The purpose of this study was to investigate differences in oral condition and health status between persons with 20 or more teeth at the age of 80 (8020 elderly) and persons of the same age with less than 20 teeth (non-8020 elderly). This study was conducted by a team belonging to the Aichi Dental Association. Number of remaining teeth, Community Periodontal Index of Treatment Needs (CPITN), salivary blood test, masticatory ability, bone mineral density (BMD), grip strength, balance test (length of time one can stand on one leg with eyes open), height, weight and body mass index (BMI) were all examined. The percentages of CPITN code 0, 1 and 2 were 68% in the 8020 male elderly and 72% in the 8020 female elderly. The positive percentage in the salivary blood test in the 8020 elderly was lower than that in the non-8020 elderly. Masticatory ability was 1.55g in the 8020 male elderly, and 1.53 g in the 8020 female elderly. Relative masticatory ability in the 8020 female elderly was 20% higher than that in the non-8020 female elderly. BMD in the 8020 female elderly was significantly higher than that in the non-8020 female elderly. Grip strength in the 8020 elderly was also significantly higher than that in the non-8020 elderly. The duration of balance test in the 8020 male elderly was 2.2 times longer than that in the non-8020 male elderly. The 8020 elderly showed good oral condition and health status was found to be better in the 8020 elderly than in the non-8020 elderly.

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To investigate whether the relationship between tooth shape ratio and incisor arrangement proposed by Peck et al. in 1972 was applicable to Japanese children, we compared two groups, one with normal permanent dentition and another with crowded permanent dentition, using chronologically constructed plaster dentition models. Tooth shape ratio was obtained by dividing the incisor mesio-distal width by the labio-lingual width and then multiplying the result by 100. The results revealed a significant difference in the coronal mesio-distal diameter of the incisors between the two groups, but the other items showed no significant differences, suggesting no clear relationship between tooth shape ratio and incisor arrangement. That was, our results suggest that there is no clear relationship between tooth shape ratio of the mandibular incisors and arrangement of the permanent incisors in Japanese children.

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The purpose of this study was to obtain percentile curves for present teeth in smokers and non-smokers for use in oral health education. Dental examinations were carried out by two dentists. The number of present teeth in each subject was counted, excluding the third molars. Subjects consisted of 2,283 men aged between 25 and 54 years enrolled in the health insurance union of a bank in Yokohama, Japan. Each subject completed a questionnaire on smoking habits and number of cigarettes smoked. They were classified into two groups: smokers and non-smokers. The mean number of present teeth in both groups was compared with the Mann-Whitney's U test. Smokers had fewer teeth than non-smokers in all age groups (p<0.05). At the age of 50, the 50th percentile for present teeth was 26 for smokers and 27 for non-smokers. However, the 3rd percentile for smokers' present teeth was 20.5 at 40 years of age and 14 at 50 years of age, while for non-smokers it was 22.5 at 40 years of age and 19 at 50 years of age. The 3rd percentile curve for smokers' present teeth decreased in those aged 45 years and over. The percentile curves in this analysis showed a clear difference between the two groups. These data should be made available for use in adult oral health education.

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The purpose of this study was to investigate digital subtraction technique in digital dental imaging for implant performance, used to quantitatively evaluate bone change around dental implants. For longitudinal assessment of peri-implant bone change, we applied subtraction technique to digital peri-apical radiographs using a digital dental imaging system in two cases at the upper canine and premolar regions. In both cases, we found two peaks of bone change at the crestal region; we also quantitatively demonstrated a marked change over the first one-month period and approximately three-month period spanning the fourth month to the end of the sixth month following implantation. Digital peri-apical radiography accommodating the digital subtraction program should be re-acknowledged as a reliable modality for assessing amount of bone change at local implantation sites.

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