2009 年 22 巻 4 号 p. 498-503
We report a case of a patient who had undergone functional reconstruction of the mandible with revascularized free bone transplantation and dental implants and had recovered from a fracture of the fixture after a six-year functional period. A 39-year-old male, who developed a recurrent ameloblastoma of the mandible, underwent mandibular segmental resection and immediate reconstruction with the revascularized scapular osteocutaneous flap. Eight months after surgery, six fixtures (diameter, 3.75 mm;length, 15 mm) were installed in the reconstructed mandible. Six months after implantation, the abutments were connected to the osseointegrated fixtures, and the superstructure extending from the right first molar to the left first premolar was seated for occlusal reconstruction. However, after functioning for six years, the right-most posterior fixture suffered a fracture at the level of the abutment screw apex. The part of the fixture retained in the bone was retrieved using a trephine bur. The bone-implant contact ratio of the retrieved fixture was 79.3%. The surrounding bone density was approximately 830 Hounsfield units as revealed by computed tomograms. New bone of 10～15 mm in thickness formed lingually to the osseous flap was also observed. This might have occurred due to unintentional periosteal distraction osteogenesis, which was caused by the suprahyoid muscles attached to the periosteum on its lingual aspect. The main reason of the fracture appeared to be a large lateral force element acting on the inclined fixture, which was amplified due to the lever action. The additional bone allowed the installation of another fixture of 5 mm in diameter in a position that was 7 mm posterior and 13 degrees inferior to that of the retrieved fixture. Three months after implantation, the abutment was connected to the additional osseointegrated fixture, and the superstructure modified to fit the abutment was seated. Approximately 10 years of the functional course have been uneventful and the bone surrounding the additional fixture has been stable.
