Aerosol and spatter mitigation in dentistry: Analysis of the effectiveness of 13 setups

Aerosol-generating procedures and associated control/mitigation measures: Position paper from the Canadian Dental Hygienists Association and the American Dental Hygienists' Association

Background

Since the outbreak of COVID-19, how to reduce the risk of spreading viruses and other microorganisms while performing aerosolgenerating procedures (AGPs) has become a challenging question within the dental and dental hygiene communities. The purpose of this position paper is to summarize the evidence of the effectiveness of various mitigation methods used to reduce the risk of infection transmission during AGPs in dentistry.

Methods

The authors searched 6 databases-MEDLINE, EMBASE, Scopus, Web of Science, Cochrane Library, and Google Scholar-for relevant scientific evidence published between January 2012 and December 2022 to answer 6 research questions about the risk of transmission, methods, devices, and personal protective equipment (PPE) used to reduce contact with microbial pathogens and limit the spread of aerosols.

Results

A total of 78 studies fulfilled the eligibility criteria. The literature on the risk of infection transmission including SARS-CoV-2 between dental hygienists and their patients is limited. Although several mouthrinses are effective in reducing bacterial contaminations in aerosols, their effectiveness against SARS-CoV-2 is also limited. The combined use of eyewear, masks, and face shields is effective in preventing contamination of the facial and nasal region while performing AGPs. High-volume evacuation with or without an intraoral suction, low-volume evacuation, saliva ejector, and rubber dam (when appropriate) have shown effectiveness in reducing aerosol transmission beyond the generation site. Finally, the appropriate combination of ventilation and filtration in dental operatories is effective in limiting the spread of aerosols.

Discussion and Conclusion

Aerosols produced during clinical procedures can pose a risk of infection transmission between dental hygienists and their patients. The implementation of practices supported by available evidence will ensure greater patient and provider safety in oral health settings. More studies in oral health clinical environments would shape future practices and protocols, ultimately to ensure the delivery of safe clinical care.

Characterization of Ag-Ion Releasing Zeolite Filled 3D Printed Resins

There has been profound growth in the use of 3D printed materials in dentistry in general, including orthodontics. The opportunity to impart antimicrobial properties to 3D printed parts from existing resins requires the capability of forming a stable colloid incorporating antimicrobial fillers. The objective of this research was to characterize a colloid consisting of a 3D printable resin mixed with Ag-ion releasing zeolites and fumed silica to create 3D printed parts with antiviral properties. The final composite was tested for antiviral properties against SARS-CoV-2 and HIV-1. Antiviral activity was measured in terms of the half-life of SARS-CoV-2 and HIV-1 on the composite surface. The inclusion of the zeolite did not interfere with the kinetics measured on the surface of the ATR crystal. While the depth of cure, measured following ISO4049 guidelines, was reduced from 3.8 mm to 1.4 mm in 5 s, this greatly exceeded the resolution required for 3D printing. The colloid was stable for at least 6 months and the rheological behavior was dependent upon the fumed silica loading. The inclusion of zeolites and fumed silica significantly increased the flexural strength of the composite as measured by a 3 point bend test. The composite released approximately 2500 μg/L of silver ion per gram of composite as determined by potentiometry. There was a significant reduction of the average half-life of SARS-CoV-2 (1.9 fold) and HIV-1 (2.7 fold) on the surface of the composite. The inclusion of Ag-ion releasing zeolites into 3D-printable resin can result in stable colloids that generate composites with improved mechanical properties and antiviral properties.

Air Quality in a Dental Skills Lab during the SARS-CoV-2 Pandemic: Results of an Experimental Study

Objectives

The study aimed to analyze different ways to control air quality during/after aerosol-generating procedures (AGPs) in a small skills lab with restricted natural air ventilation in preclinical dental training (worst-case scenario for aerogen infection control). Different phases were investigated (AGP1: intraoral high-volume evacuation (HVE); AGP2: HVE plus an extraoral mobile scavenger (EOS)) and afterward (non-AGP1: air conditioning system (AC), non-AGP2: AC plus opened door).

Methods

Continuous data collection was performed for PM1, PM2.5, and PM10 (µg/m³), CO2 concentration (ppm), temperature (K), and humidity (h⁻¹) during two summer days (AGP: n = 30; non-AGP: n = 30). While simulating our teaching routine, no base level for air parameters was defined. Therefore, the change in each parameter (Δ = [post]-[pre] per hour) was calculated.

Results

We found significant differences in ΔPM2.5 and ΔPM1 values (median (25/75th percentiles)) comparing AGP2 versus AGP1 (ΔPM2.5: 1.6(0/4.9)/−3.5(−10.0/−1.1), p=0.003; ΔPM1: 1.6(0.6/2.2)/−2.2(−9.3/−0.5), p=0.001). Between both non-AGPs, there were no significant differences in all the parameters that were measured. ΔCO₂ increased in all AGP phases (AGP1/AGP2: 979.0(625.7/1126.9)/549.9(4.0/788.8)), while during non-AGP phases, values decreased (non-AGP1/non-AGP2: −447.3(−1122.3/641.2)/−896.6(−1307.3/−510.8)). ∆Temperature findings were similar (AGP1/AGP2: 12.5(7.8/17.0)/9.3(1.8/15.3) versus non-AGP1/non-AGP2: −13.1(−18.7/0)/−14.7(−16.8/−6.8); p ≤ 0.003)), while for ∆humidity, no significant difference (p > 0.05) was found.

Conclusions

Within the limitations of the study, the combination of HVE and EOS was similarly effective in controlling aerosol emissions of particles between one and ten micrometers in skill labs during AGPs versus that during non-AGPs. After AGPs, air exchange with the AC should be complemented by open doors for better air quality if natural ventilation through open windows is restricted.

Influence of flow rate and different size of suction cannulas on splatter contamination in dentistry: results of an exploratory study with a high-volume evacuation system

Objectives

SOPs recommend high-volume evacuation (HVE) for aerosol-generating procedures (AGPs) in dentistry. Therefore, in the exploratory study, the area of splatter contamination (SCON in %) generated by high-speed tooth preparation (HSP) and air-polishing (APD) was measured when different suction cannulas of 6 mm diameter (saliva ejector (SAE)), 11 mm (HC11), or 16 mm (HC16) were utilized versus no-suction (NS).

Materials and methods

Eighty tests were performed in a closed darkened room to measure SCON (1m circular around the manikin head (3.14 m²) via plan metrically assessment through fluorescence technique. HSP (handpiece, turbine (Kavo, Germany)) or APD (LM-ProPower^TM (Finland), Airflow®-Prophylaxis-Master (Switzerland)) for 6 min plus 5 s post-treatment were performed either without suction or with low-flow (150 l/min for SAE) or high-flow rate (250 l/min/350 l/min for HC11/HC16) suction. All tests were two-tailed (p≤0.05, Bonferroni corrected for multi-testing).

Results

Irrespective the AGP, SCON was higher for NS (median [25th; 75th percentiles]: 3.4% [2.6; 5.4]) versus high-flow suction (1.9% [1.5; 2.5]) (p=0.002). Low-flow suction (3.5% [2.6; 4.3]) versus NS resulted in slightly lower but not statistically significantly lower SCON (p=1.000) and was less effective than high-flow suction (p=0.003). Lowest contamination values were found with HC16 (1.9% [1.5; 2.5]; p≤0.002), whereat no significant differences were found for HC11 (2.4% [1.7; 3.1]) compared to SAE (p=0.385) or NS (p=0.316).

Conclusions

Within study’s limitations, the lowest splatter contamination values resulted when HC16 were utilized by a high-flow rate of ≥250 l/min.

Clinical relevance

It is strongly recommended to utilize an HVE with suction cannulas of 16mm diameter for a high-flow rate during all AGPs and afterwards also to disinfect all surface of patients or operators contacted.

Efficacy of dental evacuation systems for aerosol exposure mitigation in dental clinic settings

Dental personnel are ranked among the highest risk occupations for exposure to SARS-CoV-2 due to their close proximity to the patient's mouth and many aerosol generating procedures encountered in dental practice. One method to reduce aerosols in dental settings is the use of intraoral evacuation systems. Intraoral evacuation systems are placed directly into a patient's mouth and maintain a dry field during procedures by capturing liquid and aerosols. Although multiple intraoral dental evacuation systems are commercially available, the efficacy of these systems is not well understood. The objectives of this study were to evaluate the efficacy of four dental evacuation systems at mitigating aerosol exposures during simulated ultrasonic scaling and crown preparation procedures. We conducted real-time respirable (PM₄) and thoracic (PM₁₀) aerosol sampling during ultrasonic scaling and crown preparation procedures while using four commercially available evacuation systems: a high-volume evacuator (HVE) and three alternative intraoral systems (A, B, C). Four trials were conducted for each system. Respirable and thoracic mass concentrations were measured during procedures at three locations including (1) near the breathing zone (BZ) of the dentist, (2) edge of the dental operatory room approximately 0.9 m away from the mannequin mouth, and (3) hallway supply cabinet located approximately 1.5 m away from the mannequin mouth. Respirable and thoracic mass concentrations measured during each procedure were compared with background concentrations measured in each respective location. Use of System A or HVE reduced thoracic (System A) and respirable (HVE) mass concentrations near the dentist's BZ to median background concentrations most often during the ultrasonic scaling procedure. During the crown preparation, use of System B or HVE reduced thoracic (System B) and respirable (HVE or System B) near the dentist's BZ to median background concentrations most often. Although some differences in efficacy were noted during each procedure and aerosol size fraction, the difference in median mass concentrations among evacuation systems was minimal, ranging from 0.01 to 1.48 µg/m³ across both procedures and aerosol size fractions.

Experimental evaluation of aerosol mitigation strategies in large open-plan dental clinics

BACKGROUND

Aerosols are generated routinely during patient care in dentistry. Managing exposure risk requires understanding characteristics of aerosols created during procedures such as those performed using high-speed drills that operate at 200,000 revolutions per minute.

METHODS

A trained dentist performed drilling procedures on a manikin's incisors (teeth nos. 8 and 9) using a high-speed drill and high-volume evacuator. The authors used high-speed imaging to visualize the formation and transport of aerosol clouds and particle sampling to measure aerosol concentration and size distribution at several locations. The authors studied several aerosol mitigation strategies.

RESULTS

Aerosols produced during high-speed drilling were erratic and yielded high concentrations that were at least an order of magnitude above baseline. High-speed imaging showed aerosols initially travelled at 1 m per second. Owing to erratic behavior of aerosols, supplemental suction was not effective at collecting all aerosols; however, barriers were effective.

CONCLUSIONS

Barriers are the most effective mitigation strategy. Other methods studied have limitations and risks. To the authors' knowledge, this article presents the first characterization of aerosols generated during high-speed drilling by a dentist.

PRACTICAL IMPLICATIONS

With thorough preoperative planning and the use of this investigation's findings about effectiveness of mitigation strategies as a guide, dental offices may be able to return to prepandemic productivity.

Characterization and mitigation of aerosols and spatters from ultrasonic scalers

BACKGROUND

Dental procedures often produce aerosols and spatter, which have the potential to transmit pathogens such as severe acute respiratory syndrome coronavirus 2. The existing literature is limited.

METHODS

Aerosols and spatter were generated from an ultrasonic scaling procedure on a dental manikin and characterized via 2 optical imaging methods: digital inline holography and laser sheet imaging. Capture efficiencies of various aerosol mitigation devices were evaluated and compared.

RESULTS

The ultrasonic scaling procedure generated a wide size range of aerosols (up to a few hundred μm) and occasional large spatter, which emit at low velocity (mostly < 3 m/s). Use of a saliva ejector and high-volume evacuator (HVE) resulted in overall reductions of 63% and 88%, respectively, whereas an extraoral local extractor (ELE) resulted in a reduction of 96% at the nominal design flow setting.

CONCLUSIONS

The study results showed that the use of ELE or HVE significantly reduced aerosol and spatter emission. The use of HVE generally requires an additional person to assist a dental hygienist, whereas an ELE can be operated hands free when a dental hygienist is performing ultrasonic scaling and other operations.

PRACTICAL IMPLICATIONS

An ELE aids in the reduction of aerosols and spatters during ultrasonic scaling procedures, potentially reducing transmission of oral or respiratory pathogens like severe acute respiratory syndrome coronavirus 2. Position and airflow of the device are important to effective aerosol mitigation.

Spray mist reduction by means of a high-volume evacuation system-Results of an experimental study

OBJECTIVES

High-speed tooth preparation requires effective cooling to avoid thermal damage, which generates spray mist, which is a mixture of an aerosol, droplets and particles of different sizes. The aim of this experimental study was to analyze the efficacy of spray mist reduction with an intraoral high-volume evacuation system (HVE) during simulated high-speed tooth preparation for suboptimal versus optimal suction positions of 16 mm sized cannulas and different flow rates of the HVE.

MATERIAL AND METHODS

In a manikin head, the upper first premolar was prepared with a dental turbine, and generated particles of 5-50 microns were analyzed fifty millimeters above the mouth opening with the shadow imaging technique (frame: 6.6×5.3×1.1 mm). This setup was chosen to generate a reproducible spray mist in a vertical direction towards an imaginary operator head (worst case scenario). The flow rate (FR) of the HVE was categorized into five levels (≤120 l/min up to 330 l/min). The number of particles per second (NP; p/s) was counted, and the mass volume flow of particles per second (MVF; μg/s*cm3) was calculated for 10 sec. Statistical tests were nonparametric and two-sided (p≤0.05).

RESULTS

With increasing flow rate, the NP/MVF values decreased significantly (eta: 0.671/0.678; p≤0.001). Using a suboptimally positioned cannula with an FR≤160 l/min, significantly higher NP values (mean±SD) of 731.67±54.24 p/s (p≤0.019) and an MVF of 3.72±0.42 μg/s*cm3 (p≤0.010) were measured compared to those of the optimal cannula position and FR≥300 l/min (NP/MVF: 0/0). No significant difference in NP and MVF was measurable between FR≥250 l/min and FR>300 l/min (p = 0.652, p = 0.664).

CONCLUSION

Within the limitations of the current experimental study, intraoral high-flow rate suction with ≥300 l/min with an HVE effectively reduced 5-50 μm sized particles of the spray mist induced by high-speed tooth preparation with a dental turbine.

The efficacy of an extraoral scavenging device on reducing aerosol particles ≤ 5 µm during dental aerosol-generating procedures: an exploratory pilot study in a university setting

Objective/aim

To identify small particle concentrations (eight categories: ≤0.1 µm × ≤5.0 µm) induced by aerosol-generating procedures (AGPs; high-speed tooth preparation, ultrasonic scaling; air polishing) under high-flow suction with a 16-mm intraoral cannula with and without an additional mobile extraoral scavenger (EOS) device during student training.

Materials and methods

Twenty tests were performed (16.94 m² room without ventilation with constant temperature (26.7 (1.1) °C and humidity (56.53 (4.20)%)). Data were collected 2 min before, 2 min during, and 6 min after AGPs. The EOS device and the air sampler for particle counting were placed 0.35 m from the open mouth of a manikin head. The particle number concentration (PN, counts/m3) was measured to calculate ΔPN (ΔPN = [post-PN] − [pre-PN]).

Results

Mean ΔPN (SD) ranged between −8.65E+06 (2.86E+07) counts/m³ for 0.15 µm and 6.41E+04 (2.77E+05) counts/m³ for 1.0 µm particles. No significant differences were found among the AGP groups (p > 0.05) or between the AGP and control groups (p > 0.05). With an EOS device, lower ΔPN was detected for smaller particles by high-speed tooth preparation (0.1–0.3 µm; p < 0.001).

Discussion

A greater reduction in the number of smaller particles generated by the EOS device was found for high-speed tooth preparation. Low ΔPN by all AGPs demonstrated the efficacy of high-flow suction.

Conclusions

The additional use of an EOS device should be carefully considered when performing treatments, such as high-speed tooth preparation, that generate particularly small particles when more people are present and all other protective options have been exhausted.