الفهرس 
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Abstract
The present in vitro study was aimed to evaluate the resistance of apical plugs to the internal apical bacterial leakage of infected root canals with Enterococcus faecalis utilizing different materials including:MTA, Portland cement, Calcium hydroxide and nano calcium hydroxide.
One hundred and ten freshly extracted human maxillary teeth were collected for this study. The anatomical crowns of each tooth were resected at the CEJ with a high speed tapered fissure bur under air water spray. A large round bur no.5 were used to create irregular immature depression through the apical end of the root canal. All teeth samples were sterilized in an autoclave with sterilization cycle 30 min-at 121oC .
Samples were dried using sterile gauze then two layers of nail polish were applied to the external surfaces of the roots except the apical 3 mm. The The apical foramina were sealed with melted blue wax and the root canals were dried using sterile paper point. A strain of Enterococcus faecalis (ATCC 29212) was used as a test organism in this study. Isolated 24-hours colonies of pure culture of E.faecalis were suspended in 20 ml of trypticase soy broth (TSB) and incubated for 4 hours at 37OCuntil the optical density of the bacterial suspension was adjusted to approximately 3x 10 8 CFU/ml, by comparing its turbidity to 1 McFarland standard. Root canals were preflared in the coronal and middle thirds using protaper rotary files. Then apical preparation was done using F1, F2 and F3 in the respective sequence. The apical plug material was placed through the access opening and condensed to the apical area using a messing gun and hand pluggers with rubber stop for 3mm thickness. Then the coronal access was sealed with wax. All test samples were wrapped in sterile moistened gauze and stored in a sealed container at 37o C for 48 hour, to allow complete set of the plug.
After the incubation period, the waxes at the coronal orifices were removed and then the canals back-filled with gutta-percha and a eugenol based sealer.
Teeth were then be randomly assigned to 5 groups with 20 samples each. Ten roots were used as controls.group 1: received an apical plug of conventional calcium hydroxide.group 2: received an apical plug of nano calcium hydroxide (size 25nm).group 3: received an apical plug of nano calcium hydroxide (size 8 nm).group 4: received an apical plug of MTA. group 5:received an apical plug ofportland cement. Each group were divided into 2 subgroups with 10 samples each according to whether the root canals obturated or not as follow:SubgroupA:the root canals were obturated with gutta-percha and sealer.SubgroupB:the root canals were left without obturation. Plastic vials with snap- on plastic caps ( Eppendorf tubes) were used to suspend the prepared teeth in a broth medium just enough to cover the apical 3mm of the roots. Internal apical bacterial leakage to the broth medium in the test apparatus were checked at designated periods(three days, one week, 4weeks, 8weeks and 12 weeks).
Results showed that there was no statistically significant difference between MTA and Portland cement but there was statistically significant difference between both previous materials and calcium hydroxide (conventional and nano types), while tere was a statistically significant difference between the obturated subgroups and the non-obturated in all groups