Combating Cross-Contamination

Infection control procedures are a necessity in any environment that deals with patient care. These protocols work best when enforced by everyone involved in a case; however, in dentistry, there is not always good communication between the dental office and the dental laboratory regarding infection control procedures and the decontaminated items shipped to and from the dental office to the dental laboratory. The dentist or the technician may expect the other to take the appropriate precautions when decontaminating items such as impressions, bites, implant components, denture try-ins, and finished dental devices, but often that is not the case. Communication between the dental office and the dental laboratory regarding decontamination procedures is absolutely imperative, as it helps to minimize cross-contamination between the two facilities.

This article addresses the chain of infection, how to minimize and eliminate exposure, and the methods for disinfection in both the dental office and in the dental laboratory. It is important for employers to comply with OSHA’s Bloodborne Pathogen Standard, but it is also important to evaluate the safest and most effective methods for protecting employees and, ultimately, patients.

The Chain of Infection

First, it is important to understand the chain of infection, which is shown in Figure 1 in the traditional epidemiologic triad model.¹ By understanding the chain of infection, it is possible to control or eliminate an infectious agent at the source of transmission, protect the portals of entry, and increase the host’s defenses. The following is a brief review of the components of this chain:

The reservoir of an infectious agent is the habitat in which the agent normally lives, grows, and multiplies. Humans, animals, and the environment are considered reservoirs. The transfer of organisms on an impression is an example of how the reservoir, which is the patient, may not be the mode of transmission because the pathogenic agent has been transferred from the patient to the impression. Some of the common infectious diseases that have human reservoirs and therefore can be transmitted from person-to-person include sexually transmitted diseases, measles, mumps, streptococcal infection, and many respiratory pathogens. A carrier is a person who may not show the effects of illness but can transmit the pathogen to others. A person who is a carrier of a disease may be asymptomatic— showing no signs or symptoms of the disease for a lifetime. This is why everyone in dentistry working in a risk area must practice “standard precautions,” ie, they must treat all items that have been in a patient’s mouth as though they are infectious.

The portal of exit is the path by which a pathogen leaves the agent or reservoir. In dentistry, the pathogen would leave the patient during the dental procedure. In the case of an impression, it is possible for the pathogen to be encapsulated in the impression. It is also not uncommon for pathogen-carrying bioburden to be visible on implant components or dentures received from the dentist.

The mode of transmission is the way the infectious agent is transmitted from its natural reservoir to a susceptible host. It can be via either direct contact or indirect transmission. Direct contact occurs through skin-to-skin contact, kissing, and sexual intercourse. It can also be through contact with soil or vegetation that is harboring infectious organisms. Indirect transmission refers to the transfer of an infectious agent from a reservoir to a host by suspended air particles, inanimate objects such as impressions, or animate intermediaries such as mosquitoes, fleas, and ticks.

The portal of entry is the manner in which a pathogen enters a susceptible host. The entry routes can be the skin, eyes, nose (inhalation), or mouth (ingestion). Protection of the portals of entry in the dental environment includes use of personal protective equipment (PPE) such as gloves, masks, gowns, and safety eyewear.

The susceptible host is the final link in the chain of infection. Susceptibility depends on genetic or constitutional factors, specific immunity, and other factors that limit an individual’s resistance to infection. Dental office and dental laboratory workers can make themselves less susceptible by staying healthy—eg, by eating nutritious foods and getting exercise. Other ways to reduce the possibility of contracting diseases are by having vaccinations and by keeping the immune system boosted.

Minimizing and/or Eliminating Exposure

With a solid understanding of how the chain of infection works, dentists and technicians are ready to review OSHA’s requirements for minimizing and/or eliminating exposure to bloodborne pathogens. The Bloodborne Pathogen Standard is located at 29 CFR 1910.1030.²

The Occupational Safety and Health Act requires employers to protect workers whose jobs put them at a reasonable risk of coming into contact with blood and other potentially infectious materials. Potential infectious agents that can be transmitted include the Hepatitis B virus (HBV) and the human immunodeficiency virus (HIV). According to the Centers for Disease Control and Prevention (CDC), about 2,000 to 4,000 people die in the US each year from cirrhosis or liver cancer caused by the Hepatitis B pathogen, which can live outside the body for 7 to 10 days.³ The HIV virus causes AIDS. The Bloodborne Pathogen Standard requires employers to do the following:

Establish a Written Exposure Control Plan

The purpose of this plan is to identify the risk areas and job classifications where employees have direct exposure to blood and other potentially infectious materials. The employer is required to review the plan on an annual basis and update it as necessary to reflect changes that will help eliminate or reduce exposure to bloodborne pathogens.

Review and Develop Work Practice Controls That Will Reduce the Likelihood of Exposure

As a first step toward minimizing or eliminating a hazard, the employer can change the way the task is performed to make it safer for the worker. Some examples of work practice controls in dental clinical and laboratory settings include hand washing, disposal of contaminated sharps, disinfection of items that have been in a patient’s mouth, packaging of items for shipment to the dental laboratory, handling of contaminated clothing, and cleaning of contaminated work areas.

Install Engineering Controls

Some examples of engineering controls are exhaust or ventilation, sharps containers, and safety devices for contaminated needles.

Provide Personal Protective Equipment (PPE)

If the work practice controls and the engineering controls described above do not eliminate the hazard, PPE must be provided. This PPE could include the use of gloves, gown, safety eyewear, and masks (Figure 2 and Figure 3).

Make Hepatitis B Vaccinations Available

It is the employer’s responsibility to educate his or her employees regarding the risk of transmission of Hepatitis B in the work environment, as well as make vaccines available. If an employee refuses a vaccine for any reason, the employer must have the employee sign a Refusal to Vaccinate form. The employer must pay for the vaccine series as long as the employee is employed. An employer must also make arrangements with a health care provider so that employees can be referred to that provider within 10 days of assignment to a risk area. The vaccine takes 6 months to administer, so the employer must keep track of the vaccine progress. According to the Centers for Disease Control, one to two months after completion of the three-dose vaccination series, the employee should be tested for anti-HBs. An employee who does not develop an adequate antibody response to the primary vaccine series should complete a second three-dose vaccine series or be evaluated to determine if he or she is HbsAg-positive. As after the first series, the employee should be tested for anti-HBs one to two months after completion of this series. According to the CDC, half of nonresponders to the first series will respond to the second three-dose series. The CDC states in the December 19, 2003, MMWR that booster doses of the vaccine and periodic serologic testing to monitor antibody concentrations after completion of the vaccine series are not necessary for vaccine responders.⁴

Use Warning Labels to Indicate Biological Hazards

Warning labels should be affixed to all containers of regulated waste. In a dental setting, this includes laundry containers, sharps containers, waste containers, transport bags containing extracted teeth, and impressions shipped to the dental laboratory. The dental laboratory should make every effort to decontaminate incoming items to avoid generating biohazardous waste, which would require regulated disposal and pick-up.

Provide Post-Exposure Evaluation and Follow-Up

A post-exposure evaluation and follow-up for workers who experience an exposure incident should be available at no cost to the employee. In a dental laboratory, this type of exposure incident could occur when a technician is trimming back an overextended border on an impression. Laboratory employees must be trained to minimize their risks and be provided with PPE to protect them when performing this task. While trimming an overextended border, technicians must wear gloves, a mask, a gown, and safety eyewear (Figure 4). The sharp instrument used to cut through the impression must also be decontaminated after each use. If the employee receives a cut from a potentially infectious item, the dental laboratory owner must follow OSHA’s Post Exposure Evaluation and Follow-up Procedure. The purpose of this procedure is to find out if the patient has HIV or Hepatitis B or C, which could be transmitted to the employee. The employer maintains confidentiality of this information.

Provide Proper Training

To ensure that the most up-to-date infection-control protocols are in place, employees should be trained upon hire, when transferred to an assignment where exposure could occur, and annually. This training should cover the risk of exposure, control methods such as work practices, engineering controls, use of PPE, participation in the Hepatitis B vaccine, and post-exposure procedures.

Maintain and Retain Employee Medical and Training Records

Medical records must be retained for 30 years beyond employment. Training must be documented and training records retained for 3 years. Dental practices and dental laboratories are partially exempt from OSHA’s injury and illness recordkeeping requirements, except in the states of HI, MN, WA, and NV. Dental laboratories are classified in the Standard Industrial Classification system as 8072, and dental offices are 8021. A list of exemptions is available on the OSHA Website.³

Methods for Disinfection

There are a number of methods for disinfection explained by the CDC in Appendix C of the Guidelines for Infection Control in Dental Health-Care Settings-2003. The two methods most commonly used in dental laboratories are low-level disinfection and intermediate-level disinfection.

Low-level disinfection “destroys the majority of vegetative bacteria, certain fungi, and viruses. It does not inactivate Mycobacterium bovis, a bacterium that can cause tuberculosis in humans.”⁵ Liquid contact is the standard method of application. The CDC describes low-level disinfectants such as EPA-registered hospital disinfectants with no label claim regarding tuberculocidal activity such as quaternary ammonium compounds, some phenolics, and some iodophors. Low-level disinfection is used on countertops and other surfaces in the dental environment.

Intermediate-level disinfection “destroys vegetative bacteria and the majority of fungi and viruses and inactivates Mycobacterium bovis, although it is not necessarily capable of killing bacterial spores.”⁶ Liquid contact is the standard method of application and the CDC-provided examples are EPA-registered hospital disinfectants with label claims of tuberculocidal activity (eg, chlorine-containing products, quaternary ammonium compounds with alcohol, phenolics, iodophors, and EPA-registered chlorine-based products). Intermediate-level disinfection is the method most used for the disinfection of items that are received by the dental laboratory from the dental office.

Impressions and other items that have been in a patient’s mouth are to be considered potentially infectious. The CDC recommends: “When a laboratory case is sent off-site, dental health-care personnel (DHCP) should provide written information regarding the methods (eg, type of disinfectant and exposure time) used to clean and disinfect the material (e.g., impression, stone model, or appliance). Clinical materials that are not decontaminated are subject to OSHA and US Department of Transportation regulations regarding transportation and shipping of
infectious materials.”⁷

Disinfection of Items Shipped to the Dental Laboratory

Disinfection procedures used in the clinical environment should include: (1) rinsing the item prior to disinfection; (2) using an appropriate disinfectant; (3) managing the timing of the disinfection process; (4) rinsing after disinfection; and (5) ensuring proper packaging of the item for delivery to the dental laboratory, including separation of the prescription from the items being shipped. The dental staff should also remove cotton rolls (Figure 5), retraction cords, and bioburden from impressions and implant components sent to the dental laboratory. Extracted teeth sent to the dental laboratory must be packaged and handled as biopsy specimens.⁷

Some dental laboratories ask the dentist to notify them of the type of chemical being used for disinfection so they can ensure that the chemicals are compatible. Communication between the dentist and laboratory regarding disinfection methods can help prevent distortion of impressions.

Disinfection of Items Received by the Dental Laboratory

According to the CDC, dental prostheses or impressions can be contaminated with bacteria, viruses, and fungi.⁸ These items must be thoroughly cleaned to remove blood, bioburden, and/or chemicals prior to disinfection in the dental laboratory. As in the clinical environment, during the disinfection process, the dental laboratory personnel must wear appropriate PPE, ie, gloves, mask, gown, and safety eyewear (Figure 2). The disinfection must be timed, and then the item rinsed prior to scheduling or advancement to the next production area.

The most common disinfectants being used in dentistry are glutaraldehydes and quaternary ammonium chlorides. Due to the instability of some impression materials, both the clinical staff and laboratory staff should follow the recommendations made by the manufacturer of the impression material.

Some of the most common types of impression materials in use today are vinyl polysiloxane, polyethers, and alginates (Figure 6). Whether the items are sprayed or immersed depends on the type of impression material that was used (Figure 7 and Figure 8).

Disinfection of Finished Appliances

OSHA addresses the decontamination of equipment prior to shipment to repair facilities; however, specific information on disinfection by the dental laboratory to the dentist is not covered in the Bloodborne Pathogen Standard. The CDC Guidelines state: “Appliances and prostheses delivered to the patient should be free of contamination. Communication between the laboratory and the dental practice is also key at this stage to determine who is responsible for the final disinfection process.”⁷ The State of Texas Board of Dental Examiners requires the dental laboratory to disinfect finished items prior to shipment to the dentist.⁹ That means that if a laboratory in another state is shipping finished cases to a dentist in Texas, it must not only register with the State of Texas but ensure that it is following the state’s disinfecting requirements.

For liability purposes, it makes sense for the dentist to take responsibility for the disinfection or sterilization of an appliance prior to insertion or placement in the patient’s mouth, even if the dental laboratory has disinfected the device. This is especially true for implant components, as most dental laboratories do not sterilize these types of items prior to leaving their facility.

Conclusion

Employers must identify risk areas, develop exposure controls, train employees on how to protect themselves, enforce safety rules, and communicate with anyone outside the facility who will be handling potentially infectious items. There are many infection control regulations to consider in a dental laboratory environment, but following these procedures and protocols will improve the entire laboratory team’s safety.

Acknowledgments

The author would like to thank Georgia Dental Laboratory, in Tucker, GA, for providing the photos for this article.

References

1. Centers for Disease Control and Prevention. Introduction to Epidemiology. Updated May 18, 2012. Accessed April 15, 2013. Available at: http://www.cdc.gov/osels/scientific_edu/SS1978/Lesson1/Section10.html.

2. United States Department of Labor. OSHA Bloodborne Pathogen Standard. Updated April 3, 2012. Accessed April 15, 2013. Available at: www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=10051" target="_blank">www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=10051 www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=10051.

3. Centers for Disease Control and Prevention. Hepatitis
B Vaccine Information Statement. Updated February 2, 2012. Accessed April 15, 2013. Available at: http://www.cdc.gov/vaccines/pubs/vis/downloads/vis-hep-b.pdf.

4. Centers for Disease Control and Prevention. Morbidity and Mortality Weekly Report (MMWR). 52(RR-17); pg. 11

5. Centers for Disease Control and Prevention. Morbidity and Mortality Weekly Report (MMWR). 52(RR-17); pg. 66.

6. United States Department of Labor. Non-Mandatory Appendix A to Subpart B – Partially Exempt Industries. Updated 2013. Accessed April 15, 2013. Available at: http://www.osha.gov/recordkeeping/ppt1/RK1exempttable.html.

7. Centers for Disease Control and Prevention. Morbidity and Mortality Weekly Report (MMWR). 52(RR-17); pg. 33.

8. Centers for Disease Control and Prevention. Morbidity and Mortality Weekly Report (MMWR). 52(RR-17); pg. 34.

9. Texas Administrative Code. Title 22 Examining Boards; Part 5 State Board of Dental Examiners; Chapter 108 Professional Conduct; Subchapter B Sanitation and Infection Control Rule §108.24 Required Sterilization and Disinfection. Updated February 20, 2001. Accessed April 15, 2013. Available at: http://info.sos.state.tx.us/pls/pub/readtac$ext.TacPage?sl=R&app=9&p_dir=&p_rloc=&p_tloc=&p_ploc=&pg=1&p_tac=&ti=22&pt=5&ch=108&rl=24.

About the Author

Mary A. Borg
President and Senior Compliance Advisor
SafeLink Consulting, Inc.
Cumming, Georgia