Impact of Apical Shaping Diameter on Bacterial Load Reduction in Multispecies Infected Root Canals

Aim To evaluate the impact of larger apical shaping and the efficacy of different disinfection protocols on increasing the bacterial reduction. Methods Enterococcus faecalis (E.F.) was cultivated on plate count agar (PCA) and then transferred to test tubes containing brain heart infusion (BHI) broth. Then, Pseudomonas aeruginosa (P.A.), Candida albicans (C.A.), and Proteus mirabilis (P.M.), were introduced one after the other in a specific timeline. After that, 70 lower incisors were infected by this bacterial suspension. Afterwards, these teeth were randomly divided into seven groups for different chemomechanical preparations: group A1 (25/3% + XP endo finisher XPF), A2 (25/3% + diode laser), B1 (30/3% + XPF), B2 (30/3% + diode laser), C1 (30/5% + XPF), C2 (30/5% + diode laser), and D (15/3% + syringe irrigation only). Bacterial counting was done on the PCA plates that showed us all the colonies, so it referred to the total number of microorganisms. The Wilcoxon test and the Bonferroni post hoc test were used to obtain a pairing comparison between the various groups. Results All groups induced a significantly higher bacterial reduction compared to the control group ( p < 0.001). There was no significant difference between group A1 and A2 ( p = 0.45), nor between B1 and B2 ( p = 0.22), nor between C1 and C2 ( p = 0.32), nor between B1 and C1 ( p = 0.58), nor between B2 and C2 ( p = 0.74). B1 was significantly more effective than A1 ( p < 0.001) and B2 was significantly more effective than A2 ( p < 0.001). Conclusions To remove as much bacteria as possible, it is preferred to increase the diameter of the apical part. Even with the usage of a diode laser or XPF, these methods perform better when the apical part is enlarged.