Atsushi Niimi

Autogenous bone grafts in the rabbit maxillary sinus

OBJECTIVE This study involving rabbits was undertaken to establish an experimental model for the sinus lift procedure and to clarify the repair of autogenous grafted bone in the maxillary sinus. STUDY DESIGN A corticocancellous bone block was grafted into the maxillary sinus of each of 18 rabbits. Each animal was killed at 2, 4, or 8 weeks after grafting and then histologically evaluated. RESULTS At 2 weeks, new bone formation was observed. There was no inflammation of the antral membrane. At 4 weeks, lamellar structures were observed in newly formed bone. At 8 weeks, newly formed cortical bone was observed under the elevated membrane and the medullary cavity was almost completely occupied by fat cells. CONCLUSIONS There were no histologic complications after the sinus lift procedure. Histologic results indicated that newly continuous cortical bone was formed along the elevated membrane at 8 weeks. This animal model could be useful as a sinus lift model.

Histologic study of the effect of hyperbaric oxygen therapy on autogenous free bone grafts

PURPOSE This study was undertaken to evaluate the effect of hyperbaric oxygen therapy on autogenous free bone grafts transplanted from iliac crest to the mandibles of rabbits. MATERIALS AND METHODS A piece of corticocancellous bone harvested from iliac crest was grafted to a same-size bone defect in the mandibles of 16 Japanese white rabbits. In 8 rabbits, 20 and 10 sessions of hyperbaric oxygen (HBO) treatment were carried out twice per day (2.4 ATA 60 min.) before and after operation, respectively. The other 8 rabbits served as controls. The graft and surrounding bone were sampled at 1, 2, 4, or 8 weeks after transplantation, and the effects of HBO were evaluated by light micrography and contact microradiography. RESULTS At 1 week after grafting, osteoid formation in the experimental group was much greater than in the control group. Union between the grafted and the host bone was observed in the experimental group at 2 weeks after grafting, but it was not observed in the control group until 4 weeks. Although it was difficult to differentiate grafted from host bone in the experimental group at 4 weeks, it was readily distinguishable in the control group. CONCLUSIONS These results indicate that HBO accelerates the union of autogenous free bone grafts.

Peri-implant soft tissue management through use of cultured mucosal epithelium

OBJECTIVE In implant therapy, peri-implant soft tissue management through use of mucosal grafting or skin grafting is necessary in some patients who do not have enough attached gingiva around the abutment. However, limitation of donor site size is a problem for the mucosal graft, and the different characteristics of skin, such as hair growth, are disadvantages in treatment that involves the use of skin graft. On the other hand, cultured epithelium fabricated with living mucosal cells has proved to be a good grafting material for any kind of mucosal defect. In this study, we used cultured mucosal epithelium for soft tissue management in implant therapy. STUDY DESIGN In the first surgical procedure of the implant therapy, a small segment of oral mucosa was sampled from a patient. The cultured epithelium was fabricated and then stored until it was grafted in the second surgery. RESULTS Twelve cases in which patients underwent peri-implant soft tissue management through use of cultured mucosal epithelium for implant therapy are presented, and the usefulness of this technique in the making of attached gingiva is analyzed. CONCLUSIONS From this study it was concluded that cultured mucosal epithelium can serve as a proper material for peri-implant soft tissue management.

The influence of compressive loading on growth of cartilage of the mandibular condyle in vitro.

The purpose of this study was to clarify the change in mandibular condyles under compressive loading. An organ-culture system of fetal rat mandibular condyles was used, and mechanical loading was generated by compressing the gas phase within a closed chamber. After the culture period, with compressive loading, type I collagen and fibronectin were observed in the lower half of the hypertrophic chondrocyte layer in the mandibular condyles; in contrast, without compressive loading, there was no such reaction. The size of the condyle was not increased by compressive loading. These results suggest that intermittent compressive loading could induce type I collagen and fibronectin production by chondrocytes.

Use of New Magnetic Attachments for Implant-Supported Overdentures

A newly designed magnetic attachment system for external hexed implants with a standard abutment platform has been developed. This system has certain definite advantages over bar attachments and ball attachments, which are frequently utilized for implant-supported overdentures. Especially, it can be applied to cases with reduced vertical dimension of occlusion because the total height of the magnet and the keeper is only 2.3 mm when assembled. In addition, detrimental lateral stresses to the fixture are greatly alleviated due to very low attractive forces horizontally. Favorable clinical results using this new magnetic attachment system have been obtained, and it may be considered a useful addition to overdenture therapy using any external hexel implant with a standard abutment platform, such as the Brånemark implant system.

IMPLANT-SUPPORTED PROSTHESES AFTER MAXILLARY CANCER RESECTION: PRELIMINARY REPORT

A preliminary study of 4 partial maxillectomy patients who received a total of 17 endosseous implants and implant-supported prostheses after oral cancer resection is reported. The masticatory function index (chewing efficiency) after implant placement was higher than the preoperative value. Speech with an implant-supported prosthesis improved as compared with previous prostheses or without a prosthesis. All of the patients received radiation and adjunctive hyperbaric oxygen therapy. The success rate after a 2-year follow-up period was 88.2%.

Immunohistochemical analysis of inflammatory infiltrates around the injection site of a streptococcal preparation, OK-432, in rat tongue.

On the assumption that neutrophils around the injection site of OK-432, a heat- and penicillin-treated lyophilized preparation of the Su strain ofStreptococcus pyogenes, enhance immunologic response through the production of Interleukin-1 (IL-1), OK-432 was injected into rat tongue, and specimens from the tongue were immunohistochemically investigated at various intervals after the injection, to clarify the process of inflammatory and immune responses at the injection site. Neutrophils and mononuclear cells appeared around the OK-432 injection site after 1 hour, increased to their maximum level at 24 hours, and then decreased from the 3rd to the 7th day. IL-1 was detected on neutrophils 3 hours after the injection, and OX-08-positive cells (suppressor/cytotoxic T cells and the majority of natural killer cells) remarkably increased. OX-39-positive cells (IL-2 receptor) appeared after 12 hours. These results suggest that neutrophils around the injection site of OK-432 at early phases of inflammation play a role in the expression of BRM function through IL-1.

Clinical study of osseointegrated implants in the maxillofacial region. 5th report. Prognosis and unsuccessful cases.

Prognoses were surveyed in 36 patients who underwent insertion of osseointegrated implants (Branemark system) from January 1988 to September 1992.One-hundred and forty-one fixtures were inserted in the mandibula, 66 in the maxilla, and 12 flange fixtures were inserted in the orbital or temporal region. The 1-year success rate of osseointegration was 98.2%, the 2-year rate was 97.5%, and after 3-years osseointegration was not lost in any case. In 3 cases, osseointegration was not obtained. Two of these 3 cases underwent radiation therapy before fixture insertion, and in the other an onlay bone graft was performed concurrently with fixture insertion in the maxilla. These results indicate that this implant system is very reliable in routine cases. However, irradiated patients and patients who have received bone transplants pose problems. Further studies are required to solve these problems.