Objective: To evaluate and compare the effect of accelerators on the pH and antimicrobial activity of white Portland cement and white mineral trioxide aggregate.

Study Design: Fifty Plastic tubes were filled with the test material and immersed in deionized water. The pH of the water was measured at 0, 10, 30, 60 minutes and 24 hours using pH meter. The antimicrobial activity of the cement was evaluated using agar-diffusion test. The plates containing BHI agar were inoculated with microorganisms Pseudomonas aeruginosa (ATCC 27853), Streptococcus sanguis (ATCC 10556), Enterococcus faecalis (ATCC 29212) and Candida albicans (ATCC 5314) (HiMedia). Subsequently, wells were prepared and immediately filled with test materials and incubated at 37°C for 24 hours and 48 hours. The diameters of the zone of inhibition were measured at 24 hours and 48 hours and data analysed using Anova, Post-hoc Bonferroni and paired - t test.

Results: The results showed that the maximum pH values were obtained when 15% calcium chloride was used as an accelerator with both WMTA and WPC. The antimicrobial activity of WPC and WMTA mixed with 10% and 15% calcium chloride was superior to the control group for all the tested microorganisms.

Conclusion: The use of 15% calcium chloride revealed enhanced antimicrobial activity of WPC and WMTA due to its high pH values.

Key Words: Portland cement, MTA, antimicrobial activity, accelerants.