What is the hardest substance in the body?

The hardest substance in the human body is tooth enamel. Enamel is the outermost layer of the tooth and is made up of mostly hydroxyapatite crystals, which are a combination of calcium and phosphate. It is even harder than bone and is designed to protect the inner and more sensitive layers of the tooth from wear and tear. Enamel does not contain any living cells, and once it is damaged or worn down, it cannot regenerate like other tissues in the body. Proper dental hygiene, including regular brushing and flossing, is crucial in maintaining the integrity of tooth enamel and preventing dental issues such as decay and erosion.