Periodontitis is a common chronic inflammatory and destructive disease in the mouth and is considered to be associated with systemic diseases. Accumulating evidence has suggested that periodontitis is a risk factor for pulmonary diseases such as pneumonia, chronic obstructive pulmonary disease (COPD), asthma, coronavirus disease 2019 (COVID‑19) and lung cancer. The presence of common periodontal pathogens has been detected in samples from a variety of pulmonary diseases. Periodontal pathogens can be involved in lung diseases by promoting the adhesion and invasion of respiratory pathogens, regulating the apoptosis of respiratory epithelium and inducing overexpression of mucin and disrupting the balance of immune systemin respiratory epithelium cells. Additionally, measures to control plaque and maintain the health of periodontal tissue can decrease the incidence of respiratory adverse events. This evidence suggests a close association between periodontitis and pulmonary diseases. The present study aimed to review the clinical association between periodontitis and pneumonia, COPD, asthma, COVID‑19 and lung cancer, and propose a possible mechanism and potential role of periodontal pathogens in linking periodontal disease and lung disease. This could provide a direction for further research on the association between periodontitis and lung disease and provide novel ideas for the clinical diagnosis and treatment management of these two diseases.

Circular RNAs (circRNAs) are a class of non‑coding RNAs that may have important regulatory potency in various biological processes. However, the role of circRNAs and their potential functions in bone marrow mesenchymal stem cells of mice (BMSCs) are still ambiguous. The current study aims to examine the expression of circRNAs and to investigate their effects on FOS like 2 AP‑1 transcription factor subunit (FOSL2) expression following stimulation of BMSCs with calcitonin gene‑related peptide (CGRP). RNA generated from BMSCs stimulated with or without CGRP was used in a microarray to detect expression of circRNAs. There were 58 significantly differentially expressed circRNAs following CGRP treatment, with 44 circRNAs downregulated and 14 upregulated. Bioinformatics analysis and regulatory networks were used to identify the potential interactions between circRNAs and microRNAs (miRs). mmu_circRNA_003795 was significantly increased in the CGRP‑stimulated BMSCs compared with the blank control. Silencing of mmu_circRNA_003795, significantly increased the expression of mmu_miR‑504‑3p, whereas FOSL2 expression and cell proliferation were decreased. Furthermore, silencing of mmu_mir‑504‑3p using an miR inhibitor led to increased FOSL2 expression. Additionally, silencing of mmu_circRNA_003795 using small interfering RNA induced marked alterations in the cell cycle of BMSCs. The results demonstrated that mmu_circRNA_003795 can indirectly regulate FOSL2 expression via sponging of miR‑504‑3p, resulting in alterations in BMSC proliferation.