Diffusion of sugars and carboxylic acids through human dental plaque in vitro

Abstract

Diffusion through plaque was measured with an apparatus consisting of 3 identical diffusion cells contained in an aluminium alloy block thermostatically controlled at 35 °C. In two of the cells, measurements were made of diffusion through a composite membrane consisting of 18 h dental plaque contained between bacteriological grade filters and support screens. In the third cell, diffusion occurred through a reference membrane from which the bulk of the plaque was absent. Subtraction of the diffusion resistance of this reference membrane allowed calculation of apparent tracer diffusion coefficients in the bulk of the plaque alone. Diffusion of 14C-labelled sugars and carboxylic acids was compared with that of tritiated water using dual-channel liquid scintillation counting. The diffusion coefficient of tritiated water in the plaque samples varied from 0.81 to 1.02 × 10 −9 m 2s −1 depending on the wet wt used, with coefficients of variation of ~ 15 per cent. This is between 1 4 and 1 3 of the value in aqueous solution. Diffusion coefficients relative to that of tritiated water in plaque ranged from 0.154 ± 0.014 for sucrose to 0.363 ± 0.029 for acetate. Permselectivity was low, and diffusion coefficients of I he test molecules were all between 1 4 and 1 5 of their values in free aqueous solution.