Efficacy of Different Disinfection Technologies in Molar Non-Surgical Retreatment

Post-treatment apical periodontitis in root canal-treated teeth is caused by persistent, secondary, or recurrent intra-canal infection. The complex anatomy of the root canal system-including isthmuses, fins, and lateral canals-can limit the effectiveness of conventional instrumentation and irrigation, allowing microbial biofilms to persist. As a result, nonsurgical endodontic retreatment often presents a lower success rate compared with primary root canal treatment. Conventional retreatment protocols typically involve mechanical debridement using nickel-titanium rotary instrumentation combined with irrigation using sodium hypochlorite. Irrigation activation techniques such as passive ultrasonic irrigation (PUI) are commonly used to improve irrigant penetration and enhance removal of debris and bacteria from complex canal anatomy. However, these techniques may still be limited in their ability to completely eliminate microbial biofilms and may carry a risk of irrigant extrusion. The GentleWave System (GWS) is an advanced irrigation technology that uses multisonic energy, negative pressure, and optimized fluid dynamics to enhance tissue dissolution and microbial removal throughout the root canal system. This system allows effective disinfection while minimizing the need for extensive mechanical instrumentation, potentially supporting minimally invasive endodontic approaches. Although studies have demonstrated promising results, well-designed randomized clinical trials evaluating its effectiveness in retreatment cases remain limited. This randomized clinical trial will compare the disinfection efficacy of GWS with a conventional retreatment protocol consisting of nickel-titanium rotary instrumentation combined with PUI in molars diagnosed with post-treatment apical periodontitis. Microbiological samples will be collected before treatment and prior to obturation. Intracanal bacterial load will be quantified using quantitative real-time polymerase chain reaction (qPCR), and microbial community composition will be analyzed using next-generation sequencing (NGS). In addition, residual organic debris will be evaluated using the chairside device Endocator, which provides a rapid quantitative Endoscore to determine the degree of disinfection of each group. The primary outcomes of the study are reduction in intracanal bacterial load and changes in microbial composition following disinfection. Secondary outcomes include the efficacy of the chairside device Endocator in disinfection of the root canal, compared with PCR-based methods as well as facultative bacterial culturing, and short-term postoperative pain assessment. These findings from this study aim to provide high-quality clinical evidence regarding the comparative effectiveness of advanced irrigation technologies versus conventional disinfection protocols in endodontic retreatment.