# Oral Health and Cognitive Decline: A Systematic Review of the Periodontitis-Alzheimer's Connection
## 3 Results
### Characteristics of Reviewed Studies  
The studies examined in this analysis span a wide range of methodologies, including both cross-sectional and longitudinal designs, with a focus on various pathways linking PD and AD. [PERSON] et al. (2024) [220] conducted a non-randomized clinical study to determine the feasibility of treating individuals with mild dementia and periodontitis over 24 months. [PERSON] et al. (2021) [221] explored the cognitive differences in young subjects with periodontal disease using neuropsychological tests in a cross-sectional study. In a retrospective cohort study, [PERSON] et al. (2017) [222] investigated whether chronic periodontitis increased the risk of AD, revealing long-term inflammation as a key factor. [PERSON] et al. (2024) [223] identified significant metabolic and microbial differences in AD and aMCI patients through 16S rRNA sequencing and metabolomics. [PERSON] et al. (2024) [224] examined brain MRI markers, while [PERSON] et al. (2024) [225] linked systemic  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Authors** & **Type of Study** & **Aim of Study** & **Materials and Methods** & **Results** \\ \hline [PERSON] et al. & Secondary data & & & & Periodontitis patients  
infection burden to dementia risk through a large cohort analysis using NHANES data. [PERSON] et al. (2021) [226] utilized a quasi-experimental approach to explore periodontal treatment's impact on brain atrophy markers. [PERSON] et al. (2021) [227] highlighted the abundance of _Porphyomonas gingivalis_ in neurodegenerative conditions, whereas [PERSON] et al. (2019) [228] documented a modest increase in dementia risk linked to chronic periodontitis in a nationwide cohort. [PERSON] et al. (2023) [229] correlated periodontitis with elevated Alzheimer's biomarkers, and [PERSON] et al. (2023) [230] reported distinct microbial diversity in AD patients. Similarly, [PERSON] et al. (2024) [237] conducted a case-control study on oral microbiome composition, finding increased microbial diversity in AD patients, characterized by a rise in Firmicutes and a reduction in Bacteroidetes. Specific taxa such as _Haemophilus parainfluenzae_ and _Prevotella melaninogenica_ were altered, suggesting the role of oral dysbiosis in neurodegeneration. [PERSON] et al. (2024) [231] and [PERSON] et al. (2022) [232] analyzed structural brain changes and inflammatory markers, respectively, highlighting systemic inflammation as a central mechanism. [PERSON] et al. (2022) [233] explored mitochondrial dysfunction's role as a mediator in the link between periodontitis and cognitive impairment, highlighting the fact that oxidative stress mechanisms explained a significant portion of the cognitive decline observed in individuals with severe periodontitis. [PERSON] et al. (2015) [234] found elevated A\(\beta\) retention in cognitively normal individuals with periodontal disease, supporting a long-term inflammatory pathway. [PERSON] et al. (2020) [235] identified periodontitis with tooth loss as a modifiable risk for multiple dementia types. [PERSON] et al. (2021) [236] revealed the mediation effect of pro-inflammatory diets and vitamin D deficiency on cognitive outcomes. Finally, [PERSON] et al. (2019) [238] investigated gingipain inhibitors, providing preclinical evidence for potential therapeutic interventions targeting _P. gingivalis_. These diverse approaches collectively underline the multifaceted relationship between PD and AD.