BMAT
Terms
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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 - Intergranular cement
- separation of impurities in PURE metals: weakest part of the metal.
- Cooling curve of pure metals
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Latent Heat of fusion
Nucleation
Homogeneous & heterogeneous - 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 - Results of slip
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reorientiation of grains
Fragmentation of grains
ultimate fracture of metal - 2 parts of cold work (work hardening)
- grain deformation and grain reorientation (essentially the rolling pin method)
- Effect of strain hardening on physical properties (6)
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proportional limit
UTS
toughness
resilience
elastic modulus
elongation - Methods to change grains and grain stress state
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Annealing (lower temps)
Recrystallization (intermediate temps)
Grain growth (high temps)
Graphical description - Definition of alloy and the 2 systems of alloys
- 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)
- The classification of alloys is determined how?
- By the degree of miscibility of the constituents.
- 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 - Solid solutions
- Higher strength, hardness, and ductility than constituent metals; properties resemble those of the constituent metals; coring (aka precipitation hardening); "homogenizing" anneal
- Intermetallic compounds
- narrow melting range; usually hard and brittle; doesn't resemble constituent metals in physical properties
- Eutectic mixture
- Usually hard and brittle; poor corrosion resistance; specific anodic and cathodic areas; corrosion cell results in conductive liquids (saliva)
- Precipitation Hardening
- 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.
- CARAT and FINENESS of gold
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24 carats = pure gold
1000 fine = pure gold (numerical); 1.000 fine = pure gold (decimal) - 24 grains =
- 1 pennyweight = 1.55 grams
- 20 pennyweight =
- 1 ounce = 31 grams
- 1 Troy Pound =
- 12 ounces = 372 grams
- 1 pound AV =
- 7000 Troy grains = 1.21 Troy pounds
- Primary ingredients of noble alloy
- 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)
- Nobel metal ADDITIONS include...
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platinum
palladium
silver
iridium, thodium, ruthenium, and cobalt (grain refiners) - 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 - 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 - Silver
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Substituted for gold in gold-copper alloys
- Cost factor
- Color factor "Pleasing yellow" - 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 - 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 - 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 - 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 - 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 - "Oven Cooling" method
- Cool from 450degC to 250degC over a 15 minute period in an oven. Quench.
- Most practical method for hardening heat treatment
- "Age" or heat sock at temperature recommended by manufacturer for a definite time usually 350degC for 15 minutes then quench.
- Measurement of Fusion Temperature
- Temperature at which a suspended weight will move through the alloy. Best physical properties 100-150degF above highest melting temperature given by manufacturer.
- 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% - Historically, what 4 materials were used as direct esthetic restorative materials?
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silicate restoratives
acrylic resins
composite resins
glass ionomers - Silicate cements
- 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
- Acrylic restorative resins
- 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
- Composite resins
- Excellet esthetics; wear is significantly improved and improved mechanical properties; decreased thermal coefficient of expansion and decreased dimensional change on setting.
- Definition of a polymer
- A molecule composed of numerous MERS which contain a center of unsaturation (a double bond).
- 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). - Addition Polymerization
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NO BYPRODUCTS!!
Free Radical Reaction
3-stage process
Termination Reaction - 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. - Addition polymerization reaction inhibition
- Substances that react with free radicals: oxygen ,hydroquinone, and eugenol inhibit/retard reaction.
- 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. - 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. - 1 Paste System
- Uses visible light to cause the breakdown of a ring compound to form the initiating free radicals.
- Mechanical properties of composite structure
- 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.
- 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 - 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 - Amount of filler in weight and volume %
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65-85 wt%
40-65 wt% - How do you bone the filler particle to resin?
- Coupling agents: silanes with acrylate end group; hydrolysis with acid
- The Conventional Composite
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Filler size: 5-50 microns
Filler type: quartz and radiopaque glass - Microfilled composite
- 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
- Small particle composite
- Filler size: 5-15 microns; WEAR AND ABRASION
- Hybrid or blend composite
- Filler size: .5-5 microns; matrix has fumed silica addition; sintered or agglomerated particles; etched glass.
- 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 - 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 - Post-operative sensitivity class II restorations
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Proximal: microleakage
Occlusal loading type: nature of problem and clinical solution - Placement techniques
- Layered (horizontal layers, banking); matrices, gingival margins, clinical placement sequence
- 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 - 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. - 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