For orthodontic appliances to fit perfectly to each individual patients smile there is a process in place to attain custom mold, this is called Impressions. This is the first step in making a mold of teeth.
Alginate is a mixture of powder and water produces a cream-like substance. The tray is kept in your mouth until the alginate sets. Once the substance has hardened imprints are of your gums and teeth are created. This process is done to both the upper and lower teeth.
Lastly, plaster is poured into the imprints, which allows the orthodontist to create a mold of your teeth. This impression can now be used for examination and to make your custom-fit appliances. Impressions are done before and after braces to since the alignment of your teeth changes.