No abstract

This study aimed to evaluate the mechanical stress on resected mandibular bone against occlusal force using dental implant without any bone grafting by fi nite element analysis to reduce the risk of the bone fracture. A model of marginal resection of the symphysis of the mandible, in which the bone height of the region was 5, 10 or 15 mm, was prepared. Two, four, or six implant-supported fi xed prostheses (superstructure) or overdenture were set up in the model and loaded with 500N of occlusal force. The von Mises stress on the resected region was the highest when two implants were bilaterally placed at positions closest to the resected region. The von Mises stress value on the resected region could be high enough to induce the bone fracture. The mechanical stress was reduced up to < 50 % by adding implant at posterior position and connecting all implants. The presence of superstructure on 4 or 6 implants signifi cantly decreased the von Mises stress when the residual bone height was 10 or 15 mm. Use of 6 implants showed no signifi cant advantage at the stress reduction compared to use of 4 implants. When the residual bone height was 5 mm, reinforcement of the residual bone or bone graft should be considered to avoid the bone fracture. Although the present results were obtained under restrictive conditions, the number of implant, implant position, and prostheses style could reduce the von Mises stress and the risk of bone fracture on the resected region.

This study was conducted to determine the most secure implant positioning on the marginally resected mandible to support a fixed complete denture through finite element analysis. Three or four implants were placed at near, middle, or far positions from the resected margin in a simulation model with a symmetrical marginal defect in the mandibular symphysis. The height of the residual bone was 5, 10, or 15 mm. The four possible implant patterns for 3 or 4 implants were defined as: (1) asymmetrically isolated position one to position two, (2) asymmetrically isolated position one to position three, (3) asymmetrically isolated with greater length position one to position two, and (4) two implants symmetrically positioned on each side of the defect. The von Mises stress in the resected and peri-implant bone with respect to the occlusal force was calculated. Initially, as the peri-implant bone stress around isolated implant at the near position was greater than at the middle and far positions regardless of the residual bone height, the near position was excluded. Second, the von Mises stress in the resected bone region was &gt; 10 MPa when the isolated implant was at the far position, and it increased inversely depending on the bone height. However, the stress was &lt; 10 MPa when the isolated implant was placed at the middle position regardless of the bone height, and it was significantly lower compared to the far position, and equivalent to the symmetrically positioned implants. Furthermore, the use of greater length implant reduced the peri-implant bone stress, which was even lower than that of the symmetrically positioned implants. These results suggest that the asymmetrically positioned three-implant-supported fixed denture, using a greater length isolated implant, placed neither too close to nor too far from the resected margin, can be an effective alternative to the symmetrically positioned four-implant-supported fixed denture.

Control of cervical lymph node metastases in oral cancer is very important as a prognostic factor. In case of invasion into surrounding tissues such as muscle, bone, mucosa and skin, extended radical neck dissection is necessary to avoid neck failure. We report a case of delayed cervical lymph node metastasis near the hyoid bone treated successfully by chemotherapy with TS-1 and thermoradiotherapy.A female in her 40' s with ulcer of the right tongue was referred to our department. The patient underwent right partial glossectomy. Six months after the surgery, an ipsilateral cervical lymph node metastasis near the hyoid bone was found. To avoid extended radical neck dissection including resection of the hyoid bone and pharyngeal mucosa, we performed chemotherapy with TS-1 (100 mg/day, total 2,800 mg) and thermoradiotherapy (2 Gy/day, total 40 Gy, RF capacitive hyperthermia : 4 times) as a preoperative treatment. The efficacy according to CT scan was classified as partial response. The patient underwent conservative neck dissection without extended surgery and pathological diagnosis of the metastatic lymph node was complete response. There was no recurrence of neck lymph node metastasis 13 months after the surgery.