['A correlation has been found between periodontal disease (PD) and stroke. This study was conducted to investigate whether dental prophylaxis and periodontal treatment reduce the incidence rate (IR) of ischemic stroke.', 'We identified 510 762 PD cases and 208 674 non-PD subjects from January 1, 2000, to December 31, 2010. The PD cases were divided into dental prophylaxis, intensive treatment, and no treatment groups. The stroke IRs were assessed among groups during follow-up. Cox regression analysis was used after adjustment for age, sex, and comorbidities to determine the relationship between periodontal treatment and incidence of ischemic stroke.', 'The stroke IR of the non-PD subjects was 0.32%/year. In the PD group, subjects who received dental prophylaxis had the lowest stroke IR (0.14%/year); subjects with intensive treatment or tooth extraction had a higher stroke IR (0.39%/year); and subjects without PD treatment had the highest stroke IR (0.48%/year; P<0.001). After adjustment for confounders, the dental prophylaxis and intensive treatment groups had a significant lower hazard ratios for stroke than the non-PD group (hazard ratio=0.78 and 0.95; 95% confidence interval=0.75-0.81 and 0.91-0.99, respectively), whereas the PD without treatment group had a significant higher hazard ratio for stroke (1.15; 95% confidence interval=1.07-1.24), especially among the youngest (20-44) age group (hazard ratio=2.17; 95% confidence interval=1.64-2.87) after stratifying for age.'] Are dental prophylaxis and periodontal treatment protective factors to ischemic stroke?