Improvement of the Caries Resistance of Human Dental Roots by a Two-step Conversion of the Root Mineral into Fluoridated Hydroxylapatite

Abstract

Roots of extracted human molars were treated for both 10 and 30 min with a saturated solution of dicalcium phosphate dihydrate (DCPD) of pH 2.4 and subsequently with a 5.3 mmol.L ^-1 solution of sodium fluoride of pH 7.0. The objective of these combined treatments was to convert the highly-soluble root mineral into the less-soluble fluoridated hydroxylapatite, with DCPD as an intermediate, to improve caries resistance. The mineral content of the surface layer was not affected in a significant way.

Roots treated in this way were subjected to 50 mmol.L^-1 acetate buffer solutions of pH 5.5 and with pI_OHA-values of 112, 116, and 122. The proportional reduction of the rate of demineralization (V_dem) of similarly treated roots subjected to buffer solutions of pI_OHA 112 and 116 appeared to be equal initially. Since fluoridated hydroxylapatite is insoluble under these conditions, these findings are in agreement with expectations. The reduction of V_dem amounted to about 45 and 70% for roots treated for 10 and 30 min, respectively.

When roots were treated for 10 and 30 min and then exposed to buffer solutions with a pI_OHA 122, reductions of V_dem of about 30 and 55%, respectively, were found.

Conversion of the root mineral into fluoridated hydroxylapatite can eliminate, in principle, the existing difference in caries susceptibility of the root and of the dental enamel.