Remineralization of natural and artificial lesions in human dental enamel in vitro. Effect of calcium concentration of the calcifying fluid.

Abstract

Exposure of both small carious lesions and artificial caries-like lesions to a synthetic calcifying fluid <i>in vitro</i> produced a significant degree of ‘healing’ or remineralization of the lesion. Changing the calcium concentration of the calcifying fluid had a marked effect on the degree of remineralization produced. When a low calcium concentration of 1 m<i>M</i> was employed, remineralization occurred throughout the entire depth of a lesion. Under these conditions, there was a mean reduction of 69% in area of the body of the lesion and a mean increase of 40% in orientated mineral. The dark zone at the advancing front of the lesion showed a dramatic increase in area of 526% and was much closer to the enamel surface relative to the control. When higher calcium ion concentrations of 3 m<i>M</i> were used, remineralization occurred but was limited to the surface of the lesion. Under these conditions, the mean reduction in area of the body of the lesion was 20%, brought about by a mean increase in orientated mineral of 17%. Although changes were found in relation to the dark zone, these were much smaller than those found for the 1-m<i>M</i> fluid, the increase in area being 38%. With respect to exposure times, results obtained using ten consecutive 24-hour exposures to the synthetic calcifying fluid were similar to those obtained after ten consecutive 1-hour exposures. Remineralization, therefore, occurred within each 1-hour exposure increment. Scanning electron microscopy showed that crystal diameters for sound enamel were in the range 35–40 nm. In the body of the lesion crystal diameters were reduced and found to be in the range 10–30 nm. In lesions remineralized with the high calcium-calcifying fluid containing 3 m<i>M</i> calcium, crystal diameters were larger than those found in either control lesions or in sound enamel, being in the range 50–75 nm. When the low calcium-calcifying fluid was used, remineralized lesions showed crystal diameters in the range 50–150 nm with a small number of crystals having diameters of 200 nm. Calculation of the supersaturation of the calcifying fluids revealed that the low calcium-calcifying fluid having 1 m<i>M</i> calcium favors crystal growth as opposed to nucleation.