Which protective material covers the dentin above the gum line and is the hardest substance in the body?

Enamel is the protective material that covers the dentin above the gum line and is known as the hardest substance in the human body. It plays a crucial role in dental health by providing a strong, protective layer that shields the underlying dentin and pulp from physical and chemical damage.

Enamel is composed primarily of hydroxyapatite, a crystalline structure that gives it its exceptional hardness. This hardness is essential for withstanding the forces exerted during chewing and biting, as well as providing a barrier against acid produced by bacteria that can lead to tooth decay.

The other materials listed play different roles in dental health. Dentin, while also an important part of the tooth structure, is softer than enamel and is located beneath the enamel and above the pulp. Cementum is a specialized calcified substance that covers the roots of teeth and helps anchor them to the jawbone. Plaque, on the other hand, is a soft, sticky film of bacteria that forms on teeth but does not provide any protective qualities for the tooth structure itself.