Objective:Exposure to aerosol spray generated by high-speed handpieces (HSHs) and ultrasonic scalers poses a significant health risk to oral health practitioners from airborne pathogens. Aerosol generation varies with different HSH designs, but to date, no study has measured this.Materials and methods:We measured and compared aerosol generation by (1) dental HSHs with 3 different coolant port designs and (2) ultrasonic scalers with no suction, low-volume evacuation (LVE) or high-volume evacuation (HVE). Measurements used a particle counter placed near the operator’s face in a single-chair, mechanically ventilated dental surgery. Volume concentrations of aerosol, totaled across a 0.3–25-µm size range, were compared for each test condition.Results:HSH drilling and scaling produced significantly high aerosol levels (P< .001) with total volume concentrations 4.73×108µm3/m3and 4.18×107µm3/m3, respectively. For scaling, mean volume of aerosol was highest with no suction followed by LVE and HVE (P< .001). We detected a negative correlation with both LVE and HVE, indicating that scaling with suction improved operator safety. For drilling, simulated cavity preparation with a 1-port HSH generated the most aerosol (P< .01), followed by a 4-port HSH. Independent of the number of cooling ports, lack of suction caused higher aerosol volume (1.98×107µm3/m3) whereas HVE significantly reduced volume to −4.47×105µm3/m3.Conclusions:High concentrations of dental aerosol found during HSH cavity preparation or ultrasonic scaling present a risk of infection, confirming the advice to use respiratory PPE. HVE and LVE both effectively reduced aerosol generation during scaling, whereas the new aerosol-reducing ‘no air’ function was highly effective and can be recommended for HSH drilling.