Etiology
Dentin exposure occurs through: (1) enamel loss — erosion (dietary acid, GERD), abrasion (toothbrush abrasion), attrition (bruxism), abfraction (non-carious cervical lesions from tooth flexure); (2) cementum loss — gingival recession exposing root surface, periodontal scaling and root planing removing cementum.
Tubule patency — why not all exposed dentin is sensitive: Normally, dentinal tubules at the tooth surface are occluded by the smear layer, mineral deposits, or sclerosis (tertiary dentine). Sensitivity occurs when tubules become patent, allowing fluid movement.
Risk factors for developing DH: aggressive toothbrushing (hard bristles, high force), high frequency of acidic food/drink consumption, untreated GERD, periodontal disease and treatment (scaling opens tubules), bleaching treatment (temporarily sensitizing).
The paradox of sensitivity: not all exposed dentin is sensitive, and sensitivity can fluctuate over time. This reflects the dynamic status of tubule patency.