Quantitative SEM assessment of apical foramen morphology after instrumentation with VDW Rotate and MicroMega One RECI at two preparation limits

This ex vivo study quantitatively assessed apical foramen morphology after instrumentation with VDW Rotate and MicroMega One RECI at two preparation limits. Sixty extracted human mandibular premolars with single straight canals were assigned to four groups ( n = 15) according to instrumentation system and preparation limit. Rotate and One RECI were used either at the apical foramen (AF) or 1 mm short of it (AF-1 mm). Scanning electron microscopy images were obtained before and after instrumentation. Foraminal area, circularity, and Feret diameter ratio were measured using ImageJ. Data were analysed using two-way aligned rank transform ANOVA, with Mann–Whitney U and Wilcoxon signed-rank tests for follow-up and paired comparisons. Foraminal area increased after instrumentation in all groups. Preparation at AF resulted in significantly greater ΔArea than preparation at AF-1 mm (preparation-limit main effect, p = 0.001), with no instrumentation-system main effect or instrumentation system × preparation-limit interaction for ΔArea. No significant differences were found between systems for ΔArea at corresponding preparation limits. Circularity and Feret diameter ratio showed no significant within-specimen changes, suggesting foraminal enlargement without statistically detectable changes in the assessed two-dimensional shape-related parameters. Under the tested straight-canal conditions, the preparation limit had a greater influence on foraminal enlargement than the tested system-level differences.