• The aim of this study is to assess the postoperative pain and the intake of analgesic medication after using Reciproc single-file reciprocating system or One Shape single-file continuous rotary system in patients with symptomatic irreversible pulpitis.
• Patients will be diagnosed to determine whether they are eligible for the inclusion criteria of this study or not. Patients who are eligible will then start their root canal treatment on the same visit and to be completed in one visit only. Patients will be phone called in order to record the intensity of pain, amount and frequency of analgesic intake at 6, 12, 24, 48 and 72 hours after treatment.

- Full medical and dental history using a schematic dental chart will be obtained from all eligible participants. Each tooth will be evaluated for vitality (sensitivity) of pulp tissues.

The patients will be randomly divided into 2 groups:

• Experimental group: Reciproc reciprocating instrumentation system.

• Control group: One Shape rotary instrumentation system.

  - Sequence of Procedural steps

  1. Preoperative pain will be assessed by Numerical Rating Scale (NRS) before administration of anesthesia.
  2. Local anesthesia will be achieved using 2% lidocaine (1:100,000 adrenaline).
  3. An access cavity will be performed using round bur and Endo-Z bur.
  4. The tooth will be properly isolated with rubber dam.
  5. Working length will be determined using an electronic apex locator, and working length will be confirmed by radiograph using K-file. Then the working length will be established at 0.5 mm up to the radiographic apex.
  6. Canals will be explored with hand K-file ISO sizes 10, 15, 20.
  7. Mechanical preparation for both groups will be as follows:

• Experimental group:

  • Canals will be instrumented using Reciproc reciprocating system set on an electric motor, with adjusted torque and speed according to the manufacturer's instructions.
  • There is no need for coronal preflaring with a Gates Glidden drill or an orifice opener since the design of the Reciproc instrument allows any obstructions in the coronal third to be removed, as claimed by the manufacturer.
  • Reciproc file selection: R40 (40/0.06) is to be used.

• Control group:

  • Coronal preflaring will be performed using Gates Glidden drill.

  • Canals will be instrumented using One Shape (25/0.06) set on an electric motor with adjusted torque and speed according to the manufacturer's instructions.

  • For wide canals, One Shape Apical (30/0.06, 37/0.06) will be used.

    8.The rotary files will be introduced inside the canal using EDTA gel. 9.Canals will be irrigated with 2.5% sodium hypochlorite solution between every subsequent instrument. It is prepared by adding 10 ml of sterile distilled water to 10 ml of 5.25% sodium hypochlorite solution using a 27-gauge needle fit to 5 ml disposable plastic syringe placed as far as possible in the canal space without binding.

    10.Canals will be dried with sterile paper points and obturated using lateral condensation technique. A spreader will be used to allow space for auxiliary cones, with resin-based root canal sealer.

    11.The tooth will be sealed by temporary restoration, and postoperative pain will be assessed immediately after the end of treatment.

    12.The patient will be instructed to return to complete the treatment procedures until placing a full-coverage restoration.

    13.The patient will be instructed to take one tablet 400 mg Ibuprofen if he/she experiences severe pain.

Inclusion Criteria:

Single-rooted mandibular premolar teeth with:

• Preoperative sharp pain.
• Vital response of pulp tissue.
• Normal periapical radiographic appearance or slight widening in lamina dura.

Exclusion Criteria:

i. Patients who have already consumed preoperative medication, such as analgesic, non-steroidal or steroidal anti-inflammatory drugs, within 12 hours before treatment.

ii. Patients who have more than one tooth in the same quadrant and/or opposite quadrant that require an endodontic treatment.

iii. Pregnant females. iv. Patients having significant systemic disorder. v. If antibiotics have been administrated during the past two weeks preoperatively.

vi. Patients having bruxism or clenching. vii. Teeth that have:

• Non vital pulp tissues.
• Association with swelling or fistulous tract.
• Pocket depth greater than 5 mm.
• Previous endodontic treatment.