The number of remaining teeth as a risk indicator of cognitive impairment: A cross-sectional clinical study in Sado Island.

Most studies that have demonstrated an association between number of remaining teeth and cognitive impairment have treated teeth as a continuous variable, although the relationship is nonlinear. The aim of this cross-sectional study was to determine the critical number of remaining teeth in hospital outpatients at which the association with cognitive impairment becomes apparent. Japanese adults living on Sado Island who visited Sado General Hospital were invited to participate in Project in Sado for Total Health. In total, 2,530 adults were interviewed and had their teeth counted; 1,476 of these individuals also completed the Mini-Mental State Examination (MMSE) and underwent measurement of their serum high-sensitivity C-reactive protein (hsCRP) levels. Patients on dialysis and those with hsCRP ≥ 10 mg/L were excluded. The final study group consisted of 565 adults (290 men and 275 women) of mean age 69.8 (range 29-91) years. An MMSE score < 24 was considered to indicate cognitive impairment. The subjects were categorized according to whether they had an edentulous jaw or one to 10, 11-20, 21-27, or ≥28 remaining teeth. One hundred twenty-eight of the 565 study participants were diagnosed to have cognitive impairment. Multiple logistic regression analysis revealed associations of cognitive impairment with older age, ischemic heart disease, smoking, and alcohol consumption. After adjustment for covariates, having one to 10 remaining teeth was significantly associated with cognitive impairment. There is a significant association between having only one to 10 remaining teeth and cognitive impairment in hospital outpatients.