Water-borne fluoride and cortical bone mass: a comparison of two communities

Associations between longitudinal fluoride intakes from birth to age 23 and multi-row detector computed tomography bone densitometry outcomes at age 23

OBJECTIVES

To assess the relationships between longitudinal fluoride intakes and bone densitometry outcomes in young adults.

METHODS

Data were analyzed from the Iowa Fluoride Study and Iowa Bone Development Study, which followed 1,882 infants from birth in 1992. Daily fluoride intakes were assessed using detailed questionnaires sent every 1.5-6 months, and multi-row detector computed tomography (MDCT) scans of distal tibia were obtained from 330 participants aged 23 years. Sex-specific bivariate and multivariable associations with MDCT outcomes were examined using linear regression. Because of the multiple statistical analyses being conducted, p-values < 0.01 were considered statistically significant.

RESULTS

In fully adjusted analyses, no statistically significant (p < 0.01) or suggestive (0.01 < p < 0.05) associations were found between period-specific or cumulative fluoride intake and bone measures for either sex, although there were suggestive positive relationships in unadjusted analyses.

CONCLUSIONS

Longitudinal fluoride intakes had little association with bone measures at age 23. As there were no adverse effects from fluoride intake on bone health in young adults, results support the continued use of fluorides, particularly community water fluoridation is the most cost-effective method of dental caries prevention.

A half-century of community water fluoridation in the United States: review and commentary

The nearly 50-year history of community water fluoridation is reviewed with the major emphasis on the benefits and safety of fluoridation. Other aspects of water fluoridation also described include the apparent reduction in measurable fluoridation benefits because of the abundance of other fluoride sources, the diffusion of fluoridation effects into fluoride-deficient communities, preeruptive and posteruptive effects, technical and cost aspects, sociopolitical and legal issues that affect the successful fluoridation of communities, and alternatives to community water fluoridation. The majority of studies have evaluated the effectiveness of water fluoridation on the permanent teeth of children, while there are fewer studies on deciduous teeth and in adults; the relationship between fluoride ingestion and bone health needs further clarification; the sociopolitical issues of fluoridation need to be better understood.

Osteosclerosis due to endemic fluorosis

Endemic water borne fluorosis is a public health problem in Isparta, a city located in southern Turkey. In order to investigate the association between osteosclerosis and fluorosis, we retrospectively screened the results of lumbar spine and femur neck bone mineral density (BMD) of 1500 patients who were examined before, for any reason in between 2001-2003. Sixty nine patients (67 females and 2 males, mean age 52.6+/-10.2) with vertebra T-scores>or=+2 were found only except a patient with osteoid osteoma in the femur neck (femur T-score+6.64). Thirty-four of the patients could be reexamined with lateral vertebra BMD and investigated for fluorosis and the other etiologic causes of osteosclerosis. Of 34 patients, 14 had either mottled tooth enamel or urine fluoride level greater than 1.5 mg/l. Other etiologic causes were hypothyroidism (2), hypoparathyroidism (1), history of lumbar fracture (1), use of retinoids (1), vitamin D (7), oral calcium preparations (9), and bisphosphanates (3). Lateral lumbar vertebral T-score was greater than+2 in 12 patients (35.3%). Femur T-score was greater than+2 in 7 patients (20.6%). Fourteen patients (41.2%) had lateral vertebral or femur T-score>or=+2. Five (35.7%) of these patients had signs of fluorosis, as discussed before. Mean body mass index of individuals with fluorosis was 36.4+/-7.9 and this result was significantly higher than other osteosclerotic subjects (31.6+/-4.4). In conclusion we believe that approximately one third of the osteosclerosis in our region was due to endemic skeletal fluorosis and obesity may enhance this osteosclerotic type bone changes in endemic fluorosis.

Water fluoridation, bone mass and fracture: a quantitative overview of the literature

OBJECTIVE

To use the technique of meta-analysis to address the following research questions: Is water fluoridation associated with altered fracture risk at a population level and are the differences between studies consistent with confounding or chance variation between studies?

METHOD

The data sources utilised were Medline 1966-97, reviews and bibliographies. The search terms were fluoridation, bone mass and/or fracture. We included all observational studies published in English relating water fluoridation to bone mass and/or fracture in the initial assessment.

RESULTS

Water fluoridation had no evident effect on fracture risk (RR 1.02, 95% CI 0.96-1.09, n = 18 studies). There was marked heterogeneity between studies which could be explained, in part, by the combination of gender, urbanicity and study quality (R2 0.25, p = 0.05, weighted analysis).

CONCLUSIONS

Water fluoridation both at levels aimed at preventing dental caries and, possibly, at higher naturally occurring levels appears to have little effect on fracture risk, either protective or deleterious, at a population level. The small effect on bone mass seen in studies performed at the individual level is consistent with this finding. Variation between studies is also likely to be due to differences in the distribution of other recognised fracture risk factors between different populations. Confirmation of these findings is required in large studies performed at the individual level.

The association between water-borne fluoride and bone mineral density in older adults

While the benefit of fluoridation in the prevention of dental caries has been overwhelmingly substantiated, the effect of fluoride on bone mineral density is less clear. This cross-sectional study was designed to compare the bone mineral densities of older adults exposed to various levels of fluoride from community water systems. Participants were recruited from 3 rural communities with naturally occurring fluoride in their water systems at 0.03, 0.7, and 2.5 mg/L. All adults, age 60 and over, were eligible if they were ambulatory and had a long-term history (> or = 20 yrs) of ingesting city water. Bone mineral density (BMD) was measured by means of dual-energy x-ray absorptiometry at 3 anatomical sites: lumbar spine, proximal femur, and forearm. A total of 353 white non-Hispanic women and 317 white non-Hispanic men took part in the study. When the data were stratified by city of residence and gender, men and women living in the community with high levels of fluoride in their community water system had significantly higher lumbar spine BMD than their counterparts from the communities with low and moderate fluoride levels. The women in the high-fluoride community had significantly higher proximal femur BMD, but there were no statistically significant differences among men in either proximal femur or forearm BMD. Long-term exposure (> or = 20 yrs) to higher levels of fluoride appears to have a positive impact on lumbar spine and proximal femur BMD. Based on the results of this study, exposure to fluoride at levels considered "optimal" for the prevention of dental caries (from 0.7 to 1.2 mg/L) appears to have no significant impact on bone mineral density. The relationship between higher levels of fluoride exposure and bone mineral density requires further investigation.

Effects of fluoridated drinking water on bone mass and fractures: the study of osteoporotic fractures

To determine if optimal fluoridation of public water supplies influences bone mass and fractures, we studied 2076 non-black women, all aged > or = 65 years recruited into the Study of Osteoporotic Fractures at the Pittsburgh clinic. Information on fluoride exposure was limited to community water supplies. The variable used in the analysis was years of exposure to fluoridated water in community drinking water supplies. Bone mineral density (BMD) was measured at the spine and hip using dual energy X-ray absorptiometry and at the midpoint and ultradistal radius and calcaneus using single photon absorptiometry. Prevalent and incident vertebral fractures were determined by morphometry. Incident nonspine fractures were ascertained every 4 months and confirmed by radiographic report. Exposure to residential fluoridated water had no effect on bone mass. Women exposed to fluoride for > 20 years had similar axial and appendicular bone mass to women not exposed or women exposed for < or = 20 years. There was some suggestion that women exposed to fluoride for > 20 years had a lower relative risk of nonspine fractures (relative risk, RR, = 0.73; 95% confidence interval [CI] 0.48-1.12), osteoporotic fractures, RR = 0.74 (CI 0.46-1.19), and hip fractures, RR = 0.44 (CI 0.10-1.86), compared with women not exposed, but none of these relative risks was statistically significant. There was no association with wrist or spinal fractures. Our results do not support the findings from recent ecological studies which showed an increased risk of hip fracture among individuals exposed to fluoridated public water.

Fluoride and bone health

This paper reviews some of the studies related to the effect of fluoride on the skeletal system of humans and outlines the knowns and unknowns of fluoride and bone health. Current research indicates that, in large enough doses, fluoride stimulates bone formation by osteoblastic stimulation, increases bone formation earlier and to a larger extent in trabecular bone compared to cortical bone, and increases spinal bone density. There is controversy, however, concerning the efficacy of fluoride as a therapeutic agent in the treatment of osteoporosis. Some clinical studies have found a reduction in vertebral fracture rates while others have not. To date, only ecologic studies have been conducted on the association between water fluoridation and hip fractures. The inability of ecologic studies to control for confounding variables makes their interpretation difficult. Based on the literature presented, it is concluded that there are more unknowns than knowns in terms of fluoride's effect on bone, osteoporosis, and fractures. One of the major unknowns in the relationship between fluoride and bone health is dose and duration. Two studies are underway that attempt to describe the dose-response relationship between waterborne fluoride and osteoporosis. These studies will be completed in the near future and their results, while providing new insight into fluoride's effects on bone, will by no means answer all the questions raised on this issue.

On the mechanism of drug-induced gingival hyperplasia

Proposed mechanisms of the side effect of drug-induced gingival hyperplasia are reviewed. Hypotheses with regard to inflammation from bacterial plaque, increased sulfated glycosaminoglycans, immunoglobulins, gingival fibroblast phenotype population differences, epithelial growth factor, pharmacokinetics and tissuebinding, collagenase activation, disruption of fibroblast cellular sodium/calcium flux, folic acid and a combination hypothesis are evaluated.

The biocompatibility of glass-poly(alkenoate) (Glass-Ionomer) cements: a review

The literature describing the biocompatibility of glass-poly(alkenoate) ('Glass-Ionomer') cements has been reviewed. This literature shows that these materials have generally good biocompatibility for both dental and orthopaedic use, this latter observation being very recent. There have, though, been a few reports showing that in certain circumstances these materials may cause pulpal irritation and the reasons for these particular findings are considered. Following discussion of the biocompatibility of Glass-Ionomer cements, consideration is given to the likely underlying causes of this feature. Three factors are identified as contributing to the biocompatibility of these cements. They are: (i) minimal exotherm on setting; (ii) rapid neutralization following mixing; and (iii) slow release of ions which are generally biologically beneficial or, at least, benign. This last point is considered in some detail. Previous studies of leaching of ions from Glass-Ionomer cements have shown that only inorganic species are released. The biological effects of each of these inorganic ions are described and their influence on biocompatibility discussed.