The aim of this study is to compare the effect of Neem (azadirachta indica) and 2.5% sodium hypochlorite as root canal irrigants on the intensity of post-operative pain and the amount of endotoxins in necrotic teeth.

According to the eligibility and exclusion criteria the patients will be selected and randomly divided into two groups. The operator N.S. will complete endodontic treatment of all cases in two visits as following:

1. Anaesthetizing the tooth using inferior alveolar nerve block followed by buccal infiltration technique.

2. Isolation the tooth with a rubber dam and disinfect the tooth using sterile swabs moistened with 30% H2O2 (v/v) for 30 seconds followed by 5.25% NaOCl for 30 seconds and 5% sodium thiosulphate for inactivation of the disinfecting agents .

3. Performing access cavity preparation in two stage :

   1. The first stage: will be performed to allow removal of contamination which includes carious lesions and restoration using high speed sterile round bur and diamond stone.
   2. In second stage: before entering the pulp chamber, the access cavity will be disinfected .

4. For endotoxins sampling, the first sample (S1):

   N.S. will take the sample by introducing a sterile paper point (size #15) into the full working length of the wider / largest canals or canals that show presence of the exudate.

5. N.S. will place the sample in a sterile glass for further Enzyme-linked immunosorbent assay (ELISA).

6. After the first sampling,Taking working length using electronic apex locator and then will be confirmed radio-graphically .

7. Performing the biomechanical preparation for the two groups in a crown-down technique using ProTaper Next rotary system.

8. Irrigation with 2mL of specified irrigation either 2.5% NaOCl or Neem irrigant will be performed each time instrument is changed with 30-gauge side-vented needles.

9. After complete mechanical preparation, the root canals will be flushed using 5mL of sterile saline solution.

10. Before the second sampling (S2):

    N.S. will irrigate the prepared root canal with 5 mL of 17% EDTA solution for 3 minutes followed by a final rinse with 5 mL of a sterile saline solution to remove smear layer. NS will seal the access cavity with temporary filling material.

11. Scheduling the second appointment 1 week after the first appointment;. NS will irrigate the root canals with 5 mL of a sterile saline solution.

12. N.S. will give the patients a pain diary to record the postoperative pain after 6,12,24 and 48h post-instrumentation.

13. in second appointment: After master cone fit radiograph and selection of the master cone, all canals will be filled using cold lateral condensation technique with resin-based sealer.

14. N.S. will give the patients another pain diary to record the postoperative pain after 6, 12, 24 and 48 hours post-obturation.

Inclusion Criteria:

• 1- Mandibular molar teeth:

  • Diagnosed clinically with pulp necrosis.
  • Absence of spontaneous pain
  • Pain on palpation or tenderness to percussion.
  • Periradicular radiolucency or widening of periodontal membrane space. 2- Patients' acceptance to participate in the trial. 3- Patients who can understand NRS scale and can sign the informed consent.

Exclusion Criteria:

• 1. Primary teeth and permanent teeth with immature roots which require special endodontic treatment protocol that seeking for obtaining good apical seal, proper cleaning, shaping and obturation 2. Patients who have received antibiotics for the last 3 months before the study or any medication that could alter their perception of pain, inflammation and infection .

  3. Teeth previously accessed or endodontically treated as they have low success rate .

  4. Patients with diabetes, immune-compromising and immune-suppresion disease as the healing is much more slowly and more liable to infection .

  5. Pregnant patients to avoid exposure to radiograph. Moreover, pain perception may be altered due to hormonal changes .

  6. Teeth with deep pocket >4 mm as it has poor prognosis and deep pockets are harbor area for infection which need specific surgical and periodontal treatment .

  7. Teeth that could not be isolated with a rubber-dam or could not be restorable.

  8. Tooth associated with vertical root fracture, coronal perforation, calcification and external or internal root resorption as it has poor prognosis.

• The study will be double-blinded which are the patients and the assessor.
• The participants will drag the envelop and will not know which irrigant they will be treated with to not affect their behavior and their responses to the subjective outcome measures. also, not provide biased assessment of the effectiveness of the intervention .
• The study will be double-blinded which are the patients and the assessor.
• The participants will drag the envelop and will not know which irrigant they will be treated with .
• Assessors in the microbiology laboratory in Microbiology department, Faculty of Medicine, Cairo University also will be blinded during assessment of data of endotoxins will not know the treatment group of the patients.