Different Kinematics Within a Single-File System and Postoperative Pain

This prospective, randomized, parallel-group clinical trial will evaluate whether the kinematics used during root canal instrumentation with a single-file system influence postoperative pain and the local expression of pain-related neuropeptides. The trial will be conducted in adult patients requiring endodontic treatment of mandibular molars. Eligible participants will be enrolled after clinical and radiographic assessment and after obtaining written informed consent.

Participants will be randomly allocated to one of five treatment groups. In all groups, canal shaping will be performed using the same One Curve nickel-titanium single-file system, while the kinematic motion used to activate the file will differ between groups. The tested kinematics will include CanalPro Jeni motion, continuous clockwise rotation, optimum torque reverse motion, forward reciprocating motion, and twisted adaptive motion. This design allows the effect of instrument motion to be assessed while maintaining the same file system across all study arms.

All treatments will be performed under standardized clinical conditions. Local anesthesia will be administered and the tooth will be isolated with a rubber dam. Access cavity preparation, canal identification, manual scouting, working length determination, and radiographic confirmation will be completed using a standardized approach. Initial irrigation will be performed before instrumentation, and the allocated kinematic protocol will then be used for canal preparation according to the study protocol.

Periapical fluid samples will be collected using sterile paper points at predefined procedural time points. The sampling schedule will include collection during the initial stage of canal preparation, after instrumentation, and at the follow-up visit. Samples will be transferred to sterile tubes and stored under appropriate laboratory conditions until analysis. The collected samples will be analyzed using enzyme-linked immunosorbent assay methods to quantify selected neuropeptides associated with inflammatory pain response, including substance P and calcitonin gene-related peptide.

The clinical treatment will be completed over two visits. At the first visit, the canals will be prepared using the allocated kinematic protocol and irrigated using a standardized irrigation sequence. Intracanal medicament will be placed between visits, and the tooth will be temporized. At the second visit, patient-reported pain and percussion sensitivity will be recorded, the temporary restoration and intracanal medicament will be removed, and periapical fluid will be collected before completion of the final irrigation protocol. The canals will then be dried, obturated using gutta-percha and resin-based sealer, and restored with an adhesive restorative material. A postoperative radiograph will be taken as part of routine treatment documentation.

Postoperative pain will be recorded by the participant at scheduled time points after treatment using a standardized pain scale. Clinical follow-up information and laboratory biomarker data will be collected using structured forms. The trial procedures will be performed by trained clinicians, and laboratory analysis will be performed according to the manufacturers' instructions for the selected assay kits. Data handling and storage will follow institutional requirements for clinical research.

The analysis will compare postoperative pain scores and biomarker levels between the five kinematic groups. Descriptive statistics will be used to summarize participant characteristics, pain scores, and biomarker concentrations. Appropriate statistical tests will be selected according to the type and distribution of the data. The analysis will assess whether differences in file kinematics are associated with differences in patient-reported postoperative pain and changes in pain-related neuropeptide levels.