Hydroxyapatite nanoparticles/fluoride pastes: effect on the dental demineralization in vitro

Objectives: Currently, the dental clinic does not have remineralizing and desensitizing materials based on nanotechnology. These nanoparticles have a high surface area facilitating the availability of the calcium and phosphate ions to be reorganized in form of hydroxyapatite. This in vitro study evaluated the preventive potential of experimental pastes with 10% and 20% hydroxyapatite nanoparticles (Nanop=Ca/P) with or without low fluoride concentration on dental demineralization.

Methods: Bovine enamel and root dentin specimens were divided into 9 groups according to the surface hardness: control, 20 Nanop paste (20% Ca/P), 20 Nanop paste plus (20% Ca/P + 0.2% NaF),10 Nanop paste (10% Ca/P), 10 Nanop paste plus (10% Ca/P+ 0.2% NaF), placebo paste, Fluoride paste (0.2% NaF), MI paste (CPP-ACP, RECALDENT, GC America, USA) and MI paste plus (CPP-ACP + 0.2% NaF). Fifteen enamel and dentin specimens in each group were subjected to pH-cycles (demineralization–6h/ remineralization-18h a day) for 7 days. The pastes were applied twice a day, before and after the demineralization process, using microbrush for 1 minute. The excess of paste was removed and the specimens were washed in deionized water for 5 s before being immersed in the de- or remineralizing solution. The dental subsurface demineralization was analyzed by cross-sectional hardness (KgF/mm², depth 10-220µm). Data were tested using two-way ANOVA and Bonferroni’s test (p<0.05).

Results: The only treatment able to reduce the loss of enamel and dentin subsurface hardness was Fluoride paste, which significantly differed from the control at 30 and 50 µm depth: enamel (F paste: 186±51 and 253±49, Control: 16±24 and 91±89 KgF/mm², respectively) and dentin (F paste: 6.7±5.8 and 9.9±4.8, Control: 1.2±3.3 and 4.9±4.6 KgF/mm², respectively).

Conclusions: The experimental Nanop pastes, regardless of the presence of fluoride, were unable to reduce dental demineralization in vitro.