Intracanal assessment of mineral trioxide aggregate setting and sealing properties

This study sought to assess setting time and sealing properties of intracanal mineral trioxide aggregate (MTA). Eighty-three extracted single-rooted human teeth were decoronated and instrumented using the crown-down technique. The apical 3.0 mm of each tooth was resected. After MTA was placed, the coronal openings of the canals were sealed with moist cotton pellets. Root samples were divided into three groups according to setting time periods of four hours, two days, or one week. Within each group, 15 samples were kept in wet gauze to provide a moist apical environment (WA) while the remaining 10 were kept in a dry apical environment (DA). After respective incubation periods, 20 samples per group (10 WA, 10 DA) were mounted in an apical broth turbidity determination chamber and incubated for 30 days. The remaining five teeth per group (WA-h) were sectioned into 3.0 mm slices and compared for MTA setting hardness using the Shore-D Hardness test. Remaining teeth served as negative and positive controls. Each sample was inoculated coronally with Enterococcus faecalis and checked daily for turbidity in apical broth. Microbial leakage was reduced significantly as setting time increased from four hours to two days or one week. There was no significant reduction in leakage when setting time was increased from two days to one week. Over the first 20 days, the DA samples showed a higher rate of leakage compared to the WA samples. The Shore-D hardness test correlated with leakage results; 93% of total setting hardness was reported at two days and one week compared to only 75% for the four-hour group. Results suggest that apical moisture may affect MTA setting time or sealing ability initially and that intracanal MTA may take up to two days to set completely.