Post-endodontic pain is an annoying experience for the patient, undermining the patient-clinician relationship . Despite major improvements in armamentarium and pharmacologic interventions, pain after endodontic treatment remains to be a major problem.

                      Dentin and pulp tissue debris, microorganisms and irrigating solutions may extrude into periradicular tissues during the preparation of root canals , thus causing complications such as postoperative pain and flare ups. All instruments and techniques that are used for root canal preparation may cause extrusion of different amounts of root canal contents outside the apical foramen . It has been reported that the amount of extruded contents may be influenced by the design and kinematics of endodontic files .

                         The concept of single-file canal preparation was introduced in endodontics  with the launch of  Wave One instrumentation system. These instruments are fabricated with a nickel-titanium alloy called M-Wire using an innovative thermal treatment .The reciprocating motion involves an initial rotation of the instrument in a counter clockwise direction, during which the instrument penetrates and cuts the dentin, and then a rotation in the opposite direction, during which the instrument is released.Several studies have shown that a single file reciprocating system produced more debris extrusion than single file rotary systems.

                          Periapical extrusion of debris is the main cause for postoperative pain after root canal treatment. The purpose of this investigation is to evaluate the post operative pain after root canal treatment  in patients with necrotic mandibular molar teeth  using two different instrumentation techniques: single file rotary and single file reciprocation .