MMP-9/TP levels in the periapical fluid were similar when root canals were dressed with Ca(OH)<sub>2</sub> slurries mixed with NaOCl or saline (p > 0.05).<h4>Conclusions</h4>Placing a combined NaOCl/Ca(OH)<sub>2</sub> dressing significantly reduced the microbial load in the root canals of teeth with primary apical periodontitis compared to a conventional slurry prepared with saline solution, without causing any apparent inflammatory response in the periapical tissues.<h4>Trial registeration</h4>CTRI/2020/10/028484 (Clinical Trials Registry India). This evidence concerns the gene MMP9 and periapical periodontitis.