Table 2.

Adjustment status of included studies.

Study	Adjustment for covariates	Adjustment strength
Shimazaki et al., 2001	Age, physical health, type of institution, cerebrovascular disorder, denture use	Weak
Stein et al., 2007	Age, education and apolipoprotein E4 allele	Weak
Arrive et al., 2012	Gender, body mass index, diabetes, depression, hypertension and ischemic cardiopathy / history of brain stroke	Weak
Paganini-Hill et al., 2012	Age at entry, smoking, alcohol, caffeine, active activities, other activities, body mass index, high blood pressure, angina pectoris, heart attack, stroke, diabetes mellitus, rheumatoid arthritis, cancer, education, head trauma, and family history of dementia	Strong
Yamamoto et al., 2012	Age, household income, body mass index, present illness, alcohol consumption, exercise, and forgetfulness	Weak
Batty et al., 2013	Age, sex, European Quality of Life-5 Dimensions (EQ-5D), socioeconomic, cigarette smoking, alcohol intake, vigorous physical activity in previous week, Hemoglobin A1c, creatinine, body mass index, total cholesterol, HDL cholesterol, resting heart rate, systolic blood pressure, diastolic blood pressure, age at completion of highest level of education	Strong
Stewart et al., 2015	Age, education, social class, stroke, myocardial infarction, diabetes mellitus, smoking status, systolic blood pressure, body mass index, and cholesterol level defined in quartile groups with pacifier categories for missing data	Strong
Takeuchi et al., 2017	Sex, age, occupation, education, hypertension, diabetes mellitus, history of stroke, alcohol intake, tooth brushing frequency, regular visits to the dentist, and denture use	Strong