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Abstract
Utilizing scanning electron microscope, X-ray diffraction (XRD) and microhardness
tests, we evaluated how various physiological environments affect the hydration behavior
and physical properties of mineral trioxide aggregate (MTA). We found that the microstructure
of hydrated MTA consists of cubic and needle-like crystals. The former comprised the
principal structure of MTA, whereas the later were less prominent and formed in the
inter-grain spaces between the cubic crystals. MTA samples were hydrated in distilled
water, normal saline, pH 7, and pH 5. However, no needle-like crystals were observed
in the pH 5 specimens, and erosion of the cubic crystal surfaces was noted. XRD indicated
a peak corresponding to Portlandite, a hydration product of MTA, and the peak decreased
noticeably in the pH 5 group. The pH 5 specimens' microhardness was also significantly
weaker compared to the other three groups (p<0.0001). These findings suggest that
physiological environmental effects on MTA formation are determined, in part, by environmental
pH and the presence of ions. In particular, an acidic environment of pH 5 adversely
affects both the physical properties and the hydration behavior of MTA.