needs water to dissolve. Therefore it is most advantageous to use water as a vehicle for the Calcium hydroxide paste. In contact with air calcium hydroxide forms calcium carbonate. Calcium hydroxide is a slowly working antiseptic. Direct contact experiments in vitro require a 24 hour contact period for complete kill of enterococci. Calcium hydroxide not only kills bacteria , but it also reduces the effect of the remaining cell wall material lipopolysaccharide.