What is dentin?

• A. A soft tissue inside the tooth
• B. A crystalline calcium phosphate that covers the dentin
• C. The outer enamel layer
• D. Mineralized matrix that comprises the bulk of the tooth

Answer: (D)

Dentin is the mineralized connective tissue that makes up the bulk of the tooth. It lies just beneath the enamel on the crown and beneath the cementum on the root, forming a tough but slightly more flexible scaffold that supports the outer protective layers. It’s produced by odontoblasts that line the dental pulp, and it contains a network of dentinal tubules filled with fluid and extensions of odontoblasts. The matrix is largely inorganic—hydroxyapatite crystals—interwoven with organic collagen, giving dentin its characteristic resilience and ability to transmit sensory stimuli when exposed.

This is why dentin is described as the mineralized matrix that comprises most of the tooth’s mass. The soft tissue inside the tooth is the pulp, enamel is the outer hard enamel layer, and the mineral crystals that cover dentin refer to enamel (which sits on top in the crown) rather than dentin itself.