Instrument sterilization: Preparation

April 1, 2008
Instrument processing is a set of procedures that prepares contaminated instruments for reuse.

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by Charles John Palenik, MS, PhD, MBA

Instrument processing is a set of procedures that prepares contaminated instruments for reuse. It involves six steps that comprise three sections: instrument preparation, sterilization, and monitoring and distribution. Instrument preparation includes holding, cleaning, corrosion control, drying, lubrication, and packaging.

Careful handling of contaminated instruments is necessary to avoid occupational exposures. Instrument cleaning cannot always occur immediately after use. Precleaning instruments lessens the chances of debris drying and helps remove adherent materials. Precleaning involves spraying instruments with special chemicals or placing them into holding solutions. Spraying products can be liquids, gels, or foams. Some sprays contain enzymatic cleaners and corrosion inhibitors. A holding solution contains a detergent and water or enzyme cleaning solution. Some items, such as handpieces and some plastic/resin instruments, should not be soaked. A mesh basket facilitates placement and removal. Soaking eliminates drying and helps remove adherent materials. Limit holding of instruments to several hours to prevent rusting.

There are two forms of cleaning dental instruments: manual and mechanical. Manual scrubbing is dangerous, time consuming, and less effective than mechanical cleaning. If necessary, scrubbing should occur under water. There are two types of mechanical cleaners: ultrasonic and instrument washers. Both must have Food and Drug Administration clearance for safety and effectiveness. Employees can perform other tasks while the machines are operating. Cleaning removes debris and reduces the number of microorganisms.

Ultrasonic cleaners come in a variety of sizes and shapes and work through cavitation. During operation, millions of bubbles form. Upon imploding, they generate a cleansing turbulence. Ultrasound can clean almost all instruments, except for handpieces. Cleaning includes loose instruments (15 to 20) and those held in cassettes. Hold instruments in a suspending basket. Cleaning is most effective off the floor to about an inch below the surface of the filled chamber.

Always use detergents designed for ultrasonic cleaners. They last longer than household detergents and are safer because of their neutral pH. Always have the lid on when operating the unit. Rinse instruments well after cleaning. Empty the tank and clean out the chamber at least once or twice a day. Leave chamber empty at the end of the day.

An aluminum foil test evaluates the effectiveness of ultrasonic cleaners. Suspend vertically a smooth piece of aluminum foil in an operating cleaner for 30 seconds, then inspect it. Properly operating cleaners should pit and dull the aluminum, even causing holes. Instrument washers clean using high-temperature water with special detergents. It is possible to clean loose instruments. But to achieve maximum benefit, it is best if the instruments are in cassettes. Washers come in many sizes: countertop, floor model (built-in and movable), and large production models. Washers have capacities for holding 10 to 40 cassettes. Cycles are longer, often operating almost an hour. The efficiency of some types is enough to achieve disinfection (washer-disinfectors). Like ultrasonic cleaners, washers are FDA-regulated medical devices. Never use household dishwashers to clean instruments.

Some instruments (burs and files) are difficult to clean. Studies show that offices do not clean these items well. Residual debris may hamper sterilization. Is it better to discard items that are inexpensive, hard to clean, and likely to require potentially hazardous hand scrubbing? Carbon steel items — burs, hand instruments, cutting edges of orthodontic instruments, and grasping surfaces of forceps — are prone to rusting and dulling. Spraying or dipping instruments with solutions containing sodium nitrite decreases rust. Dry heat ovens and unsaturated chemical vapor sterilizers do not rust instruments. A switch to stainless steel would be helpful.

Drying instruments prior to packaging lessens the chances of rusting and avoids wetting paper packaging. Wet paper can lead to torn packaging. Some items, including hinged instruments and handpieces, require lubrication. Excessive lubricants must be removed before packaging.

Unwrapped instruments after processing have no practical shelf life. It is imperative to maintain instrument sterility until instruments are delivered chairside. Packaging instruments prior to sterilization prevents contamination during storage and distribution. Packaging involves either wrapped instrument cassettes or organizing cleaned instruments into function sets and placing them into sterilization pouches, bags, or trays. Packaging is designed for use in a specific type of sterilizer. Incompatible wrap-sterilizer combinations can hinder sterilization, release toxic chemicals, and may result in wrapping materials and instrument damage. The FDA considers instrument wraps to be medical devices that must allow sterilizing agents to pass through to maintain sterility for six months in order to be cleared.

Dr. Charles John Palenik is the director of Infection Control Research and Services at the Indiana University School of Dentistry. Direct infection control questions to [email protected].

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