Poor oral health conditions and cognitive decline: Studies in humans and rats

BACKGROUND: The relationship between poor oral health conditions and cognitive decline is unclear. OBJECTIVE: To examine the association between oral health and cognition in humans and rats. METHODS: In humans: a cross-sectional study was conducted. Cognitive levels were evaluated by the Mini Mental State Examination (MMSE); oral conditions were reflected by the number of missing index teeth, bleeding on probing, and probing pocket depth (PD). In rats: a ligature-induced (Lig) periodontitis model and Aβ(25-35)-induced model of Alzheimer’s disease (AD) were established; tumor necrosis factor-α (TNF-α), interleukin 1 (IL-1), interleukin 6 (IL-6), and C-reactive protein levels in the hippocampus and cerebral cortex were detected. RESULTS: MMSE scores for the number of missing index teeth ≥ 7 group were significantly lower than those in the ≤ 6 group. A negative relationship (correlation coefficient ρ = −0.310, P = 0.002) was observed between MMSE scores and number of missing index teeth. More missing index teeth and lower education levels were independent risk factors for cognitive decline. A negative relationship (correlation coefficient ρ = −0.214, P = 0.031) was observed between MMSE scores and average PD. TNF-α and IL-6 levels in the hippocampus of the Lig+AD group were significantly higher than those of the AD group. IL-1 and IL-6 levels in the cerebral cortex of the Lig+AD group were significantly higher than those of the AD group. CONCLUSION: Poor oral health conditions including more missing index teeth and higher average PD may be risk factors for cognitive decline. Periodontitis may increase inflammatory cytokines in rat models of AD.