<p><b>Background</b> Alzheimer's disease (AD) is the leading cause of dementia and represents a major global health challenge. Periodontal disease (PD), a chronic inflammatory condition affecting the supporting tissues of the teeth, has emerged as a potential modifiable risk factor for cognitive decline. Biological mechanisms suggest a plausible link between PD and neurodegeneration. </p><p><b>Aim</b> The aim of this literature review is to synthesise and critically appraise the latest research assessing whether PD is associated with cognitive impairment, Alzheimer's pathology, brain structural changes and dementia risk.</p><p><b>Methodology</b> A systematic style approach was adopted for this review. Seven studies published between 2021 and 2025 were included. Data were synthesised narratively. Study quality was assessed using the CASP (Critical Appraisal Skills Programme) Cohort Checklist and ROBINS-I (Risk of Bias In Non-randomised Studies of Interventions) tool. </p><p><b>Results</b> PD consistently correlated with adverse cognitive outcomes. Evidence showed increased amyloid burden, reduced grey matter volume, greater hippocampal atrophy, accelerated cognitive decline in Alzheimer's patients and higher long-term dementia incidence. Periodontal treatment was also associated with reduced dementia risk.</p><p><b>Conclusion</b> Current evidence supports a meaningful association between PD and cognitive decline, including AD progression. </p>