In vitro determination of direct antimicrobial effect of calcium hydroxide

The objective of this study was to determine in vitro the time required for calcium hydroxide in direct contact with microorganisms to express its antimicrobial effect. The microorganisms used were: Micrococcus luteus (ATCC-9341), Staphylococcus aureus (ATCC-6538), Fusobacterium nucleatum (ATCC-25586), Pseudomonas aeruginosa (ATCC-27853), Escherichia coli, and Streptococcus sp. The strains were cultivated in Brain Heart Infusion (BHI), with the exception of F. nucleatum (BHIPRAS). Pure and mixed suspensions of the microorganisms were prepared. Paper cones immersed in these substances were covered with calcium hydroxide paste, and after 0, 1, 2, 6, 12, 24, 48, and 72 h and 7 days they were transferred to an appropriate medium to observe the growth and multiplication of the microorganisms. Incubation was conducted at 37°C for 48 h, according to the requirements of oxygen of each microorganism. The antimicrobial effect of calcium hydroxide was shown to occur after 12 h on M. luteus and F. nucleatum, 24 h on Streptococcus sp, 48 h on E. coli, and 72 h on S. aureus and P. aeruginosa. Mixture II ( M. luteus + Streptococcus sp + S. aureus) was sensitive to calcium hydroxide antimicrobial potential after 48 h, whereas mixture I ( M. luteus + E. coli + P. aeruginosa), mixture III ( E. coli + P. aeruginosa), and mixture IV ( S. aureus + P. aeruginosa) were inactivated after 72 h of exposure.