Abstract
Purpose: It has been reported that removable partial dentures with retainers that are rigidly supported had many troubles about nonvital abutment teeth, especially displacement of the prosthesis and fracture of abutment teeth, than removable partial dentures with retainers that are unrigidly supported. The purpose of this study was twofold: 1) to examine the relationship between the rigidity of a retainer and root fracture, and 2) to clarify the effect of the remaining quantity on root fracture.
Methods: Two kinds of retainers with different rigidity (Akers clasp and Konuskronen-Telescope), and three kinds of abutment teeth with different heights of remaining dentin (2 mm, 1 mm, and 0 mm), were used. Strains of the crown-margin and post-surface on abutment teeth under two different types of load were measured. The loads were a static load and a cyclic load.
Results: 1. Under a static load, strains of the crown-margin and post-surface increased as the load increased, and the strains on the Konuskronen-Telescope were significantly larger than those on the Akers clasp. 2. Under a static load, strains on the Konuskronen-Telescope decreased when the height of remaining dentin exceeded 1 mm. 3. Under a cyclic load, preliminary failure (failure of the cement layer occurred between the crown or the cast core with a post and the teeth) occurred when the heights of remaining dentin of abutment teeth were less than 1 mm, in the case of a Konuskronen-Telescope, and 0 mm, in the case of an Akers clasp.
Conclusions: It was showed that the necessary heights of remaining dentin of abutment teeth were more than 2 mm in the case of a Konuskronen-Telescope, and more than 1 mm in the case of an Akers clasp.
