Abstract Background: Aerosols generated during ultrasonic scaling is a potential risk factor for cross-contamination in dental settings. The aim of this study is to evaluate and compare the efficacy of commercially available chlorine dioxide as preprocedural mouthrinses in reducing the level of viable bacteria in aerosols. Materials and Methods: This single-center clinical double-blinded study was conducted over a period of 4 months. A total of 80 patients were divided randomly into two groups (A and B) of 40 patients each to receive the chlorine dioxide mouthwash and water as preprocedural rinse. The aerosol produced by the ultrasonic unit was collected at five standardized location with respect to the reference point, that is, the mouth of the patient. The blood agar plates were incubated at 37°C for 48 h, and total number of colony-forming units (CFUs) was counted and statistically analyzed. Results: The results showed that CFUs in test group A were significantly reduced compared with control group B, P < 0.001 (analysis of variance). The numbers of CFUs were highest in the patient chest area and lowest at the patient front, that is, 6 o′ clock position. Conclusion: This study proves that a regular preprocedural mouthrinse with chlorine dioxide could significantly reduce aerosols generated during professional oral prophylaxis.