Materials FINAL.txt

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  1. Metals
    • Any elements that ionizes positively in solution
    • Constitute ~ ¾ of the periodic table
  2. Precious Metals
    • Au, Pd, Pt, Ir, Rh, Os, Ru, Ag
    • ruthenium (Ru)
    • rhodium (Rh)
    • palladium (Pd)
    • silver (Ag)
    • osmium (Os)
    • iridium (Ir)
    • platinum (Pt)
    • gold (Au)
  3. Noble Metals
    Au, Pd, Pt, Ir, Rh, Os, Ru,
  4. Base Metals
    Ni, Cr, Co, Mn, Fe
  5. Point defects
    Imperfections involving the absence of one or a few atoms
  6. Line defects (dislocations)
    Linear imperfections through the crystal
  7. Planar defects
    2D imperfections involving external surface or internal boundar
  8. Vacancy
    • missing atom
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  9. di-vacancy
    • 2 missing atoms
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  10. ion-pair vacancy
    • Schottky defect
    • pairs of ions of opposite charge
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  11. interstitialcy
    • extra atom if APF is low
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  12. Displaced ion
    • Frenkel defect
    • extra self-interstitial atom
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  13. Grains
    • important to the clinical performance of dental alloys
    • Grain boundaries block the movement of dislocations
    • Small grains (larger grain boundary) improve the elongation and tensile strength of cast gold alloys
  14. Determination of grain size
    • Cooling rate of solidifying alloy
    • Quenching the hot invested casting in cold water (slower cooling = larger grain size)
  15. Slower cooling
    larger grain size (bad)
  16. grain refining elements
    Adding ruthenium, iridium and rhenium to the alloy
  17. Properties of Ionic Compound
    • High melting and boiling points
    • High thermal energy is required to separate the ions which are bound by strong electrical forces
    • Low electrical conductivity
    • No free electrons causes the ions to be firmly bound and cannot carry charge by moving
  18. Thermal Conductivity of Dental Materials
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  19. Cements
    good thermal insulating bases for the pulp under the metal restoration
  20. Coefficient of Thermal Expansion
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  21. Stress
    • Force per unit area within a structure subjected to an external force or pressure
    • Applied area ↓ -> stress ↑
    • Unit: N/m2 = Pa
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  22. Galvanic Shock in Dentistry
    • Dissimilar restoration
    • Dental amalgam ↔ Gold inlay
    • Silver fork (Tin) ↔ Gold inlay
    • Aluminum foil ↔ Gold inlay
    • Electrolyte
    • Saliva, tissue fluids
    • Anode: Amalgam
    • Cathode: Gold
    • Electrolyte: Saliva
  23. Resilience & Toughness
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    • Resilience=comparison of area under elastic portion curve (Straight line)Toughnesss=comparison of area under entire curve (More Ulitmate tensile Strength
  24. Graph Interpretation
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    • Stress=Y-axis
    • Strain=X-axis
    • Elastic Modulous = Slope of straight line portion
    • Yield Strenth = Maximum Stress (y-axis value)
    • Ultimate Tensile Strength = Total Area under curve
    • Elongation = Maximum strain (x-axis value)
    • Resilience=comparison of area under elastic portion curve (Straight line)
    • Toughnesss=comparison of area under entire curve (More Ulitmate tensile Strength
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  25. Grain size influences an alloy’s:
    • Strength
    • Workability
    • Corrosion susceptibility (Inc. if grain boundary Inc.)
  26. fine grain
    • usually desirable in a dental alloy
    • Smaller grain -> more grain boundaries -> higher resistance to deformation
    • Rapid cooling of dental gold alloys
    • Addition of grain refiners in the gold alloys
    • e.g 0.005% iridium in gold alloys
    • Nucleation site ↑ -> # of grains ↑ (125 times more grains/unit volume) -> size of individual grain ↓
  27. Boric oxide
    Glass modifier
  28. Pigmenting oxides
    • Simulate natural teeth
    • Iron or nickel oxides: brown
    • Copper oxides: green
    • Titanium oxides: yellowish brown
    • Manganese oxide: lavender
    • Cobalt oxide: blue
  29. Opacity
    Cerium oxide, zirconium oxide, titanium oxide, tin oxide
  30. Fluorescence (natural teeth are fluorescent)
    Lanthanide earth
  31. Binder
    • Easy manipulation of the powders
    • Starch, sugar
  32. Porcelain jacket crown (PJC)
    • Recreation of all of the aesthetic features of a tooth
    • Opaque shade
    • Mask color of the underlying structure (amalgam, metal)
    • Dentin shade
    • Enamel shade
    • Procedure
    • 1) Condensation
    • 2) Firing
    • 3) Glazing and shading ceramics
  33. Early dental porcelains (PJC)
    • Porcelain jacket crown
    • Lack of strength and toughness
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  34. Metal-ceramics (PFM)
    Aesthetic ceramic is supported by a strong and tough metal
  35. Reinforced ceramic core systems
    • Aesthetic ceramic is supported by another ceramic materials
    • High strength and toughness
    • Lack of aesthetics
  36. Resin-bonded ceramics
    • (veneer)
    • Supported by the tooth structure itself
    • Bonding the aesthetic ceramic directly to the enamel and dentine
    • Strength depends on the quality of the bond
  37. Alumina-Reinforced Porcelain
    • Alumina
    • Stronger particles than the glass
    • Effective at preventing crack propagation  crack stoppers
    • Flexural strength: 60 MPa (feldspathic porcelain) vs. 120~150 MPa (aluminous core porcelain)
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  38. Feldspathic Glass + alumina (40~50%)
    • Opaque shade
    • Use with the weaker dentine and enamel shades of the feldspathic porcelains
    • Anterior teeth restoration
  39. Ceramic coefficient of thermal expansion
    • The ceramic should have a coefficient of thermal expansion slightly LESS than that of the alloy in most cases
    • ~14 ppm / deg. celcius
  40. Desirable loading:
    Slight (COMPRESSION, tension)
  41. Dental Porcelain by Firing Temperature
    • High fusing: 1300° C: Denture Teeth
    • Medium FUsing: 1101 – 1300° C: PJC, All ceramic crown
    • Low Fusing: 850 – 1100° C: P/M restoration
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  42. Difference in the coefficient of expansion scenarios:
    between the metal and the ceramic will produce stresses depending upon the type of mismatch

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  43. Compression Fit
    • Ideal = porcleain<metal
    • a little so that compression fit will give room for tensile stress

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  44. 3 Types of P/M Bonding
    • Chemical
    • Mechanical
    • Thermal Contraction
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  45. High degree of polymerization
    • Fewer polymer chains
    • Longer polymer chains
    • More rigid, less soluble
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  46. Low degree of polymerization
    • More polymer chains
    • Shorter polymer chains
    • Less stiff, more soluble
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  47. Degree of Conversion
    • The extent to which all monomer is polymerized
    • Percentage of (Mers in polymer)/(Total initial Mers)
    • Each monomer has at least one chemical group that participates in the polymerization reaction
    • Unreacted residual monomer
    • Not all monomers may be able to react completely
    • High degree of conversion =Fewer residual monomers
  48. Condensation polymerization
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    • Two molecules (not usually the same) react to form a larger molecules
    • Production of low molecular weight byproducts
    • Water, alcohols, halogen acids, ammonia
    • Dimensional shrinkage
    • Condensation silicone, polysulfide rubber
    • Silicone byproduct is WATER
  49. Additional Polymerization
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    • Free-radical polymerization
    • Most commonly used in dentistry
    • Most prosthodontic polymers, direct restorative materials
    • Carbon-carbon double bond
    • Polymerization reaction sites
    • No byproduct
  50. Light Activation
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    • Blue light (λ = 470 nm)
    • Light sensitive initiator
    • Camphoroquinone (CQ) as the initiator in combination with dimethaminoethyl methacrylate (DMAM) accelerator
    • Direct restorative materials
  51. Plasticizer
    • Low Mw substance is added to a polymer to modify the physical properties of the polymer
    • Used to reduce the brittleness of cross-linked polymers
    • Do not participate in the polymerization reaction
    • Do not become part of the polymer chains
  52. Plasticizer Physical properties
    • Reduce the forces of attraction between the polymer chains
    • Brittle polymer -> Soft, flexible, tough polymer
  53. Dental plasticizer
    • PMMA + dibutyl phthalate  Denture soft liners
    • No leaching out of the polymer to oral tissues
    • Low vapor pressure
    • Low diffusion rate
  54. Adhesion
    Attachment of dissimilar materials by atomic or molecular attraction
    Attraction between similar atoms or molecules within a material
    • Characteristic of a material to flow over a surface
    • Need strong adhesive joint, which requires good wetting (flow in undercuts)
    • Angle formed when a drop of liquid is placed on a solid surface
    • High contact angle - poor wetting
    • Low contact angle - good wetting ->good bond
    • Extra energy of surface atoms or molecules over those in interior
    • High surface energy - good attachment
    • Low surface energy (contaminated surface) - poor attachment
    • Continuous layer - strong joint
    • Discontinuous layer - weak joint
    • Thin layer - strong joint
    • Thick layer - weak joint
    • material dependent
    • Leave intact
    • Partial removal and alteration
    • Complete removal
    • 1. If you leave smear layer, plug up tububles, drier surface = better for hydrohobic dental stuff
    • 2. Leave some of smear layer (smear plug) intact – plugging up tubules, keep dentin relatively dry, get some etching into dentin, improve MICRO of dental agent to tooth
    • 3. Stronger etching, remove smear layer – deeper penetration of dental bonding agents with tooth sturcture – improved MICRO attachment
    • Formed by permanent deformation of tooth structure during cutting and abrasion
    • Accentuated by lowering of modulus and yield strength at elevated temperatures
    • Deformed material contains hydroxyapatite particles, microorganisms
    • Lowered permeability, altered properties
    • acid etch - usually 37% phosphoric acid for 15 sec to 1 min
    • Produces spaces between rods for micromechanical attachment
    • Increases surface energy + cleans surface = better wetting
  64. Enamel Etching
    • Left: minor smear layer when you cut enamel. Enamel smear layer is smaller than dentin b/c enamel has LOW ORGANIC CONTENT (HIGHER ORGanic, more smearing)
    • Right: etching removes smear layer, puts undercuts into layer
    • When you put adhesive/resin on surface of undercuts, micromechanical attachment
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  65. Thermal Expansion
    • Absorbed heat energy increases vibration of the atoms or molecules -> material expansion
    • Thermal expansion of the restorative material does not match that of the tooth structure
    • Differential expansion/contraction -> leakage of oral fluids between the restoration and the tooth
    • Percolation
    • Decrease with time with dental amalgam
    • Space being filled with corrosion products
  66. Coefficient of thermal expansion
    • Change in length for a 1°C change in temperature
    • Unit: ppm(x10-6)/°C
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Card Set:
Materials FINAL.txt
2011-12-08 20:27:04
Materials FINAL

Materials FINAL
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