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All dentists and personnel must understand and implement the highest standards of infection control to keep patients and staff as infection-free as possible. The US Department of Labor's Occupational Safety and Health Administration (OSHA) has outlined the Centers for Disease Control and Prevention (CDC)'s recommended practice of standard precautions when treating all patients, regardless of infection status, in the healthcare setting.1 Standard precautions are a minimum level of infection prevention protocols used in patient care to minimize the risk of transmission of potentially harmful pathogens from all sources in the medical and dental setting.2 Standard precautions involve handwashing, donning personal protective equipment (PPE), cough etiquette, sharps safety, safe injection practices, sterilizing instruments and devices, and cleaning and disinfecting environmental surfaces.1,3 Standard precautions apply to contact with blood; all body fluids, secretions, and excretions except sweat; non-intact skin; and mucous membranes.1,4The ultimate goal of standard precautions is to prevent cross-contamination, which is the spread of harmful microbes from one source to another. Cross-contamination routes in the dental setting include patient to the dental team, dental team to the patient, and patient to patient through surface contamination and inadequate sterilization of dental instruments.4 Recent studies have recognized dental water lines as a potential route for cross-contamination in dental offices.5 Standard precautions are also used to prevent infection. For an infection to occur, the following chain of events must happen: 1) an infectious agent, 2) a reservoir, 3) a port of exit, 4) transmission, 5) a port of entry, and 6) a susceptible host.4 Infection occurs if there is not a break in this chain. Standard precautions disrupt the chain.
When patients present to the dental setting with known or suspected highly transmissible or epidemiologically significant pathogens, transmission-based precautions are employed in conjunction with standard precautions as an added layer of protection to prevent transmission.6-8 The CDC defines transmission-based precautions as the second tier of basic infection control principles that should be used when standard precautions are insufficient in preventing the spread of disease in the healthcare setting.9 Transmission-based precaution guidelines center around the source of the infection, type of infection, and mode of transmission for the environmental pathogen.10-11
The three types of transmission-based precautions are direct and indirect patient contact, droplets, and aerosols.10 Contact precautions should be employed for patients with known or suspected infections that can be spread through direct or indirect physical contact with items or surfaces in the patient's immediate surroundings.6,10,12 Guidelines that must be followed when implementing contact precautions include: limiting movement of the patient within the dental setting and placing the patient in a single room if available, donning personal protective equipment (PPE) prior to entering the treatment area, disposing of PPE prior to exiting the treatment area to minimize cross-contamination, and proper cleaning and disinfection of any non-disposable items utilized during patient care.12-14 Highly transmissible diseases that require implementation of contact precautions include staphylococcus aureus (MSSA or MRSA), Vancomycin resistant enterococci (VRE), Clostridium difficile infection (CDI) and scabies.15 For patients with known or suspected pathogens that can be transmitted through respiratory droplets (via coughing, sneezing, laughing, talking, or breathing), droplet precautions should be employed.6,10,13 Droplet precautions follow similar guidelines with the addition of the following recommendations: dental health care practitioners (DHCP) should cover their eyes, nose, and mouth prior to entering the treatment room, patients must wear a mask when not receiving treatment, and patients should be informed to adhere to cough etiquette.12,13,16,17 Pathogens that require implementation of droplet precautions include pertussis, influenza, rubella, and mumps.15Airborne precautions must be used for patients with known or suspected infections that can be transmitted in the air via aerosols or dust particles.6,18,19 In addition to following the guidelines for contact and droplet precautions, airborne precautions establish that patients be placed in an airborne infection isolation room (AIIR) or private patient room with a closed door if an AIIR is unavailable; the treatment room be restricted to team members involved with patient care; and those involved with care should don a NIOSH-approved N95 or higher level respirator.13 Vaccinations are also recommended for susceptible individuals immediately after unprotected contact with an infected individual.13COVID-19, tuberculosis, chickenpox, and measles are examples of diseases that warrant the use of airborne precautions.15
Modes of Transmission
The risk of cross-contamination in the dental setting remains high because of the various modes of transmission of infectious material. Exposure occurs when pathogens come in contact with non-intact skin. Modes of transmission include direct contact with infectious blood and secretions; indirect contact with contaminated instruments, dental equipment, or environmental surroundings; or contact with airborne contaminants present in either droplet splatter or aerosols of oral and respiratory fluids.4,5Cross-contamination can also occur by emanation of pathogenic microbes through the use of ultrasonic equipment, polishing, spraying of dental handpieces, and poor ventilation.5
Accidental needle sticks create the highest risk of exposure for dental professionals. Risk is determined by virulence of the pathogen, contact time, amount and frequency of exposure, and immune response.5 Dust-borne infections that travel on dust particles, such as tetanus and Staphylococcus, can occur in the dental office, so surface disinfection is imperative. Aerosols, which are invisible to the naked eye, can remain suspended in the air for long periods because of their small particle size.4 Most aerosol particles are smaller than 5 μm and are breathed deeply into the lungs. Spatter is visible and remains in the air for shorter periods because of its larger particle size.4 Spatter particles are usually larger than 50 μm. Aerosols and spatter are created during breathing, speaking, coughing, and sneezing.4In the dental setting, they are also produced by performing intraoral procedures, high-speed and low-speed evacuation devices, high-powered rotary instruments, and air-driven devices.20Worth noting is the behavior of aerosols varies based on environmental factors, such as gravity, airflow, temperature, and humidity.21 Aerosol and spatter concentrations are greater at the scene of instrumentation and decrease with distance.4
Federal Agencies That Influence Infection Control Guidelines
Several federal agencies influence infection control standards for dental office settings. The Food and Drug Administration (FDA) is an agency within the Department of Health and Human Services that is responsible for regulating dental handpieces, dental chairs and accessories, dental curing lights, dental amalgams, and x-ray equipment.22 In 2015, the FDA published a final guide that outlined steps to reduce the risk of patient infections.22 This guide provided suggestions for manufacturers to validate their reprocessing techniques to safeguard medical devices for continuous use.22 Dental-unit water lines are also regulated by the FDA.23Additionally, the Environmental Protection Agency (EPA) is responsible for providing standards for water quality in the dental office setting. The EPA also mandates protocols for disposal of amalgam and establishes guidelines for the disinfectants used for cleaning in the dental environment. OSHA is part of the Department of Labor and is responsible for protecting employees. They establish standards for blood-borne pathogens, pharmaceuticals and other chemical agents, human factors, ergonomic hazards, noise, vibration, and workplace violence.24 The CDC makes recommendations for infection control guidelines for dental practice settings.25State dental boards can promulgate CDC recommendations and make them mandatory. In 2016, the CDC released a summary of infection control practices. The summary provides a checklist for guidelines issued to prevent and control infectious diseases in the dental setting. The summary is not intended to replace the original CDC guidelines.
The Organization for Safety, Asepsis and Prevention (OSAP) is not a federal agency but is an organization "dedicated to education, research, service, and policy development to promote safety and the control of infectious diseases in dental healthcare settings worldwide."26
Pathogens in the Dental Setting
Several viruses and bacteria are relevant in the dental practice environment. These pathogens place dental professionals at risk for developing infectious diseases. Herpes simplex viruses (HSV), human immunodeficiency virus (HIV), hepatitis A through G, tuberculosis (TB), Ebola, methicillin-resistant S. aureus (MRSA), and severe acute respiratory syndrome coronavirus (SARS-CoV-2) are of particular concern.
There are various types of HSV. HSV-1 and HSV-2 are significant to dentistry. Both are highly contagious. HSVs are transmitted when the contents of an infected blister are exposed to mucosa or skin that is not intact.5 Because HSV is highly contagious, dental personnel must wear adequate PPE and avoid direct contact with infected splatter from the herpetic lesion or saliva.5 In addition, it is vital that the dental team properly disinfect the dental operatory with a disinfectant approved by the EPA to inactivate the virus.5
For HIV, the risk of contracting or transmitting the virus in the dental setting is low and correlates to blood viral counts and volume of blood exposure.5 According to one study, the risk of transmitting HIV through saliva is relatively small because of low numbers of CD4-positive target cells, the presence of anti-HIV antibodies, and antiviral factors in saliva.5 Although the risk is low, research suggests there is an incomplete understanding of risks associated with acquiring HIV after exposure to HIV-infected tissue or fluid, so the dental team needs to continue to protect themselves with standard precautions.5
Dental personnel are at a greater risk of exposure to hepatitis because of the aerosols produced by ultrasonic scaling, air polishing, and emanation of air and water through high-speed handpieces. For this reason, the dental team must take great care to prevent and protect against hepatitis.27 There are various types of hepatitis, all of which dental team members should be familiar with. Hepatitis A, also known as infectious hepatitis, is the most common viral hepatitis in the world and is transmitted through the fecal-oral route.4,27 Vaccination is recommended for dental professionals. Hepatitis B, or serum hepatitis, is the single most important occupational hazard for dental professionals.27 It can be transmitted percutaneously or by mucosal contact with infectious body fluid.28 Vaccination is recommended for dental professionals. Hepatitis C is the most common chronic blood-borne infection in the United States and shares similar risk factors to hepatitis B.4,28 Its origins have been traced to the use of injecting syringes used in the ambulatory setting and spas.28 Hepatitis D, also called the delta agent, can only be contracted if hepatitis B is present.4,27,28 Hepatis D has the same mode of transmission as hepatitis B and shares the same prevention and protection transmission protocols.27The hepatitis B vaccination protects against hepatitis D.4Hepatitis E, unlike hepatitis A through D, is not a chronic infection and mimics hepatitis A.27,28Hepatitis E is excreted in stools, is transmitted through the oral-fecal route, and is a more recent discovery.27,28 Hepatitis G is transmitted through blood and rarely occurs without a hepatitis A, B, or C co-infection.27Hepatitis G can be found in patients who have received transfusions.27
TB is a highly contagious infectious disease caused by inhaling Mycobacterium tuberculosis in airborne particles.29 It is a chronic granulomatous disease and resists most disinfecting agents; therefore, standard precautions are not sufficient to protect against transmission of TB in the dental setting.4,29 In addition, airborne particles containing TB are small enough to pass through standard surgical masks and can remain in the air suspended for hours. Therefore, treatment of a patient with active TB in a dental setting is prohibited.
MRSA is a dangerous Staphylococcus bacterial infection that originates on the skin and is resistant to most antibiotics.30,31 The primary mode of transmission in the healthcare setting is through the hands of healthcare personnel.31Transmission through airborne droplets is conceivable because MRSA can colonize in saliva, and it has been isolated from saliva and dental plaque.31
Ebola is a lethal, viral hemorrhagic disease caused by an Ebola virus strain.32,33Transmission can occur person to person with direct contact of skin, blood, and body fluids, or through animals.34 Although there have been no confirmed cases of transmission of Ebola through saliva, serum levels of Ebola RNA have been isolated in saliva.34 Therefore, dental professionals should follow standard precautions to control the spread of the disease.
Severe acute respiratory syndrome coronavirus (SARS-CoV-2), which belongs to a large family of RNA viruses that cause respiratory and intestinal infections in animals and humans, causes the novel coronavirus disease, COVID-19.35 After being declared a public health emergency on January 30, 2020 by the World Health Organization (WHO), SARS-CoV-2 spread globally, infecting over 100,000,000 individuals and claiming over 2,200,000 lives as of February 2021.36,37 SARS-CoV-2 can be transmitted by symptomatic and asymptomatic individuals from person-to person contact via infectious aerosols produced when an individual coughs, sneezes, breathes, or talks.38,39Johansson and colleagues report laboratory studies that confirm high levels of viral RNA in respiratory secretions at the time of symptom onset in presymptomatic individuals and offer that epidemiological studies suggest asymptomatic individuals are as prone to transmit SARS-CoV-2 as individuals with symptoms.40 Transmission is likely to occur when individuals are within close proximity, reportedly fewer than 6 feet apart.38 If an individual is known or suspected to be infected with SAR-CoV-2, airborne precautions should be followed. In addition, DHCP should consider modifying dental treatments to safeguard the dental practice setting, dental team, and their patients because the mouth has been recognized as a high-risk route of SARS-CoV-2 transmission, inhalation transmission in the dental setting is especially high, and a high number of dental procedures produce aerosols.41-43
Hierarchy of Controls
With regard to infection control practices in the dental setting, the hierarchy of controls is designed to eliminate or minimize the risk of the transmission of infectious agents.44Implementation of the hierarchy of controls helps to facilitate infection control measures by outlining a framework to systematically identify workplace hazards, providing direction on strategies to control occupational exposure to remove hazards (pathogens) from the workplace, and offering layers of protection for the DHCP.12,44Control measures are tiered, starting with the most effective control measures, ending with actions that rely on precise and consistent implementation.45 Because SARS-CoV-2 is highly transmissible via airborne particles and the mouth serves as the primary reservoir for aerosols, DHCP are at a high risk for exposure, and dental settings should utilize the hierarchy of controls to respond to COVID-19.46 Control measures include elimination, substitution, engineering controls, administrative controls, workplace controls, and personal protective equipment (PPE).47 Elimination controls include eliminating the risk completely, while substitution controls involve replacing the hazard with a safer alternative.48 Engineering controls involve isolating or placing a barrier between the DHCP and the hazard and often require a physical change to the environment.49,51 Engineering control strategies include the use of sharps containers, instrument cassettes, or ventilation systems that remove contaminants from the air before they can be inhaled.12,50 Administrative controls encompass policy changes that impact how individuals act in the dental setting and include personal hygiene, isolation strategies, restricting the size of gatherings, social distancing, warning labels, and training.48,50-51 The last and least effective control measures are workplace controls and PPE. Workplace controls are daily personal actions that result in safer behavior such as hand hygiene and one-handed needle capping.12PPE is frequently the focal point of infection control safety measures because their use can be easily implemented when available; however, OSHA offers that PPE should be considered the last line of defense because it is the least effective and is highly dependent upon effective use and wear by the user.45,52
Personal Protective Equipment
In the dental office setting, personal protective equipment (PPE), should be worn by DHCP at all times while providing patient care to mitigate risk and reduce occupational exposure to pathogenic microorganisms and other potentially infectious material that cause injuries and illnesses.17,53,54 The CDC issues guidance for dental employers on PPE selection and offers that dental employers must provide PPE for their employees, while OSHA laws requires dental employers to provide dental training on PPE.54 Dental professionals must wear PPE to protect their skin and mucous membranes from infectious material, aerosols, spatter, or spray.55PPE should fit comfortably and securely, ensuring full coverage to prevent exposure.55PPE includes surgical masks, gloves, eye protection, and protective clothing to include fluid-resistant gowns, and may include particulate filter respirators, face shields, surgical caps, and ear plugs.
To avoid cross contamination, dental professionals should don PPE in a sequential manner. Protective eyewear with side shields should be worn by the clinician and the patient at all times during dental procedures. Current guidelines suggest the use of a chin-length face shield.56Utility gloves must be worn when cleaning the dental operatory and handling dental instruments during the sterilization process.
The CDC mandates dental personnel follow specific guidelines for clinical garments. Clinical garments should only be worn in the dental office setting to prevent cross-contamination; they should never be worn over street clothing. The garments should have a closed front and neck, and the length should cover the knees when seated for patient treatment. They should have long sleeves with fitted cuffs to permit protective gloves to extend over the cuffs, and they should not have pockets, which could hold contaminated objects such as keys or writing implements. They should be disposable or commercially washable and able to withstand washing with bleach. If clinical garments are laundered at home, the items must be kept separated from household laundry and treated with household bleach for disinfection.4
CDC guidelines specify that dental personnel wear a mask for patient care, cleanup, and instrument processing; during any task that produces a splatter; and to prevent infection and exposure to environmental hazards.4,57Dental personnel are exposed to silica, polyvinyl siloxane, alginate, and other toxic substances that are inhaled during dental procedures.58 The American Society of Testing and Materials (ASTM) is an organization that establishes the criteria for mask performance and use in the healthcare setting. They classify masks into three different types: ASTM level 1, ASTM level 2, and ASTM level 3.59 The ASTM uses bacterial filtration efficiency and particle filtration efficiency to distinguish the three ASTM mask levels.59 ASTM level 3 masks should be worn for most dental procedures that produce a spatter or aerosol to provide the best protection against particle penetration.59Due to the recent COVID-19 pandemic, current CDC guidelines recommend the use of N95 respirators, or higher, for all aerosol generating procedures.60
Characteristics of an ideal mask: no contact with dental personnel's nose or lips; a high bacterial filtration efficiency rate; conforms to the shape of the person's face, affording a more effective seal; fits the face snugly around the entire edge of the mask; does not fog eyewear; convenient to put on and remove; made of material that does not irritate skin or induce allergic reaction; and does not collapse during wear or when wet.4Masks are single-use items and must be changed after each patient. In addition, masks should be changed 20 minutes after heavy aerosol and 60 minutes after a long procedure.4Masks lose their protective quality over time because of exposure to moisture on the outside layer from dental procedures and the wearer's breath on the inside layer.4,59When the protective quality is lost, it is possible for tiny microorganisms to penetrate the masks. To prevent cross-contamination and maintain ideal infection control standards, dental personnel should never touch the front of the mask, should not wear the mask below the nose or around the neck, should not keep the mask in pockets or on the arm, and should not twist the mask for a better fit.4
The CDC Summary of Infection Prevention Practices in Dental Settings provided clarification on sterilization guidelines for dental handpieces, including low-speed attachments. Many offices spray and wipe low-speed attachments with a surface disinfectant. On page 12 of the summary, the CDC states, "low-speed motors and reusable prophylaxis angles, should always be heat sterilized between patients and not high-level or surface disinfected."57 The CDC states that studies have shown that internal contamination with potentially infectious material may be transmitted to the next patient. After a handpiece has been contaminated internally, those contaminates are released during use.
Air/Water Syringe Tips
The CDC recommends employing single-use disposable items when possible. This includes masks and air/water syringe tips. Single use means an item should be discarded after one patient. In a 2012 study, Molinari and Nelson confirmed the presence of microbial contamination, pitting, corrosion, and other debris in 10% metal tips, suggesting the lumen of the tip be thoroughly cleaned.61 The design of air/water syringe tips involves narrow, inaccessible lumen, creating a need for disposable tips.61
The hands are the most common mode of transmission for pathogens. Hand hygiene is achieved by washing the hands with plain or antimicrobial soap or the use of an alcohol-based hand rub. Both methods prevent the spread of infection; however, handwashing reduces antimicrobial resistance. Handwashing must occur at the beginning of the day, after using the bathroom or eating, and when hands are visibly soiled. When hand rubs are used, they must contain an alcohol concentration of 60% to 95% and be used for a total of 2 minutes to effectively kill pathogens.62 In the dental environment, hand hygiene must be performed before touching a patient; before aseptic procedures; after body fluid exposure; after touching a patient; after touching patient surroundings; before, during, and after preparing food; before eating food; before and after treating a cut or wound; after using the bathroom; after blowing the nose, coughing, or sneezing; and after touching garbage.63,64
Dental personnel should always use standard precautions during patient care and treat all patients as potential carriers of infectious diseases. Infection control will protect the dental team and patients from acquiring or transmitting pathogens found in the dental office setting. Several government agencies and organizations are responsible for establishing infection control guidelines that assist with managing personnel health and safety concerns related to infection control in the dental environment. The dental team must be aware of these guidelines to remain compliant and positioned to provide the best protection for themselves and the patients they serve. As the spread of SARS-CoV-2 continues, and different variants of the virus emerge, infection control measures will be revisited to ensure the highest level of protection for dental healthcare practitioners.
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