This single-arm interventional trial investigated the effectiveness of ultrasonic irrigation as an adjunct to chemomechanical procedures (CMP) in disinfecting root canals with apical periodontitis. Researchers used quantitative polymerase chain reaction (qPCR) targeting both bacterial DNA and ribosomal RNA (rRNA) to assess bacterial levels and activity. Results showed ultrasonic irrigation significantly reduced bacterial DNA levels but did not eliminate active bacteria, as indicated by persistent rRNA detection. The study highlights the limitations of ultrasonic irrigation in completely eradicating bacterial activity and suggests the need for further research into more effective disinfection strategies. The findings contribute to understanding the complexities of root canal disinfection and the challenges in achieving complete bacterial eradication.