The Effect of Calcium Hydroxide and Nano-calcium Hydroxide on Microhardness and Superficial Chemical Structure of Root Canal Dentin: An Ex Vivo Study.

Introduction: Calcium hydroxide (CH) and nano-calcium hydroxide (NCH) as intracanal medicaments may affect the physical and chemical properties of dentin. The aim of this investigation was to evaluate the effects of CH and NCH on the microhardness and superficial chemical structure of radicular dentin.

Methods: In this in vitro trial, 80 dentin discs were randomly assigned into 2 control and 2 treatment groups (n = 20). CH and NCH pastes were used in the treatment groups. In the control groups, the samples were washed with either normal saline or 2.5% sodium hypochlorite. After 1 and 4 weeks, dentin microhardness was assessed by the Vickers test, and the phosphate/amide I ratio was evaluated by the Fourier-transform infrared spectrometry test. The data were subjected to 1-way and 2-way analyses of variance, the Tukey multiple comparison test, and the Student t test.

Results: A significant reduction in the mean microhardness was observed in the CH group after 4 weeks, whereas the differences were not significant in the NCH and control groups. The amount of reduction induced by NCH was comparable with hypochlorite. A significant increase in the mean phosphate/amide I ratio was observed in the CH and NCH groups compared with the sodium hypochlorite and intact control groups after 1 week, which did not change significantly during the observation period.

Conclusions: The use of CH as an intracanal medicament for 4 weeks reduced dentin microhardness, whereas NCH did not result in any change in the microhardness value. However, a change in the superficial chemical structure was observed earlier after 1 week and in both the CH and NCH groups.