LOW VERSUS HIGH-PRESSURE FOR IN-VITRO DETERMINATION OF HYDRAULIC CONDUCTANCE OF HUMAN DENTIN

The purpose of this study was to evaluate the effect of applied pressu re and measurement time on the in vitro measurement of hydraulic condu ctance of human dentine. Dentine slices were prepared from 50 third mo lars. Water was forced through the slices under a constant hydrostatic pressure. Five pressures were tested: 1.3 kPa (n = 10), 13.3 kPa (n = 10), 26.6 kPa (n = 10), 40 kPa (n = 10) and 53.3 kPa (n = 10). The vo lume that went through the slices was recorded every 10 min for 3 h. T he volume, the fluid flow rate and the hydraulic conductance under the five pressures were compared. The volume increased with time and pres sure. The fluid flow and hydraulic conductance decreased with time und er 13.3, 26.6 and 40 kPa, bur remained constant under 1.3 and 53.3 kPa . Use of a low pressure (1.3 kPa) may permit water to pass through den tinal tubules without disturbing intratubular contents. Medium pressur es (13.3, 26.6, 40 kPa) seemed to disturb tubule contents progressivel y, resulting in decreased fluid flow and therefore a decreased hydraul ic conductance with time. Under these pressures, the calculated values of hydraulic conductance may be unreliable because they are time-depe ndent. High pressure (53.3 kPa) seemed to pack the tubule contents aga inst intratubular resistances immediately, resulting in low fluid flow s and low hydraulic conductances. (C) 1997 Elsevier Science Ltd.