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We have encountered a rare case in which the subject underwent maxillary sinus floor elevation at another hospital, and a screw to fix the grafted bone substitute was forced into the maxillary sinus and intruded into the bone. Various different foreign bodies have been reported as being forced into the maxillary sinus due to dental treatment, and these foreign bodies are often retained on the maxillary sinus mucous membrane. However, no reports have described a screw forced in and intruded into the peculiar position in the bone, as seen in the present case, which we report here with additional discussion.

Purpose We carried out guided bone regeneration of cranial bone defects in rats using the bovine bone substitute Bio-Oss and a collagen membrane and performed histological observations of the bone repair process. Materials and methods Bone defects were created in the cranial bones of 30 15-week-old Sprague-Dawley rats. We made 3 groups. A is unfilled, B is Bio-Oss, and C is Bio-Oss plus a collagen membrane. At 4 or 8 weeks postoperatively, tissue samples were taken. The Kawamoto technique was used for histological evaluation. Results There was no new bone formation in group A. In groups B and C, new bone formation was evident around the Bio-Oss. In group C, new bone formation was evident in the centers of the bone defects, detached from the cut edge of the cranial bone. Conclusion Our results suggested that the Bio-Oss acts as a scaffold for bone repair, and the use of a collagen membrane may anchor the Bio-Oss closely to the cranial bone and assist the bone repair response.