robbypowell's version from 2016-10-30 19:41

Lab 2 Impressions


Question Answer
Inaccurate software ________ together of the sequential images can result in a virtual model (or digitally printed model made from the virtual scans) that is also inaccurate.STITCHING
Digital impressions require a ___ ___ ____ to image an intraoral structure.Line of sight
Irreversible Hydrocolloid (alginate) should be removed from the mouth when?After hard to finger nail indentation plus 2 minutes
Is alginate impression removed with sudden motion or gradual force?Sudden motion (with a snap)
When should an alginate impression be poured? why?immediately, poor dimensional stability
Alginate has a ____ (high/low) tear strengthlow
Alginate should be removed from stone model as soon as _______ ________ is doneExothermic reaction
What are the 5 components of a typical alginate powder?Sodium alginate (or potassium alginate), Gypsum (CaSO4 • 2H2O), Potassium Sulfate, Trisodium phosphate, & Diatomaceous earth
Type 1 alginate is _____ setting while Type 2 is _____ settingFast (1); Normal (2)
The difference between Type 1 and Type 2 alginate is the amount of ____ ____ in the powderTrisodium phosphate (retarder)
Warm water sets alginate faster because _____ ions are more soluble in warm waterCalcium
How is wettability of an impression material objectively measured?Contact angle (High contact angle --> low wettability)
The _______ (higher/lower) the contact angle, the less the impression material would spread out over tissues and teethHigher
The _______ (higher/lower) the contact angle, the greater potential there is for generating bubbles in the resulting stone model.Higher
rank the synthetic elastomers (polyether, rubber base, pvs) from highest to lowest contact angleRubber base > PVS > Polyether (less wettable to most wettable)
T/F: bite registration materials do not typically contain surfactantsTrue (bc they don't come into contact w water)
T/F: bite registration materials typically contain surfactantsFalse (do not, bc they typically do not come into contact with water)
Triple tray technique should/should not be used with single crown unitsshould
Triple tray technique should/should not be used when lateral guidance reproduction is unnecessaryshould
Triple tray technique should/should not be used when lateral guidance reproduction is necessaryshould not
Triple tray technique should/should not be used with multiple preparations in an archshould not
State which type impression material is preferred for the triple tray technique and why.Polyethers, because of stiffness
T/F: polyether is useful with deep sub-gingival areasFalse (low tear strength means could leave behind material)
T/F: polyether should not be used in deep-sub gingival areasTrue (low tear strength means could leave behind material)
The shrinkage of polyether on curing is _____%0.15%
T/F: Immersion disinfection is recommended for polyether materialFalse (spray, because hydrophilic)
T/F: Spray disinfection is recommended for polyether materialTrue (not immersion, bc hydrophilic)
Polyether material is hydro-______Philic
PVS material setting can be inhibited by the ______ in latex glovesSulfur
State which two synthetic elastomeric impression materials can be immersed in disinfectant solution without worry of dimensional change as a result of water uptake.Polysulfides (rubber base) and Addition silicones (PVS)

which component of alginate

Question Answer
function = forms cross-link to form set impressionSodium or Potassium alginate
function = provides calcium ions for chelationGypsum (CaSO4 • 2H2O)
function = prevents inhibiting of stone settingPotassium sulfate
function = retarder, acts with calcium ions at firstTrisodium phosphate
function = inert fillerDiatomaceous earth

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