Here are some illustrations of the process of making a dental impression with alginate and then a dental cast from the resulting mold.
The first step of the process is to choose a palate tray. We have three sizes. Select one where the tray does not touch the roof of your mouth, and you are able to cover the tray with your upper lip.
Measure alginate powder (18g) and water (45ml), then combine in a silicone bowl. Use the stiff end of a silicone spatula to mix vigorously until the medium is a creamy consistency. Resist the temptation to add additional water. Work quickly, as the alginate sets in approximately three minutes!
When the mixture is creamy, fill the tray. Make sure to completely cover the teeth and palate area of the tray. It helps to put a peak of alginate in the center of the tray to ensure a good impression of the palate.
Bite down on the tray and hold it in place for about a minute and a half.
A successful impression will show detail of the teeth and gums, all the way around the back molars. You will also see the ridges of the palate with no gaps or bubbles.
Keep the mold wrapped in a wet towel to keep it from shrinking while you prepare the dental stone to make a cast.
Mix dental stone (70g) with water (15-17ml) and mix well. The mixture should be thick.
Pour dental stone mixture into your mold and agitate it on a vibrating plate. Bubbles will emerge from the mixture, and some it will run out of the mold.
Add some more of the stone mixture to cover the top of the mold (the palate area) and set aside to dry. It takes ~20 minutes for the stone to harden enough to be removed from the mold.
The cast will be quite hard when it is ready to remove from the mold. Just pop it out to remove.
Leave the cast overnight to dry out completely before attempting to write on it or measure it.