Evaluating contaminated dental aerosol and splatter in an open plan clinic environment: Implications for the COVID-19 pandemic

Abstract

Objectives: Identify splatter/aerosol distribution from dental procedures in an open plan clinic and explore aerosol settling time after dental procedures.

Methods: In two experimental designs using simulated dental procedures on a mannequin, fluorescein dye was introduced: (1) into the irrigation system of an air-turbine handpiece; (2) into the mannequin's mouth. Filter papers were placed in an open plan clinic to collect fluorescein. An 8-metre diameter rig was used to investigate aerosol settling time. Analysis was by fluorescence photography and spectrofluorometry.

Results: Contamination distribution varied across the clinic depending on conditions. Unmitigated procedures have the potential to deposit contamination at large distances. Medium volume dental suction (159 L/min air) reduced contamination in the procedural bay by 53%, and in other areas by 81-83%. Low volume suction (40 L/min air) was similar. Cross-ventilation reduced contamination in adjacent and distant areas by 80-89%. In the most realistic model (fluorescein in mouth, medium volume suction), samples in distant bays (≥5 m head-to-head chair distance) gave very low or zero readings (< 0.0016% of the fluorescein used during the procedure). Almost all (99.99%) of the splatter detected was retained within the procedural bay/walkway. After 10 min, very little additional aerosol settled.

Conclusions: Cross-infection risk from dental procedures in an open plan clinic appears small when bays are ≥ 5 m apart. Dilution effects from instrument water spray were observed, and dental suction is of benefit. Most settled aerosol is detected within 10 min indicating environmental cleaning may be appropriate after this.

Clinical significance: Aerosols produced by dental procedures have the potential to contaminate distant sites and the majority of settled aerosol is detectable after 10 min. Dental suction and ventilation have a substantial beneficial effect. Contamination is likely to be minimal in open plan clinics at distances of 5 m or more.

Keywords: Aerosols; Dental equipment; Dental fallow time; Dental high-speed equipment; Dental infection control; SARS-CoV-2.

Fig. 1

Experimental models used in this study. Fluorescein dye was either introduced into the irrigation systems of the dental instruments (a) or the mouth of the mannequin (b).

Fig. 2

Plan view of the open plan clinic area. Red star indicates the location of the aerosol generating procedure. Air intake (square vents) and air output (long vents) are shown. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).

Fig. 3

Heatmaps presenting spectrofluorometric analysis data from a 10-minute high-speed air-turbine anterior crown preparation. Panels represent different experimental conditions. (a): no dental suction, model 1 (dye in handpiece). (b): low volume dental suction (40 L/min), model 1. (c): medium volume dental suction (159 L/min), model 1. (d): medium volume dental suction with cross-ventilation (windows open on both sides of clinic), model 1. (e): medium volume dental suction, model 2 (dye in mouth). (f): medium volume dental suction with cross-ventilation, model 2. RFU: relative fluorescence units.

Fig. 4

Stacked bar chart presenting the impact of two levels of dental suction, cross ventilation and experimental model on total contamination across the experimental rig and mannequin in experiments 1–6 (open plan clinic experiments). The y-axis represents the sum of samples from the three repetitions of experimental condition. AGP: Aerosol Generating Procedure.

Fig. 5

Bar chart presenting the total contamination across the experimental rig and mannequin as measured by spectrofluorometric analysis and presented by collection time in experiments 7–9 (time course experiments). The experimental procedure was a 10-minute anterior crown preparation with a high-speed air-turbine handpiece without dental suction. The y-axis represents the sum of all samples collected at each time point. Three data points were missing; a mean value was imputed from the other two repetitions of each of these data points to ensure comparability (n per time point = 207). RFU: relative fluorescence units. AGP: aerosol generating procedure. *Comparative data are presented from a previous study [37].