Aerosol suppression from a handpiece using viscoelastic solution in confined dental office Free

Cross-infection refers to an unexpected transfer of contaminants, including bacteria and viruses, from one individual to another under unsanitary conditions. In dentistry, cross-infection is caused by splashing, contact, or inhalation of aerosols with secretions such as microorganisms-containing saliva and blood from the patient to the dentist or vice versa.^1,2 Dental high-speed handpiece treatment that generates aerosols or splatter is the main vehicle that can cause airborne contamination by microorganisms from the oral cavity.^3,4 Because the face of the dentist is always exposed and is close to the oral cavity of the patient, the risk of such cross-infection is bound to increase.⁵ This health risk is becoming a serious problem in the current global COVID-19 scenario and with the threat of future pandemics to come. Other individuals in the dental facility are also at risk owing to droplet transport in air through the ventilation system, or the emergence of fully airborne microbes because of droplet evaporation during flight.^6–10 

A number of previous studies have been conducted on aerosol control that can prevent the spread of infectious diseases during dental procedures.^11–13 Preventive measures suggested in these studies include mouthwash before surgery, rubber dam isolation, aerosol vacuum suction, and air filtration.¹⁴ However, although these approaches can progressively reduce aerosol generation and transmission of infectious particles, none of them can fundamentally eliminate aerosol generation. Therefore, personal protective equipment (PPE) must be used in these clinical scenarios, and guidelines should exist to protect healthcare workers and patients from aerosol-borne infections. In addition, this approach to protecting individuals is expensive and depends entirely on human compliance, which creates additional psychological and ethical issues.¹⁵ 

Another approach to controlling the aerosol spread of potential infectious agents is to limit or completely eliminate aerosol production by surgical and dental instruments. Lempel and Szalma reduced aerosols generated from a high-speed handpiece by adjusting the cooling spray mode of the handpiece.¹⁶ Yarin and co-workers recently added a high-molecular-weight polymer (i.e., polyacrylic acid, which is a polymer approved by the U.S. Food and Drug Administration) to dental coolant and confirmed that the aerosols in dental instruments are strongly suppressed.⁶ This breakthrough method is more economical and efficient than the aforementioned prevention methods because it can eliminate the aerosol source by suppressing liquid atomization with highly viscoelastic polymeric solutions.

The present study is the next stage of the aerosol-limiting approach,⁶ which revealed that the use of viscoelastic polymer solutions can suppress aerosolization from a high-speed handpiece, which is widely used in dentistry. Unfortunately, a high-speed handpiece is one of the most aerosol-generating dental devices.^5,17 In this study, a micrometer-scale spatial distribution of the aerosols from a high-speed handpiece was visually confirmed, examined, and quantified. In addition, the cooling performance of a polymer-containing coolant was investigated in this study. Note that here the aerosolization suppression from dental handpiece is in focus and a detailed study of the corresponding mechanical and thermal characteristics is given. This differs the present work from that of Ref. 6, where aerosolization suppression from cavitron tip was in focus, while dental handpiece was mentioned only tangentially, without a detailed study of the corresponding mechanical and thermal characteristics. Furthermore, using a mock dental procedure, we also examined here the effect of the polymer-containing coolant on dental practitioners and patients.

It should be emphasized that respiratory viruses including SARS-CoV-2 can be transmitted among humans by respiratory droplets and aerosols.¹⁸ Respiratory droplets and aerosols transmitted through air are related to viral shedding via virus-bearing particles from an infected human by means of breathing, sneezing, talking, and coughing.^18,19 The present work deals with a model situation related to aerosol dispersion from a high-speed handpiece and an effective novel method of its suppression. The presence or absence of viruses in the aerosol is absolutely immaterial from the present perspective, and in the present model situation, droplets did not contain any viruses. Still, the present approach is equally relevant and helpful in the case of virus-carrying droplets, because their density, viscosity, viscoelasticity, and other physical properties of importance here are practically unaffected by viruses, or the mechanisms by which they are entrained into droplets.

Polyacrylic acid (PAA, M_w = 450 kDa) mixed with a conventional coolant (de-ionized water) was purchased from Sigma-Aldrich (USA). In all experiments, the coolant was maintained at a room temperature of ∼27 °C.

The volume and mass of the PAA solution were measured using a pipet controller (Falcon pipet controller, Corning, USA) and precision balances (BCE6200–1S, Satorius, Germany), respectively. The solution density, ρ, was calculated by dividing mass by volume. To measure the dynamic (absolute) shear viscosity, a rotary viscometer (DVELV, AMETEK Brookfield, USA) connected to a spindle (YULA-15) with a constant shear rate, γ, was used. A surface tension meter (BZY-102, VTSYIQI, USA) was employed to measure the surface tension, σ. To measure the thermal properties of the solution; specific heat c_p, thermal diffusivity α, and thermal conductivity k, a laser flash apparatus (LFA 457, NETZCH, Germany) was employed.

The capillary-driven self-thinning of solution threads realizing a uniaxial elongational flow was employed to investigate solution viscoelasticity.^20–23 First, a droplet of polymer solution (0.2 ml) was dripped onto a copper plate using a pipette controller. Next, an aluminum rod (2 mm in diameter) was used to gently touch the droplet on the copper plate. Then, the rod was moved 0.5 mm vertically from the droplet at a speed of 280 mm·s⁻¹. Accordingly, the drop began to elongate and formed a thin thread between the plate and rod. Then, the drop stretching has been stopped and the further change in the thread diameter driven by capillarity (surface tension) was recorded using a high-speed camera (Phantom V7, Phantom, USA).

The high-speed handpiece (KT 15-SQD) was provided by Dunamis Dental (Republic of Korea). A syringe pump (Legato 100) was purchased from KD Scientific (USA), wherein a 50-ml syringe (A50, Henke-Sass Wolf, Germany) was installed to supply the coolant at a fixed flow rate of 18 ml·min⁻¹. A portable dental unit (DRV) was purchased from 3S Medical (Republic of Korea), which allowed high-pressure air of 4 bar to be supplied to the handpiece. The high-pressure air was used for the kinetic rotation of the handpiece bur and aerosolization of the liquid (i.e., water or PAA solutions in this study).²⁴ The rotation rate of the bur was measured using a handpiece counter (HPW-2, Micron Co., Japan), and the rate was at 362 krpm regardless of the coolant type. A diamond bur set (TD2032A, Komet, Germany) was also prepared and mounted on the handpiece. Photographs of the experiments were obtained using a digital camera (EOS600D, Canon, Japan).

As shown in Fig. S1(a) in the supplementary material, an experimental setup for observing aerosols from a high-speed dental handpiece was designed and built. It comprises three main parts: (i) a high-speed camera (Phantom V10, Phantom, USA) connected to a computer, (ii) a syringe pump, and (iii) a dental handpiece connected to the dental unit. High-speed videos were obtained and processed using an imaging program (PCC 2.8, Phantom, USA). The aerosol velocities were measured using ImageJ software (1.53k version, Wayne Rasband, USA) with the Multitracker plugin. A control volume was set around the bur, and for the aerosols moving within that range, the initial velocities were measured. In the case of aerosols larger than the control volume, the control volume increased.

As shown in Fig. S1(b), an experimental setup for observing aerosols from a distance was prepared. Green short-wavelength flashlights (A100, Vastfire, China) were installed in a dark room to facilitate an effective observation of spray jets. Multiple green laser beams were installed at distance intervals of 30 cm.

Figure S1(c) shows the experimental setup used to explore the temperature variation near the pulp chamber of the tooth when shaving the tooth using PAA solutions. The experimental setup consisted of (i) a syringe pump, (ii) a handpiece connected to the dental unit, (iii) a thermocouple connected to a data logger, and (iv) a horizontally movable human tooth. Human teeth collected after dental procedures were used as a test subject. The teeth were extracted and immediately kept in a vial filled with cool distilled water. Because the teeth were collected from different patients, they were pre-processed to achieve similar sizes. This study was approved by the Institutional Review Board of Korea University, according to the protocol of the university (KUIRB-2021–0304-01). A new tooth was prepared for each case of temperature measurement. A resin (Filtek 3.5A) for filling inside a tooth was purchased from 3M (USA), and a curing gun (DTE O-light) for curing the resin was purchased from Guilin Woodpecker Medical Instrument Co., Ltd. (China). A data logger (MV 1000) purchased from Yokogawa (Japan) was connected to thermocouples (K-type, ± 0.3 °C, Omega, Inc., Republic of Korea) to measure the temperature variation of the tooth. A bending test machine (Ocean Science, Republic of Korea) was used to implement horizontal movement of the tooth. Through the bending test machine, the force applied by the handpiece to the teeth was maintained at 1.68 N.

Prior to conducting the temperature measurements in experiments, the pulp chamber inside the tooth was scraped off to install the thermocouple. Next, the rest of the pulp chamber was filled with resin, thereby fixing the thermocouple and insulating it from the surrounding parts, followed by the hardening process using a curing gun. The thickness of the enamel/dentine layer composing the tooth was maintained at 2.5 mm, which was intentionally flattened through occlusal and buccal reductions. The tooth specimen was fixed inside a 200-ml plastic bucket using a silicone adhesive, which was then attached to a bending test machine to induce repetitive movement in the horizontal direction. The speed of the leftward and rightward repetitive movements was 0.8 mm·s⁻¹. The inside of the bucket was filled with water, and the water temperature was maintained at ∼37 °C during the experiment.

To better explore the practical effects of PAA, mock dental procedures with pure water and a 2 wt. % PAA solution were carried out on a mannequin head (Taekwang Industrial, Republic of Korea) equipped with typodont model teeth [Fig. S1(d)]. The handpiece simulation was performed by an experienced operator pressing the handpiece with a force of 1.7 ± 0.2 N. During dental procedures, the syringe pump and dental unit employed in the previous experiments were used in the same way. A drop of fluorescent liquid (water-soluble fluorescent solution, Flamak Chemical Industry Co., Ltd., Germany) was mixed with 20 ml of coolant and used as a tracer of a UV light torch (UV 12LED, Robust, China). The position of the operator's face was set at a distance of 30 cm from the typodont model. During the experiment, the operator wore safety glasses, a mask, and protective clothing to observe the effect of PAA to the operator. After the simulation, the droplets splattered on the faces of both the mannequin and operator were observed with the UV light.

Aerosolization is associated with drop detachment from a body of fluid, which is a predominantly uniaxial elongation flow in the drop tail. It can be suppressed by significant elastic forces developing in the drop tail. Accordingly, uniaxial elongational flow was employed in the experiments with the capillary-driven self-thinning threads of the PAA solutions to characterize their rheological behavior [Fig. 1(a)]. In viscoelastic threads, the thread becomes uniform and its cross-sectional diameter diminishes exponentially, as D_thread = D₀·e^−t/3θ, where D₀ is the initial diameter of the thread at a certain “initial” time moment t = 0, and θ is the relaxation time.^6,20,23 Figures 1(b)–1(d) present the results for D_thread vs t for the polymer solutions according to PAA concentration. In Fig. 1(b), D_thread decreased linearly as t decreased and θ could not be measured from the results. These results revealed that the 0.2 wt. % PAA solution exhibited non-viscoelastic behavior, essentially, that of a viscous Newtonian fluid. As the PAA concentration increased to 1 wt. %, θ also could not be calculated although the graph looked slightly curved [Fig. 1(c)]. In contrast, the relation between D_thread and t was close to exponential for 2 wt. % PAA solution [Fig. 1(d)] and the relaxation time could be measured (θ = 3.56 ms). Consequently, as the concentration of PAA increased, the effect of the elastic forces in PAA solutions enhanced, making them viscoelastic.

Note that the terminology of “aerosol” and “splatter” is used herein in relation to the particle size less and greater than 50 μm, respectively.^25,26 In addition, the terminology of “droplet” is used in a broader sense that includes both aerosol and splatter. Because sub-micrometer or micrometer-scale contaminants, including bacteria and viruses, can be readily transferred to the human respiratory system in airborne droplets,^27,28 dentists and patients are always at great risk of cross-infection.⁶ 

Figures 2(a)–2(d) (Multimedia view) show the degree of aerosol generation occurring around a high-speed rotating bur when the concentration of polyacrylic acid (PAA) solution varies. The internal geometry of the handpiece used in this experiment and the initial operating conditions are provided in Fig. S2. When water was used as the working liquid of the handpiece, it was clearly observed that multiple aerosols were generated from the high-speed rotating bur. It should be noted that the droplets in the size range below 100 μm are suspended in air for a long period of time and thus pose a great infectious threat to the surrounding area.⁶ However, as the amount of PAA added to water increased from 0.2 to 2 wt. %, the aerosol generation gradually decreased because of the viscoelastic effects discussed in Ref. 6. In other words, the increased elasticity associated with the high-molecular-weight PAA facilitated a significant reduction in aerosol generation. When the concentration of PAA was 0.2 wt. %, the observed aerosol distribution was similar to that of pure water. When the concentration of PAA was 1 wt. %, splatters of several millimeters are emitted [Fig. 2(c), Multimedia view], and when the concentration of PAA was 2 wt. %, large splatters of ten millimeters or more are emitted [Fig. 2(d), Multimedia view]. Note that though the large droplets appear to fall quietly, a large droplet launched from the handpiece could fly up to several tens of centimeters, but still would not become airborne. As the concentration of PAA in the working liquid increased to 0.2, 1, and 2 wt. %, the number of aerosols decreased by 15.8%, 52.6%, and 68.4%, respectively, compared to that of the pure water case. The amount of splatter decreased by 12.5%, 51.3%, and 70% as the concentration of PAA in the solution increased to 0.2, 1, and 2 wt. %, respectively, compared to that of the pure water case. Note that over the PAA concentration of 2%, the friction losses inside the tube connecting the handpiece and the dental unit increased significantly and the syringe pump was overloaded.

The velocities of droplets of different sizes were measured from the videos at different PAA concentrations and are presented in Table I. Empty boxes indicate that no aerosols of that size were observed. The time range of the observation was limited as in Fig. 2 (Multimedia view), and there were some aerosol sizes that were not observed.

Figure 3 (Multimedia view) shows the macroscopic behavior of liquid spray jets generated by the handpiece at different PAA concentrations in the solutions. Figure 3 presents snapshots of the ejection of droplets generated from the fixed handpiece on the right, and the detailed setup is shown in Fig. S1(b). The diagonal green line in the picture is the scattering of the backlight. When pure water was used as a working liquid in the handpiece, it was clearly observed that the spray jet was ejected up to at least 90 cm from the handpiece [Fig. 3(a)]. The size of the aerosols comprising the spray jet was less than hundreds of micrometers [see Fig. 2(a), Multimedia view]. In particular, the aerosols were further diminished in size to the sub-micrometer- or micrometer-sized droplets as the distance from the handpiece increased because of droplet vaporization.²⁹ Because these subsequent micrometer-sized droplets can serve as a key factor for the long-range airborne transmission of bacteria or viruses,³⁰ the spray propagation from the handpiece should be suppressed to prevent transmission of bacteria or viruses from a patient to a dentist and/or other patients.

Figure 3 (Multimedia view) reveals aerosols (<50 μm) and splatters (>50 μm) observed in spray jets, with the trajectories presumably separated by their weight. Only the splatters are large enough to leave traceable streaklines. Figure 3(d) (Multimedia view) demonstrates that at the PAA concentration of 2 wt. %, splatters are rapidly settling down, while the data in Fig. 2(d) (Multimedia view) ascertain the fact that there are no aerosols in that case. It is to be noted that aerosols can either settle on the surfaces or remain airborne for a long time before entering the human respiratory system, whereas the arc of the splatter remains a ballistic trajectory until falling to the floor.¹⁴ Overall, as the PAA concentration in the solution increased, the propagation of the spray jets from the handpiece gradually decreased [see Fig. 3(c), Multimedia view]. For example, in the case of water, the droplets traveled longer distance, whereas in the case of the 2 wt. % PAA solution, the droplets travel distance was relatively shorter; see Fig. 3(d) (Multimedia view).

In addition to a reduction in the spraying distance from the handpiece when using PAA solutions, the cooling performance should also be explored. In dental procedures, friction occurring between the high-speed rotating handpiece bur and the tooth surface generally generates excessive heat, which can cause significant damage to the structure of the tooth tissue, resulting in pathological changes in the dental pulp.³¹ 

Figures 4(a)–4(c) show the temperature variation in the tooth with the progress of the dental procedure using different concentrations of PAA. First, the main bur (845KR31408, Komet, Germany) of the handpiece was inserted into the tooth at a depth of 2 mm, which then moved in the leftward and rightward directions to achieve a horizontal occlusal reduction [Fig. 4(a)]. When not using a coolant during the dental procedure, the temperature of the tooth increased by 2.5 °C, from 37 to 39.5 °C. By contrast, when water was used as a coolant, the tooth could be cooled by 1.2 °C, that is, from 37 to 35.8 °C. When a 0.2 wt. % PAA solution was used, the tooth temperature slightly decreased by 0.5 °C. However, when PAA solutions of 1 and 2 wt. % were used, the corresponding tooth temperature increased by 0.4 and 1.9 °C, respectively. This shows that the temperature of the tooth generally increased as the PAA concentration in the solution increased.

Second, the tooth temperature variation during an occlusal reduction, which is drilling the tooth in the vertical direction, was measured [Fig. 4(b)]. The vertical speed of the handpiece was fixed at 0.8 mm·s⁻¹, and the total drilling depth was 2.4 mm. The initial tooth temperature before the dental procedure was 37 °C. When no coolant was used during the dental procedure, a high temperature of 48.9 °C, which can cause irreversible damage to the pulp, was measured because of severe friction caused by deep penetration straight into the tooth. When pure water was used as a coolant during dental procedures, the tooth temperature could be significantly reduced to below 30 °C. This was similar to the result reported in a previous study.³¹ When the 0.2 wt. % PAA solution was used as a coolant, a cooling of 6.2 °C was observed. Similarly, when 1 and 2 wt. % PAA solutions were used, the corresponding reductions in temperature were 4.7 and 3.1 °C, respectively. Contrary to the 1 and 2 wt. % PAA solution cases in the occlusal reduction in the horizontal direction [where practically no cooling effect was observed with the PAA solutions, see Fig. 4(a)], the cooling effect provided by the 1 and 2 wt. % PAA solutions upon an occlusal reduction in the vertical direction was discernible. Overall, not only pure water, but also the 0.2, 1, and 2 wt. % PAA solutions, served as sufficiently efficient coolants in the occlusal reduction in both horizontal and vertical directions [see Figs. 4(a) and 4(b)].

Third, the temperature variation during a facial reduction using the utility bur (6856313014, Komet, Germany) was explored [Fig. 4(c)]. The dental procedure was conducted with the bur being in contact with the tooth by a width of 2.5 mm, where the bur moved horizontally at a speed of 0.8 mm·s⁻¹. When a coolant was not used during the procedure, the tooth temperature increased to 39 °C. By contrast, when pure water was used as a coolant during the procedure, the tooth temperature could be reduced by more than 7 °C from 37 to below 30 °C. The cooling performance slightly decreased when 0.2, 1, and 2 wt. % PAA solutions were used. For the latter, the tooth temperature was reduced by 5.2, 4.6, and 3.2 °C, respectively.

In general, the use of water in a dental handpiece allows the heat generated by friction between the high-speed rotating bur and the tooth to be effectively dissipated^6,32 and removed by the spray jet composed of aerosols.¹⁶ The increase in the PAA concentration suppressed the aerosolization (see Fig. 2, Multimedia view), and the spray cooling effect was diminished,³³ as shown in Figs. 4(a)–4(c). The physical parameters responsible for the heat removal by water and aqueous PAA solutions are listed in Table II. Note the reduction of the surface tension due to the presence of PAA in solution. It should be emphasized that surface tension is a restraining factor acting against aerosolization. The fact that the elastic forces associated with PAA action in the elongational flow of drop formation and detachment are capable of suppressing aerosolization even though another restraining factor diminishes, is quite notable, and reveals to what extent the coil-stretch transition of polymer macromolecules in elongational flows is a dominant factor compared to anything else.

Table II also indicates that there was no significant difference between water and polymer solutions, except in the shear viscosity. The latter increased with the PAA concentration. Accordingly, it can be concluded that the observed reduction in heat removal by the PAA solutions is caused predominantly by a lower flow velocity near the tooth at higher PAA concentrations; that is, the mechanism of the reduction in heat removal is unequivocally in a reduced advection.

Note also that the viscoelastic properties of the 2 wt. % PAA solutions were characterized in our previous work,⁶ where in Fig. 5(a), the flow curve, which characterizes the shear viscosity, is presented, and Fig. 6 characterizes the elongational properties and reveals the most important elastic property,³⁴ the relaxation time θ = 0.5 ms. The latter is the most important characteristic, which counteracts breakup into droplets, making them bigger at lower polymer concentrations, and completely suppressing their formation at higher polymer concentrations. Note that the difference in the relaxation times of θ = 0.5 ms and θ = 3.56 ms in Ref. 6 and the present work, respectively, stems from slight differences in solution preparation.

Figure 4(d) shows that, as the PAA concentration in the solution increased, the cooling performance decreased. However, it should be emphasized that, even at the highest concentration of PAA in the solution (2 wt. %), the cooling performance was superior to that of the no-cooling case, and the tooth temperature did not exceed the critical temperature (42.4 °C) at which pathological changes occur in the dental pulp.³⁵ Therefore, it is expected that the use of the PAA solutions with concentrations of 2 wt. % or less as coolants would not damage the tooth tissue during dental procedures. That is, the use of PAA solutions within the 1–2 wt. % concentration range could be recommended for dental procedures considering their ability to suppress aerosolization and achieve a sufficient temperature reduction.

The use of the PAA solution inhibited the aerosolization of the coolant during dental procedures, as discussed earlier. This effect enabled the aerosols (or splatter) to move downward rather than being distributed in all directions; see Figs. 2 and 3 (Multimedia view). A simulated dental experiment was conducted to investigate the effect of PAA in a real dental environment. A mannequin with teeth was mounted on a dental chair in a confined dental operating room as shown in Fig. 5. PAA solution was supplied to a handpiece with an external syringe pump, and an experienced operator performed facial reduction on the mannequin's maxillary front teeth for 20 s with the handpiece. Details of the dental simulation are presented in Fig. S1(d). As a result, when the PAA solution was employed, larger droplets were splattered and fell down to the mannequin head than in the water case [Fig. 5(b)], which corresponds to the result of Fig. 3(d) (Multimedia view). The bigger droplets settling down near the dental equipment alleviate the main danger of spreading viral infections such as COVID-19 due to aerosolization and formation of airborne smaller droplets. These settling bigger droplets may cause some discomfort to a patient in an actual treatment and can be simply removed by applying a cloth to the patient's face or a local suction pipe.³⁶ In contrast, smaller droplets did not fell down and spread everywhere, which could make the surroundings more contaminated. Accordingly, in Fig. 5(c), more droplets were observed on the mask of the operators in the water case than that in the PAA case. This clearly demonstrates the importance of using a viscoelastic polymer solution (polyacrylic acid solution here) to prevent cross-infection during dental procedures by inhibiting the spraying of aerosols.

The trajectories, velocities, and sizes of aerosolized droplets resulting from a dental handpiece operation were investigated both quantitatively and qualitatively for various concentrations of viscoelastic polyacrylic acid (PAA) in aqueous solutions. As the PAA concentration in the solution increased, the aerosol formation was gradually suppressed, although complete suppression was not achieved. The liquid interface near the rotating bur of a handpiece was photographed, which allowed the analysis of the size and velocity distributions of the aerosolized droplets. In addition, a fluorescent lighting technique was used to visualize the trajectories of the aerosolized droplets at different PAA concentrations. The PAA solutions of all concentrations explored (i.e., 0.2, 1, and 1 wt. %) demonstrated a sufficient cooling capability, which prevented thermal damage to the tooth nerves when the cutting bur was operated in the horizontal and vertical directions and the polishing bur was operated during a facial reduction (or side operation). The aerosolized droplets of the PAA solutions were larger in size than those of pure water because of the elastic resistance to liquid aerosolization, and they were not readily dispersed in air because of the relatively heavier weight of the viscoelastic droplets. As a result, these heavier droplets rapidly settled onto the facial area of the patient, whereas the aerosolized droplets of pure water dispersed widely and reached the facial area of the dental practitioner. These results demonstrate the risk of using pure water, which leads to potential dispersion of pure water droplets contaminated with viruses such as COVID-19. Thus, the benefit of using a viscoelastic PAA solution, which minimized liquid aerosolization and facilitated quick settling of PAA droplets, was demonstrated.

It should be emphasized that the irrigations liquids are delivered to a handpiece by pressure-driven flow from a bottle through a supply line in dental chair. Therefore, the shear viscosity should be sustained as low as possible, while using only minimal polymer concentrations, which guarantee a sufficient viscoelasticity for the aerosolization suppression. This goal is already achieved by the 2 wt. % PAA solution, which makes higher (as well as lower) concentrations redundant. Note also that the suppression of breakup of capillary jets of polymer solutions by significant elastic forces they develop in the uniaxial elongational flows was studied in detail in relation to the formation of the beads-on-the-string structures and similar phenomena (e.g., the fundamental coil-stretch transition), and significant theoretical and numerical results are available in the literature.^34,37,38 The main achievement of the present work is in the realization and experimental demonstration of the fact that such practically important detrimental phenomenon as aerosolization by a dental handpiece can be modified and/or suppressed by means available in the framework of the non-Newtonian fluid mechanics and polymer science.

See the supplementary material for details of the experimental method and to check the physical properties of the PAA solution.

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) Nos. NRF-2020R1A5A1018153, NRF-2021R1A2C2010530, and NRF-2022M3J1A106422611. This research was supported by Technology R&D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health & Welfare, Republic of Korea (No. HI21C0049010021). This research was also supported by Korea University (No. K2211851).

The authors have no conflicts to disclose.

Yong Il Kim and Seongpil An contributed equally to this work.

Yong Il Kim: Conceptualization (equal); Formal analysis (equal); Investigation (equal); Methodology (lead); Visualization (lead); Writing – original draft (lead). Seongpil An: Formal analysis (equal); Validation (equal); Writing – original draft (equal). Jungwoo Huh: Data curation (equal); Formal analysis (equal); Resources (equal); Software (equal). Yang-Soo Kim: Funding acquisition (equal); Resources (equal). Jihye Heo: Resources (equal). In-Seok Song: Conceptualization (supporting); Funding acquisition (lead); Methodology (equal); Project administration (supporting); Resources (equal); Supervision (equal). Alexander L. Yarin: Conceptualization (equal); Formal analysis (equal); Investigation (equal); Project administration (equal); Supervision (equal); Validation (equal); Writing – original draft (equal). Sam S. Yoon: Conceptualization (equal); Funding acquisition (equal); Project administration (equal); Supervision (equal).

The data that support the findings of this study are available within the article and its supplementary material.