Impact of Taper Design on Cleaning Efficacy, Stress Generation, and Irrigant Performance: A Combined Experimental, Finite Element Analysis, and Computational Fluid Dynamics Assessment

<b>Background/Objectives:</b> 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. <b>Methods:</b> Transparent 3D replicas of mandibular mesial roots filled with a gel-like pulp tissue were instrumented with the three systems (<i>n</i> = 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. <b>Results:</b> All systems left residual tissue, with no statistically significant differences in cleaning efficacy among them (<i>p</i> > 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. <b>Conclusions:</b> Cleaning efficacy was comparable across systems. CFD/FEA from representative models illustrated patterns of irrigant dynamics and dentin preservation without supporting system superiority.