Simulated Porcelain Firing Research Articles

Change in hardness of an as-cast and softening heat-treated low-gold-content alloy for bonding porcelain by simulated porcelain firing and its mechanism

This study examined the change in hardness of a low-gold-content alloy for bonding porcelain induced by simulated porcelain firing after casting and softening heat treatment along with its mechanism. In the as-cast specimen, the hardness was increased by oxidation, and as the specimen underwent a further porcelain-firing process, the hardness decreased gradually to be softer than the as-cast state. The hardening in the as-cast specimen by oxidation was induced by the grain interior precipitation of the ordered Pd3 (Sn,In) phase, which resulted in the formation of severe lattice strain in the matrix. Softening by the complete firing process in the as-cast specimen was due to the coarsening of the ordered Pd3 (Sn,In) precipitates, which resulted in release of lattice strain by the reduced interphase boundaries between the coarsened precipitates and surrounding matrix. In the softening heat-treated specimen before simulated porcelain firing, the decrease in hardness by the softening heat treatment, which was performed to allow easy alloy processing before porcelain firing, was almost recovered in the oxidation-treated state, which is the first stage of the porcelain-firing cycles. From the first opaque-treated state, there was little difference between the hardness of the as-cast specimen and softening heat-treated specimens. The mechanism of hardening by oxidation and subsequent softening by the complete firing process was unaffected by the softening heat treatment before porcelain firing in a low-gold-content alloy for bonding porcelain.

Changes in hardness and microstructure of a solution-treated Au-Pd-In alloy for porcelain bonding during porcelain firing simulation

Changes in hardness and microstructure of a solution-treated Au-Pd-In alloy for porcelain bonding during porcelain firing simulation were elucidated by means of hardness test, field emission scanning electron microscope (FE-SEM) observations, X-ray diffraction (XRD) analysis and energy dispersive spectrometer (EDS) analysis. The most effective hardening of alloy during cooling after porcelain firing was obtained when the firing chamber moved immediately to upper end position and then air cooled. In the solution-treated specimen after casting, the hardness decreased dramatically. However, after degassing treatment which is the first firing stage, the hardness value of solution-treated specimen increased rapidly, and such a high hardness was maintained during the consecutive firing stages. In a Cu-free Au-Pd-In alloy for porcelain bonding, the hardening effect of the solution treatment on simulated porcelain firing was caused by the grain interior precipitates of fine scale, which was composed of the ordered Ga₂Pd<SUB>5</SUB> phase containing Au and In. From the above results, solution treatment is recommended to improve hardness of the Au-Pd-In alloy during porcelain firing.

The Effect of Porcelain Firing on Electrochemical Behavior of a Dental Alloy in Hydrogen Peroxide.

The aim of this study was to evaluate changes in electrochemical corrosion properties of porcelain firing simulated nickel-chromium dental casting alloy exposed to a 10% hydrogen peroxide bleaching agent. The electrochemical corrosion behavior of a Ni-Cr alloy was evaluated by cyclic polarization test in the aerated electrolyte (pH = 6.5). Test groups were produced in as-cast (group 1, control group) and simulated porcelain firing (group 2: heat-treated/mean value; group 3: heat-treated/cycle) conditions. Scanning electron microscopy (SEM) was also used to examine the alloy surfaces before and after the corrosion test. The ranking of the groups with respect to Ecorr and Icorr was as follows: 1, 2, 3 and 3, 1, 2, respectively. Group 3 exhibited the greatest and group 2 displayed the least corrosion tendencies. An increase in corrosion rates was observed after heat treatment/cycle state. Post-corrosion SEM photographs were also consistent with the test results. Within the parameters of this study, a single heat treatment is insufficient to cause upheaval in corrosion behavior of a Ni-Cr alloy subjected to 10% hydrogen peroxide.

Hardening effect of pre- and post-firing heat treatment for a firing-simulated Au-Pd-In metal-ceramic alloy

The hardening effect of the pre- and post-firing heat treatments and their dual treatment was examined for a firing-simulated Au-Pd-In metal-ceramic alloy to determine if an additional post-firing heat treatment is effective in the hardening of an Au-Pd-In metal-ceramic alloy as well as to compare the hardening effects of pre- and post-firing heat treatments for a firing-simulated Au-Pd-In metal-ceramic alloy. The post-firing heat treatment was much more effective than the pre-firing heat treatment or dual treatments. The hardening effect of the pre- and post-firing heat treatments was caused by the induction of fine grain interior precipitation. In the pre-firing heat-treated specimen after casting, the apparent hardening was achieved during simulated porcelain firing, but an additional post-firing heat treatment did not introduce severe grain interior precipitation, resulting in very weak hardening. In the as-cast specimen without the pre-firing heat treatment, apparent hardening by grain interior precipitation was achieved only by post-firing heat treatment and not by simulated porcelain firing.

XPS and electrochemical impedance spectroscopy studies on effects of the porcelain firing process on surface and corrosion properties of two nickel–chromium dental alloys

The aim of this study was to evaluate the effects of a simulated porcelain firing process on the surface, corrosion behavior and cell culture response of two nickel-chromium (Ni-Cr) dental alloys. A Be-free alloy and a Be-containing alloy were tested. Before porcelain firing, as-cast specimens were examined for surface composition using X-ray photoelectron spectroscopy and metallurgical phases using X-ray diffraction. Corrosion behaviors were evaluated using electrochemical impedance spectroscopy. 3T3 fibroblasts were cultured and exposed indirectly to specimens. MTT assays were counted after 3 and 6 days. The cell culture mediums exposed to specimens were analyzed for metal ion release. After porcelain firing, similar specimens were examined for the same properties. In both as-cast and fired conditions, the Be-free Ni-Cr alloy showed significantly more resistance to corrosion than the Be-containing Ni-Cr alloy, which exhibited BeNi phase. After porcelain firing, the corrosion resistance of the Be-free Ni-Cr alloy decreased statistically, corresponding with evident decreases of Cr and Ni oxides on the alloy surface. Also, the alloy's MTT assay decreased significantly corresponding with an obvious increase of Ni-ion release after the firing. For the Be-containing Ni-Cr alloy, the firing process led to increases of surface oxides and metallic Be, while its corrosion resistance and cell culture response were not significantly changed after porcelain firing. The results suggested that the corrosion resistance and biocompatibility of the Be-free Ni-Cr alloy decreased after porcelain firing, whereas the firing process had little effect on the same properties of the Be-containing Ni-Cr alloy.

Strain Gauge Analysis of the Effect of Porcelain Firing Simulation on the Prosthetic Misfit of Implant-Supported Frameworks

This study investigated the effect of porcelain firing on the misfit of implant-supported frameworks and analyzed the influence of preheat treatment on the dimensional alterations. Four external-hex cylindrical implants were placed in polyurethane block. Ten frameworks of screw-retained implant-supported prostheses were cast in Pd-Ag using 2 procedures: (1) control group (CG, n = 5): cast in segments and laser welded; and test group (TG, n = 5): cast in segments, preheated, and laser welded. All samples were subjected to firing to simulate porcelain veneering firing. Strain gauges were bonded around the implants, and microstrain values (με = 10⁻⁶ε) were recorded after welding (M1), oxidation cycle (M2), and glaze firing (M3). Data were statistically analyzed (2-way analysis of variance, Bonferroni, α = 0.05). The microstrain value in the CG at M3 (475.2 με) was significantly different from the values observed at M1 (355.6 με) and M2 (413.9 με). The values at M2 and M3 in the CG were not statistically different. Microstrain values recorded at different moments (M1: 361.6 με/M2: 335.3 με/M3: 307.2 με) did not show significant difference. The framework misfit deteriorates during firing cycles of porcelain veneering. Metal distortion after porcelain veneering could be controlled by preheat treatment.

Effect of firing cycle and surface finishing on the sag resistance of long-span metal ceramic framework using base metal alloys—an in vitro study

BackgroundThe search for the ideal restorative material or combination of materials in dentistry is still the subject of modern dental research. In clinical practice, there are increased numbers of ceramo-metal restorations being fabricated which replace multiple missing teeth in a single framework. The literature is scanty with regard to investigations of the ‘sag’ resistance of base metal alloys commonly used for ceramo-metal restorations and specifically for long-span restorations.An in vitro study was carried out to investigate the effects of surface finishing and simulated porcelain-firing on the sag resistance of long-span ceramo-metal frameworks using base metal alloys. MethodFour types of alloys were used. A total of 80 samples were selected for the study and they were divided into four groups of 20 samples each. ‘As cast’ metal specimens in group I, group II and with surface finishing in group III and group IV. Each test sample was mounted on the sample holding accessory of the custom made thermo mechanical analyser and subjected to three firing cycles. Each sample was evaluated for the sag-related deflection recorded by the dial gauge with an accuracy of 1 µm. The data recorded was subjected to a statistical analysis using unpaired t-test to compare the relative difference in the sag-related deflection values. ResultsIt was observed that the values for sag-related deflection were significantly less for the ‘as cast’ samples of all the alloy groups. Nickelchromium (NiCr) and cobaltchromium (CoCr) exhibited value of 19.4 μm and 14.8 μm, respectively. ConclusionAmong the four groups of alloys tested, CoCr based alloy exhibited the least amount of sag-related deflection. The results show that the sag-related deflection was less in Co-Cr alloys as compared with the NiCr alloys, still Ni-Cr alloys in fixed dental prostheses frameworks are used due to their desirable physical and chemical properties.

Microstructure, elemental composition, hardness and crystal structure study of the interface between a noble implant component and cast noble alloys

Casting a high-gold alloy to a wrought prefabricated noble implant-component increases the cost of an implant. Selecting a less expensive noble alloy would decrease implant treatment costs. The purpose of this study was to investigate the interfacial regions of a representative noble implant component and cast noble dental alloys and to evaluate the effects of porcelain firing cycles on the interface. Six representative alloys (n=3) were cast to gold implant abutments (ComOcta). Scanning electron microscopy (SEM) was used to characterize microstructures. Compositions of interfacial regions and bulk alloys were obtained by energy-dispersive spectroscopy. Vickers hardness was also measured across the interface. By using Micro-X-ray diffraction, the phases were evaluated at 7 points perpendicular to the interface. The effects of porcelain firing cycles on microstructures, diffusion, hardness, and phases were also evaluated. For statistical evaluation of diffusion length and hardness, a 3-way repeated measures ANOVA was used. Pairwise comparisons of interest were conducted with Tukey pairwise comparisons or, when a significant interaction was found, Bonferroni-adjusted t-tests (overall α=.05). Microstructures of bulk alloys were predominantly maintained to a well-defined boundary for both as-cast and heat-treated conditions. An interaction band, 5-6 μm wide, was observed. The alloy grain size at the interface and the interaction band width increased after simulated porcelain firing. The extent of elemental diffusion from the interface was about 30 μm and not affected by simulated porcelain firing. Differences in Vickers hardness for the alloys were consistent with their compositions. Micro-XRD patterns indicated that substantial amounts of new phases had not formed at the interfacial regions. Less expensive noble alternatives to high-gold alloys provided comparable metallurgical compatibility with the noble implant component.

Effect of Porcelain-Firing Cycles and Surface Finishing on the Marginal Discrepancy of Titanium Copings

The aim of the study was to evaluate the effect of simulated porcelain firing cycles and surface finishing on the marginal fit of commercially pure titanium (Cp Ti) copings. A machined stainless steel die system with standard 0.5-mm copings was fabricated. Wax patterns were prepared by pouring the molten wax on a two-part stainless steel die. Thirty specimens were cast in Cp Ti. These were divided into three groups with ten specimens in each group. Group 1 was treated with conventional cold working and later oxidized. Group 2 specimens were oxidized initially and then cold worked. Group 3 was heat treated in its original investment and later treated as in group 1. All specimens were later subjected to sequential simulated porcelain firing cycles, that is, oxidation, bonder, opaque, body, and glaze firing. Following the completion of each firing cycle, marginal discrepancy was measured in μm using a traveling microscope. The obtained data were subjected to one-way analysis of variance (ANOVA) and Student's t-test. The statistical level of significance was set at 1%. The results showed that the mean and SD values (in μm) were 55 ± 2.6, 43 ± 3.0, and 68 ± 4.0 after oxidation for groups 1, 2, and 3, respectively. Mean and SD values (in μm) after glaze firing were 76 ± 3.9, 64 ± 4.1, and 89 ± 4.3 for groups 1, 2, and 3, respectively. The mean marginal opening was largest for group 3 specimens. One-way ANOVA showed the difference within the three groups was highly significant after oxidation (F-value 149.37 at p-value 0.0000) and glaze firing (F-value 82.43 at p-value 0.0000). (1) The Student's t-test values demonstrated that increased marginal openings of the specimens resulted after the sequential simulated porcelain firing cycles. (2) Marginal discrepancy values improved when the specimens were thermocycled prior to cold working.

Corrosion behaviour and surface analysis of a Co–Cr and two Ni–Cr dental alloys before and after simulated porcelain firing

This study evaluated the corrosion behaviour and surface properties of a commercial cobalt-chromium (Co-Cr) alloy and two nickel-chromium (Ni-Cr) alloys [beryllium (Be)-free and Be-containing] before and after a simulated porcelain-firing process. Before porcelain firing, the microstructure, surface composition and hardness, electrochemical corrosion properties, and metal-ion release of as-cast alloy specimens were examined. After firing, similar alloy specimens were examined for the same properties. In both as-cast and fired conditions, the Co-Cr alloy (Wirobond C) showed significantly more resistance to corrosion than the two Ni-Cr alloys. After firing, the corrosion rate of the Be-free Ni-Cr alloy (Stellite N9) increased significantly, which corresponded to a reduction in the levels of Cr, molybdenum (Mo), and Ni in the surface oxides and to a reduction in the thickness of the surface oxide film. The corrosion properties of the Co-Cr alloy and the Be-containing Ni-Cr alloy (ChangPing) were not significantly affected by the firing process. Porcelain firing also changed the microstructure and microhardness values of the alloys, and there were increases in the release of Co and Ni ions, especially for Ni from the Be-free Ni-Cr alloy. Thus, the corrosion rate of the Be-free Ni-Cr alloy increased significantly after porcelain firing, whereas the firing process had little effect on the corrosion susceptibility of the Co-Cr alloy and the Be-containing Ni-Cr alloy.

Study of Pd–Ag dental alloys: examination of effect of casting porosity on fatigue behavior and microstructural analysis

The goals of this study were to investigate the fatigue limits of two Pd-Ag alloys (Ivoclar Vivadent) with differing mechanical properties and varying proportions of secondary alloying elements, examine the effect of casting porosity on fatigue behavior, and determine the effect of casting size on microstructures and Vickers hardness. The alloys selected were: IPS d.SIGN 59 (59.2Pd-27.9Ag-8.2Sn-2.7In-1.3Zn); and IS 64 (59.9Pd-26.0Ag-7.0Sn-2.8Au-1.8 Ga-1.5In-1.0Pt). Tension test bars, heat-treated to simulate dental porcelain application, were subjected to cyclic loading at 10 Hz, with R-ratio of -1 for amplitudes of compressive and tensile stress. Two replicate specimens were tested at each stress amplitude. Fracture surfaces were examined with a scanning electron microscope (SEM). Sectioned fatigue specimens and additional cast specimens simulating copings for a maxillary central incisor restoration were also examined with the SEM, and Vickers hardness was measured using 1 kg load. Casting porosity was evaluated in sectioned fatigue fracture specimens, using an image analysis program. The fatigue limit (2 × 10(6) loading cycles) of IS 64 was approximately 0.20 of its 0.2% yield strength, while the fatigue limit of d.SIGN 59 was approximately 0.25 of its 0.2% yield strength. These relatively low ratios of fatigue limit to 0.2% yield strength are similar to those found previously for high-palladium dental alloys, and are attributed to their complex microstructures and casting porosity. Complex fatigue fracture surfaces with striations were observed for both alloys. Substantial further decrease in the number of cycles for fatigue failure only occurred when the pore size and volume percentage became excessive. While the heat-treated alloys had equiaxed grains with precipitates, the microstructural homogenization resulting from simulated porcelain firing differed considerably for the coping and fatigue test specimens; the latter specimens had significantly higher values of Vickers hardness.

A comparative evaluation of the effect of simulated porcelain firing cycle on the mechanical properties and microstructure of nickel-chromium-based ceramic alloys

The present study was carried out to evaluate the effect of porcelain firing cycle on the mechanical properties and microstructure of nickel-chromium-based alloys. Four different alloys were used: Supercast-np, d-Sign 10, Remanium CSe and Maxibond EMCS. Tensile bars and disks were prepared for testing according to specifications. For each alloy, ten tensile bars and six disks were prepared. For each alloy, five tensile bars and three disks were randomly selected for heat treatment. For heat treatment, the specimens were subjected to simulated porcelain firing cycle in a ceramic furnace. Both as-cast and heat-treated tensile bars were tested on a universal testing machine, and the values for the ultimate tensile strength, 0.2% offset yield strength and percentage elongations were obtained. Hardness was measured using Vickers's hardness tester. Microstructures were evaluated under an optical microscope. The data collected were tabulated and subjected to statistical analyses.

High temperature dimensional alterations of implant supported frameworks

The present in vitro study was designed to evaluate the effect of high temperature firing cycles used for application of porcelain veneer in the misfit of implant supported frameworks, and the effect of a pre-heating treatment on the dimensional alterations of implant supported frameworks. The investigation was conducted based on the results given by 14 nickel-chromium (06 elements) metal structures. Half of the structures formed the control group and were exposed to simulated porcelain firings. The other half formed the test group, and were submitted to a pre-heating treatment with the implant frameworks embedded in investment, before the porcelain firing simulation. The marginal misfit measurements in both groups were made before and after the porcelain firing simulation, by using a scanning electron microscope. The results were submitted to statistical analysis of variance. The multiple comparisons were made by means of the Bonferroni “t” test. For the frameworks produced in the usual manner, without the preheating treatment (control group), misfit deteriorates during the high temperature firing cycles employed for porcelain application. In the test group, pre-heating treatment did not change the final metal distortion resulting from the porcelain firing cycles, and the greatest amount of the distortion took place before the conventional porcelain firing cycles.

Potentiodynamic polarization study of the in vitro corrosion behavior of 3 high-palladium alloys and a gold-palladium alloy in 5 media

Statement of Problem. Corrosion of cast alloy restorations may lead to their failure or adversely affect their biocompatibility. Although some documentation of the corrosion behavior of the high-palladium dental alloys exists, questions remain about their corrosion resistance and mechanisms. Purpose. This study compared the in vitro corrosion characteristics of 3 high-palladium alloys and 1 gold-palladium alloy in simulated body fluid and oral environments. Material and Methods. Two Pd-Cu-Ga alloys and 1 Pd-Ga alloy were selected; an Au-Pd alloy served as the control. The corrosion behavior for the as-cast and simulated porcelain-firing (heat-treated) conditions of each alloy (N = 5) was evaluated in 0.9% NaCl, 0.09% NaCl, and Fusayama solutions. Heat-treated specimens of each alloy (N = 5) were also tested in N2-deaerated 0.09% NaCl and Fusayama solutions (pH 4). After immersion in the electrolyte for 24 hours, the open-circuit potential (OCP) was measured, and linear polarization was performed from −20 mV to +20 mV (vs. OCP) at a scanning rate of 0.125 mV/s. Cyclic polarization was performed from −300 mV to +1000 mV and back to −300 mV (vs. OCP) at a scanning rate of 1 mV/s. Data were evaluated with analysis of variance and the Ryan-Einot-Gabriel-Welsch multiple-range test (α=.05). Results. The OCP of each alloy varied with the condition (as-cast or heat-treated) and electrolyte used. Corrosion resistance was similar for the 4 alloys tested. For cyclic polarization, all alloys showed active-passive or spontaneous passive behavior in nearly all electrolytes. During some reverse scans, the 3 high-palladium alloys displayed 3 or 5 anodic peaks. No positive hysteresis was observed for any of the alloy/electrolyte combinations evaluated. Conclusion. The corrosion resistances of the 3 high-palladium alloys in simulated body fluid and oral environments were comparable to that of the gold-palladium alloy. The similar corrosion resistance for the 3 high-palladium alloys was attributed to their high noble metal content and theorized stable structure at the submicron level. Selective corrosion of different phases and elements, surface enrichment of palladium, and adsorption of species are possible corrosion mechanisms. The cyclic polarization results suggest that none of the 4 alloys would be prone to pitting or crevice corrosion under in vivo conditions, but crevice conditions should nonetheless be avoided for these alloys in the oral environment. (J Prosthet Dent 2002;87:86-93.)

Inductively coupled plasma-mass spectroscopy measurements of elemental release from 2 high-palladium dental casting alloys into a corrosion testing medium

Statement of Problem. The biocompatibility of high-palladium alloy restorations has been of some concern due to the release of palladium into the oral environment and sensitivity reactions in patients. Purpose. This study measured the in vitro elemental release from a Pd-Cu-Ga alloy and a Pd-Ga alloy into a corrosion testing medium. Material and Methods. Both alloys were cast into 12-mm-diameter × 1-mm-thick disks, subjected to heat treatment that simulated porcelain firing cycles, polished to a 0.05-mm surface finish, and ultrasonically cleaned in ethanol. Two specimens of each alloy were immersed 3 times (at 7, 70, and 700 hours) in an aqueous lactic acid/NaCl solution used for in vitro corrosion testing and maintained at 37°C. The specimens were removed after each immersion time, and the elemental compositions of the solutions were analyzed with inductively coupled plasma-mass spectroscopy (ICP-MS). Elemental concentrations for the 2 alloys at each immersion time were compared with Student t test (α=.05). Results. No significant differences in palladium release were found for the 7- and 70-hour solutions, but significant differences were found for the 700-hour solutions. Mean concentrations of palladium and gallium in the 700-hour solutions, expressed as mass per unit area of alloy surface, were 97 (Pd) and 46 (Ga) μg/cm2 for the Pd-Cu-Ga alloy and 5 (Pd) and 18 (Ga) μg/cm2 for the Pd-Ga alloy. Conclusion. Relative proportions of the elements in the solutions were consistent with the release of palladium and breakdown of microstructural phases found in the alloys. The results suggest that there may be a lower risk of adverse biological reactions with the Pd-Ga alloy than with the Pd-Cu-Ga alloy tested. (J Prosthet Dent 2002;87:80-5.)

Comparison of mechanical properties for equiaxed fine-grained and dendritic high-palladium alloys.

Two Pd-Cu-Ga alloys and a Pd-Ga alloy were selected for study. Bars of each alloy were tested in tension for the as-cast and simulated porcelain-firing conditions, and values of mechanical properties were measured. Fracture surfaces and microstructures of axially sectioned fracture specimens were observed with the SEM. The two Pd-Cu-Ga alloys exhibited similar mechanical properties. The Pd-Ga alloy had lower strength and higher percentage elongation. Heat treatment simulating porcelain firing cycles decreased the strength of both Pd-Cu-Ga alloys and increased their ductility. However, this heat treatment did not significantly affect the mechanical properties of the Pd-Ga alloy. All three high-palladium alloys had the same modulus of elasticity. The amount of overall porosity was relatively minimal (< 1%) and not significantly different among the three alloys. However, porosity was a significant factor for UTS of one Pd-Cu-Ga alloy and the Pd-Ga alloy.

Shear bond strengths of a two-paste system resin luting agent used to bond alloys to enamel

Statement of problem. Adhesive resin luting agents are used to successfully bond the metal surfaces of fixed prostheses to teeth. Panavia 21 luting agent is a new addition to the series of Panavia adhesive resin luting agents. Purpose. This investigation measured the shear bond strengths of two types of alloy specimens (Olympia and Rexillium III) bonded to prepared human enamel (etched and unetched) with Panavia 21. Material and methods. After a simulated porcelain firing sequence, the alloy specimens were bonded to the teeth and subjected to shear testing after water storage for 2 weeks, thermocycling for 500 cycles, and water storage for an additional 2 weeks. Data were analyzed with a two-way analysis of variance (alpha = 0.05). Results. The shear bond strengths of Rexillium III and tinplated Olympia specimens bonded to prepared and unetched enamel were significantly lower than for specimens bonded to prepared and etched enamel with Panavia 21 luting agent. (J Prosthet Dent 1997;78:132-5.)

The effect of metal surface treatment on the shear bond strengths of base and noble metals bonded to enamel

Adhesive resin luting agents provide a way for bonding metal surfaces to teeth through a combination of micromechanical retention to the rough metal surface and chemical adherence to metal oxides. The purpose of this study was to measure the effect of metal alloy surface treatments that would produce different textures and oxide layers on the shear bond strength of three alloys luted to etched enamel with one adhesive resin luting agent (Panavia). After a simulated porcelain firing sequence, high noble (Olympia), noble (Jelstar), and base metal (Rexillium III) alloy specimens were subjected to one of the following treatments: (1) sandblasting and simulated glazing, (2) simulated glazing only, (3) simulated glazing and sandblasting, or (4) simulated glazing, sandblasting, and tin plating. The specimens were bonded to extracted teeth and subjected to shear testing after water storage for 2 weeks, thermocycling for 500 cycles, and water storage for an additional 2 weeks. Data were analyzed with a two-way analysis of variance (α = 0.05). The base metal specimens and the tin-plated high noble and noble metal specimen groups exhibited similar mean shear bond strengths that were greater than the other groups. Those high noble and noble metal alloys sandblasted after simulated porcelain firing cycles and before the simulated glaze cycle exhibited nonsignificant increases in shear bond strengths compared with the groups that were either sandblasted after the simulated glaze cycle or not sandblasted at all.

Veterans Administration Cooperative Studies Project No. 147/242. Part VII: The mechanical properties of metal ceramic alloys as cast and after simulated porcelain firing

Comparison of mechanical properties of seven metal ceramic alloys in as-cast and heat-treated conditions resulted in significant differences. Tested alloys included one Au-Pd (control), three palladium-based, and three nickel-based alloys. Mechanical properties included strength, elongation, modulus, and microhardness. Twenty-four tensile bars were cast for each alloy. Twelve of the 24 bars for each alloy were randomly selected for heat treatment by the Ceramco technique. After heat treatment the Au-Pd alloy became stronger and harder and showed an increased elongation. The effects of heat treatment on the strength of the palladium-based alloys were variable, showing a decrease in hardness and an increase in elongation. The nickel-based alloys were weakened by the heat treatment and showed a decrease in hardness and an increase in elongation. Heat treatment did not significantly affect the modulus of any of the tested alloys.

Influence of heat treatment on the surface texture of an etched cast nickel-chromium base alloy: An evaluation by profilometric records

Profilometric measurements were performed to test the electrochemically etched surface roughness of a Ni-Cr-Be alloy in the as-cast state and after porcelain firing simulation. A Student's t test at 5% risk leads to the conclusion that a heat-treated surface is significantly rougher than an as-cast surface after electrolytic etching. The exact cause of the increased roughness and how it improves metal-to-resin bonding must be evaluated by further research.