Determination of minimum instrumentation size for penetration of diode laser against Enterococcus faecalis in root canals using scanning electron microscope: An in vitro study

Aim: The aim of this study was to determine minimum instrumentation size for penetration of diode laser against Enterococcus faecalis in root canals using scanning electron microscope (SEM). Methodology: Fifty-five single-rooted human permanent maxillary anterior teeth were selected. The sterilized specimens were inoculated with 5 μl E. faecalis culture grown in diluted brain–heart infusion broth and incubated at 37°C for 4 weeks. After 4 weeks, 5 samples were selected as baseline group to evaluate the depth of penetration of E. faecalis. Remaining 50 samples were divided into 5 groups based on the apical enlargement size using ProTaper file system: Group 1 – canal preparation done till #F1 size file; Group 2 – canal preparation done till #F2 size file; Group 3– canal preparation done till #F3 size file; Group 4 – canal preparation done till #F4 size file; Group 5 – canal preparation done till #F5 size file. The canals were prepared and then irradiated with 940 nm diode laser at a power setting of 1.5W for 5 s. The procedure was repeated 4 times with intervals of 10 s between each one. All the samples were then transversely sectioned at 2 mm and 5 mm from the apex. Each section was then examined under a SEM to evaluate the depth of penetration of E. faecalis in the baseline group and depth of penetration of diode laser in the experimental groups. The results were analyzed using the two-way ANOVA and Tukey's multiple post hoc test. Results: Depth of penetration of laser was highest in Group 3 in apical third region and was statistically significant when compared to Group 1 and Group 2 in the middle and apical third regions. However, no statistically significant difference was noted between Group 3, Group 4, and Group 5. Conclusion: It can be concluded that the apical instrumentation to a size F3 using ProTaper file system along with irradiation using a diode laser showed a greater depth of penetration into dentin and thus reducing residual microorganisms. Furthermore, conserving as much tooth structure as possible, thereby increasing the predictability of success