['To evaluate the absence of IL-22 on the progression of periapical lesions in wild-type (WT) and IL-22 knockout (IL-22 KO) mice.', "The evaluation of the oral microbial profile of mice was performed by Checkerboard DNA-DNA hybridization from saliva samples. Periapical lesions were induced in manbibular first molars by pulpal exposure and evaluated after 7, 21 and 42 days (n = 15). Haematoxylin-eosin-stained sections were analysed under conventional and fluorescence microscopy to evaluate the tissue features and size of periapical lesions and tartrate-resistant acid phosphatase histoenzymology (TRAP), Brown & Brenn staining and immunohistochemistry. The scores of the number of bacterial cells present in the oral cavity were analysed by the Mann-Whitney test, and the results and comparisons for periapical lesion size and number of osteoclasts were subjected to one-way anova and Bonferroni's post-test (α = 0.05).", 'Significant differences were observed for bacterial load between the groups of animals for 6 bacterial species (P < 0.05), with five species found in higher levels in the WT group, and one in the IL-22 KO group. WT mice had significantly larger periapical lesions (P < 0.05) between 7 and 42 days and between 21 and 42 days, with an increase in the mean size and number of osteoclasts. IL-22 KO mice had an increase in periapical lesion size and number of osteoclasts between 7 and 21 days (P < 0.05). No differences were found between bacteria localization in the root canal system between the experimental groups. Small variations related to the location of immunostaining were found between the groups.'] Does absence of interleukin 22 affect the oral microbiota and the progression of induced periapical lesions in murine teeth?