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64 Cards in this Set

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Crystallization of PURE metals
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
Latent Heat of fusion
Nucleation
Homogeneous & heterogeneous
Wrought structures: Deformation of metals
Lattice imperfections --> point defects and dislocations
Slip --> exceeding elastic limit at imperfections; grain boundary as a slip barrier
Results of slip
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)
proportional limit
UTS
toughness
resilience
elastic modulus
elongation
Methods to change grains and grain stress state
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
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
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...
platinum
palladium
silver
iridium, thodium, ruthenium, and cobalt (grain refiners)
Platinum
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
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
Substituted for gold in gold-copper alloys
- Cost factor
- Color factor "Pleasing yellow"
BASE metal additions
[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
Subject to very light stress and where burnishing is required.
VHN 50-90
BHN 40-75
Type II gold casting alloy
Those subject to moderate stress; 3/4 crowns, abutments, pontics, full crowns, saddles
VHN 90-120, BHN 70-100
Type III gold casting alloy
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
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?
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?
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?
Random
Block
Graft (add a side chain to it to improvie the physical properties).
Addition Polymerization
NO BYPRODUCTS!!
Free Radical Reaction
3-stage process
Termination Reaction
3 stage process of addition polymerization
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
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
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
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
Hoop stress: shrinkage around filler particle
Interparticle shrinkage stress (radial stress): pulls away from the particles
Amount of filler in weight and volume %
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
How do you bone the filler particle to resin?
Coupling agents: silanes with acrylate end group; hydrolysis with acid
How do you bone the filler particle to resin?
Coupling agents: silanes with acrylate end group; hydrolysis with acid
The Conventional Composite
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
Conventional: uniform loss and contact area wear
Microfilled: margin ditching and contact area wear
Role of unfilled resin bonding agent
Elastic interface: will take off the stresses between the composite and the enamel.
In absence: microleakage & margin gaps
Post-operative sensitivity class II restorations
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
Class III, IV
I not needed bc preparation is end on to rod direction.
II: interproximal and gingival
General composition of paste
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
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