Lack of Fluid Movement between Dentin Tubule and Pulp Tissue: An In Vitro Study

Objective: In vitro studies supporting the hydrodynamic theory have reported that cavity provocation results in fluid flow from dentin tubules via pulp tissue to a capillary connected apically. Our preliminary findings did not corroborate this. Therefore, the aim was to perform experiments closely following the descriptions in the mentioned articles to find out if there is a direct fluid flow communication from a prepared cavity to pulp tissue detectable with this method. Material and Methods: Class V cavities were prepared and provocations (air blast, scraping, temperature change) initiated within 1 hour of extraction in 17 teeth and after 1 week in 3 teeth. Fluid flow was monitored during and after stimulation using a microscope. Results: No fluid flow was registered during stimulations performed within an hour of extraction. One week after extraction fluid movement was registered during the air blast. Conclusions: The finding of no direct continuum in freshly extracted teeth from cavity surface via dentin fluid to pulp tissue to an apically placed capillary does not per se disprove the hydrodynamic theory. As the in vitro experiment by Brännström et al. has been a major foundation for the hydrodynamic theory, it may be time to investigate the true mechanism(s) of dentin sensitivity.