Root canal samples of 15 necrotic immature teeth were analyzed by quantitative polymerase chain reaction. Bacteria were counted before treatment (S1), after irrigation with 6% NaOCl (S2), and after intracanal dressing (S3) using either triple antibiotic paste (TAP) (n = 7) or calcium hydroxide with chlorhexidine (CHP) (n = 8). The Wilcoxon test for related samples and the Mann-Whitney test were used for statistical analysis (p < 0.05). After a follow-up period of 12-48 months, clinical and radiographic findings were correlated with microbiological data using a linear regression model (p < 0.05).
All S1 and S2 samples were positive for bacteria, but the number of positive S3 samples decreased to 53.3% (p = 0.001). Overall, there was a significant reduction of bacterial levels after each treatment step (S1-S2, p = 0.001; S2-S3, p = 0.02). In TAP and CHP groups, 57.1% and 50% of S3 samples were positive, with median numbers of 6.97 x 10 and 3.59 x 10 bacterial cells, respectively. No significant differences were found between groups. Periapical healing occurred in all cases despite the presence of low levels of residual bacteria. However, the latter had a negative impact on the thickness of dentinal walls (R = 0.0043).
Although the bacterial levels were drastically reduced after the regenerative endodontic procedures, residual bacteria influenced on the thickness of dentinal walls.
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