Shear stress dynamics in root canal irrigation: a systematic review of computational fluid dynamics studies on syringe irrigation with various needle designs.

The efficacy of endodontic therapy is critically dependent on effective irrigation, which facilitates the removal of debris and biofilm from anatomical regions inaccessible to mechanical instrumentation. Computational Fluid Dynamics (CFD) offers an in silico framework for analyzing irrigant flow dynamics and wall shear stress distribution across varying needle designs and canal morphologies. This systematic review was conducted in accordance with PRISMA 2020 guidelines and registered on the Open Science Framework (DOI: 10.17605/OSF.IO/CYNME). A comprehensive search of PubMed, Scopus, and Web of Science through September 2025 identified CFD studies evaluating syringe-based irrigation with diverse needle configurations. Inclusion criteria encompassed in silico investigations assessing WSS within simulated or extracted root canal systems. Data regarding needle type, flow parameters, apical preparation size, and shear stress outcomes were extracted and synthesized qualitatively. Of the 151 records initially identified, 36 studies met the eligibility criteria, and 10 CFD studies provided needle-specific WSS data. Across these models, open-ended needles consistently produced the highest and most apically concentrated WSS and apical pressure, whereas side-vented needles yielded moderate WSS with comparatively lower pressure. Double side-vented and modified multi-outlet designs demonstrated a reduction in peak stress while enhancing wall coverage. Smaller apical preparations and narrow canal tapers were associated with elevated WSS, while larger preparations attenuated WSS and facilitated smoother flow dynamics. These trends are consolidated within a structured evidence map and a heatmap summarizing the directionality and relative magnitude of WSS across studies. CFD-based evidence highlights the critical influence of needle geometry and canal morphology on irrigation efficacy and safety. Side-vented needles emerge as the most clinically balanced configuration, while open-ended designs warrant cautious application. Advancing the standardization of CFD protocols and integrating anatomically realistic canal models are imperative for improving translational applicability and informing evidence-based irrigation strategies in contemporary endodontic practice. https://doi.org/10.17605/OSF.IO/CYNME.