Social & Preventive Medicine General f4b317cd Crippling fluorosis occurs at what level ? A 0.5-0.8 mg/litre B 1.5 mg/litre C 3-6 mg/litre D > 10 mg/litre High-Yield Explanation Ans. is 'd' i.e., 10 mg/liter Crippling fluorosis This occurs at fluoride level > 10 mg/litre (PPM). Patient is crippled and bed ridden.