Comparative Evaluation of Calcium Hydroxide Removal from Curved Root Canals Using Flexible and Side-Vented Irrigation Needles: An In Vitro Study

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Abstract The aim of the study is to compare the relative effectiveness of a flexible polypropylene irrigation needle (flexible polypropylene irrigation needle) and a stainless-steel side-vented needle (side-vented stainless-steel needle) in removing calcium hydroxide from moderately curved root canals using a standardized in vitro model. Thirty-six extracted molars (15–25° curvature) were randomly assigned to two groups (n = 18). Following canal preparation and 7-day calcium hydroxide placement, removal was performed using either a side-vented stainless-steel needle or flexible polypropylene irrigation needle. Residual material was assessed in the cervical, middle, and apical thirds using a validated ordinal scoring system under stereomicroscopy. Examiner reliability and effect sizes were calculated. To isolate the effect of needle geometry on irrigant delivery, no auxiliary sonic or ultrasonic activation was employed. The side-vented stainless-steel needle group showed significantly higher residual scores in the apical third (p <0.05), whereas no significant differences among thirds were observed in the flexible polypropylene irrigation needle group. Intergroup comparison revealed lower apical scores with flexible polypropylene irrigation needle (p = 0.036; r = 0.37). Within the limitations of a two-dimensional semi-quantitative evaluation model, the flexible polypropylene irrigation needle demonstrated improved apical cleaning performance compared with a conventional stainless-steel needle in curved canals. These findings should be interpreted as comparative rather than quantitative evidence, and further validation using three-dimensional imaging techniques is warranted.