To elucidate the mandibular morphological changes due to occlusal and masticatory alterations in addition to aging, 66 Donryu male rats (30-74 weeks old) were divided into three groups, the control group (solid diet), the soft diet group (powder diet containing the same components as the solid one from the 43rd week) and the molarless group (all molars were removed at 43 weeks and then fed a powder diet) . The powder diet group and the molarless group were compared with the control group by using a handy microscope system with a CCD camera, soft X-ray pictures and light microscopy. The results obtained are as follows: 1. The height of the mandibular ramus, the length and the width of the condyle in the experimental group were shorter than that of the control group, showing a statistical signifi-ance (p<0.01) . 2. Volumetric bone mineral density of the condyle measured by the image analyzer system in the experimental group was less than that of the control group, showing a statistical signifi-cance (p<0.01) . 3. Age-related change and chewing style-related alterations were observed in the condylar cartilage area. These findings suggested that the bone remodeling in the condyle of aged rats was consider-ably influenced by occlusal and masticatory alterations in addition to aging
A questionnaire about dental health was given to 6846 new students in the University of Tokyo. The results were as follows: 1. 5.3% of students had experienced periodontal diseases. The percentage of students with gingival bleeding was 20.7%. 2. Most of the students brushed their teeth 3 minutes at a time, 2 times a day. 3. 11.5% of the students had experienced orthodontic treatments. The percentage of female students was significantly higher than the percentage of male students. 4. 0.9% of the students had experienced TMJ disorders. TMJ symptoms were noted in 9.7%. 5. More than 90% of the students usually chewed on both sides of the mouth.
The purpose of this study was to investigate the growth direction and the function of the mandibular condyle with the observations of the bone structure. Seven week-old rats were used as materials and the condylar processes were studied by macroscopic, light microscopic and electron microscopic observations. The results were as follows 1. Many types of bone of different degree of calcification and differentiation were obser-ved in the condylar processes. The calcified cartilage and immature bone, which were highly calcified, function as the core of bone trabecullae and compact bone. Each core was surrounded by other types of bone, and then, it seemed that some of these types of bone gave the characteris-tics of stiffness and flexibility to the bone trabecullae and compact bone. 2. The bone trabecullae indicated the rational arrangements in the condylar process, and as a result, the pressure from the mandibular fossa was transmitted to the compact bone efficiently in the masticatory movement. 3. The condylar processes in these week-old rats were growing only backward. 4. It seemed that the function as the articular head was enhanced mainly after seven week-old though the condylar process grew while it was functioning until this stage.
Incorporation of rhodamine-labelled serum albumin (R-ALB) into the developing dentine was investigated by fluorescent microscopy. Male Japanese white rabbits were injected with R-ALB at a dose of 50mg/kg and the undecalcified section of the incisor dentine was obtained 11 days after the injection. The orange-red fluorescent labelling of R-ALB was observed in the internal dentine. The labelling consisted of several periodic stripes and decreased its intensity toward the predentine-dentine junction. Serum concentration of R-ALB rapidly decreased after the injection and 10% of the initial value was present after 12 hours. The concentration gradually decreased thereafter. No relationship was observed between the fluorescent labelling pattern and the change in the concentration of serum R-ALB. These results suggest that R-ALB fluorescent labelling is related to the diurnal dentine formation by the odontblasts in the rabbit incisor.
The present study was aimed at evaluating the clinical usefulness of a new type of dental implant, one piece-type artificial root made of a titanic core coated with HAp by plasma-spray coating. A total of 227 artificial roots were implanted in 78 healthy subjects (44 females, 34 males) ranging in age from 17 to 74 years. Each of them was examined on several given occasions by both radiography and a method used in periodontal disease screening. Prognostic observation lasted up to 4 years and 3 months. No implants were rejected in 77 subjects, although marked mobility of the implants resulted in their withdrawal in 1 subject (2 implants) . They were functioning favorably during the study period, affording great satisfaction to the subjects. No side effects were found in any of the subjects excluding one case of oral lichen planus in which the presence of a direct cause-effect relation remained unclear. From the above results, we conclude that this new type of artificial root is of extremely high clinical use.
In 1991, dental health examination was carried out in Nigeria : ILE-IFE (urban) and Ashipa (rural) located in the southwest of Nigeria. The number of the subjects was 205 (aged 8, 10, 12) in ILE-IFE and 511 (aged 8, 10, 12, 15 to 75) in Ashipa. The purpose of this study is to clarify the distribution of plaque, calculus and gingivitis and to reveal the correlation between the plaque score (DI-S, OHI-S), calculus score (CI-S, OHI-S) and gingivitis score (GI) among the Nigerian by age. Results were as follows: 1. In the comparison between urban and rural schoolchildren, CI-S was higher in the rural children statistically but DI-S was not. This evidence is to be expected as a consequence of using PACO (traditional twig) for tooth brushing, because 73.1% of rural children were using the PACO whilst 92.1% of urban children were using the tooth-brush. 2. Because of the poor oral cleanliness using PACO, the changing pattern of DI-S, CI-S and GI by age could be natural and physiological. 3. DI-S and CI-S among the rural people were of a high level in the children 8 and 10 years of age and decreased to the bottom level in the 20's. After the lowest scores in the 20's, these increased with age. 4. The correlations between DI-S and GI were higher in the young people than in the elder people.