Authorities on prosthetic dentistry agree that, beforetaking an impression, a careful and comprehensive study of the mouth from both the physiologic and the pathologic aspects should be made. In an edentulous mouth, the thickness and firmness of the soft tissues are noted, as well as stomatitis, leukoplakia and other diseased conditions, if they are present. The bony ridges are studied with regard to undue pressure which may be brought to bear on them.
If natural teeth are to be retained, they and their supporting structures must be restored to health, and in either case the attachments of muscles are noted. All of these conditions are studied in order that the denture may meet the following requirements, namely, that they may be useful, look well and be comfortable (Prothero). Primarily all of these depend on their retention which is made possible by two physical factors, adhension, which plays the lesser rôle,