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Year : 2007  |  Volume : 18  |  Issue : 4  |  Page : 177-180
Assessment of atmospheric microbial contamination in a mobile dental unit

1 Department of Community Dentistry, College of Dental Sciences, Davangere, Karnataka - 577 004, India
2 Department of Oral Pathology and Microbiology, College of Dental Sciences, Davangere, Karnataka - 577 004, India
3 Department of Preventive and Pedodontics, College of Dental Sciences, Davangere, Karnataka - 577 004, India

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Date of Submission27-Jul-2006
Date of Decision05-Mar-2007
Date of Acceptance13-Mar-2007


Introduction: Bioaerosols are important considerations in infection control as well as in occupational health. Bioaerosols may carry potentially hazardous microbes, viruses, fungi, allergens, and other toxic substances that may harm the dental operator, patient, and the dental assistant by causing nosocomial infections.
Objective: To assess the level of atmospheric microbial contamination before, during, and after dental treatment procedures in the dental operatory of a mobile dental unit (MDU).
Materials and Methods: The study included three treatment sessions on different working days, with an interval of one month. The MDU was fumigated before the start of the study. Brain Heart Infusion Agar with 5% sheep blood was used to collect the gravitometric settling of aerosols produced before, during, and after dental treatment procedures. The agar plates were sent for aerobic and anaerobic culture.
Results: The results showed that atmospheric microbial contamination (CFUs/plate) was 4 times higher during working sessions as compared to the levels before the working sessions. At the end of the working day, aerosols decreased by almost 3 times that seen during work.
Conclusion: The aerosols increased during and after work sessions. This shows the increased risk of transmission of infectious agents to the dentists who work in the MDU. Hence, all necessary preventive measures should be advised and need to be followed strictly.

Keywords: Bioaerosols, brain heart infusion agar, dental operatory, mobile dental unit

How to cite this article:
Shivakumar K M, Prashant G M, Madhu Shankari G S, Subba Reddy V V, Chandu G N. Assessment of atmospheric microbial contamination in a mobile dental unit. Indian J Dent Res 2007;18:177-80

How to cite this URL:
Shivakumar K M, Prashant G M, Madhu Shankari G S, Subba Reddy V V, Chandu G N. Assessment of atmospheric microbial contamination in a mobile dental unit. Indian J Dent Res [serial online] 2007 [cited 2023 Oct 4];18:177-80. Available from:

   Introduction Top

For long, infection control has been one of the major concerns of the dental community. [1],[2] Nosocomial infections can be caused by a variety of infectious agents from the patients, staff, operating instruments, visitors, ventilation and air-conditioning systems, and even from the environment. Particles with < 50 µm diameter are invisible to naked eye and can remain in the environment as aerosols for long periods of time. These aerosols may be inhaled into the lungs to reach the alveoli or may come in contact with the skin or mucous membranes. Most of the aerosols produced during treatment procedures have a diameter of 5 µm or less, and these can cause respiratory or other health problems because they can penetrate into, and remain within, the lung. [3],[4],[5] Aerosol that are 100 µm or more in diameter are thought to be too large to be inhaled; however, they may still come into contact with the skin, eyes, and mucous membranes, or may settle on exposed hair and clothing. [3]These bioaerosols may carry potentially hazardous microbes, viruses, fungi, allergens, or other toxic substances that may harm the dental operator, patient, and the dental assistant. [2],[3],[6],[7] The propelling force of a high-speed dental drill and the cavitation effect of an ultrasonic scaler, both being used in combination with a water spray, can generate numerous airborne particles derived from blood, saliva, tooth debris, dental plaque, calculus, and restorative materials. [1],[2],[3] Thus, diseases like pneumonia, influenza, hepatitis, and skin and eye infections may be transmitted during dental treatment procedures from these infectious bioaerosols. [1],[2],[8] At present, the most serious diseases threatening dentists and their staff are hepatitis B and acquired immunodeficiency syndrome (AIDS); dental personnel are at risk of contracting these diseases during dental operative procedures. [9]

The mobile dental unit (MDU) used for dental camps is of great help in rendering care to the needy. On the other hand, in the closed operatory of the MDU, with the limited space and ventilation, there is an increased risk for acquiring infections during treatment. Most of the aerosols generated during dental treatment procedures have been found to radiate toward the patient's chest and the operator, as well the dental assistant's face. It is known that poorly maintained ventilation and air-conditioning systems can be a potential source of fungal and other microbial organisms. The air-conditioning system could therefore act as a vehicle for the transmission of bacteria and other microorganisms in the dental clinic. [3]

Since no studies have been done to assess the level of atmospheric microbial contamination in an MDU, the present study was undertaken. An evaluation needed to be done to find out whether the MDU is doing more harm (cross-contamination) than good (rendering care to the needy).

   Objective Top

The objective of this study was to assess the level of atmospheric microbial contamination before, during, and after dental treatment procedures in the dental operatory of the MDU of the College of Dental Sciences, Davangere, Karnataka, India.

   Materials and Methods Top

This experimental study was conducted in the dental operatory of the MDU of the Department of Community Dentistry, College of Dental Sciences, Davangere, Karnataka, India. Ethical clearance was obtained from ethical committee, College of Dental Sciences, Davangere. Prior permission was taken from the head of the department. The study was conducted from 1 st April 2006 to 30 th June 2006. The dental operatory of the MDU consists of two working dental chairs, with facilities like ultrasonic scaler unit, airotor handpiece, two-way syringe, and micromotor handpiece. The MDU is provided with a centralized air-conditioning system and has an area of 4.5 × 2.3 × 1.9 m 3 . For the sake of convenience, the study was carried out in the campus of the College of Dental Sciences, Davangere. The study subjects were selected from the dental screening camps and were asked to report to the hospital on the day of study. Subjects who were diagnosed with chronic generalized periodontitis were selected for procedures like oral prophylaxis. Also included for the study were those who required any permanent restorations like silver amalgam restorations. Informed consent was obtained from all the study subjects. Eight patients were treated in each treatment session.

Before the start of the study, the MDU was fumigated. All aseptic precautions were carried out. The mobile unit was left unused and locked for 15 h. To find out the baseline atmospheric microbial contamination, a set of two  Petri dish More Detailses (90 mm diameter) containing brain heart infusion (BHI) agar with 5% sheep blood was exposed in the middle of the MDU for 30 min prior to the start of the work. The microbial aerosols were allowed to settle down by gravitometric settling. [2] These petri dishes were sent for aerobic and anaerobic culture.

Then a patient, a dentist, an dental assistant entered the MDU. They kept their movements down to the minimum. At the start of the actual treatment procedures, a second set of petri dishes were exposed on 1) the patient's chest, 2) approximately 40 cm away from patient's mouth, and 3) on the operator's mouth mask (on which the petri dishes were stuck). These were the areas which were considered more prone to be contaminated. [2] At the same time, a similar procedure was followed for another dental chair. These petri dishes were exposed for 20 min. Dental treatment was done for 2 h. The third set of petri dishes was exposed for 20 min in middle of the MDU, 2 h after finishing the treatment. The same procedure was repeated over three sessions on different working days. The MDU was fumigated before the start of each session.

The petri dishes were sent to the laboratory for microbial analysis after incubating at 37°C for 2 days aerobically and for 3 days anaerobically. After this period, colonies were counted to assess the number of colony forming units (CFUs per plate). Wilcoxon signed ranks test was used to compare the differences in the CFUs and to assess their significance. The values are expressed as mean ± SD. The level of atmospheric microbial contamination was assessed by using Air Microbial Index (AMI) by the 'plate' method. [7]

   Results Top

[Table - 1] shows the total number of CFUs sampled at the specified locations in the dental operatory of the MDU.

[Table - 2] show the calculated mean number of CFUs / plate / h before, during, and after treatment procedures, using AMI values.

[Table - 3] shows the comparison of CFUs at the different periods.

   Discussion Top

This study was conducted in the dental operatory of the MDU of the Department of Community Dentistry, College of Dental Sciences, Davangere, India. A safe environment is an important consideration for all dental personnel and patients. [2] This is the first experimental study in the dental operatory of an MDU. When community dentists go for screening and treatment camps, the MDU gets exposed to various types of microbes. The College of Dental Sciences, Davangere, has adopted the primary health centers (PHCs) of Davangere district for dental screening and treatment procedures. Most of the dental problems observed during the treatment procedures are various types of periodontal problems and dental caries, as well as other medical problems. This stimulated the authors to take up the study. Patients with dental problems were screened and treated in the MDU.

The numbers presented as culture / plate are relative values, representing aerobic and anaerobic bacteria capable of growing on BHI agar with 5% sheep blood. This medium was used because it was valid for collecting airborne microorganisms and for cultivation of fastidious pathogenic microorganisms. [1],[10] It is a nonselective, enriched medium and is used for general purposes; it promotes the growth of microbes such as those sampled from air. [8],[10] It is likely that the actual microbial content in the specified areas was much higher than that reported, because the growth conditions used did not allow the identification of all types of organisms, e.g., viruses, anaerobic bacteria, and other organisms requiring specialized media. [1] Anaerobic culture conditions were used because most of the bacteria that originate from the oral cavity are facultative anaerobes. [1]

[Table - 1] shows that the microbial contamination generated during dental treatment was four times more than what was seen before and after the treatment. Larato et al. [11] have observed similar patterns of microbial air contamination before, during, and after dental treatment in a closed operatory. A subsequent decrease of atmospheric microbial contamination was noticed 2 h after the end of the working period. This is in agreement with the results reported by Grenier, [1] Larato et al., [11] and Travaglini et al. [12] The AMI values in our study showed significant results, which was in contrast with the findings of the study conducted by Timmerman et al. [7] This may be because they used suction devices during ultrasonic scaling procedures.

Larato et al. [11] and Williams et al. [13] reported that when heavy droplets fall to the floor they become part of the floor dust. Aerosols particles, which are light in weight, remain suspended in the air, leaving a residue called droplet nuclei that can reach the respiratory passages of those who are exposed. Dental operators and dental assistants should always wear mouth masks, gloves, eyeglasses, lateral protective shields, and head caps. [14] However, adherence to strict infection control procedures may increase the cost of treatment, which can affect the pattern of dental practice. [15] The studies conducted by Mills [16] has shown that there is a microbial growth when the layer from turbine handpiece was sent for culture after treatment procedures. Unscreened HIV patients may get treatment in MDU. This may lead to the formation of bioaerosols containing HIV virus, which can be transmitted to the operator through the mucocutaneous route of conjunctiva. In America, the number of dentists treating AIDS patients increased from 9% in 1987 to 29% in 1990 and it is still increasing. [17] In India, there is no reliable data on the number of AIDS patients seen by a dentist.

A study conducted by Fine, [18] as also many other studies, has proved that preprocedural oral rinsing with an antiseptic mouthwash significantly reduces the viable microbial content of bioaerosols generated during dental operative procedures. They concluded that this preprocedural rinsing may have a potential role in reducing the risk of cross-contamination with infectious agents in the dental operatory. [18],[19] The Occupational Safety and Health Administration (OSHA) has mandated that all known blood splatter and aerosols must be controlled. [20] Respiratory diseases and elevated levels of antibody to Legionella pneumophila Scientific Name Search  have both been shown to be more common in dental health workers. [21]

   Conclusion Top

The present study demonstrates that there is atmospheric microbial contamination during dental treatment procedures in the MDU. Dental personnel who are working in the MDU are found to be more prone to cross-infections, because of the limited dimensions of the MDU and the poor ventilation. Hence, utmost care has to be taken to prevent the cross-contamination. As suggested by infection control guidelines it is essential that all dental personnel wear a mouth mask, head cap, gloves, lateral protective shield, and eye glasses and follow all aseptic precautions. [14] Before the start of any dental operative procedure, a preprocedural mouth rinsing with an antiseptic mouthwash is advisable; it significantly reduces the airborne microorganisms in the MDU. It is suggested to fumigate the MDU atleast once in every month. Further studies are recommended to isolate the individual types of microorganisms.

   Acknowledgement Top

The authors would like to thank the management, Dr. Praveen Reddy B, Head of the Department of Oral and Maxillofacial Surgery, all the department post-graduate colleagues, paradental staff, Mr. Manjunath.K. and Mr. Mallikarjun.K.H, laboratory technicians, Department of Oral Pathology and Microbiology, College of Dental Sciences, Davangere, India for their kind help during the entire course of the study.

   References Top

1.Grenier D. Quantitative analysis of bacterial aerosols in two different dental clinic environments. Appl Environ Microbial 1995;61:3165-8.  Back to cited text no. 1      
2.Al Maghlouth A, Al Yousef Y, Al Bagieh N. Qualitative and quantitative analysis of bacterial aerosols. J Contemp Dent Pract 2004;5:91-100.  Back to cited text no. 2  [PUBMED]  [FULLTEXT]  
3.Leggat PA, Kedjarune U. Bacterial aerosols in the dental clinic: A review. Int Dent J 2001;51:39-44.  Back to cited text no. 3  [PUBMED]    
4.Bentley RD, Burkhart NW, Crawford JJ. Evaluating Spatter and Aerosol contamination during dental procedures. J Am Dent Assoc 1994;125:579-84.  Back to cited text no. 4      
5.Miller RL, Micik RE, Abel C, Ryge G. Studies on dental aerobiology II: Microbial splatter discharged from the oral cavity of dental patients. J Dent Res 1971;50:621-5.  Back to cited text no. 5  [PUBMED]  [FULLTEXT]  
6.Kedjarune U, Kukiattrakoon B, Yapong B, Chowanadisai S, Leggat P. Bacterial aerosols in the dental clinic-effect of time, position and type of treatment. Int Dent J 2000;50:103-7.  Back to cited text no. 6  [PUBMED]    
7.Timmerman MF, Menso L, Steinfort J, Van Winkelhoff AJ, Van Der Weijden GA. Atmospheric contamination during ultrasonic scaling. J Clin Periodontol 2004;31:458-62.  Back to cited text no. 7  [PUBMED]  [FULLTEXT]  
8.King TB, Muzzin KB, Berry CW, Anders LM. The effectiveness of an aerosol reduction device for ultrasonic scalers. J Periodontol 1997;68:45-9.  Back to cited text no. 8  [PUBMED]    
9.Runnells RR. An overview of infection control in dental practice. J Prosthet Dent 1988;59:625-9.  Back to cited text no. 9  [PUBMED]  [FULLTEXT]  
10.Available from: [Last cited on 2006 Mar 15].  Back to cited text no. 10      
11.Larato DC, Ruskin PF, Martin A, Delanko R. Effect of a dental air turbine drill on the bacterial counts in air. J Prosthet Dent 1966;16:758-65.  Back to cited text no. 11      
12.Travaglini EA, Larato DC, Martin A. Dissemination of organism-bearing droplets by high-speed dental drills. J Prosthet Dent 1966;16:132-9.  Back to cited text no. 12      
13.Williams GH, Pollock NL 3 rd , Shay DE, Barr CE. Laminar air purge of microorganisms in dental aerosols-Prophylactic procedures with the ultrasonic scaler. J Dent Res 1970;49:1498-504.  Back to cited text no. 13      
14.Infection control recommendations for the dental office and the dental laboratory. Council on Dental Materials, Instruments, and Equipment. Council on Dental Practice. Council on Dental Therapeutics. J Am Dent Assoc 1988;116:241-8.  Back to cited text no. 14      
15.Nash KD. How infection control procedures are affecting dental practice today. J Am Dent Assoc 1992;123:67-73.  Back to cited text no. 15      
16.Mills SE, Kuehne JC, Bradley DV. Bacteriological analysis of high speed handpiece turbines. J Am Dent Assoc 1993;124:59-62.  Back to cited text no. 16      
17.Gruninger SE, Siew C, Chang SB, Clayton R, Leete JK, Hojvat SA, et al . Human immunodeficiency virus type-1. Infection among dentists. J Am Dent Assoc 1992;123:57-64.  Back to cited text no. 17      
18.Fine DH, Mendieta C, Barnett ML, Furgang D, Meyers R, Olshan A, et al . Efficacy of Preprocedural rinsing with an antiseptic in reducing viable bacteria in dental clinic. J Periodontol 1992;63:821-4.  Back to cited text no. 18  [PUBMED]    
19.Trenter SC, Walmsley AD. Ultrasonic dental scaler: Associated hazards. J Clin Periodontol 2003;30:95-101.  Back to cited text no. 19  [PUBMED]  [FULLTEXT]  
20.Rivera-Hidalgo F, Barnes JB, Harrel SK. Aerosol and splatter production by focused spray and standard ultrasonic inserts. J Periodontol 1999;70:473-7.  Back to cited text no. 20  [PUBMED]    
21.Bennett AM, Fulford MR, Walker JT, Bradshaw DJ, Martin MV, Marsh PD. Microbial aerosols in general dental practice. Br Dent J 2000;189:664-7.  Back to cited text no. 21  [PUBMED]  [FULLTEXT]  

Correspondence Address:
G N Chandu
Department of Community Dentistry, College of Dental Sciences, Davangere, Karnataka - 577 004
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0970-9290.35828

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  [Table - 1], [Table - 2], [Table - 3]

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