The exact mechanisms of such actions are obscure. Fluoride consumption by human beings increases the general cancer death rate. In 1975 Dr. John Yiamouyiannis published a preliminary survey which showed that people in fluoridated areas have a higher cancer death rate than those in non-fluoridated areas. The National Cancer Institute attempted to refute the studies. Both reports confirmed the existence of a link between fluoridation and cancer.
Fluorides have little or no effect on decay prevention in humans.
In 1990 Dr. John Colquhoun was forced into early retirement in New Zealand after he conducted a study on 60,000 school children and found no difference in tooth decay between fluoridated and unfluoridated areas. He additionally found that a substantial number of children in fluoridated areas suffered from dental fluorosis. He made the study public. There is no scientific data that shows that fluoride mouth rinses and tablets are safe for human use. In 1989 a study by Hildebolt, et al.