الفهرس 
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Abstract
The present in-vitro study aimed to evaluate the sealing ability of Mineral trioxide aggregate (MTA) and Nano hydroxyapatite (NHA), when used as retrograde filling materials, and the effect of obturation against internal apical bacterial leakage of infected root canal with staphylococcus aureus bacterial species.
One hundred recently extracted mature human single-rooted teeth were collected for this study. The crowns were removed so that all roots segments were standardized to about 17mm Long. After checking of patency and working length determination, all canals were prepared to #40 master apical file, then sterilized by autoclaving for 15 min at 121°C and 1½ atmospheric pressure.
Specimens were coated by two successive layers of nail polish and one layer of blue wax. A strain of staphylococcus aureus was used as test bacteria in this study. Isolated colonies of pure culture of staphylococcus aureus, were suspended in normal saline in test tube until the optical density of the bacterial suspension was adjusted to approximately 3x108 colony forming unit (CFU) /ml, by comparing it’s turbidity to 1 McFarland standard. 10 μl of the bacterial suspension was carefully inoculated into the instrumented canal of each specimen coronally. Thereafter, the coronal orifices were sealed with wax and the specimens were enclosed individually in sterile plastic eppendorf tubes of 1.5 ml size, placed in upright position in perforated trays and incubated at 37°C for 48 hours.
The prepared 100 specimens were classified to experimental (n=80), and controls (n=20). The experimental specimens were equally grouped
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as following; group A: non-obturated canals either with gutta-percha or endofill sealer, group B: obturated canals with gutta-percha and endofill sealer.
The apical 3mm were resected at 90 degree to the long axis, then 3mm deep retrograde cavity (class I) was prepared.
After retrograde cavities preparation, each group (A, B) was subdivided into 2 equal subgroups according to tested retrograde filling materials (n=20). The control specimens were subdivided into; negative control (n=10): the root canals were obturated and retrograde cavities were sealed with wax, and positive control (n=10): the root canals were neither coated with nail polish or wax nor obturated and the retrograde cavities were left without sealing.
All the specimens were stored in a sealed container at 37°C, 72 hours to allow complete setting of retrograde filling materials.
After storage each specimen was rinsed with 5 ml of distilled water and secured with wax within the hole of the cap of an eppendorf tube containing sterile mannitol salt broth to a level sufficient to cover the sectional apical parts with its corresponding retrograde filling material. The caps of the eppendorf tubes were snapped into place, and then the tubes with the enclosed specimens were vertically oriented in perforated trays, and placed in an incubator at 37°C, for designated check up at 3, 9, 30, 60, and 90 days.
At the end of each interval, the specimens which showed bright yellow color with turbidity were recorded for each subgroup and bacterial count was performed. While the specimens which did not show evidence of color change were removed from eppendorf tube using sterile tweezers,
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rinsed with distilled water and placed in a new sterile tube containing another sterile mannitol salt broth.
Statistical analysis of the results of the leaked samples showed that NHA had less sealing ability than MTA at the first two periods (day 3, 9), while no significance difference was observed between MTA and NHA at the rest of the study periods (day 30, 60, 90) in both non-obturated and obturated root canals.
Significant increase in the numbers of bacterial leakage count of failed samples observed with non-obturated than obturated groups for MTA and NHA after 90 days.
The significance difference in the rate of bacterial leakage with non-obturated group was observed at day 30, while in obturated group observed at day 60 for Mineral trioxide aggregate and Nano hydroxyapatite when used as retrograde filling.