Attention needs to be given, in negligibly water-fluoridated as well as in optimally water-fluoridated communities, to reducing the daily intake of fluoride by young children in order to avoid putting them at risk of developing dental fluorosis.

This study was conducted to test the hypothesis that physiological changes which occur during aging increase the biological impact of fluoride and reduce the threshold of safe fluoride exposure. Four groups of rats were fed a low-fluoride diet (< 1.2 ppm) ad libitum and received 0, 5, 15, or 50 ppm fluoride in their drinking water. Animals were killed after three, six, 12, or 18 months of treatment. Blood and urine were monitored for biochemical markers of tissue function, and plasma, urine, feces, and representative tissues were analyzed for fluoride. In addition, bone marrow cells from animals killed after 18 months of treatment were examined for frequency of sister chromatid exchange (SCE), a marker of genetic damage. Study results indicated that, within treatment groups, fluoride intake, excretion, and retention did not change significantly between three and 18 months. Fluoride concentration in soft tissues did not change with treatment duration in the fluoride-treated animals. Mineralized tissue fluoride concentration and the total fluoride in the carcasses increased continually as the animals aged. In spite of significant, dose-related differences in tissue fluoride levels which occurred in all age groups in this study, there were no indications that increased fluoride in the tissues caused any adverse physiological or genotoxic effects. None of the monitored clinical "wellness" markers of tissue integrity and function was altered by fluoride in a clinically significant manner. Therefore, there was no evidence from this study that aging reduces the threshold of safe chronic fluoride exposure.

Secondary caries is a major reason for the replacement of restorations. Because it is hypothesized that the development of secondary caries is closely associated with pathogenic oral bacteria, an in vitro microbial model has been developed to produce secondary carious lesions. A mixture of overnight cultures of Streptococcus mutans and Lactobacillus casei in dextrose-free trypticase soy broth, supplemented with 5% sucrose (TSBS), at 37°C was used in this model as the inoculum for the experimental groups. Uninoculated control groups were incubated with medium only. Groups of human tooth specimes restored using composite, together with their respective controls, were exposed for 7 or 12 days to circulating cycles of TSBS (30 min each, 3 times per day) and a mineral wash solution (for a total of 22.5 h per day), at 37°C. The pH of the experimental groups dropped to 4.1–4.5 during the test periods. The pH of the control groups remained at 6.8–7.0. The inoculated bacteria remained viable throughout the study. No contamination of experimental or control samples occurred. Laser scanning confocal microscopy demonstrated the development of incipient surface and wall lesions in all the specimens of experimental groups in as few as 7 days. Reproducibility of the model was confirmed in a second investigation. Therefore, it was concluded that this model can be used for studying the microbial etiology and prevention of secondary caries.

Abstract– While the level of fluoride intake that affords optimal cariostatic efficacy without causing dental fluorosis is not precisely known, it has been suggested that the threshold of fluoride exposure above which fluorosis may occur is between 0.05 and 0.07 mg/kg/day. Objective: To monitor and compare fluoride intake from diet and dentifrice use (theoretical F: 0.10–0.11%) by three groups of 16‐ to 40‐month‐old children: two groups living in the negligibly water‐fluoridated communities of San Juan, Puerto Rico, and Connersville, Indiana, and the third group residing in the optimally water‐fluoridated region of Indianapolis, Indiana. Methods: Fluoride intake from diet was monitored by the “duplicate plate” method, and fluoride ingested from dentifrice was determined by subtracting the amount of fluoride recovered after brushing from the amount originally placed on the child's toothbrush. Results: The mean combined amount of fluoride ingested daily by children living in the negligibly fluoridated communities was not significantly different from that ingested by children in the fluoridated community. The major component of fluoride ingested by children in the negligibly fluoridated communities came from fluoridated dentifrice, and in the fluoridated area children ingested as much fluoride from toothpaste as they did from beverages. In San Juan mean daily fluoride intake was within the estimated range for safe fluoride expo‐sure; however, in the “halo” community of Connersville and in Indianapolis, daily fluoride ingested by many of the children may have exceeded this level. Conclusion: Attention needs to be given, in negligibly water‐fluoridated as well as in optimally water‐fluoridated communities, to reducing the daily intake of fluoride by young children in order to avoid putting them at risk of developing dental fluorosis.

Substantial amounts of tooth minerals are lost during dental caries formation. Transversal microradiography, a well-accepted method used to quantify mineral loss, is a time-consuming technique which requires a thin enamel section (100 µm) and involves the use of x-rays. In an attempt to solve these difficulties, a procedure has been developed in which a human tooth specimen with demineralized enamel is cut in half (HT), stained with a fluorescent dye (rhodamine B) and analyzed using a laser scanning confocal microscope. A series of three studies was conducted to correlate measurements of enamel demineralization obtained from enamel thin (100 µm) sections (TS) using transversal microradiography with three parameters (area of the lesion; total and average dye fluorescence intensities) measured on the same TS or on a thicker section (HT) of the same specimen by laser scanning confocal microscopy. Results showed that a 0.1 mM rhodamine B solution provided the most adequate imaging conditions for confocal microscopy. Pearson’s correlation coefficients, calculated between microradiography and confocal microscopy data obtained using a 0.1 mM rhodamine B solution, were: ΔZ vs. HT lesion area = 0.95; ΔZ vs. HT total fluorescence = 0.80; ΔZ vs. HT average fluorescence = 0.74; ΔZ vs. TS lesion area = 0.95; ΔZ vs. TS total fluorescence = 0.74; ΔZ vs. TS average fluorescence = 0.55. All these correlations coefficients were statistically significant (p < 0.01). It is concluded that in enamel demineralization studies statistically significant correlations exist between parameters measured using transversal microradiography and parameters quantified using confocal microscopy.