Comparison of Resistance of Dentin to Erosive Acid after Application of Fluoride to Teeth

In recent years, tooth erosion due to tooth root exposure has increased. This is associated with an increase in remaining teeth in the elderly and frequent ingestion of acidic foods. Fluoride application is a clinical method for preventing tooth erosion; however, dentin solubility after topical fluoride application, according to the type of erosive acid, has not been adequately investigated. We studied the characteristics of demineralization and acid resistance of dentin to four erosive acids and evaluated the efficacy of topical fluoride application in preventing tooth erosion. Small blocks with a smooth surface were prepared by mirror-finishing the labial side of a bovine tooth root. In the experimental group, acidulated phosphate fluoride (APF) was applied topically for 4 minutes, while the control group received no fluoride treatment. Both groups were immersed in a remineralization solution for 1 h at 37 degrees C. Five samples from each group were subjected to tooth erosion and demineralization by immersion in lactic acid, phosphoric acid, acetic acid, and citric acid for 6 h at 37 degrees C. Demineralization and dentin solubility were evaluated by calculating mineral loss (Delta Z) and lesion depth (Ld) from the average surface roughness (Sa), difference in height profile, and contact microradiogram (CMR). We also performed electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS) qualitative analysis to assess fluoride dynamics and properties of the compounds formed on the dentin surface after APF application. Samples with APF application showed greater resistance towards all four erosive acids. While a highly calcified layer was found with lactic and acetic acid, resistance was not adequate against citric acid, which has chelating properties. Fluoridated calcium formed on the tooth surface after topical fluoride application. Fluoride ions are taken up by peritubular dentin through the dentinal tubules, resulting in increased acid resistance.