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

### **Sadayuki Hashioka 1,\*, Ken Inoue 2, Tsuyoshi Miyaoka 1, Maiko Hayashida 1, Rei Wake, Arata Oh-Nishi 1 and Masatoshi Inagaki 1**


Received: 22 May 2019; Accepted: 25 July 2019; Published: 30 July 2019

**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:** periodontitis; neuropsychiatric disorders; Alzheimer's disease; Parkinson's disease; major depression; schizophrenia; neuroinflammation; microglia
