Abstract:

BACKGROUND: Although the citric acid solution has been gradually applied to prepare models of dentine hypersensitivity, but there is still not a uniform concentration and etching time.
OBJECTIVE: To study the effect of different concentrations and different etching time of citric acid on the dentin disc to acquire a reliable in vitro model for the research of dentin hypersensitivity. 
METHODS: Thirty premolars were selected and made into the dentin discs. Each dentin disc surface was wet polished using silicone carbide papers to form a smooth and platten surface. The morphology of dentin discs surface etched by the citrate acid was observed by scanning electron microscopy and the diameter of the dentin tubules was measured. A comparative analysis was made on the ability of different concentrations of citric acid solution (5%, 10%, 15%) at different times (30, 60, 120, 180 s) to remove the smear laye on the dentin surface and open the dentinal tubules. 
RESULTS AND CONCLUSION: The etching capability of citric acid to remove the smear layer was enhanced with the etching time expansion and concentration increase. Each time group of 5% citric acid and 30 s and 60 s groups of 10% and 15% citric acid had the limited ability to remove the smear layer, since some dentinal tubules were still subjected to be covered by different levels of smear layer. When the etch time was 120 s and 180 s of 10 % and 15% concentration groups, they all had the capability to remove the smear layer completely and expose dentin tubules. The diameter of the dentin tubules of 120 s and 180 s groups when citric acid concentration was 15% was larger than that of 10% groups, with a statistically significant difference (P < 0.05). Furthermore, the diameter of dentin tubules in 10% groups when the etch time was 120 s and 180 s had no significant difference (P > 0.05). 10% citric acid to etchthe dentin discs for 120 s was demonstrated as the best etching condition for removing the smear layer and acquiring a reliable in vitro model for the research of dentin hypersensitivity.