インプラントの植立角度が顎骨のひずみ分布に及ぼす影響

抄録

We investigated the dynamic effects of varying the fixture insertion angles and various methods of occlusion on the nature of occlusal force conduction through implants that were attached to human edentulous dried mandibles, and the effects on the surrounding alveoli and the mandibular bone itself while applying static loads to these mandibles.
Fifteen dry human edentulous mandibular bones were used. Five Branemark system implants (tianium screw type, Nobel Biocare) were inserted between the bilateral mental foramens of the mandibular bone (implants R2, R1, M, L1, and L2, from the right). In these specimens, a tentative occlusion plane was established at a site that was parallel to the lower marginal plane of the mandible and 20 mm from the alveolar crest in the median area. The implants were inserted at right angles to this tentative plane (vertical implant group), at a tilt of 10° toward the labial side (labially tilted implant group), or at a tilt of 10°toward the lingual side (lingually tilted implant group). Each of the 3 groups consisted of 5 specimens. After insertion of the fixture, a superstructure and a complete maxillary denture were produced. As the mode of occlusion, central occlusion and edge-to-edge occlusion were used. A static load (10 kgf) was applied to the central area of the dental arch,the anterior teeth area, and the left molar area. Microstrain occurring in the mandibular surface and the abutment surface of the implant was measured by attaching a stress concentration gauge to the bone surface (labial and lingual sides) and a uniaxial gauge to the abutment surface (labia, lingual, mesial, distal sides). In addition, the axial force occurring in each abutment was calculated by Hook's law, from the amount of strain on the abutment surface.
The results of transmission and dispersion of occlusal force in this study suggested that compression force tends to concentrate on the distal implant in the labially tilted implant group when a load is applied on the central area of the dental arch, which corresponds to the state of occlusion of the entire dental arch,when a load is applied on the molar area, which corresponds to chewing in the molar area.Insertion of a fixture tilted in this direction may be disadvantageous for load bearing. The results of me a surement of strain on the bone surface also showed more marked strain in the labially tilted implant group than in the other two groups. This indicates that labially tilted implants carry a high risk for destruction of osseointegration.