The purpose of this report is to investigate influence of difference in shape of ridge (height) and load (point, direction and strength) on bearing stress of basal seat. The stress against various loads (200-2, 000 gf) onto artificial tooth (maxillaly first molar) were measured by using dentures, buried stress sensor, upon simulations of maxillaly edentulous posterior ridges with three types in height (9-15mm). The summary of results are shown below:
1. When vertical loads onto mesial pit were applied, stress in working was most at ridge. The stronger load was, the more increased stress, and the shorter height of ridge was, the more decreased stress. Stress in balancing was most at palate. The stronger load was and the shorter height was, the more increased stress.
2. When oblique loads onto buccal cusp were applied 30° to vertical, stress in working was most at palate. The stronger loads was, the more increased stress. In balancing, the stronger load was and the shorter height was, the more happened negative atmospheric pressure and breakaway of denture.
3. When oblique loads onto lingual cusp were applied 30° to vertical, stress were most at buccal in working and at palate in balancing. At both areas, the stronger load was and the shorter height was, the more increased stress.