CATEGORY 60 AUSTRALASIAN DENTIST LINICAL Dental high-speed handpiece and ultrasonic scaler aerosol generation levels and the effect of suction and air supply By Joanne Jung Eun Choi PhD1, Jason Chen PhD2, Yunsun Jane Choi MOH1, Susan M. Moffat PhD1, Warwick J. Duncan PhD1 , J. Neil Waddell PhD1 and Mark Jermy PhD2 1 Sir John Walsh Research Institute, Faculty of Dentistry, University of Otago, Dunedin, New Zealand and 2 Department of Mechanical Engineering, University of Canterbury, Christchurch, New Zealand Abstract 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/m3 and 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 (1.98×107 μm3/m3) whereas HVE significantly reduced volume to −4.47×105 μm3/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. (Received 27 March 2022; accepted 6 July 2022) In dentistry, the high-speed handpiece (HSH) is used for removing tooth structure to prepare teeth for restoration.1 Most modern HSHs incorporate air or air– water coolant ports, designed to spray water to improve cutting and polishing efficiency while minimizing pulp injury.2 The water coolant and the rotary cutting bur generate aerosol which, when combined with oral fluids creates bioaerosol.2 (Bio)aerosols may remain in the air for protracted periods, and they have the potential to transmit respiratory infections to oral health practitioners.3,4 The ongoing coronavirus disease 2019 (COVID-19) pandemic has recorded >476 million cases and >6.1 million deaths so far.5 Oral health practitioners face the greatest risk of contracting COVID-19 from aerosol exposure, more so than nurses and general physicians,6–8 and the WHO recommends that oral health clinicians employ strict personal protection measures to avoid or minimize aerosolproducing procedures.9 Guidelines on the provision of dental services during the COVID-19 pandemic have been frequently updated.8,9 Policy documents focus on dental instruments as aerosol sources and recommend rubberdam and high-volume evacuation (HVE) suction as mitigating measures.2,4,9,11,12 Severe acute respiratory coronavirus virus 2 (SARS-CoV-2) is the primary current concern, but our findings apply to many airborne pathogens. Depending on the design, HSHs generate different levels of aerosol.1,13 For example, air-turbine HSHs allow rapid preparation of dental hard tissues with minimal pulpal damage, but they create considerable aerosol.14,15 Conversely, electric-motor HSHs offer constant power and rarely stall, potentially creating less bioaerosol. Some dental HSHs include a function that directs air onto the cutting surface to help cool the tooth, disperse water spray, and clear debris.15,16 This ‘chip air’ function produces higher aerosol levels but can be deactivated in newer handpieces. Currently, few reports have quantified how much aerosol is produced by different types of HSHs, including those with or without the ‘chip air’ function.15 Furthermore, the literature shows that ultrasonic scalers produce ∼3 times the bioaerosol compared to hand instruments.12,17 To reduce aerosol production and to provide a drier operation field during dental procedures, low-volume evacuation (LVE) or high-volume evacuation (HVE) suction systems may be employed.17,18 Evaluating the effectiveness of different types of suction systems for drilling and scaling is important in developing standard guidelines for oral health practitioners to minimize cross infection by airborne pathogens. In this study, we compared aerosol generation (1) in dental HSHs with 3 different coolant port designs (1, 3, or 4 ports), with and without the new aerosolreducing function(ie,water jet only, no ‘chip air’) and (2) in ultrasonic scalers operated under 3 different suction conditions (ie, no suction, low-volume evacuation [LVE], or HVE). We formulated 2 null hypotheses: (1)
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