Impact of Cross-Sectional Design in Single-File Rotary System on Apical Debris Extrusion

Root canal shaping represents a critical phase in endodontic treatment, as it facilitates effective cleaning and disinfection while preserving the original canal anatomy. The objective is to create a continuously tapered conical shape from coronal to apical regions without inducing procedural errors such as canal transportation, ledge formation, zipping, or perforation.

With advancements in nickel-titanium (NiTi) technology, modern rotary systems have been developed to enhance shaping efficiency, improve debris removal, and reduce preparation time. Recently, single-file rotary systems have gained popularity due to their simplified protocols, reduced instrument fatigue, and improved clinical efficiency.

A novel concept in instrument design involves flat-sided rotary files manufactured from proprietary heat-treated NiTi alloys, such as AF One Blue and Platinum V.EU. These instruments exhibit a modified S-shaped cross-section with an inactive tip and a distinctive flat surface. The flat-sided design reduces the metal mass of the instrument, potentially enhancing flexibility, cyclic fatigue resistance,and facilitating coronal transportation of debris during instrumentation.

In contrast, One Curve is a single-file rotary system manufactured from heat treated C-wire alloy, which offers controlled memory properties, improved flexibility, and enhanced resistance to cyclic fatigue. It operates in continuous rotation and features a variable cross-sectional design that promotes efficient cutting while maintaining effective debris removal during canal preparation.

Apical extrusion of debris is an inevitable consequence of root canal instrumentation. The extrusion of dentinal debris, microorganisms, and irrigants beyond the apical foramen may induce an inflammatory response in the periapical tissues, which is considered a major contributing factor to postoperative pain. The amount of apically extruded debris has been shown to vary according to the design and kinematics of the instrumentation system used.

Despite the continuous evolution in instrument design, there is limited evidence regarding the influence of flat-sided rotary systems compared to non-flat cross-sectional systems on apical debris extrusion and postoperative pain,particularly in curved canals. Furthermore, the potential relationship between debris extrusion and the severity of postoperative pain remains insufficiently explored.