What is the hardest tissue in the body that covers the crown of a tooth?

Enamel is the hardest tissue in the body and serves as a protective layer covering the crown of a tooth. Composed primarily of hydroxyapatite, a crystalline calcium phosphate, enamel can withstand the forces of chewing and protects the underlying dentin and pulp from bacteria and physical damage. Its high mineral content gives it strength and durability, making it essential for maintaining the integrity of teeth throughout an individual's life.

Other options, such as bone, dentin, and gingiva, do not match the hardness or specific location described in the question. Bone is indeed a hard tissue, but it is not found in the structure of a tooth. Dentin is softer than enamel and forms the bulk of the tooth structure beneath the enamel. Gingiva refers to the gums surrounding the teeth, which provide support but do not cover the crown. Therefore, enamel is the correct answer, as it is specifically designed for the purpose of protecting teeth while being the hardest tissue in the human body.