Is high fluoride causes tooth decay?

actually as far as fluoride is good for protecting teeth from decay during child hood even giving super protection for root of teeth after teenage years ,but at the same time can cause osteoporosis in most of teeth especially after stoppage of development in which catabolism will be more than anabolism and we should put that in our mind that nothing is good as it is used more than its normal level for that reason fluoride should be used in 1 part to 1 part per million parts of water.