Aim To study whether dental caries, periodontal disease, and stomatitis, and the related inflammatory burden associate with diagnosed Alzheimer's disease (AD) and dementia among older people. Methods The study population included 170 individuals aged ≥75 years. The primary outcome was diagnosed AD and the secondary outcome was any types of diagnosed dementia. Information about participants’ oral diseases and the related inflammatory burden was based on the clinical oral examination. Relative risks (RRs) and confidence intervals (CIs) were estimated using regression models. Results Dental caries, the presence of ≥3 carious teeth (RR: 3.47, 95% CI: 1.09–11.1) and the number of carious teeth (RR: 1.24, CI: 1.11–1.39), and inflammatory burden (RR: 1.44, CI: 1.04–2.01) were associated with a higher likelihood of having AD. Also, periodontal disease and stomatitis were associated, although nonstatistically, with AD and dementia. The risk estimates for any type of dementia were in most cases lower than for AD. Conclusion Oral diseases and the related inflammatory burden were in most cases associated more strongly with diagnosed AD than dementia in general. Of the oral diseases studied, the strongest association was between dental caries and AD.