Alginate Impressions

Questions and Answers

Author: Boban Fidanoski

Three clinical tips to help control gag reflex while taking an alginate impression ?


- Use fast set alginate

- Do not overfill the tray

- Seat the tray in the posterior first, then anterior


Two common uses for an alginate impression ?


- For fabrication of study models

- For fabrication of whitening appliances or sportguards


Three important points for removal of alginate trays from the mouth ?


- Lift the cheeks to break the seal

- Protect the opposing teeth and

- Separate with one firm continuous motion


 What is the operator position for taking an upper impression ?

 What is the operator position for taking a lower impression ?


For taking upper impressions operator’s position should be at 9 or 12 o’clock and dental chair should be raised. For taking lower impressions operator’s position should be at 8 to 9 o’clock. Operator’s elbow should be the same height as the client’s shoulder.


Three safety precautions while using the cast trimming machine ?


- Protective eye glasses should be worn while using the model trimmer

- Grinding wheel should never be used dry

- Fingers should be kept away from the grinding wheel along the edge of the shelf.


What causes excess alginate to be extruded from the back of the tray while taking an alginate impression ?


First cause is tray seated in anterior region first, then posterior forcing alginate out the back. Second cause is tray overfilled with alginate


If an alginate impression is removed too soon what can happen to the impression ?


Impression will be either distorted or a double imprint will appear.


What causes an alginate to be grainy and have lack of detail and how would you prevent that from happening ?


Incomplete mix of powder and water causes alginate to be grainy and have a lack of detail. To prevent this, all of the powder has to be wet and mixed to creamy consistency.


Why it is recommended to wipe alginate on occlusal surfaces before seating tray ?


To prevent occurrence of trapping bubbles.


How should an alginate impression be stored while waiting to be sent to a laboratory ?


When one or both alginates are completed, they should be rinsed under water (remove excess debris) and then wrapped in paper towel and sprayed (dampen) with disinfectant prior to taking to the laboratory.




author: Boban Fidanoski

© February, 2007 Copyright - Text
by B.Fidanoski- Port Credit, ON - Canada