Fluoride

“Recent ecological comparison studies have suggested a positive association between fluoridation and hip fracture. Using data from the Rochester Epidemiology Project, we found the incidence of hip fracture for the 10 years before the fluoridation of the Rochester, Minn, public water supply was 484 per 100,000, compared with 450 per 100,000 in the following 10 years. When the effects of calendar time and age were controlled for, the relative risk associated with fluoridation was 0.63. These ecologic trend data suggest that the fluoridation of public water supplies is not associated with an immediate increase in rates of hip fracture. Further studies of this association at the individual level are clearly required before public policy decisions can be made.”

“Background: Although a recent bioassay showed increased frequency of bone cancer in rats with high oral intake of fluoride, the data are reported as equivocal evidence of carcinogenicity. In humans, occupational fluoride exposure may cause skeletal fluorosis, and our earlier follow-up of fluoride-exposed workers showed increased incidence of respiratory cancers. Purpose: To further evaluate occupational fluoride exposure as a carcinogenic risk factor, we extended by approximately one decade the follow-up of a cohort of 425 men and 97 women employed for at least 6 months in the period 1924–1961 at the Copenhagen cryolite processing plant. Cryolite ore contains about 50% fluoride. Methods: Cancer mortality was determined for the period 1941–1989, and incidence for 1943–1987. For comparison, we used national mortality rates and cancer incidence rates for the Copenhagen area. Results: Among the men, 300 deaths occurred; 223 were expected. Respiratory lung and laryngeal) cancers and violent death were responsible for most of this excess; rates for mortality from cardiovascular disease were close to the rates expected. Of the 423 male workers, 119 developed cancers; 103.6 were expected. There was excess incidence of cancers of the lungs (35 men; standard incidence ratio [SIR] = 1.35), larynx (5 men; SIR = 2.29), and urinary bladder (17 men; SIR = 1.84). Maximum incidence occurred after 10–19 years of employment, but otherwise, no stable relationship between cancer incidence and duration of employment was observed. The incidence of respiratory and urinary cancers was particularly high in men less than 35 years old at first employment, Cancers in female workers were too few to allow detailed evaluation. Conclusions: The increased incidence of respiratory cancers suggests that cigarette smoking was frequent in this cohort, despite the unremarkable cardiovascular mortality, but the disproportionate increase in the incidence of bladder cancer is difficult to explain by smoking habits alone. Because this industrial cohort was exposed to high concentrations of fluoride dust, heavy respiratory exposure to fluoride may have contributed to the increased cancer risk. If these workers inhaled a carcinogenic substance partly excreted in the urine, an increased incidence of respiratory and bladder cancers would not be inconceivable. Implication: The potential role of fluoride as a cause of bladder cancer needs to be explored.”

This in vitro study evaluated the amount of fluoride released from glass ionomer-lined amalgam restorations over a period of 1 year. Class V cavities (2 x 2 x 7 mm) were prepared on the facial and lingual surfaces of 50 extracted human molars randomly distributed into 5 groups: Group 1: No restorations; Group 2: Dispersalloy amalgam alone; Group 3: same as Group 2 except 1 mm of Ketac-Silver was placed on the axial wall before amalgam insertion; Group 4: GC Lining/amalgam; and Group 5: Miracle Mix/amalgam. After restoration, each tooth was thermocycled (100x) at 5 degrees C and 55 degrees C with a dwell time of 30 seconds for baseline fluoride release levels. The teeth were placed in a polyethylene vial containing 4 ml of deionized water. At weekly intervals, each tooth was transferred to a fresh vial. Fluoride release was measured with a fluoride ion specific electrode for 10 consecutive weeks and then again at the end of 1 year. Calibration curves for low level measurements were prepared so the readings could be expressed in micrograms/ml F. At 1 year, fluoride released in micrograms/ml was: Group 1: less than 0.08; Group 2: less than 0.08; Group 3: 0.28; Group 4: 0.68; Group 5: 1.12. An ANOVA was used to evaluate the statistical difference between the groups. At the end of 1 year, measurable amounts of fluoride were recorded for all glass ionomer-lined groups with Miracle Mix and GC Lining releasing significantly more fluoride than Ketac-Silver (P less than 0.002).

This paper presents the events surrounding the dissemination of the results of a major preventive dentistry demonstration program designed and conducted to provide evidence of the effectiveness and actual costs of a combination of commonly used preventive procedures. It then reviews the controversy provoked when the results of that program were counter to the conventional wisdom of the day, prevailing national policy, and public health practice. An analysis of possible reasons for this reaction follows. The paper concludes with some observations about how such a situation might be approached to minimize similar controversy in the future.

Fluoride was measured in femurs of black-crowned night-herons (Nycticorax nycticorax) living adjacent to a phosphate processing complex near Pocatello, Idaho. Fluoride (ash wt.) in femurs ranged from 540 micrograms/g to 11,000 micrograms/g and increased (P = 0.0001) with age, but with no difference (P = 0.80) between sexes. Adult males (greater than or equal to 4 years) contained 5,409 micrograms/g compared to 6,042 micrograms/g for adult females. The tibiotarsus (= tibiae in text) increased in diameter with age (P = 0.015) in this study; fluoride was nearly related (P = 0.065) to the increase. As the diameter increased with age, wall thickness decreased (P = 0.011) suggesting excessive internal bone resorption, but fluoride concentrations were not implicated in the relationship (p = 0.64). The apparent increase in diameter and decrease in wall thickness may have partially neutralized each other’s effects on strength. Although significantly higher concentrations of fluoride were present in adults than in Third Year herons, no significant change in bone strength (maximum load or modulus of rupture) was detected between the two age classes, but three of the four comparisons showed adults with less strength (i.e., a hint of diminished strength with age). The tibiae of Hatch Year birds were significantly weaker than documented in older age classes, but incomplete growth was thought responsible. The strong relationship between age and fluoride concentrations reduced our ability to separate a “fluoride effect” from an “age effect.” Other authors believed fluoride was responsible for an increase in bone diameter and the fluoride residues encountered in adults were within the range indicative of poisoning in cattle.

Fluoridated mouthrinses are not advised for preschool children who may swallow much of the agent. An alternate method of delivering topical fluoride to the interproximal tooth surfaces in these young patients may be fluoridated dental floss. The purpose of this study was to determine the fluoride levels of demineralized primary enamel both before and after the use of a commercially available dental floss impregnated with commercially available fluoride-containing products. The results showed that demineralized primary tooth surfaces treated with fluoride-impregnated dental floss exhibited significantly higher fluoride levels than those surfaces treated by immersion in a fluoridated mouthrinse or deionized water.

Genotoxicity of Sodium fluoride was evaluated in mice in vivo with the help of different cytogenetic assays. The frequency of chromosome aberration was dose—and time—dependent but not exactly route-dependant. Fractionated dosing induced less aberration. Incidence of micronucleus and sperm abnormality increased with dose. Relative sensitivity of the three assays has been found to be: Sperm abnormality > Chromosome aberration > Micronucleus. The present results have revealed the mutagenic property of NaF.

The effects on reproduction in screech owls (Otus asio) of chronic dietary sodium fluoride administration at 0, 40, and 200 ppm were examined. Fluoride at 40 ppm resulted in a significantly smaller egg volume, while 200 ppm also resulted in lower egg weights and lengths. Day-one hatchlings in the 200 ppm group weighed almost 10% less than controls and had shorter crown-rump lengths. No gross abnormalities were apparent. Skeletal clearing and staining revealed significantly shorter tibiotarsus lengths in the 40 ppm and 200 ppm groups and a shorter radius-ulna length in the 200 ppm group. By 7 days of age, body weights and lengths did not differ from controls, but the tibiotarsus in the 200 ppm group remained shorter. No significant differences were detected in hematocrit, hemoglobin, plasma calcium or alkaline phosphatase. Plasma phosphorus levels were higher in the 40 ppm group than in controls. These results, in combination with the findings of Pattee et al. [25], revealed significant impairment of overall reproduction, suggesting that sodium fluoride could cause slight to moderate reproduction disorders in owls in fluoride-polluted areas.

The purpose of this project was to examine the effect of various toothcleaning procedures on fluoride
uptake by enamel of human permanent teeth.

In this paper we report on a preliminary investigation into the accumulation of fluoride by a number of marine and intertidal animals. The work was prompted by the recent building of an aluminium smelter at Lynemouth in Northumberland which discharges a fluoride-loaded effluent into the sea. However, dilution by seawater renders contamination negligible and it is suggested that tissue fluoride concentrations represent background levels for the animals studied.

In both vertebrates and invertebrates, fluoride is largely accumulated in skeletal structures. There is little or no accumulation in soft, edible tissues, with the exception of fish skin.

Preliminary toxicity tests were carried out on a number of marine invertebrates. Even at unnaturally high ambient fluoride levels, no adverse effects were seen, except possibly in the case of the filter-feeding mollusc Mytilus edulis.