Possibility of Blood and Hepatitis B Contamination Through Aerosols Generated During Debonding Procedures

Cross-infections may occur with the transmission of infectious agents between patients and staff within a clinical environment. Infections may spread in clinics by means of person to person contact or through contaminated objects. Inhalation, inoculation, and, rarely, direct contact are the modes by which the pathogens gain access to the host tissues in a dental clinic environment.1 The emergence of new infectious diseases and the reemergence of diseases once thought to be under control now challenge the practices of all health care professionals. Failure of antimicrobial therapy because of bacterial resistance to drugs has become a major problem.1 Tuberculosis has returned, often in a multidrug-resistant form.2,3 New viral diseases, which were unknown 20 years ago, have recently been identified with the help of advances in technology.4,5 

Protecting patients from cross-contamination and preventing exposure of office staff to infectious diseases have become major concerns in dentistry in recent years. The nature of dental procedures routinely involves the risk of occupational exposure to blood, saliva, or other body fluids that might carry disease germs, which could infect dental personnel.1 In many routine dental procedures, high-speed air-driven dental hand pieces are used for various purposes. All high-speed dental hand pieces produce a significant amount of frictional heat at the working tip. Considerable amounts of coolant water are needed to cool the tip to prevent heat transfer to the tooth surface. The presence of coolant water or other fluid to cool and lavage the working site is responsible for the negative side effects of producing a large amount of aerosol and the collection of excess water in the patient's mouth.6–8 

The water coolant system is designed to operate within the hand piece and allows for an automatic flow of water when the dental hand piece is activated. The concept used in most designs allows the water spray to hit the bur as it rotates on the tooth surface. The coolant water interacting with the bur produces an aerosol spray, which comes in contact with fluids such as saliva, blood, or gingival fluid, producing the aerosol suspension of fine particles. It has been shown in the literature that high-speed dental hand pieces produce an increase in the number of bacterial colony–forming units9–12 and that bacteria can be recovered 6 to 12 inches from the mouth of the patient.12–14 Airborne infective microorganisms in the form of infectious aerosols may be inhaled, thus causing diseases such as influenza, the common cold, and tuberculosis.15–17 

Dental treatments are often performed in the presence of gingival inflammation and bleeding. Saliva is of particular concern during dental treatment because it is frequently contaminated with blood. Although blood is not visible in the saliva, it may be present.6–8 When a high-speed dental hand piece is used in the presence of blood, it is logical to think that the blood is aerosolized and incorporated into the larger volume of aerosol cloud associated with the coolant water and can remain airborne for a significant time. Therefore, there may be a risk that the aerosols contain hepatitis B virus (HBV), hepatitis C virus (HCV), and hepatitis D virus, which can be found in the blood of patients with hepatitis. Aerosols generated by high-speed dental hand pieces and composed of various combinations of coolant water, tissue, tooth dust, blood, and saliva could contaminate skin, mucous membranes of mouth, eyes, and respiratory passages of dental personnel.

Mucosal contact, nonintact dermal contact, and parenteral contact with potentially infectious materials are generally the accepted routes of infections.1 Although there have been no definitive epidemiological studies that showed a direct link between dental aerosols and disease transmission, aerosols generated by high-speed dental hand pieces are potential hazards to health for the dental personnel.

The clinician can expect aerosol generation during orthodontic therapy when stripping, trimming removable appliances, debonding procedure, or air-power polishing before banding or bonding.12,18–20 Once the active orthodontic treatment phase has been completed, the bands and bonded attachments are removed. The gross amounts of the attached adhesive resin can be removed from the teeth using specially designed pliers.21 Removal of residual excess adhesive from the tooth surface often requires the use of a suitable dome-tapered tungsten carbide bur in a high-speed dental hand piece at a speed of approximately 30,000 rpm.21 Water cooling must be used to the tip to prevent permanent damage or necrosis of the dental pulps. This water spray may create an aerosol spray around the operatory, threatening the orthodontist and the dental assistant with possible infection risks.

A previous study has shown that orthodontists are exposed to high levels of aerosol and, as a result, are exposed to bacterial contamination during the debonding procedure.12 A significant increase in aerosol generation has been demonstrated in orthodontic procedures even where the use of high-speed dental hand piece is not required. The objective of the previous study was to investigate the bacteriological qualities of the aerosol cloud and not the presence of blood or blood-borne pathogens within the aerosol cloud.

Full-banded orthodontic appliances are commonly associated with an increased bacterial accumulation and can compromise both the self-cleansing component of the dentition and the ability of the patient to effectively remove plaque. Thus, hyperplastic marginal gingivitis is an almost inevitable result of poor plaque control in patients undergoing orthodontic treatment.22,23 In addition, among all orthodontic procedures, banding and debanding are considered to cause greatest damage to the gingival margins.24 As a result, gingival inflammation and bleeding are usually encountered during the debonding procedure.25 

The aim of this study was to determine the presence or absence of blood and hepatitis B in the aerosols generated by a high-speed dental hand piece used during the debonding procedure.

The study group consisted of 26 patients (10 girls and 16 boys) who were at the debonding stage of their orthodontic treatments. The mean age of the study group was 16 ± 2 years. To participate in the study, the subjects had to meet the following criteria: treated with full-banded edgewise extraction or nonextraction treatment with bands on their molars and brackets on the rest of the teeth; no signs of respiratory infection or rheumatic heart disease and any other systemic disease requiring antibiotic medication; no current anticoagulant or steroid therapy and no periodontal therapy including scaling, root planing, or prophylaxis during the past six months. Subjects with extremely poor oral hygiene and gingival health were excluded.

At the planning stage of the study, we aimed to find out only if blood or blood elements were present in the aerosols generated during the debonding procedure. A closer look at the diagnostic records of the patients included brought up a secondary objective. Three of the patients were reported in their medical history to be carriers of hepatitis B. Therefore, we decided to also investigate the possibility of HBV contamination within the high-speed dental hand piece aerosols. The patients were informed about the purpose of the study, and they gave their consent to participate.

The molar bands were removed using band remover pliers (Dentaurum, Pforzheim, Germany), and care was taken not to traumatize the gingiva. After the removal of the braces using bracket-removing pliers (Dentaurum), the patients were directed to the experimental room. To prevent the possibility of any mistake, all procedures were done in the same room. The patients were scheduled as the first to be treated in the early hours of the mornings to ensure the lowest rate of air turbulence.14 Before any procedure, the assistant, who was blind to the study, recorded the gingival status of each patient. The assistant was instructed to observe and record the occurrence of bleeding at the gingival margins of even a single tooth. The orthodontist and the assistant were seated and positioned following the guidelines of the four-handed dentistry.6 The orthodontist and the assistant wore sterilized surgery gloves, masks, and face shields during all the procedures in the study.

A tungsten carbide bur in a high-speed dental hand piece, operated at 30,000 rpm with water coolant, was used to remove the excess adhesive material left on the lower teeth. A dental unit with contained-water system was used. It was not connected to the public water supply. The system had external water containers that were sterilized and refilled with sterile water for every patient. The water flow of the high-speed dental hand piece was adjusted to the same value before each trial.

Collection of aerosol samples was done using a saliva ejector that fit on the handle of the high-speed dental hand piece (Figure 1A). It consisted of a disposable plastic tube that was attached to the handle of the high-speed dental hand piece. The tip of the saliva ejector was attached three or four cm away from the tip of the high-speed dental hand piece to prevent the immediate capture of coolant water, so that an adequate volume of coolant water was provided, otherwise, the coolant water from the hand piece might be drawn before it had cooled or rinsed the tooth. Also, this way the saliva ejector captured the aerosol after the coolant water contacted the tooth surface, gingiva, or saliva. A small-diameter suction tube ran down the side of the high-speed dental hand piece and was attached to a mobile oral evacuator (Figure 1B).

While working with the high-speed dental hand piece, care was taken not to touch any of the fluid accumulated in the mouth to assure that the suction device captured only the aerosol produced by high-speed dental hand piece. The assistant used the second mobile evacuator to remove excess liquid from the mouth and tried to hold the tip of the saliva ejector on the lingual surface, and this aided in retracting the tongue. The evacuation level was monitored at 5.2 inches of mercury and adjusted for both the evacuators to ensure consistent evacuation levels.14 As necessary, the assistant retracted the patient's lips with a mouth mirror to ensure that the orthodontist could readily see and reach the working area. The assistant was again instructed to observe the occurrence or absence of gingival bleeding at the gingival margins during the procedure. The volume of collected aerosol and excess fluid samples was measured in a graduated cylinder and recorded for each patient.

The presence or absence of occult blood in aerosol and excess fluid samples was tested by guaiac method26,27 (Hemoccult II slide test; Smith Kline Diagnostic, San Jose, Calif). Occult blood strips were moistened with the aerosol and excess fluid samples. Two strips were moistened for each sample. Therefore, 104 strips were tested for 26 patients. To detect hemoglobin, the strips were left for drying, and the dried strips were treated with the solution provided by the manufacturer. The presence of hemoglobin fractions was confirmed by distinct blue coloration on the test strips. Two strips were moistened by the uncontaminated spray from the high-speed dental instrument before each trial to serve as a negative control (a total of 52 control strips).

Before debonding procedures, three to five mL of blood sample was obtained from the hepatitis B carriers by using a sterile syringe following a strict aseptic technique. Serum samples obtained from three patients were tested for hepatitis B surface antigen (HBsAg) using commercial enzyme-linked immunosorbent assay kits (Biokit, Barcelona, Spain) according to the manufacturer's instructions. Aerosol and excess fluid samples of these patients were also evaluated for HBsAg. In addition, sera, aerosol, and excess fluid samples were analyzed for HBV-deoxyribonucleic acid (DNA) by polymerase chain reaction (PCR) using specific primers HBV1 (5′GCT TTG GGG CAT GGA CAT TGA CCC 3′) and HBV2 (5′ TGA TAA GAT AGG GGC ATT TGG TGG 3′), which target the 433-bp DNA fragment in HBV core region. In brief, to extract DNA, 200 μL sample and 200 μL lysis buffer consisting of five M guanidinium thiocyanate (Sigma, St Louis, Mo), 0.5% bovine serum albumin (Sigma), 80 mM ethylenediaminetetraacetic acid, 400 mM Tris-HCl (pH 7.5), and 0.5% sodium-N-lauroylsarcosine (Sigma) was mixed. The mixture was incubated at 60°C for one hour and then at 37°C overnight. DNA was extracted from each specimen using a phenol-chloroform method.

PCR was performed in a final volume of 50 μL reaction mixture containing five μL of extracted DNA, four μL of each deoxynucleoside triphosphate(2.5 mM), 0.5 μL primer HBV2 (100 pmol), 0.5 μL primer HBV1 (100 pmol), 0.5 μL Taq polymerase (5 U), three μL MgCl₂ (25 mM), five μL 10 times PCR buffer, and 31.5 μL distilled water. This reaction mixture was kept at 99°C for five minutes for first denaturation. Amplification was carried out for 25 cycles consisting of denaturation at 94°C for one minute, primer annealing at 52°C for two minutes, and extension at 74°C for two minutes, followed by a final elongation for five minutes at 72°C. PCR products were separated on a 1.5% agarose gel stained with ethidium bromide after electrophoresis. The samples, which gave the 433-bp DNA fragments, were considered HBV-DNA positive.

The assistant observed bleeding in 18 out of 26 patients (70%) after bracket removal and in 16 out of 26 patients during the debonding procedure (62%, Table 1). The mean volume of excess fluid collected was 158 mL (range of 100 to 190 mL), and the mean volume of aerosol sample collected was 2.28 mL (range of 1.3 to 3.1 mL) (Table 1).

In 17 out of 26 patients, all strips tested for aerosol and excess fluid samples gave positive results for the presence of occult blood. In the remaining nine patients, one of the strips tested for aerosol samples was found to be positive and the other one was found to be negative for occult blood. In this situation, the result of the test was accepted as positive for the presence of occult blood. Therefore, blood was found in all the aerosol and excess fluid samples (Table 1). All control strips were negative for blood.

HBsAg and HBV-DNA were detected in serum samples of patients who were informed that they are hepatitis B carriers (Table 2). HBsAg was detected in excess fluid samples of the two of these patients, whereas HBV-DNA was detected only in one of the sample (Table 2). HBsAg and HBV-DNA were detected in aerosol sample of only one hepatitis B carrier (Table 2).

It has been generally demonstrated that oral bacteria are aerosolized during dental procedures involving devices such as air turbines and ultrasonic scalers.9–14 Aerosol generated during the debonding procedure has been shown to be routinely contaminated with oral bacteria,12 most of which are considered to be nonpathogenic.1 

Many reports in the literature also demonstrated the presence of blood in aerosols.26–28 Barnes et al27 found that aerosols produced by ultrasonic scalers during subgingival scaling always contain blood. Subgingival scaling is often undertaken in areas of intense inflammatory gingivitis and periodontitis with bleeding from the gingival sulcus.29 Thereby blood is always expected around the working area and also elsewhere in the mouth.

Previous studies have reported that orthodontists' compliance with the use of barrier protection, sterilization, and disinfections is less than that of general dentists.30–33 McCarthy et al32 concluded that orthodontists show less compliance with infection control procedures because they might think that they are exposed to blood-borne pathogens less frequently. However, the incidence of blood exposures in orthodontic practice is higher than expected. In a study by Woo et al,31 it was found that orthodontists reported observing blood in the mouth 10 times per week. According to the results of McCarthy et al,32 18% of the orthodontists were exposed to blood splashes to eyes, nose, or mouth in a year. Davis and BeGole33 reported that 99% of the chairside assistants observed blood in the mouth during daily orthodontic procedures. The presence of blood in orthodontic treatment may be explained by its special stress on the oral environment, as stated previously.

According to the data obtained from the previous investigations, most of the orthodontists stated that they were exposed to blood through cuts, puncture wounds, and needle sticks.30–33 

However, there is a possibility of exposure to blood through aerosol in orthodontic practice whenever the use of a high-speed instrument is required. In this study, when a high-speed dental instrument was activated to remove the excess adhesive or cement from the tooth surface, a fine, pressurized coolant water spray was also released that interacted with the bur, creating an aerosol spray. Excess fluid, which is composed of coolant water, saliva, adhesive pieces, cement pieces, and possibly blood, accumulated in the mouth of patients. The presence of occult blood in accumulated fluid or in excess fluid samples collected from oral cavity was confirmed by the guaiac test. Gingival inflammation and irritation effect of coolant water spray on the gingiva could be the reasons for the presence of blood in excess fluid.7 

The incidence of visible blood during the removal of excess adhesive was found to be less than that just after bracket removal. An explanation for this reduction could be that the pressurized water spray emitted from the high-speed dental hand piece washed away the visible blood together with adhesive and cement pieces (Figure 2A,B). There were variations in the amount of aerosol captured and fluid samples collected. Because of the requirements of the procedure, the orthodontist and the assistant moved the high-speed dental hand piece and saliva ejector closer to or farther from the working area, which might result in an increase or decrease in the amount of aerosol captured and excess fluid collected. Eleven patients were treated by removal of four premolars. It might also be expected that the absence of teeth would yield minimal decreases in the amount of aerosol captured and excess fluid collected.

The hypothesis of the present study was that the periphery of the generated aerosol spray may be near the gingival margin and also may interact with saliva or blood-contaminated saliva and therefore blood may become part of the aerosol cloud formed by the coolant water. Because the evacuation system designed for this study captured only the aerosol that had been formed by the high-speed instrument (not the excess fluid accumulated in the mouth), our results showed that aerosols generated during the debonding process were routinely contaminated with blood. Interestingly, we found no direct relationship between clinically visible blood and the presence of occult blood in aerosol. The aerosol, however, was contaminated with blood all the time even when the blood was not visible in the patient's mouth. In nine out of 26 patients, one of the two strips detecting hemoglobin in aerosol sample was negative for the presence of occult blood. The reason for this could be explained by the sensitivity of the guaiac method. There might be lack of retention of fluid or blood adequate to test.27 

It has been estimated that viruses harbored in blood or blood-contaminated saliva can be transmitted to a new host by aerosols.1 This study also demonstrated the possibility of transmission of HBV during the debonding procedure by generated aerosol and excess fluid. HBsAg, which is the surface component of HBV and a serologic marker for HBV infection,34 was detected in excess fluid sample of the two hepatitis B carriers, and HBV-DNA was detected in one sample. HBsAg and HBV-DNA were detected from the collected aerosol sample of only one of the hepatitis B carriers. Therefore, aerosols generated during the debonding procedure should always be considered as potentially pathogenic. Because HBV is only one of the most infectious agents that may be present in the blood, the results of this study should also be extended to all other infectious diseases.

Aerosols are composed of solid and liquid particles having size of 0.001 to more than 100 μm.28 The literature indicates that both the large and the small particles in the aerosol routinely contain bacteria and blood.35 Particles within the aerosol cloud tend to travel upward in “a vertical, expanding, funnel-shaped, circular pattern, striking the operator's chest, shoulder and face and falling in a heavy rain on the lower arms.”11 This is of concern because the skin of the dental personnels' hands, face, lower neck, or arms may become chapped, cracked, or irritated with a failure to maintain epithelial integrity that compromises the essential innate defense barrier.1 This can substantially increase the possibility of entry of blood-borne pathogens into tissues. Although the risk of transmission of infection through direct contact of tissues with secretions and blood is much more lower than that through contaminated sharps and instruments,1 the possibility should not be ignored. In addition, protection of areas such as neck, chest, and arms is often unrecognized.36 

Larger particles within aerosol cloud settle very quickly on surfaces as a result of gravitational pull and contaminate the dental equipment near the working area.1 Considering that HBV is potentially infectious for seven days in 10⁻⁹ mL of blood after drying37,38 and blood containing human immunodeficiency virus (HIV) can remain infectious for up to three days after drying,39 the blood and blood-contaminated saliva from each patient's mouth that falls on dental equipment can be transmitted to successive patients. In this study, debonding area was limited to lower teeth only. Because larger volume of cooling water would be required during full mouth debonding, production of higher volumes of contaminated aerosols should be expected.

The risk of acquiring blood-borne pathogen from occupational exposures is dependent on the frequency of exposure to blood or to other human body fluids. Dental professionals are relatively more at risk than is general population because of their close contact with saliva and blood. In the United States, unfortunately, 140,000 to 320,000 new HBV infections and 5000 to 6000 deaths associated with chronic HBV infection occur each year.4 Four million people in the United States are infected with HCV, and 30,000 new HCV infections occur each year.40 It was estimated that if effective preventive strategies are not developed, there will be more than three times the number of deaths over the next two decades.41 All patients who are carriers of blood-borne disease certainly do not seek orthodontic treatment. But some blood-borne carriers do seek orthodontic treatment from orthodontists, some of whom may not be adequately protecting themselves, their staff members, and other patients from the risk of contracting disease. Comparison of the practice profile in terms of numbers of patients treated per week between orthodontists and general dentists showed that orthodontists treat more patients per week than do general dentists.31,33 Although a recent study indicated an improvement, orthodontists' compliance with infection control practices is still lacking in comparison with general dentists.33 

Orthodontists may assume that their younger population of patients is to be at less risk of blood-borne infections with HIV, HCV, or HBV. However, it was indicated that approximately 25% of new HIV infected patients are under 20 years of age.32 Also, at younger ages acute HBV infections are asymptomatic with less than 10% of them exhibiting jaundice, and the younger the person is at the time of infection, the higher the risk of developing chronic HBV infection.42 

The present study showed that aerosols generated during the debonding procedures were routinely contaminated with blood. Occupational Safety & Health Administration recommends taking adequate protection for minimizing the risk of blood or other body fluid exposures that might place a healthcare worker at risk of infection.43 The Centers of Disease Control,44 the American Dental Association,45 and the American Association of Public Health Dentistry46 recommend numerous detailed guidelines for practicing infection control. Single-use gloves, a surgical mask or full-length plastic face shield, protective eyeglasses with side shields, a protective uniform, receipt of vaccines as well as routine autoclaving of instruments, and means of handling potentially infectious materials are recommended. The use of a rubber dam may be impractical to impossible in orthodontics, but patient positioning, use of a high-velocity evacuator, and proper angulations of the high-speed instruments are other essential methods to reduce the amount of aerosol.6–8 Nevertheless, current data indicated that there is no significant risk of contracting blood-borne diseases through the provision of dental treatment when universal precautions and recommended infection control procedures are routinely followed.44,47 

Orthodontic treatment often involves contact with blood and blood-contaminated saliva, and orthodontists and their assistants may therefore be commonly at risk. Many individuals who are infected with variety of pathogens are asymptomatic. Patients referred to our clinics may know that they are previously infected with blood-borne pathogens, but they may be hesitant to report their complete health status or they may have been exposed to the blood-borne pathogens and may be coming down with a blood-borne disease but may not yet have obvious symptoms. Therefore, the philosophy in any dental practice should be to assume that any patient, or any person working in the dental office, might carry a serious infection. We should realize the ease of transmission of blood-borne diseases and should not forget that a single exposure incident might result in infection and subsequent illness and, in some cases, death. All phases of treatment are then conducted so as to minimize the risk of cross-infection.