Effects of Sequential Antimicrobial Phases on Root Canal Microbiome Dynamics in Two-Visit Treatment of Primary Apical Periodontitis: A Longitudinal Experimental Study

Although calcium hydroxide treatment did not induce statistically significant changes in overall root canal microbial composition, trends such as a reduction in the <i>Firmicutes</i>/<i>Bacteroidetes</i> ratio and a relative increase in <i>Bifidobacterium longum</i> numbers suggest potential ecological shifts. The observed relative increase in <i>Bifidobacterium longum</i> numbers may represent a hypothesis-driven observation reflecting indirect ecological effects rather than direct pH modulation. While visual patterns (e.g., PCA clustering) were observed, they lacked statistical support. Further studies with larger sample sizes are needed to validate these observations and assess the potential role of beneficial bacteria in root canal treatments.