Periodontitis is the microbial infection often causing inflammation of the gingiva, bone loss and tooth mobility. Apart from periodontitis, periodontal bacteria like Porphyromonas gingivalis, Spirochetes, Treponema denticola are known to cause systemic diseases such as cardiovascular diseases, preterm low birth weight infants, Alzheimer's diseases etc. Alzheimer's disease is a progressive mental deterioration of the brain that can occur in middle or old aged individual due to generalized regeneration of neurons in the brain. Literature has shown that inflammation plays a vital role in the progression of Alzheimer's disease where periodontitis is a risk factor proving the focal infection theory. This article reviews the relationship of periodontitis in Alzheimer's disease and its role in modifying the disease.