Association Between Oral Dysbiosis and Alzheimer’s Disease: A Systematic Review

Objective: The main objective of this systematic review is to select and critically synthesize the available evidence from studies that aimed to verify whether there is a relationship between dysbiosis of the oral cavity and the development of Alzheimer’s disease. Methodology: A search was conducted on 30 November 2024 and updated on 9 January 2025, in the PubMed, SciELO Scopus, and Web of Science databases, limiting the search to the last 5 years. The review was carried out under the criteria of the PRISMA 2020 guide for systematic reviews and has been accepted into the PROSPERO registry (CRD42025636275). We analyzed the risk of bias of studies using the JBI guidelines. Results: Initially, 2009 articles were obtained. After eliminating duplicates, we obtained 1716; of these, following the inclusion and exclusion criteria, 185 articles were reviewed by title and abstract, discarding 171. Of the remaining 14 articles, 12 final articles were selected. In the results obtained, it has been observed that there is a relationship between inflammation derived from oral dysbiosis caused by periodontal disease and its extension to the neuronal tissue via the hematogenous blood–brain barrier (BBB) and nerve (V pair). Among the most frequently found oral microbiota are Veillonella, Fusobacteria, Prevotella, Porphyromonas, Lactobacillus, and Streptococcus. Conclusions: Oral dysbiosis gives rise to the establishment of inflammatory processes that lead to neurological degeneration, either through its passage across the blood–brain barrier or by a direct connection between the free nerve endings of the periodontium and the proprioceptors found in the central nervous system. Therefore, the chronic inflammation caused by oral dysbiosis and its role in systemic inflammation could be associated with the onset and progression of Alzheimer’s disease (AD); however, more studies are needed to show the association between oral dysbiosis and Alzheimer’s disease.