CATEGORY AUSTRALASIAN DENTIST 61 LINICAL There is no significant difference in aerosol levels generated between dental HSH with the 3 different coolant-port designs and (2) there is no significant differences in aerosol levels generated during ultrasonic scaling with the 3 different suction conditions. Materials and methods Particle concentration measurements Tests were conducted using a dental mannequin in an enclosed, windowless dental surgery. The floor space measured ∼3.9 m × 3.5 m × 2.7 m. The room was mechanically ventilated (supply at 0.042 m3/s or 4.1 air changes per hour [ACH]). Air entered the room through a ceiling grille above the foot of the dental chair and passively exhausted through a ceiling grille above the head of the dental chair. To reduce background particle concentration, all surfaces (eg, floor) were cleaned, and operators wore clean personal protective equipment (PPE). A Sheffield HEPA-13 air purifier (Prolink, Auckland, NZ) was run at maximum fan speed, with a clean air delivery rate of 320 m3 per hour (the equivalent of an additional 8.6 ACH). The purifier was run for 40 minutes before the sequence of measurements commenced, and it ran continuously throughout the measurements at maximum fan speed. The air filtration rate, being twice the ventilation rate, had a significant effect on the background particle concentrations but was not expected to significantly affect the concentration at the operators’ location. The concentration of particles here is dominated by the production of aerosol at the patient’s mouth, and the particles are measured within seconds of their generation. Particle concentrations were measured with 2 AeroTrak particle counters (TSI, Shoreview, MN, USA): (1) an AeroTrak 9306 (with isokinetic inlet, TSI part no. 700003) mounted on a tripod at roughly the position of the dental practitioner’s face and (2) an AeroTrak 9310 (with isokinetic inlet 700068) placed on a bench located along the wall opposite the dental chair. Both counters independently measured particle concentrations in 6 size ranges: 0.3–0.5 μm, 0.5–1.0 μm, 1.0–3.0 μm, 3.0–5.0 μm, 5.0–10.0 μm, and 10.0– 25.0 μm. A Kestrel 5000 Environmental Meter (Nielsen-Kellerman, Boothwyn, PA, USA) logged temperature and humidity at 1-minute intervals. The Dental Council of New Zealand does not normally specify ventilation rates for dental surgeries, but it did release some guidance during COVID-19 alert level 2 in 2021. (This was the second of 4 alert levels, and level 2 applied during periods when there was a low rate of community transmission.) This guidance stated that rooms with 1–2 ACH were to be considered poorly ventilated and that high-volume suction was to be considered essential in such rooms. It specified standdown periods after aerosol-generating procedures of 10–30 minutes depending on what combinations of evacuation and dental dams were used. The net ventilation rate of 8.6 ACH in our test room is high for mostmechanically ventilated buildings, but it falls within ASHRAE recommendations of ≥6 ACH for most treatment rooms other than operating theatres. We considered that, given that the building ventilation supply is filtered, 8.6 ACH provided an acceptably low level of background particle concentration for these tests. Data processing and classification of activities Various oral health activities simulated by an operator and assistant were classified into 17 types: ‘consultation: talking, no purifier’; ‘consultation: silence, no purifier’; ‘triplex, no purifier’; ‘movement of people (pax) (simulating a patient/ person), no purifier’; ‘lunch, no purifier’; ‘preparation, no purifier’; ‘consultation: talking’; ‘consultation: silence’; ‘triplex’; ‘movement of pax’; ‘purifier ON’; ‘scaling’; ‘rest (persons present with minimal movement)’; ‘preparation’; ‘drilling’; ‘test of handpiece setting’; and ‘room empty.’ Suction was classified into HVE suction, LVE suction, or no suction. For drilling, 4 location classifications were used: upper incisor, upper left molar, lower front incisor, patient’s right, or lower right molar. Also, 3 drilling directions were used: rear, front, or occlusal. Finally, 3 handpiece configurations were used: ‘1 port, water and spray, NSK Z85 at maximum air pressure,’ ‘4 ports, water and spray, NSK Z95L at maximum air pressure,’ or ‘4 ports, water, NSK Z95L at maximum air pressure and no spray.’ Calculation of excess total particle volume concentration The AeroTrak instruments accumulated particle counts in 6 size ranges (channels 1–6): 0.3–0.5 μm, 0.5–1.0 μm, 1.0–3.0 μm, 3.0–5.0 μm, 5.0–10 μm, and 10–25 μm. Assuming that all measured particles were spherical with a uniform size distribution, the volume mean diameters for each channel were 0.42 μm, 0.83 μm, 2.4 μm, 4.2 μm, 8.3 μm, and 20 μm, respectively. The particle concentration (number per unit volume) in each channel was multiplied by the volume mean diameter for that channel to calculate the particle volume per unit volume of air sampled. These data were summed over all 6 channels to calculate total particle volume per unit volume of air sampled. In our experiment, a persistent background level of particles was not generated by dental treatment activity (ie, mainly shed skin cells, clothing fibers, etc). During the ‘rest’ activities, the concentrations measured by the Aerotrak 9310 instrument (at a distance from the practitioner) corresponded well with the Aerotrak 9306 instrument (near the practitioner). Therefore, the Aerotrak 9310 measurements were assumed to be equal to the background aerosol concentration. Minute differences between the 2 instruments during these rest periods were attributed to the noise inherent in particle counting and the spatial nonhomogeneity of the air currents. The AeroTrak 9310 data were subtracted from the AeroTrak 9306 data to obtain the excess aerosol concentrations released in the vicinity of the dental practitioner by the activities of interest. The mean over each consecutive 30-second counting interval during each activity of interest was calculated.Themean over the repeated measurements of the same type of activity was then calculated. Dental operative procedures Two operators (1 clinician and 1 assistant) were present, dressed in minimum PPE requirements (surgical mask to ASTM F2100 standard, eye protection, gloves, and outer protective clothing or gown) according to the DCNZ COVID-19 level 1 guidelines.11 The clinician performed the ultrasonic scaling and drilling operative procedures following the same sequence for each test (Fig. 1). All simulated dental operative procedures were conducted using a Viva Ace portable dental unit (NSK, Japan) and simulation teeth (PRO2001-UL-SCFEM-32, Nissin, Japan). Teeth sets were attached to a Nissin type 1 dental simulator head set (including head, type 1 articulator, and small mask) mounted on the dental chair. The ultrasonic scaler and HSHs used are listed in Table 1. For ultrasonic scaling, each test was carried out with a Varios2-LUX scaler (NSK) with a type G6 tip and the recommendedG8 Fig. 1. Dental test room layout.
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