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We have previously developed a computer-aided system for examination of the three-dimensional bone structure around implants and observed the bone changes in the healing period after implant placement. This paper describes the bone changes around hydroxyapatite (HA) and titanium (Ti) implants after abutment placement using histological and three-dimensional examinations. Twenty-four HA and Ti implants were embedded in the tibias of adult male New Zealand white rabbits. After 8 weeks, the abutment had passed through periosteum and was placed under the skin. Rabbits were sacrificed 4 and 8 weeks following abutment placement. In conclusion, histological examination showed that, at 4 weeks after abutment placement, bone resorption around the implant neck was seen in both HA and Ti implants, and at 8 weeks, excessive bone formation was seen around the implant neck. Three-dimensional bone examination showed that abutment placement may affect bone formation and cause additional bone hypertrophy in the bone marrow area.

Long-term support of dental implants requires adequate bone thickness in the area surrounding the implant. A three-dimensional examination, including calculations of percent boneGmplant contact and percent bone volume, was conducted to clarify the bone structure around pure titanium (Ti) and dense hydroxyapatite (HA) implants. The implants were installed in the tibiae of rabbits, and the bone structure was examined after 2, 4, 6 and 8 weeks. The bone formation following implantation differed in the cortical bone and cancellow bone areas. In the cortical bone area, the percent bone implant contact and percent bone volume were comparatively consistent for both Ti and HA implants during the observation period. In the cancellous bone area, both findings were influenced by the implantation period, and the chronological bone structure in the cancellous bone area also differed between Ti and HA implants. The percent bone-implant contact and percent bone volume in the Ti implant increased over 8 weeks, whereas the dense HA implant increased for the first 4 weeks and then decreased. The implant materials, Ti and HA, affected the bone remodeling in the cancellous bone area.

Adequate bone quality and stress distribution to the bone are of decisive importance for implant success. The purpose of this in vitro study was to investigate the influence of bone quality on the stress distribution using 2 implant-bone mimicking models, simulating compact and cancellous bone quality. The resin model was made of an acrylic resin only simulating compact bone quality. The hybrid model was made of 2 kinds of materials, acrylic resin covered with a 1-mm layer of urethane to simulate cancellous bone quality. An implant was embedded in each model, and the abutment and suprastructures were connected to the implant. A strain gauge was placed perpendicular to the implant on the surface of the model and a small accelerometer was attached to the abutment. When an impact load was applied to the suprastructure, both strain and acceleration were measured. Both abutment acceleration and surface strain in the hybrid model decreased rapidly as time progressed when compared to the resin model. Abutment accelerations in the resin model were significantly lower than those in the hybrid model. In the hybrid model, the strain increased as the loading site was moved closer to the strain gauge. The influence of loading sites on strain in the resin model was greater than in the hybrid model. Therefore, the occlusal stress was distributed more widely in the hybrid model than in the resin model. This may indicate that occlusal stress in compact bone may have a tendency to concentrate in particular regions.

Dental treatment must meet the needs of the rapidly increasing elderly people in Japan. In addition, geriatric inpatients also increased with the increase of elderly people. Investigation was carried out to determine the oral condition and microflora in denture plaque of elderly patients in two geriatric hospitals and Tokushima Dental Hospital. The difference between healthy patients and geriatric inpatients was. discussed. The results of the preliminary survey were as follows:1. Inpatients in a geriatric hospital were more elderly, and the frequency of edentulous patients was fairly high. The prognosis of the denture was poor because of high frequencies of low residual ridge and oral diskinesia.2. Denture plaque of geriatric inpatients had the following characteristics compared to that of healthy elderly patients.1) Numbers of total bacteria, Streptococci, Candida, and Staphylococci in isolated denture plaque of the geriatric inpatients were larger than those of healthy patients.2) Linear relationships between numbers of total bacteria and Streptococci and between numbers of Candida and Staphylococci were found.3) The frequency of MRSA in the geriatric inpatients was higher than in the healthy patients.4) Numbers of total bacteria and Streptococci in denture plaque obtained in the inpatients with heart disease and cerebrovascular accident were much larger than those in the inpatients without these diseases.

The purpose of this study was to investigate efficacies of acidic and neutral electrolyzed water as denture cleansers from the bacteriological aspect.Twenty-five upper full dentures of patients of an elderly care center were used in this study. Nine dentures were immersed in acidic electrolyzed water, eight in neutral electrolyzed water and eight in denture cleanser (Pika®). Plaque samples were collected from fitting surface of the dentures by scrubbing before and after immersion, and the changes in the number of bacteria were observed.The results were as follows:1. Acidic and neutral electrolyzed water were effective as denture cleansers, and the rates of removal [log10 (bacteria number after immersion)/logic, (before immersion)] tended to be constant.2. MRSA decreased by immersion in acidic electrolyzed water and in denture cleanser (MRSA was isolated from four dentures. Two were immersed in acidic electrolyzed water and two in denture cleanser).