Efficacy of graphene nanocomposites for air disinfection in dental clinics: A randomized controlled study

Abstract

BACKGROUND

Aerosols containing disease-causing microorganisms are produced during oral diagnosis and treatment can cause secondary contamination.

AIM

To investigate the use of graphene material for air disinfection in dental clinics by leveraging its adsorption and antibacterial properties.

METHODS

Patients who received ultrasonic cleaning at our hospital from April 2023 to April 2024. They were randomly assigned to three groups (n = 20 each): Graphene nanocomposite material suction group (Group A), ordinary filter suction group (Group B), and no air suction device group (Group C). The air quality and air colony count in the clinic rooms were assessed before, during, and after the procedure. Additionally, bacterial colony counts were obtained from the air outlets of the suction devices and the filter screens in Groups A and B.

RESULTS

Before ultrasonic cleaning, no significant differences in air quality PM_2.5 and colony counts were observed among the three groups. However, significant differences in air quality PM_2.5 and colony counts were noted among the three groups during ultrasonic cleaning and after ultrasonic treatment. Additionally, the number of colonies on the exhaust port of the suction device and the surface of the filter were significantly lower in Group A than in Group B (P = 0.000 and P = 0.000, respectively).

CONCLUSION

Graphene nanocomposites can effectively sterilize the air in dental clinics by exerting their antimicrobial effects and may be used to reduce secondary pollution.

Key Words: Graphene, Nanocomposites, Oral clinic, Air disinfection, Secondary contamination

Core Tip: Our proposed method offers efficient antimicrobial performance without secondary pollution. We have employed graphene nanocomposites to enhance their adsorption and antibacterial properties through a modified approach to study their impact on air disinfection and purification in dental clinics.

INTRODUCTION

Dentistry poses a significant risk for hospital-acquired infections. Numerous studies have confirmed that the dental diagnostic and treatment procedures generate substantial amounts of aerosols containing saliva, blood, nasopharyngeal secretions, and pathogenic microorganisms. This can significantly elevate the microbial content and the risk of cross-infection in the clinical setting. High-speed turbine handpieces and ultrasonic scalers aerosolize compressed air and water and continuously produce aerosols. Consequently, high concentrations and amounts of aerosols in dental offices can facilitate the transmission of pathogens, such as Mycobacterium tuberculosis, hepatitis B virus, human immunodeficiency virus, varicella-zoster virus, and severe acute respiratory syndrome coronavirus 2 coronavirus[1]. Additionally, PM_2.5 particles mixed with aerosols containing pathogenic microorganisms can be inhaled into the lungs and reach the alveoli upon after contact with skin and mucous membranes. PM₁ particles can enter the bloodstream, potentially leading to healthcare-acquired infections[2]. Therefore, healthcare workers and patients face a high risk of infection exposure during dental procedures.

The current air purification technology has several drawbacks, including high air resistance, potential for secondary pollution, inadequate overall purification performance, and the ability to adsorb only a single pollutant[3]. Thus, there is an urgent need for air disinfection methods with antimicrobial properties that are both highly efficient and do not cause secondary pollution. Graphene and its derivatives represent a new class of two-dimensional materials, comprising a single layer of carbon atoms arranged in a hexagonal honeycomb pattern with sp2 hybridization[4-6]. Graphene is widely used in air purification due to its significant specific surface area and its effects in adsorption, filtration, antibacterial, and antimicrobial activities. The porosity and pore volume of graphene can be increased to fully leverage its role in air purification via further catalytic activation and other modifications[7].

To the best of our knowledge, there is no research on the application of graphene materials during oral diagnosis and treatment. In the present study, we enhanced the adsorption and antibacterial properties of graphene nanocomposites via modifications and investigated their impact on air disinfection and purification in the dental clinic setting.

MATERIALS AND METHODS

Experimental site

Three periodontal clinics, each with an area of 15 m², were selected, and one dental treatment chair was placed in each.

Materials and equipment

The following equipment and materials were used in the study: A power supply of 60 W, an airflow of 52.45 CFM, air pressure of 41.1 mm H₂O, a suction device, a Heck Smart PM_2.5 air quality detector, and graphene oxide (GO; transverse size 0.5 to 5 um, thickness 1 to 5 layers, monolayer rate > 99%.

Trial design

This trial is reported according to the Consolidated Standards of Reporting Trials guidelines. The study comprised 60 patients (30 men and 30 women) aged 25-45 years old who were diagnosed with the same degree of periodontitis and underwent ultrasonic scaling treatment at our hospital between April 2023 and 2024. Those with a minimum of 24 teeth and no underlying diseases, and no antibiotic usage in the past 4 weeks were selected.

Randomization and masking

The participants were randomly assigned (1:1:1) to receive different attraction devices through an online random assignment system. They were randomly divided into three groups (n = 20 each): Group A used a suction device containing a graphene nanocomposite filtration, Group B used a suction device with ordinary filtration, and Group C had no filtration in its suction device. The randomization was performed using parcels of random variable length (parcel sizes 2 and 4). The randomization sequence was generated by an independent statistician, and allocation was concealed from the investigators and participants before recruitment. Masking of investigators and participants was not possible because of the different attraction devices received.

Experimental method

Preparation of graphene nanomaterials: The fiber filters in the ordinary suction device were soaked with GO suspension using impregnation method, dried naturally for 24 hours, and then placed into the suction device.

Air disinfection: Prior to the consultation, the consultation room desktop and floor were thoroughly cleaned and disinfected using a 500 mg/L chlorine disinfectant for each group. The room was further subjected to 40 minutes of ultraviolet irradiation, while maintaining a steady room temperature of 24-26 °C and a relative humidity of 50%-55%. Throughout the procedure, no windows were opened, and the room accommodated one nurse, one doctor, one sampler, and one patient undergoing ultrasound treatment. The duration of ultrasonic cleansing for each patient was set at 45 minutes. During the treatment, the suction devices in Groups A and B were positioned 0.5 m away from the operating position for effective suction.

Air sampling: A standard nutrient agar petri dish (diameter, 9 cm) was positioned at the center of the patient's head, at a horizontal distance of 0.5 m. Sampling was conducted for the three groups: Before the consultation, at the beginning of the consultation for 30 minutes, and at the end of the consultation for 30 minutes[8], with restricted access to other individuals throughout the process. The number of colonies was assessed after 5 minutes of exposure using the natural sedimentation method. The calculation formula utilized was based on the Hospital Disinfection Hygiene Standard issued by the Ministry of Health of China in 2012 as follows: Total number of colonies N_air = 50000 N × A^-1 × T^-1, where A is the plate area (cm²), T is the plate exposure time (min), and N is the average number of colonies[9].

Object surface sampling: According to the microbial sampling method outlined in the 2012 Hospital Disinfection Hygiene Standards issued by the Ministry of Health of China, after the conclusion of the consultation, a single cotton swab soaked in saline sampling solution was used to swab each surface of the graphene nanomaterial filters and ordinary filters. The swab was moved back and forth horizontally and vertically five times and rotated accordingly. The hand-contact portion of the cotton swab was removed, and the remaining part was placed in a test tube containing 10 mL of sampling solution for further examination.

PM_2.5 air quality detection: The three groups were tested using an air quality detector before the consultation, 30 minutes at the beginning of the consultation, and 30 minutes at the end of the consultation. The instrument was positioned at 0.5 m from the level of the patient's head.

All operations and experiments were performed by the same trained person to avoid bias.

Statistical analysis

The continuous variables are summarized as mean ± SD. All data were checked for normality before analysis. Skewed data were statistically analyzed using the nonparametric Wilcoxon signed-rank test. Normally distributed data were assessed for equality of variances using Levene's test, followed by the analysis of variance test. A P-value of < 0.05 was considered to be significant differences. Statistical analysis was performed using IBM SPSS software (version 26; IBM, Armonk, NY, United States).

RESULTS

Before ultrasonic cleaning, there were no statistical differences in air quality PM_2.5 and colony count between the three groups (P = 0.539 and P = 0.768) (Tables 1 and 2). During ultrasonic cleaning and after ultrasonic treatment, there were differences in air quality PM_2.5 and colony counts among the three groups (Tables 1 and 2).

Table 1 Airborne colonization in the consultation room (CFU/m³), mean ± SD.

		Graphene group, group A	General group, group B	Blank group, group C	P value
Pre-treatment		2.62 ± 11.72	5.24 ± 16.13	2.62 ± 11.72
	Min-value	0	0	0	0.768
	Max-value	52.41	52.41	52.41
During treatment		584.37 ± 211.20	1540.85 ± 356.84	2463.27 ± 208.95
	Min-value	262.05	524.10	2096.40	0.000
	Max-value	1100.61	1991.58	3092.19
Post-treatment		414.04 ± 115.20	833.32 ± 172.49	2195.98 ± 296.91
	Min-value	262.05	576.51	1519.89	0.000
	Max-value	576.51	1153.02	2620.50

Table 2 PM_2.5 in clinic (μg/m³), mean ± SD.

		Graphene group, group A	General group, group B	Blank group, group C	P value
Pre-treatment		28.30 ± 3.61	29.75 ± 4.19	29.55 ± 4.30
	Min-value	21	23	22	0.539
	Max-value	34	38	38
During		77.45 ± 9.82	117.10 ± 12.67	153.20 ± 8.78
	Min-value	53	101	135	0.000
	Max-value	92	150	168
Post-treatment		39.15 ± 7.24	71.26 ± 9.59	101.20 ± 5.12
	Min-value	20	58	90	0.000
	Max-value	49	90	112

In order to be able to further clarify the effect of graphene nanocomposites on air purification, air sampling was carried out at the exhaust ports of the suction devices of the two groups A and B respectively during the ultrasonic cleansing process, and after the end of the suction, the surfaces of the graphene nanomaterials and the surfaces of the ordinary filters were sampled as the surfaces of the objects, respectively. The number of colonies at the exhaust port of the suction device and the number of colonies on the surface of the filter were found to be lower in group A than in group B (P = 0.000 and P = 0.000, respectively) (Table 3).

Table 3 Number of colonies at the exhaust port of the suction unit and on the surface of the filter for groups A and B, mean ± SD.

	Suction device exhaust port colony number (CFU/m3)		Colony count on the surface of the filter (CFU/m3)
	Graphene attraction	Convention attraction	Graphene coating	Regular filter
	2.62 ± 11.72	83.86 ± 52.13	0.055 ± 0.16	20.06 ± 7.06
Min-value	0	0	0	11
Max-value	52.41	209.64	0.7	33
P value	0.000		0.000

DISCUSSION

As per the 2009 Technical Code for Hospital Isolation issued by the Ministry of Health of China, airborne transmission involves the spread of disease through the air via microparticles (≤ 5 μm) carrying pathogenic microorganisms[10]. The dental diagnosis and treatment process generates significant amounts of aerosols, which, if not promptly and effectively removed, can potentially threaten the health of both medical personnel and patients. While the standards in Chinese dental offices primarily focus on colony counts after disinfection and before treatment, research indicates that the colony counts in the air during treatment are notably higher than those before treatment[11]. In March 2020, the National Health Commission of the People's Republic of China explicitly stated in the "Diagnostic and Treatment Program for Novel Coronavirus Pneumonia (seventh edition for trial implementation)"[12] that "there is a possibility of aerosol transmission in relatively closed environments with prolonged exposure to high concentrations of aerosols". This implies that aerosol transmission may occur under the following conditions: A closed environment, at high concentrations, and with prolonged exposure. In many dental clinics, the varying number of chairs, limited layout, and differing operating times result in prolonged exposure of medical staff and patients to high aerosol concentrations. Therefore, improving the air quality during dental treatment is a crucial measure for effectively preventing and reducing hospital-acquired infections.

In the present study, the static air samples obtained from all clinic rooms before the diagnostic and therapeutic procedures met the Hospital Disinfection Hygiene Standards. Furthermore, the graphene nanocomposites demonstrated excellent adsorption properties. The PM_2.5 levels in Group A were significantly lower than those in Groups B and C. According to a previous study, the exposed surfaces of graphene nanocomposite fibers exhibit strong interactions with the surface chemical groups of PM_2.5, leading to enhanced capture of PM_2.5[13].

Consistent with previous findings[14], graphene nanocomposites effectively inhibit airborne microorganisms and bacteria on the surfaces in this study. Our results demonstrated a significantly lower number of colonies in the air discharged from the extraction device in Group A than in Group B. Furthermore, we found that the number of colonies on the surface of the graphene nanomaterial was notably lower than that on ordinary filters. These findings indicate the potential efficient use of graphene nanocomposites for air sterilization in dental clinics.

The findings of this study also confirmed the excellent antibacterial properties of graphene nanomaterials and highlighted the avoidance of secondary contamination compared to filters made of ordinary materials via bacterial sampling of the surfaces. Research indicates that graphene and its derivatives possess high specific surface area and both antibacterial and antiviral effects[15,16]. High filtration efficiencies can be achieved during air purification by retaining particulate pollutants via interception, inertial deposition, Brownian motion, electrostatic effect, and gravity, while maintaining relatively low resistance and inactivating the airborne microorganisms[17,18]. Yan et al[19] conducted a study where they uniformly sprayed graphene oxide films on polypropylene nonwoven fabrics using a SG9617S spray gun and investigated the effect on PM_2.5 filtration performance. The results demonstrated that the large specific surface area of graphene oxide provided the foundation for the capture and adsorption of PM_2.5, with an efficiency of 99.97% and a pressure drop of only 8 Pa, owing to the large number of oxygen-containing functional groups in graphene oxide.

Moreover, the antimicrobial effect of graphene-based materials has been extensively examined. Ye et al[20] explored the antibacterial activity of Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus by non-covalently modifying graphene nanocomposites and found that the composite exhibited strong antimicrobial properties and reduced the cytotoxicity of the pure antimicrobial agent. Graphene nanocomposites were found to interfere with the bacterial respiratory chain, block bacterial energy synthesis by seizing electrons from the cell membrane, and generate reactive oxygen species that destroy the cell wall and bacterial membrane, thus inhibiting bacterial activity[21,22].

The present study has three potential limitations. Firstly, investigations on the antibacterial properties of graphene were limited to sampling the surface of the object; measuring the bacterial activity would have been more relevant in the clinical setting. Second, the graphene used in this study was a single layer; thus, additional verifications of the bacteriostatic effects of different layers of graphene are warranted. Third, we did not analyze the adsorption saturation of the material. The filter material was cleaned or replaced due to potential clogging when it reached adsorption saturation. The exceptional filtration performance of graphene nanocomposites can only be maintained in a stable filtration stage, and frequent replacements will increase the cost of use. Moreover, the disinfection effect of the clinical air will be affected if graphene nanocomposites are not replaced on time after adsorption saturation. Therefore, evaluating the adsorption saturation is important during the clinical use of graphene nanocomposites. Although introducing graphene material through impregnation can increase the active sites on the fiber surface to a certain extent and improve its adsorption performance on particles, its dust holding capacity is minimal compared to the multi-channel pore structure of three-dimensional materials. Therefore, the development of three-dimensional nanofiber filtration materials with high continuity and hierarchical porous structure will aid in prolonging the filtration performance.

Aerosols can remain suspended in the air for extended periods of time. The deposition rate of particles with an initial size of 10 μm varied from 0.6% to 18.3% on the floor and 51% to 86% on the ceiling or walls, based on a simulated fluid force analysis[23]. This highlights the overlooked aspect of disinfecting the ceiling and walls of dental clinics, despite these areas having the highest aerosol deposition rates. Thus, it is worthwhile to explore the potential purification effects of graphene nanocomposites when applied to the ceilings and walls of the clinics using electrostatic spinning technology.

CONCLUSION

This randomized controlled study underscores the favorable air disinfection and bacteriostatic properties of graphene nanocomposites during dental procedures and offers promise in mitigating secondary pollution.