Not so clean after all

Feb. 1, 2006
Correct decontamination is an essential step in preparing dental instruments for sterilization.

Correct decontamination is an essential step in preparing dental instruments for sterilization. Cleaning reduces the bioburden (microorganisms, blood, saliva, oral hard and soft tissues, and dental materials) present. Bioburden could isolate or protect microorganisms from sterilizing agents. There are two ways to clean dental instruments - mechanically (ultrasonic cleaning, instrument washers, and instrument washer-disinfectors) or manually. If performed well, the level of remaining contamination is low. Sterilization should readily neutralize these modest amounts of bioburden.

The emergence of variant Creutzfeldt-Jakob disease (vCJD) has presented a new and increased challenge to effective cross-infection. vCJD is thought to be caused by an unusual pathogen called a prion. Although they lack nucleic acid, prions are isoforms of normal proteins, capable of self-propagation. vCJD readily produces serious clinical signs and symptoms, and - invariably - is fatal.

Prions exhibit unusual resistance to conventional chemical and physical decontamination procedures. Prions can adhere to stainless steel. vCJD presents a potential for onward transmission with contaminated reusable dental instruments. Potential infectivity of vCJD remains an unresolved concern; however, proper decontamination of reused items is essential.

Two recent studies question the effectiveness of cleaning schemes on reprocessed endodontic files. One study examined visually 10 files from 25 general practice offices. The files had been used, cleaned, and sterilized. The files were observed with a dissecting light microscope, and then were tested for residual blood. The offices also completed a questionnaire concerning the procedures used to reprocess the files.

Of the 25 offices, 19 used stainless steel files exclusively. The majority of offices (92 percent) changed files when they were bent or damaged. None of the practices used files as single-use disposable items. The most common reason for this was increased cost. Two cleaning regimens dominated - manual cleaning with a brush followed by autoclaving (40 percent); and manual cleaning followed by ultrasonic cleaning and autoclaving (28 percent). The latter technique is the one recommended by most file manufacturers.

Of the 250 files examined, 75 percent had some degree of visual contamination. Seven percent of all files tested positive for blood. Most blood-contaminated files had heavier amounts of adherent materials. Large variations in residual contamination of files existed among practices that used the same method of decontamination.

Results indicate that endodontic files were never used just once and discarded. In addition, the files routinely remain contaminated after reprocessing. Thus, they pose a risk for cross-infection. Most cleaning regimens, especially those relying primarily on manual scrubbing, proved inadequate. No attempt was made to determine the number of times a given file was used. So, cumulative buildup of contamination was possible. Many of the files could be seen as contaminated even without magnification. Yet offices accepted these files for reuse.

Study results support the position that endodontic files cannot be reliably cleaned following use. Single use of files would eliminate the problem. Also, practitioners need marked improvement in decontamination methods.

Endodontic files from 22 general practice offices were evaluated in the second study. Methods used were the same as in the first study except that residual protein was measured instead of blood.

Results indicated that 216 of the 220 (98 percent) files were visually contaminated. All files demonstrated residual, yet widely differing, amounts of protein contamination. Differences among cleaning methods regarding the presence of contamination and protein could not be determined. Once again, cleaning regimens used by offices routinely failed to decontaminate endodontic files.

Proper cleaning of reusable instruments, followed by correct sterilization, are essential functions of infection control in dentistry. Endodontic files, rasps, drills, and burs are difficult to clean universally. Serious consideration should be given to the concept that such items are best considered as single-use and disposable.

OSAP, the Organization for Safety & Asepsis Procedures, is dentistry’s prime source for evidence-based information on infection control and prevention, and human safety and health. More information about instrument handling, cleaning, and sterilization is available on the OSAP Web site at

Dr. Charles John Palenik is an assistant director of Infection Control Research and Services at the Indiana University School of Dentistry. Dr. Palenik is the co-author of the popular “Infection Control and Management of Hazardous Materials for the Dental Team.” He serves as chair of the OSAP publications committee. Questions about this article or any infection-control issue may be directed to [email protected].