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Instrument management: cleaning and sterilization in the dental office: Part 2.


Sterilization and disinfection are of paramount importance in the dental office. Disease transmission has been well documented when improper or incomplete cleaning, disinfection and sterilization of instruments/devices occur. (1,2) In order to minimize the risk of disease transmission in health care, the Centers for Disease Control and Prevention (CDC) published ah updated Guideline for Disinfection and Sterilization in Healthcare Facilities, 2008. (1) This evidence-based document reviews the most up-to-date guidelines for disinfection and sterilization processes. In a previous article, instrument classification, handling and packaging of contaminated instruments were discussed in detail taking the evidence-based recommendations contained in the new 2008 guideline into account. (1) Once they are properly cleaned and packaged, instruments must be sterilized before use on the next patient. This follow-up article will discuss the new CDC guidelines, the most recent recommendations for instrument sterilization and sterilization monitoring in the dental office.



The CDC defines sterilization as a "process that destroys, eliminates or inactivates (kills) all forms of microbial life including bacterial endospores." (1,2) Bacterial spores are among the most resistant forms of microbial life to inactivate. Therefore, they are used as a biological indicator that other microorganisms have also been killed (Figure 1). (1-3) Any agent/process that kills the highly resistant spores will effectively inactivate all forms of microbial life that are of lesser resistance; i.e., the common microbial contaminants found on patient care items, which includes HIV, hepatitis B and C, influenza and herpes viruses. (1-3) The CDC and the American Dental Association (ADA) recommend strict adherence to the principles of sterilization. (1-3) Sterilization is carried out in healthcare facilities by physical or chemical methods depending on the type of healthcare facility, the volume of patients treated in the facility, the type(s) of procedures performed and the instruments or devices required to perform the medical/dental treatment. (1) The most commonly used sterilization agents in healthcare facilities include:

* steam under pressure (autoclave)

* unsaturated chemical vapor

* dry heat

* ethylene oxide gas (ETO)

* hydrogen peroxide gas plasma

* liquid chemicals. (1)

Each process has its strengths and weaknesses, and some may not be indicated and/or readily available in the dental office. By definition, sterilization is intended to be absolute; all microorganisms are killed. (1) However, confusion on the part of some health professionals, commercial representatives and the technical/commercial literature exists. Many incorrectly refer to "disinfection" as "sterilization" and describe items as "partially sterile." (1) According to the CDC, "disinfection describes a process that eliminates many or all pathogenic microorganisms, except bacterial spores, on inanimate objects" usually by means of the use of Environmental Protection Agency (EPA) approved liquid chemicals or wet pasteurization. (1) Sterilization kills all forms of microbial life inclusive of those that are highly resistant and dissimulates to kill bacterial spores. (1-3) Sterilization can be accomplished by chemical means, and when chemicals are used to destroy all forms of microbiologic life, the agents are called chemical sterilants. Any chemical sterilant is regulated by the Food and Drug Administration (FDA); disinfectants are regulated by EPA. While sterilization can be achieved by chemical means, this process should be limited to a very few heat-sensitive items. In practice, every effort should be made to use either disposable or heat-stable instruments or devices. In the dental office, critical or semi-critical dental instruments and materials that are heat-stable should be sterilized by steam under pressure (autoclave), chemical (formaldehyde) vapor and dry heat. (1-3) Clinicians should be aware that sterilization of any medical/dental instruments or devices should be performed only on FDA-cleared devices; use of non-FDA-approved devices could result in sterilization failures and possible legal ramifications. (1-3)

Steam Sterilization

The most widely utilized inexpensive, nontoxic and easy-to-operate sterilization methodology is moist heat in the form of saturated steam under pressure (autoclave). (1-3) Steam sterilization is rapidly microbicidal and sporicidal. This result is accomplished as each item is exposed to the four parameters of steam sterilization: steam, pressure, temperature and time. (1-3) Once dry saturated steam is generated, pressure serves as a means to obtain the high temperatures necessary to quickly kill microorganisms. (1-3) The temperature is critical; specific temperatures, most commonly 121[degrees]C (250[degrees]F) and 132[degrees]C (270[degrees]F), must be obtained and sustained for a minimal time to kill microorganisms. (1-3) Minimum exposure periods for sterilization of wrapped instruments and textile packs as well as the sterilizer type are listed in Tables I and II. (1-3)

There are two basic types of steam sterilizers (autoclaves): the gravity displacement autoclave and the high-speed prevacuum sterilizer. (1-3) Gravity displacement sterilizers are the most commonly used in dentistry and these tabletop sterilizers utilize an older but reliable technology. (1-3) In these devices, a heating element generates steam which is introduced at the top or the sides of the sterilizing chamber. As steam is lighter than air, the unsaturated air in the chamber is forced out of the chamber through a vent in the chamber wall by means of gravity displacement. (1-3) Removal of air trapped in the chamber is inefficient and this residual air must be heated to critical temperature. The presence of this residual air in the chamber results in a longer exposure time, and possibly cool air pockets and items not being sterilized (Tables I and II). (1-3) The high-speed prevacuum sterilizer is similar to the gravity displacement sterilizer but utilizes newer technology that is fitted with a pump that creates a vacuum (ejector) in the chamber. (1-3) The air is forcibly, rapidly and efficiently removed from the sterilizing chamber before the chamber is pressurized with steam, resulting in nearly instantaneous steam penetration, even into porous loads. (1-3) Furthermore, this process facilitates more positive steam penetration throughout the entire load, resulting in a much shorter sterilization cycle (Tables I and II). (1-3) Although significantly more expensive than the gravity displacement autoclave, the increased cost of a prevacuum sterilizer may be offset by more rapid turnaround of patient care items and need for fewer instruments in the office inventory. (1-3) Regardless of the type of steam sterilizer employed, the manufacturer's recommendations for loading, cleaning and servicing should be reviewed and followed.

Unsaturated Chemical-Vapor

The unsaturated chemical-vapor sterilizer uses a chemical solution, primarily alcohol with 0.23 percent formaldehyde, instead of water in a closed pressurized chamber. (1-3) Parameters for sterilization are listed in Table II. Similar in function to the steam sterilizer, the low water level in this process causes less corrosion than saturated steam sterilization of carbon steel instruments, such as dental burs. (1-3) Minimal corrosion is the major advantage of this device. However, disadvantages include the need for instruments to be dry before sterilizing, emission of ah unpleasant odor (requiring adequate ventilation) and additional hazardous waste disposal requirements for the sterilizing solution. (1-3)

Dry-Heat Sterilization

Dry heat is used to sterilize materials that might be damaged by moist heat and may be the best choice for delicate orthodontic instruments and burs. (1-3) The benefit of reducing damage caused by moist heat is somewhat outweighed by the prolonged processing time and high temperatures needed. There are two types of dry-heat sterilizers used in dentistry: static-air and forced-air.(1-3) The static-air type is essentially an oven with heating coils in the bottom or sides of the unit. As these coils heat, they cause hot air to rise inside the chamber through natural convection.(1-3) The forced-air type, commonly referred to as the rapid heat-transfer sterilizer, circulates heated air throughout the chamber at a high velocity. (1-3) This action facilitates more rapid transfer of energy from the air to the instruments, thereby reducing the time needed for sterilization. (1-3) While more expensive than the static dry-heat models, the forced air's 12-minute cycle allows for very fast and efficient instrument sterilization. Scorching and burning of packaging and wrapping may occur. Sterilization parameters for both static-air and forced-air dry heat devices are listed in Table II. Clinicians should consult the manufacturer for the best material in which to package instruments whenever using dry-heat sterilization and should follow manufacturer's recommendations for operation and maintenance.(1-3)

Low-Temperature Sterilization

Most medical and dental devices are heat-stable and capable of withstanding heat, usually steam, sterilization. However, some devices are constructed with plastics and other materials that cannot be subjected to heat without damage. Low-temperature sterilization has been developed for this situation. (1) ETO gas has been used since the 1950s for heat-and moisture-sensitive medical/dental devices. (1) The Occupational Safety and Health Administration (OSHA), however, considers exposure to ETO gas an occupational hazard and regulates the acceptable vapor levels of this agent (1 ppm averaged over eight hours). (3,4) CDC also states that handpieces cannot be effectively sterilized with ETO because of decreased penetration of ETO gas flow through a small lumen.(1-3) These restrictions minimize the use of ETO in the dental office. New technologies such as hydrogen peroxide gas plasma, peracetic acid immersion and ozone for low-temperature sterilization in the healthcare setting have been developed and are commercially available. (3) Unfortunately, these devices are usually large in size and expensive to purchase, which may limit their use in the dental office.

Chemical Sterilization

To date, most instruments and devices used in dental practice ate heat-resistant or disposable. Whenever possible, heat-tolerant or disposable instruments and devices should be used. This includes the dental handpiece. While considered a semi-critical device, handpieces are contaminated both internally and externally and should always be heat-sterilized between uses and not just high-level disinfected. (1-3) The new 2008 CDC Guideline states that "handpieces that cannot be heat sterilized should not be used. " (1) Anyone still using non-autoclavable handpieces should give strong consideration to discontinuing their use. Although small in number, heat-sensitive critical and semi-critical instruments and devices may exist. In these infrequent instances, sterilization may be accomplished by immersion in liquid chemical germicides registered by FDA as sterilants. (1-4) Although effective, immersion is problematic because chemical sterilization can require as much as 10 to 12 hours of complete immersion, making instruments unavailable for a protracted period of time. (1-4) More importantly, these chemicals (glutaraldehyde, peracetic acid and hydrogen peroxide) are highly toxic, and manufacturer instructions regarding dilution, immersion time, temperature and safety precautions for using chemical sterilants/high-level disinfectants must be clearly understood and all safety precautions rigidly followed. 1-4) Obtaining and reading the material safety data sheet (MSDS) to become familiar with the agent, its properties and the recommended precautions for safe handling of the product is mandatory. Contact with the health care workers (HCWs) and patient must be minimized. Therefore, all patient care items must be:

1. thoroughly rinsed with sterile water after removal from agent to eliminate any toxic or irritating residues;

2. handled using sterile gloves and dried with sterile towels; and

3. delivered to the point of use in an aseptic manner. (1-4)

Rinsing is essential as residual chemicals can cause tissue necrosis and induce allergic reactions that can be severe and sometimes life-threatening. (1-3) Immersion sterilization should be used as little as possible and only for the few heat-sensitive items or in extreme circumstances, such as long-term power failure or in areas totally without electrical power. Another disadvantage with chemical sterilization is that the process cannot be verified with biological indicators. (1-4) It is of utmost importance that clinicians follow the manufacturer's directions for use, read the MSDS and minimize unprotected contact with these chemical agents, as HCWs and patients can be sensitized to the various chemical components or can develop allergic reactions. (1-4)

Sterilization Monitoring

The sterilizer, regardless of the type in use, is a mechanical device; malfunction for a variety of reasons can and does occur. Operator error, improper packaging, timing and temperature can contribute to failure of the device to properly sterilize. Therefore, monitoring the device is essential to ensure proper function. Monitoring of sterilization procedures (both the sterilizing conditions and the processes involved in sterilization) should be multifaceted and include mechanical, chemical and biological assessments. (1-3)

Mechanical Monitoring

Sterilizers are equipped with a variety of gauges, dials or displays that can be viewed for immediate monitoring of cycle time, temperature and pressure of sterilization equipment. (1-3) When mechanical monitoring is recording correct readings, according to manufacturer's recommendation, the device is most likely working properly; correct readings do not ensure sterilization but are a reasonable indicator of proper function. Incorrect readings can be the first indication of a problem with the device or process.(1-3) Any instruments within a load where any mechanical monitoring parameter is outside of recommended range should not be used for patient care until it has been reprocessed and sterilization cycle readings are within the recommended range. Multiple abnormal mechanical indicators warrant immediate evaluation and possibly repair of that sterilizer.

Chemical Indicators

Chemical indicators assess physical conditions such as temperature during the sterilization process and are usually attached externally or inserted internally into items to be sterilized. (1-3,5,6) One of the most familiar chemical indicators is heat-sensitive tape, which will change color rapidly when a given parameter, time or temperature is reached. Like mechanical monitors, chemical indicators allow detection of certain equipment malfunctions, and they can help identify procedural errors. (1-3,5,6) External indicators, such as chemical indicator tape, are applied to the outside of a package and the indicator changes color rapidly when a specific parameter is reached. This is verification that the package/ bag/cassette has been exposed to the sterilization process. (1-3,5,6) Failure of the chemical indicator to change color is an indication that proper pressure and/or temperature were not achieved and sterilization may have been compromised. (1-3,5,6) Internal chemical indicators should be used inside each package or bag to ensure the sterilizing agent has penetrated the packaging or wrapping material and actually has reached the instruments inside. A single-parameter internal chemical indicator provides information regarding only one sterilization parameter (time or temperature). (1-3,5,6) Multi-parameter internal chemical indicators are designed to react to two or more parameters such as time and temperature or time, temperature and the presence of steam. Assessing multiple parameters can provide a more reliable indication that sterilization conditions have been met. Multi-parameter internal indicators are available only for steam sterilizers. (1-3,5,6) If the internal or external indicator suggests inadequate processing, the item(s) in question should not be used. (1-3,5,6) Recurrent failure of a chemical indicator warrants evaluation and possibly repair of the sterilizer. Chemical indicators do not prove sterilization has been achieved; therefore, they are not a replacement for biological indicators (spore test). (1-3,5,6)

Biological Indicators

Mechanical monitoring and chemical indicators, while useful, do not document that the conditions for sterilization have been met. (1-3,5,6) That is the function of biological indicators (BIs), which are capable of directly determining that the most resistant viable microorganisms (the bacterial endospores of Geobacillus stearothermophilis [formerly Bacillus stearotherrnophilis] or Bacillus atrophaeus [formerly Bacillus subtilis]) have been killed (Table III). (1-3,5,6) As these spores are among the most resistant types of microbes to inactivate, the other potential pathogens in the load are killed as well (Figure 1). (1-3,5,6) Biological monitoring is an essential component to document that sterilization has occurred. Ali dental offices should follow CDC and ADA recommendations; correct functioning of sterilization cycles should be verified for each sterilizer, at least weekly, with BIs (spore strip testing). (1-3,5,6) In offices or large institutions where the instrument demand is high (more than several loads a day), more frequent use of BIs may be indicated. More frequent use facilitates earlier discovery of equipment malfunctions or procedural errors. (1-3,5,6) Additionally, some state dental boards may require more frequent biological monitoring; clinicians should consult their local board for the exact requirement. Placement and location of BI in the sterilizer should be completed according to the manufacturer's recommendations. (1-3,5,6) Best practices recommend that in addition to the test BI that is exposed to the sterilization process, a second BI from the same lot marked "control" and not exposed to the sterilization cycle should be incubated with the test BI. (1-3,5,6) The control BI should test positive for bacterial growth, confirming that the spores contained in the lot of the BI are viable and capable of growth. This finding validates the biological monitoring process; sterilization has been confirmed. (1-3,5,6) Should a positive BI occur, the suggested protocol for management of positive biological indicator in a steam sterilizer is outlined in the box on page 30. (1,7) Biological monitoring can be performed either by in-office biological monitoring or mail-in sterilization monitoring services. It is essential that the person or persons responsible for the biological monitoring read the manufacturer's instructions, be thoroughly trained on exactly how the test should be performed and adhere strictly to the recommended protocol. (1-5) A log of the results of biological monitoring should be maintained and sterilization monitoring records (mechanical, chemical and biological) retained long enough to comply with state and local regulations. (1-3,5,6) Such records are discoverable in litigation and can play a major role in documenting compliance with CDC/ADA recommendations.


1. Every clinician in the dental office should have a clear understanding of the principles of sterilization as recommended by CDC and ADA.

2. Steam under pressure, chemical vapor and dry-heat sterilization are all effective, and clinicians should understand the advantages, disadvantages and properties of each.

3. The new 2008 CDC guideline states that "handpieces that cannot be heat sterilized should not be used." (1)

* Anyone still using non-autoclavable handpieces should give strong consideration to discontinuing their use.

4. Both CDC and ADA recommend that correct functioning of sterilization cycles should be verified for each sterilizer, at least weekly, with biological indicators (spore strip testing).


(1.) Centers for Disease Control and Prevention (CDC). Guideline for disinfection and sterilization in healthcare facilities, 2008 Available at: Nov_2008.pdf.

(2.) Centers for Disease Control and Prevention (CDC). Guidelines for infection control in dental health-care settings, 2003. MMWR 2003; 52(RR-17): 1-68. Available at

(3.) American Dental Association (ADA). Sterilization and disinfection of dental instruments. Available Dec. 1, 2005 at: resources/topics/cdc/cdc_sterilization.pdf.

(4.) Weber DJ, Rutala WA. Occupational risks associated with the use of selected disinfectants and sterilants. In: Rutala WA, ed. Disinfection, sterilization, and antisepsis in healthcare. Champlain, New York: Polyscience Publications, 1998: 211-26.

(5.) American Dental Association (ADA) Dental Topics A-Z, sterilization monitoring. Available Dec. 1, 2005 at: sterilization.asp

(6.) Centers for Disease Control and Prevention (CDC). Oral health resources-sterilization monitoring, Apr. 21, 2005, Available at: sterilization_monitoring.htm

(7.) Bryce EA, Roberts FJ, Clements B, MacLean S. When the biological indicator is positive: investigating autoclave failures. Infect Control Hosp Epidemiol 1997;18: 654-6.

* Suggested Protocol for Management of Positive Biological Indicator in a Steam Sterilizer

1. Take the sterilizer out of service. a. Notify employer/dentist and infection control coordinator/office manager.

2. Objects, other than implantable objects, do not need to be recalled because of a single positive spore test unless the sterilizer or the sterilization procedure is defective.

a. As soon as possible, repeat biological indicator test in three consecutive sterilizer cycles.

b. If additional spore tests remain positive, the items should be considered non-sterile, and supplies processed since the last acceptable (negative) biological indicator should not be used and should be recalled.

c. The items from the suspect load(s) should not be used and should be recalled and reprocessed.

3. Check to ensure the sterilizer was used correctly. a. Verify correct time and temperature settings. b. If not within recommended parameters, repeat using appropriate settings, and do not use and recall and reprocess all inadequately processed items.

4. Check with building maintenance for irregularities (e.g., electrical), or if plumbed to steam centrally, check for changes/maintenance of steam supply (i.e., from standard [greater than or equal to] 97 percent steam, <3 percent moisture).

a. Any abnormalities should be reported to the person who performs sterilizer maintenance (sterilizer manufacturer, etc).

5. Check to ensure the correct biological indicator was used and appropriately interpreted.

a. If not, repeat using appropriate settings.

6. If Steps 1 through 5 resolve the problem, then:

7. Retest sterilizer with three repeat biological indicators.

a. If all three repeat biological indicators from three consecutive sterilizer cycles are negative, put the sterilizer back in service.

b. If one or both biological indicators are positive, do one or more of the following until problem is resolved.

i. Request an inspection of the equipment by sterilizer maintenance personnel.

ii. Have service or maintenance inspect the steam supply lines.

iii. Discuss the abnormalities with the sterilizer manufacturer.

iv. Repeat the biological indicator using a different manufacturer's indicator.

8. If Step 7 does not resolve the problem:

9. Close sterilizer down until the manufacturer can assure that it is operating properly.

a. Retest at that time with biological indicators in three consecutive sterilizer cycles.

Modified from references 1 and 7.

Louis G. DePaola, DDS, MS, is a professor in the Department of Oncology and Diagnostic Sciences, Dental School, University of Maryland, Baltimore. He received his DDS in 1975, completed a master's degree in oral biology, is a diplomate of the American Board of Oral Medicine and the American College of Dentists and has a certificate in prosthodontics. He is an international lecturer and executive director of Biosafety and Continuous Quality Improvement, Dental School, University of Maryland, Baltimore. Active in research, he has authored and coauthored of over 130 journal articles, book chapters and abstracts and serves as a consultant to the American Dental Association and numerous other professional groups and private industry.

Jacquelyn L. Fried, RDH, MS, received her Bachelor of Arts in political science and her Certificate in Dental Hygiene from Ohio State University. She also holds a Master of Science in Dental Hygiene from Old Dominion University. She is associate professor and director of the Dental Hygiene Program in the Department of Health Promotion and Policy at the University of Maryland Dental School. She has been in dental hygiene education for almost 30 years. She has been involved with clinical, research, didactic and community activities related to tobacco. She currently serves as principal investigator for a tobacco training grant funded by the State of Maryland. An active member of the American Dental Hygienists' Association, Fried is widely published and has authored numerous manuscripts and book chapters. She teaches both didactically and clinically and has received student awards for her teaching abilities.
Table I. Minimum Cycle-Times for Steam Sterilization Cycles

                                             Exposure time at
Type of Sterilizer     Item                  121[degrees]C

Gravity displacement   Wrapped instruments       30 min
                       Textile packs             30 min
Dynamic-air-removal    Wrapped instrument
                       Textile packs

                                             Exposure time at
Type of Sterilizer     Item                  132[degrees]C

Gravity displacement   Wrapped instruments       15 min
                       Textile packs             25 min
Dynamic-air-removal    Wrapped instrument         4 min
                       Textile packs              4 min

Type of Sterilizer     Item                  Drying time

Gravity displacement   Wrapped instruments    15-30 min
                       Textile packs             15 min
Dynamic-air-removal    Wrapped instrument     20-30 min
                       Textile packs          5 -20 min

Modified from Table 7, Guideline for Disinfection and Sterilization
in Healthcare Facilities, 2008.

Table II. Conditions for Sterilization of the
Most Commonly Encountered Devices in
the Dental Office

Method                                Temperature
                            Time      ([degrees]C/
                          (minutes)   [degrees]F)

Steam autoclave
  Gravity displacement        30        121/250
  Pre-vacuum sterilizer        4        132/270
Dry heat
  Static air                  60        170/340
                             120        160/320
                             150        150/300
  Forced air                  12        190/375
Unsaturated chemical          20        132/270

Modified from references 1-3,5,6

Table III: Biological Monitoring Indicated for Various Sterilizers

Method                 Biological Monitoring
                            (Spore Used)

Steam autoclave
  Gravity          Geobacillus stearothermophilus
  displacement    (Formerly B. stearothermophilus)
  Pre-vacuum       Geobacillus stearothermophilus
  sterilizer      (Formerly B. stearothermophilus)

Dry heat                Bacillus atrophaeus
                       (Formerly B. subtilis)

Unsaturated        Geobacillus stearothermophilus
chemical          (Formerly B. stearothermophilus)

Modified from references 1-3,5,6
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Title Annotation:infection control
Author:DePaola, Louis G.; Fried, Jacquelyn L.
Article Type:Report
Geographic Code:1USA
Date:Dec 1, 2009
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