Jul/Aug 2007
Volume 3, Issue 7

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Cleaning Instruments: A Critical Step to Instrument Reprocessing

Eve J. Cuny, RDA, MS

The heat sterilization of critical and semicritical instruments is the standard of care in modern dental offices.1 Not many years ago, it was common practice to soak instruments in a disinfectant solution between patients, often at chairside, in a small glass container with a lid. This method was fallible in a number of ways.2 Some of the obstacles to effective chemical disinfection or sterilization include:

• the relatively weak antimicrobial strength of many solutions;
• the likelihood of improper dilution of the disinfectant;
• the inability to verify the antimicrobial activity (such as being able to measure a biologic indicator in heat sterilizers);
• the lack of packaging for aseptic storage of instruments; and
• the lack of debris removal before soaking instruments.

The use of heat sterilization for critical and semicritical instruments results in a higher certainty of safety for patients. However, the reprocessing of dental instruments involves much more than just the sterilization process itself. Every step in reprocessing is critical to ensure achievement of the objective: to deliver instruments to the dental operatory that are free of all body fluids and microorganisms from previous patients. Ensuring that all instruments are free of debris before packaging and sterilizing is one of the most important aspects of instrument reprocessing.


Hand scrubbing used, contaminated instruments increases the amount of handling of sharp items by dental personnel, which in turns provides opportunity for accidental injuries resulting in an occupational exposure to blood or body fluids. Additionally, hand scrubbing is ineffective and inconsistent in its ability to remove blood from dental instruments.3 For specialized items that cannot withstand mechanical cleaning or that have debris remaining after ultrasonic cleaning, handle individually and carefully scrub to remove all debris before sterilization (Figure 1).


Ultrasonic cleaners are an inexpensive and effective means of cleaning instruments in preparation for sterilization. The mechanism of an ultrasonic is that inaudible sound waves create small bubbles that are densely distributed in the ultrasonic solution. When the bubbles implode, they create cavitations within the chamber and this activity dislodges debris from the instruments. This method of mechanical cleaning is more reliable than hand scrubbing instruments. When personnel hand scrub instruments, there is a tendency to rush the procedure because of the pressure of little time being available between patients. Using an automated procedure allows personnel to place instruments in the ultrasonic cleaner, set a timer, and walk away. Automated cleaning provides a more predictable outcome and is the preferred method for routine cleaning of dental instruments before sterilization.

A variety of solutions are available for use in ultrasonic cleaners. Plain detergents, antimicrobial detergents, and enzymatic cleaners are the most commonly available types. It is not advisable to use household detergents or environmental surface disinfectants as these may damage the dental instruments and the ultrasonic chamber. Plain water alone is not as effective in the cleaning of instruments as the use of a cleaning agent.


The use of a presoak for instruments before sterilization is optional. It is unclear how beneficial the routine use of a presoak solution is in enhancing the cleaning ability of an ultrasonic cleaner, especially for items that are not heavily contaminated. For surgical practices, a presoak using an enzymatic product may provide some benefit, as it will help break down blood and other organic debris in the grooves and hinges of surgical instruments. Some studies indicate that using a presoaking agent followed by the use of either an ultrasonic or instrument washer is more effective for removal of blood than the use of an ultrasonic or instrument washer alone.4,5 These studies involved heavily blood-contaminated instruments and, in at least one of the studies, the blood remained on the instruments to dry for approximately 1 hour. Another study, testing the efficacy of presoaking compared to an ultrasonic on the cleanliness of endodontic files, found that presoaking did not provide any benefit over the use of an ultrasonic alone.6 Whether personnel presoak instruments or place them directly into the ultrasonic cleaner, immersing the instruments before blood and other debris have the opportunity to dry improves the efficacy of the cleaning procedure.

Each individual dental practice should make the decision regarding the use of a presoak based on its needs and practice type. Some issues to consider are whether debris remains on instruments after removal from the ultrasonic, the amount of time available to reprocess instruments, and whether or not other less time-consuming alterations of procedure are effective in improving the cleaning ability of the ultrasonic. Some examples of alternatives to troubleshoot ineffective cleaning are:

• using a different ultrasonic solution;
• avoiding overloading the ultrasonic;
• maintaining an appropriate level of solution in the chamber;
• increasing the amount of time the ultrasonic is activated; and
• ensuring that the instruments are in a basket or other holder that prevents them from touching the floor of the ultrasonic (Figure 2).

Bacterial Contamination

Bacterial contamination of the ultrasonic cleaning solution may occur when placing used, contaminated instruments into the device for cleaning. Most ultrasonic solutions do not contain antimicrobial agents and are not necessarily effective in the destruction of microorganisms.7 Extraordinary measures are not necessary to prevent the exposure to personnel of contaminated ultrasonic solutions. A combination of personal protective attire, using a lid on the ultrasonic when it is in operation, and routinely changing the solution should effectively reduce the risk of exposure (Figure 3).


Upon removal of instruments from the ultrasonic, it is important to rinse the items with water before drying and packaging. The rinsing of instruments helps remove residual debris that may be present but not visible in the grooves and crevices of instruments. Instruments may also pick up debris from the ultrasonic solution left from previous instruments.8 After rinsing, instruments should be thoroughly dried and then packaged in material appropriate to the method of heat sterilization.


Automated washer/disinfectors provide yet another alternative for cleaning instruments before sterilization. Instrument washers clean instruments before sterilization and may or may not have a drying cycle. Automated instrument washers are effective in removing debris from instruments and are an acceptable alternative to hand scrubbing or ultrasonic cleaning. Products marketed as instrument washers without the designation of being a disinfector do not render instruments safe to handle during the remainder of the reprocessing procedures. Personnel must still wear heavy-duty gloves to protect against accidental exposure while drying and packaging instruments and loading the sterilizer. Instrument washers clean instruments contained in baskets or cassettes and cannot process loose instruments. These devices are available in both countertop and built-in models. The built-in model resembles a household dishwasher, but is specifically designed for dental instruments.

Instrument disinfectors wash, dry, and disinfect instruments in preparation for sterilization. Similar in design to instrument washers, these devices are Food and Drug Administration–cleared medical devices that disinfect instruments in addition to cleaning and drying. The full dis-infection cycle on these devices is longer than on most instrument washers, but the instruments are safe to handle upon removal from the disinfector. Instruments or instrument cassettes must still be packaged and sterilized as the terminal process for reuse on patients.


Instrument reprocessing using appropriate cleaning methods and materials is an important part of the dental infection-control program. Personnel responsible for this important duty must receive proper training in the rationale for the procedures and the potential consequences of failure to follow all of the appropriate steps (Table 1). Blood, tissue, and other debris left on dental instruments through the sterilization cycles may impair the sterilization process.


1. Kohn WG, Collins AS, Cleveland JL, et al. Guidelines for infection control in dental health-care settings—2003. MMWR Recomm Rep. 2003;52(RR-17): 1-61.

2. Thrash RJ, Reich RR. Physical Factors Influencing the Activity of Antimicrobial Agents. In: Block SS. Disinfection, Sterilization, and Preservation. 5th ed. Philadelphia, Pa: Lippincott, Williams & Wilkins; 2000:57-64.

3. Cafruny WA, Brunick A, Nelson DM, et al. Effectiveness of ultrasonic cleaning of dental instruments. Am J Dent. 1995;8(3):152-156.

4. Sanchez E, Macdonald G. Decontaminating dental instruments: testing the effectiveness of selected methods. J Am Dent Assoc. 1995;126(3):359-366.

5. Walker N, Burke FJ, Palenik CJ. Comparison of ultrasonic cleaning schemes: a pilot study. Prim Dent Care. 2006;13(2):51-56.

6. Aasim SA, Mellor AC, Qualtrough AJ. The effect of pre-soaking and time in the ultrasonic cleaner on the cleanliness of sterilized endodontic files. Int Endod J. 2006;39(2):143-149.

7. Bettner MD, Beiswanger MA, Miller CH, et al. Effect of ultrasonic cleaning on microorganisms. Am J Dent. 1998;11(4): 185-188.

8. Burkhart NW, Crawford J. Critical steps in instrument cleaning: removing debris after sonication. J Am Dent Assoc. 1997;128(4): 456-463.

Figure 1 Clean delicate items carefully, while wearing appropriate protective attire.   Figure 2 Use a basket to elevate the instruments away from the floor of the ultrasonic.
Figure 3 Keep the lid on the ultrasonic cleaner when in operation to prevent the dispersion of bacterial contamination to the surrounding areas.  
About the Author
Eve J. Cuny, RDA, MS
Assistant Professor
Director of Environmental Health and Safety
University of the Pacific
Arthur A. Dugoni School of Dentistry
San Francisco, California

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