Effect of Instrumentation Kinematics on Intraoperative and Post-operative Pain in Maxillary Premolars With Acute Irreversible Pulpitis: A Randomized Clinical Trial

Post-endodontic pain refers to the discomfort experienced following endodontic procedures. The incidence of post-operative pain is reported to be 25-40% regardless of the pulp and periradicular condition. It has been shown that pain prevalence declined from 40% in the first 48 h after treatment to 11% 7 days post-treatment. The mechanisms behind post-endodontic pain are complex and multifactorial that include host-dependent factors such as host immunity and preoperative pain history as well as operator-related factors such as chemical, mechanical or bacterial injury that occurs during endodontic procedure. A major contributor to this pain is the extrusion of infected debris as dentin chips, microorganisms, and the remnants of pulp tissue to the periradicular area. The intensity of pain is directly proportional to the extent of tissue injury caused.

During root canal preparation, a variety of materials including dentin debris, pulp remnants, microorganisms, endotoxins, and irrigating solutions may be extruded into the periapical tissues, potentially leading to inflammation, increased vascular permeability, oedema, nerve compression and postoperative pain. Studies suggest that apical extrusion is affected by file systems, file kinematics and instrumentation techniques used during root canal preparation .

Rotary systems vary in the amount of debris they extrude due to variations in cross-sectional design, flute depth, cutting blade, kinematics, taper, file sequence, tip size and cutting efficiency. Both rotary and reciprocating NiTi files are effective in reducing endotoxins and bacterial by-products from infected root canals. NiTi files enhance biomechanical preparation and canal centering and exhibit greater resistance to cycle fatigue due to their super elasticity and

greater flexibility. However, the extent of periapical inflammation may differ among NiTi systems due to variations in the amounts of extruded irritantsEdgeOne Fire reciprocating system (EdgeEndo, Albuquerque, New Mexico, USA) features a parallelogram cross-section having two cutting edges and an off-center design. these endodontic instruments are treated with a proprietary heat process called FireWire™, that it is claimed to provide high flexibility and a negligible restoring force. It operates using alternating cutting and releasing angles through a reciprocating motion; with an exchange in the direction of rotation.

Jizai rotary file systems (JZ) (MANI, Tochigi, Japan) is a recently developed NiTi rotary system made of a proprietary heat-treated NiTi alloy. JZ system exhibits bending deformation indicating that it is not purely austenitic but contains R-phase and/or martensite at room or body temperature. It has an off-center quasi-rectangular cross-section with a radial land on one of the short sides. According to the manufacturer, this cross-sectional design produces low screw-in forces owing to the radial land and provides wide spaces for debris removal. EdgeOne Fire reciprocating system (EdgeEndo, Albuquerque, New Mexico, USA) features a parallelogram cross-section having two cutting edges and an off-center design. these endodontic instruments are treated with a proprietary heat process called FireWire™, that it is claimed to provide high flexibility and a negligible restoring force. It operates using alternating cutting and releasing angles through a reciprocating motion; with an exchange in the direction of rotation.

Jizai rotary file systems (JZ) (MANI, Tochigi, Japan) is a recently developed NiTi rotary system made of a proprietary heat-treated NiTi alloy. JZ system exhibits bending deformation indicating that it is not purely austenitic but contains R-phase and/or martensite at room or body temperature. It has an off-center quasi-rectangular cross-section with a radial land on one of the short sides. According to the manufacturer, this cross-sectional design produces low screw-in forces owing to the radial land and provides wide spaces for debris removal.A systematic review of the literature suggested that debris extrusion is influenced by instrument kinematics . However, evidence is still conflicting and sometimes even contradicting regarding the association of kinematics with debris extrusion and post-operative pain.