Final answer:
The exposed part of the tooth is covered by a tough, durable layer called enamel, which is the hardest substance in the body. This layer covers the tooth's crown, the part that is visible above the gum line.
Step-by-step explanation:
The student is asking about the tough, durable layer that forms the exposed part of the tooth. This layer is called enamel, which is the hardest substance in the body and covers the part of the tooth known as the crown. The crown is the portion of the tooth that projects above the gum line. Beneath the enamel is a layer of dentin, a bone-like tissue, and within the tooth is the pulp cavity with nerves and blood vessels. The enamel plays a critical role in protecting the tooth from mechanical and chemical erosion, although it is still susceptible to decay, commonly through the formation of cavities