COMMENT Periodontics Beyond the mouth: the impact of periodontal disease on dementia Morteza Banakar 1,2 ✉ , Yoones Sadabadi 2 , Majid Mehran 2 and Farid Abbasi 3 © The Author(s), under exclusive licence to British Dental Association 2023 A COMMENTARY ON Asher S, Stephen R, Mäntylä P, Suominen A L, Solomon A. Periodontal health, cognitive decline, and dementia: a systematic review and meta-analysis of longitudinal studies. J Am Geriatr Soc 2022; 70: 2695–2709. PRACTICE POINTS ● Longitudinal studies with lengthy follow-ups validated cognitive assessments, and comprehensive control of confounding are needed to better elucidate the relationship between oral and cognitive health. ● Clinicians should be aware of the potential association between poor oral health and cognition, but the evidence is currently insufficient to recommend specific guidelines for dementia prevention. DATA SOURCES: The authors searched Medline via PubMed, Scopus, CINAHL, Web of Science, and PsycINFO for relevant studies published until April 2022. STUDY SELECTION: Longitudinal studies that assessed periodontal health as the exposure and cognitive decline and/or dementia as the outcome were included. Case reports, reviews, cross-sectional studies, and animal studies were excluded. DATA EXTRACTION AND SYNTHESIS: Two authors independently reviewed studies for inclusion, extracted data, and assessed study quality. Meta-analysis was conducted to generate pooled odds ratios (ORs) for cognitive decline and hazard ratios (HRs) for dementia. Sources of heterogeneity were explored through subgroup analyses. RESULTS: A total of 24 studies were included for cognitive decline and 23 for dementia. Poor periodontal health was associated with increased odds of cognitive decline (OR = 1.23; 95% CI: 1.05–1.44) and dementia (HR = 1.21; 95% CI: 1.07–1.38). Tooth loss also appeared to increase the risk independently. However, significant heterogeneity existed between studies. CONCLUSIONS: Poor periodontal health may increase the risk of cognitive decline and dementia, but the quality of evidence was low. Further high-quality, longitudinal studies with standardized assessments are needed to establish causality. Evidence-Based Dentistry; https://doi.org/10.1038/s41432-023-00925-0 GRADE Rating: COMMENTARY The mouth is the gateway to the body, and emerging studies provide increasing evidence for the bi-directional relationship between oral health and systemic health conditions. Recent research has suggested a noteworthy correlation between period- ontal disease and dementia, an association that may have profound implications for both dental and mental health care 1,2 . Periodontal disease, a chronic oral condition, is the 11th most prevalent condition in the world, with a prevalence ranging from 20 to 50% worldwide 3 . It is characterized by the inflammation of the periodontium, the specialized tissues that both surround and support the teeth. An accumulating body of evidence has suggested an intimate link between periodontal disease and dementia, a multifaceted and devastating neurodegenerative condition 1,2,4–8 . In a 20-year follow-up study, individuals with severe periodontal disease had a 70% increased risk of developing Alzheimer’s disease compared to those without periodontal disease 5 . A population-based cohort study by Chen et al. found that dementia and Alzheimer’s disease were associated with a higher risk of periodontal disease, dependent on age and independent of systemic confounding factors 9 . A recent meta-analysis of 20 observational studies also showed a strong relationship between periodontitis and cognitive impairment 4 . Asher et al. conducted a systematic review and meta-analysis to investigate the link between poor periodontal health and the risk of cognitive decline and dementia. The study employed appropriate meta-analytic methods and explored potential sources of heterogeneity through subgroup analyses. It also considered the issue of reverse causation to some extent. While the review suggested an association between periodontal disease and cognitive decline, several limitations affected the strength of the conclusions. Significant heterogeneity among studies could not be fully Received: 25 July 2023 Accepted: 27 July 2023 1 Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran. 2 Department of Pediatric Dentistry, Faculty of Dentistry, Shahed University, Tehran, Iran. 3 Department of Oral Medicine, Faculty of Dentistry, Shahed University, Tehran, Iran. ✉ email: Dr.mbanakar@gmail.com www.nature.com/ebd 1234567890();,: