• Angsana Jainaen
• Mettachit Nawachinda
• Ratana Serinirach

Objective  The purpose of this study was to determine the bactericidal effect of calcium hydroxide at different pH and different time to the 4 bacteria.

Materials and Methods  First, calcium hydroxide solution was prepared to have the pH 12.5, 12.0, 11.5, 10.5, 9.5, 8.5 and 7.5 using distilled water. Each pH was mixed with the solution containing each bacteria which was as concentrated as the McFarland No 1 at the room temperature. Then, we put each mixed solution into 2 tryptic soy broths at the time of 10 min, 30 min, 1 hr, 6 hr, 24 hr, 48 hr and 72 hr, respectively and we used normal saline as a control. All broths were incubated at 37°C for 48 hours. If calcium hydroxide can not inhibit the growth of bacteria, the solution in the tubes presence of turbidity. Second, we mixed each bacteria with each pH of calcium hydroxide, as described previously and measured the pH change at the time of 10 min, 30 min, 1 hr, 6 hr, 24 hr, 48 hr and 72 hr, respectively. All the process above were triplicate.

Results  Calcium hydroxide pH 12.5 can kill all 4 bacteria, Repeated-Measures ANOVA test shows that the decreasing of calcium hydroxide concentration begin from pH 12.5 is significant in statistic (p=0.00), Whereas calcium hydroxide pH below 10 can not kill any bacteria. Besides, calcium hydroxide pH 12.5 took 30 min, 1 hr, 6 hr to kill Streptococcus mutans, Actimomyces viscosus as well as Staphylococcus aureus, and Enterococcus faecalis, respectively.

Conclusion  Calcium hydroxide pH 12.5 can kill all 4 bacteria at different time.

(CU Dent J 2002;25:161-73)