Introduction

The fluoridation of municipal water in cities of Canada and the United States for the purpose of reducing dental decay is perhaps the most important and successful public health initiative ever undertaken in these countries. Since its inception more than 50 years ago, water fluoridated at 1 ppm has dramatically reduced the incidence of caries, and this positive effect has reached across all socioeconomic groups. However, since fluoride is a mineral-seeking ion, it is incorporated into bone as well as teeth. The response of bone is known to depend on the dose, and studies in both animal models and in humans have assessed the effect of moderate to high doses of fluoride. As a consequence, it is known that moderate doses of fluoride increase bone mass, making fluoride a potential therapy for osteoporosis (see below). However, chronic exposure to high doses of fluoride (>8 mg/day), while rare in North America, can cause skeletal fluorosis, characterized initially by hypermineralization of bone and later by calcification of ligaments, bone deformation, and other crippling symptoms (Kaminsky et al., 1990). Ingestion of low doses of fluoride through water involves somewhat different mechanisms. Typically, individuals receive less than 5 mg/day of fluoride (less than a tenth of the clinical dose), but it accumulates passively in bone mineral over a timespan of decades.