Periodontitis and Alzheimer's Disease

Author: Gum Specialist Dr Sajni

Periodontitis and Alzheimer's disease are chronic, inflammatory, and degenerative conditions. Epidemiological studies have provided evidence of an association between the two diseases.  Alzheimer's disease is the most common cause of dementia but despite years of research, the pathogenesis is not completely understood. Alzheimer's disease is characterised by neurofibrillary tangles within neurons, amyloid plaques containing amyloid beta peptides, along with the symptoms of clinical dementia. 

Periodontitis could potentially affect the pathogenesis of Alzheimer's disease via genetic and environmental factors, microorganisms and the immune-inflammatory response.  

Genetic studies have found genes with single nucleotide polymorphisms implicated in both periodontitis and Alzheimer’s disease. These genes encode for proteins involved in cellular functions, membrane transport and immune-inflammatory functions. Shared environmental and behavioural risk factors for both Alzheimer's and disease and periodontitis include diabetes mellitus, atherosclerosis and smoking. 

Periodontal pathogens have been identified in brain tissues affected by Alzheimer's disease. bacteria have been shown to contribute to uncontrolled neuroinflammation. Specifically, spirochaetes have been identified in more than 90% of these tissues. Spirochaetes have been shown to form amyloid beta peptides. In mice, oral inoculation of P. gingivalis which induced periodontitis resulted in increased levels of Il-1beta, TNF alpha, and endotoxin in the brain. Cognitive function was significantly impaired in mice affected by periodontitis. 

The predominant immune cell in the brain is microglia, and this can become pro-inflammatory when stimulated by peripheral inflammation for example as in periodontitis. This in turn can cause further neurodegeneration. In addition, neutrophils which are highly prevalent in inflamed periodontal tissues, can cross the blood-brain barrier. They can then contribute to the pathogenesis of Alzheimer's disease. Peripheral infection and inflammation can affect the clearance mechanisms for amyloid beta peptides leading to their build-up within the brain.

With impaired cognitive function, a person’s ability to perform adequate oral hygiene can be negatively impacted. This can then increase the risk of periodontitis and further increase neurodegeneration.