Park, Ki Hong2025-01-282025-01-282022-08https://hdl.handle.net/11299/269518University of Minnesota M.S. thesis. August 2022. Major: Dentistry. Advisor: William Noblett. 1 computer file (PDF); vii, 46 pages.Introduction: The purpose of this study was to analyze the antimicrobial activity in extracted molars with a history of pulp necrosis after conventional treatment with passive ultrasonic irrigation (PUI) technique or minimal instrumentation with multisonic irrigation. Materials and Methods: Twenty-three extracted mandibular molars were prepared for collection of superficial (crown surface control), pre-treatment and post-treatment samples. The teeth were divided into two groups: Group 1: Conventional treatment with PUI (n=11), Group 2: Minimal instrumentation with multisonic irrigation (n=12). The collected samples were processed with 16S rRNA high-throughput sequencing to measure microbial diversity before and after the antimicrobial treatment. The Chao1 index, and Shannon index evaluated alpha diversity, and the Bray-Curtis dissimilarity test was used to measure beta diversity and was visualized by ordination using principal coordinate analysis (PCoA). Kruskal-Wallis test was performed to evaluate the differences in abundances of genera and abundance of each genera in the samples. Differences in each community composition were evaluated using analysis of similarity (ANOSIM) with Bonferroni correction for multiple comparisons. Results: The total number of reads in biological samples ranged from 2 to 120,298. The numbers of OTUs showed a significant difference from pre-treatment to post-treatment in conventional treatment, whereas no significant difference was observed in minimal instrumentation with multisonic irrigation (p < 0.001). Overall, pre-treatment samples presented greater relative abundance of Lactobacillus, Parvimonas, Prevotella, Lacticaseibacillus in the minimal-instrumentation group than in the conventional group although without statistical significance. After treatment, there was a significantly greater reduction of Eubacterium using conventional treatment with PUI and a significantly greater reduction of Prevotella using minimal-instrumentation with multisonic irrigation (Kruskal-Wallis p=0.007 and p=0.002 respectively). Conclusion: There was no statistically significant difference in pre or post-treatment samples between conventional treatment with PUI, minimal instrumentation with multisonic irrigation, and surface controls. All treatments reduced the level of bacteria on the crown surface and in the root canal system.enMicrobiomeMultisonic IrrigationNext Generation SequencingPassive Ultrasonic IrrigationThesis or Dissertation