OBJECTIVES
We have carried out a systematic review of longitudinal studies examining the association between oral health and cognitive decline.

DESIGN
Studies, published 01/1993-03/2013, were identified by search of English language publications in PubMed/Medline using relevant MeSH terms and title/abstract keywords, and from CINAHL using relevant subject headings. After applying eligibility criteria, and adding four studies identified from article references, 56 of the 1412 articles identified remained: 40 were cross-sectional, and 16 longitudinal; 11 of the latter examined the impact of oral health on change in cognitive health or dementia incidence, five examined the reverse.

SETTING
Sources of information included administrative data, subject evaluations in parent studies, medical and dental records, self-reports, and in-person evaluations.

MEASUREMENTS
Most studies used subjects whose oral or cognitive status was known, adding the missing piece using standard measures. The oral health information most frequently studied included number of teeth, periodontal and caries problems, and denture use. Cognition was most frequently evaluated using the MMSE, or by determination of dementia.

RESULTS
Some studies found that oral health measures such as number of teeth and periodontal disease were associated with increased risk of cognitive decline or incident dementia, while others did not find the association. Similarly, cognitive decline was not consistently associated with greater loss of teeth or number of caries. Methodological limitations likely play a major role in explaining the inconsistent findings.

CONCLUSION
It is unclear how or whether oral health and cognitive status are related. Additional research is needed in which there is greater agreement on how oral health and cognitive states are assessed, in order to better examine the linkages between these two health outcomes.