The COVID-19 pandemic has resulted in amended regulations and guidelines governing the practice of dentistry and dental hygiene to ensure the protection of both patients and clinicians from transmission of the SARS-CoV-2 virus. These guidelines include changes in personal protective equipment and, under some guidelines, the institution of a fallow period after any aerosol-generating procedure (AGP). This study aimed to investigate the effect of both ventilation and 4-handed dentistry in clinical practice with patients undergoing supportive periodontal therapy (SPT) by air polishing, ultrasonic and hand instrumentation in a closed operatory. We studied 34 patients during SPT using either 2- or 4-handed dentistry in an operatory with either 0 or 20 additional air changes/h (ACH). Under clinical conditions, 20 additional ACH are adequate to eliminate aerosols produced during an SPT and before the cessation of the AGP. The presence of an assistant had no significant effect on the time needed for aerosol particles to return to baseline values following the AGP. This study supports the efficacy of 20 additional ACH during the process of AGP, but does not support the need for an extended fallow period or 4-handed dentistry to provide additional high-volume evacuation throughout the procedure.