One of the things we work on often int he practice is improving the quality of our alginate impressions. They are one of the critical factors in our success, and yet something we often take for granted that we do well. Small inaccuracies in an alginate can introduce errors that then get magnified downstream in the restorative process. The accuracy begins with selection of the proper tray size and customizing it with rope wax. Once we have the tray picked out and customized we are ready for the alginate. There are a variety of alginates on the market. Deciding which one to use is about the properties you prefer, like color change or double pour and the handling properties. Working with alginate is the same no matter which brand you use. Measuring the powder and the liquid is one of the critical steps and is often not done. We think we can mix alginate without measuring, and we are correct. the challenge is it will set even when the proportions are off, but we don’t know when to pull it from the mouth if we haven;t measured. Pulling an alginate too soon or too late will affect the accuracy as it can introduce distortion. When you measure you simply have to follow the manufacturers directions on the timing of the set.
Mix the alginate thoroughly so that there are no color streaks or areas of powder that is not wet. Once mixed I place a small amount of alginate on the counter and load a monoject syringe that has had the tip cut off. While my assistant is loading the tray I use the monoject syringe and inject around the vestibule. I then seat the tray over the second molars first, and roll in over the centrals. this allows me to see to seat the posterior and the excess to be expressed to the anterior for patient comfort. I hold the impression in place for the entire set time to prevent movement. Once set I have the patient close to create room in the buccal space. Using the pad of my finger I push on the posterior labial flange of the tray until I hear the suction release. I then move to the opposite side and do the same process. Finally I can use the tray handle to remove the impression. Do not use the handle to release the suction as you will pull the alginate from the tray int he posterior and introduce distortion.
Lastly Evaluate the impression making sure you had adequate material in the vestibule and have a nice roll, did not perforate the alginate on the cusp tips of the teeth or have any voids. If you do pull it out of the tray and do the impression again. Otherwise, wrap the impression in a wet paper towel until you can pour and hang from a Z tree.