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