45 teeth will be sub-divided at random with a computerized method, according to the type irrigant and duration of its application into 3 groups (15 teeth in each group):

Group1(control group):

The teeth will be irrigated by 2 ml 1% NaOCl after each file.

Group2:

The teeth will be irrigated by 2 ml 1% NaOCl after each file then with 5 ml of 0.2% chitosan for one minute.

Group 3:

The teeth will be irrigated by 2 ml 1% NaOCl after each file then with 5 ml of 0.2% chitosan for 3 minutes.

Evaluation

Clinical evaluation will be done for all groups at one, three, six and 12 months. The following parameters will be evaluated: Pain (spontaneous pain and pain with percussion) Degree of mobility Resolution of signs of infection (fistula) at the mucobuccal fold.

Radiographical evaluation will be performed to each patient immediately after the final restoration and three, six and 12 months postoperatively.

The decrease of radiolucency and the presence of internal or external root resorption will be evaluated.

Bacteriology :

The microbiological evaluation will be done at the Biotechnology Research Institute - Suez Canal University.

PCR will be used for detection of Enterococcus faecalis. Microbiological investigation will be used for counting the number of Enterococcus faecalis.

45 teeth will be sub-divided at random with a computerized method, according to the type irrigant and duration of its application into 3 groups (15 teeth in each group):

Group1(control group):

The teeth will be irrigated by 2 ml 1% NaOCl after each file.

Group2:

The teeth will be irrigated by 2 ml 1% NaOCl after each file then with 5 ml of 0.2% chitosan for one minute.

Group 3:

The teeth will be irrigated by 2 ml 1% NaOCl after each file then with 5 ml of 0.2% chitosan for 3 minutes.

The root canals will then be flushed with 5 ml saline. Second microbiological sample will be collected. The tooth will be dried using paper points and then will be temporarily sealed with glass ionomer restoration.

Second Visit (after two days):

Glass ionomer will be removed and the third microbiological sample will be collected.

Zinc oxide and eugenol will be used as root canal filling material. All cases will be subjected to clinical and radiographical evaluation.

Evaluation

Clinical evaluation will be done for all groups at one, three, six and 12 months. The following parameters will be evaluated: Pain (spontaneous pain and pain with percussion) Degree of mobility Resolution of signs of infection (fistula) at the mucobuccal fold.

Radiographical evaluation will be performed to each patient immediately after the final restoration and three, six and 12 months postoperatively.

The decrease of radiolucency and the presence of internal or external root resorption will be evaluated.

Bacteriology :

The microbiological evaluation will be done at the Biotechnology Research Institute - Suez Canal University.

PCR will be used for detection of Enterococcus faecalis. Microbiological investigation will be used for counting the number of Enterococcus faecalis.

Microbiological sample collection protocol:

Two sterile paper points will be introduced into the canals until they reached the full working length, and kept in place for 60 seconds (19). Each paper point will be immediately embedded in 3ml sterile tube containing adequate transporting medium or saline solution.

The first tube will be transported to the microbiological laboratory for culturing within a maximum of 2 hours, while the other tube will be kept at -80 °C for DNA extraction and direct detection of Enterococcus faecalis via multiplex PCR assay.

Inclusion Criteria:

• Apparently healthy Children aged from three to seven years.
• No previous history of antibiotics for at least two weeks.
• Non- Vital primary teeth that can be fully isolated.
• Presence of clinical signs or symptoms suggesting a non-vital tooth, such as intra-oral fistula.
• Infection diagnosed by presence of periapical radiolucency in a periapical radiograph.
• Root resorption not more than one third of the root.
• Patient and parent cooperation.

Exclusion Criteria:

• Non-restorable tooth
• Serious reduction in bone support and/or extreme tooth mobility.
• Radiographic indication of extensive internal or external root resorption.