Measurement of Functional Space for Fluid Movement in Dentinal Tubules

Objective: Quick movement of the fluid in dentinal tubules can produce sharp pain. But functional space for the fluid movement has not been clarified. The aim of the present study was to measure the functional space in human and rat dentinal tubules using fluorescent microspheres. Methods: Human: Fourteen premolars were extracted from 14 patients (14-29yrs) for orthodontic reasons. Cavities were prepared on the tooth crown surfaces to expose dentin immediately after extraction. Fluorescent microspheres with different diameters (0.1-4.0µm) and excitation wave-lengths were mixed and applied to the cavities for 30min. Rat: Cavities were prepared on the crown of rat molars to expose dentin, and microspheres of 0.02-4.0µm in diameter were applied to the cavities for 10, 15, 20 and 30 min. Then, the rats were perfused, and the jaws were removed. All the samples were cut into cryostat sections. Localization of the applied microspheres was confirmed with fluorescent/confocal microscopes and analyzed using image-analysis software. Results: Microspheres of 0.02-0.04µm in diameter were accumulated in the outer middle third of rat dentin, while those of 0.1-0.5µm in diameter were found just beneath the bottom of the cavities and also in the outer third of dentin both in rat and human teeth. A small number of bigger microspheres (1.0µm in diameter) were accumulated only in the outer third of human dentin. The biggest ones (2.0-4.0µm in diameter) could not be detected in human or rat dentin. Conclusions: Dentinal tubules in the inner third of the human coronal dentin may have a functional space of 0.5-1.0µm, through which dentinal fluid can move. Microspheres larger than 1.0µm may not be able to pass this space. However, in the rat, this space may be less than 0.5µm. Intropulpal pressure could work as an obstacle for the diffusion of microspheres.