Instrument sterilization

March 1, 2004
The Centers for Disease Control and Prevention issued its new set of infection control recommendations ("Guidelines for Infection Control in Dental Health-Care Settings — 2003") on Dec. 19, 2003.

By Ginny Jorgensen, CDA, EFDA, EFODA, AAS, and Charles John Palenik, MS, PhD, MBA

The Centers for Disease Control and Prevention issued its new set of infection control recommendations ("Guidelines for Infection Control in Dental Health-Care Settings — 2003") on Dec. 19, 2003. The guidelines are available in print (MMWR 2003;52(RR-17):1-68) or electronically at

The CDC guidelines consolidate recommendations for preventing and controlling infectious diseases and managing personnel health and safety concerns related to infection control in dental settings. The report updates and revises previous CDC recommendations, incorporates relevant infection-control measures from earlier guidelines, and discusses concerns not addressed in prior recommendations for dentistry. Although some may complain about the fact that new guidelines have been issued, they are based on recommendations that were written in 1993.

Transporting instruments

After a dental procedure is completed and the patient has been escorted to the reception area, the dental health-care practitioner (DHCP) should return to the treatment room where cleaning, disinfection, and instrument-processing begins. After donning clean gloves, the DHCP should place all disposable items other than sharps, solid wastes soaked or saturated with blood or saliva (contaminated cotton products), extracted teeth, or surgically removed hard and soft tissues (regulated medical waste) into the waste system. Sharps should be placed into a color-coded, leakproof, puncture-resistant container. Nonsharp items should be put into color-coded, labeled, leakproof containers (biohazard bags). All regulated medical waste should be handled, stored, and disposed of according to applicable federal, state, and local regulations. Orally-soiled instruments should be put into covered containers or cassettes prior to transporting them to the instrument-processing area. Minimize the handling of loose, contaminated instruments during transport.

Instrument-processing areas should be designed with adequate space for separation of the following procedures:

  1. Receiving and cleaning
  2. Wrapping and packaging
  3. Sterilization
  4. Storage and distribution

Actual physical dividers are the best method for separation. This separation also also can be accomplished through the use of signs and the training of DHCP who are responsible for processing patient-care items.

Receiving and cleaning

Ideally, all visible blood and other contamination should be removed from instruments before sterilization. If instruments cannot be processed immediately, they should be placed into a "holding solution" that will prevent patient material from drying on the instruments, making cleaning easier and less time-consuming. The chemicals recommended for use as "holding solutions" are detergents, disinfectant and detergents, or enzymatic cleaners. The solution should be placed into a puncture-resistant container. Instruments should be put into a strainer-type basket and lowered into the container. Liquid chemicals such as steriliant and high-level disinfectants (glutaraldehydes) are not to be used as "holding solutions."

When the DHCP is ready to proceed, the basket should be removed from the holding solution. The instruments should be rinsed under running water, drained, and transferred, using forceps, o an automated cleaning device, such as an ultrasonic cleaner or an instrument washer-disinfector. (DHCPs should not reach into solutions to retrieve instruments.) Follow the manufacturer's instructions to maximize the cleaning process. If manual scrubbing cannot be avoided, carefully use a long-handled scrub brush to prevent the hands from coming in contact with any sharp surfaces. Always wear puncture- and chemical-resistant/heavy-duty utility gloves when handling and cleaning instruments. Other appropriate personal protective equipment (masks, protective eyewear and gowns) should be used when splashing or spraying is anticipated.

After the cleaning process is completed, the instruments should be rinsed and dried without removing them from their containers.

Wrapping and packaging

Several types of instrument-packaging materials are available. Choose the most appropriate wraps and packages (click here to download a .pdf of Table 1). Materials should not compromise the integrity of the sterilization process, especially during storage.

If at all possible, instruments should be processed-wrapped or packaged. Critical instruments intended for immediate reuse can be processed unwrapped. These instruments must be cleaned and dried, and a chemical indicator should be placed inside each load. Care should be taken that the DHCP does not receive a thermal injury when removing the sterilized items. In addition, special precautions should be implemented to maintain sterility when transporting the sterilized items to the point of use.


Use several criteria when choosing a sterilizer. The area in which the sterilizer is placed should provide adequate space for loading, unloading, and cool-down of the instruments. The sterilizer chamber should be big enough to accommodate the amount of instruments needed in a reasonable number of cycles. Manufacturer recommendations and local codes have specifications for adequate ventilation. Only units that have received FDA clearance as a true medical device should be used. Questions sometimes arise about the use of household ovens or even broilers!

A number of sterilization methods can be used. Follow the manufacturer's instructions concerning the use and maintenance of your instruments (see Table 1).

Steam autoclaves are the most common type of sterilizer. They are a popular choice because they are economical, easy-to-use, and dependable. Autoclaves are best for critical and semicritical patient-care items that can tolerate heat and moisture. Steam under pressure must directly contact the items being sterilized for a specified amount of time to kill microorganisms.

Unsaturated chemical-vapor sterilizers use a solution of alcohol, formaldehyde, and rust inhibitors in a closed, pressurized chamber. Because the solution contains very little water, there is usually less corrosion and dulling of carbide-steel instruments, such as dental burs. However, the solution can be used only once. It is a hazardous chemical and disposal is regulated in some areas.

Dry-heat sterilization is employed when rusting and dulling of instruments is the primary concern. There are two types of dry heat sterilization:

  1. Static air (oven-type, heating through natural convection)
  2. Forced air (rapid heat transfer in which the heated air is rapidly circulated)

Static-air sterilizers usually require long cycle times. In forced-air units, rapid transfer of energy to instruments reduces sterilization time. Most handpieces cannot be sterilized using dry heat.

Liquid-chemical germicide sterilization may be used for critical and semicritical patient-care items that cannot tolerate heat. These must be FDA-approved sterilants. Items must be cleaned thoroughly and allowed to completely dry prior to immersion. After processing, items must be rinsed well with sterile water, handled with sterile gloves, dried with sterile towels, and transported to the point of use in a sterile manner. It is impossible to accurately verify sterilization with biological monitors. Due to the extended length of immersion time (up to 12 hours) required for the sterilization process to be completed, liquid- chemical germicides are almost never used for routine sterilization of instruments. Their greatest value comes as high-level disinfectants for semicritical items. These chemicals should not be used for surface disinfectants or "holding solutions." Liquid-chemical germicides can cause adverse health effects, such as skin irritations, respiratory problems, and eye irritations.

Bead sterilization has been used in the past to sterilize endodontic files. Bead sterilizers are not approved by the FDA as a safe or effective method of sterilization.

How a sterilizer is loaded is extremely important. Items must be arranged to permit free circulation of the sterilizing agent. Always follow the manufacturer's instructions for correct loading procedures. In most cases, packaged instruments should be allowed to dry inside the sterilizer chamber. This prevents handling of wet packs which can cause wicking or tearing.

Storage and distribution

The ultimate goal of sterilization is the routine delivery of sterile instruments chairside. Sterilized and disposable patient-care items should be stored in an enclosed space, such as closed or covered cabinets and drawers. Dental instruments should remain in the packages in which they were sterilized until they are used. Limit the amount of handling of sterilized packages. If they should become torn, the instruments must be cleaned again, repackaged, and reprocessed. Organize sterilized items for easy access, so less handling is required. Prior to use, sterile instrument packages should be inspected to verify the integrity of the packaging.


Sterilization-monitoring must be performed and recorded on a routine basis. The process of sterilization-monitoring should include a combination of mechanical, chemical, and biological means.

An example of mechanical sterilization-monitoring is observing the gauges on the machine's every cycle. Some sterilizers are equipped with an actual print-out for each load. Mechanical monitoring does not ensure sterilization; however, improper readings may indicate an initial problem.

Chemical monitoring includes the use of inks or tapes that contain chemicals sensitive to heat. These inks or tapes do not prove that sterility has been achieved. However, chemical indicators can show procedural errors or equipment malfunction. An internal chemical indicator is placed on the inside of each instrument package to assure the sterilization agent has penetrated the package. An external chemical indicator can be applied to the outside of an instrument package.

When either mechanical or chemical indicators indicate inadequate processing, the items in the sterilizer should be repackaged and reprocessed prior to use.

Biological indicators, such as spore tests. are the most accurate method of sterilizer-monitoring. The reason for their reliability and acceptance is because their assessment is dependent on the sterilizer not only having to complete the process, but also proving its ability to kill highly resistant microorganisms. BIs are superior to the mechanical or chemical indicators because they address the entire sterilization process. BIs should be processed at least weekly and in every situation when implants are included in the sterilizer load. Follow manufacturers' directions for placement and processing of BIs is imperative. A control BI from the same lot as those being processed should also be incubated. The control BI should indicate bacterial growth when incubated. Biological monitoring can be performed in the office or through a mail-in sterilization-monitoring service.

Final thoughts

Achieving a safe environment for DHCP and dental patients should be the goal of all dental offices. It takes hard work and commitment by dental-office team members to learn and follow established guidelines and regulations. Understanding and practicing the concepts of infection control and proper processing of contaminated patient-care items are essential first steps.

Dr. Charles J. Palenik is director of Infection Control Research at Indiana University School of Dentistry in Indianapolis, Ind. He may be reached by e-mailing [email protected]. Ginny Jorgensen is the Clinical Procedures instructor at Portland Community College, Dental Assisting Program, Portland, Ore. She may be reached at (503) 977-4036 or by e-mail at [email protected].