The purpose of this study was to investigate the ideal locations and dimensions of bristles for the patients who were installed with fixed prostheses and severely involved periodontitis. The models of 16 pts were analysed and the resullts were as follows: 1. There were no tooth brushes in the market, which were proper for the patients who were installed with fixed prostheses and had severely periodontally involved teeth. 2. The neck portion of the tooth brush should be narrow as possblly. 3. The size of tooth brush should be analyzed by the size of arch. 4. The width of tooth brush should be analyzed by the degree of bone recession. 5. The custom made tooth brush may be ideal, if possible.