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64 Cards in this Set
- Front
- Back
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what is a mechanical instrument that represent the TMJ and jaws to which maxillary and mandibular cast are attached to simulate some or all of the mandibular movements
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articulator
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what material is used for impressions?
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jeltrate - irreversible hydrocolloid material - alginate impression material
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what material is used for pouring casts?
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gypsum
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______ means to
1. join together as a join 2. the relating of contacting surfaces of teh teeth or their artificial replicas tin the maxilla to those in the mandible |
articulate
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what is irreversible hydrocolloid used for?
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preliminary impressions for complete dentures
partial dentures with clasps orthodontic models and study models |
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what is irreversible hydrocolloid NOT used for?
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crown and bridge impressions - lack of accuracy
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what are the reactants in alginate?
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sodium alginate (18%)
calcium sulfate dihydrate (14%) - it is soluble in h20 |
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T/F alginate acid is soluble in h20 and forms a "sol"
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true
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What is a "sol"
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resembles a sln, but is made up of colloidal particles dispersed in liquid
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What is the retarder in alginate/
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NaPO4 (2%) -
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In the setting reaction from "sol" to gel transformation two types of controls are there?
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chemically controlled (irreversible - what we use)
temperature controlled (reversible) |
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_ is an entangled framework of solid colloidal particles in which liquid is trapped in the interiscies and held by capillary forces -
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gel - JELLO
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What is the reinforcing filler in alginate?
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diatomaceous earth (70%) - controls the stiffness of the gel
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what is the purpose of Ksulfates or other alkali zinc flourides in alginate?
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provides good surfaces on gypsum dies
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The alginate powder is mixed with water to form two main reactions what is the first reaction?
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provides adequate working time (Retarder - NaPO4)
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The alginate powder is mixed with water to form two main reactions what is the second reaction?
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after the sodium P has reacted the remaining calcium sulfates reacts with sodium alginate to form and insoluble calcium alginate, which forms gel with h20
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the _____ time is from start of mix to beginning of setting reaction
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working
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the _ time is from start of reactino to completion of reaction
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setting
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What is the regular working time?
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3- 4.5 min. (60 sec. mix time
2 - 3.5 min. to load tray and get seated in mouth) |
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What is the regular setting time?
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2 - 4.5 min.
affected by water temp hot-faster cold-slower rate doulbes with 10 degree C increase |
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What are some problems with alginate impressions?
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The dimensional stability
they lose water from evaporation (shrink) undergo syneresis imbibe water if allowed to stand submersed (swell) |
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How do you best avoid the problems with alginate impressions? (avoid distoration
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pour immediately, if cannot pour immediately - place in 100% humidity (wrap in damp towel
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what are the advantages of alginate?
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stock trays, easy to use, fair taste economical, quick setting, hydrophilic, displaces saliva and blood
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what are the disadvantages of alginate?
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limited detail reproductions, low tear resistance, single pour only, quick pouring required, low dimensional stability
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what must trays have?
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mechanical - rim lock, perforated
chemical - adhesive spray |
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T/F alginate requires greater bulk of material to capture everything in mouth
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true
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pick the _____ tray that will fit comfortably in the patients mouth
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largest
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impression should have a _____- deformation with a ____- strain - ADA specifications
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<3% 10%
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100% deformation occurs when you are ________
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removing the impression from the teeth, the ability to recover to original state depends on alginate vs. agar agar
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What recovers to original state and has less deformation? agar-agar, or alginate?
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agar-agar (1.5%)
alginate (4.5%) - ADA says need to be less than 3% |
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What can you use to modify your tray to fit the patient?
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wax or modeling compound
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_________ can occur if the impression material is unsupported or moves during setting
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distortion
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T/F rinse and dry the mouth before making impresion
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true, but not too dry otherwise alginate will stick
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when you seat the tray you should place it from _________- to ________- and line up the labial frenum with the frenum space.
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post. anter
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T/F Don't overseat
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true - patient should relax facial muscles and let lips over tray
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Should you remove the tray with 3 slow motions?
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NO! ONE QUICK!
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you need to pour the cast within _ of impression
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15 min.
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T/F rinse, disinfect, and store in humid environment when done taking impression.
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true
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if you whip air into your mix, what may be the result in your cast/impression
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porosity
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if you have a poor stone surface on your cast what went wrong?
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left cast in alginate for TOO long
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what type of stone do you use for diagnostic casts?
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laboratory stone
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What is the weakest and softest gypsum compound (dental stone)
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dental plaster
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what is the hardest and strongest dental stone? what about inbetweenhard and soft?
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hard - improved stone
dental ston - middle |
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What type of gypsum is white?
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type II - dental plaster
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What type of gypsum is yellow?
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tyep II dental stone
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what type of gypsum dental stone is pink
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type IV - improved stone - high strength stone (Vel mix)
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what type of dental stone is green?
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type V - high strength - low expansion stone
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T/F ALL gypsum products formed from gypsum = calcium sulfate dihydrate
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true
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What is the difference between the types of stone depends on the ______
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manner in which the water is driven off the gypsum
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The principle difference between the dental plaster, ston and improved stone is the shape and form of the _---
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hemihydrate - CaSO4-1/2H20
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Dental plaster is ________ shpaed and porous
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irregular
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dental stone and improved ston _____- shaped and denser
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more regular
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the less water needed the ___ the stone
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denser
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the setting reaction is related to the difference in solubilty between the two crystalline forms. At room temp the hemidyrate is 4.5 times more soluble than dihydrate form of CaSO4 therefore the ____________ precipitate is favored
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dihydrate
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When set ALL gypsum product show some _____ expansion
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linear
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what is the linear expansion in all gypsum products caused by?
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the growth of the crystal and the thrusting action which occurs
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Remember: there is also an associated volumentric contraction of the hemihydrate to the dihydrate. the overall expansion of the dihydrate by crystal growth coupled with the volumetric contraction fo the dihydrate leads to a _____- structure
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porous
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plaster is composed of the _-form of calcium sulfate hemihydrate crystals
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beta
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T/F plaster is WEAKER than dental stone
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true - due to porosity (requires more water for a plaster mix) and irregular particle shapes - prevent fit
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stone is _____- hemihydrate form
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alpha - plaster was beta
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what is the greatest disadvantage of gypsum?
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poor resistance to abrasion - can add hardeners - colloidal silica or syntetic resin
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what is directly proportional related to the W/P ratio when speaking of gypsum products?
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manipulation and setting times
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what is inversely related to the W/P ratio when speaking of gypsum products?
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strength and cutting expansion
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what is the 2 pour technique?
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pour and get all structures and then pour base
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