Objective: This study investigated the shaping efficiency of four reciprocating systems—WaveOne Gold, Reciproc Blue, Excalibur, and One Reci—in three dimensional (3D) resin models of natural mandibular premolar teeth with two canals. Methods: Forty 3D-printed mandibular premolars (Vertucci configuration type V) were divided into four groups, each of which was assigned one of the reciprocating systems. According to the manufacturer’s protocols, each canal was prepared, with pre- and post-instrumentation micro computed tomography (micro-CT) scans evaluating canal volume, surface area, percentage of unprepared canal walls, and resin reduction in the pericervical area. Instrumentation time and screw-in sensation were recorded as qualitative performance indicators. Statistical analysis was performed using one-way ANOVA and chi-square tests with a significance of (p < 0.05). Results: All systems increased canal volume and surface area, primarily in the apical third, with Reciproc Blue and One Reci achieving the largest volume. WaveOne Gold had the highest percentage of unprepared walls (27.03%) and Reciproc Blue the lowest (19.65%), though these differences were not statistically significant (p > 0.05). Reciproc Blue caused the highest pericervical resin loss (22.24%), significantly higher than Excalibur (15.09%) and One Reci (15.17%) (p = 0.035). Reciproc Blue exhibited the highest incidence of screw-in sensation (70%), while WaveOne Gold achieved the shortest instrumentation time (86.7 s), although neither variable showed statistical significance. Conclusions: All systems effectively shaped complex canal anatomies, with Reciproc Blue demonstrating the highest dentin removal and WaveOne Gold proving the most time efficient. Clinically, these findings suggest that instrument selection should balance shaping efficiency with dentin preservation. Minimizing unprepared areas and preserving pericervical dentin are essential for enhancing disinfection and reducing the risk of root fractures, ultimately contributing to the long-term success of endodontic treatment.

Background/Objectives: This study aimed to compare the cleaning efficacy, biomechanical stress distribution under simulated occlusal loading after instrumentation, and irrigant dynamics of three NiTi rotary systems, namely ProTaper Gold, TruNatomy, and SlimShaper, using a combined experimental, finite element analysis (FEA), and computational fluid dynamics (CFD) approach. Methods: Transparent 3D replicas of mandibular mesial roots filled with a gel-like pulp tissue were instrumented with the three systems (n = 13 per group). Standardized irrigation was performed with 4% NaOCl delivered through IrriFlex^® needles positioned 2 mm from the working length. Cleaning effectiveness was assessed through digital image analysis, FEA simulation of occlusal loading, and CFD evaluation of irrigation flow, wall shear stress, and dynamic pressure. Results: All systems left residual tissue, with no statistically significant differences in cleaning efficacy among them (p > 0.05). Descriptively, ProTaper Gold showed the lowest mean residual tissue (0.15 ± 0.25%), followed by SlimShaper (2.50 ± 3.81%) and TruNatomy (4.20 ± 5.12%). CFD revealed that ProTaper Gold generated the highest irrigant velocities and wall shear stresses, while SlimShaper showed the highest dynamic pressure. FEA indicated that ProTaper Gold produced the highest stress concentrations, especially in the pericervical dentin, whereas TruNatomy and SlimShaper preserved more dentin. Conclusions: Cleaning efficacy was comparable across systems. CFD/FEA from representative models illustrated patterns of irrigant dynamics and dentin preservation without supporting system superiority.