For many years, diagnostic impressions weren’t given the attention they deserved. As I began to utilize diagnostic models in my practice, the need to obtain quality impressions to generate these became glaringly apparent. The first thing I realized is I couldn’t help my team members with this, as I hadn’t taken an alginate in years and needed to work on the details first. One of the first things I did was return to utilizing rim lock metal trays for my alginate impressions. Even with tray adhesive, I found it very inconsistent to keep the alginate from pulling slightly with plastic trays, and it showed up as inaccuracies in the models. A good friend advised that I rim the entire tray with blue periphery wax, and it works great. The wax extends the border so the impression gets adequate vestibular extension. It also serves to create a soft stop so that when the tray is fully seated you have comfortable wax against the tissues.

I have become a fan of the alginate that changes color; it makes keeping track of the set times very easy. Although alginate will set in many ratios of powder to water, the only way to know how long to leave it for a full set is to measure. If you remove the alginate too soon or too late, it introduces inaccuracies as well. Part of getting beautiful models is filling the tongue on the lower. An easy way to do this is to take this impression first. Fill the tongue space with a wet paper towel, and the use the excess from the upper mix to close this space. There are many techniques to getting accuracy, and reducing voids. I use a large monoject syringe with the tip cut off, and inject material into the vestibules and occlusal tables.

Once the material is fully set, release the suction at the posterior buccal border of the impression, and then remove from the mouth with the handle. Store the impressions in a full humidity environment, and never rest them on the occlusal surface of the impression to prevent distortion.

Here’s to getting great impressions the first time!


Commenter's Profile Image Doug Phillips
October 19th, 2009
What do I do to make it easier to remove an upper alginate impression?? Have the patient seal their lips around the tray handle and ask them to blow air under the set impression. The impression often just come out after this with minimal effort and it preserves the accuracy of the upper impression. It sometimes helps with the lower, but I use it almost every time when removing an upper alginate impression.