The Possible Causal Link of Periodontitis to Neuropsychiatric Disorders: More Than Psychosocial Mechanisms

Abstract

Increasing evidence implies a possible causal link between periodontitis and neuropsychiatric disorders, such as Alzheimer's disease (AD) and major depression (MD). A possible mechanism underlying such a link can be explained by neuroinflammation induced by chronic systemic inflammation. This review article focuses on an overview of the biological and epidemiological evidence for a feasible causal link of periodontitis to neuropsychiatric disorders, including AD, MD, Parkinson's disease, and schizophrenia, as well as the neurological event, ischemic stroke. If there is such a link, a broad spectrum of neuropsychiatric disorders associated with neuroinflammation could be preventable and modifiable by simple daily dealings for oral hygiene. However, the notion that periodontitis is a risk factor for neuropsychiatric disorders remains to be effectively substantiated.

Keywords: Alzheimer’s disease; Parkinson’s disease; major depression; microglia; neuroinflammation; neuropsychiatric disorders; periodontitis; schizophrenia.

Figure 1

Scheme for presumed mechanisms by which periodontitis causes neuroinflammation. These consist of three possibilities as follows: (1) Peripheral pro-inflammatory cytokines associated with periodontitis communicate with the brain via the neural pathway, humoral pathway, and cellular pathway. (2) Periodontal bacteria/bacterial molecules can directly invade the brain either through the blood stream or via cranial nerves. (3) Communication between periodontal bacteria/bacterial molecules and brain-resident microglia could occur through the leptomeninges.