Effects of etchant on the nanostructure of dentin: an atomic force microscope study

The objective of this study is to investigate effects of etchant on dentin surface as a function of etching time by atomic force microscopy (AFM). Twenty intact, freshly extracted noncarious human teeth were used to make 40 dentin discs and the discs were randomly divided into 4 groups. A commercial etchant was applied on these dentin discs. The main component of the etchant is 32% phosphoric acid and the etching time for the four dentin disc groups was 0, 20, 40, and 60 s. The AFM results show progressive changes of the surface morphology as the etching time increases. Significant difference of average roughness (Ra) exists in the dentin surface among all four groups (p<0.05). The statistic difference of diameters of dentinal tubule orifice (Dt) exists between the control group and all other groups (p<0.05), whereas the Dts for the 40-s group and 60-s group are not statistically different (p>0.05). Our results showed that acid treatment has a significant influence on dentin demineralization and the effective etching time of the dentin surface appears to be 60 s. We provide a new nanoscale insight into the dentin surface treatment and this can help us to select the optimal etching time in clinic.