Materials FINAL.txt

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Materials FINAL.txt
2011-12-08 15:27:04
Materials FINAL

Materials FINAL
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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
  9. di-vacancy
    • 2 missing atoms
  10. ion-pair vacancy
    • Schottky defect
    • pairs of ions of opposite charge
  11. interstitialcy
    • extra atom if APF is low
  12. Displaced ion
    • Frenkel defect
    • extra self-interstitial atom
  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
  19. Cements
    good thermal insulating bases for the pulp under the metal restoration
  20. Coefficient of Thermal Expansion
  21. Stress
    • Force per unit area within a structure subjected to an external force or pressure
    • Applied area ↓ -> stress ↑
    • Unit: N/m2 = Pa
  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
    • Resilience=comparison of area under elastic portion curve (Straight line)Toughnesss=comparison of area under entire curve (More Ulitmate tensile Strength
  24. Graph Interpretation
    • 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
  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
  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)
  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
  42. Difference in the coefficient of expansion scenarios:
    between the metal and the ceramic will produce stresses depending upon the type of mismatch

  43. Compression Fit
    • Ideal = porcleain<metal
    • a little so that compression fit will give room for tensile stress
  44. 3 Types of P/M Bonding
    • Chemical
    • Mechanical
    • Thermal Contraction
  45. High degree of polymerization
    • Fewer polymer chains
    • Longer polymer chains
    • More rigid, less soluble
  46. Low degree of polymerization
    • More polymer chains
    • Shorter polymer chains
    • Less stiff, more soluble
  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
    • 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
    • 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
    • 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
  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