After having gold dental crowns removed, you can melt them down to repurpose the gold. Melting the gold requires you to use a propane torch, and it is critical that you take care to avoid injury or property damage. Use safety equipment, and do not perform the work in an area that contains flammable substances.
Place the gold dental crowns that you would like to melt into a crucible. A crucible is a container made from metal or thick ceramic that is used to melt gold by placing it under very high temperatures. After filling the crucible with the gold, place it on a fireproof surface such as brick or cement
Put on safety goggles and leather gloves. Light the propane torch with a lighter, and turn the gas to the highest setting. Place the flame to the gold, moving it in a slightly circular pattern so the heat reaches the edges of the metal. As the gold begins to liquefy, add 1/2 tsp. of borax to prevent oxidation of the metal. Continue to heat the gold until it has completely melted, then turn off the torch.
Pour the melted gold from the crucible into a button-style mold using the metal tongs. The gold will re-harden in the mold as it cools, and can be used to create something at a later date.
TL;DR (Too Long; Didn't Read)
Purchase a mold from a jewelry supply company, or make your own by hollowing out a small hole in a cube of charcoal.