Demineralized enamel grooves were exposed to oral cavities of healthy adults after irradiation by a KrF excimer laser with a wavelength of 248nm (total energy dose = 172 J/cm^2) or with the second harmonic wave of a Q-switched Nd : YAG laser with a wavelength of 532 nm (total energy dose = 100 J/cm^2). The mineral distributions were assessed quantitatively by transversal microradiography. Compared with unlased controls, the mineral parameters of interest, i.e. the lesion depth (l_d, μm) and the mineral loss value (△Z, vol%・μm) at the bottom of the grooves, were not significantly different in lased samples. No remarkable evidence of remineralization was detected in any sample. The results suggested the possibility that subsurface demineralization of early enamel lesions is not inhibited by irradiation with Q-switched Nd : YAG or KrF excimer lasers.

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The effects of beryllium chloride (Be) on calcium (Ca) accumulation, cell proliferation, alkaline phosphatase (ALPase), acid phosphatase (ACPase), lactate dehydrogenase(LDH), and cyclic AMP (cAMP) levels in MC3T3-E1 osteoblastic cells were estimated. MC3T3-E1 cells were seeded into 24-well plates(4,000 cells/well) in α-MEM containing 10% PCS, and then treated with Be at day 3 or 7. Ca accumulation was decreased by 0.001 μM Be in a dose-dependent manner. Ca accumulation in cells was completely blocked at a concentration of 0.1μM Be. The addition of 0.1μM Be did not affect ^3H-thymidine and ^<14>C-leucine uptake into the cells. The effects of Be on ALPase activity in MC3T3-E1 cells were also studied. After treatment with various concentrations of Be for 24 hrs, the cells were washed with phosphate buffer, and then ALP activity was analyzed. ALPase activity was not affected by up to 1.0 μM Be. However, in the presence of Be, ALPase activity in cell debris was significantly decreased at a concentration of 0.01 μM Be. On the other hand, ACPase activity, LDH activity, and cAMP level in cells were not affected by 0.1 μM Be. These results suggest that Be may inhibit the mineralization in osteoblastic cells, by inhibition of ALPase activity.

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The purpose of this study was to identify risk factors influencing tooth loss and reasons for tooth loss during the recall period in adults who had participated in the oral health check-up system at the outpatient clinic in the Affiliated Hospital of Niigata University School of Dentistry for 10 years or longer. We assessed individual characteristics like age and gender, tooth status, and periodontal health status at baseline as risk factors from the longitudinal data of 663 adults (males, 291 ; females, 372 ; average age at baseline, 37.6). 40.6 percent of the subjects lost one or more teeth and 7.1 percent lost more than 5 teeth during the recall period. Logistic regression analysis showed that subjects who had more decayed teeth, crowned teeth, higher percentage of teeth with a periodontal pocket, of more than 3 mm or more caluculus deposits (VM-index) at baseline were more likely to lose teeth. Decayed teeth and crowned teeth had a higher percentage of loss during the recall period than sound teeth, showing that caries risk and caries prevalence affected tooth loss greatly. Subjects who were older at baseline were more likely to lose more than 5 teeth in a logistic regression analysis among subjects who lost teeth during the recall period. The percentage of teeth lost due to periodontal disease (52.0%) was relatively higher than that due to caries (40.2%). The percentage of teeth lost due to periodontal disease (64.6%) was higher than that due to caries (32.3%) in subjects who lost more than 5 teeth, suggesting that individuals with high risk for tooth loss had high risk for periodontal disease.

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The purpose of this study was to examine the possible effects of implementing a preventive dental program on medical costs in a corporate dental clinic. About three hundred employees insured with a corporate health insurance program were provided with a preventive dental program which consisted of dental examinations, counseling, preventive treatments, and, if necessary, referrals for advanced treatments to community general practitioners. In dental examinations, a health questionnaire, photography of the oral cavity, a clinical examination of the teeth, and scoring of community periodontal index of treatment needs (CPITN) and O'Leary's plaque control record (PCR) were included. The dental counseling consisted of instruction in tooth brushing. Preventive treatments were mostly dental calculus scaling, root planing for incipient periodontal diseases, and resin restorations for incipient dental caries. The preventive dental program was used for five consecutive years. The costs for the corporate health insurance program and the number of treatments were monitored semiannually during the study period. The changes in costs and treatment needs in this group were compared with those of the control which was a comparative group of employees in the same corporate organization but in a different city. The number of requested dental examinations and treatments done resulted in an interim rise in the claims of medical costs immediately after the implementation of the preventive program. These figures, however, became lower statistically than those of the control group without the preventive program, after two and three years. The results suggest that, although there may be some immediate rise in medical costs, these costs can be lowered in time by implementing a preventive dental program in a corporate dental clinic.

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The purpose of the present study was to evaluate the effect of regular professional toothbrushing on tooth loss over a period of six years. A retrospective cohort study of 224 subjects in a university dental hospital was performed. The test cases were defined as patients with periodontal supportive therapy based on regular professional toothbrushing. The control cases were those with conventional periodontal treatment. The two groups were well balanced with respect to age, sex, and the number of remaining teeth. The total numbers of lost teeth in the test and control groups were 91 and 189, respectively. The difference between the two groups was obvious in the subjects at the age of 40-59 years. Only one lower anterior tooth was lost in the test group, whereas more teeth were lost in the control group. The average number of visits druring the 6 years was 46 and 27 in the test and control group, respectively. Forty-eight out of 112 control subjects received surgical therapy, whereas only 4 subjects underwent it in the test group. Our data suggested that regular professional toothbrushing followed by supportive periodontal therapy contributes to good preservation of teeth.

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An in vitro study was designed to evaluate the effects of sugar substitutes on remineralization potential using an artificial dental caries model. Palatinose, sorbitol, and xylitol were selected as sugar substitutes. The enamel samples were remineralized in a remineralizing solution containing 3.0 mM Ca, 1.8 mM phosphate, and 2 ppm fluoride with or without sugar substitutes. Remineralized or demineralized groups without sugar substitutes served as positive or negative control groups. The degree of remineralization was evaluated by the changes in lesion depth and mineral loss values. The lesion depth values decreased approximately 20 μm in the groups of palatinose and sorbitol compared with the positive control. Positive control and sugar substitute groups except for xylitol showed a better trend toward remineralization than the negative control (p&lt;0.05). The improvement rate of the lesion depth was in the order of palatinose 34.6%, sorbitol 32.0%, positive control 20.3% and xylitol 8.5%. However, there were no statistically significant differences among any sugar substitute groups when they were compared with the positive control. Only the palatinose group showed mineral increase effect compared with positive control. The trend of remineralization from the mineral gain point of view was similar to the lesion depth, that is, the positive control and sugar substitute groups except for xylitol showed more remineralization than the negative control (p&lt;0.05). The improvement rate of the mineral gain was in the order of palatinose 42.8%, positive control 37.8%, sorbitol 34.4%, and xylitol 19.6%. However, there were no statistically significant differences among any sugar substitute groups when they were compared with the positive control. It is conceivable that sugar substitutes have no promotional or inhibitory effect on remineralization potential of fluoride in remineralizing solutions.

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We investigated the effects of de〜 and remineralization balance on acid resistance of human enamel. Human premolar enamel was demineralized and subsequently remineralized with 3 ppm fluoride. After treatment, 60 enamel samples were exposed to demineralizing and remineralizing solutions for 1-6 days (D1R1-D6R6). For the acid resistance test (ART), treated enamel samples were exposed to 0.1M lactic acid solution (pH : 4.5) for 1, 3, and 7 days, and the dissolved calcium (Ca) and the mineral loss values were measured with atomic absorption spectrometry and transversal microradiography, respectively. The amount of dissolved Ca increased linearly in proportion to the periods of ART. At day 1 of ART, we recognized two types of Ca solubility ; comparatively more soluble groups (D1R1, D2R2, D5R5) and less soluble groups (D3R3, D4R4, D6R6). Mineral loss values at day 1 showed no difference among the 6 groups. At day 3 of ART, 3 types of Ca solubility were distinguished : highly soluble groups (D1R1, D5R5), moderately soluble groups (D2R2, D4R4) and less soluble groups (D3R3, D6R6). Although mineral loss values did not completely correspond to the dissolved Ca data, both D6R6 and D3R3 still showed less mineral loss values and the formation of acid-resistant lamination. At day 7 of ART, since many samples showed an erosive lesions, it seemed that day 7 of ART was too long to evaluate the acid resistance. Too short periods of demineralization and remineralization could not produce acid resistance on enamel. Our results suggest that there is a subtle optimal balance between demineralization and remineralization to obtain acid resistance. Regarding the evaluation method, by combining these two methods it is possible to interpret from where the mineral was lost during ART.

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