Effect of curing conditions on physical and chemical properties of MTA

Aim To evaluate setting time, pH, solubility and surface roughness of MTA+ and ProRoot MTA and characterize their hydration under several curing conditions. Methodology Specimens were prepared to evaluate setting time (n = 6 for each group, specimen dimensions 10 x 8 x 5 mm), solubility (n = 6 for each group, specimen dimension 20 mm in diameter and 1.5 mm thick) after 1 and 28 days, pH (n=10 for each group, specimen dimensions 10 mm in diameter and 1 mm thick) after 1, 7, 14, 21 and 28 days and surface roughness (n=10 for each group, specimen dimensions 4 mm in diameter and 3 mm high) after 28 days when cements were cured at 95% humidity or immersed in saline or HBSS at 37 degrees C. The powder and liquid were mechanically mixed by an amalgamator. The set materials were characterized using X-ray diffraction analysis, scanning electron microscopy and X-ray energy-dispersive analysis. Statistical comparisons were employed using one-way anova. The level of significance was set at P = 0.05. Results Setting time was significantly shorter when cements were cured at 95% humidity compared to those in saline (P < 0.001) and HBSS (P < 0.001). Setting time of MTA+ was significantly shorter than that of ProRoot MTA (P < 0.001), which had a significantly higher pH than MTA+ (P < 0.05) for all periods and immersion liquids. After immersion in saline, MTA+ was significantly less soluble than ProRoot MTA (P < 0.001); when immersed in HBSS, no significant difference was found (P=1.00). The surface roughness of both cements was affected when exposed to HBSS (P < 0.001 for both cements) and saline (P < 0.001 for both cements). Storage in HBSS created a homogenous surface; incubation in saline or humidity created a biphasic surface. The main crystalline phases in both cements were tricalcium silicate, bismuth oxide and calcium hydroxide. Conclusions MTA+ had a shorter setting time than ProRoot MTA, promoted lower pH and had lower solubility in saline. Curing conditions affected the surface roughness and microstructure of the cements.