Porcelain Layer Research Articles

Influence of surface and heat treatments on the flexural strength of Y-TZP dental ceramic

The aim of the investigation was to assess the influence of sandblasting, grinding, grinding orientation, polishing and heat treatment on the flexural strength of a yittria stabilized tetragonal zirconia polycrystals ceramic (Y-TPZ). The specimens (160 beams) were equally divided into four groups according to the surface treatment (sandblasted, polished, ground parallel to the tensile axis, ground perpendicular). Twenty specimens from each group underwent heat treatment under the firing conditions used to fire a layer of porcelain and glaze. After treatment, the three-point flexure test was used to calculate the flexural strength and X-ray diffraction analysis was used to estimate the relative amount of monoclinic phase. The reliability of strength was assessed through the Weibull distribution. Statistical analysis was conducted with multiple regression analysis, one-way ANOVA and Tukey's pairwise multiple comparisons. Treated and fractured surfaces were observed with SEM. The following values of strength and relative content of monoclinic phase of zirconia were measured for each group: sandblasted (1540MPa; 9.5%); ground parallel (1330MPa; 8.3%); ground perpendicular (1525MPa; 8.3%); ground parallel and heated (1225MPa; monoclinic content not detectable); ground perpendicular and heated (1185MPa; monoclinic content not detectable); polished and heated (1165MPa; monoclinic content not detectable); polished (1095MPa; 0.8%); sandblasted and heated (955MPa; 0.3%). The present study suggests that sandblasting and grinding may be recommended to increase the strength of dental Y-TZP, provided they are not followed by heat treatment. Fine polishing may remove the layer of compressive stresses and therefore, lower the mean flexural strength.

A numerical/experimental study of contact damage in non-planar porcelain/metal bilayers

In this report, we investigate and visualize the effect of shape irregularity on contact damage in a brittle coating on a stiff metal substrate. Hertzian contact damage in a dental porcelain layer of thickness between 0.25 and 0.75 mm , fused onto a Ni–Cr alloy substrate in both curved and planar geometries was studied with the aid of the finite element method and experimental investigation. Three failure modes were examined with varying porcelain layer thickness: cone cracking at the upper surface of the porcelain, median or interface cracking at the layer/substrate interface and plastic deformation below the contact area in the substrate. It is shown that curvature has very little effect on the initiation of surface cone cracks in this system, but substantial effect on the initiation of interface radial cracks. In particular, curvature reduces the critical load for the onset of interface cracks.

A comparison of the porcelain fracture resistance of screw-retained and cement-retained implant-supported metal-ceramic crowns

Statement of problem The presence of a screw opening on the occlusal surface of implant-supported metal-ceramic crowns may decrease the porcelain fracture resistance and shorten the longevity of the crown. Purpose The purpose of this study was to compare the porcelain fracture resistance between screw-retained and cement-retained implant-supported metal-ceramic crowns and to assess whether narrowing the occlusal table or offsetting the screw-access opening affects fracture resistance. Material and methods Forty standardized maxillary premolar metal copings were fabricated with a Pd-Ga alloy (Protocol) on an implant abutment. Copings were divided into 4 groups (n=10): Group 1 (Screw-retained; occlusal surface buccolingual width=5 mm), screw access opening placed in the center of the occlusal surface; Group 2 (Screw-retained; occlusal surface buccolingual width = 5 mm), screw access opening positioned 1 mm offset from the center of the occlusal surface toward the buccal cusp; Group 3 (Cement-retained; occlusal surface buccolingual width = 5 mm), copings were not altered; and Group 4 (Cement-retained; occlusal surface buccolingual width = 4 mm), copings designed to have a reduced occlusal surface width. All castings were finished with aluminum oxide stones and airborne-particle abraded. Two layers of opaque and dentin porcelain were applied, respectively, on all specimens, which were then glazed. The crown specimens were positioned in a custom testing apparatus and vertically loaded on the middle of the occlusal surface with a universal testing machine at a crosshead speed of 0.5 mm/min until fracture. Mean values of load at fracture (Kgf) were calculated in each group and compared with a 1-way analysis of variance and Tukey's Studentized test (α=.05). Results Mean values of loads required to fracture the crowns were as follow: Group 1: 95.01±46.6 Kgf; Group 2: 108.61±57.9 Kgf; Group 3: 390.94±151.3 Kgf; Group 4: 380.04±211.8 Kgf. Groups 1 and 2 required a significantly lower force to fracture the crowns compared with Groups 3 and 4 ( P=.0001). Comparing Group 1 with 2 ( P=.9) and Groups 3 with 4 ( P=.6), no significant differences were noted. Conclusions Screw-retained implant-supported metal-ceramic crowns demonstrated a significantly lower porcelain fracture resistance than cement-retained crowns. Placing the screw access opening 1 mm offset from the center of the occlusal surface did not result in lower fracture resistance. Cement-retained crowns with 4- or 5-mm buccolingual width of the occlusal surface showed similar porcelain fracture resistance.

Fracture resistance of three all-ceramic restorative systems for posterior applications

Statement of problem The failure loads of all-ceramic crowns are influenced not only by the fracture resistance of the component materials but also by prosthesis geometry and size and location of flaws, thus there is a need for a study that compares the fracture resistance of all-ceramic systems using a simple and reproducible specimen geometry that includes flaws occurring at material interfaces. Purpose The research aim was to compare the in vitro fracture resistance and origin of failure of simulated first molar crowns fabricated using 3 all-ceramic systems, IPS Empress 2, Procera AllCeram, and In-Ceram Zirconia. Material and methods Twenty axisymmetric crowns of each system were fabricated to fit a preparation with 1.5- to 2.0-mm occlusal reduction. The center of the occlusal surface on each of 15 specimens per ceramic system was axially loaded to fracture in a universal testing machine, and the maximum load (N) was recorded. Fractured surfaces were examined using optical and electron microscopy to determine the most prevalent origin of failure in each ceramic system. Five crowns per system were sectioned, and thickness of the luting agent, core material, and veneer porcelain layers were measured. The 95% confidence intervals of the Weibull modulus and characteristic failure load were compared between the 3 systems. Two-way multivariate analysis of variance was used to analyze the thickness of the luting agent, ceramic core, and veneer porcelain layers (α=.05). Results The 95% confidence intervals for Weibull modulus were 1.8 to 2.3 (IPS Empress 2), 2.8 to 3.6 (Procera AllCeram), and 3.9 to 4.9 (In-Ceram Zirconia). The 95% confidence intervals for characteristic failure load were 771 to 1115 N (IPS Empress 2), 859 to 1086 N (Procera AllCeram), and 998 to 1183 (In-Ceram Zirconia). The origin of failure was most commonly found at the interface between the ceramic core and veneer porcelain for IPS Empress 2 and between the ceramic core and luting agent layer for the other systems. Conclusions There was no significant difference in fracture resistance; however, there was a significant difference in failure origin between the all-ceramic systems studied.

Contact Damage in Curved Porcelain/Metal Bilayers

This paper aims to assess the effect of shape irregularity on contact damage in a brittle coating on a stiff metal substrate. Hertzian contact damage in a dental porcelain layer over a Ni-Cr alloy substrate in both curved and flat geometries was studied using finite element analysis and experimental investigation. Three failure modes were examined with varying porcelain layer thickness: cone cracking at the top surface of the porcelain, interface cracking at the layer/substrate interface and plastic deformation below the contact area in the substrate. It is shown that curvature has very little effect on the initiation of surface cone cracks in this system, but substantial effect on the initiation of interface radial cracks. In particular, curvature reduces the critical load for the onset of interface cracks

A numerical study of fracture modes in contact damage in porcelain/Pd-alloy bilayers

Finite element analysis (FEA) is used to assess contact damage in dental prostheses, using a Hertzian contact model, consisting of a spherical tungsten carbide indenter contacting a porcelain layer over a palladium alloy substrate. Three failure modes—plastic deformation in the substrate, cone cracking in the layer and cracking in the layer at the layer/substrate interface—are examined with varying porcelain layer thicknesses. Resulting critical loads agree well with experimentally observed figures. In particular, use of an observed surface stress to predict cone cracking has given excellent agreement where high stress gradients have previously made crack onset difficult to predict using fracture toughness values. This leads to the conclusion that FEA can be a valuable tool in assessing material combinations, and design of prostheses.

Microstructural Design and Evaluation of Porcelain/Mullite/Alumina Layered Structure for Dental Application

AbstractPorcelain (veneer layer)/alumina (core layer) is a typical dental crown structure. Due to its high incidence of failure, a new porcelain/mullite (buffer layer)/alumina trilayer structure is designed, fabricated, and evaluated. Alumina green bodies were prepared by gel-casting process, and then calcined at 900 and 1100°C to infiltrate mullite precursor slurry of silica-rich (Al2O3·2SiO2) composition into the bodies. Porosity in the bodies is not dependent on calcination temperature, resulting in a similar infiltration depth. Porcelain was coated on the alumina sintered at 1600°C with and without mullite buffer layer. There are no delamination or cracks observed after firing the layered materials. Rod type microstructure and continuous composition are indicated at the interface in the case of the layered structure with mullite buffer layer. To investigate the cracking resistance behavior for this new structure, Vickers indentation and Hertzian contact fatigue tests were conducted. Cracks do not penetrate the interface with mullite buffer layer into the porcelain, showing a reversal case for the layered structure without mullite buffer layer. The layered structure with mullite buffer layer shows higher critical load for fracture than that without mullite buffer layer. Fracture mode of the layered structures in cyclic fatigue shows a top layer (porcelain) fracture at relatively low load (P = 250 N) and higher cycles (n = 106), and a bottom layer (alumina) fracture at higher load (P = 300 N) and relatively low cycles (n = 105).

The influence of porcelain layer thickness on the final shade of ceramic restorations

Statement of problem Ceramic restorations should be made of porcelain layers of different opacity, shade, and thickness in order to provide a natural appearance. By means of CAD/CAM layering technology such as CICERO, it is feasible to produce all-ceramic crowns with porcelain layers of predetermined thickness. However, it is not yet known whether changes in thickness of these porcelain layers within the clinically available space can perceivably influence the overall shade of the restoration. Purpose The purpose of this study was to determine, quantitatively, the effect of different thickness ratios of opaque porcelain (OP) and translucent porcelain (TP) layers on the overall shade of all-ceramic specimens. Material and methods The CIELAB values of 5 assembled specimens, each consisting of 2 or 3 discs (CORE 0.70 mm/OP - 0, 0.25, 0.50, 0.75, or 1.00 mm/TP 1.00, 0.75, 0.50, 0.25, or 0 mm) were determined with a spectrophotometer for the Vita shades A1, A2, and A3. Distilled water was used to attain optical contact between the layers. Black or white backgrounds were used to assess the influence of the background on the final shade. Color differences (ΔE) between layered specimens were determined. Correlation between the thickness ratio and the L*, a*, and b* values was calculated by 2-tailed Spearman correlation analysis. Results The results indicated that small changes in OP/TP thickness ratio can perceivably influence the final shade of the layered specimens (ΔE >1). Redness a* and yellowness b* increased with the thickness of OP for all shades. Redness a* ( P < .01 for all shades) correlated more strongly with thickness than yellowness b* ( P < .01 for A1 and A3; P < .05 for A2). The lightness (L*) was shade dependent. The correlation (r) between OP/TP thickness and L* was 0.975 ( P < .01) for shade A1, 0.700 (not statistically significant) for shade A2, and 0.900 ( P < .05) for shade A3. Conclusion Small changes in thickness and shade of opaque and translucent porcelain layers can influence the final shade of the layered porcelain specimen.

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 interfacial variables on ceramic adherence to cast and machined commercially pure titanium

Statement of problem Titanium-ceramic bonding is less optimal than conventional metal-ceramic bonding, due to excessive oxidation of titanium during porcelain firing. Purpose This in vitro study evaluated the effects of porcelain firing atmosphere and gold sputter coating on titanium surfaces on porcelain bonding to machined and as-cast titanium substrates. Material and methods Eight groups of ASTM grade 2 commercially pure (CP) titanium specimens (13 mm ×13 mm ×1 mm) were prepared (n=10). A conventional Au-Pd-In metal-ceramic alloy (Orion) and an ultra low-fusing porcelain (Finesse) served as the control (n=10). Forty machined titanium specimens were prepared from 1.00-mm thick titanium sheets with a diamond band saw. Forty titanium specimens were produced in a centrifugal dental titanium casting machine. All titanium specimens were airborne particle abraded with 110-μm alumina particles, whereas the control specimens were airborne particle abraded with 50-μm alumina particles. Forty titanium specimens (20 specimens each of as-cast and machined titanium) were randomly selected for gold sputter coating before ceramic firing. An ultra low-fusing porcelain (Vita Titankeramik) was fused on the central 6-mm diameter circular area on each titanium specimen. Porcelain firing environments for the titanium specimens consisted of vacuum and a reduced argon atmosphere. Porcelain was debonded by a biaxial flexure, constant strain test at a cross-head speed of 0.25 mm/min. Specimens were analyzed by standardized SEM/EDS analysis 3 times throughout the study to determine the silicon atomic percentage (Si at %): (1) after airborne particle abrasion, before porcelain application; (2) after the application of the first layer of porcelain; and (3) after the fracture of porcelain from the metal substrate. The titanium-ceramic adhesion was characterized by determining the area fraction of adherent porcelain (AFAP). Results were analyzed by analysis of variance and the Student-Newman-Keuls test (α=.05). Results Statistical analysis showed a significant difference in the AFAP values among all the groups. AFAP value of the control group was significantly higher (135.35 ± 23.68) than those of the experimental groups ( P<.001). For the machined titanium, AFAP value of gold sputter-coated/argon group (91.38 ± 7.93) was significantly higher than the rest of the groups ( P<.001). For the as-cast titanium fired in vacuum, significantly lower AFAP values ( P<.001) were found in the gold sputter-coated group (50.2 ± 11.26 vs 66.15 ± 10.41). AFAP values between the argon groups with or without the gold coating were not significantly different ( P=.303); however, both argon groups (93.83 ± 4.65 and 98.09 ± 6.35) showed significantly higher AFAP values compared with the vacuum groups ( P<.001). Conclusion Firing porcelain in a reduced argon atmosphere significantly improved titanium-ceramic bonding for machined and as-cast titanium. The sputter-coated gold layer on titanium provided improved titanium-ceramic bonding only when combined with firing porcelain in reduced argon atmosphere. When porcelain was fired in vacuum in the presence of the gold layer, the titanium-ceramic bonding was weakened in as-cast titanium and was not affected in machined titanium. Conventional noble metal-ceramic bonding was superior to titanium-ceramic bonding regardless of the interfacial variables examined in this study.

127 陶材焼付鋳造冠の製作過程における熱変形に関する研究

A metal-ceramic crown used in the clinical stage is manufactured by burning 3 layers of the dental porcelain on the metal coping. Then the deformation of the crown occurs by a hardening shrinkage and thermal shrinkage of dental porcelain. Therefore, a study on deformation of the metal coping in production process of metal-ceramic crowns has been done by using the finite element method (FEM). As a result, the following conclusions were obtained. : (1) Neighborhoods of ends of the collar extended into outsides of the crown. In particularly, the largest deformation was observed at ends of the collar. (2) Extension of neighborhoods of end of the collar increased with increasing the length of the collar. (3) The thickness of the first layer of the dental porcelain was largely influenced in the deformation of the metal coping.

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.)

X-ray diffraction characterization of dental gold alloy-ceramic interfaces.

X-ray diffraction (XRD) was employed to study dental alloy-ceramic interfaces. A Au-Pd-In alloy, which requires oxidation before porcelain firing, and a Au-Pt-Pd-In alloy, which does not require oxidation before porcelain firing, were selected in this study. Alloy specimens were centrifugally cast. Specimen surfaces were metallographically polished through 0.05 microm Al2O3 slurries. A thin layer (< 50 microm) of a dental opaque porcelain was fired on the alloy surfaces with and without initial oxidation. XRD was conducted at room temperature on four types of alloy specimens: polished, oxidized, porcelain fired after alloy oxidation, and porcelain fired without initial alloy oxidation. XRD was also performed on fired opaque porcelain without an alloy substrate. The detection of prominent gold solid solution peaks from alloy-ceramic specimens indicated that the incident X-ray beam reached the alloy-ceramic interface. In2O3 and beta-Ga2O3 were identified on the oxidized Au-Pd-In alloy, while In2O3 and SnO2 were detected on the oxidized Au-Pt-Pd-In alloy. Preferred orientation was observed for all the oxides formed on the alloys. Minimum lattice parameter changes (<1%) for the gold solid solutions were observed for both alloys before and after oxidation and porcelain firing. Leucite (KAlSi2O6, TiO2, ZrO2 and SnO2 were detected on the fired opaque porcelain. For both alloys, no additional oxides were identified at the metal-ceramic interfaces beyond those present in the oxidized alloys and the opaque porcelain. Similar results were obtained from alloy-ceramic interfaces where there was no prior alloy oxidation. The results indicate the critical role of alloy surface oxides in metal-ceramic bonding and support the chemical bonding mechanism for porcelain adherence.

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.)

Effect of different high-palladium metal-ceramic alloys on the color of opaque porcelain.

The purpose of this study was to assess the effect of different high-palladium alloys on the resulting color of opaque porcelain. Three Pd-Cu-Ga alloys, Spartan Plus (S; Williams Dental Co/Division of Ivoclar North America, Amhest, NY), Liberty (B; J.F. Jelenko & Co, Armonk, NY), and Freedom Plus (F; J.F. Jelenko & Co); 4 Pd-Ga alloys, Legacy (L; J.F. Jelenko & Co), IS 85 (I; Williams Dental Co), Protocol (P; Williams Dental Co), and Legacy XT (X; J.F. Jelenko & Co); and a Pd-Ag alloy, Super Star (T; J.F. Jelenko & Co), were examined. The Au-Pd alloy Olympia (O; J.F. Jelenko & Co) served as the control. Three cast 16-mm discs, 1-mm thick, were prepared from each of the alloys. After metallurgically polishing and air-abrading, the specimens were oxidized following the manufacturer's recommendations. Shade B1 opaque porcelain (Vita-Omega; Vident, Baldwin Park, CA) was applied at a final thickness of 0.1 mm using a mold. After 2 opaque porcelain firing cycles, the surfaces were air-abraded. The colors of the specimens were measured using a colorimeter and expressed in Commission International de l'Eclairage (CIE) L*a*b* coordinates. Color differences (delta E) were determined between the control and each experimental group. Analysis of Variance and Tukey-Kramer tests were performed on the delta E data. The 3 Pd-Cu-Ga alloys showed significantly greater (p < .01) delta E values (S = 2.8 +/- 1.1, B = 3.0 +/- 0.6, and F = 2.1 +/- 0.2) than the remaining 5 experimental groups (L = 0.7 +/- 0.5, I = 0.7 +/- 0.4, P = 0.7 +/- 0.2, X = 0.7 +/- 0.4, and T = 0.7 +/- 0.5). The directions of the significant color changes were relatively equally distributed along the L*, a*, and b* axes, and all delta L*, delta a*, and delta b* values were negative (lower value, more green and blue relative to control O). This work suggests that a 0.1-mm-thick layer of opaque porcelain in the Pd-Cu-Ga alloys studied, did not reliably reproduce the color of porcelain.

Thermal incompatibility analysis of metal-ceramic systems based on flexural displacement data.

The feasibility of simple tests or analytical methods for prediction of residual stress states in metal-ceramic (MC) prostheses has not been demonstrated. Biomaterial metal-ceramic strips have been proposed to provide sensitive measures of transient and residual stress states through the measurement of midpoint deflection after cooling from the ceramic sintering temperature. The objective of this study was to apply the elastic-viscoelastic analogy to calculate transient and residual midpoint deflections in MC biomaterial strips and to compare these values with deflections measured with a beam-bending viscometer (BBV). Calculations and measurements were made for five MC systems that were found from a clinical study to be "thermally compatible" systems. Metal strips, 64 mm in length, 3 mm wide, and either 0.5 mm, 1.0 mm, or 2.0 mm in thickness, were veneered with four 0.25-mm thick layers of opaque porcelain. Midpoint deflection of the MC strips (ceramic oriented in the posterior position) was measured during cooling from an initial temperature of 700 degrees C. In general, the directions of the measured residual deflections did not agree with the "textbook" convention that negative deflections are associated with positive thermal contraction mismatch (alpha(M) - alpha(c) > 0) regardless of metal thickness. For a metal thickness of 0.5 mm, the residual midpoint deflection for all thermal contraction mismatch cases, except one, was positive (upward deflection) whereas the residual midpoint deflections were all negative when the metal thickness was increased to 1 or 2 mm, independent of the thermal contraction mismatch. The best agreement between calculated and measured values of residual midpoint deflection (+16 microns vs. +14 +/- 2.3 microns, respectively was obtained for MC biomaterial strips with a Ni-Cr alloy (0.5 mm thick) while the largest difference (+346 microns vs. +61 +/- 43.8 microns) was obtained for MC bimaterial strips with a Au-Pd allow (0.5 mm thick). In all but one case, changes in deflection direction as a function of metal thickness were correctly predicted by the viscoelastic analysis. The results of this study indicate that a viscoelastic model is useful for estimating thermal compatibility conditions of MC systems.

Quartz antenna for radio frequency ion source operation

Radio-frequency (rf) driven multicusp ion sources developed at the Lawrence Berkeley National Laboratory use an internal induction coil (antenna) for plasma generation. The copper rf-antenna with a thin layer of porcelain coating, which is presently used, cannot fully satisfy the increasing demands on source cleanliness and antenna lifetime under high power cw or pulsed operation in applications where water cooling is not possible. A quartz antenna has been designed and operated in the multicusp ion source. It has been demonstrated that the overall performance of the new antenna exceeds that of the regular porcelain-coated antenna. It can be operated with a long lifetime in different discharge plasmas. The quartz antenna has also been tested at the Paul Scherrer Institute for cw source operation at rf power higher than 5 kW. Results demonstrated that the antenna can survive under dense plasma discharge operations.

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.

Analysis of Tempering Stresses in Metal-Ceramic Disks

Previous studies showed that residual compressive stresses induced by thermal tempering retarded the growth of surface cracks in bilayered porcelain disks. The objectives of the present study were: (1) to determine whether thermal tempering by air blasting reduces the length of cracks induced by microhardness indentation in metal-ceramic disks, and (2) to use visco-elastic finite element analyses to calculate transient and residual stresses in metal-ceramic disks. Ni-Cr-Be disks, 16 mm in diameter and 0.3 mm in thickness, were prepared with a 0.5-mm-thick layer of opaque porcelain and a 1.5-mm-thick layer of body porcelain. Metal-porcelain combinations were selected to provide a range of thermal contraction mismatch values. The disks were fired to the maturing temperature of body porcelain and then were subjected to three cooling procedures: (1) slow cooling in a furnace (SC), (2) cooling in air (FC), and (3) air tempering (T) by blasting the surface of the body porcelain with compressed air. The lengths of cracks induced in the surface of the body porcelain by a microhardness indenter were measured immediately after indentation at 20 points along diametral lines. The results of Tukey's multiple-contrast analyses indicated that the mean crack lengths of air-tempered specimens were significantly smaller (p < or = 0.05) than the crack lengths of the fast-cooled and slow-cooled groups. Except for one case, there were no statistically significant differences in the mean crack lengths between FC and SC specimens independent of thermal contraction mismatch. Residual tensile stresses were calculated for SC and FC specimens for all thermal contraction mismatch cases, with the largest values being associated with combinations containing the body porcelain with the smaller contraction coefficient. Calculations by use of the model confirmed that tempering induces large residual compressive stresses in the surface of body porcelain for all of the thermal contraction mismatch cases included in this study.

マスキングポーセレンに関する色彩学的検討 Ｈｉｄｉｎｇ ｐｏｗｅｒを指標とした不透明性の評価

Translucency is a very important factor for obtaining an esthetic porcelain laminate veneer crown. This translucency is greatly affected by the opacity of the masking porcelain layer, but there is no objective criterion to evaluate the opacity. In general, opacity is well evaluated by hiding power. Therefore, hiding power of masking porcelain was calculated in this study using the ASTM (American Society for Testing and Materials) method.The reflectance value of each masking porcelain sample containing 5, 10, 15, 20, 25, or 30% opacity of pink, white, yellow, and blue were measured with white and black backing, and hiding power was calculated using its scattering coefficients. Hiding power increased in proportion to the opacity and ranged from 100 to 1, 400 for any shade. Color difference dE between white and black backing increased rapidly under the 25% opacity.It was concluded that (1) the opacity could be analyzed as hiding power and (2) hiding power under 20% opacity is very effective on visibility.