Comparative Study Using Scanning Electron Microscopy and Energy Dispersive X-Ray Spectroscopy to Assess Morphological Modifications to the Enamel Surface Produced by Three Sodium Fluoride Solutions

Aims: The first aim of this in vitro study was the comparative assessment of enamel surface morphology and analytical assessment of calcium and fluoride ions after topical application of three sodium fluoride solutions: solutions A and B having the same concentration (0.05% sodium fluoride) and solution C having a higher concentration (0.1% sodium fluoride). The second aim was to assess the remineralisation capability of solution A, which has not previously been studied. Methods: Twelve sound premolars, extracted for orthodontic purposes from patients aged between 12-15 years, were used. Demineralisation areas were created by etching with 37% phosphoric acid gel for 60 seconds. Enamel sections were immersed in 100 ml of three solutions, twice daily for 30 days: solution A—Fluorostom (0.05% sodium fluoride), solution B—Colgate Total Protection (0.05% sodium fluoride), and solution C—Sensodyne ProNamel (0.1% sodium fluoride). Surface examination was performed using a scanning electron microscope. The calcium and fluoride concentrations in the enamel surfaces were assessed using energy-dispersive X-ray spectroscopy. Results: Mean remineralisation depths were: 5.73 μm [95% CI, 2.4-12 μm] for A, 5.63 μm [95% CI 2.5-12.7 μm] for B, and 8.28 μm [95% CI 2.91-15.54 μm] for C. There were significant differences between A versus C (P=0.0006) and B versus C (P=0.003) but no significant differences between A versus B (P=0.83). Morphological appearance of fluoride as globular precipitates was revealed in all treated specimens, regardless of ionic fluoride (F-) content. The distribution of the deposits was more homogeneous and smaller in groups treated with higher fluoride concentrations and larger in groups treated with lower fluoride concentrations. The energy-dispersive x-ray spectroscopy revealed that the intensity of signals for calcium and fluoride varied significantly across the three groups (P=0.0001). Conclusions: In the teeth studied, the remineralisation depths depended on the fluoride concentration of the solutions. Globular structures of amorphous calcium fluoride precipitates, which act as a fluoride reservoir, were observed on the enamel surface after the action of all solutions. The differences between solutions A and B were not statistically significant.