Dentin

Dentin is a hard, light yellow, porous layer of tissue directly beneath the enamel and cementum. Dentin constitutes the largest portion of the tooth and consists of approximately 70% inorganic matter and 30% organic matter and water. The inorganic component consists primarily of calcium and phosphate ions, which form hydroxyapatite crystals. While these crystals are similar to those in enamel, they are approximately 30 times smaller, making dentin softer and more flexible than enamel.⁹

Unlike enamel, dentin is a living tissue with the ability for constant growth and repair. This is facilitated by the presence of odontoblasts, which are specialized cells located on the outer layer of the pulp. These cells are responsible for the continuous formation of new dentin throughout life. Tiny dentinal tubules extend from the cementoenamel junction (the interface between enamel and the cementum covering the root) to the pulp, aiding in the regeneration process. Odontoblast extend into these tubules, allowing them to produce new dentin and mineralize it over time. In addition to this regenerative function, the dentinal tubules also carry nerves, which enable dentin to transmit pain, a feature not found in enamel.⁸