The goal of this clinical trial is to compare the post-operative pain occurrence after single visit root canal treatment using Two NiTi Rotary Files. The main question it aims to answer is:

• Does an instrument design and instrumentation technique could affect postoperative pain incidence and intensity? Researchers will use ProTaper Universal rotary system or M-Pro rotary system for root canal preparation and compared postoperative pain intensity.

Participants will receive single visit endodontic treatment using either ProTaper or MPro systems for root canal preparation.

Participants will record Pain intensity at 24 hours and 7 days post-operative. Analgesics will be prescribed for the patients in need.

The main cause of patient fear is expecting pain during root canal treatment. It is considered a major concern for dentists as well. During root canal preparation, periapical extrusion of pulpal tissue remnants, microorganisms or dentin chips may be one of the causes of postoperative pain. Depending on the fact that, instrument design and instrumentation techniques have an impact on the amount of extruded debris apically, many studies proved the ability of some rotary systems to reduce debris extrusion, permitting to achieve less pain sensation.

Therefore, the present clinical study aims to compare the postoperative pain intensity in molars with symptomatic irreversible pulpitis after single endodontic treatment visit using a full-sequence rotary Ni-Ti system either ProTaper or MPro systems Eighty patients with symptomatic irreversible pulpitis in mandibular first molars will be assigned into two groups. In group A (n=40): root canal preparation will be performed in single visit using ProTaper Universal system and in group B (n=40): root canal preparation will be performed in single visit using M-Pro rotary system. Pain intensity will be recorded by the patient using Numerical Rating Scale (NRS) at 24 hours and 7 days postoperative. Analgesics will be prescribed for the patients in case of need.

Inclusion Criteria:

• Patient's diagnosis is symptomatic irreversible pulpitis in mandibular first molar.
• Males and females patients in a good health.
• Aged from 25 to 45 years old.
• Pulp vitality is confirmed with cold pulp test and an electric pulp test.

Exclusion Criteria:

• Pregnant females.
• Patients complaining from pain in more than one molar on the same side.
• Patients whose teeth react positively to percussion test.
• Patients who receive analgesics 12 hours before the start of the root canal treatment.
• Teeth having grade 2 or 3 mobility.
• Presence of periapical radiolucency or teeth with extra oral or intraoral sinus tract or fistula.