dentin

Dentin is the mineralized tissue that forms the bulk of a tooth, located beneath the enamel in the crown and beneath cementum in the roots. It surrounds the dental pulp and provides the tooth with its major structure, resilience, and shape.

Dentin is composed of about 70% inorganic hydroxyapatite, 18% organic matrix (primarily type I collagen), and 12% water. It contains dentinal tubules that run from the pulp toward the outer dentin, with odontoblasts lining the pulp and extending processes into the tubules. Tubule density and diameter vary by region and with age. The organic matrix also includes non-collagenous proteins, such as dentin sialophosphoprotein (DSPP), which is processed into dentin sialoprotein and dentin phosphoprotein and plays a role in mineralization.

Dentinogenesis is driven by odontoblasts at the pulp-dentin border. Predentin is laid down first and then mineralized to form dentin. Primary dentin forms during tooth development, secondary dentin forms gradually after eruption, and tertiary dentin forms in response to injury (reaction or reparative dentin). Root and crown dentin differ in structure and exposure but share the same basic tubule system.

Dentin is harder than bone but softer than enamel. Its tubules contain dentinal fluid and odontoblastic processes, enabling diffusion and contributing to tooth sensitivity. The hydrodynamic theory posits that fluid movement within tubules mediates dentin hypersensitivity in response to thermal, chemical, or physical stimuli.

Clinically, dentin permeability influences caries progression and restorative choices. Cavity preparation creates a smear layer that affects bonding; dentin bonding systems aim to seal tubules and protect the pulp. Dentin sensitivity is managed with desensitizers and appropriate sealing in restorative procedures.