Effects of Storage Temperature on Surface Hardness, Microstructure, and Phase Formation of White Mineral Trioxide Aggregate

Abstract

Introduction: Storage temperature influences the properties of Portland cement during mixing. Because of similarities between Portland cement and mineral trioxide aggregate, the aim of the present study was to evaluate surface microhardness, topography, and phase structure of white mineral trioxide aggregate (WMTA) after storage in a range of temperatures. Methods: Thirty WMTA sachets were divided into 3 groups of 10. The 3 groups were stored at 4 degrees C, 25 degrees C, and 40 degrees C for 48 hours with accompanying ampules. Sachets were immediately mixed after removal from storage according to manufacturer's instructions and mixed and packed into cylindrical glass tubes at room temperature. Surface microhardness of each specimen was measured after 3 days. Four specimens from each group were prepared and observed under scanning electron microscope and x-ray diffraction. Data were subjected to one-way analysis of variance and a post hoc Tukey test at P < .05. Results: Mean surface hardness +/- standard deviation after storage at 4 degrees C, 25 degrees C, and 40 degrees C were 25.23 +/- 5.99, 53.56 +/- 3.28, and 62.89 +/- 1.76, respectively. Statistically significant differences were observed among the groups (P < .001). More voids and a disorganized, flake-like topography were observed in specimens stored at 4 degrees C in comparison with those stored at 25 degrees C and 40 degrees C. X-ray diffraction meter generated similar peaks at 40 degrees C and 25 degrees C, but slight differences were observed at 4 degrees C. Conclusions: This study indicated that storage temperature might influence surface hardness and microstructure of WMTA. (I Endod 2010;36:1414-1418)