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28 Cards in this Set
- Front
- Back
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impressions
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reproduce the form of the teeth as a negative reproduction. hard& soft tissues, existing restoration and prepared teeth.
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types of impression materials
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moldable or plastic state that can adapt to the teeth and tissues
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ways to classify impression materials
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inelastic/rigid or elastic
hydrocolloids or rubberbased preliminary or final |
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rubber base
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a mixture of 2 chemicals which form a compound that has the ability to stretch. set by chemicals
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hydrocolloids
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suspension of molecules in which water is the suspension medium
agar sets by a physical reaction alginate sets by a chemical reaction |
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inelastic/rigid
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once material sets it cannot change shape to be removed from the oral cavity. doesn't expand around undercuts
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impression trays
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carry impression materials to oral cavity.
stock or custom made metal/acrylic/plastic cover entire arch or segment |
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types of elastic impression materials
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polysiloxane
polyether polysulfide polyvinylsiloxane |
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polysiloxane
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condensation silicon
molecules of alcohol are lost sets in 5-7 mins pour up within few mins to avoid shrinkage |
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polysulfide
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shrinks as it sets
molecule of water is lost for each set of bands it makes |
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polyether
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doesn't shrink
stiffest of all rubber based impressions crown & bridge impressions bite registration work time 1-1 1/2 mins time in mouth 3-4 1/2mins set time 4-6 mins |
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polyvinylsiloxane
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doesn't shrink as it sets
stability, easy to manipulate most expensive pour immediately or wait 1-2 hours for release of hydrogen gas to avoid porosities |
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final impressions
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impression made that does contain final details of tooth preparation that will be sent to the lab for fabrication of permanent restorations
(rubber impression or agar) |
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preliminary impressions
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initial impression that does not contain fine details and should not be used to fabricate permanent restorations
(alginate or rubber based putty) |
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elastic
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material will stretch around undercuts in order to be removed from the oral cavity
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hydrocolloids
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a glue like material composed of two or more substances, one solution does not go into a solution but is suspended within another substance.
reversible or irreversible |
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imbibition
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uptake of water with resulting in swelling
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syneresis
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loss of water with resulting in shrinkage
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reversible hydrocolloid
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agar derived from seaweed
85% water pour right away or store up to 1 hour |
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working time for alginate
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regular set: 2-3mins
fast set: 1 1/2-2 mins work time starts when powder and liquid are mixed |
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impression making objectives
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reproduce oral structures with acceptable accuracy
maintain proper infection control maintain patient comfort |
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irreversible hydrocolloid
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alginate is the most widely used
easy to manipulate, no special equipment, reasonably accurate doesn't reproduce fine details |
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seating the tray (mandible)
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-always make lower impression first
-stand in front of patient, insert 1 side to another -posterior to anterior -patient raises and extends tongue the relaxes tongue -mold by gently pulling or the lips and cheeks in upward motion -1 min beyond setting |
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tray selection for alginate
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stock trays
not to big/small covers all teeth & extends without impinging on tissues |
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seating the tray (maxillary)
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stand behind patient
posterior to anterior patient tilt head forward gently pull down on cheeks and lips |
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impression compound
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supplied as cakes and sticks
preliminary impressions for complete dentures or used as a tray for a wash impression |
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zinc oxide eugenol paste
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initial set 3-6 mins
final set 10 mins |
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impression wax
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stiff at room temperature
lacks accuracy distorts easily |
