The durability of a hydroxyapatite paste used in decreasing the permeability of hypersensitive dentin.

Objectives: Various agents are currently available for treatment of hypersensitive dentine, however, their resistance to erosion intraorally by various erosive drinks is still questionable. The aim of this study is to test the efficacy of a hydroxyapatite paste to decrease dentine permeability and resist an erosion challenge.
Methods: Hydroxyapatite powder was mixed with 25% phosphoric acid to form a paste which was applied on dentine having patent dentinal tubules orifices (treated with EDTA, 2 min) and the resulting layer formed on top of dentine was irradiated by Nd:YAG laser. The treated dentin surfaces were exposed to erosion challenge (6% citric acid, 1 min). Dentine permeability was measured before/after the application of the hydroxyapatite paste before/after the erosion challenge before/after the application of Nd:YAG laser using a split chamber device. The top and the fractured dentine surfaces were examined with scanning electron microscope (SEM). Moreover, the chemical nature of the compounds formed on top of dentine surface was examined using the SEM equipped with energy- dispersive X-ray spectroscope (EDS) and FTIR/ATR (Attenuated Total Reflectance Fourier Transform Infrared) techniques. The Mann-Whitney test (p < 0.05) was used to compare the effects of using the hydroxyapatite paste on dentine permeability and calcium/phosphate ratio of the treated dentine surfaces.
Results: The application of the hydroxyapatite paste to dentine significantly decreased dentine permeability (p < 0.05). Hydroxyapatite paste was able to occlude patent dentinal tubule orifices with a layer of calcium-phosphate compounds and the application of Nd:YAG laser on the aforementioned layer improved its erosion resistance.
Conclusion: Hydroxyapatite paste applied with the technique adopted in the current study has a high potential to be a useful aid in the treatment of dentine hypersensitivity. However, cost and knowledge for using Nd:YAG laser are important factors should be taken into consideration before using the aforementioned technique.