How to Make a Good Alginate Impression

1. Check patient's mouth for size (eyeballing).  Get stock trays (two sizes in case eyeball error) from the lab and try them in patient's mouth.  If there are models, try trays on the models
2. Consistently measure water and powder.  Since we like to mix relatively thin alginate, try to increase water ratio first.  For example increase 3 cups to 3.5; 2 to 2 and 1/3
3. Dispense water first, 3 cups for upper, 2 for bottom
4. Use dry spatula and powder cup to dispense powder.  Do not use the spatula to press the power while dispensing
5. Take impression if doctor is busy, opposing first
6. Remember: retract lips and ask the patient to raise the tongue when impression is being seated
7. Add small wet paper towel and then alginate to the tongue area, press alginate into undercut area, make two alginate fuse together, but do not make platform higher than the lingual margin (border), smooth the alginate very well and flat
8. Try not to use too much water while smoothing alginate.  Keep impression wet, but do not let water soak the impression surface.  It is very difficult to shake off water before pouring plaster.  Too much water will make model weak
9. If we do not have time to pour model immediately, place a piece of wet paper towel over the impression(s), but not too much water (not dripping)
10. Use the spatula to remove remaining alginate from the bowel, then use water and paper towel to clean the bowel spotless.  You need to make sure that you clean well enough so that when the bowl is dry, you cannot see any trace of alginate attached to the bowel
11. While the doctor is taking upper impression, you may go ahead to clean the bowl if you do not want to look how the doctor is doing.  Save the wet towel for tongue area
12. Save wet paper towel if possible, for example, to cover the impression if we do not have time to pour models immediately
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Xin Wei, DDS, PhD, MS 1st edition 06/09/2011, last revision 06/09/2011