The effect of molecular size on reflection coefficients in human dentine

Abstract

Previous investigations of dentine sensitivity using osmotic stimuli have noted that very high molar concentrations (2–6 M) were required to elicit pain. When hydrostatic pressures were used, far smaller pressures were required, indicating that only a fraction of the theoretical osmotic pressure of solutions is effective for moving fluid across dentine. The ratio of the effective to theoretical osmotic pressures, termed the reflection coefficient (σ). is a measure of the degree of semi-permeability of dentine and can vary from 0 (complete solute permeability) to 1.0 (complete solute impermeability). Dentine discs were placed in a split chamber device connected to a pressure transducer. The effective osmotic pressures of solutions containing solutes of various molecular sizes were determined on sanded, acid-etched and oxalate-treated dentine. Reflection coefficients in sanded dentine increased with increasing molecular size from 3 × 10 −4 for sucrose to 0.38 for albumin. Acid-etching produced a statistically significant 5–9 fold decrease in reflection coefficients (increased solute permeability) but oxalate treatment restored them to sanded dentine levels.