• Sample size calculation: The aim of this study is to evaluate the antibacterial action of TheraCal (light-cured Calcium Silicate base/liner), comparing this material with Calcium Hydroxide paste. If the expected clinical differences in bacterial count by digital colony counter, agar diffusion test is 1± 1. Using power 80% and 5% significance level , we will need to study 17 in each group to be able to reject the null hypothesis that the population means of the experimental and control groups are equal. This number is to be increase to 24 in each group to compensate for possible losses during follow up according to Petrou et al., 2014. The sample size was calculated by PS program.