Influence of Continuous Rotation Versus Reciprocation Motion of MG3 Blue Rotary File on Postoperative Pain and Intracanal Bacterial Reduction of Teeth With Necrotic Pulps.

Background and RationaleA fundamental aim of root canal therapy is controlling pain and resolving apical periodontitis by thoroughly disinfecting the root canal system. Residual bacteria-particularly virulent species like Enterococcus faecalis-and their byproducts inside dentinal tubules are the leading cause of post-treatment complications and endodontic failure. During instrumentation, extruded infected debris can injure periapical tissues, triggering an inflammatory immune response and leading to postoperative pain and flare-ups. While previous research has evaluated how reciprocating versus continuous rotary systems affect postoperative pain and remaining bacteria, most studies used different file designs, cross-sections, or numbers of files, making it difficult to determine whether outcomes were driven by kinematics or file characteristics. This randomized clinical trial isolates the effect of motion kinematics by using identical MG3 Blue rotary files under two different motion dynamics. Study ObjectivesTo compare the effect of different kinematics (continuous rotation versus reciprocation) using MG3 Blue rotary files on:The intensity of postoperative pain. The amount of remaining intracanal cultivable bacteria. Trial DesignType: Parallel, single-center, randomized controlled trial (superiority framework). Allocation Ratio: 1:1. Setting: Post-graduate outpatient clinic of the Endodontics Department, Faculty of Dentistry, Cairo University, Egypt. Participants and Eligibility CriteriaInclusion Criteria:Patients aged between 18 and 50 years (males and females). Systemically healthy (ASA I or II) with no history of anti-inflammatory or antibiotic medications in the past month. Mandibular premolars presenting with a single canal and non-vital pulps (negative response to ethyl chloride cold test, absence of spontaneous pain, and no apical periodontitis). Patients capable of understanding the pain scale and signing the informed consent. Exclusion Criteria:Medically compromised patients (ASA III or IV), pregnant females, or teeth with swelling, fistulous tracts, acute/chronic periapical abscesses, grade II/III mobility, previous root canal therapy, non-restorable structure, or open/immature apices. Intervention Procedures \& Protocol StepsPreoperative Evaluation: Medical/dental history collection and baseline pain assessment using a Modified Visual Analogue Scale (VAS). Local Anesthesia \& Disinfection: Local anesthesia administration followed by disinfection of the oral cavity using 0.2% chlorhexidine gluconate mouthwash and rubber dam isolation. Access Cavity \& Working Length: Access cavity preparation, followed by patency confirmation using stainless steel K-files (#10 and #15). Working length is determined via an electronic apex locator and verified radiographically to be 1 mm shorter than the radiographic apex. Pre-instrumentation Sampling (S1): Initial intracanal microbiological samples are collected using sterile paper points retained for 60 seconds (placed in LAL water for endotoxin assay and VMGA III transport medium for microbial cultivation). Randomized Mechanical Preparation: Patients are allocated via computer-generated randomization to one of two groups: Intervention Group (Reciprocation Motion): Canals are prepared using MG3 Blue rotary files in reciprocation motion (#20/0.10, #15/0.03, #20/0.04, #25/0.04, #30/0.04, and #35/0.04 at 300 RPM and 2 Ncm torque). Comparator Group (Continuous Rotation Motion): Canals are prepared using the same MG3 Blue rotary files in continuous rotation motion following manufacturer instructions (same sizes, 300 RPM, and 2 Ncm torque). Irrigation Protocol: Canals are thoroughly irrigated between file sizes using 3 mL of 2.25% sodium hypochlorite via a 27-gauge side-vented needle, finalized with a saline wash. Post-instrumentation Sampling (S2): Second microbial sample collected identically to S1. Canals are dried, temporarily sealed, and patients are scheduled for a 7-day follow-up appointment for root canal obturation via warm vertical compaction. Outcomes and AssessmentPrimary Outcome: Post-instrumentation pain measured at 72 hours post-procedure using the Visual Analogue Scale (VAS ranging from 0 to 10). Secondary Outcomes:Post-instrumentation pain measured at 7 days post-procedure. Amount of remaining intracanal cultivable bacteria measured via microbiological culture techniques in colony-forming units (CFU/mL) pre- and post-instrumentation.