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64 Cards in this Set
- Front
- Back
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Crystallization of PURE metals
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Dendrites --> only for impure metals or for alloys
Formation of grains Grain size Cooling rate: equized grains (random throughout mix, uniformly shaped grains) & mold orientation of grains Metallographic examination: polish then selective etching by acids |
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Intergranular cement
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separation of impurities in PURE metals: weakest part of the metal.
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Cooling curve of pure metals
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Latent Heat of fusion
Nucleation Homogeneous & heterogeneous |
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Wrought structures: Deformation of metals
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Lattice imperfections --> point defects and dislocations
Slip --> exceeding elastic limit at imperfections; grain boundary as a slip barrier |
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Results of slip
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reorientiation of grains
Fragmentation of grains ultimate fracture of metal |
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2 parts of cold work (work hardening)
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grain deformation and grain reorientation (essentially the rolling pin method)
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Effect of strain hardening on physical properties (6)
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proportional limit
UTS toughness resilience elastic modulus elongation |
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Methods to change grains and grain stress state
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Annealing (lower temps)
Recrystallization (intermediate temps) Grain growth (high temps) Graphical description |
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Definition of alloy and the 2 systems of alloys
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Blend of 2 or more metals in all possible combinations; binary system (gold and copper or zinc and copper) and ternary system (gold, silver, copper)
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The classification of alloys is determined how?
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By the degree of miscibility of the constituents.
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Types of alloys
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Solid solution (melting range)
Intermetallic compounds (melting range) Eutectic mixteru ==> melting POINT; metals immiscible in solid state, miscible in the liquid state |
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Solid solutions
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Higher strength, hardness, and ductility than constituent metals; properties resemble those of the constituent metals; coring (aka precipitation hardening); "homogenizing" anneal
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Intermetallic compounds
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narrow melting range; usually hard and brittle; doesn't resemble constituent metals in physical properties
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Eutectic mixture
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Usually hard and brittle; poor corrosion resistance; specific anodic and cathodic areas; corrosion cell results in conductive liquids (saliva)
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Precipitation Hardening
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Prior to formation of a distinct phase, a precipitate is formed that is part of the lattice, which creates a strain which limits the slip within the lattice = hardening; the precipitate can weaken the strucutre if formed at GRAIN BOUNDARIES.
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CARAT and FINENESS of gold
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24 carats = pure gold
1000 fine = pure gold (numerical); 1.000 fine = pure gold (decimal) |
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24 grains =
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1 pennyweight = 1.55 grams
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20 pennyweight =
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1 ounce = 31 grams
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1 Troy Pound =
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12 ounces = 372 grams
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1 pound AV =
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7000 Troy grains = 1.21 Troy pounds
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Primary ingredients of noble alloy
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Gold (650-950 fine for use in mouth!!!) and copper (forms both a solid solution and intermetallic compound with gold); copper is added for strength and hardness of gold alloys (Brinell hardness changes from 32 to 54)
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Nobel metal ADDITIONS include...
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platinum
palladium silver iridium, thodium, ruthenium, and cobalt (grain refiners) |
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Platinum
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Forms a solid solution with gold
Content limited to ~10% Increases tensile strength and proportiona llimit Imparts grey color to the alloy Increases melting temp of alloy |
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Palladium
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Forms a solid solution with gold
Increased hardness reduces tarnish caused by the gold Significantly increases tensile strenght and prop. limit Increases melting range up to 200 degrees C |
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Silver
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Substituted for gold in gold-copper alloys
- Cost factor - Color factor "Pleasing yellow" |
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BASE metal additions
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[Cheaper and stronger attachment]
Nickel: lowers melting range of alloy, whitens the alloy Zinc or Indium: oxide scavenger! lowers the melting range too |
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Type I gold casting alloy
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Subject to very light stress and where burnishing is required.
VHN 50-90 BHN 40-75 |
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Type II gold casting alloy
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Those subject to moderate stress; 3/4 crowns, abutments, pontics, full crowns, saddles
VHN 90-120, BHN 70-100 |
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Type III gold casting alloy
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Those subject to high stress; thin 3/4 crowns, thin case backings, abutments, pontics, full crown and saddles
VHN 120-150, BHN 90-140 |
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Type IV gold casting alloy
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Those thin in cross section and subject to very high stress; saddle bars, clasps, crowns, thimbles, and unit casting for partial denture frameworks.
VHN 150 BHN 130 |
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"Oven Cooling" method
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Cool from 450degC to 250degC over a 15 minute period in an oven. Quench.
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Most practical method for hardening heat treatment
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"Age" or heat sock at temperature recommended by manufacturer for a definite time usually 350degC for 15 minutes then quench.
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Measurement of Fusion Temperature
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Temperature at which a suspended weight will move through the alloy. Best physical properties 100-150degF above highest melting temperature given by manufacturer.
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Alternative Noble Alloys: what is the noble metal content in the 3 classifications?
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High noble metal: noble metal content > 60%; gold > 40%
Noble: NMC > 25%; gold < 40% Predominantly base metal: NMC < 25% |
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Historically, what 4 materials were used as direct esthetic restorative materials?
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silicate restoratives
acrylic resins composite resins glass ionomers |
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Silicate cements
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Etched glass held together with a gel matrix; slow release of fluoride (anticariogenic); needs a base or liner under restoration to decrease pulpal inflammation; NOT esthetic
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Acrylic restorative resins
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Unfilled low MW polymers; susceptible to wear; very susceptible to picking up stains; high polymerization shrinkage; high thermal dimensional change 10x of tooth; recurrent caries
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Composite resins
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Excellet esthetics; wear is significantly improved and improved mechanical properties; decreased thermal coefficient of expansion and decreased dimensional change on setting.
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Definition of a polymer
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A molecule composed of numerous MERS which contain a center of unsaturation (a double bond).
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Individual mers in a copolymer can be arranged in what ways?
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Random
Block Graft (add a side chain to it to improvie the physical properties). |
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Addition Polymerization
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NO BYPRODUCTS!!
Free Radical Reaction 3-stage process Termination Reaction |
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3 stage process of addition polymerization
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Initiation by free radicals (generated by heat, light, peroxides, tertiary amine, trialkyl borane)
Propagation (mers added to free radical) Termination -- annihilation and disproportionation and transfer. |
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Addition polymerization reaction inhibition
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Substances that react with free radicals: oxygen ,hydroquinone, and eugenol inhibit/retard reaction.
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Ring-opening polymerization
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1) Epoxy reaction: epoxide oligomer + difunctional amine
2)Ethylene imine reaction: 3 ring with N atom in polyether oligomer--> forms cross-linked elastomer like polyether impression material. |
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Paste-paste system
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Universal paste contains peroxide;
Catalyst paste contains a tertiary amine in place of the peroxide. The amine paste is usually darker yellow in color. |
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1 Paste System
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Uses visible light to cause the breakdown of a ring compound to form the initiating free radicals.
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Mechanical properties of composite structure
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Dispersed phase bonded to a continuous phase; strength of the composite depends on the geometry of dispersed phase; composition of each phase; volume fraction of each phrase.
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Typical monomers of the matrix phase of composite resins
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BIS-GMA --> polymerization shrinkage = 6.5, very very viscous
TEGDMA --> 10.5; this is a lower mol. wt. diacrylate |
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Filler particle interaction with the matrix resin
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Hoop stress: shrinkage around filler particle
Interparticle shrinkage stress (radial stress): pulls away from the particles |
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Amount of filler in weight and volume %
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65-85 wt%
40-65 wt% |
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How do you bone the filler particle to resin?
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Coupling agents: silanes with acrylate end group; hydrolysis with acid
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How do you bone the filler particle to resin?
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Coupling agents: silanes with acrylate end group; hydrolysis with acid
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How do you bone the filler particle to resin?
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Coupling agents: silanes with acrylate end group; hydrolysis with acid
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The Conventional Composite
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Filler size: 5-50 microns
Filler type: quartz and radiopaque glass |
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Microfilled composite
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Filler: fumed silica; 0.02-0.04 microns; problem of filler loading due to high surface-volume ratio (max loading about 50% vol); paste has large partidles; elastic modulus HIGHER than conventional; high coefficient of thermal expansion
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Small particle composite
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Filler size: 5-15 microns; WEAR AND ABRASION
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Hybrid or blend composite
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Filler size: .5-5 microns; matrix has fumed silica addition; sintered or agglomerated particles; etched glass.
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Generalized wear: conventional composites vs. microfilled resin composites
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Conventional: uniform loss and contact area wear
Microfilled: margin ditching and contact area wear |
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Role of unfilled resin bonding agent
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Elastic interface: will take off the stresses between the composite and the enamel.
In absence: microleakage & margin gaps |
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Post-operative sensitivity class II restorations
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Proximal: microleakage
Occlusal loading type: nature of problem and clinical solution |
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Placement techniques
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Layered (horizontal layers, banking); matrices, gingival margins, clinical placement sequence
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Need for bevels with area of preparation
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Class III, IV
I not needed bc preparation is end on to rod direction. II: interproximal and gingival |
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General composition of paste
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Matrix phase: resins
Dispersed phae: inorganic filler particles 0.05-50 microns; types are quartz, fused quartz and barium glasses. Treated with a coupling agent. |
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3 portions to flame
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Inner dark blue: gases mixing; low temperature
Light blue middle portion: tip has HIGHEST TEMPERATURE Outer darker-transparent blue flame: mixing with outside air; oxidizing atmosphere |
