Abstract
A photoelastic stress analysis technique has been conducted for many years as a test to analyze the stress distribution of the abutments and the alveolar bone under a load. The purpose of this study was to investigate the stress distribution of the abutments and the alveolar bone produced by the direct retainers of unilateral distal-extension removable partial dentures under a static load. Three types of direct retainers (R. P. I., Akers and Double Akers) were chosen, since they were frequently used in clinical case.
In the case of R. P. I., a load was transmitted vertically to the abutment and the alveolar bone. And the value of internal stress around the second premolar root apex was greatest. When Akers was applied, it forced the second premolar to lean distally. And the value of internal stress of the mesial bone near the second premolar root apex was greatest. Furthermore, when Double Akers was applied, it forced the premolars to lean distally, but a load was distributed vertically to the abutments and the alveolar bone. And the value of internal stress around the each premolar root apex was least. And the value of internal force under the denture tended to be least.
