Objectives:  To assess setting-time and sealing properties of intracanal mineral trioxide aggregate (MTA).

Methods:  Seventy-five extracted single-rooted human teeth were de-coronated and instrumented using crown-down technique. Apical 3mm of each tooth was subsequently resected. After placement of MTA, coronal openings of the canals were sealed with moist cotton pellets. Root samples were divided into three groups according to setting-time periods of 4 hours, 2 days, or 1 week. Within each group, 15 samples were kept in wet gauze to provide a moist apical environment while the remaining 10 were kept in a dry apical environment. After respective incubation periods, 20 samples per group were mounted in an apical broth turbidity determination chamber and incubated for 30 days. The remaining 5 teeth per group were sectioned into 3mm slices and compared for MTA set-hardness using the Shore-D Hardness test. Three teeth sealed with resin and three teeth with no filling material served as negative and positive controls respectively. Each sample was inoculated with Enterococcus faecalis coronally and checked for turbidity in apical broth daily.

Results:  Microbial leakage was delayed by increase in set-time with the 4-hour sample group showing the highest number of early leaked samples (14), averaging 11 days. However, ANOVA analysis failed to show any statistical difference between setting-times, number of samples showing leakage and time to leakage. Similarly, dry-apical samples showed higher leaked samples with earlier leakage (11 days) compared to the wet-apical samples (16 days), but T-test analysis revealed no significant difference. MTA hardness in 4 hours was significantly less compared to 2-day and 1-week sample groups. Comparison of hardness values between 2-day and 1-week group was not significant.

Conclusion:  Results suggest that apical moisture may not affect MTA set-time or sealing ability and that intracanal MTA may take up to 2 days to completely set.