Dental Casting Alloys PDF Past Paper

Dental Casting Alloys 1) The noble metals used in dentistry include all of the following except? a.Gold. b. Platinum. c. Palladium. d. Silver 2) Precious metals in dentistry include which of the following? a. Gold. b. Platinum. c. Palladium. d. Silver. e. All of the above 3) Which of the following i...

Dental Casting Alloys 1) The noble metals used in dentistry include all of the following except? a.Gold. b. Platinum. c. Palladium. d. Silver 2) Precious metals in dentistry include which of the following? a. Gold. b. Platinum. c. Palladium. d. Silver. e. All of the above 3) Which of the following is the gold content of an 18K gold alloy (by weight percentage)? a. 50%. b. 75%. c. 30%. d. 90% 4) Cold foil has which of the following number of carats? a.12. b. 16. c. 18. d. 24. 5)Dental casting alloys should be Compatibile with porcelain in order to construcrt ceramometallic restoration as regard: a. coefficient of thermal expansion. b. modulus of elasticity. c. forming of oxides to help bonding. d. all of the above 6) Ag-Pd alloys: a. Have low density b. Have low % elongation c. Are noble metal alloys alternative to gold alloys d. Have high tendency to gas absorption during melting and casting e. all of the above 7) Which of the following statements are true regarding the grain structure of gold alloys? a.Fine-grained alloys generally are stronger than coarse-grained alloys. b. Coarse-grained alloys are more stronger than fine-grained alloys. c. Fine-grained alloys generally are more ductile than coarse-grained alloys d. Coarse-grained alloys have high modulus of elasticity than fine-grained alloys. 8) The fineness of a 24 Carat gold alloy is: a.500 b. 750 c. 1000 d. 300 9) The purpose of adding small amounts of tin and indium to high-carat gold alloys used in the construction of ceramo-metallic is: a.To provide corrosion resistance. b. To cause hardening of the alloy. c. To lower the fusing temperature of the ceramic. d. To form oxides that bond with ceramic. 10) A Type IV partial denture gold alloy exceeds a base-metal alloy in numerical value in a. compressive strength b. casting shrinkage c. hardness d. specific gravity (density) e. modulus of elasticity 11)The gold content of Economy gold is: a. 20-35% b. 20-40% c. 32-42% d. 42 to 58% 12)To avoid tarnish & corrosion of the economy dental gold alloys: a. Silver & Palladium % should be balanced 3:1 b. Copper & silver % should be balanced to avoid the precipitation of silver rich phase c. Gold and copper % should be balanced 5:1 d. Platinum and silver % should be balanced 3:1 13) Which of the following elements is not noble by the ADA definition? a.Au. b. Pd. c. Zn. d. Pt. 14) Grain refiners act in casting alloys by making the grains smaller: a.True. b. False. 15) Resistance of noble metals to corrosion is due to their; a.Inertness. b. Passivity. c. High position in the electromotive series. d. A & C 16) 5% of…………………………….. has a pronounced effect on whitening the color of gold alloy and it decreases the greening of silver and reddening of copper: a.Platinum. b. Palladium. c. Indium. d. Tin. 17) All of the following are properties of Iridium EXCEPT; a.It increases the strength of noble metal alloys. b. It acts as a scavenger. c. It constitute 0.005% of the alloy d. It has high melting point 18) The highest % elongation of gold alloys is present in: a.Type I. b. Type II. c. Type III. d. Type IV. 19) To achieve heat treatment of noble metal alloys, the relative ratio of Cu: Au should be: a.Greater than 12:88. b. Less than 12:88. c. 1 : 1. d. None of the above. 20) Compared to Au-Cu3, the super-lattice Au-Cu formed in the gold-copper system: a.Has less strengthening effect. b. Has lower coefficient of thermal expansion. c. Has less corrosion resistance. d. Is more preferable to be used in dental restorations. 21) The disadvantages of base metal dental casting alloys include: a.High melting temperature. b. High surface hardness. c. Difficult casting. d. All of the above. 22) Chromium should not exceed 30% in base metal alloys: a.To avoid formation of brittle sigma phase. b. To avoid formation of weak sigma phase. c. To reduce the melting point of the alloy. d. All of the above. 23)An increase by 0.2% over the desired percentage of carbon in base metal alloys a. gives a too hard and brittle alloy b. gives an alloy with low strength, and hardness. c. gives an alloy with high percentage elongation. d. gives an alloy with high toughness 24) Which of the following elements improves fluidity of the molten base metal alloys: a. Molybdenum. b. Silicon and manganese. c. Nickel. d. Aluminium. 25) Aluminum is added to base metals containing nickel in order to: a.Increase fluidity of the alloy through formation of nickel alumide eutectic alloy. b. Increase strength of the alloy through formation of nickel aluminide eutectic alloy. c. Increase strength of the alloy through formation of nickel aluminide intermetallic compound. d. Increase strength of the alloy through formation of nickel alumide solid solution 26)..............has a pronounced effect on increasing strength and rigidity of base metal alloys: a.Chromium. b. Nickel. c. Cobalt. d. All of the above. 27) Shaping titanium without melting and casting is known as: a.Sintering. b. Spark erosion. c. Molding. d. None of the above. 28) Casting of titanium is a highly technique sensitive procedure due to: a.Very low density. b. High melting temperature. c. High chemical reactivity. d..All of the above 29)...................is/are used a substitute for gold alloys type IV: a.Ni-Cr. b. Co-Cr. c. Stainless steel. d. B & C 30) For base metal alloys: a.Pickling is desirable to improve their surface finish. b. Pickling is indicated to avoid formation of thick passive layer. c. Pickling is contraindicated to avoid removal of passive layer. d. Pickling is indicated to induce formation of passive layer. 31) Using the non reducing zone of the gas- air torch during melting of the gold alloy causes: a. Alloy discoloration that cannot be removed by pickling. b. Alloy discoloration that can be removed by pickling. c. Carbon contamination that can be removed by pickling. 32) in noble metal casting alloys, platinum may be substituted by a. palladium b. carbon c. nickel d. iron 33)Which of the following elements act as a grain refiner in base metal alloys: a. Molybdenum. b. Silicon and manganese. c. Nickel. d. Aluminium. 34) Of the following common metals used in dentistry, the lowest melting point of 960°C is of a.platinum b. chromium c. cobalt d. palladium e.silver 35)Biocompatibility of gold alloys is related their; a. nobility. b. Passivity. c. High position in the electromotive series. d. sensitization 36)Resistance of base metal alloys to corrosion is due to their; a. inertness. b. Passivity. c. High position in the electromotive series. d. sensitization 37)Biocompatibility of base metal alloys is related their; a. nobility. b. Passivity. c. High position in the electromotive series. d. weld decay phenomenon 38) Nickel when added to base metal alloys, increases its a.strength b. hardness and fusion temperature c. modulus of elasticity d. ductility 39)Which one of the following types of alloys not respond to heat treatment a. Co-Cr alloys b. Ni-Cr alloys c. Type III gold alloys d. Type IV gold alloys 40) The material of choice for root form dental implants is a.cobalt - chromium - molybdenum alloys b. stainless steel c. ceramics d. titanium e.tantalum-zirconium-carbon alloy 41)beryllium free nickel chromium alloys are introduced now because: a. Beryllium vapor is toxic b. Beryllium vapor is allergic c. Beryllium vapor is carcinogenic d. Beryllium vapor is irritant 42)Nickel free nickel chromium alloys are introduced now because: a. Nickel is toxic to some patients b. Nickel is carcinogenic to some patients c. Nickel is allergic to some patients d. Nickel is irritant to some patients 43)Zinc in gold alloys: a. Increases malleability and ductility b. Is important in heat treatment c. Acts as scavenger d. Produces oxides that help bonding with porcelain 44)copper in gold alloys: a. Increases malleability and ductility b. Produces oxides that help bonding with porcelain c. Is important in heat treatment d. Acts as scavenger 45)Which of the following is used in polishing base metal alloys: a. Pickling. b. Electropolishing. c. Electroplating. d. Sandplasting 46)Pickling is performed after casting of : a. Gold alloys. b. Cobalt chromium alloys. c. Titanium alloys. d. Nickel chromium alloys. 47) The most powerful grain refiner in noble metal dental casting alloys is a.palladium b. nickel c. iridium d. gallium e.indium 48) The primary oxygen scavenger in noble metal casting alloys is a.iron b. zinc c. copper d. silver e.rhenium 49) Type IV gold casting alloys are used for fabricating a.short span bridges b. removable partial denture frameworks c. inlays d. 3/4 crowns 50) ---------may be present as a grain refiner in dental gold alloy as it has a high melting point. a. Platinum b. Palladium c. Iridium d. Iron 51) A noble metal casting alloy containing iridium will have a.high yield strength b. fine grain size c. high hardness d. all of the above 52) All of the following metals have a whitening effect on gold alloys, except a.silver b. platinum c. palladium d. Copper 53) An alloy contains 18 parts gold and 6 parts other metals. The alloy is a.200 fine b. 180 fine c. 1000 fine d. 600 fine e.750 fine 54) All of the following are grain refiners of noble metal casting alloys, except a. Ruthenium b. Rhodium c. iridium d. iron 55) Usually gold casting alloys are softened heat treated, by heating at a. 700 °C for 2 min and then quenching in water b. 400 °C for 30 min and then slow cooling to room temperature c. 700 °C for 10 min and then quenching d. 400 °C for 15 min and then quenching in water 56)Casting should be done under well controlled vacuum atmosphere in base metal alloys to avoid: a. incorporation of more than 0.1 nitrogen which makes the alloy brittle b. formation of thick, oxygen enriched and hard surface layer on titanium alloys , which decreases its strength and ductility c. carbon pick up during casting to avoid alloy embitterment. d. all of the above 57)Because of its low density casting of Co-Cr alloys should be done by the use of : a. Air pressure casting machine b. Centrifugal casting machine under well controlled vacuum atmosphere. c. Special designed casting machine using centrifugal and air pressure casting force under well controlled vacuum atmosphere. d. Machine milling and spark erosion 58) All of the following are properties of cobalt - chromium - nickel alloy, except: a.they can be casted in silicate bonded investment b. they have excellent tarnish and corrosion resistance c. their hardness number is high d. they can be casted in normal environment 59) Compared to base metal alloys, Gold alloys are: a) Higher in density b) More difficult in casting c) More difficult to finish and polish d) Lower in ductility e) None of the above 60) Base metal dental casting alloys a. Have good corrosion resistance due to high nobility b. Are easy to finish and polish c. Are easy to cast d. Are light in weight 61) A gold alloy, designated as 20 karat, contains a. 80% pure gold b. 20 parts of pure gold with 4 parts of other metals c. 20 parts of pure gold with 80 parts of other metals d. only gold 62) Ag-Pd alloys: a. Have low density b. Have high % elongation c. Are base metal alloys alternative to gold alloys d. a & c e. all of the above 63) The solidification shrinkage of gold alloys is in the range of a. 2.3% b. 1.25% c. 4.2% d. 1.6% 64) Tin in gold alloys: a) Increases malleability and ductility b) Is important in heat treatment c) Acts as scavenger d) Produces oxides that help bonding with porcelain 65) A potentially carcinogenic element in base metal alloys is a. molybdenum b. beryllium c. boron d. magnesium 66) A gold alloy, designated as 750 fine, indicates that a. the alloy is 20 karat b. three-fourths of the alloy is pure gold c. the grain size of the alloy is 75 microns d. the alloy has been distilled 750 times 67) Type II gold alloys are appropriate for casting a. inlays subject to moderate stresses b. full crowns c. long span bridges d. short span bridges 68)Compared with type IV gold alloys, cobalt chromium alloys: a. Are about half as dense. b. Have lower casting shrinkage. c. Are easier to finish and polish d. Use the same type of melting and casting equipment. 69) Base metal alloys have casting shrinkages in the range of a. 2.3% b. 1.25% c. 4.2% d. 1.6% 70) Which of the following alloy elements participate in the strengthening of gold alloys: a. iron b. molybdenum c. aluminium d. Nickel 71) All of the following alloy elements participate in the strengthening of base metal alloys, except a. iron b. molybdenum c. aluminium d. Nickel 72) Which of the following is a noble metal? a. Cobalt b. Copper c. Zinc d. Palladium 73)Which the following mechanical properties affect the burnishability of a soft inlay gold alloys: a. Modulus of elasticity b. Ultimate strength c. Yield strength and hardness d. Percentage elongation 74)How the hardening heat treatment of the gold alloys change the properties of the gold alloy? a. Higher stiffness. b. Lower ductility. c. Lower hardness. d. Lower strength. 75) The phosphate bonded investment attached to base metal castings is cleaned by: a. dipping in cold hydrofluoric acid b. grinding with a bur or stone c. heating in hydrochloric or sulfuric acid d. sand blasting 76)Addition of 1% beryllium to nickel-chromium alloys, because: a. It lowers the melting range of the alloy by 100oC b. It improves the fluidity of the molten alloy c. It improving castability of the alloy d. All of the above 77) Of the following, the most ductile metal is a. silver b. palladium c. platinum d. gold 78) Gold casting alloys can be age hardened by heating the softened alloy at: a. 500°C for 10 min followed by slow cooling to room temperature b. 300°C for 1 hour followed by slow cooling to room temperature b. 700°C for 10 min and then quenching in water d. 450°C for 2 min and then cooling to 200°C in 30 minutes followed by quenching in water 79) A method of imparting hardening heat treatment to dental gold alloys, is to a. heat the soft alloy to 450°C and gradually cool to 250°C in half an hour and quench in water b. heat the alloy to 700°C and quench in cold water c. heat the soft alloy to 500°C, and bench coo! for 2 days d. heat the soft alloy to 200°C, hold for 20 minutes and then further heat to 600°C and quench in water Answers of MCQs 1-d 2-e 3-b 4-d 5-d 6-e 7-a 8-c 9-d 10-d 11-d 12-a,b 13-c 14-a 15-d 16-b 17-b 18-a 19-b 20-d 21-d 22-d 23-a 24-b 25-c 26-c 27-b 28-d 29- b 30-c 31-b 32-a 33-a 34-e 35-a 36-b 37-b 38-d 39-a 40-d 41-c 42-c 43-c 44-c 45-b 46-a 47-c 48-b 49-b 50-c 51-d 52-d 53-e 54-d 55-c 56-d 57- b 58- d 59-a 60 d 61-b 62-d 63- d 64-d 65-b 66-b 67-b 68- a 69- a 70- a 71-a 72-d 73-d 74-b 75-d 76d 77- d 78- d 79-a  II. Give reasons for: 1-Base metal alloys are difficult to be finished and polished. Because of their high hardness number. 2-Type III and IV gold alloys can be heat treated while type I and II cannot. Because the gold /copper ratio in gold alloys type III and IV necessary to produce the ordered structures (AuCu3 and AuCu) is suitable. 3-Nickel-chromium alloys are commonly used in crown and bridge work rather than cobalt chromium alloys. the presence of nickel increases the ductility of the alloy, thus allowing better burnishability. 4-The addition of chromium and/or titanium in dental base metal alloys is essential. To form the passive layer of chromium oxide and titanium oxide respectively which is nonporous, adherend, continuous, thin and translucent oxide layer that protect the alloy against further corrosion. 5-The addition of molybdenum, silicon and manganese in dental base metal alloys. Molybdenum acts as a grain refiner. Therefore, it increases the strength of the alloy. While, silicon and manganese act as deoxidizing agent during melting and casting the alloys. They improve the castability and fluidity of the alloy. 6-Addition of tungesten to base metal alloys Tungesten increases the density and improves castability of base metal alloy 7-Aluminum is added in small amount in nickel-chromium alloys. Aluminum and nickel form an intermetallic compound known as nickel aluminide (Ni 3Al) that increases the strength of the alloy. 8-Oxyacetylene flame is used for melting base metal alloys. Because oxyacetylene flame produces temperature suitable for the high melting temperature base metal alloys (1300-1500 °C) 9-The ratio of oxygen to acetylene should be adjusted for melting base metal alloys. Because too much oxygen results in alloy oxidation while, too much acetylene increases carbide precipitation. 10-The use of carat or fineness rating as classification of gold alloys in dentistry is not suitable. As they refer to the amount of gold only and do not determine the other metals which may have a pronounced effect on the properties. However the fineness rating may be used in denoting the gold solder. 11-During age hardening of gold alloys slow cooling is performed. To allow for atomic diffusion and solid-solid transformation of the disordered to the ordered solid solution. Depending on the gold to copper ratio, the ordered phases Au Cu 3 or Au Cu (super lattices) are formed. Age hardening will increase the strength, hardness and decreases ductility. 12-The percentage of chromium and carbon should be adjusted in base metal alloys. - Chromium percentage: A minimum of 12% chromium is required to form the protective passive layer. A maximum of 30% chromium ,additional chromium would produce a highly brittle phase (sigma phase). - Carbon percentage: (0.4 wt %), carbon can combine with any of the other alloying elements to form carbides. A decrease by 0.2% less than the desired percentage gives an alloy with low strength. On the other hand, an increase 0.2% over the desired percentage gives too hard and too brittle alloy. 13-Type IV gold alloy is harder than type I gold alloy. Because type IV gold alloy responded to the age hardening heat treatment process with the precipitation of the ordered structures Au Cu3 or Au Cu (super lattices). While type I gold can not respond to such type of heat treatment due to the unsuitable gold: copper ratio. 14-Casting of cobalt-chromium and nickel-chromium alloys is technique sensitive. Casting should be done in well-controlled vacuum under argon. Otherwise, nitrogen and carbon will be incorporated in the alloy. If nitrogen is incorporated more than 0.1% a brittle casting is obtained. 15-In economy gold, palladium and silver/copper ratio is very critical. -For the economy gold alloys, about 1% palladium was needed for every 3% silver to offset the tarnish tendency of the silver. - If the silver – copper ratio was not carefully balanced, the alloy would also tarnish, This is due to the precipitation of a silver – rich phase in the microstructure. 16-Addition of 1% beryllium to nickel-chromium alloys. To lower the fusion temperature by 100°C and increase the fluidity of the molten alloy thus improving the castability, also it increases the strength of the alloy. 17-Some base metal alloys used in dentistry may represent health hazard. As nickel is allergic. While, beryllium vapor is carcinogenic to the dental technician. 18-Indium and tin may be added to dental casting gold alloys. They are added in small amounts to produce oxides, which help chemical bonding with porcelain. 19-Zinc is added in small quantities in gold alloys. Zinc acts as a scavenger (deoxidizing agent) during melting and casting the alloys. It improves the castability and fluidity of the alloy. 20-Base metal alloys have high sag resistance than gold alloys. Because of there higher melting temperature therefore, they have higher sag resistance than gold alloys (high temperature creep) during firing of porcelain. 21-Casting of titanium is technique sensitive. Because of -its low density, -high melting temperature and - its High reactivity at high temperature. 22-Recasting of base metal alloys should be avoided. Due to carbides precipitation and therefore, the properties of the alloy can not be controlled. 23-The type of dental porcelain used with cobalt-chromium-nickel alloys may differ slightly than that used with titanium alloys. Due to the lower coefficient of expansion /contraction (α) of titanium that requires more thermally compatible porcelain to help in achieving strong bonding with porcelain. 24-Dental casting alloys should have high sag resistance. to resist high temperature creep during firing of porcelain or during soldering. 25-Iron may be added to dental casting gold alloys The addition of iron (1%) to porcelain alloys results in precipitation hardening (Pt3 Fe) in dental casting gold alloys. 26-Base metal alloys are especially useful for construction of large and bulky maxillary dentures. Because they have low density therefore, they are more retentive and comfortable to the patient. 27-In long span bridge, base metal alloys can be used in thinner sections than gold alloys. Because they have higher modulus of elasticity than gold alloys that allows even stress distribution in thin section without excessive bending under function. 28-Carbon free investment should be used for casting base metal alloys. To avoid the increase in carbide precipitations that leads to brittleness of the alloy. 29-Iridium is added to dental gold alloys. It acts as grain refiner due to its very high melting temperature (nucleating centers). Thus, it increases the strength of the alloy. 30-Alloys for all-metal restorations should not be used for metal ceramic restorations. Because they are not compatible with porcelain as regard a) Coefficient of thermal expansion, b) Modulus of elasticity, c) Oxides formation to help in the porcelain bonding, d) Composition as some components may discolor the porcelain. 31-Addition of palladium and copper in dental gold alloys. Palladium in quantities as low as 5% have a pronounced effect on whitening the color of gold alloy, and it decreases the greening effect of the silver as well as the red color of the copper. Copper is an important element in heat treatment. 32-Types III and IV gold alloys have two values for their yield strength but Type I, II have only one value. Because type III and IV gold alloys respond to softening and hardening heat treatments while, type I and II do not respond to such heat treatments. 33-Graphite crucible should not be used for melting base metal alloys. Because if graphite crucible is used, the alloy will pick up carbon that increases the carbide precipitations. This leads to brittleness of the alloy. Therefore, melting of base metal alloys should be done in quartz crucible. 34-Pickling of base metal alloys should be avoided. As the acid (hydrochloric) can attack the passive layer and destroy the corrosion resistance of the alloy. 35-Heat treatment of dental alloys prior to porcelain application. To allow the formation and migration of certain oxides (tin and indium oxides) to the surface that will facilitate chemical bonding with porcelain. 35-Cobalt Chromium alloys are suitable for the construction of denture frameworks(alternative to type IV gold alloys). This is because their a. High modulus of elasticity allows the denture base to be made thinner in cross-section while b. lower density that is almost half that of gold alloys, which makes the dentures lighter and more to the patient. III- State true or false and give reasons for your answers: 1. Economy dental gold alloys resemble Type I, II gold alloys in their properties. False 2. In titanium alloys, aluminum is a β-stabilizer. False 3. Carbon free investment should be used for casting base-metal alloys. False 4. Carat and fineness rating of gold alloys are commonly used in dentistry. False 5. Type II gold alloys can be heat treated. False 6. Nickel-chromium alloys have higher percent elongation than cobalt-chromium. True 7. Tin and indium are responsible for whitening dental gold alloys. False 8. Conventional casting machines are recommended for casting of titanium alloys. False 9. Pickling is performed in casting of titanium alloys. False 10. Zinc may be added in small quantities in gold alloys. True 11. Silver-palladium alloys are porcelain alloys. False 12. Casting of titanium is done easily. False 13. The lower density of base metal alloys requires more centrifugal force during casting than gold alloys.True 14. 18 carat gold solder contains 75% gold. False 15. Recasting of base metal alloys is recommended. False 16. Base metal alloys should not be subjected to pickling. True 17. Beryllium increases the fusion temperature of base metal alloys. False 18. The percentage of nickel increased in base metal alloys when burnishability is not required. False 19. Nickel-chromium alloys are considered an alternative to gold alloys type IV. 20. 0.005% of silver is effective in refining the grain size of gold alloys. False 21. Cobalt-chromium alloys are heat treated in the same way, as are gold alloys. False 22. The higher the hardness number of the dental casting alloys, the easier it's finishing and polishing. False 23. Type I gold alloy is harder than type IV gold alloy. False 24. Types III and IV gold alloys can be heat treated while type I and II cannot. True 25. Nickel-chromium alloys are commonly used in crown and bridge work rather than cobalt- chromium alloys. True 26. In long span bridge, base metal alloys can be used in thicker sections than gold alloys. False 27. Nickel-chromium and cobalt-chromium alloys have lower density than gold alloys. True 28. Nickel-chromium and cobalt-chromium alloys are stiffer than gold alloys. True 29. Nickel-chromium and cobalt-chromium alloys are tarnish resistant in the mouth. 30. Softening heat treatment is useful because it increases the tensile strength of gold alloys. False 31. Slowly cooled gold-copper alloy yield a softer and more ductile material than a rapidly cooled one. False 32. Low density is a useful characteristic of chromium type partial denture alloys. False 33. All types gold copper alloys can be order hardened during heat treatment. False 34. If the palladium percentage increases than 5%, it tends to whiten the alloy together with silver and platinum. True