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Long span base metal alloy fixed prosthesis and partial dental prosthesis frameworks most often require welding for better fit and adaptation. The type of metal alloys used and its effect on the weld strength of the prosthesis have to be investigated. The aim of the study is to comparatively analyze the weld strength of nickel-chromium (Ni-Cr) and cobalt-chromium (Co-Cr) base metal alloys when subjected to tungsten inert gas (TIG) welding. 10 nickel- and cobalt-based specimens were obtained by casting of castable resin patterns of dimension 25 mm × 3 mm × 1 mm. Welding of the samples was carried out using the Lampert PuK 2 welding equipment, and a three-point bend test using a universal testing machine was carried out to evaluate the weld strength of the specimens. Statistical analysis was carried out using the SPSS software version 23. Higher weld strength was observed in the Co-Cr alloy (mean = 898 MPa) than in the Ni-Cr alloy (mean = 690 MPa), when submitted to TIG welding (P < 0.05). TIG welding could be a better alternative for joining base metal alloys for long span edentulous cases, and cobalt-based alloys could be better alternatives to nickel-based alloys that usually tend to cause hypersensitivity reactions.

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PURPOSE: To compare the load to fracture of cobalt-chromium (Co-Cr) 3-unit posterior fixed partial denture (FPD) frameworks manufactured by conventional and digital techniques and to evaluate the influence of the framework design on the fracture load. MATERIAL AND METHODS: Eighty 3-unit Co-Cr posterior FPD frameworks were fabricated with two designs: intermediate pontic (n = 40) and cantilever (n = 40). Each design was randomly divided into four groups (n = 10): casting, direct metal laser sintering, soft metal milling, and hard metal milling. After thermal cycling, all specimens were subjected to a 3-point bending test until fracture. Data were statistically analyzed using one-way ANOVA, Welch and Brown-Forsythe test, Ryan-Einot-Gabriel-Welsch F and Tamhane T2 post hoc test, Student's t test, and Weibull statistics (α = 0.05). RESULTS: Significant differences (p < 0.001; F = 39.59) were found among intermediate pontic frameworks (except between laser sintering and hard metal milling), and cantilevered frameworks (F = 36.75) (except between laser sintering and hard metal milling, and casting and soft metal milling). The cantilever groups showed load to fracture values significantly lower than those of the intermediate pontic (p < 0.001; F = 28.29). The Weibull statistics corroborated the results. CONCLUSIONS: Hard metal milling and laser sintered frameworks exhibited the highest load to fracture values. However, all tested frameworks demonstrated clinically acceptable load to fracture values. The framework design directly affected the fracture load, with drastically lower values in cantilevered frameworks.

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Introduction: This study aimed to investigate the effect of different surface treatments on the bond strength of resin cement to nickel-chrome (Ni-Cr) alloy. Methods: Forty disk-shaped specimens of Ni-Cr alloy were prepared and divided into 4 groups. In the first group, the specimens' surface was sandblasted with 50 µ Al2 O3 particles. In the second group, the specimens were prepared with the Er:YAG laser. In the third group, the specimens were prepared using the Er:YAG laser after sandblasting. In the fourth group, the specimens' surface was covered with a thin layer of MKZ metal primer after sandblasting. Then the cylinders of composite resin were bonded to the treated metal surfaces using Panavia F2.0 resin cement. All of the samples were subjected to 2000 thermal cycles. The shear bond strength was tested using a universal testing machine at the crosshead speed of 0.5 mm/min. The failure mode was also observed by a stereomicroscope. Data were analyzed using the one-way ANOVA and the Tukey HSD test at a significance level of 0.05. Results: The shear bond strength from the highest to the lowest were as follows: the Er:YAG laser group, the sandblast and MKZ primer combination group, the sandblast group, and the sandblast and Er:YAG laser combination group. The mean differences of shear bond strength between the Er:YAG laser group and the sandblast group (P=0.047) and also between the Er:YAG laser group and the sandblast and Er:YAG laser combination group (P=0.015) were statistically significant. Conclusion: Among the different surface treatments employed in this study, Er:YAG laser treatment increased the shear bond strength between the metal alloy and the resin cement (Pavnavia F2).

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AIM AND OBJECTIVES: In dentistry, base metal casting alloys are extensively used for the fabrication of inlays, onlays, crowns, bridges, partial dentures, etc. During the casting of these alloys, excess amount of material used than needed will be collected as sprue buttons at the end, which is either added to the fresh alloy during casting and reused or disposed of. MATERIALS AND METHODS: The aim of the present in vitro experimental study was to investigate the effect of the complete recasting of four commercially available cobalt-chromium (Co-Cr) and nickel-chromium (Ni-Cr) base metal casting alloys on their cytotoxicity. During the study, four groups of alloys were subjected to complete recasting up to twenty times without the addition of new alloy. The cytotoxicity assessment of the selected alloys after recasting (Co-Cr and Ni-Cr alloys) was carried out using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. RESULTS: The results indicated that Co-Cr alloys exhibit superior cell viability compared to Ni-Cr alloys, and cytotoxic potential of the alloys increased with repeated casting and led to increased cell death. The recasting of alloys in the present study did not show high cytotoxicity even after the 20th recasting. CONCLUSION: From the results of the present study, it can be concluded that the alloys generated as a waste in the dental laboratory can be safely reused up to five times or at least once before they can be disposed, which reduces the cost of the treatment and also helps in conserving the natural resources.

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AIMS: The aim of this study was to evaluate and compare the shear bond strength of porcelain to the alloys of nickel-chromium (Ni-Cr), cobalt-chromium (Co-Cr), and titanium. MATERIALS AND METHODS: A total of 40 samples (25 mm × 3 mm × 0.5 mm) were fabricated using smooth casting wax and cast using Ni-Cr, Co-Cr, and titanium alloys followed by porcelain buildup. The samples were divided into four groups with each group containing 10 samples (Group A1-10: sandblasted Ni-Cr alloy, Group B1-10: sandblasted Co-Cr alloy, Group C1-10: nonsandblasted titanium alloy, and Group D1-10: sandblasted titanium alloy). Shear bond strength was measured using a Universal Testing Machine. STATISTICAL ANALYSIS USED: ANOVA test and Tukey's honestly significance difference post hoc test for multiple comparisons. RESULTS: The mean shear bond strength values for these groups were 22.8960, 27.4400, 13.2560, and 25.3440 MPa, respectively, with sandblasted Co-Cr alloy having the highest and nonsandblasted titanium alloy having the lowest value. CONCLUSION: It could be concluded that newer nickel and beryllium free Co-Cr alloys and titanium alloys with improved strength to weight ratio could prove to be good alternatives to the conventional nickel-based alloys when biocompatibility was a concern.

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PURPOSE: The purpose of this study was to compare the mechanical properties of beryllium-free nickel-chromium (Ni-Cr) dental casting alloy before and after each porcelain firing cycle (once fired, twice fired, and thrice fired) and to relate these properties to the microstructural changes and changes in X-ray diffraction patterns of Ni-Cr alloy that occur after each porcelain firing cycle. MATERIAL AND METHODS: Forty tensile bar specimens and 20 disc-shaped specimens of Ni-Cr alloy were prepared. These specimens were divided into four groups. The first group was not heat treated and tested in the as-cast condition, thus serving as control group. The second, third, and fourth groups were fired once, twice, and thrice, respectively. Tensile bar specimens were loaded to failure in tension using a universal testing machine. Values of ultimate tensile strength, 0.1% yield strength, and percentage elongations were determined. Microstructural study and hardness testing were done using an optical microscope and digital Vickers hardness tester, respectively, on disc-shaped specimens. Disc-shaped specimens were again used to obtain the X-ray diffraction patterns by using diffractometer Bruker D8 focus. Statistical comparisons of the mechanical properties and hardness of the alloy were made with ANOVA. Intergroup comparisons of the data in the as-cast and fired specimens were analyzed by applying Tukey's HSD multiple comparison tests. RESULTS: Before porcelain firing, the alloy exhibited higher ultimate tensile strength (548 MPa), 0.1% yield strength (327 MPa), hardness (192 HV), and lower elongation values (18%). After each firing cycle, there was a significant (p < 0.001) decrease in ultimate strength (464 MPa for three times fired specimens), 0.1% yield strength (284 MPa for three times fired group), and hardness (164 HV for three times fired group) and significant (p < 0.001) increase in elongation value (28% for three times fired group) of Ni-Cr alloy. The microstructure of the control group specimen exhibited heterogeneous microstructure, and after each firing, microstructure of the alloy was gradually homogenized by formation of grain boundaries at the interdendritic interfaces. X-ray diffraction pattern shows that the alloy exhibited four strong diffraction peaks within the range of 2θ = 40° to 100°. After a third firing, intensity of these planes increased. CONCLUSIONS: Results of this study confirmed that nickel-based alloys become weaker after each firing process. After firing treatment, the microstructure of alloys showed decreased dendritic structure (i.e., homogenization, which was responsible for decrease in strength and an increase in ductility of the alloy); however, this decreased strength and hardness of Ni-Cr alloy after heat treatment was still superior to those of the most noble metal alloys used in dentistry. X-ray diffraction study showed that firing process led to relieving of stresses, which ultimately resulted in stability in the crystal structure of alloy.

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Cobalt-Chromium (Co-Cr) alloys are classified as predominantly base-metal alloys and are widely known for their biomedical applications in the orthopedic and dental fields. In dentistry, Co-Cr alloys are commonly used for the fabrication of metallic frameworks of removable partial dentures and recently have been used as metallic substructures for the fabrication of porcelain-fused-to-metal restorations and implant frameworks. The increased worldwide interest in utilizing Co-Cr alloys for dental applications is related to their low cost and adequate physico-mechanical properties. Additionally, among base-metal alloys, Co-Cr alloys are used more frequently in many countries to replace Nickel-Chromium (Ni-Cr) alloys. This is mainly due to the increased concern regarding the toxic effects of Ni on the human body when alloys containing Ni are exposed to the oral cavity. This review article describes dental applications, metallurgical characterization, and physico-mechanical properties of Co-Cr alloys and also addresses their clinical and laboratory behavior in relation to those properties.

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Cobalt-Chromium (Co-Cr) alloys are classified as predominantly base-metal alloys and are widely known for their biomedical applications in the orthopedic and dental fields. In dentistry, Co-Cr alloys are commonly used for the fabrication of metallic frameworks of removable partial dentures and recently have been used as metallic substructures for the fabrication of porcelain-fused-to-metal restorations and implant frameworks. The increased worldwide interest in utilizing Co-Cr alloys for dental applications is related to their low cost and adequate physico-mechanical properties. Additionally, among base-metal alloys, Co-Cr alloys are used more frequently in many countries to replace Nickel-Chromium (Ni-Cr) alloys. This is mainly due to the increased concern regarding the toxic effects of Ni on the human body when alloys containing Ni are exposed to the oral cavity. This review article describes dental applications, metallurgical characterization, and physico-mechanical properties of Co-Cr alloys and also addresses their clinical and laboratory behavior in relation to those properties.

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BACKGROUND: The 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. METHOD: Four 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. RESULTS: It 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. CONCLUSION: Among 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.

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Castability plays an important role in selection of an alloy for cast dental restorations. This study was conducted to assess the effect of recasting of nickel-chromium alloy on its castability. Different percentage combinations of new and once casted alloy were used to produce a total of twentyfive cast samples using modified Whitlock's method and castings obtained from new alloy were used as control group. Castability value was obtained by using Whitlock's formula. Results were analyzed using student 't' test. There is no statistical difference between the castability value of the new alloy and the recasted alloy (confidence level 95%). Within the limitations of the study it is concluded that the castability value will not be affected by recasting the nickel-chromium alloy. Complete castings of any metal restoration are mandatory and to know the completeness of castings of any alloy, castability test is of prime importance.

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STATEMENT OF PROBLEM: As per the review of literature very few studies have been carried on recasting of dental casting alloy and in particlular its effect on occurrence of porosities. PURPOSE OF STUDY: This study was designed to find out occurrence of porosities in new alloy and recasted alloy using a scanning electron microscope. MATERIALS AND METHODS: Different percentage combinations of new and once casted alloy were used to produce twenty five samples. Castings obtained from new alloy were used as control group. All the samples were scanned under scanning electron mocroscope and photographs were taken from three specific sites for comparison. RESULTS: There is no significant difference in occurrence of porosities in casting obtained by using new alloy and recasted alloy. CONCLUSION: With in the limitations of the study it is conducted that the prorosities will not be affected by recasting of neckel-chromium alloy. CLINICAL IMPLICATION: Porosities in dental casting alloy can alter physical and mechanical properties of the mental which inturn may lead to failure of crown and bridge, and also cast partial denture prosthesis.