This study aims to research the effect of different instrument designs by comparing protaper ultimate versus protaper gold systems on root canal preparation by evaluating bacterial count reduction and post-operative pain following single visit treatment in patients with necrotic pulp in maxillary premolar teeth.

Inclusion Criteria:

• Patient's age ranges between 22 to 45 years with no sex predilection.

• Medically free patients.

• Maxillary permanent premolar teeth:

  • Diagnosed clinically with pulp necrosis.
  • Absence of pain.
  • Radiographic evidence of two roots or single root with double canals.
  • Slight widening in the periodontal membrane space or with peri-apical radiolucency
  • No response to cold pulp tester and ethyl chloride spray.

• Patients who can understand Modified Visual Analogue Scale (VAS).

• Patients' acceptance to participate in the trial.

Exclusion Criteria:

• Medically compromised patients.

• Pregnant women.

• If analgesics or antibiotics have been administrated by the patient during the past 24 hours preoperatively.

• Patients reporting bruxism or clenching.

• Teeth with:

  i. Vital teeth. ii. Single canal maxillary premolar teeth iii. Association with swelling or fistulous tract. iv. Acute peri-apical abscess and swelling. v. Mobility Grade II or III. vi. Pocket depth more than 5mm. vii. Previous root canal therapy. viii. Non-restorable teeth: Hopeless tooth

• Immature teeth.

• Radiographic evidence of external or internal root resorption vertical root fracture, perforation, calcification, root caries.