Dentine Permeability Under Etiologically Relevant Conditions

Objectives: The hydraulic conductance of dentine is widely used for quantitative assessment of putative occlusion-based desensitisers. The ability to accurately control changes in the dentine temperature in vitro offers more realistic conditions to those experienced in vivo. The purpose of this study was therefore to investigate the role of temperature on fluid flow through dentine with an aim of developing a more realistic model to simulate the variable temperatures experienced within the oral environment. Methods: Etched dentine disks were prepared from bovine incisors and placed pulpal side down in a split-chamber device. Hydrostatic pressure (Earle's solution at 1. p.s.i) was applied to the pulpal side of the dentine disk. The baseline fluid flow rate through the disk was measured three times for 5min. The first measurement was made at ambient temperature (20ºC), the temperature of the model was then raised and held at 35ºC for the second measurement, before reducing the temperature to 20ºC for the third measurement. Following the baseline measurements, a 6% oxalic acid treatment was applied to the disks, and the flow rate re-measured at 20, 35, and 20ºC. Results: Baseline fluid flow was markedly increased on raising the temperature from 20ºC to 35ºC. On cooling, fluid flow returned to its original rate. Application of oxalic acid effected a decrease in the fluid flow rate of >95% irrespective of the temperature at which flow was measured. Independent image analysis of dentine tubule radius as a function of temperature revealed no significant change. Conclusions: This model can measure the hydraulic conductance of dentine as a function of temperature. Under the specific conditions employed, changes in fluid flow rate were attributed to viscosity changes rather than temperature-mediated changes in dentine ultrastructure.