Effect of aging and caries on dentin permeability.

Extracted human teeth were collected from young (20-28 yrs) versus old (45-69 yrs) patients. The teeth were divided into carious and noncarious groups. Slabs were created from the mid-coronal occlusal dentin. Carious lesions were excavated and the smear layers on both normal and excavated carious dentin were removed with 37% phosphoric acid (1 min). The permeability (hydraulic conductance) of old normal dentin was only 20% of that obtained in young normal dentin but all of the specimens were permeable. Young carious dentin was only 14% as permeable as young normal dentin and only 1 out of 7 specimens was not permeable. All 7 specimens of old carious dentin were impermeable. Scanning electron microscopy of old and carious dentin exhibited far more intratubular crystals than normal dentin, providing a structural basis for the functional observation.