Stimulus Induced Fluid Movement Measured Across Human Dentin In vitro

The hydraulic conductance of dentin is widely used for assessing the efficacy of desensitising agents in vitro. The method offers a quantitative description of the ease with which fluid can move through dentinal tubules. Objective: The purpose of this study was to develop a fast screening, sensitive and highly responsive (up to 50 Hz) model, that could accurately measure and compare both the magnitude and direction of fluid shifts across human dentin in response to clinically relevant stimuli, before and after preventative treatment. Methods: Etched dentin disks were prepared from human molars and placed pulpal side down in a split-chamber device. Hydrostatic pressure (Earles' solution/1. p.s.i) was applied to the pulpal side of the dentin disk. The rate of fluid flowing through the dentin disk was measured using a solid-state CMOS flow sensor. Fluid displacement and flow rates as low 2.5nl/s could be measured accurately and with a fast response time. Flow rates and responses to hydrodynamic stimuli were measured before and after the application of a preventative treatment. Result: Distinct responses in the magnitude and direction of fluid shifts were observed as a function of applied stimuli. Figure 1 provides an example of the results obtained using this model. Following the application of a hot water stimulus a rapid inward flow followed by a prolonged outward flow was observed. The magnitude of this flow revealed a direct relationship with temperature. On application of cold water stimuli no inward flow was observed. Following the application of a preventative treatment the reactive outward fluid shifts were attenuated. Conclusion: This model can measure, with a high degree of sensitivity, the magnitude and direction of fluid shifts across dentin in response to hydrodynamic stimuli.