Demand for dental treatment has been increasing in recent years as people have become more aware of their oral health and the benefits of good dental aesthetics. Maintaining and practising stringent cross-infection control procedures therefore have never been more essential to ensure the health and safety of dentists, dental hygienists and assistants, as well as other supporting staff who may be indirectly involved in the treatment process.
Dental professionals are at high risk of cross-infection. A report published in 1999 has shown that in developing countries, for example, the number of dental staff contaminated during treatment is increasing by almost 6 per cent each year. Research has shown that infectious micro-organisms can be transmitted by blood or saliva via direct or indirect contact, aerosols, or contaminated instruments and equipment. As stated by the US Centers for Disease Control and Prevention (CDC) in their 2003 guidelines, the transmission of infectious disease can occur in four ways: direct contact with blood or body fluids, indirect contact with contaminated objects or surfaces, contact with bacterial droplets or aerosols, and inhalation of airborne micro-organisms.
The most likely mode of transmission in dentistry is through inhalation of bacterial aerosols or splatters. Their potential health hazards are well documented and acknowledged.[4–9] Both can be host to a large variety of micro-organisms and viruses, which can be infectious to susceptible individuals. During treatment, the dentist’s face and patient’s chest are most affected by splatter, as the majority of the splatters are radiated towards them.[10, 11] According to studies, the most contaminated area on the dentist’s face during treatment is around the nose and inner corner of the eyes.
Splatter consists of large particles of greater than 100 µm generated during the use of dental equipment, such as turbines, ultrasonic scalers, or water and air syringes. Owing to this, splatter tends to travel in a trajectory, thereby contacting objects in its path. Aerosol consists of smaller particles that can remain in the air for a long time and travel with air currents. Most dental aerosols are less than 5 µm in diameter; therefore, they are able to penetrate and stay within the lung, causing respiratory or other health problems. Among dental procedures that produce high aerosol concentration are ultrasonic scaling, tooth preparation using high-speed handpieces, and dental extraction involving bone removal via a dental handpiece.
The World Health Organization (WHO) has reported a rise in airborne infections worldwide. Tuberculosis in particular has increased in the developing world. It has been stipulated that the risk of exposure to tuberculosis in susceptible DHCP is greater than in healthy individuals. Bennett et al. concluded that dentists and their assistants, who are exposed for approximately 15 minutes during peak aerosol concentration, have a slightly higher risk of exposure to Mycobacterium tuberculosis than the general public does. During this period, the DHCP inhales about 0.014–0.12 µl of aerosolised saliva, which may contain viable pathogens that can have a detrimental effect on the health of susceptible DHCP.
With all of this in mind, it is the responsibility of DHCP to adhere strictly to recommended infection control guidelines and policies. Several measures should be taken to reduce and control airborne contamination in the dental clinic. For example, it has been demonstrated that the use of a mouthrinse, high-volume evacuation or a combination of both methods significantly reduces the number of colony-forming units in aerosols emitted during ultrasonic scaling. Routine use of rubber dam isolation provides a clean and dry area for placement of dental restorations, prevents salivary and blood splatter, and protects the patient’s mouth and airway.
Using personal protective equipment (PPE), such as surgical masks (with at least 95% efficiency against particles 3–5 µm in diameter; changed for every patient or every 20 minutes in an aerosol environment or 60 minutes in a non-aerosol environment), safety glasses with lateral protection to prevent contact with eyes, as well as disposable gowns and gloves to reduce the penetration of or contact with bacterial aerosols and splatters, is vital.
Regular maintenance of the air-conditioning system is recommended too, as good ventilation has a diluting effect on the airborne microbial load, especially at night when the clinic is closed. Air samples taken at different times at a multi-chair dental clinic showed that bacterial aerosols are more concentrated during treatment and that there is higher concentration of circulating bacterial aerosols at the beginning of the day, which may be related to reduced ventilation. Residual bacterial aerosols can be removed through air filters or ultraviolet light.
As splatters can travel as far as the door or supply counter in the middle of a multi-chair dental clinic, all clean, unused instruments and equipment should be kept in closed cabinets or drawers to prevent contamination. Other important measures that must be taken to prevent cross-infection include adequate sterilisation of dental instruments, disinfection of work surfaces before and after each dental procedure, disinfection of all dental materials and work sent out to the laboratory, and regular maintenance of the dental water lines and equipment, which has the potential to harbour bacteria. All dental water lines should be purged at the beginning of each day for between 5 and 10 minutes and flushed thoroughly with water, as residual water may become contaminated overnight and biofilm may develop along the inner side of the tube. Purging will result in a significant decrease in bacterial counts.[15, 16]
The Canadian Dental Association recommends running high-speed handpieces for 20–30 seconds after each treatment to purge all potentially contaminated air and water. This procedure has been proven to reduce the bacterial load in the water line significantly. Blood cells, as well as bacterial and viral particles, can survive inside handpieces even after disinfection. They must therefore be sterilised between patients.[17, 18]
The clinic floor should be disinfected and cleaned with an antimicrobial disinfectant solution at least twice per day to eradicate any bacterial residue from splatter or aerosols.
It is a well-known fact that private dental clinics sometimes employ dental assistants who have not received certified training. Improperly trained personnel, however, may lead to poor infection control practices. It is the responsibility of every dentist to educate and train his or her assistants in the standard procedures. Furthermore, DHCP immunisation status should be up to date.
Eliminating the risk of exposure to dental aerosols remains a difficult task. The best way to reduce the risks, however, is to employ routine cross-infection protocols recommended by the health authorities, such as the CDC, WHO and ministries of health. To date, various infection control reports and procedures have been published to inform and educate dental health care personnel (DHCP) about the importance of practising adequate infection control.