures at stresses well below the yield stress. Purpose This study evaluated by means of indentation technique the effects of acid hydrolysis and mechanical polishing on the surface residual stresses of low-fusing ceramic materials. Material and methods A total of 64 ceramic bars were formed to produce 4 groups of 16 bars each for 4 ceramic materials (Duceram-LFC Dentin, Duceram-LFC Enamel, Finesse Dentin, and Finesse Enamel). Four surface-treatment groups (n=4) were then formed for each of the 4 materials. The 4 surface treatments were control (autoglaze), hydrolysis, glaze/polish, and polish/glaze. A Vickers indenter contacted the Duceram-LFC specimens with a 5-N load and the Finesse specimens with a 3-N load for 10 seconds. Scanning electron microscope (SEM) was used to study surface texture before and after hydrolysis and polishing. Differences in mean crack lengths were analyzed with 1-way analysis of variance and least significant difference test (α=.05.) Results SEM showed obvious surface flaws as a result of hydrolysis on Duceram-LFC Enamel and Dentin specimens. However, statistical analysis of the resulting crack lengths revealed no significant differences between values for the control groups (58.16 ± 3.88) (53.53 ± 2.67) and hydrolysis groups (57.11 ± 4.09) (54.54 ± 3.15) for Enamel ( P=.081) and Dentin ( P=.093) respectively. When comparing polished groups and nonpolished groups, the mean crack lengths were significantly shorter for polished specimens of Duceram-LFC Enamel (53.76 ± 3.17), Finesse Enamel (40.56 ± 3.31), and Finesse Dentin (39.76 ± 3.81) porcelains compared with their control groups (58.16 ± 3.88) (43.54 ± 4.12) (41.19 ± 3.47), respectively ( P<.0001). The mean crack lengths were significantly longer for polished specimens of Duceram-LFC Dentin (59.16 ± 3.52) porcelain compared with the control group (53.53 ± 2.67) ( P<.0001). Conclusion Within the limitations of this study, hydrolysis did not improve surface residual stresses of Duceram-LFC and Finesse ceramic materials. Mechanical polishing improved surface residual stresses of all materials tested, except Duceram-LFC Dentin porcelain.

Mechanism of strength increase for a hydrothermal porcelain

Objectives. The objectives of this study were to verify the formation of a hydrolyzed surface layer on Duceram LFC, to determine the effects of such a layer on mechanical material properties, and to identify a specific mechanism responsible for any strength increase observed. Methods. Specimens were fabricated from dentin porcelain by a vibration blotting technique and were prepared to have either blunt or sharp surface flaws. Half of the specimens underwent accelerated aging. Specimens were fractured in three-point flexure to measure their strength, and fractographic analysis was used to determine fracture toughness and residual surface stress. Surface hardness and elastic modulus were measured using a microindentation method. Porcelain surface topography was examined using atomic force microscopy, and Fourier transform infrared spectroscopy was used to determine the composition of the surface layer. Results. The aging treatment modified the porcelain surface topography but did not create a layer with increased hydroxyl ion content. Porcelain strength increased upon aging, and the increase was proportional to initial flaw severity. The apparent fracture toughness of sharp flaw specimens increased to match that for specimens containing blunt flaws upon aging. Surface hardness and elastic modulus decreased upon aging. Significance. Previous studies on the strength increase of hydrothermal porcelain were contradictory because a variety of specimen preparation procedures were used. This study resolves the apparent contradiction by determining the effect of specimen preparation on material strength.

The effect of thermocycling on the strength of porcelain laminate veneer (PLV) materials

Objectives. Postoperative cracking and resultant failure of porcelain laminate veneer (PLV) restorations are considered a possible consequence of thermal variations that the restoration is likely to encounter ‘in service’. The purpose of the study was to examine the impact of thermocycling on the development of surface flaws on the ‘fit’ surface of PLV restorations. Methods. Sets of 30 Vitadur-Alpha dentin porcelain discs (15 mm diameter, 0.9 mm thickness) were thermocycled on the glazed and unglazed surfaces at three different temperature regimes to simulate the conditions encountered in service. Mean fracture strengths, standard deviations and associated Weibull Moduli (m) were determined using bi-axial fracture (ball-on-ring). Results. The student- t-test analysis revealed a significant difference ( P<0.05) between the porcelain control group mean strength values exposed on the glazed and unglazed surfaces. The one-way analysis of variance revealed no significant differences between the means of the porcelain specimens exposed to different thermocycling regimes. However, a discontinuity existed at the lower strength values in the survival probability plots for porcelain specimen groups that were thermocycled. Significance. Large flaws on the surface of the specimens may become extended due to the thermocycling regimes imposed. The greater the tensile stresses imposed on the disc specimen surface by the thermocycling regimes employed the more likely the flaws are to become extended resulting in premature fracture. Consequently, the discontinuity in the survival probability distributions may be attributed to a different defect mechanism (possibly an extension of large surface flaws) superimposed on the distributions at these low values of strength.

Effect of hydrolyzed surface layer on the cytotoxicity and chemical resistance of a low fusing porcelain

Objectives. The objectives of this study were to verify the formation of a hydrolyzed surface layer on Duceram LFC and to determine its effect on the cytotoxicity of the porcelain as measured by cellular activity and concentrations of leached ionic species. Methods. Specimens were fabricated from dentin porcelain by a vibration blotting technique. Half of the specimens underwent accelerated aging by subjecting them to the standard test for hydrolytic resistance (ISO 6872). Fibroblast cell cultures were placed in direct contact with specimens. Cell viability was assessed using succinic dehydrogenase activity. Chemical resistance was determined by leaching specimens with a continuous flow of deionized water and measuring the concentrations of soluble ions in the leachates. Porcelain surface topography was examined using atomic force microscopy, and Fourier transform infrared spectroscopy was used to detect the composition of the surface layer. Results. Hydrolyzation treatment created a smooth texture on the porcelain surfaces but did not result in a hydrolyzed surface layer with increased hydroxyl content. There was a decreased alkali ion content in the surface layer of hydrolyzed specimens. Mean cellular SDH activities for non-hydrolyzed and hydrolyzed porcelain were 75±7 and 80±5% of Teflon ® controls, respectively. Only sodium ions were present in significant concentrations in collected leachates. The sodium concentration decreased over the initial 4.5 h of leaching. Significance. The changes in surface layer texture and composition as the result of the aging treatment had little effect on the cytotoxicity and chemical resistance of Duceram LFC. The results suggest that Duceram LFC would pose no biocompatibility risk even after extended exposure to the oral environment. These data also provide baseline material properties to be used in future studies of the effects of porcelain additives.

Relative translucency of six all-ceramic systems. Part II: Core and veneer materials

STATEMENT OF PROBLEM All-ceramic core materials with various strengthening compositions have a range of translucencies. It is unknown whether translucency differs when all-ceramic materials are fabricated similarly to the clinical restoration with a veneered core material. This study compared the translucency of 6 all-ceramic materials veneered and glazed at clinically appropriate thicknesses. Core specimens (n = 5 per group) of Empress dentin, Empress 2 dentin, In-Ceram Alumina, In-Ceram Spinell, In-Ceram Zirconia, and Procera AllCeram were fabricated as described in Part I of this study and veneered with their corresponding dentin porcelain to a final thickness of 1.47 +/- 0.01 mm. These specimens were compared with veneered Vitadur Alpha opaque dentin (as a standard), a clear glass disc (positive control), and a high-noble metal-ceramic alloy (Porc. 52 SF) veneered with Vitadur Omega dentin (negative control). Specimen reflectance was measured with an integrating sphere attached to a spectrophotometer across the visible spectrum (380 to 700 nm); 0-degree illumination and diffuse viewing geometry were used. Measurements were repeated after a glazing cycle. Contrast ratios were calculated from the luminous reflectance (Y) of the specimens with a black (Yb) and a white backing (Yw) to give Yb/Yw with CIE illuminant D65 and a 2-degree observer function (0.0 = transparent, 1.0 = opaque). One-way analysis of variance and Tukey's multiple-comparison test were used to analyze the data (P<.05). Significant differences in contrast ratios were found among the ceramic systems tested when they were veneered (P<.0001) and after the glazing cycle (P<.0001). Significant changes in contrast ratios (P<.0001) also were identified when the veneered specimens were glazed. Within the limitations of this study, a range of translucency was identified in the veneered all-ceramic systems tested. Such variability may affect their ability to match natural teeth. The glazing cycle resulted in decreased opacity for all test materials except the completely opaque In-Ceram Zirconia and metal-ceramic specimens.

Relative translucency of six all-ceramic systems. Part II: Core and veneer materials

Statement of Problem. All-ceramic core materials with various strengthening compositions have a range of translucencies. It is unknown whether translucency differs when all-ceramic materials are fabricated similarly to the clinical restoration with a veneered core material. Purpose. This study compared the translucency of 6 all-ceramic materials veneered and glazed at clinically appropriate thicknesses. Material and Methods. Core specimens (n = 5 per group) of Empress dentin, Empress 2 dentin, In-Ceram Alumina, In-Ceram Spinell, In-Ceram Zirconia, and Procera AllCeram were fabricated as described in Part I of this study and veneered with their corresponding dentin porcelain to a final thickness of 1.47 ± 0.01 mm. These specimens were compared with veneered Vitadur Alpha opaque dentin (as a standard), a clear glass disc (positive control), and a high-noble metal-ceramic alloy (Porc. 52 SF) veneered with Vitadur Omega dentin (negative control). Specimen reflectance was measured with an integrating sphere attached to a spectrophotometer across the visible spectrum (380 to 700 nm); 0-degree illumination and diffuse viewing geometry were used. Measurements were repeated after a glazing cycle. Contrast ratios were calculated from the luminous reflectance (Y) of the specimens with a black (Yb) and a white backing (Yw) to give Yb/Yw with CIE illuminant D65 and a 2-degree observer function (0.0 = transparent, 1.0 = opaque). One-way analysis of variance and Tukey's multiple-comparison test were used to analyze the data (P<.05). Results. Significant differences in contrast ratios were found among the ceramic systems tested when they were veneered (P<.0001) and after the glazing cycle (P<.0001). Significant changes in contrast ratios (P<.0001) also were identified when the veneered specimens were glazed. Conclusion. Within the limitations of this study, a range of translucency was identified in the veneered all-ceramic systems tested. Such variability may affect their ability to match natural teeth. The glazing cycle resulted in decreased opacity for all test materials except the completely opaque In-Ceram Zirconia and metal-ceramic specimens. (J Prosthet Dent 2002;88:10-5.)

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°/0° configuration. Repeated-measures analysis of variance was used to evaluate within-group differences among the porcelain systems for the total color difference (ΔE) and direction of the color parameters (ΔL, Δa, and Δb). The Ryan-Einot-Gabriel-Welsch multiple range test was used for post-hoc analysis (α=.05). Results. The largest mean ΔE 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). (J Prosthet Dent 2002;87:657-66.)

Sintering of dental porcelain: effect of time and temperature on appearance and porosity

Objective: Mechanical condensation of powder-method dental porcelains can only achieve a limited effect—the majority of consolidation and porosity elimination is achieved by sintering. However, there is a surprising lack of information on the process in the literature, and the effects of the two basic conditions of sintering, time and temperature, are very poorly described despite theoretical expectations. The present study was to investigate the effects of these conditions on porosity and to consider its relationship to the recognizable firing stages of low and high biscuit, and other aspects of appearance, with a view to schedule recommendations. Methods: The variation of appearance, pore form and percentage porosity with sintering time and temperature was studied for five dental dentine porcelains, two aluminous: Alpha (Vita Zahnfabrik, Bad Säckingen, Germany) and Vitadur-N (Vita); and three feldspathic: Omega (Vita), VMK68 (Vita) and Carmen (Esprident, Ispringen, Germany). Disc specimens were sintered for 0–1000 min over 750–1100°C in a systematic search pattern to establish limits of acceptable appearance (high biscuit to not quite slumped). Porosity was measured using an image analyser on specimens fired for sintering times of 24 and 30 s; 1, 3, 6 and 30 min; 1, 5, 10, 15 and 20 h; with sintering temperatures from 750 to 950°C for Carmen and 800–1050°C for the others, all with 50°C increments. Measurements were made on a ground and polished surface (1 μm diamond), five fields on each of five specimens per condition. The percentage porosity, pore count, median pore area and pore size distribution were analyzed. Results: The boundaries of the acceptable appearance areas in maps of sintering temperature vs. sintering time were clearly delineated; analysis showed that they may be related to the activation energy of the diffusive processes occurring during sintering. Minimum porosity was obtained at high temperature and short time, close to but not consistently coincident with the manufacturers’ recommendations. There is also a conductivity-related minimum sintering time at high temperatures. The theoretical reduction on prolonging sintering at high temperature was not a general result, and porosity increased markedly in the feldspathic porcelains, particularly VMK-68. Significance: The reduction of porosity of dentine porcelain is much more sensitive to temperature than to time. It is possible systematically to identify optimum conditions using the present approach. Detailed study of the effects of formulation on the sintering process may be made by reference to the activation energy.

The CICERO system for CAD/CAM fabrication of full-ceramic crowns

The CICERO method of crown fabrication consists of optically digitizing a gypsum die, designing the crown layer buildup, and subsequently pressing, sintering, and milling consecutive layers of a shaded high-strength alumina-based core material, a layer of dentin porcelain, and a final layer of incisal porcelain. Final finishing is performed in the dental laboratory. The CICERO method allows efficient production of all-ceramic restorations without compromising esthetics or function. This article reviews the process involved in the fabrication of a CICERO crown. (J Prosthet Dent 2001;85:261-7.)

Evaluation of high-temperature distortion of high-palladium metal-ceramic crowns

Statement of problem. Crown fit is a prerequisite for long-term clinical success; however, crown distortion may occur during porcelain firing. The dimensional stability of some high-palladium alloys at high temperatures has been questioned. Purpose. The purpose of this study was to use a new method to measure the distortion of copings for metal-ceramic single units of selected high-palladium alloys with compositions representative of commercial alloys. Material and methods. Four high-palladium alloys containing copper and 3 containing no copper were tested. A palladium-silver alloy was included for comparison, and a gold-palladium alloy served as the control. By using reference points scribed on the margin, the mesiodistal and buccolingual margin diameters of identical copings were measured with a traveling microscope at 4 stages: as-cast, oxidized, after 2 simulated opaque porcelain firings, and after 2 simulated dentin porcelain firings. The margin distortions for the various specimen groups representing combinations of alloys, stages, and measurement diameters were compared with the use of 1-way analysis of variance and a multiple range test. Results. Most of the high-palladium alloys had high-temperature distortions that were not significantly different from those of the control alloy. The distortions occurred principally during the oxidation cycle. The effect of mesiodistal groove reinforcement on preventing distortion was not the same for all alloys. Conclusion. The results suggest that small observed distortions of these alloys will not produce clinical problems. Several laboratory techniques are available to counteract the distortions. (J Prosthet Dent 2001;85:133-40.)

Effect of soldering on metal-porcelain bond strength in repaired porcelain-fused-to-metal castings

Statement of problem. Chemical bonding plays a major role in the adherence between metal and porcelain. The formation of an oxide layer on solder material has not been described in the literature. It is unknown whether the application of solder negatively affects the bond strength between porcelain and metal.Purpose. This in vitro study assessed the effect of solder on the bond strength between metal and porcelain.Material and methods. Forty 20 × 6 × 0.5 mm patterns were divided into test (20) and control (20) groups. Test samples were perforated and repaired with solder, and 2 layers of opaque and dentin porcelain subsequently were applied on all samples. The samples were subjected to a 3-point flexural test on a screw-driven mechanical testing machine at a crosshead speed of 0.5 mm/min. Failure type (adhesive vs cohesive) was quantified by digitizing photographs of test and control samples. Three samples in each group also were examined with an SEM coupled with an x-ray energy-dispersive spectroscopy apparatus (SEM/EDS). Means and standard deviations of loads at failure, sample thickness, and surface area covered with porcelain were calculated, and data were analyzed with Student t test (P≤.05).Results. The mean fracture load for test samples was significantly greater than for control samples (P=.0038). Test samples also were significantly thicker (mean thickness difference 0.14 mm) (P=.0001). When the data were controlled for thickness by using a multiple linear regression analysis, no significant difference was found (P=.68). Test samples had a greater surface area covered with opaque porcelain (P=.0006) as determined by visual inspection.Conclusion. In this study, soldered and nonsoldered samples did not show any significant difference in porcelain-to-metal bond strength. Visual analysis revealed a significant difference in the amount of porcelain remaining on the fracture surface of the test and control samples; a complete quantitative elemental analysis with SEM/EDS is in progress. (J Prosthet Dent 2001;85:88-94.)

An assessment of the influence of mixing induced variability on the bi-axial flexure strength of dentine porcelain discs and the implications for laboratory testing of porcelain specimens

Objectives: The proportions of dentine powder and modelling fluid employed to produce a “creamy” porcelain slurry consistency used in veneer construction are assessed by the technical experience of the operator so that variability is inevitable. The present study investigated the implications of mixing variability on the slurry consistency used in the manufacture of dentine porcelain disc specimens for laboratory testing. Methods: Vitadur-Alpha dentine porcelain was fabricated into disc specimens and the mean fracture strength, standard deviation and associated Weibull Moduli ( m) were determined by fracturing sets of 30 specimens prepared to different powder contents for a constant 0.33 ml of liquid using bi-axial flexure (ball-on-ring). Results: The strength data showed variation in magnitude and consistency ranging from 85.1±12.9 MPa ( m=7.2±1.3) at 0.82 g to 87.3±11.9 MPa ( m=8.0±1.5) at 0.91 g and 81.9±13.2 MPa ( m=6.7±1.2) at 1.0 g of powder. Increasing or decreasing the powder content of the slurry (compared with specimens condensed using 0.91 g of powder) resulted in an increase in porosity and a decrease in the apparent solid density. Significance: No significant decrease in the mean bi-axial flexure strength or reliability of the fracture strength data was identified for the slurry consistencies investigated, however, the results suggested that an optimum consistency existed wherein consistent reproducibility of test results was achieved. A comparison between materials can only be achieved if specimen preparation occurs consistently between test centres and therefore these results appear to have implications for the laboratory testing of materials.

Predicting porcelain thickness required for dental shade matches

Statement of problem. Production of a ceramic dental restoration that matches a target shade is dependent on porcelain thickness. Even when adequate porcelain thickness exists, clinical shade matches are difficult to achieve. Purpose. This study predicted the thickness of dentin porcelain required to obtain a clinical shade match (≤3 ΔE units) for a variety of dental porcelain systems and shades. Material and methods. Three all-ceramic crown systems (Empress, Inceram-Alumina, Inceram-Spinell) and 2 metal ceramic systems (Vintage, VMK-95) were evaluated, each in shades A1, A3, and C2. Five specimens of each porcelain, of each shade, were fabricated at thicknesses of 1.0, 1.2, 1.5, and 2.0 mm. CIE-LAB coordinates were recorded for each specimen, and for the midgingival third of corresponding shade tabs with a Minolta CR-321 colorimeter. Results. Seventy percent of the color difference between specimen and shade tab was due to high L* (Munsell value) in the specimens. At thicknesses of ≤2.0 mm of dentin porcelain, the all-ceramic systems exhibited more shade matches than the metal ceramic systems. Conclusions. Specimens made from semi-translucent all-ceramic systems exhibited clinical shade matches that were superior to those made with the metal ceramic systems. Increasing thickness of the semi-translucent systems from 1.0 to 2.0 mm did not improve shade matching. (J Prosthet Dent 1999;82:143-9.)

Wear of low-fusing dental porcelains

The resistance of wear of dental porcelains is of concern when selecting a material for metal-ceramic and all-ceramic restorations. 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. 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. 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.

オールセラミッククラウンの色調発現に層構成が及ぼす影響

The purpose of this study was to fabricate all-ceramic crbwn with a target color. The color of all-ceramic crown was analyzed by measuring the color of all-ceramic specimens made by the refractory model technique (G-Cera), and lost wax technique (IPS Empress). The ceramometal specimen was used for the target color. The color of all-ceramic specimens was measured with a small area colorimeter by translucent and reflecting methods and evaluated by the CIE L* a* b* color system.The results were as follows:1. The color of each system was different, though the same shade of porcelain was used. Both systems showed lower L* and higher b* than the target color.2. The layer of enamel porcelain had an influence on the L* value, and the layer of dentine porcelain had an influence on the L* and b* values.3. The system using the layering technique had greater changeability of colors than the system using the lost wax technique.4. It can be concluded that the luminous value must be adjusted after reproducing the yellowness to fabricate all-ceramic crown with the target color.

陶材焼付鋳造冠の裏装金属色遮蔽効果に及ぼすオペーク・デンティン陶材の厚さの影響

The purpose of this study was to examine the influence of various thicknesses of opaque and dentin porcelain on the color of ceramometal restorations. A spectrophotometer was used to measure the color of the specimens and the color differences were calculated to determine the masking effect on the metal base color. The masking effect of the opaque porcelain (Vita shade A 1) fired on seven commercial ceramic alloys was different for each alloy. 86.5%-gold-content alloy specimens with 0.3-mm thickness of opaque porcelain demonstrated the maximum masking effect of the opaque single-layer. The masking effect of the opaque-dentin double-layer specimens was different for thickness and shade of porcelain. Palladium-silver alloy specimens with 0.2-mm thickness of opaque porcelain and 1.2-mm thickness of dentin porcelain demonstrated the maximum masking effect of double-layer of shade A 1. 52.5%-gold-content alloy specimens with 0.2-mm thickness of opaque porcelain and 1.2-mm thickness of dentin porcelain demonstrated the maximum masking effect of double-layer of shade C4.