Effects of pH on surface hardness and microstructure of mineral trioxide aggregate and Aureoseal: an in vitro study.

INTRODUCTION: The aim of the study was to evaluate the surface hardness and the morphologic microstructure of white mineral trioxide aggregate (WMTA) and Aureoseal in acid environment. METHODS: WMTA and Aureoseal were mixed and packed into 64 cylindrical stainless steel molds. Thirty-two of each group were exposed to pH values of 4.4 and 7.4, respectively, for 7 days. Four specimens, 2 exposed to acid pH and 2 exposed to pH of 7.4, were prepared for evaluation under scanning electron microscope by using scattered electron (SE) and backscattered electron (BSE) detectors. Vickers surface hardnesses were measured in the remaining 60 samples. RESULTS: The mean surface hardness values ± standard deviation were 37.54 ± 1.52 and 30.24 ± 1.47 for WMTA and 40.63 ± 1.35 and 28.67 ± 1.07 for Aureoseal after exposure to pH values of 7.4 and 4.4, respectively. WMTA showed higher hardness values in acid environment than Aureoseal, which showed the highest microhardness at pH values of 7.4. The SE detector revealed crystal formation on the WMTA surface at pH values of 7.4 and 4.4. In the WMTA specimens the BSE detector showed more unhydrated structures at pH values of 4.4 than at 7.4. The SE detector did not reveal crystal formation on the Aureoseal specimens at pH 7.4 and 4.4. BSE detection showed amorphous microstructures in the Aureoseal specimens treated in the pH 4.4 acid environment. CONCLUSIONS: There was significant interaction between the cements and the environments where the cements hardened.