Oral Health, Periodontitis, and Respiratory Diseases: Biological Pathways

Poor oral hygiene and periodontitis influence lung diseases such as pneumonia, chronic obstructive pulmonary disease (COPD), COVID-19, and asthma. The normal lung is not sterile, with a distinct microbial ecosystem that is spatially varied along the respiratory tract. The biogeography of the lung microbiome is balanced between microbial microaspiration from the oral-pharynx and clearance. The mouth is an important reservoir for respiratory pathogens including Streptococcus pneumoniae, Haemophilus influenzae, Pseudomonas aeruginosa, and Staphylococcus aureus, as well as oral microbes (Porphyromonas, Prevotella, Fusobacterium, etc.). Poor oral hygiene and periodontitis increase the bacterial load that can be aspirated, and the host produces pro-inflammatory components that enhance microbial virulence and compromize epithelial integrity. Both poor oral hygiene and periodontitis have been associated with pneumonia, particularly in hospitals and nursing home settings. Periodontitis may also facilitate viral pneumonia (including COVID-19) by altering receptor expression and immune function. Periodontitis correlates with COPD severity and exacerbation frequency through pathways involving matrix metalloproteinases and cytokines. Periodontitis also is associated with asthma and acute exacerbations. Inflammation shapes the lung microbiome by impacting microbial nutrient availability through vascular leakage, inducing changes to epithelial cells which facilitate bacterial adherence, and inducing the production of cytokines, leading to mucus overproduction, inhibition of phagocytosis, and enhancement of microbial pathogen virulence. Multiple biological pathways have been examined in vitro that suggest how "the oral-lung axis" influences pneumonia, COPD, and asthma. Periodontal treatment and effective oral hygiene should be well integrated into medical care to prevent and manage respiratory diseases.