الفهرس 
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Abstract
It was conducted to evaluate the effect of MTAD, EDTA, and chlorohexidine as final rinse after cleaning and shaping, and the effect of anaerobic bacteria in infected root canals on healing capacity of periapical lesions.
A total of fourty patients-males and females-were included in this study, their ages ranged between 20-40 years. Each of them was diagnosed for being healthy, not suffering from any systemic illness, having a radiographically evident periapical radiolucency related to either mandibular or maxillary single rooted teeth. Standardized intraoral periapical radiographs were taken at the baseline using bite blocks with a long-cone paralleling technique.
Before biomechanical preparation, root canals were irrigated using sterile saline prior to sampling. They were then sampled using three paper points per each sample. The paper points were placed into transport medium of thioglicolate broth and carried in pre-sterilized Eppendorf tubes for microbial culturing.
Root canals were then prepared using protaper files. Throughout biomechanical preparation, they were irrigated frequently using sodium hypochlorite 5 ml 2.5% after each file using sterile disposable syringe.
The patients were divided into four groups - according to the type of irrigant used as a final rinse-; the first group (group I) included 10 cases finally rinsed with Bio pure MTAD, the second group (group II) included 10 cases finally rinsed with chlorohexidine digluconate, the third group (group III) included 10 cases finally rinsed with EDTA 17%, and the fourth group (group IV) included 10 cases finally rinsed with normal saline and served as control group.
The final irrigation was then performed with the irrigant assigned for each group. Then, bacterial samples were collected again following the same protocol of the first sample. The two samples were sent to the microbiological laboratory for culturing within a maximum of 2 hours to be cultivated aerobically and anaerobically.
All root canals were obturated using gutta percha and restored by permanent filling using resin composite. All groups were evaluated radiographically for one year (with six months follow up interval). The Digora software was used to measure the bone density in each case in all groups, and size of periapical lesion.
The results of the present study revealed no statistically significant difference regarding changes in bone density in all assigned groups throughout the whole study period.
Regarding bacterial counts, CHX group showed the highest reduction in bacterial counts, and then comes MTAD and EDTA groups that showed lower values, and finally came the saline group showing the lowest reduction.
Besides, reduction in bacterial counts was associated with increase in bone density and decrease in size of periapical lesion.
from the results of the present study it can be concluded that:
• Staphylococcus aureus, Peptostreptococcus, and Streptococcus species were the most prevalent types of bacteria in the non-vital teeth with periapical lesions in tested samples of Egyptian population.
• The type of irrigant as a final rinse has no significant effect on healing of periapical lesions.
• Removal of bacteria from the infected root canal increase the chance and rate of healing of the periapical lesion (size and density)
• No correlation was found between the type of bacteria and healing of periapical lesion (size and density)