Effects of fluoride on two chemical models of enamel demineralisation

Abstract

Objectives: To study the demineralisation of enamel induced by two commonly used chemical models and the effect of addition of fluoride on these two models. Methods: Twenty-four enamel blocks were prepared from extracted teeth with patient’s consent. They were equally allocated to four groups. Group 1 was lactate buffer solution at pH 5.0 containing lactate 3 mM, calcium chloride, 3 mM potassium dihydrogen phosphate, 6 µM tetraethyl methyl diphosphonate and 0.02% sodium azide. Group 2 was the lactate buffer solution at pH 5.0 with sodium fluoride at 0.02 ppm; Group 3 was acetate buffer solution at pH 5.0 containing 50 mM acetate, 2.2 mM calcium chloride, 2.2 mM potassium dihydrogen phosphate and 0.02% sodium azide. Group 4 was the acetate buffer solution with sodium fluoride at 0.02 ppm. The blocks were immersed into the respective solutions at 25°C for 2 weeks. Surface integrity and lesion depth of the blocks was studied by micro-computed tomography. Elemental analysis of the enamel surface was evaluated using energy-dispersive X-ray spectroscopy. Results: Three of the 6 samples in group 3 showed damage of the enamel surface. The mean lesion depth(SD) of Groups 1 to 4 were 68.6(11.0)mm, 67.4(17.5)mm, 93.5(22.4) mm and 76.6(27.8)mm, respectively. The mean lesion depth of Group 3 and 4 was significantly larger than groups 1 and 2 (Group 3>4>1,2; p<0.05). The fluoride weight percentage(SD) of groups 1 to 4 were 0.96(0.11)%, 1.03(0.18)%, 1.04(0.13)% and 1.08(0.09)%, respectively (p=0.051). Conclusions: Chemical model using acetate buffer solution created significantly deeper zone of demineralisation of the blocks. However, it could damage the enamel surface. The damage can be avoided by adding sodium fluoride. Moreover, the addition of fluoride to the two models would not affect the content of fluoride on the surface of the carious lesion.