According to WebMD, the hardest tissue in the human body is tooth enamel. Tooth enamel is the thin, hard, white covering that protects the dentin of the teeth.
WebMD says that tooth enamel is vital for protecting the teeth against damage from daily use, including biting, chewing and grinding. Despite its hardness, enamel often sustains some damage over a typical lifetime. Acids in soda, coffee and tea break down the enamel and cause erosion. Additionally, enamel loss can occur as a result of biting hard objects, causing cracks or chips. Because enamel is not alive, it does not regenerate itself after damage occurs and requires professional attention from a cosmetic dentist.