This research will study the effect of Boswellia Sacra versus calcium hydroxide as an intracanal medicament on postoperative pain intensity measured using numerical rating scale (NRS) and bacterial load reduction reduction determined by bacterial counting using agar culture technique after root canal preparation (CFU/ml) in mandibular premolars with necrotic pulp.

Primary outcome Postoperative pain measured using numerical rating scale (NRS)

1. After placement of intracanal medicament at 6, 12, 24 and 48 hours.
2. After root canal obturation at 6, 12, 24 and 48 hours.

Secondary outcomes Bacterial load reduction determined by bacterial counting using agar culture technique after root canal preparation (CFU/ml) .

1. Sample 1 (S1): after access preparation and pre-instrumentation.
2. Sample 2 (S2): post-instrumentation.
3. Sample 3 (S3): post-intracanal medicament removal at 3 or 7 days according to the group.

Inclusion Criteria:

1. Age between 25-45 years old.

2. Males or females.

3. Healthy patients whom are categorized as I or II according to The American Society of Anesthesiologists. (ASA I or II)

4. Patients' accepting to participate in the trial.

5. Patients who can understand pain scale and can sign the informed consent.

6. Mandibular Single rooted premolars, having single root canal:

   • Diagnosed clinically with pulp necrosis.
   • Absence of spontaneous pulpal pain.
   • Positive pain on percussion denoting apical periodontitis.
   • Periapical radiolucency not exceeding 2*2 mm radiographically.
   • Normal occlusal contact with opposing teeth.

Exclusion Criteria:

1. Medically compromised patients having significant systemic disorders (ASA III or IV).

2. If analgesics or antibiotics have been administrated by the patient during the past 24 hours preoperatively as it might alter their pain perception.

3. Pregnant women: to avoid radiation exposure, anesthesia, medication and hormonal Fluctuation that might increase pain prevalence.

4. Patients reporting bruxism, clenching, TMJ problems or traumatic occlusion: to avoid further pressure on inflamed tooth which induce subsequent irritation and inflammation.

5. Patients with two or more adjacent teeth requiring endodontic treatment.

6. Teeth that requires further procedural steps or multidisciplinary approach, which is out of this experiment's scope:

   i. Association with swelling or fistulous tract. ii. Acute periapical abscess. iii. Mobility Grade II or III. iv. Pocket depth more than 5mm. v. Previous root canal treatment. vi. Non -restorable vii. Immature roots viii. Radiographic evidence of external or internal root resorption, vertical root fracture, perforation, calcification.

7. Inability to perceive the given instructions.

Outcome assessors (patients, microbiologist and statistician) will not know Which group the participants will be related to?