Effects of Instrumentation and NaOCl Concentration on Microbial DNA Load Employing a Sonic Activation Device

To evaluate the bacterial DNA load reduction in mesial root canals of mandibular molars using quantitative polymerase chain reaction, examining the effects of instrumentation, irrigant type, and their interaction after the use of sonic activation.

Twenty-one extracted human mandibular molars were sterilized and contaminated with human supragingival plaque under anaerobic conditions for 14 days. After sealing the apices and coating external surfaces to simulate a closed canal system, the teeth were randomly assigned to 3 irrigant groups (n = 7): 7.55% sodium hypochlorite, 1.88% sodium hypochlorite, or sterile saline. Microbiologic sampling was performed at baseline (S1), after preparation to size 25/.04 with sonic activation (S2), and after enlargement to size 30/.04 with sonic activation (S3). Bacterial DNA was quantified by quantitative polymerase chain reaction (Log₁₀ molecules/μL). Data were analyzed using two-way repeated-measures ANOVA with Geisser-Greenhouse correction and Tukey's honest significant difference tests.

The interaction between irrigant type and instrumentation was not significant (P = .852), and irrigant type alone showed no significant effect (P = .502). In contrast, instrumentation significantly reduced bacterial load (P < .0001), accounting for 68.44% of variance. Significant reductions occurred from S1 to both S2 and S3, with no difference between S2 and S3, indicating that most of the decrease in bacterial DNA load occurred during initial enlargement to size 25/.04 with sonic-activated irrigation.

Root canal instrumentation combined with sonic activation was the most significant factor associated with reduction in bacterial DNA load, while irrigant type and concentration provided minimal additional effect.