During the coronavirus disease 2019 (COVID-19) pandemic, oral healthcare workers were considered high risk for infection due to their close proximity to patients and the use of aerosol-generating procedures, particularly periodontal treatment with ultrasonic scalers and airflow devices. 1 Respiratory particles, such as aerosols, droplets, or splatters, can transfer viruses but also other microorganisms like bacteria. Reference Doron and Gorbach2 Given that the oral cavity contains >1,000 taxa, oral healthcare providers are continually exposed to a multitude of bacteria, some of which are antimicrobial-resistant pathogens. Importantly, Staphylococcus aureus, which can lead to several infectious disease syndromes, such as skin and soft-tissue infection or endocarditis, is frequently detected in the nose and throat and this can be the source of transmission and dissemination to other body sites. Reference Dewhirst, Chen and Izard3–Reference McCormack, Smith, Akram, Jackson, Robertson and Edwards10
To mitigate the spread of microorganisms via respiratory particles, numerous infection control and prevention measures, including personal protective equipment and cleaning and disinfection protocols, have been established. Reference Guo, Xie and Wu11,12 In addition to personal protective equipment, diminishing aerosol or droplet generation during dental procedures should decrease transmission risk.
We evaluated the dissemination of S. aureus during standardized dental procedures, and focused specifically on the influence of various scaling devices and rinsing solutions. Our findings provide valuable insights into potential infection prevention and control strategies. We hypothesized that different combinations of scaling and suction devices, as well as the choice of antiseptic solutions, would affect the dissemination of S. aureus. To test this hypothesis, we designed an experimental study simulating droplet and aerosol generation during dental biofilm management (ie, guided biofilm therapy or GBT). GBT is a conceptual stepwise cleaning approach that combines modern technologies to achieve efficient and comprehensive dental biofilm removal in routine clinical dentistry incorporating disclosing agents, airflow devices and ultrasonic scalers. Reference Vouros, Antonoglou, Anoixiadou and Kalfas13 The combinations of cleaning and suction apparatuses and the selection of rinsing solutions varied throughout the research phase.
Methods
This research was conducted over nine experimental days at the Center for Dental Medicine, University of Zurich, Switzerland. Each day comprised three runs.
Setting
A dental model simulation head was placed on the patient chair in a designated consultation room (Fig. 1A). The room was equipped with air conditioning and a window. The biofilm-targeted therapy was performed according to Vouros et al Reference Vouros, Antonoglou, Anoixiadou and Kalfas13 and was completed after ∼10 minutes. Each day, 3 treatment courses were performed (ie, 3 runs). All designated sampling surfaces were cleaned with ethanol (80% v/v) between runs after samples were taken. Each day, a different combination of suction, handheld device, and rinsing solution was randomly applied (Table 1).
Figure 1. Schematic representation of the consultation room and sampling locations. Blue circles, surface sampling locations; green, air sampler/air sampling location.
Figure 2. Model simulation head with air sampler (black circle).
Figure 3. Prototype suction device (pink) and airflow device (white).
Table 1. Experimental Schedule and Results
Note. H2O: water; CHX: chlorhexidine; N/A: not applicable; CFU: colony-forming unit; CFU/mL: CFU per milliliter.
Dental treatment
The model simulation head, which simulated varying stages of periodontal disease, underwent GBT Reference Vouros, Antonoglou, Anoixiadou and Kalfas13 through either an ultrasonic piezo instrument or an erythritol air-polishing device (AIRFLOW-One with AIRFLOW-1 PLUS powder, EMS, Switzerland). Two distinct suction devices, a conventional saliva ejector or a prototype provided by EMS Switzerland (Fig. 1C), were used alongside either a chlorhexidine digluconate 0.1% (CHX, BacterX, EMS, Switzerland) containing rinsing solution or water. Compared to the conventional saliva ejector, the prototype suction collects splatters in a more efficient way because of two soft flanges. The device is similar to the commercially available product GBT Flowcontrol (ref FV-112, EMS Elector Medical System SA, Nyon, Switzerland). The rinsing solution was used during the entire treatment period. Following each run, the oral cavity of the model was disinfected with ethanol (94% v/v). The window of the room was open during experiments. No treatment was performed for 20 min after each procedure and the window was left open.
Staphylococcus aureus suspension used to simulate contaminated saliva
An overnight liquid culture of Staphylococcus aureus (Cowan I) was diluted in phosphate-buffered saline (PBS) on the morning of each treatment day to create sampling stock. Prior to each run, the solution was diluted in PBS to achieve a concentration of 105 CFU/mL. Simultaneously, the resuspension was streaked onto agar to assess the bacterial count for each run. To mimic saliva, this suspension was steadily rinsed into the mouth of the model simulation head with a constant flow of 4 mL/min.
Air and surface sampling
An air sampling device [MAS-100 NT, MBV AG, Switzerland; flow rate, 100 L/min; Columbia agar + 5% sheep blood (COS) agar plates] was placed on a chair in 1 m distance to the dental model simulation head during treatments (Fig. 1 A and B). In addition, the following control experiments were performed on an additional day: (1) air sampler next to air conditioner; (2) air sampler 1 m from oral cavity but without treatment; and (3) air sampler 1 m from oral cavity with treatment (settings of experimental day 1, using PBS without S. aureus). COS plates were incubated for 24±2 hours at 36±2°C.
Surface contamination was assessed by sampling 5 distinct room areas using gauze wipes (Mesoft 5×5 cm, Mölnlycke Health Care AB, Göteborg, Sweden). The wipes, stored in a sterile tube with 0.9% sodium chloride, were swiped over the defined areas in a zigzag pattern and were then returned to the NaCl solution. Wipes were shaken for 30 minutes at 250 bpm and were sonicated for 5 minutes at 44 Hz. Subsequently, the solution was plated on COS agar and was then incubated for 24±2 hours at 36±2°C.
Microbiology analysis
If growth was evident on the COS plates, species verification was carried out using MALDI Biotyper Sirius (Bruker Daltonics GmbH, Germany). If colonies were morphologically identical, only 1 colony was evaluated.
Statistical analysis
Medians and interquartile ranges (IQRs) for overall growth during the air sampling were calculated using R software (R Foundation for Statistical Computing, Vienna, Austria). The Wilcoxon rank-sum test was performed to compare CFU counts between the rinsing solutions (chlorhexidine and water).
Results
Setting
The different treatment settings are shown in Table 1. The same settings were applied on experimental days 1 and 9. The mean inoculum ranged between 3.73×104 and 5.16×105 CFU/mL.
Air sampling
In total, 27 air samples were collected. Growth was detected in all of them. S. aureus was identified in 7 runs (25.9%) across 3 different experimental days (days 1, 2, and 9) (Table 1). On experimental days 1 and 9, all 3 runs tested positive (day 1, 13 CFU/3 runs; day 9, 63 CFU/3 runs). On experimental day 2, 1 run (1 CFU/3 runs) tested positive. On all 3 days, the saliva ejector was used in combination with the airflow.
In total, 31 CFU grew on average on each experimental day. On days using water, higher CFU counts were detected compared to CHX: median, 31 CFU (IQR, 14.00–58.50) versus 23 CFU (IQR, 9.75–31.00) (P = .24).
All control experiments showed no growth of S. aureus.
Surface samples
Except for day 1, 15 samples were collected each experimental day, for a total of 120 samples. Surface areas varied between 0.02 m Reference Doron and Gorbach2 and 0.225 m Reference Doron and Gorbach2 (Fig. 1A). S. aureus growth was detected in 1 sample (an investigator’s face shield) on experimental day 4 (ie, saliva ejector + ultrasonic piezo instrument + CHX).
Discussion
Our findings demonstrate the presence of S. aureus in the air around the oral healthcare providers and the patient. Furthermore, we observed that certain treatment settings, such as the use of an ultrasonic piezo instrument or a prototype suction device, can potentially mitigate a transmission risk. Conversely, surface contamination was a rare occurrence and was primarily detected in the immediate vicinity of the oral cavity.
The issue of bacterial or viral spread through droplets or aerosols became a focal point during the coronavirus disease 2019 (COVID-19) pandemic. 1 Rautemaa et al Reference Rautemaa, Nordberg, Wuolijoki-Saaristo and Meurman7 reported significant bacterial contamination at various sites during the operation of high-speed dental instruments. Consistent with other studies, Reference Boccia, Di Spirito and D’Ambrosio14 our air sampling revealed a diverse microbial population, but only a fraction (25.9% of the runs) confirmed the presence of S. aureus. This finding suggests that only this proportion of positive samples represented a true reflection of bacterial dissemination from the oral cavity during treatment. Prior research indicated that treatment tools and methods can affect oral microorganisms, such as decreasing bacterial counts in biofilm when ultrasonication is applied. Reference Stahli, Lanzrein, Milia, Sculean and Eick15 Interestingly, 1 combination of treatment settings (airflow and saliva ejector) accounted for all episodes of the air contamination. In addition to demonstrating the potential for bacterial transmission during dental procedures, these findings highlight the necessity for optimized device combinations.
To minimize bias by improving investigator’s skills over time, we repeated the experiment with the same settings on the first and the last days. We detected S. aureus in all runs, indicating that these findings are truly due to the treatment settings. This observation supports that the combination of an ultrasonic piezo instrument or prototype suction device with airflow does not result in detectable aerial spread of S. aureus. Compared to water, the application of CHX, a compound included in a protection protocol for dental personnel, Reference Weber, Bonn and Auer16 resulted in a reduction of S. aureus in CFU counts when airflow and a saliva ejector were used. The reduced median overall growth for CHX and water (23 CFU vs 31 CFU) was not statistically significant (P = .24).
Surface contamination with S. aureus within the consultation room was rare. Although other studies have identified contaminated surfaces in dental settings, Reference Umar, Basheer, Husain, Baroudi, Ahamed and Kumar17–Reference Bahador, Alfirdous, Alquria, Griffin, Tordik and Martinho19 our investigation of potential patient-to-surroundings bacterial transmission did not mirror these findings; we observed only 1 positive sample of 120 samples collected. The low contamination rate was indeed surprising. Unlike many studies with agar plates at varying distances, we used gauze wipes (adapted from Oie et al Reference Oie, Hosokawa and Kamiya20 ) to sample surface areas. Bahador et al Reference Bahador, Alfirdous, Alquria, Griffin, Tordik and Martinho19 showed a positive correlation between treatment duration and the level of bacterial contamination, suggesting that our exposure time (∼10 minutes) may have been too brief. Although this is a valid consideration, the total duration from the first run to the final surface sampling exceeded 1 hour. Furthermore, we cannot exclude residual effects of the disinfectant. Nevertheless, surface disinfection after every run is simulating real-life infection control measures. Previous studies have shown a decrease in contamination during scaling therapy as the distance from the oral cavity increases Reference Veena, Mahantesha, Joseph, Patil and Patil21 and that the highest contamination levels are detected nearest to the oral cavity. Reference Kaufmann, Solderer, Gubler, Wegehaupt, Attin and Schmidlin22 The fact that the face shield was contaminated in only 1 of the 24 runs was surprising but emphasizes the importance of personal protective equipment.
In addition to its clinical significance and its potential presence in the nose and throat, S. aureus has been detected in surface samples in other studies. Reference Tong, Davis, Eichenberger, Holland and Fowler8–Reference McCormack, Smith, Akram, Jackson, Robertson and Edwards10,Reference Bahador, Alfirdous, Alquria, Griffin, Tordik and Martinho19 Therefore, we believe that S. aureus is a good indicator for spread of any pathogens during dental procedures. The chosen inoculum reflects CFU counts in saliva and dental plaques, and therefore also contributes to the real-life scenario of this experimental study. Reference Ohara-Nemoto, Haraga, Kimura and Nemoto23
Our study had several limitations. We did not assess different bacterial concentrations, exposure times, or air sampling locations. All treatment procedures were performed by the same investigator. Although no evidence suggests that the negative results after day 2 were due to improved skills, this remains a possibility. It is uncertain whether the detected numbers of S. aureus colonies in the air and on the face shield actually would result in clinical transmission. Furthermore, we evaluated only the potential effect of contaminated saliva; we did not evaluate whether other colonized materials such as dental plaque could increase the bacterial load in the air or on surrounding surfaces. Future trials should incorporate this aspect.
In conclusion, our findings indicate that bacterial microorganisms can be transmitted into the air during scaling therapy if certain treatment settings (eg, using airflow and a saliva ejector) are employed. However, adjusting these settings to incorporate the use of an ultrasonic instrument or a prototype suction device resulted in no detection of S. aureus in the air. In our experimental setup, surface contamination was exceptionally rare (1 of 120 samples) and was only observed in the immediate vicinity of the oral cavity.
Acknowledgements
We thank Pascal M. Frey for the critical review of the manuscript. Parts of this manuscript derived from a master’s thesis at the University of Zurich by a coauthor. Both the author and the University granted their permission for publication. During manuscript preparation, ChatGPT by OpenAI was used for text editing. ChatGPT helped refine language clarity in specific sections but was not employed for content generation, analysis, or literature review. The authors thoroughly reviewed and verified all ChatGPT-edited text, taking full responsibility for the manuscript’s content and scientific integrity.
Financial support
The suctioning prototype was provided by EMS Switzerland. The study was partially funded by EMS Switzerland (to P.R.S.). The company had no influence on the study design or results of the publication. This work was supported by the Swiss National Science Foundation (grant no. 211422) and University of Zurich CRPP Precision medicine for bacterial infections to S.D.B.
Competing interests
P.W.S. received travel grants from Pfizer and Gilead, speaker’s honorary from Pfizer, and fees for advisory board activity from Pfizer and Gilead outside the submitted work. P.R.S. received speaker’s honorary and other (non-)financial research support from E.M.S. All other authors declare no conflicts of interest.
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