This mold was taken after my teeth were shaped, just before the temporary bridge was made.
The mold is tricky to make: one problem to be solved is that the rubbery goo in the mold frame (either the U-shaped piece of plastic seen in an earlier page, or in this case, the smaller white plastic carrier) won't be able to get a good impression of the tooth right around the gum line.

To solve this problem, a small cord is run around the base of the tooth and pressed down beneath the gum line. The cord is impregnated with aluminum chlorhydrate, or alum, which sucks water out of the gum tissue and makes them shrink away from the tooth slightly. Just before I bite down on the goo to make the mold, the cords are removed. This gives the rubbery goo a chance to slide down around the entire tooth, and even slightly below the gum line before the gums get a chance to "bounce back" into their normal position. Cool tech tricks of the dentists...