Background  The dysbiosis of oral microorganisms aggravates the process of several oral diseases and systemic diseases. Postmenopausal women are at increased risk of oral mucosal disease and accelerated periodontal bone loss, but the association between changes in oral microbiota and postmenopause in women is unclear.

  Objective  To explore the changes of oral microbiota in ovariectomized mice via 16S rDNA amplicon sequencing.

  Methods  Sixteen female C57BL/6J mice were randomly divided into Ovariectomy group (OVX) and sham-operated group (Sham). The femurs were taken for MicroCT scanning and bone mineral density and bone parameters analysis at 4 weeks after the operation, and the oral swabs samples were collected for 16S rDNA high-throughput sequencing.

  Results  The bone mineral density, bone volume/total volume, trabecular thickness and trabecular number were decreased, while the bone surface area/bone volume and bone trabecular spacing were increased in OVX group (P<0.05). Two groups of oral samples contained common 687 ASVs, OVX group contained specific 1086 ASVs and OVX group contained specific 930 ASVs. There was no significant difference in Chao1 index between OVX group and Sham group, Simpson index in OVX group was significantly lower than that in Sham group (P<0.05). At the phylum level of oral samples, the relative abundance of Fusobacteriota and Bacteroidota in OVX group was decreased (P<0.05). At the genus level, the relative abundance of Fusobacterium, Lactococcus, Sutterella and other genera in OVX group were decreased, Actinomyces and other genera were increased (P<0.05). LEfSe analysis showed that the relative abundance of Firmicutes and Bacilli increased in the Sham group (P<0.05).

  Conclusion  Bone loss occurs in ovariectomized mice, and the diversity and structure of oral microbiota are changed, which preliminarily provides reference for the study of the relationship between the change of oral microbiota and the aggravation of oral diseases in postmenopausal women.