Background/objectives <p>Post-endodontic pain remains a significant clinical challenge, impacting patient quality of life despite meticulous treatment. Its multifactorial origins include procedural factors such as foraminal enlargement and irrigation techniques, as well as patient-specific variables. While advanced irrigation activation methods like passive ultrasonic irrigation (PUI) and the XP-Endo Finisher have been shown to improve canal disinfection, their effects on postoperative pain are not fully established. We aim to compare the influence of foraminal enlargement combined with different activation methods ultrasonic and XP-Endo Finisher on postoperative pain levels in necrotic, single-rooted teeth, to identify approaches that optimize patient comfort.</p> Methods <p>We conducted a randomized, single-blind, four-arm clinical trial involving 60 patients with necrotic, asymptomatic single-rooted teeth exhibiting periapical lesions. Participants were randomly assigned to four groups: (1) foraminal enlargement with passive ultrasonic irrigation, (2) foraminal enlargement with XP-Endo Finisher activation, (3) no foraminal enlargement with passive ultrasonic irrigation, and (4) no foraminal enlargement with XP-Endo Finisher activation. Standardized root canal preparation, irrigation protocols, and obturation techniques were employed across all groups. Postoperative pain was self-recorded by patients using a visual analog scale (VAS) at 8&#xa0;h, 24&#xa0;h, 48&#xa0;h, 3 days, and 1 week post-treatment. Data were analyzed using non-parametric statistical tests to compare pain levels among groups.</p> Results <p>Analysis revealed no statistically significant differences in postoperative pain levels between the four groups at any assessed time point. Pain peaked within the first 8&#xa0;h and gradually decreased over the week across all groups. The mean pain scores showed similar temporal patterns regardless of foraminal enlargement or activation technique used. The overall trend indicated that neither foraminal enlargement nor the specific irrigation activation methods significantly influenced postoperative discomfort in the studied sample.</p> Conclusions <p>Our findings suggest that, in single-rooted necrotic teeth with periapical lesions, foraminal enlargement and the application of advanced irrigation activation techniques passive ultrasonic and XP-Endo Finisher do not significantly affect postoperative pain levels. These procedures can be incorporated into endodontic protocols without increasing patient discomfort when performed within standardized guidelines. The results underscore the importance of proper technique and disinfection strategies in achieving effective treatment outcomes while maintaining patient comfort. Further research with larger, more diverse populations and extended follow-up is warranted to confirm these findings and explore long-term effects.</p> Trial registration <p>The trial was registered on February 6, 2020, under the number (UDDS-284-21012020/SRC-1450).</p>