Dental Materials
2011-03-23 23:40:20
chapter nine

week seven
Show Answers:

  1. What is the most widely used material in restorative and corrective dentistry?
  2. an alloy of mercury
  3. What 5 metals make up the amalgam alloy in dentistry?
    • mercury
    • silver
    • copper
    • tin
    • zinc
  4. true or false. silver is susceptible to corrosion
  5. why is copper added to amalgam?
    to minimize corrosion (eliminate gamma-2 phase)
  6. Why was less microleakage and marginal recurrent decay seen in old amalgam alloys?
    due to higher levels of corrosion - the biproducts of it block dentinal tubules
  7. What are 3 desireable features of amalgam?
    • durable
    • similar compressive strength to enamel
    • relatively inexpensive
  8. What are 6 undesireable features of amalgam?
    • unattractive
    • high thermal conductivity
    • dimensionally unstable (creep)
    • delayed expansion if contaminated with saliva
    • requires tooth support
    • fracturable by excessive occlusion
  9. true or false. When polishing amalgam, you should move from coarse to fine agents. What are 3 agents that can be used?
    • true
    • bur
    • pumice
    • tin oxide
  10. _______ amalgam is to remove surface tarnish, stains, flash, and roughness
  11. How does polishing reduce the rate of corrosion?
    causes less surface area for it to happen
  12. what is the final polish of amalgam in the mouth?
    tin oxide
  13. What are 2 ways to avoid amalgam overhangs?
    • use properly placed band and wedge
    • detect overhangs with explorer
  14. How much has the use of dental amalgams reduced in the last 15 years?
    by 40%
  15. What are 2 main disadvantages of using dental amalgams?
    • lack of aesthetics
    • pts fear of mercury being unsafe
  16. true or false. testing shows that amalgam is safe
  17. Amalgam composition contains what 4 main metals?
    • silver
    • copper
    • tin
    • mercury
  18. The addition of mercury to dental amalgams causes a reaction called what?
  19. What percent of MODERN AMALGAM is made up of copper?
  20. What is the purpose of HIGH COPPER (modern amalgams)?
    • increase longetivity
    • 50% strength in one hour
    • sets completely in 24 hrs
  21. In what type of amalgam does expansion occur if moisture contamination occurs during placement?
    low copper amalgam
  22. In spherical alloy amalgams, _______ mercury is required, and sets ______ than lathe-cut
    • less
    • faster
  23. Mercury makes up what percent of amalgam (BY WEIGHT)?
  24. What metam material in amalgam inhibits corrosion by reducing oxidation of other metals?
    zinc (0.01%-2%)
  25. In ____-_____ amalgams, _______ was responsible for gradual expansion of the amalgam over time (delayed expansion) when moisture contamination was present during placement
    • low-copper
    • zinc
  26. What type of reaction is the setting transformation of amalgam?
    CHEMICAL reaction of powder alloy mixed with liquid mercury
  27. How long does it take for most amalgams to completely set?
    24 hours
  28. What are the 3 different phases of the chemical reactions of amalgam?
    • gamma phase
    • gamma-1 phase
    • gamma-2 phase
  29. Which phase of the chemical setting reaction of amalgam is the silver alloy phase, strongest phase, and has the least corrosion?
    gamma phase
  30. which phase of the chemical setting reaction of amalgam is when mercury reacts with silver, it is strong, and corrosion resistant?
    gamma-1 phase
  31. Which phase of the chemical setting reaction of amalgam is when mercury racts with tin, it is the weakest phase, and corrodes easily?
    gamma-2 phase
  32. What metal is used to control the rate of set of amalgam?
  33. which type of amalgams have NO gamma-2 phase? And why does this happen?
    • high-copper amalgams
    • the copper reacts with the tin so tin is not availabled for mercury to react with it
  34. Oxidation on amalgam surface and slightly below; from contact with OXYGEN, CHLORIDES and SULFIDES in the mouth
  35. What type of oxidation of amalgams is not very destructive, rougher the surface the more of it occurs, palladium is added to reduce it, and polishing reduces it?
  36. true or false. higher copper amalgams tarnigh less
  37. chemical reaction between amalgam and substances in saliva or food resulting in oxidation of amalgam; can occur from two dissimilar metals in electrolyte solution (including saliva)
    corrosion of amalgam
  38. What is the electric current generated when two dissimilar metals in electrolyte solution (saliva) come in contact called? What process causes this event?
    • galvanism
    • one metal oxidizes
  39. ________ is responisble for the corrosion of amalgam
  40. What are 3 interactions within amalgam between different metals?
    • weakens amalgam
    • stains tooth structure (corrons enters dentinal tubules and stains dentin)
    • marginal deterioration
  41. What type of amalgam alloy makes up most amalgams now?
  42. What are 4 main benefits of high-copper alloys?
    • ELIMINATES gamma-2 reaction that weakens the alloy
    • MORE durable
    • LESS deterioration of margins (better marginal integrity)
    • LESS corrosion
  43. What are 3 main affects of amalgam corrosion?
    • weakens over time
    • stains surrounding tooth
    • breaks down at margin
  44. gradual change in shape from compression of opposing dentition from chewing (opposing teeth) or pressure (adjacent teeth)
    CREEP of amalgam
  45. true or false. Creep of amalgam is occureing less now that most amalgams are high-copper
  46. Creep is a phenomenon associated with ______ phase in ___-_______ amalgam alloys
    • gamma-2
    • low-copper
  47. true or false. All amalgams expand and contract on setting
  48. Which type of dimensional change of amalgam will put pressure on cusps causing biting pain/cusp fracture?
    EXPANDS too much
  49. Which dimensional change of amalgam will result in open gaps which=marginal leakage and hypersensitivity?
    CONTRACTS too much
  50. Amalgam restorations are ________ in compression than compsite or glass ionomer.
  51. Amalgam restorations are ______ in tension and shear pressure
  52. What is needed for amalgam restorations to resist breaking from tension and shear pressures?
  53. higher copper amalgams have high ___________ compressive strength; and sets in less than _______ hrs (which is late compressibe strength)
    • EARLY
    • 24 hours
  54. Which type of high-copper alloy establishes contact easily, uses more mercury (50% by weight), and has a longer working time?
    admix (both spherical and lathe-cut)
  55. Which type of high-copper alloy uses less condensation pressure-little resistance, uses both vertical and lateral condensation, must use heavier wedging to get contact, has high early compressive strength (1 and 24 hours), uses 10% less mercury, and has a faster set?
  56. How will the alloy appear if it has been properly triturated?
    satin appearance
  57. How will the alloy appear if it has been UNDER triturated?
    dry, crumbly, and sets too quick which=a weak filling
  58. How will the alloy appear if it has been OVER triturated?
    too wet, sets too quickly also which=a weak filling
  59. Why must you use larger condensers for the condensation of high copper alloys?
    What is a good analagy to remember this concept?
    • it has less resistance to condensation pressure
    • "high-heel" shoe - more pressure per square inch on smaller condensers
  60. What is the purpose of oerfilling the cavity preparation?
    to have enough to carve the tooth contours
  61. It is important to remove excess mercury from condensation, what results if it is not removed?
    physical properties are poorer
  62. Carving amalgams after the set starts will do what?
    damage the margins
  63. How long should the pt wait before eating on amalgam restorations? Why
    • 8 hours
    • the restoration will be at 80% strength at that point
  64. Which type of alloys are shiny, so no polish is needed?
    modern, high-copper alloys
  65. When is it appropriate to polish amalgam restorations?
    no earlier than 24 HOURS after placement; once the crystallization of amalgam is complete
  66. Polishing is done with ______ as a coolant, and a _______ touch
    • water
    • light
  67. What happens if amalgams are heated more than 140*? Which is the reason water is used to cool while polishing.
    mercury is released
  68. Why must you use a light touch when polishing amalgams?
    heavy touch creates friction, which creates heat
  69. true or false. Heat from the friction of polishing can injur pulp tissue
  70. amalgams are retained in the cavity preparation by what 3 things?
    • parallel walls
    • undercut walls
    • irregularities in tooth wall
  71. what are 3 features of bonded amalgams?
    • etched with phosphoric acid
    • one or two bonding resins
    • amalgam is applied to WET bonding agent which is chemically cured resin
  72. Why is amalgam applied to wet chemical cured resin?
    wet resin mechanically intermixes with amalgam during condensation
  73. What are two tools that can be used to help minimize swallowing amalgam particles or inhaling released amalgam vapors (from drilling out amalgam>heat)
    • rubber dam
    • high-volume evacuation
  74. true or false. Most dental offices are far below the recommended levels of mercury exposure levels accepted by OSHA
  75. Where should scrap mercury be stored?
    in an airtight container underwater
  76. true or false. dental offices should NOT have carpet or tile floors, because it is hard to clean mercury or amalgam spills
  77. true or false. mercury free amalgams are no longer used in the U.S.