Which is the hardest substance in the human body?

Tooth enamel, the thin outer layer of your teeth, is the hardest substance in the human body. It is made of about 96% mineral, mostly a crystalline form of calcium phosphate called hydroxyapatite. On the Mohs scale of mineral hardness it rates around 5, similar to the mineral apatite and harder than bone. Unlike bone, enamel contains no living cells, so the body cannot repair it once it is damaged by decay or wear. Fluoride helps protect it by turning some of the hydroxyapatite into a tougher, more acid-resistant mineral called fluorapatite.