Fluoride has the potential for very negative biochemical effects . As noted by Barbier et al. (2010):
“Until the 1990s, the toxicity of fluoride was largely ignored due to its “good reputation” for preventing caries via topical application and in dental toothpastes. However, in the last decade, interest in its undesirable effects has resurfaced due to the awareness that this element interacts with cellular systems even at low doses. In recent years, several investigations demonstrated that fluoride can induce oxidative stress and modulate intracellular redox homeostasis, lipid peroxidation and protein carbonyl content, as well as alter gene expression and cause apoptosis. Genes modulated by fluoride include those related to the stress response, metabolic enzymes, the cell cycle, cell-cell communications and signal transduction” .
The NRC’s 2006 review offers further reading on the subject , whilst Mullenix (2009) provides a detailed toxicological overview .
 Fluoride and Biochemistry, FAN
 Molecular mechanisms of fluoride toxicity, Chem Biol Interact
 A Scientific Review of EPA’s Standards, Pharmacokinetics of Fluoride
 The Toxicity of Water Fluoridation, IAOMT