gt;20%) in individual cystic fluids. Also, DNA from the genus Fretibacterium was significantly more commonly found in cryopulverized teeth and cystic fluids than in supragingival plaque samples. The relative abundances of this gram-negative bacterial genera in cryopulverized teeth differed from NCs; the difference from cystic fluids was borderline insignificant. Conclusions: Although the alpha-diversity in the cystic fluids is much lower compared to supragingival plaques, most cystic fluids are not sterile. DNA from specific anaerobic gram-negative bacterial genera dominated the fluids from AP-related RCs.