The increasing average life expectancy has brought some age-related diseases to the spotlight one of which being Alzheimer’s disease. Additionally, chronic inflammatory diseases, such as periodontal disease, is a concern in the elderly. In a systematic review published in 2020 in the Journal of Clinical Medicine, Dioguardi et al posed the question, “how can periodontal disease effect the onset and progression of Alzheimer’s disease?”1
Dioguardi et al hypothesized that “the inflammatory process related to periodontal disease may influence Alzheimer’s disease pathogenesis by worsening dementia, its main manifestation, in a synergic way.” Upon searching for articles to include in the systematic review, Dioguardi et al found 1088 articles, after applying inclusion and exclusion criteria a total of 15 articles were used in this qualitative analysis.
There are over 700 bacterial species in biofilm found in the mouth, not all of which are pathogenic. The host response to the accumulation of pathogenic biofilm begins with inflammation. In a perfect world, this elicits an immune response that removes the assaulting pathogenic bacteria. However, in many cases the bacteria aren’t removed via the inflammatory process and the inflammation becomes chronic leading to periodontal destruction. The inflammatory process elicits proinflammatory cytokines that become highly concentrated in the periodontal pockets, a source that can allow these pathogenic bacteria to be released into the blood stream and redistributed to other areas of the body. The theory claims that β-amyloid precipitation could be caused by this inflammatory process. This is often referred to as the “inflammatory theory.”
This “inflammatory theory” is supported by studies on non-steroidal anti-inflammatory drugs which show the administration of NSAIDS at the first sign of Alzheimer’s disease delay the progression of the disease. However, other studies have shown contradicting results. As a rule, the central nervous system (CNS) is protected from invaders via the hematoencephalic barrier. However, activated inflammatory cells such as, B and T lymphocytes and macrophages, can interact with the CNS via neuronal pathways. This interferes with peripheral nerve fibers causing an induction of proinflammatory cytokines that make their way to the CNS. This shows the possibility that peripheral inflammation could increase cytokines inside the CNS.
Periodontal disease and neurodegenerative diseases share common risk factors though they have different etiopathogenesis. The pathogenesis of Alzheimer’s disease is not clear; however, inflammation likely plays a role. This includes inflammation from periodontal disease. Additionally, theories regarding bacteria invading the brain and CNS links periodontal disease to Alzheimer’s disease as well. Various studies have shown spirochetes in the trigeminal ganglion indicating the bacteria can travel through peripheral nerves and invade the CNS.
This review goes on to discuss, in detail the different periodontal bacterium and their association with Alzheimer’s disease as well as tooth loss and the loss of cognitive function. This review is quite comprehensive, and we encourage you to read it for yourself to better understand the association between periodontal disease and Alzheimer’s disease.
The authors conclude by stating, “there is no definitive evidence to consider periodontitis as a risk factor, so more research will have to be conducted on this topic. Future studies that correlate periodontitis and Alzheimer’s disease should mainly focus on the possibility of preventing the onset of periodontal disease, the loss of dental elements, the reduction of local inflammation, and the predisposing oral factors of AD. Furthermore, the role of periodontal bacteria in the etiopathogenesis of Alzheimer’s disease should be investigated.”
Do you think there will be definitive evidence to consider periodontitis as a risk factor for Alzheimer’s disease in the future? One of the questions that is posed in this study pertains to which disease comes first or if they have some bidirectional association, from your clinical experience, do you think periodontal disease or Alzheimer’s disease presents first? Do you currently discuss the risk of Alzheimer’s disease and the association with periodontal disease with your patients?
- Dioguardi M, Crincoli V, Laino L, Alovisi M, Sovereto D, Mastrangelo F, Russo LL, Muzio LL. The Role of Periodontitis and Periodontal Bacteria in the Onset and Progression of Alzheimer’s Disease: A Systematic Review. J Clin Med. 2020 Feb 11;9(2):495. doi: 10.3390/jcm9020495. PMID: 32054121;