DYNAMICS OF THE PULPO-DENTIN COMPLEX

Dentin has a relatively high water content due to its tubular structur e. Once dentin is exposed, this intratubular water is free to move in response to thermal, osmotic, evaporative, or tactile stimuli. Fluid s hifts across dentin are thought to cause sufficient shear forces on od ontoblasts, nerve endings, nearby fibroblasts, and blood vessels to ca use significant mechanical irritation, disruption, or damage, dependin g on the magnitude of the fluid shift. Even in the absence of fluid sh ifts, the water-filled tubules provide diffusion channels for noxious (i.e., bacterial products) substances which diffuse inward toward the pulp, where they can activate the immune system, provide chemotactic s timuli, cytokine production, and produce pain and pulpal inflammation. Viewed from this perspective, dentin is a poor barrier to external ir ritants. However, pulpal tissues react to these challenges by increasi ng the activity of nerves, blood vessels, the immune system, and inter stitial fluid turnover, to make the exposed dentin less permeable eith er physiologically, via increased outward fluid flow, or microscopical ly, by lining tubules with proteins, mineral deposits, or tertiary den tin, thereby enhancing the barrier properties of dentin, and providing additional protection to pulpal tissues. These reactions involve dent in and pulp, both in the initiation of the processes and in their reso lution. These responses of the dental pulp to irritation of dentin dem onstrate the dynamic nature of the pulpo-dentin complex.