インプラント上部構造における前装材破折と主機能部位との関連について

Prosthetic complications such as resin or porcelain veneer fractures of superstructures have occurred frequently during long-term follow-up after implant treatment. In this study, we focused on the main occluding areas according to Kato et al. (1996), investigated these areas in case of free-end missing, and examined the factors relating to the main occluding areas with veneer fractures of the implant superstructures.<br/> Seventy superstructures of 38 patients treated for partial free-end missing both in the maxilla and the mandible were examined for the site of the implant prosthesis, the situation of the antagonist, the presence and the site of the veneer fracture of the superstructure, the maximum bite force and the occlusal contact area. To assess the location of the main occluding area, each subject was instructed to clench a test piece freely on the left and right side, alternately. This study was approved by the Tokushima University Hospital Clinical Research Ethics Committee (approval number 974) and informed consent was obtained from the patients.<br/> A total of 58 cases of each of the left and right sides in 38 patients were divided into 12 superstructures fabricated as short-arch (SA : extended to first molar) and 46 superstructures as full-arch (FA : extended to second molar). In the SA group, 16.7% of the main occluding areas were on the second premolar and 83.3% on the first molar. Veneer fractures occurred in 6 superstructures, and the main occluding areas for all fractures were located on the first molars. In the FA group, 13.0% of the main occluding areas were on the second premolar, 65.2% on the first molar and 21.8% on the second molar. In this group, veneer factures had occurred in 12 superstructures, and 50% were coincident with main occluding areas.<br/> This study confirmed that the main occluding areas were present on the superstructures supported by implants in free-end missing cases ; many of them were found on the first molar as well as the natural dentition. Many of the veneer fractures of the superstructures were observed in the main occluding areas. Discriminant analysis showed that the veneer fractures of the superstructures particularly tended to occur in the cases in which the recovered dentition extended to the first molar, the main occluding area was located in the posterior part of the dentition, or the antagonist dentition was supported by implants.