Microbial Interactions between Periodontal Disease and Dementia

Oral bacteria and their byproducts have been found in brain tissue1,2,5,73 and increased levels of serum antibodies to periodontopathogenic bacteria have been found in patients with Alzheimer’s disease and dementia.20,24,71 These bacteria may enter the brain through several pathways: 1) bacteremias allow for bacteria within the bloodstream and degradation of the blood-brain barrier is seen in age, chronic infection, and in the presence of inflammation, 2) direct access to the brain may be gained through perivascular spaces, and 3) via olfactory and/or trigeminal nerve pathways.83 In addition to the bacteria themselves, influence on the brain by bacterial byproducts including virulence factors such as lipopolysacchride, capsular material, proteolytic enzymes, and gingipains may contribute to progression of dementia.1,2,20,64,84,85 Finally, epigenetic alterations of the genome at local or distant sites may alter gene expression and influence the risk conferred by those genes. Bacteria and their byproducts have been shown to increase DNA methylation and histone acetylation, which has been indicated in the development of periodontal disease, cancers, and other diseases.86,87

Oral hygiene status in elderly dentate patients has also been associated with development of dementia.88 Alteration of the oral microbiome may be achieved through oral hygiene interventions, which then can alter serum levels of microorganisms and change a potential pathway for bacteria and their byproducts to cross the blood-brain barrier.1,2,89 Improved oral hygiene delivery is associated with decreases in dental diseases in these populations90,91 and has been suggested as an intervention to reduce the direct and indirect influences of oral bacteria and their byproducts on the brain and the potential influence of these bacteria and their byproducts on cognitive decline.92