ABSTRACT
Airway casts may be classified into two main groups: negative casts, which are solid and represent the lumen of the tube; and positive casts, which are hollow and represent the walls of the tube. Metallic alloys can be made with remarkably low melting points, but probably the most often used is Woods metal, which has a melting point of 70 °C. Schummer introduced methyl methacrylate for casting purposes. It can cast structures as fine as capillaries, but it has been superseded by the polyester resins for bronchial tree casting. Casts made from polyester resins are strong and stable, but rather brittle where thin branches have been cast. This actually makes pruning easier, as long as it is done with care. With some casting materials, such as wax and Woods metal, it is necessary to use dry, air-filled lungs. After a pneumothorax is induced, the thorax should be opened widely and the entire mediastinal contents removed, including a length of trachea.
