Using chemical indicators should be a standard part of the office infection-control program.
Chris Miller, PhD
Chemical indicators are visual aids that show if an item has been subjected to the sterilization process. Most of these indicators change color (some change form, from solid to liquid) when exposed to the high temperatures achieved in a sterilizer, or to a combination of temperature and time. The color change occurs because the indicator contains one or more chemicals that change color when exposed to high heat or other sterilizing conditions. Since these indicators contain chemicals that are affected by high heat, they are referred to as chemical indicators (CI). This is in contrast to biological indicators (BI) that contain a biological system (bacterial spores) that is affected by high heat.
Types of CI
There are basically two types of CI: those that are affected only by heat (temperature-specific CI) and those that respond to a combination of conditions such as temperature, time, and the presence of steam (multi-parameter CI or integrators).
Temperature-specific CI: Temperature-specific CI are in the form of tapes (autoclave tape) - paper strips or tabs or printed markings on the outside of sterilization pouches, usually in the shape of an arrow or circle. The stripes on autoclave tapes, the indicator areas on paper strips, and the printed pouch markings contain a thermochromic ink sensitive to heat. Once the CI is exposed to a certain temperature (such as 121°C, which is 250°F), the chemical quickly changes color.
Integrator: This multi-parameter CI may be in the form of a paper strip, liquid in a vial, or a pellet in a packet. These CI require the interaction of temperature and time, temperature and steam, or temperature, steam, and time before a noticeable change occurs. Some of these CI use thermochromic ink while others use other systems that are affected by the heat and moisture.
Use of CI
The routine use of CI is a part of the overall office sterility-assurance program of following strict sterilization protocols involving both BI and CI. While use of a BI (spore-testing) is the main standard for measuring the sterilization process, it requires two to seven days. One of the important properties of a CI is that it gives an immediate reaction that is visible as soon as the packages are removed from the sterilizer. When a CI changes color or form, it indicates that the processed items have been exposed to at least high temperatures for some amount of time and that they are likely safe to use (as long as other sterility-assurance procedures of spore-testing and protocol compliance are in place and functioning properly). CI should be not used as a substitute for BI and acceptable sterilization protocols.
One of the most important uses of a CI in dentistry is as a process indicator. A process indicator is a temperature-specific CI that is simply used to identify packages or cassettes of instruments that have been processed through a sterilizer (in contrast to items that have not yet gone through the sterilizer). Process indicators are usually autoclave tapes or special markings printed on pouches and other sterilization packaging materials. They are on the outside of packages to be processed through a sterilizer so they can be easily seen; thus, they have been referred to as "external indicators."
A glance at a pouch or wrapped cassette marked with a process indicator gives the assurance that that item has at least been processed through a sterilizer. This helps eliminate the intermingling of packages that are ready to use at chairside with those that still need to be processed. This differentiation can be important in the sterilizing room (especially when "things are hectic"), in storage areas, and on transport trays or carts, where both processed and unprocessed items may appear. It also helps avoid possible confusion by those in the office who may be sent to the sterilizing room to retrieve "sterilized" instruments, but are less familiar with how the room is organized (such as temps or a receptionist substituting for a chairside assistant). Also, a quick look by the hygienist or dentist at the changed CI on packages at chairside can give a "final" indication that those instruments are, indeed, ready to use. It`s a simple mechanism to prevent the accidental use of unprocessed instruments. Sometimes strips or tabs of temperature-specific indicators are placed inside packages to confirm penetration of heat to the instruments inside.
Integrators are used inside instrument packages to assess whether the instruments have been exposed not only to high temperatures, but also to other conditions necessary for sterilization, such as time or steam.
Besides routinely monitoring the processing of instruments for patient care, a CI also can be used to determine if a new or different type of instrument container or new packaging material is, indeed, allowing the heat or steam to penetrate.
Recommendations from the CDC
The CDC recommends that all dental offices use both biological and chemical indicators as quoted in the following paragraph from the most current recommendations.
"Proper functioning of sterilization cycles should be verified by the periodic use (at least weekly) of biologic indicators (spore tests). Heat-sensitive chemical indicators (those that change color after exposure to heat) alone do not ensure adequacy of a sterilization cycle, but may be used on the outside of each pack to identify packs that have been processed through the heating cycle. A simple and inexpensive method to confirm heat penetration to all instruments during each cycle is the use of a chemical indicator inside and in the center of either a load of unwrapped instruments or in each multiple instrument pack; this procedure is recommended for use in all dental practices." (CDC.Recommended infection control practices for dentistry-1993. Morbidity & Mortality Weekly Reports May 28, 1993; 4[No. RR-]:1-12).
In summary, using chemical indicators should be a standard part of the office infection-control program to help assure the safety of dental instruments.
Chris Miller, PhD, is professor of oral microbiology and associate dean at the Indiana University School of Dentistry.