The purpose of present study was to compare the speed of coronal leakage before and after post space preparation using Streptococcus mutans.

Forty straight extracted human teeth were selected. The crowns were removed to a uniform remaining root length 14 mm. Canals were enlarged by 06 taper Profiles® to a size #40 as a master apical file. And these were filled with gutta percha point and Tubuliseal® sealer, using continuous wave technique. Groupings are as follows.

Group 1 - These teeth were obturated without sealer.

Group 2 - These teeth were obturated and covered the surface of the root completely with sticky wax.

Group 3 - These teeth were obturated.

Group 4 - These teeth were obturated and prepared for post space remaining 5 mm of gutta percha.

The teeth were suspended in plastic tubes. The upper chamber received the bacterial suspension everyday to simulate clinical situation. The lower chamber consisted of BHI added Andrade's indicator.

All roots in the positive control group (Group 1) turned yellow within 24 h and those of negative control group (Group 2) remained red throughout the experimental period (70 days). The samples of group 3 were contaminated within an average of 27.2 days. The samples of group 4 were contaminated within an average of 15.7 days, ranging from 9 to 22 days.

There was significant difference between group 3 and group 4 statistically (p < 0.05).