Periodontal disease is the main cause of tooth loss; however, some reports have identified a correlation between tooth loss and AD. Tooth loss may be a risk factor for AD [28, 29]. Tooth loss reduces chewing function, which results in reduced cerebral blood flow and might lead to reduced cognitive function. However, tooth loss itself often does not accompany chronic inflammatory response, which suggests that the effects of tooth loss are not necessarily identical to those of periodontal disease. Oue et al. found that cognitive function was reduced by tooth removal in AAP transgenic mice, but there was no effect on the molecular pathology of AD [30]. On the other hand, when we induced periodontal disease in the same mouse, we found that intracerebral Aβ deposits increased and the intracerebral inflammatory response was enhanced in addition to the reduced cognitive function. Both periodontal disease and tooth loss reduce cognitive function, but their molecular mechanisms are thought to differ.