This is disease caused by deficiency of Iodine.If the Fluorine amount in water falls bellow 1ppm,the teeth are pro ne to decay easily.Too much Fluorine in water:the teeth developes brown stain.Manage:Brush your teeth with a proved tooth paste atleast 2 times a day but mostly after food and after eating sweety meals;eat iodised salt;people living in areas with inadequate fluorine compounds in drinking water may use tooth pastes cotaining fluorides bestly before bed.People drinking water added fluorine(chlorine)should not use fluoride tooth pastes