A critical element for a safe dental practice.
Safe processing of reusable dental instruments is a basic tenet of patient safety in healthcare settings. As simple as it may seem, it is important to understand that sterilization is only one element of instrument processing. If any element is performed improperly, it can result in risk to either personnel or patients. All of the elements put together that result in successful sterilization practices lend themselves very well to a systematic approach. A systematic approach is methodical, repeatable, and learnable through a step-by-step process. Instrument processing is most successful when a set of appropriate steps and activities is identified, organized in the correct sequence, put into place, and then followed consistently each time the process is repeated.
Sterilization of medical instruments is not a purely modern concept. From the time Pasteur developed the germ theory of disease transmission in 1860s, medical scientists have been looking for ways to ensure that medical instruments and equipment can be rendered safe for reuse on multiple patients.1 In the 1880s, Chamberland’s Autoclaves in France introduced the first steam autoclave developed specifically for the sterilization of medical instruments. In the past 130 years, additional methods of heat sterilization and increasingly sophisticated autoclaves have emerged.
Instrument processing, as with many system processes, lends itself well to following standard operating procedures. Standard operating procedures are a list of instructions that help guide the person(s) performing the process through the steps involved in successful completion. An example of standard operating procedures for instrument processing is depicted in Table 1. The physical space in which instrument processing is performed should be arranged to create a natural and one-directional flow from dirty to clean areas.
Delivery from the Treatment Area
After completion of dental treatment, all reusable instruments and equipment should be removed to the sterilization area. Disposable sharps should be discarded into appropriate sharps containers at the location of use, not taken to the sterilization room for disposal. According to the Occupational Safety and Health Administration (OSHA) Bloodborne Pathogens Rule, contaminated reusable sharp instruments should be place in containers that are puncture-resistant, labeled or color-coded, and leak-proof on the sides and bottom. The OSHA regulation goes on to say that, “Reusable sharps that are contaminated with blood or other potentially infectious materials shall not be stored or processed in a manner that requires employees to reach by hand into the containers where these sharps have been placed.”2 This means that in addition to transporting instruments from chairside to the sterilization area in a rigid container, personnel must also refrain from reaching into ultrasonic cleaners to retrieve instruments. The use of instrument forceps or a basket that can be turned out onto a surface would be acceptable alternatives.
Presoaking and Cleaning
It is important to thoroughly clean instruments of all debris, including dental materials, blood, and tissue before sterilization. The presence of debris can interfere with the success of the sterilization process.3 In addition to pre-cleaning, it may be necessary to hold instruments for extended time periods before cleaning. In this case a pre-soak or pre-spray may be used to prevent the instruments from drying out. A pre-soak or pre-spray may also be used to pre-treat instruments that are particularly difficult to clean, such as surgical instruments with grooves that may contain blood or tissue.
The most effective methods for cleaning dental instruments before sterilization are mechanical devices such as ultrasonic cleaners and washers or washers/disinfectors.3 Ultrasonic cleaners employ sound waves in a chamber of liquid to create cavitation. When the cavitation comes into contact with the instruments, it dislodges debris. Although more study is needed, there is some evidence that ultrasonic cleaners may be more effective in cleaning small items with complex shapes, such as endodontic files, than are washer/disinfectors.4 However, there is also evidence that sterilization may not be 100% effective in decontaminating endodontic files and dental burs. In fact, one study found that contamination rates following sterilization were as high as 15% for burs and 58% for files.5 Dental professionals should evaluate whether single-use disposable burs and endodontic files are feasible for their practice or ensure that measures are taken to thoroughly clean items with complex shapes before sterilization.
Washers or washer/disinfectors clean instruments using high-pressure water jets in combination with cleaning agents such as enzymatic detergents. Washer/disinfectors have a high-temperature thermal disinfection cycle in addition to the cleaning cycle(s). Washer/disinfectors in combination with instrument cassettes appear to be more effective in cleaning dental instruments than ultrasonic cleaners.5 Washer/disinfectors must be cleared by the US Food and Drug Administration (FDA) in order to make the claim of high-level disinfection. These devices are manufactured and marketed as medical devices and should not be confused with household dishwashers, which have not been designed for cleaning dental instruments (Figure 1).
After washing, instruments should be thoroughly rinsed if they may have detergent residue and then dried before packaging. If using instrument cassettes, the entire cassette should be rinsed without opening. These should also be allowed to dry before packaging.
There are several types of packaging available for sterilization. The type selected by an individual practice should be based on the type of sterilization process and the method of delivery of instruments to the treatment area. Pouches are available for packaging individual or sets of instruments, while sterilization wrap is intended for wrapped trays or cassettes. Pouches are constructed of paper, clear plastic, paper and plastic, or nylon. Nylon pouches are intended for dry-heat sterilizers and paper and plastic are for use in steam autoclaves and sterilizers using unsaturated chemical vapor (eg, Chemiclave®). Instruments should be placed carefully into pouches, ensuring that the pouch does not become torn or punctured. Holes and tears in the pouch will compromise the sterility of the contents during storage. Pouches should be sealed before sterilization, ensuring that there are no gaps or openings that may allow contamination of the contents during storage and handling. Sterilization wrap and pouches are made of specialized material that allows steam and/or heat to penetrate and provides a sealed environment to maintain sterility during storage. Materials that are not specifically intended for this purpose should not be used to package instruments for sterilization.
In rare circumstances, it may be necessary to sterilize an item unwrapped. Often referred to as “flash” sterilization, this should only be done for special circumstances when an item is needed quickly on an emergency basis.5,7 The reasons that flash sterilization is not recommended as a routine means of processing instruments is the absence of protective packaging after sterilization, minimal sterilization parameters (time, pressure, temperature) and the potential for contamination of instruments while transporting them from the location of the sterilizer to the treatment area.7
“Sterilization is the act or process, physical or chemical, that destroys or eliminates all forms of life, especially microorganisms.”8 There are three methods of heat sterilization commonly used in dentistry. These are steam under pressure (autoclave), dry heat, and unsaturated chemical vapor.
There are two basic types of steam sterilization; gravity displacement and dynamic air removal (pre-vacuum). Most tabletop-style autoclaves, which are commonly used in dental practices, are gravity displacement. In these sterilizers, steam is injected into the chamber, forcing the air out of the chamber via the drain. The minimum time for sterilization in gravity displacement sterilizers is 30 minutes at 121°C (250°F). Pre-vacuum sterilizers employ a pump to remove air from the chamber before injecting steam, resulting in nearly instantaneous steam penetration.7 Complete removal of air in a pre-vacuum sterilizer allows for a much faster cycle time than is required in a gravity displacement autoclave. Pre-vacuum sterilizers require only 4 minutes of exposure time at 121°C (250°F). The time required to dry wrapped packs is similar for both gravity and pre-vacuum sterilizers at 15 to 30 minutes. Because the pre-vacuum sterilizer relies on complete air removal to allow the shorter cycle time, a daily air removal test is necessary before the first load of instruments for the day. Commercially available Bowie-Dick type tests used according to the manufacturer’s instructions will verify complete air removal.
Dry-heat sterilization is indicated for the sterilization of items that may be damaged by moist heat. It is noncorrosive and penetrates materials well, providing a suitable alternative for steam sterilization when needed. However, the longer cycle times and higher temperatures are incompatible with some commonly used items in dentistry, such as dental handpieces and most items constructed of plastic. Typical cycles for dry heat are 170°C (340°F) for 60 minutes or 160°C (320°F) for 120 minutes. There are also rapid dry-heat sterilizers that operate at 370°F for 6-, 8- or 12-minute cycles.
Unsaturated Chemical Vapor
Unsaturated chemical vapor sterilization uses a proprietary chemical formula to generate a chemical vapor with low humidity. Unlike steam, the unsaturated chemical vapor is noncorrosive to metals. The brand of unsaturated chemical vapor sterilizer most recognizable in dentistry in the United States is the Harvey Chemiclave® (Thermo Scientific, wwwtermo.com). For wrapped items, the sterilization temperature and time parameters are 132°C (270°F) for 20 minutes.
Monitoring the sterilization process helps to identify equipment malfunction and operator error that may not otherwise be immediately apparent. Monitoring can be performed using mechanical, chemical, and biological methods.
Mechanical monitoring relies on the gauges, tape, and digital indicators to provide information regarding temperature, pressure, duration, and other variables that are involved in the specific type of sterilization process. These should be monitored for proper functioning during each cycle.
Chemical indicators include strips, paper, and tape embedded with chemicals that will measure various parameters of sterilization, including temperature, duration, and presence of steam. Available in a variety of forms, these should be used on the inside of each package of instruments to ensure that the sterilizing agent has reached the instruments in a pack and on the outside of each package as an indicator to personnel that the package has been subjected to a sterilization process.9
Biological indicators are strips of paper or vials that contain microbial spores that are specifically resistant to the sterilization process. The test strip (in a glassine envelope) or vial is placed in the sterilizer with a load of instruments and removed at the end of the cycle. It is then either sent to a laboratory for processing and reading or incubated in the office. The Centers for Disease Control and Prevention (CDC) recommend that dental office sterilizers be monitored using biological indicators at least weekly.10
A systematic approach to sterilization, including workflow, physical layout, equipment selection, and sterility assurance will help to ensure a safe patient-care environment. A small error, such as placing unsterilized packs of instruments in a location where another person may mistake them for sterilized packs, has potentially disastrous consequences for patients and for the dental practice. Good standard operating procedures, regular training, and consistent monitoring of sterilization procedures are all part of an effective instrument processing and sterilization program.
1. Toledo-Pereyra LH. Joseph Lister’s Surgical Revolution. J Invest Surg. 2010;23(5):241-243.
2. US Department of Labor, Occupational Safety and Health Administration. 29CFR Part 1910.1030. Occupational exposure to bloodborne pathogens; needlesticks and other sharps injuries; final rule. Fed Regist. 2001;66:5317-5325.
3. Harte JA, Molinari JA. (2010) Instrument Processing and Recirculation. In: Molinari JA, Harte JA, eds. Practical Infection Control in Dentistry. 3rd ed. 2010; Philadelphia PA: Lippincott Williams & Wilkins; 221-231.
4. Perkaki K, Mellor AC, Qualtrough AJE. Comparison of an ultrasonic cleaner and a washer disinfector in the cleaning of endodontic files. J Hosp Infect. 2007; 67:355-359.
5. Morrison A, Conrod S. Dental burs and endodontic files: Are routine sterilization procedures effective? J Can Dent Assoc. 2009;75;1:39-39d.
5. Sanchez E, Macdonald G. Decontaminating dental instruments: testing the effectiveness of selected methods. J Am Dent Assoc. 1995; 359-362.
6. Miller CH, Palenik CJ. Sterilization, Disinfection, and Asepsis in Dentistry. In: Block SS. Disinfection, Sterilization, and Preservation. 5th ed. 2001; Philadelphia, PA: Lippincott Williams & Wilkins.
7. Rutala WA, Weber DJ. Healthcare Infection Control Practices Advisory Committee. Guideline for disinfection and sterilization in healthcare facilities. CDC. 2008.
8. Block SS. Disinfection, Sterilization, and Preservation. 5th ed. 2001; Philadelphia, PA: Lippincott Williams & Wilkins.
9. Harte JA, Molinari JA. Sterilization Procedures and Monitoring. In: Molinari JA, Harte JA, eds. Practical Infection Control in Dentistry. 3rd ed. 2010; Philadelphia, PA: Lippincott, Williams & Wilkins; 148-163.
10. CDC. Guidelines for Infection Control in Dental Health-Care Settings—2003. MWRM. 2003;52(RR17):1-66.
About the Author
Eve Cuny, MS, Assistant Professor, Dental Practice, Director, Environmental Health and Safety, University of the Pacific, Arthur A. Dugoni School of Dentistry, San Francisco, California