Casts and models are an important part of dental services. Plaster and stone are the usual materials used to prepare casts and models. However, it must be remembered that other materials can also be used for this purpose. Models are used primarily for observation, diagnosis, patient education, e.g., orthodontic study models.A working model or master cast. It is the positive replica on which restorations or appliances are fabricated, e.g., complete denture, removable partial denture, orthodontic appliances. Casts should be made with a high level of accuracy. They should be handled with great care, taking care not to scratch or damage its surface. A positive replica of a prepared tooth or teeth in a suitable hard substance on which inlays, crowns and other restorations are made. Similar care should be taken in ensuring its accuracy as well as handling.