In partially edentulous patients with considerable loss of tooth structure, it is recommended that a remaining tooth with a C/R ratio greater than approximately 1.5 should be used as an overdenture abutment to minimize lateral occlusal forces. Abstract Purpose:The clinical decision to use abutments for overdentures in cases with loss of tooth structure has not been fully assessed in relation to the periodontal condition. The aim of this study was to investigate the stresses around overdenture abutments with and without crown restoration for various bone heights.Methods: Three-dimensional finite element models of the mandibular right first and second premolars, a periodontal ligament, and one of five alveolar bone models of different heights were constructed. The crown-to-root ratios at the second premolar were 0.86 (Model A), 1.05 (Model B), 1.28 (Model C), 1.56 (Model D), and 1.96 (Model E). The second premolar root was also modeled without crown restoration. A single oblique load of 80 N at a 30-degree angle distal from the vertical axis was directed at the center of the occlusal or root surface of the second premolar. Results:The maximum stresses were observed at the distal cervical regions for all models. These increased as the crown-to-root ratio increased. The highest maximum stress in the cortical bone (35.8 MPa) was observed in Model E with crown restoration. In the regions near the overdenture abutments, the maximum stresses in the bone and the periodontal ligament were 33.9% to 61.7% lower than those observed near the crown restorations. Conclusion:The use of the premolar as an overdenture abutment in cases with loss of tooth structure can effectively sustain the stress in the periodontal tissues, particularly under conditions of reduced bone height.

Reduction in the intensity of the occlusal contact, or decreased occlusal height of an implant-retained single restoration, allows the establishment of an equivalent occlusal stress with the natural molars under the maximum bite force. This adjustment, either during fabrication or try-in procedure, can suppress excessive stress that may be created in the tissues. With this procedure, however, the restoration does not contact the antagonistic tooth under a relatively low bite force.