Assessment of Vickers hardness, microstructure, and surface roughness of dentin after initial dissolution by acidulated phosphate-fluoride

Acidulated phosphate-fluoride (APF) is widely used for the prevention of enamel caries. The topical application of fluoride is a promising treatment for improving the acid-resistance of tooth, promoting its remineralization, and improving its crystallinity. APF contains a high concentration of fluorine ions (9,000 ppm); it first decalcifies the apatite in dentin, generating calcium and phosphate ions, which bind to fluoride ions, thus precipitating calcium fluoride. APF is prepared as an acidic solution (pH 3.5) and is used to reinforce the enamel. However, dentin is less resistant to acid than enamel. As such, APF treatment at the same acidity carries a risk of weakening the dentin after application. In many cases, wedge-shaped defect (WSD), root caries, and attrition can cause dentin exposure, to which the APF can attach. Therefore, in this study, we analyzed the effect of APF treatment on dentin by measuring Vickers hardness, making observations with scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM), and measuring average surface roughness (Ra). The findings of this study suggested that an acidulated phosphate fluoride (APF) treatment of 3 min or longer caused marked dissolution of dentin and posed the risk of deterioration of its initial strength. Therefore, careful management is required to preclude dentin dissolution when performing APF treatment for preventing dental caries.