Determination of the functional space for fluid movement in the rat dentinal tubules using fluorescent microsphere.

Objectives: The size of the functional space available for hydrodynamic fluid movement between cellular components and the walls of dentinal tubules has not yet been investigated. We attempted to measure the space using small diameter fluorescent microspheres.

Methods: The coronal enamel of 144 rat molars was removed to expose the dentine, which was acid-etched. Fluorescent microspheres of different diameters (0.02-4.0μm) were applied to the exposed dentine for 60min before the rat jaws were cut into cryostat sections. The distribution and fluorescent intensities of the fluorescent microspheres were examined with confocal laser scanning microscope and analyzed using image analysis software.

Results: Microspheres with a diameter of 2.0-4.0μm were detected only on the surface of the cavities. A small number of microspheres with a diameter of 1.0μm accumulated primarily in the outer third of the dentine. Microspheres with a diameter of 0.2-0.5μm were found in the outer and middle thirds of the dentine. Microspheres with a diameter of 0.02-0.1μm accumulated in the middle and occasionally inner thirds of the dentine. Some of the microspheres measuring 0.02-0.04μm in diameter reached the dental pulp.

Conclusions: The dentinal tubules in the inner third of the rat coronal dentine may have a space less than 0.1μm through which dentinal fluid can move, despite outward tapering of the dentinal tubules. Retrograde tapering may increase the pressure in the inner third of the dentine layer, and this elevated pressure may contribute to mechanical deformation of the content in the dentinal tubules.