The effect of apical preparation size and passive ultrasonic activation on microbial load in root canals with periapical lesions.

This study compares intracanal bacterial reduction between two apical enlargement approaches in teeth with periapical lesions, evaluating the influence of shaping size with irrigation activation during root canal treatment. Twenty-four patients were divided into two groups: minimally invasive (25/0.04) and conventional (35/0.04). Root canal samples were obtained before and after chemomechanical preparation and passive ultrasonic irrigation (PUI). Bacterial load was quantified by droplet digital PCR, and bacterial species were identified by sequencing. Both groups demonstrated a significant reduction in bacterial load exceeding 95% (p < 0.01), with no significant intergroup differences (p > 0.05). The conventional group exhibited higher preoperative pain scores (p = 0.042), while postoperative pain levels were comparable between groups. Pseudomonas spp. were more prevalent at baseline in the conventional group (p = 0.048). Despite effective bacterial reduction in both groups, Enterococcus faecalis and Pseudomonas persisted after treatment, indicating the need for improved disinfection protocols and activation techniques for resistant biofilm-forming microorganisms.Trial registrationThe protocol was registered at www.clinicaltrials.gov (NCT07005219) on 22/5/2025.