Vinyl Polysiloxane/Addition Silicone (e.g. 3M™ Express Impression Materials)
Advantages
Excellent dimensional stability (retains its original shape over time)
Most accurate material available
Excellent recovery from deformation (Impression returns to its original shape after being deformed. Impressions may be deformed when the tray is being removed from the mouth.)
Odorless and tasteless
Available in auto-mix cartridges
Stable in disinfectant solutions (will not shrink or swell)
Disadvantages
Relatively expensive
Sensitive to contaminates which may inhibit the setting reaction of the material (latex, sulfur, methacrylate residues)
Hydrogen gas is released during polymerization which may require a delay in pouring stone casts
Alginate (e.g. Jeltrate®, Dentsply Caulk)
Advantages
Inexpensive
Hydrophilic (compatible with moist tissue and dental stone)
Easy to use
Disadvantages
Poor dimensional stability (water may evaporate from the impression after mouth removal causing the impression to shrink)
Impressions must be poured immediately (due to poor dimensional stability)
Low tear strength (the impression may tear when removed from the mouth or when the stone cast is separated from the impression)
Poor reproduction of surface detail
Difficult to disinfect without affecting accuracy (too much moisture will make the impression swell, too little will cause it to shrink)
Hydrocolloid (e.g. Reversible Hydrocolloid Syringe Materials, Van R)
Advantages
Hydrophilic (compatible with moist tissue and dental stone)
Inexpensive after equipment purchase
Odorless
No mixing required
Disadvantages
Poor dimensional stability (water may evaporate from the impression after mouth removal causing the impression to shrink)
Impressions must be poured immediately (due to poor dimensional stability)
Low tear strength (the impression may tear when removed from the mouth or when the stone cast is separated from the impression)
Requires special and costly equipment
Requires advance preparation of material (heating in water bath to make it fluid enough to syringe into the tray and on the prepared teeth)
Technique sensitive (if the material is too hot it may burn the patient, if too cool it may be too thick to capture detail)
Difficult to disinfect without effecting accuracy (too much moisture will make the impression swell, too little will cause it to shrink)
Rubber Base - also known as Polysulfide (e.g. Coe-Flex® GC America)
Advantages
Relatively inexpensive
High tear strength
Long working time
Good detail reproduction
Easily disinfected with liquid disinfectants
Disadvantages
Unpleasant odor and taste
Poor dimensional stability (polymerization continues after mouth removal)
Impressions must be poured immediately (due to poor dimensional stability)
Difficult to hand-spatulate (sticky and hard to mix to a streak-free consistency)
Poor recovery from deformation
Long setting time (8 to 10 minutes)
Hydrophobic (less compatible with moist tissue and dental stone)
Condensation Silicone (e.g. CutterSil®, Heraus Kulzer, Inc.)
Advantages
Relatively inexpensive
Odorless and tasteless
Excellent recovery from deformation (impression returns to its original shape even after being deformed as when removed from the mouth)
More accurate than rubber base or alginate
Adjustable working and setting time (by changing the ratio of catalyst to base)
Disadvantages
Poor dimensional stability (evaporation of alcohol byproduct causes shrinkage)
Impressions must be poured immediately (due to poor dimensional stability)
Requires hand-spatulation
Poor bond with tray adhesive (the impression may pull-away from the sides and bottom of the tray which distorting the original shape if the impression)
Some are hydrophobic (less compatible with moist tissue and dental stone)
Polyether (e.g. Impregum F, ESPE America)
Advantages
Excellent dimensional stability (retains its original shape over time)
Highly accurate
Rigid setting (support for flexible trays)
High tear strength
Hydrophilic (compatible with moist tissue and dental stone)
Disadvantages
Unpleasant taste and odor
Difficult to hand-spatulate (an auto-mix machine is also available)
Relatively expensive
Rigid setting (may be difficult to remove from the mouth)
Higher permanent deformation than VPS materials (Impression may not return completely to its original shape after being deformed during mouth removal.
May distort during disinfection (ref. 21)




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