High Noble Alloy Research Articles

Practice‐based clinical evaluation of metal–ceramic and zirconia molar crowns: 3‐year results

This practice-based study evaluates the clinical performance of conventionally luted metal-ceramic and zirconia molar crowns fabricated with pronounced anatomical core design and a prolonged cooling period of the veneering porcelain. Fifty-three patients were treated from 07/2008 until 07/2009 with either metal-ceramic crowns (MCC) (high-noble alloy+low-fusing porcelain) or zirconia crowns (Cercon System, DeguDent, Germany). Forty-nine patients (30 women/19 men) with 100 restorations (metal-ceramic: 48/zirconia: 52, mean observational period: 36·5±6months) participated in a clinical follow-up examination and were included in the study. Time-dependent survival (in situ criteria), success (event-free restorations) and chipping rates (defects of the veneering ceramics) were calculated according to the Kaplan-Meier method and analysed in relation to the crown fabrication technique, using a Cox regression model (P<0·05). Three complete failures (metal-ceramic: 1, zirconia: 2) were recorded (survival rate after 3years: metal-ceramic: 97·6%, zirconia: 95·2%). Of the metal-ceramic restorations, 90·9% remained event-free (two ceramic fractures, one endodontic treatment), whereas the success rate for the zirconia was 86·8% (two ceramic fractures, one endodontic treatment, one secondary caries). No significant differences in survival (P=0·53), success (P=0·49) and ceramic fracture rates (P=0·57) were detected. The combination of a pronounced anatomical core design and a modified firing of the veneering porcelain for the fabrication of zirconia molar crowns resulted in a 3-year survival, success and chipping rate comparable to MCC.

Influence of framework design on the cervical color of metal ceramic crowns

The replication of natural teeth, especially for single tooth restorations in patients with high esthetic needs, represents a challenge. The purpose of the study was to analyze the color of the cervical portion of single metal ceramic crowns fabricated with different metal framework designs. The color, as measured on the CIELAB color scale, of 3 different groups of restorations (n=10) fabricated with a high noble metal alloy (V-Deltaloy) and feldspathic porcelain (Noritake Super Porcelain) was analyzed with a colorimeter. Conventional metal ceramic crowns with metal facial margins were compared to metal ceramic crowns with porcelain facial margins and a horizontal reduction of the metal framework (1.0 mm reduction) or an additional vertical reduction (1.0 mm reduction). In all specimens, the finish line was positioned at a subgingival or equigingival level. The 6 groups obtained by the combination of the levels of the 2 factors (framework extension and finish line location) were examined with an ANOVA Fisher's F-test and a post hoc Tukey's HSD test (α=.05). The mean color difference for all the groups was clinically acceptable (ΔE<3.7). Conventional metal ceramic crowns showed higher differences in relation to finish line location (ΔE=2.34), while a vertical reduction of the framework was related to lower values (ΔE=0.96). Mean Lab* values were reported for all the groups of crowns. Statistically significant differences were present for L*, a*, and b* values when related to framework extension. Considering each value in relation to the interaction between framework extension and finish line location factors, significant differences were present only for L* and a* values. No significant differences in base shade were present among the investigated crowns. Nevertheless metal ceramic crowns with vertical cut-back and porcelain facial margins presented more consistent results that tended to be closer to those of natural teeth.

Shear bond strengths of pressed and layered veneering ceramics to high-noble alloy and zirconia cores

Heat-pressed ceramics to metal alloys and zirconia have been available for some time. However, information regarding their shear bond strengths is limited. The purpose of this study was to evaluate the shear bond strengths of heat-pressed and layered ceramics with regard to their corresponding high-noble alloy and zirconia cores. Forty cylinders (approx. 5 mm in diameter) of high-noble alloy (Olympia) were cast and divided into 4 groups (n=10). Metal cylinders were veneered with ceramics to produce shear test specimens: Group PMI with IPS InLine POM; Group LMI with IPS InLine; Group PMC with Pulse press-to-metal; and Group LMC with Authentic Pulse Metal ceramic. Forty cylinders (approx. 5 mm in diameter) of zirconia (Lava) were obtained and divided into 4 groups (n=10). These cylinders were veneered with ceramics to produce shear test specimens: Group PZI with IPS e.max ZirPress; Group LZI with IPS e.max. Ceram; Group PZV with VITA PM9; and Group LZV with VITA VM9. The veneering ceramics, 3 mm in thickness, were either pressed or layered to their corresponding cylinders. Thermal cycling was performed at 5°C and 55°C for 20,000 cycles with a 20 second dwell time. Shear bond strength testing was conducted in a universal testing machine, and the failure strengths were recorded. Fracture surfaces were characterized visually, under a stereomicroscope, and with a scanning electron microscope (SEM). Data were analyzed using rank-based Kruskal-Wallis and Mann-Whitney tests with Bonferroni correction to adjust for multiple comparisons (α=.05). For metal ceramic specimens, the mean (SD) shear bond strengths ranged from 37.8 (20.6) MPa to 66.4 (22.1) MPa. There were significant differences between Groups PMI and PMC and between Groups LMI and PMC, in which Groups PMI and LMI had significantly higher strength values than Group PMC (P=.041). For zirconia ceramic specimens, the mean (SD) shear bond strengths ranged from 30.03 (9.49) MPa to 47.2 (13.0) MPa, with Group LZV having a significantly higher shear bond strength value than Group LZI (P=.012). Half of the Group PZV specimens failed during thermal cycling, and Group PZV was, therefore, excluded from statistical analysis. For all shear bond strength testing specimens, cohesive failures in the veneering ceramics were observed. For shear bond strength of veneering ceramics to high-noble alloy, there was no significant difference between pressing and layering with the same manufacturer. For shear bond strength of veneering ceramics to zirconia, there was no significant difference between the pressed and layered groups.

Microstructural analyses of two high noble gold-platinum alloys before and after conditioning in a cell culture medium

Microstructures of two high noble experimental Au-Pt alloys were compared before and after conditioning for biocompatibility, in order to identify phases and microelements responsible for the alloys’ corrosive behaviour. Microstructural characterization was carried-out by optical and scanning electron microscopy, in addition to energy dispersive X-ray analysis. X-ray diffraction was applied to determine the phases’ composition and their contribution in the alloys. Additionally, simultaneous thermal analysis was used to identify the temperatures of phase transformations. An overall assessment before conditioning showed that Au-Pt I is a two-phase alloy containing a dominant Au-rich α1 phase and a minor Pt-rich α2 phase, while the Au-Pt II alloy contains in addition three minor phases: AuZn3, Pt3Zn and Au1.4Zn0.52. The highest content of Zn (up to 6.76 wt.%) was detected in the Pt3Zn phase. After RPMI cell culture medium conditioning, the Pt3Zn and AuZn3 phases disappeared, suggesting that they are predominantly responsible for Zn loss and the lower corrosive stability of the Au-Pt II alloy.

The influence of incisal veneering porcelain thickness of two metal ceramic crown systems on failure resistance after cyclic loading

In some clinical situations, the length of either a prepared tooth or an implant abutment is shorter than ideal, and the occlusal clearance to be restored by a porcelain crown is large. Incisal thickness of the coping and the veneering porcelain should be considered to prevent mechanical failure of the crown. The purpose of this study was to investigate the influence of incisal veneering porcelain thickness of metal ceramic systems on failure resistance after cyclic loading. With a standardized technique, 60 metal ceramic anterior crowns with 2 different incisal thicknesses of porcelain veneer (2.0 and 4.0 mm) and 2 different metal alloys (Pisces Plus (B), base metal, and Leo (N), high noble metal) were fabricated to fit a custom abutment and divided into 4 groups (B20, B40, N20, N40) (n=15). The crowns were then cemented using resin cement (PANAVIA 21) and thermal cycled and mechanically cycle loaded (49-N load) for 2,000,000 cycles. The specimens were evaluated for cracks and/or bulk fracture with an optical stereomicroscope (x10) and assigned a score of success, survival, or failure. The specimens without bulk fracture after cyclic loading were loaded along the long axis of the tooth, on the incisal edge, in a universal testing machine at a crosshead speed of 1.5 mm/min until fracture. The fracture strength value (N) was recorded. The exact logistic regression and Fisher's exact test were used to study the effect of different alloys and porcelain incisal thicknesses on the success and survival rates after cycle loading. The forces at failure (fracture) of different groups were compared using the rank transform-based nonparametric 2-way ANOVA (alpha=.05). According to exact logistic regression, crowns of the high noble alloy group showed significantly higher success rates (P=.002) than those of the base metal group after cyclic loading. The success rate of the crowns with 2 mm of incisal veneering porcelain was significantly higher (P<.001) than that of the crowns with 4 mm of incisal veneering porcelain. For crowns with a 4-mm incisal thickness, N40 showed a significantly higher success rate than B40 (P=.04, Fisher's exact test). As for survival rate, the exact logistic regression indicated that neither metal type (P=.11) nor thickness (P=.60) had a significant effect. The 2-way ANOVA showed a significant effect of thickness (P=.001) and no significant effect of metal type (P=.08) on the failure load. The high noble metal ceramic crowns demonstrated a significantly higher success rate after cyclic loading than the base metal ceramic crowns. Crowns with a porcelain incisal thickness of 2 mm showed, for both metal ceramic systems, a greater success rate than those with a 4-mm incisal thickness.

Influence of Background Color on the Chromatic Value of Four All-Ceramic System Core Materials

This study aims to investigate the effect of background color on the chromatic value of four all-ceramic system core materials at clinically appropriate thicknesses. Disc specimens with 15 mm in diameter and thicknesses ranging from 0.5±0.01mm In-Ceram zirconia core, Cercon base zirconia core, and Cercon base color zirconia core) to 0.8±0.01mm (Empress II) were fabricated. A colorimeter (CIE- 1976-Lab) measured the chromatic value of all samples placed on a high-noble metal-ceramic alloy and a visible light-cured dental composite resin (A2 color) background, after which the color difference was calculated. The color difference of Empress II samples was more than 1.5 among different background color groups, while that of Zirconia was less than 1.5. The influence of background color on the Empress II dentin was visible, such that it could be used on a tooth color post. Meanwhile, the influence of background color was invisible for the three kinds of Zirconia core materia1s, such that the materials developed excellent color-masking abilities and could be adapted for use on any color background.

Comparison of cutting efficiencies between electric and air-turbine dental handpieces

Dentistry is gravitating toward the increased use of electric handpieces. The dental professional should have sufficient evidence to validate the switch from an air-turbine handpiece to an electric handpiece. However, there is little research quantifying the cutting efficiency of electric and air-turbine handpieces. Studies that do quantify cutting efficiency typically do so with only a single material. The purpose of this study was to compare the cutting efficiency of an electric handpiece and an air-turbine handpiece, using various materials commonly used in dentistry. Seven materials: Macor (machinable glass ceramic), silver amalgam, aluminum oxide, zirconium oxide, high noble metal alloy, noble metal alloy, and base metal alloy, were each cut with a bur 220 times; 110 times with an electric handpiece, and 110 times with an air-turbine handpiece. The weight difference of the material was calculated by subtracting the weight of the material after a cut from the weight of the material before the cut. The cutting efficiency was calculated by dividing the weight difference by the duration of the cut (g/s). Data were analyzed by a 2-way analysis of variance followed by Tukey's Honestly Significant Difference (HSD) test (alpha=.05). The electric handpiece cut more efficiently than the air-turbine handpiece (F=3098.9, P<.001). In particular, the high noble metal alloy, silver amalgam, and Macor were cut more efficiently with the electric handpiece (0.0383 +/-0.0002 g/s, 0.0260 +/-0.0002 g/s, and 0.0122 +/-0.0002 g/s, respectively) than with the air-turbine handpiece (0.0125 +/-0.0002 g/s, 0.0142 +/-0.0002 g/s, and 0.008 +/-0.0002 g/s, respectively). The electric handpiece is more efficient at cutting various materials used in dentistry, especially machinable glass ceramic, silver amalgam, and high noble alloy, than the air-turbine handpiece.

Minimally Retentive Gold Onlays: A Six-Year Case Report

Partial veneer gold restorations, such as gold onlays, have changed little in preparation design over the past 40 years, as evidenced by textbooks that have long been in print. Such designs must have been based on the assumption that restorations would be luted with zinc phosphate cement but have not altered, despite the introduction of stronger luting cement classes, such as resin composite and resin-modified glass ionomer cements. It is well-established that both porcelain and base metal materials, which have been etched on the intaglio surface, can be combined with resin composite luting cements to produce restorations retained largely through adhesion. However, neither of these materials can equal the combination of minimal tooth reduction and margin adaptation that is possible with high noble gold restorative materials. Although high noble gold alloys cannot be etched, air abrasion of the intaglio surface of restorations likely improves micromechanical retention, but it is unknown whether this, along with a strong luting cement, is sufficient to stabilize high noble gold alloys in preparations with considerably less retention and resistance form than traditional designs.

The influence of the microstructure of high noble gold-platinum dental alloys on their corrosion and biocompatibility in vitro

The aim of this work was to compare the microstructures of two high noble experimental Au-Pt alloys with similar composition with their corrosion and biocompatibility in vitro. We showed that Au-Pt II alloy, composed of 87.3 wt.% Au, 9.9 wt.% Pt, 1.7 wt.% Zn and 0.5 wt.% Ir + Rh + In, although possessing better mechanical properties than the Au-Pt I alloy (86.9 wt.% Au, 10.4 wt.% Pt, 1.5 wt.% Zn and 0.5 wt.% Ir + Rh + In), exerted higher adverse effects on the viability of L929 cells and the suppression of rat thymocyte functions, such as proliferation activity, the production of Interleukin-2 (IL-2), expression of IL-2 receptor and activation — induced apoptosis after stimulation of the cells with Concanavalin-A. These results correlated with the higher release of Zn ions in the culture medium. As Zn2+, at the concentrations which were detected in the alloy’s culture media, showed a lesser cytotoxic effect than the Au-Pt conditioning media, we concluded that Zn is probably not the only element responsible for alloy cytotoxicity. Microstructural characterization of the alloys, performed by means of scanning electron microscopy in addition to energy dispersive X-ray and X-ray diffraction analyses, showed that Au-Pt I is a two-phase alloy containing a dominant Au-rich α1 phase and a minor Pt-rich α2 phase. On the other hand, the Au-Pt II alloy additionally contained three minor phases: AuZn3, Pt3Zn and Au1.4Zn0.52. The highest content of Zn was identified in the Pt3Zn phase. After conditioning, the Pt3Zn and AuZn3 phases disappeared, suggesting that they are predominantly responsible for Zn loss, lower corrosion stability and subsequent lower biocompatibility of the Au-Pt II alloy.

Shear bond strength of veneering porcelain to zirconia and metal cores

STATEMENT OF PROBLEMZirconia-based restorations have the common technical complication of delamination, or porcelain chipping, from the zirconia core. Thus the shear bond strength between the zirconia core and the veneering porcelain requires investigation in order to facilitate the material's clinical use.PURPOSEThe purpose of this study was to evaluate the bonding strength of the porcelain veneer to the zirconia core and to other various metal alloys (high noble metal alloy and base metal alloy).MATERIAL AND METHODS15 rectangular (4×4×9mm) specimens each of zirconia (Cercon), base metal alloy (Tillite), high noble metal alloy (Degudent H) were fabricated for the shear bond strength test. The veneering porcelain recommended by the manufacturer for each type of material was fired to the core in thickness of 3mm. After firing, the specimens were embedded in the PTFE mold, placed on a mounting jig, and subjected to shear force in a universal testing machine. Load was applied at a crosshead speed of 0.5mm/min until fracture. The average shear strength (MPa) was analyzed with the one-way ANOVA and the Tukey's test (α= .05). The fractured specimens were examined using SEM and EDX to determine the failure pattern.RESULTSThe mean shear strength (± SD) in MPa was 25.43 (± 3.12) in the zirconia group, 35.87 (± 4.23) in the base metal group, 38.00 (± 5.23) in the high noble metal group. The ANOVA showed a significant difference among groups, and the Tukey's test presented a significant difference between the zirconia group and the metal group. Microscopic examination showed that the failure primarily occurred near the interface with the residual veneering porcelain remaining on the core.CONCLUSIONThere was a significant difference between the metal ceramic and zirconia ceramic group in shear bond strength. There was no significant difference between the base metal alloy and the high noble metal alloy.

Marginal accuracy of combined tooth–implant‐supported fixed dental prostheses after in vitro stress simulation

Caries, periodontal disease, and peri-implant inflammation caused by deficient marginal adaptation of fixed prostheses are reasons for clinical failure of combined tooth-implant-supported fixed dental prostheses (TISFDP). This in vitro study examined the marginal accuracy in TISFDP after simulated stress in an artificial oral environment. Twelve three-unit TISFDPs were fabricated using a high noble alloy on models containing a human premolar with an artificial periodontium and an implant. Four three-unit tooth-supported prostheses (TSFDP) represented the control group. The experimental TISFDPs (four per group) were luted with three different cements: group 1, zinc phosphate; group 2, glass ionomer; group 3, self-adhesive resin. The specimens were mechanically loaded (1.2 million cycles/50 N) and thermally cycled (8000 cycles with 5/55 degrees C). The vertical marginal gap was measured before and after cementation, after chewing simulation and after thermal cycling by light microscopy (x 560). The results were subjected to statistical analysis (t-test/one-way analysis of variance/Bonferroni). Significant increase (P< or =0.05) in the marginal gap was found after cementation within the experimental TISFDPs (implants, 11.7-18.7 microm; teeth, 13.4-24.2 microm) and the control TSFDPs (28.5 microm). Comparison of groups 1 and 2 revealed significant differences for the teeth while comparison of the implants showed significant differences among all groups. Chewing simulation and thermal cycling caused statistically insignificant changes in the marginal gaps of the experimental as well as the control TSFDPs. The cementation of the TISFDPs with different luting materials caused a specific enlargement of the marginal gap in teeth and implants. Subsequent to simulated oral stress in an artificial oral environment, no significant changes of the marginal accuracy could be found.

Flexural and shear strengths of ZrO2 and a high-noble alloy bonded to their corresponding porcelains

Flexural and shear strength between ZrO(2) cores and veneering porcelains require investigation to facilitate clinical use. The purpose of this study was to assess the strength of ZrO(2) and a high-noble alloy with corresponding porcelains. Forty rectanglar (12 x 10 x 3 mm) and 20 cylindrical (5 x 5 mm) specimens of ZrO(2) (Lava) and high-noble alloy (Olympia) were fabricated for 4-point flexural testing and shear testing. IPS d.SIGN veneering porcelain for high-noble alloy and Lava Ceram, 2 mm thick, were fired, joining the 2 corresponding rectangles of high-noble alloy and ZrO(2) to create flexural test specimens. The same types of veneering porcelains, 3 mm in thickness, were fired on 1 side of the corresponding high-noble alloy and ZrO(2) cylinders to produce shear specimens. The flexural and shear specimens were divided into 4 groups (n=10); metal ceramic and ZrO(2) with and without thermal cycling. Thermal cycling was performed at 5 degrees C and 55 degrees C for 5000 cycles with a 20-second dwell time. Flexural and shear tests were performed using a universal testing machine. Fractures were characterized using a stereomicroscope and SEM. Data were analyzed with a 1-way ANOVA and Tukey HSD post hoc test (alpha=.05). The ANOVA revealed a significant difference among flexural groups (P=.008) and among shear groups (P<.001). In flexure, the Tukey HSD post hoc test revealed a significant difference (P=.005) between metal ceramic thermal cycled and ZrO(2) thermal cycled groups, with a higher value of 91.01 (22.33) MPa for the metal ceramic group. In shear, the Tukey HSD post hoc test revealed a significant difference between metal ceramic and ZrO(2) groups, with a higher value of 82.00 (22.49) MPa for the metal ceramic group. Thermal cycling did not have a significant effect on flexure or shear strength. ZrO(2) specimens failed cohesively within the veneering porcelain. There were no significant differences among the groups in flexure, except between thermal cycled metal ceramic and ZrO(2) groups. There was a significant difference between the metal ceramic and ZrO(2) groups in shear. Thermal cycling did not have a clear effect among different groups in both tests.

Corrosion behavior of as-received and previously cast high noble alloy

The rationale for using high noble alloys is based largely upon their alleged ability to resist corrosion. However, combining previously cast metal with new alloy might have a detrimental effect on the corrosion behavior of a high noble alloy. The purpose of this study was to characterize the elemental composition of an as-received and recast high noble alloy and to examine the in vitro corrosion behavior in 2 media, using a potentiodynamic polarization technique. Disk-shaped specimens, 6 mm in diameter and 3 mm thick, were prepared from a high noble alloy (Ney-Oro-B2) under 3 casting protocols, according to the proportion of as-received and recast gold alloy (n=26); the groups included an as-received (100% as-received metal) group, 50% to 50% group (50 wt% new metal, 50 wt% once-recast metal), and recast group (100% once-recast metal). The surface structures of 20 specimens from each group were examined under scanning electron microscopy (SEM), the elemental compositions were determined using x-ray energy-dispersive spectroscopy at 3 sites on the specimen, and the data were averaged. Further, the potentiodynamic cyclic polarization between -1000 and +1000 mV (SCE, or saturated calomel electrode) was performed for 6 specimens from each casting protocol in 0.09% NaCl solution (n=3) and Fusayama artificial saliva (n=3) at 37 degrees C. Zero-current potential and corrosion current density were determined. The data were analyzed with 1-way and 2-way analysis of variance and the Ryan-Einot-Gabriel-Welsch multiple-range t test (alpha=.05). Elemental composition was significantly different among the casting groups (P<.001). The mean weight percentage values were 72.7% to 75.7% Au, 4.5 to 7.0% Pd, 10.7% to 11.1% Ag, 7.8% to 8.4% Cu, and 1.0% to 1.4% Zn. The mean values for zero-current potential (ZCP) and corrosion current density (I(CORR)) for all the casting protocols were not significant (P=.67 and P=.51, respectively). Moreover, the mean values were not significant for corrosion current density with the electrolyte effect (P=.45). Only zero-current potential had a significant electrolyte effect (P<.001). Furthermore, the interaction between casting protocols and electrolyte were not significant among all corrosion parameters. High noble alloy in all casting protocols evaluated retained passivity under electrochemical conditions similar to the oral environment.

Variations of color with alloying elements in Pd-free Au–Pt-based high noble dental alloys

The effects of alloying addition of a small amount of base metals (In, Sn, Fe, Zn) on color variations in Pd-free Au–Pt-based high noble dental alloys were investigated in terms of rectilinear and polar color coordinates. The ternary Au–Pt–X (X = In, Sn, Fe, Zn) and quaternary Au–Pt–In–Y (Y = Sn, Fe, Zn) alloys were prepared from high purity component metals. The amount of alloying base metals, X and Y, were restricted up to 2 at.%. The alloying addition of a small amount of Fe, In, Sn, to a binary Au–10 at.% Pt alloy (referred to as AP10) effectively increased chroma, C * . On the other hand, the addition of Zn to the parent alloy AP10 did not change color coordinates greatly. The increase in chroma in the present Au–Pt-based high noble alloys was attributed to the increase in the slope of spectral reflectance curve at its absorption edge near 515 nm. It was found that the addition of a small amount of Fe to the parent alloy AP10 markedly increased lightness, L *, and the addition of Sn gave a very light tint of red to the parent alloy. Although red–green chromaticity index a * contributed to chroma to some extent, contribution of yellow–blue chromaticity index b * was much greater in determining chroma in this Pd-free Au–Pt-based multi-component alloys. The present results are expected to be valuable in case color is to be taken into account in designing Pd-free Au–Pt-based high noble dental alloys.

Color analysis of oxidized Pd-free Au-Pt-based high noble dental alloys for porcelain veneering

Color analysis of oxidized Pd-free Au-Pt-based high noble dental alloys for porcelain veneering

Optical properties of Au−Pt−Pd-based high noble dental alloys

The effects of the addition of various alloying elements (In, Sn, Zn) of up to 4 mass % on the optical properties of Au-Pt-Pd-based high noble dental alloys were investigated by means of spectrophotometric colourimetry. Spectral reflectance data from the mirror-polished flat samples were collected at 10 nm intervals in the wavelengths ranging from 360 nm to 740 nm under the CIE standard illuminant D65 and the observer of 10 degrees. Three dimensional colour coordinates in the CIEL *a*b* andL *C*h colour spaces were also obtained to specify the alloy colour. The alloying addition of a small amount of Sn and/or In increased the reflectance in the long-wavelength range and decreased the reflectance in the shortwavelength range. As a result, the maximum slope of the spectral reflectance curve at the absorption edge near 520 nm apparently increased with the additions of Sn and/or In. This change in shape of the spectral reflectance curve caused the increased chromaticity indices,a*, b*, and chroma,C*. On the other hand, the hue angle was not greatly affected by the alloying elements, with the exception of the alloy containing 4 mass % Sn showing a slightly lower hue angle. It was evidenced that in the single-phase structured alloys the average number of valence electrons per atom,e/a, in an alloy is a controlling factor of the colour of Au−Pt−Pd-based high noble dental alloys. That is, by increasinge/a-value,a*-, b*-, C*- coordinates systematically increased, giving a slight gold tinge to the parent Au-Pt-Pd alloy within the limitation that the structure of an alloy is a single phase. The addition of Sn of 2 mass % or more produced a small amount of the second phase of possible intermetallic compounds between Sn and Pd or Pt. The coexistence of a small amount of the second phase of possible intermetallic compounds further increased a gold tinge. However, the inclusion of 4 mass % Sn to the parent Au-Pt-Pd alloy gave a very light tint of red to the alloy. Results of the present study are expected to be useful in controlling colour of Au-Pt-Pd-based high noble dental alloys.

Ion release from dental casting alloys as assessed by a continuous flow system: Nutritional and toxicological implications

Objectives The aims of this study were to quantify the metallic ions released by various dental alloys subjected to a continuous flow of saliva and to estimate the nutritional and toxicological implications of such a release. Methods Four pieces of three nickel-based, one noble, one high-noble and two copper–aluminum alloys were cast and then immersed in a continuous flow of artificial saliva for 15 days. To simulate three meals a day, casts were subjected to thrice-daily episodes, lasting 30 min each and consisting of pH decreases and salinity increases. After 15 days, the metallic ions in the artificial saliva were analyzed. Data were expressed as averaged release rate: μg/cm 2/day of ion released for each alloy. The highest value of 95% Cl of each ion was adapted to a hypothetical worst scenario of a subject with 100 cm 2 of exposed metal surface. The results were compared with the tolerable upper daily intake level of each ion. Results The copper–aluminum alloys released copper, aluminum, nickel, manganese and iron. The nickel-based alloys essentially released nickel and chromium, while the beryllium-containing alloy released beryllium and significantly more nickel. The noble and high-noble alloys were very resistant to corrosion. The amount of ions released remained far below the upper tolerable intake level, with the exception of nickel, released by beryllium-containing nickel-based alloy, whose levels approach 50% of this threshold. Significance The daily amount of ions released seems to be far below the tolerable upper intake levels for each ion.

Basic Evaluation of Cast Joining for Electroformed Coping using Multi-purpose Alloys

The purpose of this study was to evaluate the bonding interface and bonding strength of electroformed coping when cast joining was used with a multi-purpose alloy. The multi-purpose alloy was cast at a mold temperature of 700, 750 or 800 degrees C. A high noble alloy tab was also soldered onto an electroformed coping as a control. Sectioned surfaces of cast joining and soldered specimens were observed using a scanning electron microscope and analyzed using an electron probe micro analyzer. Shear bonding strength of specimens cast at 750 degrees C and that of soldered specimens were determined. The edge of the cast joining alloy was round, but this improved as temperature increased. Diffusion of elements from the cast joining alloy and electroformed coping was detected at the interface, which contributed to a significantly higher bonding strength in the cast joining specimen than in the soldered specimen. These results suggested that the cast joining could be potentially employed for electroformed copings.

The effect of a resin-based sealer on crown retention for three types of cement.

In an effort to control postoperative sensitivity, dentin sealers are being applied following crown preparation with little knowledge of how crown retention might be affected. A previous study demonstrated no adverse effect when using a glutaraldehyde-based sealer, and existing studies have shown conflicting results for resin-based products. This study determined if a resin sealer applied to prepared dentin affected retention of cemented castings when using 3 common types of luting agents. Extracted human molars (n=55) were prepared with a flat occlusal, 20-degree taper, and 4-mm axial length. The axial surface area of each preparation was determined and specimens were distributed equally among groups (n=11). A 2-step, single-bottle adhesive system (One Step) was used to seal dentin following tooth preparation. Sealer was not used on the control specimens except for the modified-resin cement (Resinomer) specimens that required use of adhesive with cementation. Using ceramometal high noble alloy (Olympia), a casting was produced for each specimen and cemented with a seating force of 20 Kg using either zinc phosphate (Fleck's), glass ionomer (Ketac-Cem) or modified-resin cement (Resinomer) with the single-bottle adhesive. Castings were thermal cycled at 5 degrees C and 55 degrees C for 2500 cycles; then removed along the path of insertion using a universal testing machine at 0.5 mm/min. A single-factor ANOVA was used with alpha=.05. The nature of failure was also recorded and the data analyzed with a chi-square test. Mean dislodgment stresses for unsealed and sealed conditions were 3.7 +/- 1.0 and 2.2 +/- 0.8 MPa for zinc phosphate; 2.7 +/- 1.2 and 4.2 +/- 0.9 MPa for glass ionomer, respectively (P<.001). Retentive stress of castings cemented with modified-resin cement was 6.4 +/- 1.7 MPa. With resin sealer in combination with zinc phosphate, cement resided totally on castings in 82% of the situations and was on both surfaces without sealer. The tooth failed before casting dislodgment in 9 of 11 specimens cemented with modified-resin cement. Resin sealer decreased casting retentive stress by 42% when used with zinc phosphate. However, sealer use resulted in 55% increased retention when used with glass ionomer. The modified-resin cement produced the highest mean dislodgment stress, nearly always exceeding the strength of the tooth.

The effect of a resin-based sealer on crown retention for three types of cement

Statement of problem In an effort to control postoperative sensitivity, dentin sealers are being applied following crown preparation with little knowledge of how crown retention might be affected. A previous study demonstrated no adverse effect when using a glutaraldehyde-based sealer, and existing studies have shown conflicting results for resin-based products. Purpose This study determined if a resin sealer applied to prepared dentin affected retention of cemented castings when using 3 common types of luting agents. Material and methods Extracted human molars (n=55) were prepared with a flat occlusal, 20-degree taper, and 4-mm axial length. The axial surface area of each preparation was determined and specimens were distributed equally among groups (n=11). A 2-step, single-bottle adhesive system (One Step) was used to seal dentin following tooth preparation. Sealer was not used on the control specimens except for the modified-resin cement (Resinomer) specimens that required use of adhesive with cementation. Using ceramometal high noble alloy (Olympia), a casting was produced for each specimen and cemented with a seating force of 20 Kg using either zinc phosphate (Fleck's), glass ionomer (Ketac-Cem) or modified-resin cement (Resinomer) with the single-bottle adhesive. Castings were thermal cycled at 5°C and 55°C for 2500 cycles; then removed along the path of insertion using a universal testing machine at 0.5 mm/min. A single-factor ANOVA was used with α=.05. The nature of failure was also recorded and the data analyzed with a chi-square test. Results Mean dislodgment stresses for unsealed and sealed conditions were 3.7 ± 1.0 and 2.2 ± 0.8 MPa for zinc phosphate; 2.7 ± 1.2 and 4.2 ± 0.9 MPa for glass ionomer, respectively ( P<.001). Retentive stress of castings cemented with modified-resin cement was 6.4 ± 1.7 MPa. With resin sealer in combination with zinc phosphate, cement resided totally on castings in 82% of the situations and was on both surfaces without sealer. The tooth failed before casting dislodgent in 9 of 11 specimens cemented with modified-resin cement. Conclusions Resin sealer decreased casting retentive stress by 42% when used with zinc phosphate. However, sealer use resulted in 55% increased retention when used with glass ionomer. The modified-resin cement produced the highest mean dislodgment stress, nearly always exceeding the strength of the tooth.