Efstratios Papazoglou

Porcelain adherence vs force to failure for palladium–gallium alloys: a critique of metal–ceramic bond testing

OBJECTIVES The purpose of this study was to characterize the metal-ceramic bond of four commercial Pd-Ga alloys by two separate tests: porcelain adherence and bond failure force. A Pd-Ag alloy was the control. A secondary goal was to investigate a possible correlation between the percent porcelain retained and bond failure forces. METHODS For adherence testing, five cast plates of each alloy were air abraded and oxidized. The porcelain was applied on a circular area in the center of each plate and fractured using constant-strain flexure. The area fraction of adherent porcelain (%) was calculated via a standardized spectrometric technique. Bond failure forces were measured in three-point bending using bar specimens. The modulus of elasticity of the five alloys was also measured. No attempt was made to calculate bond strength since the residual thermal stresses at the interfacial region were unknown. Data were compared via ANOVA and the Tukey multiple range test (p < 0.05). RESULTS All failures occurred at the porcelain termination sites with no tensile fracture of the porcelain. Two Pd-Ga alloys exhibited porcelain adherence comparable with previously studied Pd-Cu-Ga alloys. There was no correlation between the porcelain adherence and the force to failure (r2 = 0.0159). Additionally, no statistically significant differences were found among the moduli of elasticity of the five alloys. SIGNIFICANCE The new Pd-Ga alloys have been commercially introduced with little information on the quality of the bond with porcelain. The use of two different means for assessing the metal-ceramic bond provides information on the relationship of data using different experimental techniques.

Porcelain adherence to high-palladium alloys

The adherence of porcelain to four representative high-palladium alloys of the first generation (Pd-Cu-Ga) and second generation (Pd-Ga) was measured by use of a gold-palladium alloy as a control. The area fraction of adherent porcelain after metal-ceramic specimens were debonded in biaxial flexure at constant strain was calculated from the characteristic Si x-ray intensity with a standardized scanning electron microscope/energy-dispersive spectroscopy technique (SEM/EDS). The gold-palladium alloy exhibited the highest percentage of cohesive fracture through the porcelain, the two first-generation alloys were intermediate, and the two second-generation alloys exhibited the lowest area fractions. This study demonstrated that conventional visual (naked eye) or microscopic examination of the fractured metal-ceramic specimens at moderate magnification and the use of standard quantitative metallographic techniques were inadequate to provide accurate measurements of the area fraction covered with porcelain.

X-ray diffraction studies of oxidized high-palladium alloys.

OBJECTIVE The purpose of this study was to use x-ray diffraction (XRD) to obtain new information about the oxide layers on four representative oxidized high-palladium alloys. METHODS Cast specimens of two Pd-Cu-Ga alloys and two Pd-Ga alloys, with both polished and etched surfaces and air-abraded surfaces, were subjected to oxidation procedures recommended by the manufacturers. The specimens were analyzed by x-ray diffraction using CuK alpha radiation, and the peaks were compared to appropriate Joint Committee on Powder Diffraction Standards (JCPDS). RESULTS The surface preparation procedure had a profound effect on the phases present in the oxide layers. For the specimens that had been polished and etched, CuGa2O4 and beta-Ga2O3 were detected on the 79Pd-10Cu-9Ga-2Au alloy, whereas SnO2 and CuGa2O4 were detected on the 76Pd-10Cu-5.5Ga-6Sn-2Au alloy. The oxide layers on both Pd-Cu-Ga alloys contained Cu2O1 and the oxide layer on the 76Pd-10Cu-5.5Ga-6Sn-2Au alloy may contain beta-Ga2O3. The principal phase in the oxide layers on both Pd-Ga alloys that had been polished and etched was ln2O3, which exhibited extreme preferred orientation. No other phase was detected in the oxide layer on the 85Pd-10Ga-2Au-1Ag-1 ln alloy, whereas beta-Ga2O3 was found in the oxide layer on the 75Pd-6Ga-6Au-6Ag-6.5ln alloy. For the air-abraded specimens, beta-Ga2O2 was not present in the oxide layers on the Pd-Cu-Ga alloys, and beta-Ga2O3 was the major phase in the oxide layers on the Pd-Ga alloys. Palladium oxide(s) in varying amounts were detected for both surface preparations of the Pd-Cu-Ga alloys and for the air-abraded Pd-Ga alloys. Except for the 76Pd-10Cu-5.5Ga-6Sn-2Au alloy, the oxide layer caused minimal change in the lattice parameter of the palladium solid solution compared to that for the as-cast alloy. SIGNIFICANCE Knowledge of the phases found in the oxide layers on these high-palladium alloys is of fundamental importance for interpreting differences in the adherence of dental porcelain to the metal substrates under static and dynamic conditions, and may provide guidance in the development of new high-palladium alloys with improved metal-ceramic bonding.

Shear bond strengths for composite and autopolymerized acrylic resins bonded to acrylic resin denture teeth

Statement of problem. Composite has been used to modify acrylic resin denture teeth. Purpose. This in vitro investigation examined the shear bond strengths between composite and autopolymerized acrylic resin bonded to acrylic resin denture teeth. Material and methods. The surface treatments used for the denture teeth included wetting with methyl methacrylate (MMA), vinylethyl methacrylate monomer (VEMA), unfilled liquid resin, composite bonding agent, and composite color modifier. Nonhydrated and hydrated denture tooth groups were included. A commercial composite was bonded to the denture teeth. The control group consisted of autopolymerized PMMA resin bonded to the acrylic resin denture teeth, and another group consisted of polyvinylethyl methacrylate bonded to acrylic resin denture teeth. The samples were thermocycled and tested in shear. Results. Acrylic resin denture teeth prewetted with MMA and treated with unfilled resin or a bonding agent had bond strength values comparable to the control group. VEMA was not as effective in promoting the bond. Composite color modifier did not produce a significantly weaker bond between the acrylic resin teeth and added composite. No prewetting of the teeth with MMA resulted in the lowest bond strength. Mean shear bond strengths for corresponding hydrated and non-hydrated groups were not significantly different. Conclusion. Bond strength of composite-to-acrylic resin denture teeth was comparable to the bond strength of autopolymerized acrylic resin.

X-ray diffraction studies of as-cast high-palladium alloys

OBJECTIVES The purpose of this study was to use x-ray diffraction (XRD) to investigate four representative high-palladium alloys in the as-cast condition and obtain new information about the metallurgical phases. METHODS Two Pd-Cu-Ga alloys and two Pd-Ga alloys were cast into plate-shaped specimens (20 mm x 1.5 mm) which were bench-cooled. Polished and etched specimens were analyzed using two different x-ray diffractometers and CuKa radiation. RESULTS All four alloys exhibited strong XRD peaks for the face-centered cubic (fcc) palladium solid solution matrix, and variations in the lattice parameter were consistent with alloy compositions. Comparison of the relative peak intensities for the alloys and the pure palladium powder standard indicated that the as-cast microstructures had preferred crystallographic orientation. Because the two Pd-Cu-Ga alloys contained appreciable amounts of near-surface lamellar interdendritic or eutectic constituents, it was possible to determine previously unreported XRD peaks for the Pd2Ga phase in these alloys. Low-intensity peaks in the Pd-Ga alloys were attributed to small amounts of secondary phases observed in the microstructures. SIGNIFICANCE Knowledge of the metallurgical structures of these high-palladium alloys can be important for interpretation of microstructural observations, mechanical properties, corrosion behavior and clinical performance.

Effects of three soldering techniques on the strength of high-palladium alloy solder joints

STATEMENT OF PROBLEM Little information is available on the optimum technique for soldering high-palladium alloys, which have gained considerable popularity for prosthodontic applications. PURPOSE The objective of this study was to compare the flexural stress at the proportional limit of four noble dental alloy specimens soldered with torch, oven, and infrared-techniques. MATERIALS AND METHODS The high-palladium alloys studied were Legacy XT (Jelenko), Freedom Plus (Jelenko), and IS 85 (Williams/Ivoclar). A gold-palladium alloy, Olympia (Jelenko), served as the control. Thirty round bars, 18 x 3 mm, were cast from each alloy, cut in half, aligned, and joined using Olympia Pre solder (Jelenko) for the gas-oxygen torch and the infrared technique and Alboro LF solder (Jelenko) for the oven technique. Each soldered bar was subjected to three-point bending, and the maximum elastic stress or strength of the solder joint was calculated at the proportional limit. Data were analyzed by two-way ANOVA and the Ryan-Einot-Gabriel-Welsch (REGW) multiple range test at the 0.05 level of significance. RESULTS There was no significant difference between torch and oven-soldering, but both were significantly different from the infrared technique. ANOVA showed a significant difference between alloys, but this difference could not be detected with the REGW test. SEM examination of the fracture surfaces revealed grooves associated with the path of crack propagation. X-ray energy-dispersive spectroscopic analysis failed to detect copper in the solders, and there were no significant changes in the solder compositions after the melting procedures. CONCLUSIONS All three techniques can yield satisfactory solder joints in high-palladium alloys. These joints should be well-polished to achieve optimal strength.

The complementary nature of x-ray photoelectron spectroscopy and angle-resolved x-ray diffraction part II: Analysis of oxides on dental alloys

X-ray photoelectron spectroscopy (XPS) and angle-resolved x-ray diffraction (ARXRD) were used to analyze the oxide layer on three palladium-gallium-based dental casting alloys. The oxide layers were approximately 10 Μm thick. The use of the techniques helped to determine which mechanism was responsible for oxide formation—either (a) oxide layer growth via diffusion of oxygen through the scale to the metal, causing the scale to grow at the metal-oxide interface, or (b) an oxide layer formed by metal ions diffusing through the scale to the surface and reacting with oxygen, causing the scale to grow at the oxide-air interface. The oxide growth mechanisms were correlated to previous layer adhesion results determined with biaxial flexure testing.

Direct versus indirect inlay/onlay composite restorations in posterior teeth. A systematic review and meta-analysis

OBJECTIVE To evaluate the long-term clinical performance of direct versus indirect composite inlays/onlays in posterior teeth. DATA Screening for inclusion eligibility, quality assessment of studies and data extraction was performed independently by two authors. SOURCES The electronic databases MEDLINE, EMBASE, Cochrane Oral Health Groups Trials Register and CENTRAL were searched (14.12.2015), with no restriction to publication date or language. We included only randomised controlled trials (RCTs) and evaluated them according to Cochrane risk of bias tool. The main outcome assessed was the restoration failure, determined by several clinical parameters. STUDY SELECTION Two studies concerning direct and indirect inlays (82 patients with 248 restorations) and one study for onlays (157 patients with 176 restorations) satisfied the inclusion criteria. Two trials, one of unclear and one of high risk of bias, could be mathematically combined. The meta-analysis indicated no statistically significant difference in the risk failure between direct and indirect inlays, after 5 years (RR: 1.54; 95% Cl: 0.42, 5.58; p=0.52) or 11 years of function (RR: 0.95; 95% Cl: 0.34, 2.63; p=0.92). Only one parameter, the marginal discoloration, slightly favored direct inlays after 11 years (RR: 0.41; 95% Cl: 0.17, 0.96; p=0.04). Only one study dealt with onlays; an overall 5-year survival of 87% (95% CI: 81-93%) was reported. CONCLUSION The difference of the two techniques did not reach statistical significance in order to recommend one technique over the other. The scarcity of primary studies support the need for further well-designed long-term studies in order to reach firm conclusions about both techniques. CLINICAL SIGNIFICANCE Resin composite materials, placed directly or indirectly, exhibit a promising long-term clinical performance when rehabilitation of posterior teeth is needed. Although many years in clinical practice, the selection of the best treatment protocol still remains subjective. The available studies, and their synthesis, cannot provide reliable evidence in this field.

Change of optical properties of contemporary resin composites after one week and one month water ageing.

OBJECTIVES To compare color and translucency changes after water ageing for one-week and one-month in light and dark shades of contemporary polychromatic resin composites. METHODS Enamel (e) and dentine (d), light and dark (A1 and A4 or equivalents) shades were selected from the composites Enamel-Plus HRi/Micerium, Miris-2/Coltene, IPS Empress-Direct/Ivoclar and Filtek-Supreme/3M ESPE and light and dark shades from the TPH-Spectum/Densply monochromatic composite. Five disks (d = 10mm, h = 1mm) per material, enamel/dentine and light/dark shade were prepared. A colorimetric evaluation, over white and black background, according to the CIELab system was performed just after preparation and after one-week and one-month dark water-storage at 37°C. Color (ΔEab) and translucency (ΔTP) differences were calculated. Results were analysed by ANOVA and Scheffes test, paired t-test and linear regression analysis (a = 0.05). RESULTS One-week water ageing provided a wide range of ΔEab values (0.79 Filtek(e)/D2 to 5.19 Filtek(d)/A1) and ΔTP values (-2.74 Hri/UD1 to 1.03 TPH/A1). After one-month water ageing ΔEab ranged from 1.09 Filtek(e)/D2 to 7.94 Filtek(d)/A1 and ΔTP values from -2.71Hri/UD1 to 1.07 Filtek(d)/A4. Significant changes in ΔEab between one-week and one-month water ageing were noted for Filtek and Miris dentine and Miris light enamel shades. As for ΔTP, significant difference was recorded only for IPS(e)/A4. ΔEab was significantly correlated with ΔL, Δα, Δb and ΔTP after one-week and with ΔL and Δα after one-month ageing. CONCLUSIONS Water ageing caused remarkable color changes, which were material and shade depended. Thirteen out of eighteen of the tested composites exhibited clinically perceptible (ΔEab>2.6) color changes even after short water ageing period.

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.