In the occurrence of AD, it is thought that oral pathogenic microbes and their toxic substances damage the BBB and trigger or aggravate neuroinflammation, amyloid deposition and Tau protein phosphorylation, subsequently leading to cognitive impairment (Wu et al., 2017; Dominy et al., 2019; Zeng et al., 2020). This evidence concerns the gene MAPT and Alzheimer disease.