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

Abstract Objectives The current study aims to investigate the aerosol and spatter mitigation quality of 13 dry‐field isolation methods in a simulated setup that replicates real‐life work scenarios encountered in dental practices. Methods A crown preparation on a manikin was performed on tooth number 30 and repeated five times for each setup to simulate a patient under care. Aerosol, environmental, and operator face shield spatter, and sound intensity was measured. Generalized linear mixed models were used, and posthoc pairwise comparisons were performed to compare least‐squares means when appropriate using a Tukey adjustment. Results All tested setups showed some environmental spatter formation; however, these were able to control most (and in some cases all) spatter on the operator face shield. All methods resulted in excellent aerosol mitigation when a second line of high‐volume evacuation (HVE) was added to the device setup. However, in most setups, total sound levels exceeded 85 dB, posing a concern for prolonged noise exposure. Conclusions The Prototype device and four other tested setups with secondary HVE addition completely eliminated aerosol creation as tested. Spatter of the Face Shield was best eliminated using the Prototype device. Clinical Significance Within the limitations of this study, it can be concluded that the dental community has at its disposal equipment that can effectively mitigate aerosol and spatter.


| INTRODUCTION
The effect of SARS-CoV-2 in dentistry has been particularly concerning. 1,2 The SARS-CoV-2 virus appears to be unique compared to other viruses. The virus apparently can spread in the absence of clinical symptomology, or more likely, the symptoms may be so subtle that it is often unrecognized by those who are affected or their caretakers. 3,4 It was submitted that one of the primary mechanisms of SARS-CoV-2 virus transmission is via aerosols 5,6 known to be generated throughout dental procedures. [7][8][9][10][11][12] It has been shown that the SARS-CoV-2 virus can be detected in the saliva of affected patients. 13,14 The virus binds to the human angiotensin-converting enzyme-2 receptor, 14,15 that is highly concentrated in human salivary glands and ducts, leading to the postulate that the SARS-CoV-2 virus is transmitted via salivary droplets. 15,16 Furthermore, SARS-CoV-2 RNA has been detected in saliva for 37 days after onset. 17 Spatter (mists) consists of droplets up to 50 μm in size that sink quickly, whereas aerosols are defined as droplet particles smaller than 5 μm that can remain airborne for extended periods. These small particles can reach deep into the bronchioles and have been reported to be significant in viral infections. [18][19][20] Therefore, these drops might contain infectious particles that pose a health threat to those within the spray's pattern. [21][22][23][24] It is reasoned, therefore, that aerosol generation from the use of a dental handpiece or an ultrasonic scaler in a patient's mouth has, at least in theory, the potential of transmitting the virus, [7][8][9][10][11][25][26][27][28][29][30] even though to date no conclusive evidence of viral transmission occurring in a dental treatment environment has been documented. 31 The half-life of SARS-CoV-2 in aerosols is reported to be approximately 1.1-1.2 h and larger droplets settled on surfaces as spatter have a median half-life of 5.6 h. 32 Therefore, this issue has raised a concern about the potential spread of the virus in the dental setting and has contributed to the need for the development of aerosol and spatter mitigation strategies.
In response to this challenge, new devices were introduced into the dental market. In a previous paper, 33 eight dry-field isolation methods were tested in a typodont setup in which air-water spray was generated with a high-speed handpiece without cutting teeth.
Although standardized procedures were employed, the study was limited in that it did not reproduce real-life work scenarios. The current study aims to investigate the mitigation quality of 13 dry-field isolation methods in a simulated real-life setup that more closely replicates work scenarios encountered in dental practices.
This study attempts to compare the effectiveness of the following techniques: 1. High-volume evacuation-(HVE) 2. Rubber dam (RD) with HVE (RD and HVE) 3. Prototype 3D printed lip retractor with internal suction and funnel (PROTO) (Figure 1

| Grid around manikin
A custom four by three-foot wooden board with black plastic coating was cut to fit around the manikin head and marked with a grid to score the spatter ( Figure 2). The grid was created with florescent tape fixed tightly at 5 cm intervals to create areas of 5 cm 2 . One clinician performed all crown preparations on tooth #30. Each preparation was completed in 2 min, with the operator sitting at the 8 o'clock position at a standard distance from the patient of 40 cm.

| Handpiece
A single high-speed handpiece (NSK Ti-Max X95L, Hoffman Estates, IL) was used and operated at the maximum torque and rotation speed of 200,000 revolutions per minute. The water flow through the handpiece was set at 25 ml/min, and the air pressure was selected to achieve an aerosol plume. The standard all-ceramic crown preparation was done using a diamond bur 878K016 (Brasseler USA, Savannah, GA) placed in the dental handpiece.

| Suction device setups
The dental chair (ADEC, Newberg, OR) setup used in this investigation is equipped with two separate HVE lines and one saliva ejector line.
The following settings were used: 1. In this setup, and whenever a secondary HVE was used in our testing, a conventional disposable vented tip (Henry Schein, Melville, NY) was used in one of the HVE lines and positioned 4 cm from the tooth to be prepared.

A 3D printed internally irrigated retraction device (PROTO) was
created with the Prusa MK3s 3D printer using Prusament PLA (Prusa Research, Prague, Czech Republic) with a layer height of 100 mm, extruder temperature of 220 C, and a bed temperature of 68 C with an infill of 100%. The frame included suction ports attached to the saliva ejector and the HVE line (Figures 1 and 2).
4. For the ISO (Zyris, Santa Barbara, CA) trials, a medium-size mouthpiece was used to obtain the best fit for the dental simulator head.  The resulting spatter that escaped suction during the high-speed handpiece operation was visualized with a light-emitting diode dental curing light (Elipar™ S10, 3 M, Inc., St. Paul, MN) emitting blue light with a spectral range of between 425 and 500 nm. The diode was held 8 cm from the paper's surface to fluoresce spatter droplets that had collected, and visualization was achieved using amber-colored protective glasses (Figure 3).
A calibrated operator reviewed the droplet field created during the trials. If even one spot of fluorescence was identified within a 5 cm 2 square, the cell was then scored as being contaminated. The number of squares with contamination were counted to determine the amount of spatter produced in each trial. Spatter generated using the high-speed handpiece with no suction served as the positive control value.
2.Face shield spatter: A grid was placed on a Face Shield (ZShield Health, ZVerse, Columbia, SC) worn by the operator during preparation of the typodont tooth in the manikin. The grid squares were 5 cm 2 in area and were created using the same fluorescent tape. If one spatter was detected in a grid cell, it was counted as positive ( Figure 4). sounds are perceived as 10-20 dB louder than outside this range at the same intensity 35 and in this frequency range, we also find essential parts of speech information. 36 For the analysis, we are reporting the total sound level (TSL) as computed by the application. We do not report the sound for the setup HVE and RD because we found it sufficient to report HVE alone. The same approach was implemented for the VAC setup, for which we only report sound measured when the VAC was placed 15 cm from the manikin mouth, that is, VAC15.

| Statistical analysis
Based on previous publications, 34 it was determined that five trials were necessary for each setup to achieve a power of 0.80 (effect size = 0.20; p < 0.05). For each outcome (Aerosol, Environmental, and Face Shield Spatter and Sound), generalized linear mixed models were used to look at differences between groups. A random intercept was included in the model to account for replicates. Normality assumptions were checked, and a log transformation was needed for all outcomes. Post-hoc pairwise comparisons were performed to compare least-squares means when appropriate using a Tukey adjustment. All statistical analyses were performed using SAS v9.4 (SAS Institute, Inc.). The graphs show the median values of the five trials performed for each group, and the bars show the 25th and 75th percentiles.

| RESULTS
Descriptive statistics of the results can be found in Table 1. The ambient room results obtained before operating the high speed are considered negative control values. In contrast, the positive control results labeled as "Control" were obtained when the high speed was used to prepare the tooth without any suction mitigation devices.

| Environmental spatter
The environmental spatter analysis (

| Face shield spatter
The primary observation (

| Aerosol
It is worth noticing (

| Total sound level
Although the VAC had the lowest noise level (less than 80 dB), it loses this advantage when an HVE line is added to the mix (   The creation of aerosol and spatter during dental procedures has been a keen focus of concern during the COVID-19 pandemic. Many different mitigation strategies and devices have been created and advertised to address these concerns. However, there has not been, any clear understanding if these devices are effective. Ravenel et al. 33 demonstrated that several of the conventional evacuation apparatuses found in the dental practice could effectively reduce and eliminate aerosol and spatter when used in combination, typically with both and intra and extraoral high volume evacuation. However, it did not replicate aerosol and spatter creation that occurs when actually working with a handpiece intraorally since the preparation of teeth was not part of that study. This paper attempts to demonstrate  Regarding RD use with HVE, our results show that it is an efficient aerosol mitigation strategy. These results are consistent with previously reported data. 33 This is surprising because our study showed that HVE alone provided only partial aerosol mitigation. We can postulate that the use of RD limits the dispersion of aerosols in the patient's mouth and the resulting turbulence that may cause the aerosols to escape from the HVE suction. Sound also comes into play when attempting to mitigate aerosol and spatter in the dental workplace. As previously discussed in Ravenel et al. 33 the sound output of these various mitigation devices can be problematic, especially in light of the Occupational Safety and Health Administration (OSHA) 38 and National Institute for Occupational Safety and Health (NIOSH) maximum noise standards 39 of 90 and 85 dB respectively. In this study, the TSL of the setups tested ranged from a low of 76.9 dB for VAC 15 to a high of 98.72 dB for PROTO. Most setups TSL measured between the OSHA and the NIOSH standards, that is, between 85 and 90 dB. One reason the PROTO device might be loud is that it was a 3D printed prototype with an irregular surface.

| CONCLUSION
Within the limitations of this study, it can be concluded that the dental community has at its disposal equipment and instrumentation that can significantly mitigate the creation of aerosol when performing AGPs. The simplest and most widely used solution setup HVE + RD (HVE with RD) allows satisfactory mitigation of spatter and most aerosols when the clinical situation allows. However, this study demonstrates that there are other mitigation strategies that are more effective, particularly when used in conjunction with a secondary HVE apparatus. These simple setups can be quickly incorporated into every practice, often without requiring a significant capital investment.