Background To evaluate the association of dental diseases and oral hygiene care with incidence of heart failure (HF) among patients with type 2 diabetes. Methods and Results This study included 173 927 patients with type 2 diabetes aged ≥40 years, who underwent Korean National Health Insurance Service health examinations in 2008 and were followed up until the end of 2017. Hazard ratios (HRs) and 95% CIs for HF were estimated using multivariable Cox proportional hazards regression analysis. During a median follow‐up of 9.3 years, 1.94% of participants developed HF. An increased number of missing teeth was associated with a higher risk of HF ( P <0.001). HRs of HF increased among individuals with ≥15 missing teeth (HR, 1.37 [95% CI, 1.14–1.64]) compared with those without missing teeth. Decreased risk of HF was observed in individuals with ≥1 time/year of professional dental cleaning (HR, 0.93 [95% CI, 0.87–0.99]) and in those with ≥2 times/d of toothbrushing (HR, 0.90 [95% CI, 0.82–0.98]) compared with those without these practices. While combined presence of missing teeth and periodontal disease ( P =0.004) or dental caries ( P =0.007) increased HF risk, combined oral hygiene care was associated with further HF risk reduction ( P =0.024). Better oral hygiene care was associated with decreased HF risk, even as the number of missing teeth increased ( P <0.001). Conclusions Among patients with type 2 diabetes, dental diseases and oral hygiene care are important determinants of HF development. Dental disease management and good oral care may prevent HF in patients with type 2 diabetes.