Mouth-props are usually plastic devices which are used when the orthodontist is fixing appliances in your mouth. In order for braces, bands, or any other kind of appliance to stick to your teeth, the surface of your teeth must be perfectly dry. If a tooth gets wet, the glue will not hold and the bracket will fall off. Mouth-props ensure a dry environment for your orthodontist so his work is secure and holds well.
See some mouth-props in person at Gleason Orthodontics.