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57 Cards in this Set
- Front
- Back
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name some polymers which are used in dentistry
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-Plastics: denture bases and teeth, resin cements, impression trays,etc
- impression materials: alginate, polysulfides and silicones -polycarboxylate cement |
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What is a macromolecule formed by linkage of many similar simple structural units
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polymer
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what is polymerization
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chemical rxn by which single units (monomers) link to form a multiple unit polymer
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light cured, heat cured, and chemical cured are all examples of what stage of polymerization
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initiation stage: requires the input of energy, light, thermal, chemical
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what is the function of the initiator
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the function of the initiator is to open unstable bonds in the monomer to begin the polymerization process
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In this stage of polymerization the newly opened unstable bonds influence other adj. molecules to open their unstable bonds. This produces a chain rxn. linking them together to form very lg. molecules
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propagation stage
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this stage of polymerization ends propagation
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termination stage: this occurs because
-all forming molecules have joined or - no more adj linkages (free radical are available |
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what is the difference between, the condensation type polymerization and addition type polymerization
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these are both setting characteristics of polymers:
condensation type: produces by-products (ex. polysulfide rubber base, and impression materials) and addition type polymerization produces NO by products (ex. Acrylics and vinyls) |
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a polymer made up of 2 different types of monomers
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copolymer
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a polymer made up of 3 different types of monomers ex. methyl-ethyl-propyl methacrylate
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terpolymer
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name the 3 spatial structures of polymers
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linear, branched, and cross-linked chains
property distinctions aren't very clear but cross linked chains usually flow at higher temps than linear or branched |
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what is the difference btw the 2 types of thermal reactivity:
-thermoplastic and thermosetting |
1. thermoplastic: softens by heating and returns to its orig. hard cond. upon cooling repeatedly
2.thermosetting: once solidifid it will never again soften by re-heating. ex.vulcanite (early denture material) |
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methyl methacrylate is
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ACRYLIC
monomer= liquid component -heat-cured: inhibitor is hydroquinone -cold cured: activator is a tertiary amine, inhibitor is also hydroquinone polymer = powder component initiator = benzoyl peroxide |
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describe the reaction that is taking place in the methyl methacrylate (acrylic)
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1. mixing the powder and liquid components allows polymerization.
2. activator must be present in the monomer otherwise heat is required to begin the polymerization reaction. 3. Once started, it is exothermic. 4. Hydroquinone inhibits the monomer (liquid) from premature aurtopolymerization to extend its shelf life |
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Elastic materials able to register undercuts, spring over those undercuts and return, without distortion, to their pre-registered position; after removal from the mouth.
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elastomeric impression materials
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I am an impression material that is composed of 85.5% water and Agar-Agar (12%). I exhibit hysteresis (memory), syneresis (extraction or expulsion of a liquid from a gel) and imbibition (displacement of fluid by another immiscible fluid)
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Agar reversible hydrocolloid
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this impression material is made up of diatomaceous earth (70%) and water
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alginate irreversible hydrocolloid
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when working with alginate irreversible hydrocolloid what factors should you keep in mind to be concerned about
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-pouring ASAP: syneresis and imbibition
-working time: water temp is important -distortion of my impression: correct removal (snap motion) -tearing: correct tray size, removal and powder/liquid ratio -dimensional change: if you delay pouring or have incorrect storage -porosity: excess air incorporated |
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this type of impression material is also known as rubber base, mercaptan, and thiokol
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polysulfide
base: polysulfide RUBBER polymer catalyst: lead dioxide reaction: condensation polymerization: has water as a by prod causing shrinkage |
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the advantages of this impression material are:
-low cost, good tear strength and flow, very flexible, easily disinfected, good surface detail, multiple pours, long working time (good and bad), mono or biphasic disadvantages: requires a custom tray with adhesives, unpleasant color and odor, STAINS clothing, heat and moisture cause a faster set, HYDROPHOBIC, SLOW SET, distorts with time, MUST POUR IN 1 HR., difficult to dispense and mix, poor dimensional stability |
polysulfide: used in complete denture final impressions
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this impression material has:
-base: a low molecular wt. polyether -catalyst: an aromatic acid ester -an exothermic cationic polymerization |
polyether
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the advantages of this impression material:
very accurate, pleasant color and odor, HYDROPHILLIC (adsorbs moisture), easy mixing, high tear strength, multiple pours, MONOPHASIC, NOT heat or moisture sense, easily disinfected Disadvantages: STIFFNESS when set, BITTER TASTE, difficult to dispense and mix (need machine) and difficult to remove from the mouth (block out undercuts |
Polyether
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this impression material is made up of
base: polysiloxane +filler catalyst: tin octoate undergoes a condensation polymerization rxn (has a by prod.) |
condensation silicone
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the advantages of this impression material are:
- ODORLESS and TASTELESS, mono or bi-phasic, strong, multiple pours, short setting time Disadv: ETHYL ALCOHOL BYPRODUCT = polymerization shrinkage = accuracy is questionable, HYDROPHOBIC, VERY SHORT SHELF LIFE, short working time, expensive, must pour immediately |
condensation silicone
commercial prods: citricon, elasticon, cuttersil, accoe |
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this impression material has:
base: silicone polymers catalyst: chlorplatinic acid (platinum) -an addition polymerization reaction which liberates hydrogen gas by prod |
Addition silicone (polyvinylsiloxane
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this impression material advantages:
-no alcohol by prod so no shrinkage, highly accurate with multiple pours, pleasant colors, Does NOT stain, cartridge sys. available, up to 2 wks pouring time Disadvantages: COSTLY, low tear strength in thin area, HYDROPHOBIC (like polysulfide and condensation silicone), RELEASE OF HYDROGEN GAS, SENSITIVE TO SULFUR CONTAMINANTS (in latex gloves and astringedent blood coagulant |
ADDITION SILICONE
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a downfall of addition silicone is release of hydrogen gas what is the problem that it causes and how do you decrease/ eliminate this problem
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pallidium is added to decrease/eliminate porosity
-wait before pouring the model (15-30 mins check directions) |
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why would you want to use a custom acrylic or triad tray for impression materials
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to conserve the very expensive material and also helps to prevent gagging, also helps to obtain a more accurate impression
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why is an adhesive applied to the tray in impressions
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you don't want the impression to separate from the tray
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what impression materials would you want to sp. use a custom tray b/c they are expensive
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addition silicone, condensation silicone, polyether
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any element that ionizes positively in solution
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metal
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how is a metalloid diff. than a metal
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metals: elements that ionizes + in soln.
metalloid: elements that don't ionize positively but are good conductors and con combine with metals to form alloys ex: carbon, silicon, boron |
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A combination of 2 or more metals
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alloy
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what is an alloy system
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a blend of 2 or more metals in all their possible combinations
binary: 2 metals ternary: 3 metals * diff. %s of various metal constituents alter the strength, ductility etc ex. silver:Tin ratio is strongest at 73:27 |
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true or false alloys can combine in an alloy system, solid solution, intermetallic compounds, eutectic mixture or in phases
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true
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what is the diff btw a one-phase system and a two phase system
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one phase: has the same structure throughout. ex. copper gold
two phase: has 2 or more metals separated into regions with surface boundaries ex. silver-copper 72% silver and 28% copper will solidify into crystals of silver and crystals of copper which will appear as fine layers of one metal over the other |
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this type of alloy is harder, stronger, and more ductile than the metals composing the alloy.
there is a melting range rather than a point. |
solid solution
solidification of an alloy from the molten state yields a random scattering of the different atoms in the space lattice |
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in this alloy the solidification results in chem. cmpds and a definite pattern of position in the space lattice of the component atoms. These cmpds are usually very hard and brittle which is diff. from the metals composing the alloy
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intermetallic compound - the alloy used in dental amalgam
ex. silver tin |
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what is a eutectic mixture type alloy
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forms small regions (usually crystals) of the components
similar to the 2 phase systems solid solution and intermetallic cmpds. |
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these are single crystals in an alloy mixture
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grains
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how do grains add strength to resist deformation (flexure and bending)
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developing grains of the same orientation coalesce. those of mismatched orientation form grain boundaries. smaller grains inc. the # of grain boundaries which adds strength to resist deformation
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name the types of deformation that can happen to metals
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1. lattice imperfections
2. Plastic deformation |
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name the two types of plastic deformation whats the difference btw the 2
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1. elastic deformation: when atoms in one plane begin to ride up on the eminences of an adjacent layer of atoms but can still slip back
2. plastic deformation: when atoms in one plane slide clear over the eminences of an adj. layer of atoms and interlock one (or more) atomic space from the orig. location ** grain boundaries impede deformation from passing through, therefore smaller grain sizes inc. the metal's strength |
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what is the disordered phase or "solid solution" of the heat treatment principles
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atoms of the different metals are scattered randomly in the space lattice
*the disordered phase is softer than the ordered phase* |
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what is the ordered phase "intermetallic compounds" of the heat treatment principles
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atoms of the different metals are well ordered in the space lattice
*the disordered phase is softer than the ordered phase* |
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what are the ordered areas or regions of the crystal referred to as
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domains
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In heat treatment what % of copper must be present in noble metal alloys for softening or hardening to occur
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12-36%
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true or false: there are always some domains present which grow in size and coalesce as temps are increased during heat treatment
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true
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explain what is occuring in the heat treatment of molten gold an copper
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1. molten gold an copper form a sloution in the liquid state. as the liquid cools:
- above 450 deg.C: a disordered phase first starts occurring in a solid solution state -below 450 deg. C: an ORDERED phase of Au-Cu and Au-Cu3 intermetallic cmpds. occur from slow cooling - quenching at 450 C freezes the disordered phase at that moment preserving a higher proportion of solid solution and prod. a SOFTER alloy |
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true or false quenching molten god and copper at 450 deg. freezes the disordered phase at that moment preserving a higher proportion of solid solution and prod. a harder alloy
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false: softer
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what heat treatment procedure will you perform to soften
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1. quench immediately after casting or
2. heat back to 700 C for 10 min then quench |
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what heat treatment procedure will you want to follow to harden
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1. heat to 450 for 2 min. then let cool slowly for 30 mins. to approx to 250 and quench
* you are quenching at a lower temp less of a solid solution is acquired (random pattern) so more of a ordered pattern |
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pouring an impression is what type of imprint
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negative
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this type of cast is the patinet's original condition
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record casts
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what type of cast is altered to demonstrate proposed treatment
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study casts
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what type of cast is used for construction of treatment aids or restorations
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working casts
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what gypsum prod. is the softest
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softest = plaster < stone < improved stone = hardest
fire stone can withstand high temps |
