What do they do when molding braces at the orthodontic's?

Records for ortho: I'm not sure of the question by the way it was asked… but molds (or impressions) are taken of your teeth. These are studied along with other tracings and x-ray to create a plan for your case. Often-times the dentist may also send these molds to a lab to help fabricate appliances that will be made for your mouth.

Impressions: They will mix a material called alginate and place it in a tray which is then inserted in your mouth over your teeth. After it sets, about 2 minutes, they remove it and have an impression / imprint of your teeth. Dental stone is poured into it and they get a replica of your teeth. The alginate goes in like pudding and comes out like jello.

Orthodontic molding: Molding or orthodontic impressions is a way the orthodontist makes a duplicate of the teeth for study so they can develop a treatment plan to correct the bite and sometimes custom fabricate braces or different appliances to assist in the correction of the bite. The molding is a simple procedure and uses a material that is initially soft placed in the mouth then turns rubbery and is removed.

Impressions: I am assuming that you are asking about dental impressions - not the placement of the actual braces on teeth. An impression is made of your upper and lower teeth using a material that will produce an accurate mold of your jaw form and teeth. This mold is then filled with dental plaster to create a study model of your teeth and they way they fit together to assist in diagnosis for your problems.

Need more info: Are you asking about taking impressions for study models, for indirect bonding, for clear aligner fabrication, or for som other reason? Best suggestion is see a qualified orthodontic specialist and ask what exactly is planned to resolve your individual malocclusion.