Measurement of the velocity of fluid flow in dentinal tubules

Method: Coronal slices, 1.6, 1.8 and 2,0 mm in thickness (n=5) were cut from freshly extracted human molars and cleaned with 0.5 M EDTA solution (pH 7.4) for 2 min. Each slice was clamped between 2 acrylic chambers and sealed with O-ring. Prior to testing all specimens were stored in deionized water. The chamber attached to the occlusal side was closed with a glass coverslip and filled with a solution of 0.02% luminol and 1% sodium hydroxide of chemiluminous source. Then, an aqueous solution of 1% hydrogen peroxide and 1% potassium ferricyanide as trigger for the photoreaction with luminol was injected at constant pressure of 2.5 kPa into the chamber attached to the pulpal side, to flow immediately into the patent dentinal tubules. A traveling time of the trigger solution through the specimen was measured as delay from starting of trigger injection until starting of chemiluminous emission, recorded with a photodetector. Each of the five specimens in the three groups was measured in duplicate. The relationship between crossing time of the liquid and dentin specimen thickness was determined using linear regression analysis. 

Result: The delay times were 31±29 s for 1.6 mm, 46±24 s for 1.8 mm and 78±32 s for 2 mm dentin thickness. The average velocity of fluid flow at the occlusal openings of the dentinal tubules was 52, 39 and 25 μms^-1, and exponentially correlated with the thickness of the dentin specimens.

Conclusion: As suggested by Hagen-Poiseuille’s law, the velocity of the liquid flowing through capillaries, i.e. the dentinal tubules of the measured dentin area, was inversely proportional to the thickness of the dentin specimens.