EFFECT OF MOLECULAR-SIZE ON REFLECTION COEFFICIENTS IN HUMAN-DENTIN

Previous investigations of dentin 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 dentin. The ratio of the effective to theoretical osmotic pressures, termed the reflection coefficient (.sigma.) is a measure of the degree of semi-permeability of dentin and can vary from 0 (complete solute permeability) to 1.0 (complete solute impermeability). Dentin 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 dentin. Reflection coefficients in sanded dentin increased with increasing molecular size from 3 .times. 10-4 for sucrose to 0.38 for albumin. Acid-etching produced a statistically significant 5- to 9-fold decrease in reflection coefficients (increased solute permeability) but oxalate treatment restored them to sanded dentin levels.