Effect of molecular size on permeability coefficients in human dentine

The effect of increasing molecular radius on the rate of permeation of human dentine discs was determined. The substances tested were water, urea, fluoride, lidocaine, glucose, sucrose, inulin, dextran, polyvinylpyrrolindone and albumin. A 19-fold increase in molecular radius from 1.9 Å (³H₂O) to 37 Å (¹³¹I-albumin) resulted in a 100-fold decrease in permeability coefficients calculated by the Fick equation. Acid-etching the dentine produced a 4-fold increase in ³H₂O permeability and a 9-fold increase in ¹³¹I-albumin permeability. Both fluoride and chlorhexidine permeabilities were much lower than expected for their molecular weight or size, suggesting that they are bound to dentine. It is concluded that dentine permeability is determined, in part, by the nature of the dentine surface.