[Stress analysis of abutment teeth on removal moment of R.P.D.'s].

During function, every R.P.D. shows denture movement that is converted into stress to the abutments. Our two investigations revealed that guide surfaces on the retainers was effective in reducing the stress. In R.P.D. treatment, many different designs of clasp systems have been used with less consideration of this guiding function. In this study, four types of clasps, Aker's clasp, Krol R.P.D., Kratochvil R.P.D. and the Crown Ledge preparation, having different guide surfaces were examined to measure the mobility of abutments under the pull out force. Metal frame dentures were provided in order to measure these movement with electronic sensor. Each retainer had interchangeable feature to facilitate the investigation. The following results were obtained, 1. Aker's clasp showed small amplitude with high frequency during removal periods. 2. Both R.P.I. clasps give only small vibration when the path of removal is adjusted. To get this direction is difficult. 3. Guide surface of Crown Ledge clasp. is effective in reducing the mobility of abutment tooth. 4. The guiding surface therapy has an effect in reducing the abutment vibration.