THE IN SITU POTENTIAL OF SYNTHETIC NANO-HYDROXYAPATITE FOR TOOTH ENAMEL REPAIR

Abstract

This study was designed to evaluate whether nano-hydroxyapatite toothpastes with or
without fluoride would be more advantageous than a fluoride toothpaste in the repair of eroded
enamel in situ. Twenty-one subjects participated in this single-blind, randomized, cross-over
design study with three 7-day treatment phases. In each phase, the subjects wearing a palatal
appliance containing five sterilized enamel specimens used either one of the two test regimens (1%
nano-hydroxyapatite toothpaste and 2.25% nano-hydroxyapatite/1450 parts per million (ppm)
fluoride toothpaste) or one control (1400 ppm fluoride toothpaste). Enamel specimens were
extraorally demineralized (4 × 5 min/day) and were intraorally treated with the toothpastes (2 ×
2 min/day). The nano-hydroxyapatite toothpaste groups exhibited significantly higher surface
microhardness than did the standard fluoride toothpaste group (p < 0.05). Enamel surface
hardness was increased only by nano-hydroxyapatite toothpastes after in situ treatment compared
with the baseline (p < 0.05). Morphological analysis demonstrated an apatite-type crystal
deposition on the eroded enamel surface produced by nano-hydroxyapatite toothpastes, while
fluoride toothpaste failed to show any significant surface deposition. Chemical analysis showed a
higher content of calcium and phosphorus in the enamel surface treated with nano-hydroxyapatite
toothpastes compared with that in the control one (p < 0.05). It is concluded that home use of
nano-hydroxyapatite containing toothpastes may have a protective effect against erosion at the
enamel surface.