The aim of this clinical study is to evaluate the influence of early coronal flaring upon postoperative pain following root canal treatment in a single session approach.

All patients will be treated in a single session approach regardless of the group. All molars will be anesthetized either through infiltration in case of maxillary molars or inferior alveolar nerve block in case of mandibular molars using Octocaine 2% with epinephrine 1: 100,000 (Lidocaine HCl, Novocol Pharmaceutical, Ontario, Canada.). Rubber dam will be applied; and access will be opened using Endo access bur.

Canals will be scouted using manual patency file in a watch winding maneuver. In group A, ProGlider PG (size 16, .02 taper) instrument with a length of 25 mm will be used to the working length, then early coronal flaring will be performed using Gates Glidden drill #3 in a brushing motion away from dangerous zone. In group B no coronal flaring will be performed following minimally invasive approach.

Root canals will be copiously irrigated using 10 ml 2.5% sodium hypochlorite NaOCl (Clorox; Egyptian Company for household bleach, Egypt) delivered using 28 Gauge safety Steri Irrigation Tip (DiaDent Group International, Burnaby, BC, Canada) inserted 3 mm below cementoenamel junction. Working length will be determined using electronic apex locator Root ZX II (J. Morita Mfg. Corp, Kyoto, Japan) and confirmed radiographically using parallel technique with receptor holding device.

Canals will be irrigated again with 10ml 1.5% NaOCl, which will be delivered 2mm coronal to apical canal terminus. Irrigation will be hydro-dynamically agitated with EndoActivator device (Dentsply Maillefer, Baillagues, Switzerland) using yellow tips #15/02 inserted 2mm short of working length for 60 seconds. ProGlider PG (size 16, .02 taper) instrument with a length of 25 mm will be used to the working length. Root canals will be shaped using ProTaper next rotary Ni-Ti files (Dentsply Maillefer, Baillagues, Switzerland) till # X3 (Elnaghy et al. 2014). Each file will be used in one molar. Finally, Root canals will be obturated using cold lateral compaction technique. The molars will be permanently restored using composite resin restoration and will be scheduled for extra coronal restoration.

Inclusion Criteria:

• 1. Patient age above 18-70 years old.

  • 2. Both males and females will be included.
  • 3. All patients are in a good health without systemic condition.
  • 4. The offending tooth is a molar.
  • 5. The offending molar is indicated for root canal treatment.
  • 6. One molar for every patient.
  • 7. All patients will sign an informed consent.

Exclusion Criteria:

• 1. Necrotic molars

  • 2. The offending tooth has previous attempt of pulp therapy or root canal treatment.
  • 3. The patient showing any clinical or radiographic evidence of periapical pathosis.
  • 4. Patients received analgesics or systemic antibiotic prior to treatment.
  • 5. Immunocompromised patients.
  • 6. Any unknown infectious disease (e.g. HBV, HCV, HIV, or T.B.)
  • 7. History of cancer with radio or chemotherapy.
  • 8. Offending molar with mobility score ≥2.
  • 9. Offending molar with pocket depth ≥6mm.
  • 10. Immature molars.
  • 11. Nonodontogenic pain.
  • 12. Patients with more than one tooth requiring endodontic intervention