Calcium and fluoride interaction in human enamel at nanoscale: an XPS assessment

Abstract

Objective This research aimed to assess qualitatively and quantitatively the penetration depth of fluoride ions on nanosurface enamel (30 nm). Topical fluoride application reduces acid erosion on tooth enamel, which is the main contributing factor to tooth decay and dental caries. Our goal is to study the mechanics of chemically reacting free fluoride into the CaP crystals in the enamel's first atomic layers.Materials and Methods Unerupted third molars were randomly selected, and enamel tooth samples were fragmented. Two fluoridated agents (gel and foam; APF 1.23% F ion) were used: at two application times (1 and 4 min; n-6). X-ray photoelectron spectroscopy (XPS) technique was utilized to characterize the enamel nanosurface of the samples to a profile depth of 0, 10, 20, and 30 nanometers. Statistical analysis using three-way ANOVA (factors: agent, time, and depth) was performed on the results (α = 0.05)Results There was a statistically significant difference between the control and the fluorinated surfaces (p = 0). However, factor time was not significantly different (p = 0.47), and in the same way, its interaction with the factors APF agent (p = 0.16). Factor depth was significantly different (p = 2.29×10−11).The highest atomic percentage of elemental fluoride was discovered within the surface layers of enamel at a profile depth of 10 nm for both application times and either fluoridated agent. This study showed that CaF2-like is formed mainly by substituting CaOH than HAp in the first layers of enamel (30 nm depth).Conclusion This research has demonstrated that fluoride ions stay in a very superficial layer of enamel regardless of application time and or the APF agent utilized. This information is critical to understanding the demineralization and remineralization processes.

Keywords

• Fluoridation
• Human enamel
• Hydroxyapatite surface composition
• Nanotechnology
• XPS
• Topical agents