dental materials 4th year winter

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emm64
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dental materials 4th year winter
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2015-03-17 06:25:37
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dental materials 4th year winter
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  1. metal refiner
    • rapid cooling
    • increase grain boundary which cause less dislocation
  2. wrought alloy
    • cast alloy shaped mechanically (draw, roll, machine)
    • distinct properties
  3. noble metal
    • corrosion resistant, precious
    • **Au, Pd, Pt
    • Ir, Rh, Ru, Os
  4. base metal
    • not noble, stong, flex, wear resistance
    • Ti, Ni, Cu, Ag, Zn
  5. PFM bond
    ceramic & Oxide coating(Sn, In, Fe tin, Iridium, Iron) via Firing
  6. Base metal alloys have ____ on their surface.
    • passivating Cr2O3 oxide films
    • high moduli & Tm
  7. To enhance corrosion resistance add ___
    Chromium to form oxide layer
  8. Imperfections in crystals :
    dislocation
  9. Plastic deformation -> Motion of
    dislocation
  10. Mechanisms of strengthening
    • control grain size -> fast cooling, adding Ir
    • dental alloying-> solid soln, intermetallic compounds
    • strain hardening->bend, forge wrought alloy
  11. The grain boundary area (increases, decreases) as the grain size decreases
    increases
  12. As the grain size decreases, strength of metals (increases, decreases)
    increases
  13. In order to obtain the best __________ properties, ________ rather than pure metals are used in dentistry
    mechanical, alloys
  14. types of alloys
    • solid solution-> gold crown, Au, Cu
    • intermetallic compound-> Amalgam Ag3Sn
  15. (Cast, Wrought) alloy is shaped into its final form by mechanical force. It has a
    • ______ grain structure responsible for (increased, decreased) mechanical properties compared with the cast form of the alloy
    • Wrought, FIBROUS, increased
  16. corrosion resistance metal
    noble
  17. strong metal
    base metal
  18. high gold alloy->
    FGC(Cu) or Fusing(no Cu)
  19. base metal alloy->
    fusing metals, x-Cr alloys
  20. Gold substitute alloys
    fusing metals, Pd-x alloys
  21. element: increases hardness
    Cu, Cobalt
  22. element: produces fine grained alloys
    Ir
  23. element: reduces corrosion
    Chromium
  24. element: whitens the alloy
    Ag, silver to counter orange Cu
  25. element: forms oxide layer
    • Chromium
    • Indium: forms better bonding with porcelain layer. Forms the oxide layer. But different than chromium oxide layer. Acts as a coupling agent for noding with porcelain
  26. Solidification of a Metal
    • Nucleation of crystals
    • Crystal growth
    • Grains (Crystal fragments)
    • Grain boundaries (Crystalline mismatching zone between adjacent grains)
  27. nucleation point:
    initiation point for crystallization
  28. ___ block the movement of dislocations
    Grain boundaries
  29. element: hardness
    Cu, solid soln hardening, Type III, IV gold alloy
  30. element: Increase MP and hardness
    Palladium Pd
  31. element: prevent oxidation during melting (O2 getter)
    Zinc Zn
  32. Commercially Pure (CP) Ti Grades
    most efficient element is oxygen; you can double the strength of the pure titanium by adding oxygen
  33. Ti-6AL-4V highlights
    Tensile strenght, elastic modulous, Ductility
  34. Co-Cr alloy has ___ ductility,
    low ductility but strong
  35. Ti alloy has ___ ductility and good strength
    high
  36. Higher grades have _____ tensile strength and yield strength, while they have _____ ductility
    • increased tensile strength and yield strength
    • lower ductility
  37. CP-Ti medical applications
    • Corrosion resistance
    • Dental implants
  38. Ti-6Al-4V Medical applications
    • Mixture of α and β phase
    • Higher tensile strength (~1030 MPa)
    • All-metal and metal-ceramic prostheses
    • Implants
    • Removable partial denture frameworks
    • Mechanical quality
    • Orthopaedic implants
    • Dental prostheses
    • Bone screws
    • Partial and total hip, knee, elbow, jaw, finger, and shoulder replacement joints
  39. Al: Ti-6Al-4V
    • α phase (HCP) stabilizer
    • α → β transformation at higher temperature on heating
  40. V: Ti-6Al-4V
    • Vanadium
    • β phase (BCC) stabilizer
    • β → α transformation at lower temperature on cooling
  41. Osseointegration
    • Extremely close proximity (<100 A) between an implant material and the supporting bone with no intervening fibrous tissue
    • No measurable mobility of the implant
    • Ability to maintain integration when subjected oral forces over time
  42. Mechanical Treatments: Grit Blasting
    • Bombardment of the surface by hard particles of high velocity
    • Local plastic deformation and removal of the material
  43. Mechanical Tx: Roughness
    • Osteoblasts attach better to a rough surface than to a smooth one
    • Rough implants osseointegrate better than smooth ones
  44. Mechanical Tx: Fatigue strength
    Induce residual compressive stress in the bombed surface
  45. implants vs natural teeth
    • natural-> tensile force(via PDL)->bone deposition
    • implants-> compressive force-> resorption
  46. Implant designed to ___
    limit compressive stress in bone
  47. mechanical tx: griding
    hard abrasive->rough topography 1~5um
  48. mechanical tx: polishing
    hard abrasive->smooth surface finish <0.1um
  49. mechanical tx: machining
    lathe, mill, thread->specific surface topography/composition
  50. chemical tx: etching
    • dissolve oxide/underlying metal->roughen surface
    • HNO3, HF, HCl, H2SO4
  51. chemical tx: passivation
    • dissolve contaminants->rapid thick protective surface
    • dense stable oxide film (TiO2)
    • via immersion in mild oxidizing acid-> + corrosion resistance
    • + osseointegration (Ca & PO4 into surface layer)
    • no change in topography
  52. bioactive coating
    • enable an interfacial chemical bond between the implant and the bone tissue due to a specific biological response
    • eg: HA
  53. Thermal spray coatings
    plasma
  54. bioactive coating
    chemical deposition: simulated body fluid immersion
  55. ____ alloy is the most successful material for endosseous dental implants and the amount of ____ determines the grade of alloy
    Titanium, oxygen
  56. Small amounts of impurities form interstitial ____ and (increase, decrease) the mechanical properties of CP-Ti
    solid solution (impurities), increase
  57. Grade 1 titanium has (lower, higher) tensile strength than Grade 4 titanium
    lower
  58. Grade 1 titanium has (less, more) oxygen in it than Grade 4 titanium
    less
  59. When _____ are added to titanium the strength of the alloy is much increased over that of CP-Ti. aluminum and vanadium
  60. ____ is considered to be an α-stabilizer (HCP)
    Aluminum
  61. ______ acting as a β-stabilizer (BCC)
    vanadium
  62. When Al & v are added to titanium ____
    both the α and β forms can exist at room temperature
  63. Surface treatments to improve bone-implant bond strengths
    • Mechanical treatment, Chemical treatment: ROUGHNESS
    • Biological treatment: CELLULAR RESPONSE
  64. ____have been widely used as coatings on titanium alloys to try to promote a better implant-bone bond that forms in less time
    Hydroxyapatite Ca5(PO4)3(OH)
  65. stress analysis
    • extrapolation from the study of static or dynamic forces or loads
    • experimental or theoretical
  66. experimental stress analysis techniques
    • strain gage
    • photoelasticity
  67. theoretical stress analysis
    • mathematical
    • finite element analysis
  68. Birefringence
    • Double refraction
    • Decomposition of a light into two waves when it passes through certain types of material
    • This effect can occur only if the structure of the material is anisotropic (directionally dependent)
  69. more photoelastic lines
    higher stress, fringe order
  70. closer photoelastic lines
    concentrated stress
  71. modulus mismatch:
    stress conc near the ceramic filler or the metallic filler, due to the difference in modulus comparing ceramic vs metal
  72. reduce the modulus difference between the two materials, to reduce the stress conc
  73. stress analysis concentrated areas
    • bearing-contact
    • geometric discontinuity
    • modulus mismatch
  74. biological response to stress
    • stimulus for change
    • Greatest proclivity for cellular change
    • Resorption, apposition
  75. Finite Element Analysis (FEA)
    most common numerical methods to solve mechanical problems concerning systems with complex geometry and subject to complex loading conditions
  76. FEA elements
    • Subdivision of a structure into a collection of much smaller and simpler domains  finite elements (with mechanical properties that are relatively easy to describe)
    • Simple geometry: bars, wedges, tetrahedrons, etc.
    • Properties are uniform for a specific element
  77. stress distribution in FEA model will not change ___
    gradually but in steps
  78. Discretization
    • dividing the structure of interest into nodes and elements to create a mesh
    • element possesses a set of distinguishing points  nodal points or nodes
    • Each elements are connected together at nodal points
    • Nodal points are subjected to certain loading conditions
  79. The finite element technique is a (experimental, theoretical) procedure for investigating the mechanical behavior of structures
    theoretical
  80. The basic concept in the FEA is the subdivision of the mathematical model into disjoint components of simple geometry called ___
    finite elements.
  81. Each element in FEA possesses a set of distinguishing points called ___
    nodal points or nodes
  82. ____is the decomposition of a ray of light into two rays when it passes through certain (isotropic, anisotropic materials
    Birefringence, anistropic
  83. Closer fringe lines in a loaded photoelastic model is related to (less, more) concentrated stress
    more
  84. A stress concentrating mechanism such as a constriction, a sharp angle, or other non-uniform shape factors is geometric discontinuity
  85. ________ between two portions of a structure can cause a stress concentrating effects where metal fillers are imbedded in a low modulus matrix
    Modulus mismatch
  86. Ultimate tensile strength (UTS):
    fracture from tensile stress
  87. Yield Strength (YS):
    The stress at which material strain changes from elastic deformation to plastic deformation, causing it to deform permanently
  88. Proportional Limit (PL):
    Maximum stress at which stress is proportional to strain and above which plastic deformation occurs
  89. Modulus of Elasticity (E):
    Slope of the stress-strain curve in the initial straight-line portion (elastic deformation). This will tell you the material’s stiffness
  90. Flexibility: a temporal deformation (the linear portion of the graph)
  91. Ductility: A permanent deformation (the non-linear portion of the graph)
  92. Stress-strain Energy
    • Elastic->Resilience
    • Plastic->Toughness
  93. ____ is the ability of a material to store or absorb energy without permanent deformation
    Resilience (elasticity)
  94. _____ is the ability of a material to absorb energy without fracture
    Toughness (plasticity)
  95. (Flexible, Ductile) material is one that exhibits a large plastic deformation prior to failure.
    Ductile
  96. _____ material, on the other hand, shows a sudden failure w/o undergoing a large plastic deformation
    Brittle
  97. flexibility
    remain elastic (straight Stress/strain)
  98. ____ is the resistance of a material to indentation. The larger the indentation, the (smaller, larger) the value
    Hardness, smaller
  99. ___ is weakening of a material or device caused by repeated loading at a stress level below the fracture strength
    Fatigue
  100. _____ is time-dependent permanent deformation of a material subject to a constant stress; related to clinically observed extrusion of amalgam
    Creep
  101. stress-strain & impression material
    • multiple SS curves, better to use time
    • shorter, less force, lower strain-> more accurate
    • avoid permanent deformation w short, sharp pull
  102. composite materials
    Different mechanical properties from point to point within the same tissue (nonhomogeneous) and different response to forces applied in different directions (anisotropic)
  103. almost all biological tissues are
    viscoelastic
  104. bone Mechanics:
    • composite material with various solid and fluid phases
    • factors: composition, tissue mechanic, size/geometry, rate/direction of applied loads
  105. bone cells
    • Osteoblasts: bone-forming cells
    • Osteoclasts: bone-destroying cells
    • Osteocytes: bone-maintaining cells which are inactive osteoblasts trapped in the extracellular matrix
  106. Extracellular matrix
    • Responsible for the mechanical strength of the bone tissue
    • Organic phase: mainly composed of collagen fibers (flexibility, resilience)
    • Mineral phase: hydroxyapatite crystals (hard, rigid)
    • Vary with species, age, gender, type of bone and bone tissue, and presence of bone disease
  107. Cortical bone is ____ material
    anisotropic: Mechanical properties vary according to the direction of load
  108. Bone tissue subjected to rapid loading has a greater
    E and YS
  109. Energy absorbed by the bone tissue increases
    • with an increasing strain rate
    • During normal daily activities, bone tissues are subjected to a strain rate of ~ 0.01 s-1
  110. Bone strength is highest under
    compressive loading in the longitudinal direction (direction of osteon orientation)
  111. Bone strength is lowest under
    tensile loading in the transverse direction
  112. Effect of intensification of strain
    • Microscopic scale: bone density is raised
    • Macroscopic scale: bone external dimensions are incremented
  113. Effect of reduction of strain
    • Microscopic scale: bone density is lowered
    • Macroscopic scale: bone external dimensions are reduced
  114. Change in direction of load
    • Microscopic scale: structural rearrangement of trabecules and osteons
    • Macroscopic scale: change in bone shape
  115. Elastic materials show time-(dependent, independent) material behavior
    independent
  116. Elastic materials deform (instantaneously, gradually) when they are subjected to externally applied loads
    instantaneously
  117. Viscoelastic materials show time-(dependent, independent) material behavior
    dependent
  118. Viscoelastic materials deform (instantaneously, gradually) when they are subjected to externally applied loads
    gradually
  119. Spring, Dashpot) is a basic mechanical element that is used to simulate elastic solid behavior
    Spring
  120. (Maxwell, Voigt) is a viscoelastic model consisting of a spring and a dashpot connected in a series arrangement
  121. If a load is applied to an elastomeric impression for a longer time or the magnitude of the load is greater, the amount of permanent strain will be (less, greater)
    greater
  122. Bone is stiffer and stronger at (higher, lower) strain rates
    higher
  123. The chemical compositions of cortical and cancellous bone tissues are similar. The distinguishing characteristic of the cancellous bone is its
    porosity
  124. Cortical bone is an (isotropic, anisotropic) material behavior and mechanical properties vary according to the direction of load
    anisotropic
  125. Cortical bone strength is highest under (compressive, tensile) loading in the (longitudinal, transverse) direction (direction of osteon orientation)
    compressive, longitudinal
  126. dry bone is ________ than wet bone
    stiffer, has higher YS, and is more brittle

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