Characterization of chemical reactions of silver diammine fluoride and hydroxyapatite under remineralization conditions

M. Kaur, S. Shahid, N. Karpukhina, P. Anderson, F. S. L. Wong
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Abstract

Silver Diammine Fluoride (SDF) is a clinically used topical agent to arrest dental caries. However, the kinetics of its chemical interactions with hydroxyapatite (HA), the principal inorganic component of dental enamel, are not known. The aim was to characterize the step-wise chemical interactions between SDF and HA powder during the clinically important process of remineralization.Two grams of HA powder were immersed in 10 ml acetic acid pH = 4.0 for 2 h to mimic carious demineralization. The powder was then washed and dried for 24 h and mixed with 1.5 ml SDF (Riva Star) for 1 min. The treated powder was then air-dried for 3 min, and 0.2 g was removed and stored in individual tubes each containing 10 ml remineralizing solution. Powder was taken from each tube at various times of exposure to remineralization solution (0 min, 10 min, 2 h, 4 h, 8 h, 24 h, and 10 days), and characterized using Magic Angle Spinning-Nuclear Magnetic Resonance (MAS-NMR) spectroscopy.19F MAS-NMR spectra showed that calcium fluoride (CaF2) started to form almost immediately after HA was in contact with SDF. After 24 h, the peak shifted to −104.5 ppm suggesting that fluoride substituted hydroxyapatite (FSHA) was formed with time at the expense of CaF2. The 31P MAS-NMR spectra showed a single peak at 2.7 ppm at all time points showing that the only phosphate species present was crystalline apatite. The 35Cl MAS-NMR spectra showed formation of silver chloride (AgCl) at 24 h. It was observed that after the scan, the whitish HA powder changed to black color. In conclusion, this time sequence study showed that under remineralization conditions, SDF initially reacted with HA to form CaF2 which is then transformed to FSHA over time. In the presence of chloride, AgCl is formed which is subsequently photo-reduced to black metallic silver.
再矿化条件下二氨化银和羟基磷灰石化学反应的特征
二氨基氟化银(SDF)是一种临床上用于抑制龋齿的局部制剂。然而,它与牙釉质的主要无机成分羟基磷灰石(HA)之间的化学作用动力学尚不清楚。将两克 HA 粉浸泡在 10 毫升 pH = 4.0 的醋酸中 2 小时,以模拟龋齿脱矿。然后将粉末清洗并干燥 24 小时,再与 1.5 毫升 SDF(Riva Star)混合 1 分钟。然后将处理过的粉末风干 3 分钟,取出 0.2 克粉末并保存在每个装有 10 毫升再矿化溶液的试管中。在暴露于再矿化溶液的不同时间(0 分钟、10 分钟、2 小时、4 小时、8 小时、24 小时和 10 天)从每个试管中取出粉末,并使用魔角旋光-核磁共振(MAS-NMR)光谱进行表征。19F MAS-NMR 光谱显示,氟化钙(CaF2)几乎在 HA 与 SDF 接触后立即开始形成。24 小时后,峰值转移到 -104.5 ppm,这表明随着时间的推移,氟取代羟基磷灰石(FSHA)的形成牺牲了 CaF2。31P MAS-NMR 光谱在所有时间点都显示出 2.7 ppm 的单峰,表明存在的唯一磷酸盐物种是结晶磷灰石。35Cl MAS-NMR 图谱显示在 24 小时后形成了氯化银(AgCl)。据观察,扫描后,白色的 HA 粉末变为黑色。总之,这项时序研究表明,在再矿化条件下,SDF 最初与 HA 反应生成 CaF2,然后随着时间的推移转化为 FSHA。在氯化物存在的情况下,形成 AgCl,随后被光还原成黑色金属银。
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