Technology advances in heat sterilization

Sept. 1, 2006
A long-standing fundamental guideline for effective infection control is: Do not disinfect when you can sterilize.

A long-standing fundamental guideline for effective infection control is: Do not disinfect when you can sterilize.

The process of sterilization is an essential component of an infection control program. Sterilization is defined as the destruction of all forms of life with particular reference, in this instance, to microbial organisms. Historically, the use of heat has been recognized as the most efficient, reliable method of achieving sterilization. The most recent reinforcement of this axiom is found in the 2003 Centers for Disease Control infection control recommendations:

“Critical items used to penetrate soft tissue or bone have the greatest risk of transmitting infection and should be sterilized by heat. Semicritical items touch mucous membranes or nonintact skin and have a lower risk of transmission; because the majority of semicritical items in dentistry are heat-tolerant, they also can be sterilized by using heat.”

Three accepted methods of heat sterilization in patient care settings are: 1) moist heat at higher temperatures in the form of saturated steam under pressure (autoclave), 2) dry heat, and 3) unsaturated chemical vapor. Although each has distinct advantages and disadvantages, the majority of dental facilities utilize autoclaves for instrument sterilization.

This type of sterilizer has been available for more than a century, primarily as gravity displacement autoclaves. This unit sterilizes with self-generated steam that is created within the chamber, or by a steam generator that is a component of the equipment and passively displaces residual air through a port or drain in or near the bottom of the chamber.

Most of the early gravity sterilizers were large, free-standing pieces of equipment with extensive plumbing and electrical requirements. The introduction of efficient tabletop models for smaller facilities, such as dental offices, led the way for primary use of heat sterilization as a replacement for chemical immersion, or “cold” sterilization.

The evolution of steam sterilization has continued with the development of a number of technological advances to address common problems, such as formation of air pockets in the chamber and wet sterilized packages at the end of the cycle. This is exemplified by developments such as pulse injection of steam during the process instead of steam entering the chamber all at once. This allows for less mixing of air with steam within the chamber during the sterilization interval. This type of autoclave remains a popular, efficient component of an infection control program.

The most recent major innovations were originally developed in Europe. Sterilizers with these features have been available with FDA approval in the U.S. only within the past few years. These are pre- and post-vacuum steam sterilizers, also termed “Class B” sterilizers. The Class B designation is taken from the European Standard responsible for small-steam sterilizer requirements.

In the pre- and post-vacuum sterilizer, a pump housed within the unit creates a vacuum at the beginning of the cycle to prevent mixing of air and steam, thereby ensuring more rapid and efficient penetration of steam to instrument surfaces. The presence of a post-vacuum cycle component at the end of the sterilization interval is designed to facilitate drying, thereby providing the clinician with dryer instrument packages at the end of the process.

Another benefit noted with the post-vacuum portion of the sterilization cycle is the lower potential for corrosion of carbon steel instruments.

Despite recent, current, or future improvements in sterilizer technology, the clinician’s responsibility remains the same - to use the units appropriately while following manufacturers’ instructions. Do not devise “shortcuts” to established sterilization practices. Examples here include not arbitrarily shortening the cycle time to retrieve instruments quickly, and to be sure not to overload the chamber with wrapped pouches and cassettes. Even the most sophisticated equipment only can be as effective as the way in which it is being used.

References available upon request.

Dr. John A. Molinari received a PhD in microbiology from the University of Pittsburgh School of Dental Medicine. He is a professor and chairman of the Department of Biomedical Sciences at the University of Detroit Mercy School of Dentistry. He has published and lectured in the areas of infectious diseases, clinical immunology, and infection control. He also addresses these areas as a consultant to the CDC, ADA Council on Dental Practice, and Council on Scientific Affairs. Contact him at (313) 494-6632, or [email protected].

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