As a result of ongoing demographic transitions, populationsthroughout the world are ageing. Cognitive decline is a leadingcontributor to dependence and disability among older adults. Declinein cognitive abilities can also influence lifestyle factors associatedwith oral health. Increasing evidence suggest that more teethare retained throughout life and therefore an increasing number ofteeth are at risk of oral diseases.Periodontitis is an inflammatory disease affecting the supportivetissues of the teeth resulting in alveolar bone loss and eventuallytooth loss. Associations between periodontitis and systemic diseaseswith an inflammatory profile have been reported.The overall aim of the present thesis was to evaluate a potentialassociation between tooth loss, periodontitis, and cognitive declineand to describe changes in oral health-related parameters amongolder adults in a twelve-year follow-up.In Paper I the impact of tooth loss on the risk for lower cognitivetest score was evaluated in 1147 older adults. An examination includingclinical and radiographic registration of number of teethpresent was performed. Cognitive functioning was evaluated usingMini-Mental State Examination (MMSE) (cut-off <25) and Clocktest(CT) (cut-off <8). Number of teeth was categorised into edentulous,1-19 and ≥20 teeth. The risk for low cognitive test scorewas statistically related to number of teeth. Results from the multiplelogistic regression after adjustments for age and educationdemonstrated a statistically significant impact of being edentulous on cognitive functions. In addition, having 1 to 19 teeth had a significantimpact on the risk for Clock-test