Masayoshi Wadamoto

Clinical application of short hydroxylapatite-coated dental implants to the posterior mandible: A five-year survival study

STATEMENT OF PROBLEM The surgical and restorative procedures at the posterior region of the maxilla and the mandible present a complex task in the treatment of partially edentulous patients. PURPOSE The purpose of this study was to investigate the applicability of short hydroxylapatite-coated dental implants to the posterior mandible of partially edentulous patients. MATERIAL AND METHODS Eight and 11 mm implants were evaluated as to their cumulative survival rate, clinical status (plaque index, gingival index, probing depth), and marginal bone loss over a 5-year period. RESULTS AND CONCLUSIONS The verified overall cumulative survival rate was 94% for implants and 91% for prostheses. These results suggest predictable success for the application of short implants to the posterior mandible.

The three-dimensional bone interface of an osseointegrated implant. I: A morphometric evaluation in initial healing

Direct bone-implant interface as an indicator of endosseous implant success appears to have been overinterpreted because 100% bone apposition is not necessarily obtained at the surface of the endosseous dental implant. The purpose of this study was to obtain quantitative information about the three-dimensional bone structure around three hydroxyapatite-coated titanium alloy dental implants. Implants were placed in the mandible in three monkeys, and the surface bone contact ratio in the buccal, lingual, mesial, and distal directions was computed. Computer graphics were generated by the integration of data for serial ground surfaces obtained at 75 microm intervals of the tissue block involved with the implant. The bone contact ratio of the whole surface of each of the three implants was 80.8%, 68.1%, and 68.8%, and the bone contact ratio for each direction and portion varied with the conditions of implant placement. The bone volume ratios around the implant at the 0 to 300 microm zone were also calculated, and total ratios ranged from 58% to 81%. These results may provide useful quantitative information about the bone structure around the hydroxyapatite-coated implants and contribute to the development of realistic finite element analysis models based on the biologic bone structure around the implants.

The three-dimensional bone interface of an osseointegrated implant: A method for study

To clarify the three-dimensional bone structure around a plasma-sprayed hydroxyapatite-coated endosseous dental implant, bone contact with the implant at 75 microns intervals was evaluated. Based on digitized data, three-dimensional graphics of the bone around the implant was clearly shown. These graphics provide adequate information on the bone-implant interface and also suggest development of a realistic finite element model.

The three-dimensional bone interface of an osseointegrated implant. II: A morphometric evaluation after three months of loading.

To clarify the three-dimensional bone structure around two plasma-sprayed hydroxyapatite-coated titanium implants loaded for 3 months in a monkey, computer graphic evaluation was performed after computer-assisted integration of 70 serial buccolingual sections at 75 microm intervals. Quantitative analysis of the bone contact ratio (BCR) was also conducted with programmed software. The graphics revealed the macroscopic bone structure. The BCR values varied in portions from the top to the bottom of the implant and in the buccolingual or mesiodistal directions. Because these two implants had more cortical bone at the top portion in the lingual direction, the BCR was greatest in the lingual direction. The BCR values at the bottom portion of the two implants were greater than those at the top portions along the horizontal plane, which suggested the effect of loading. The lowest BCR value was observed at the top portion of one implant at a site where moderate periimplant gingivitis was observed. The total surface BCR value for the implants was 69.3% and 64.5%. These results provide additional detailed information on the bone structure around the hydroxyapatite-coated implant after short-term loading.

DIRECT BONE INDUCTION IN THE SUBPERIOSTEAL SPACE OF RAT CALVARIA WITH DEMINERALIZED BONE ALLOGRAFTS

In order to clarify the understanding of bone induction with crude bone morphogenetic protein (BMP)-containing allografts in subperiosteal conditions, chondrogenesis and osteogenesis were histologically evaluated following the implantation of the demineralized bone (DB) in the subperiosteal space of calvaria of 30 Wistar rats. On the forehead of the rat, DB particles were placed onto the denuded calvarial bone and covered by the skin-periosteum flap without any perforations of the marrow space of the calvaria. Sintered hydroxylapatite particles (HA) were also placed as a control. In the DB group, new bone formation on the surface of calvaria was achieved between 2 and 8 weeks after the operation. However, no chondrogenesis was seen throughout the experimental period. In the HA implantation group, fibrous tissue encapsulation of HA particles was generally seen. These results suggest that DB containing crude BMP might have the capacity for direct osteoblast induction from undifferentiated mesenchymal progenitor cells in vivo in specific situations, that is, in a subperiosteal space of uninjured rat calvaria.