Abstract
Stress analysis concerning the mechanical effects of cracks in roots on the tooth structure of the crack tips in the abutment tooth on the upper central incisor with a cemented dowel, depending upon the difference of the crack position and the conditions of supporting bone, in case where the tooth axis was loaded from the lingual side to the cracks at 45° was conducted by means of the two-dimensional finite element method. Further, effects of the cracks in roots on root fracture were examined by calculating the crack tip stress intensity factors K, for the opening mode and for the in-plane shear mode.
The following results were obtained:
1. The larger vertical cracks on the side around the dowel in the loaded lingual side become, when the loss of supporting bone is great and the dowel surface is configuration-threaded, the more liable are the cracks in roots to spread during the opening mode.
2. Parallel cracks on the side of the apex of the dowel are more liable to appear during the opening mode than during the in-plane shear mode, and there is little difference among the forms of the dowel.
