The Effect of Endodontic Disinfection on Microbial Reduction and Biodiversity of Root Canal Systems with Necrotic...

To analyze microbial reduction and diversity changes after cleaning and shaping procedures, and calcium hydroxide interappointment medication. The influence of clinical and radiographic factors was assessed as well.

Thirty-two teeth diagnosed with pulp necrosis and evidence of apical periodontitis were included. Five samples were collected on each tooth: surface sample before access (C1), before treatment (S1), after cleaning and shaping with ultrasonic irrigant activation (S2), at the second visit before removal of the temporary restoration (C2), and after removal of calcium hydroxide (S3). All samples were processed using quantitative real-time polymerase chain reaction (qPCR) and 16S rRNA next-generation sequencing. The Shannon and Chao1 indices were used to measure alpha diversity. Differences in abundances of genera were evaluated using the Kruskal-Wallis test. Differences in community composition (beta diversity) were evaluated using analysis of similarity (ANOSIM) with Bray-Curtis dissimilarity matrices.

The qPCR analysis revealed significant differences between S1 and S2 as well as between S1 and S3 (P = .0001). No significant differences between S2 and S3 were observed for qPCR (P = .400) as well as for Chao1 alpha diversity. ANOSIM revealed differences between S1 and S3 (P < .001, R = 0.59), and between S1 and S2 (P < .001, R = 0.40). Microbial composition differed according to percussion sensitivity (ANOSIM R = 0.07, P = .023) and sinus tract presence (ANOSIM R = 0.06, P = .03), although the effect sizes were small. Most of preoperative taxa (top 20) found before treatment were significantly impacted by root canal procedures except Peptostreptococcus and Clostridiales (P > .05). The relative abundance of Schaalia (P = .004) and Enterococcus (P = .001) increased significantly after treatment.

A significant reduction in microbial load after instrumentation (S2) and after calcium hydroxide medication (S3) was observed. The effect on root canal composition (beta diversity) was impacted after the cleaning and shaping. No additional changes in qPCR and beta diversity were observed after the use of calcium hydroxide. The effects produced by clinical factors although significant were low, and the results reinforce the value of robust chemical and mechanical disinfection procedures.