Antibacterial activity and smear layer removal efficiency of silver nanoparticles as a final irrigant against Enterococcus faecalis using confocal laser scanning microscopy and scanning electron microscopy

Abstract Introduction: Silver nanoparticles (AgNPs) have garnered significant attention for their potent antibacterial properties, making them promising candidates for use as root canal irrigants in endodontics. The persistent presence of Enterococcus faecalis in treated root canals often leads to endodontic failures. This study aimed to evaluate the effectiveness of neem-synthesized AgNPs, chemically synthesized AgNPs, sodium hypochlorite (2.25%), and saline solution in reducing viable bacteria and removing smear layers in E. faecalis -infected mandibular premolar teeth. Materials and Methods: After decoronation, mandibular premolar, single-rooted, teeth (120) were instrumented until ProTaper Gold F3. In all samples, inoculation of E . faecalis was done and divided into four groups depending on the irrigating solution used into Group A: neem-synthesized AgNPs, Group B: chemically synthesized AgNPs, Group C: sodium hypochlorite (2.25%), and Group D: saline solution. After irrigation, roots were divided longitudinally and analyzed for confocal laser scanning microscopy and scanning electron microscopy. Data were statistically analyzed using Tukey’s honestly significant difference test. Results: The minimum reduction in live bacteria percentage was seen in Group C rather than Groups A and B; although there was no significant difference between them. Group D showed the maximum percentage of live bacteria and a greatest score of smear layer compared to other groups. In contrast to Group B, Group A scored higher, although the results were nonsignificant. Group C showed the least score of smear layer presence. The P value between the experimental groups was found to be <0.05, indicating statistical significance. Conclusion: Both neem-synthesized AgNp and sodium hypochlorite irrigants reduced the proportion of viable bacteria most significantly. This work demonstrates the possibility of employing nanoparticles as an irrigant that can effectively remove smear layers while also acting as an antimicrobial.