F.C.M. Driessens

Effect of laser irradiation on the permeability of bovine dental enamel.

The transport of ionic and non-ionic compounds through bovine dental enamel was measured before and after irradiation with a carbon dioxide laser (energy density 10J/cm2). The irradiation increased the permeability of enamel rather than decreased it as postulated by other workers to explain the increased resistance to surface demineralization produced by such irradiation.

The effect of some phosphates and a phosphonate on the electrochemical properties of bovine enamel

Abstract The effect of orthophosphate, pyrophosphate, trimetaphosphate, hexametaphosphate, phytate and 1,1-hydroxyethyldiphosphonate on the ion-selective properties of bovine tooth enamel was investigated using electrochemical methods. All phosphates increased the ion-selectivity of enamel, an effect that increased with increasing number of phosphate groups. The effects of phytate and the diphosphonate were more pronounced than those of the corresponding phosphates.

A quantitative radiochemical study of ionic and molecular transport in bovine dental enamel.

A radiochemical method was developed to determine quantitatively and simultaneously the transport of up to four different compounds through dental enamel. The compounds chosen were [3H]-sorbitol, [14C]-glycerol, 36Cl− and 86Rb+. Effective diffusion coefficients of these compounds determined at 4 °C were considerably different for different specimens of enamel. Thus values for [3H]-sorbitol varied from 0.04 × 10−8 to 2.5 × 10−8cm2s−1. Most enamel membranes showed an ion selective behaviour by which the cations were more mobile than the anions. A molecular sieve effect was observed for glycerol and sorbitol.

Diffusion in mammalian tooth enamel in relation to the caries process

For the rate of demineralization of enamel during caries, three physicochemical processes are of importance: the diffusion into and out of the enamel, the dissolution of mineral and the complexation of ions. The interpretation of diffusion experiments in conjunction with artificial caries experiments and computer simulations is described. In the caries process, relevant diffusion coefficients of small ions and molecules are of the order of magnitude 10(-9)--10(-7) cm2 s-1.

A phenomenological interpretation of the frequency-dependent impedance behaviour of bovine dental enamel

The permeability of dental enamel can be estimated by means of diffusion measurements with radio-isotopes. Because of the low intrinsic permeability of enamel membranes, determination via this route may take two weeks. A much faster electrochemical method is presented, in which the real and imaginary part of the membrane impedance are measured at discrete intervals in the frequency-range 1 Hz-1 MHz. Using the principles of network-analysis, a phenomenological interpretation of these electrochemical data in terms of a 6-parameter model is given. The model contains R0, the intrinsic membrane resistance, R infinity, the residual membrane resistance and the four parameters, necessary to describe the postulated enamel diffusion impedance, which bears strong resemblance to the Warburg impedance. Starting from this model, optimal estimates (with standard-errors) of a membranes R0 and vmax (the log of the frequency where the imaginary part of the membrane impedance is maximal) were derived. These parameters were predictors of the permeability of enamel.

Effect of mono- and divalent ions on diffusion and binding in bovine tooth enamel

Abstract A radiochemical method was used to determine quantitatively the effect of RbCl, CaCl 2 and MgCl 2 on the transport of [ 3 H]-sorbitol, [ 14 C]-glycerol, 45 Ca 2+ , 36 Cl − and 86 Rb + through dental enamel. The findings indicate that the transport of 45 Ca 2+ is influenced strongly by surface exchange reactions. The influence of Ca 2+ and Mg 2+ on the transport of 86 Rb + and 36 Cl − indicates that, at a concentration of ~10mmol/l, these ions alter the fixed charge of enamel from negative to less negative, or positive values. Previously adsorbed 45 Ca 2+ ions are desorbed at higher Ca 2+ and Mg 2+ concentrations. Rb + ions at 10 mmol/l have no such effect. The results indicate that Ca 2+ and Mg 2+ can be adsorbed reversibly on the crystal surfaces or in their Stern layers in the pores of dental enamel.

Diffusion through bovine tooth enamel as related to the water structure in its pores.

Abstract Diffusion coefficients of 86 Rb + , 36 Cl − , [ 3 H]-sorbitol and [ 14 C]-glycerol through enamel were determined both in the absence and the presence of urea or t -butanol which are known for their structure-breaking and structure-promoting properties respectively in aqueous solutions. Their effect on the diffusion coefficients could be explained solely on the basis of the respective shifts in the relative viscosities of the aqueous solutions, indicating that the water of the transport phase is probably free water, in accord with explanation for the extra increase of diffusion coefficients with temperature (Burke and Moreno, Archs oral Biol. 17 , 433–437 (1975)) by the hypothesis that the amount of free water increases with temperature at the expense of bound water.

The effect of fluoride and monofluorophosphate treatment on the electrochemical properties of bovine tooth enamel.

Abstract The effect of fluoride and monofluorophosphate on the ion selective properties of bovine tooth enamel was investigated using electrochemical methods. The effect of monofluorophosphate was fundamentally different from that of fluoride. The anti-cariogenic properties of fluoride or monofluorophosphate cannot be deduced from their effect on the ion selectivity of enamel.

Effect of phytate and hexadecylamine on the permeability of bovine dental enamel

The effect of hexadecylamine on the permeability of bovine dental enamel was investigated using a radiochemical diffusion technique. Treatment with an aqueous solution of hexadecylamine reduced the permeability of the enamel by about 20 per cent. Pre-treatment of the enamel with an aqueous solution of phytate followed by hexadecylamine yielded a reduction in permeability of approximately 70 per cent. The observed effects were similar for ionic (86Rb+ and 36Cl-) and non-ionic [( 3H]-sorbitol and [14C]-glycerol) compounds. The strong permeability-reducing effect of the combined phytate-amine treatment may also be anticariogenic.