Abstract:

Objective To systematically analyze the effect of antimicrobial photodynamic therapy （aPDT） on root canal microbiota in infected root canals using 16S ribosomal DNA（rDNA） amplicon sequencing technology， and to evaluate its clinical efficacy as an adjunct to root canal disinfection. Methods Fifteen patients with chronic pulpitis （CP） were enrolled as CP group， and 15 patients with chronic apical periodontitis （CAP） were enrolled as CAP group. Root canal microbiota samples were collected from patients in two groups at four key treatment stages： after access cavity preparation （Pre group）， after routine root canal preparation and disinfection （Post group）， after aPDT intervention （PDT group）， and after calcium hydroxide（CHM） dressing （CHM group）. 16S rDNA amplicon sequencing method was used to analyze qualified samples that passed quality inspection and library construction， including Alpha diversity indices （Chao1 index， Shannon index， Simpson index）， Beta diversity， and community composition differences of root canal microbiota in samples from patients in two groups. Results In samples of patients in CP group， compared with Post group， the sequencing failure rate was significantly increased in PDT group （P<0.05）， and 6 samples were subsequently included for analysis. The Alpha diversity indices in four groups of CP patients all showed a decreasing trend， with no statistically significant differences （P>0.05）. No statistically significant difference was observed in Beta diversity between Post group and PDT group of CP patients （P>0.05）. Compared with other three groups， the relative abundances of Firmicutes， Lactobacillus gasseri， and uncultured Lactobacillus were significantly increased in samples in CHM group （P<0.05）. As for samples of patients in CAP group， no statistically significant difference was observed in the sequencing failure rate between PDT group and Post group （P>0.05）， and 12 samples were subsequently included for analysis. The Chao1 index in four groups of CAP patients showed a decreasing trend， with no statistically significant differences in any Alpha diversity indices （P>0.05）. A statistically significant difference was observed in Beta diversity between post group and PDT group of CAP patients （P<0.05）. Compared with Post group， the relative abundances of Actinobacteria， Streptococcus， Actinomyces， and Porphyromonas gingivalis were significantly decreased in samples in PDT group （P<0.05）. Compared with other three groups， the relative abundances of Porphyromonas and Porphyromonas gingivalis were significantly increased in samples in CHM group （P<0.05）. Conclusion As an adjunct to root canal disinfection， aPDT exerts significant synergistic antimicrobial effects， with efficacy varying by disease type. In CP patients， aPDT enhances sterilization efficacy and shows a trend of decreasing the richness and evenness of root canal microbiota. In CAP patients， aPDT not only shows a trend of reducing root canal microbiota richness but also alters the community composition of root canal microbiota. The effect of aPDT on microbiota alterations may be associated with patient prognosis.

Key words: Antimicrobial photodynamic therapy, Chronic pulpitis, Chronic apical periodontitis, Root canal microbiota, 16S rDNA amplicon sequencing