This study investigated the effect of interdental brushes on the reduction of interproximal bleeding in adults without periodontal disease. Forty-six adults were enrolled in a 3-month, observer-blinded, parallel-group randomized control trial. The test group used a standard manual toothbrush twice daily and an interdental brush daily. The control group used a standard manual toothbrush. At each visit, a calibrated colorimetric probe was used in all interdental spaces to determine the appropriate size of the interdental brush required, the brush of the corresponding size was introduced into the interproximal space, and the presence of bleeding was recorded. The outcome was the frequency of bleeding after application of the appropriate interdental brush. All participants were evaluated 1 wk, 1 month, and 3 months after the baseline visit. The overall preventive fraction with respect to bleeding frequency was 46% at 1 wk and 72% at 3 months. More bleeding reduction was observed in anterior sites than in posterior sites (80% vs. 69%, respectively). Participants with low baseline bleeding frequency presented with less bleeding (OR = 2.3). This study shows that daily use of calibrated interdental brushes reduces interdental bleeding. These findings may support interdental cleaning as an effective means to help individuals maintain and/or achieve optimal oral health.