DECONTAMINATING DENTAL INSTRUMENTS: TESTING THE EFFECTIVENESS OF SELECTED METHODS

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DECONTAMINATING DENTAL INSTRUMENTS: ETHODS

TESTING THE EFFECTIVENESS OF SELECTED

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ESTELA SANCHEZ, D.D.S.; GAYLE MACDONALD, PH.D., M.S., M.S.ED., R.D.H.

Onfection control has become a critical issue in the practice of dentistry since the early 1980s. In light of the need for recirculating instruments, the dental team must ensure the safety of both patients and personnel by adequately sterilizing dental instruments and other equipment before their use. There are various agents for sterilizing dental instruments: dry heat, steam, chemicals. Safe and effective decontamination procedures must be carried out before instruments are put into the appropriate equipment for sterilization. These procedures should be performed to remove gross contamination by blood, saliva and dental materials that harbor microorganisms and impair the sterilization process. In addition, the method of handling, packaging and wrapping instruments during decontamination and sterilization also has become significant due to recent concerns regarding the transmission of bloodborne pathogens. The challenge confronting the health care industry is to develop safe, practical decontamination and sterilization procedures that effectively remove pathogens. This is mandated by the U.S. Occupational Safety and Health Administration (OSHA), which requires employers to protect health care workers against

.1.

The decontamination of dental instruments before sterilization is designed to safeguard dental

personnel from exposure to bloodborne pathogens and to remove gross contamination.

The authors studied the relative

effectiveness of decontamination methods that included

ultrasonic cleaning, presoaking with an enzymatic cleaner and

dishwashing. Results indicated that the most effective methods involved presoaking followed by

cleaning. However, no single

item is rendered safe for handling, use or disposal." According to Miller,5 heavily contaminated instruments pose a threat to personnel because the dried blood, saliva or dental materials may insulate bloodborne pathogens from the direct treatment effects of heat or chemical sterilization. This necessitates longer sterilizing cycles to destroy the pathogens. Miller also suggested that organic contaminants may retard or inactivate chemical disinfectants and may appear as sterile dirt, contributing to corrosion and interfering with the instrument's functioning. TYPES OF DECONTAMINATION METHODS

procedure eliminated detectable concentrations of blood

contamination.

contracting bloodborne diseases in the workplace.23 In December 1991, OSHA released its bloodborne pathogens standard.4 This regulation defines decontamination as "the use of physical or chemical means to remove, inactivate, or destroy bloodborne pathogens on a surface or item to the point where they are no longer capable of transmitting infectious particles and the surface or

Four types of decontamination methods are most commonly used in U.S. dental practices: instrument cassette systems, presoaking solutions, ultrasonic cleaners and automatic dishwashers. Instrument cassette systems. An instrument cassette system offers a practical solution for the safe handling of dental instruments while they are cleaned and packaged before sterilization. Such a system has a perforated protective container in which instruments are processed, thus minimizing the JADA, Vol. 126, March 1995 359

CLINICAL PRACTICE risk of personnel's injury and exposure. Use of a cassette system, considered by some to be the state of the art, provides a safer alternative to direct handling of individual instruments by allowing the continuous and recirculating use of instruments within the cassette. These systems have been designed by manufacturers for use with various decontamination procedures, including presoaking agents, ultrasonic cleaning and dishwashing.26-8 Presoaking agents. The majority of presoaking agents contain detergents with enzymes or chemical disinfectants such as phenols or quaternary compounds. These agents partially dissolve organic debris and provide some antimicrobial activity during the interval between use and sterilization.9 The proteolytic presoaking agent (Klenzyme, Calgon Vestal Laboratories) used in this study also was recommended by the manufacturer for subsequent use in the ultrasonic cleaner, thus eliminating the need for a second cleansing agent. Ultrasonic cleaner. The ultrasonic cleaner has proven to be effective in removing contaminated debris from dental instruments while eliminating the handling of sharp instruments and the brushing splatter of manual scrubbing."1012 The OSHA standard states that "all procedures involving blood or other potentially infectious materials shall be performed in such a manner as to minimize splashing, spraying, spattering and generation of droplets of these substances."4 Uncovered ultrasonic cleaners may present a potential risk to dental personnel, because they produce a sonic-induced aerosol, which 360 JADA, Vol. 126, March 1995

should be considered a contaminant.8 Automatic dishwasher. In the U.S. food industry, an automatic dishwasher was developed as decontamination equipment. Many hospitals and universities have modified washers that are used to decontaminate and/or properly dry surgical instruments and linens. With the added advantage of the drying cycle, the dishwasher can eliminate the corrosion of instruments.13"4 Automatic cleaning and disinfecting machines manufactured in Europe (such as Germany's

I

Previous infection control studies have not evaluated the effectiveness of these readily available decontamination methods, either individually or in combination.

Miele model) have been approved by regulatory agencies and are commonly used in private dental and medical offices. The newer models incorporate thermal disinfection."5 Previous infection control studies have not evaluated the effectiveness of these readily available decontamination methods, either individually or in combination. Therefore, we undertook this study to evaluate the relative effectiveness of a proteolytic presoaking agent, an ultrasonic cleaner and a dishwasher as a means for blood decontamination. We compared methods individually and in combination. The enzymatic presoak we used is marketed as both a presoaking agent and an ultrasonic cleaning agent; we

examined its efficacy in this dual role. This study will attempt to determine the most effective and practical method of decontaminating instruments while maximizing patient and personnel safety. MATERIALS AND METHODS

Contamination of cassettes. A total of 10 Instrument Management System cassettes (IMS, HuFriedy, Chicago) were used in seven different experimental groups. Each cassette contained dressing pliers, a Gracey 13/14 curette, an excavator and a perio probe. We chose these instruments because they are commonly found in a general practitioner's armamentarium and also because their handles all differ in serrations or patterns. The working ends and a portion of the handles were contaminated by dipping them to a depth of 50 millimeters of freshly drawn human blood. We then placed the instruments in the cassette in the same order as listed above. Instruments were allowed to dry for at least one hour before being decontaminated. Experimental groups. We selected seven types of decontamination methods, identifying them as Experimental Groups 1 through 7. Experimental Group 1: dishwasher with water. Ten contaminated cassettes were placed in a KitchenAid Washer Model No. KUDS220T (Hobart Corp.). We used the "normal" wash cycle, a 78-minute cycle that included two wash and two rinse cycles as well as one drying cycle. These cassettes were numbered one through 10 and placed on their sides in the

CLINICAL PRACTICE dishwasher rack. The total water consumption was 10 gallons. The incoming tap water was heated by the element in the dishwasher to a temperature of 140 F. We did not use detergent, trying to assess only the jet action of heated water as a decontaminant. Experimental Group 2: ultrasonic cleaner with water. Ten contaminated cassettes were placed in an ultrasonic cleaner in three separate batches. The five-gal cleaner, Health Sonics Model No. T19.9C (Health Sonics Corp.), was filled with 100 F tap water. No detergent was used. Batch No. 1 included cassettes 1 through 4 with cassettes 1 and 2 placed on top of 3 and 4. Batch No. 2 included cassettes 5 through 8 with cassettes 5 and 6 on top of 7 and 8. Batch No. 3 included cassettes 9 and 10. We covered the unit and operated it for 20 minutes, then thoroughly rinsed it and allowed it to dry after each use. Each cassette was then dipped three times in each of four twogal rinse-water containers. Fresh rinse water was used for every second cassette. (We used this rinsing procedure to standardize the volume of rinse water used.) The ultrasonic cleaners used a total of 10 gal of water, and the rinsing procedure consumed a total of 40 gal. Experimental Group 3: presoak (1 ounce /gal). We prepared Klenzyme in accordance with the lowest concentration recommended by the manufacturer for use as a presoaking agent. One oz of enzymatic presoak was mixed with 1 gal of tap water at 100 F. We placed the cassettes in the presoaking agent for 20 minutes and then rinsed them as was done for Group 2. 362 JADA, Vol. 126, March 1995

Experimental Group 4: presoak (4 oz Igal). The procedure we used for this group was the same as the one we used for Experimental Group 3, except that the presoak concentration was prepared at the upper limits of the manufacturer's recommendation (4 oz of menzyme diluted with 1 gal of tepid water). Experimental Group No. 5: presoak (4 ozlgal) and ultrasonic cleaning with detergent. Cassettes in this group were presoaked in a 4 oz/gal concen-

We analyzed the instruments in each cassettefor the presence of blood after they were decontaminated by one of the seven methods. tration of enzymatic presoak for 20 minutes, rinsed and then placed in the ultrasonic cleaner for 16 minutes. The ultrasonic cleaner contained IMS detergent (HuFriedy) at a concentration of 1 oz detergent/gal of water. We used the rinsing procedure described for Group 2. Experimental Group 6: presoak (4 ozlgal) and dishwasher with water. We presoaked the cassettes in a solution of 4 oz of enzymatic presoak per gal of water for 20 minutes, rinsed them and placed them in the dishwasher for a normal cycle in the rack position we used for Group 1. Experimental Group 7: presoak (4 ozlgal) and ultrasonic cleaning with same enzymatic presoaking solution. The ultrasonic cleaner was filled with a concentration of 4 oz of enzy-

matic presoak per gal of water. We presoaked cassettes for 20 minutes and then activated the unit for 16 minutes. In this group, the enzymatic presoak served as the presoaking agent and the detergent. We rinsed the cassettes as described for Group 2. Cleaning the instruments. We analyzed the instruments in each cassette for the presence of blood after they were decontaminated by one of the seven methods. The blood-contaminated portion of each instrument was submerged in a 3-oz plastic cup containing 6 millimeters of distilled water and scrubbed with a new and sterile No. 201 screw-shank prophylaxis brush. The total manual scrubbing of each instrument consisted of 40 up strokes and 40 down strokes per instrument tip. We put the brush and the residual water into a clean 7-ml test-tube and vortexed them for 10 seconds. The presence of blood in the washings was determined by using qualitative colorimetric blood-indicating strips (Hemastix, Miles Inc.). We dipped the test strips into the washings and interpreted the results after 40 seconds, as suggested by the manufacturer. We compared the color-indicating strips to the standard colorimetric chart to determine blood concentrations of "negative," "nonhemolyzed trace," "hemolyzed trace," "small," "moderate" and "large." Any reading greater than "negative" indicated the presence of blood. We assigned to each result a numerical "blood score," which ranged from 0 to 5, with 5 indicating the greatest concentration of blood (Table, Figure). ANALYSIS OF DATA

The colorimetric strip we used

CLINICAL PRACTICE ITABLE

ment methods.) The methods used for Groups 5 and 6 were the most effective in removing blood from instruments. The methods used for Groups 1, 4 and 7 were all less effective in removing blood, but the three groups were statistically equivalent. The methods used for Groups 2 and 3 were the least effective in removing blood from contaminated instruments. DISCUSSION

gave a qualitative measure. For statistical analysis, we gave these color readings a numerical value ranging from 0 to 5, as noted above. We then completed our statistical analysis with the Kruskal-Wallis test, which is a non-parametric alternative to the one-way ANOVA for use with comparisons of ordinal data. The null hypothesis tested was that all decontamination methods were the same. The Dunn Procedure Test was then applied to compare specific decontamination groups against each other.

another. Groups 5 and 6 were statistically equivalent but significantly different from the other five groups (P < 0.001). We determined the mean colorimetric scores (mean blood scores) for each group as a means of better visualizing the differences between and among the groups (Figure). Only Groups 5 and 6 had a relative mean blood score of less than 1.0, which would indicate a level below trace. (The figure shows the effectiveness of treat-

Effective methods. In this study, the most effective methods for the removal of blood from the dental instruments were the use of a presoaking agent followed by use of either an ultrasonic cleaner with detergent (Group 5) or a dishwasher (Group 6). It may be argued that the presoaking agent allowed for the initial attack on contaminated surfaces as was suggested by Kneedler and Darling.9 After the initial presoak, the cavitational activity of the ultrasonic

RESULTS

When we analyzed all treatment groups by the Kruskal-Wallis test, we found a statistically significant difference (P < 0.001) among the groups. Thus, we rejected the null hypothesis and considered each treatment as different. Our goal then became determining which treatment was more effective than the others. The Dunn Procedure Test for Kruskal-Wallis allowed for comparison between groups. A larger "z" value indicated a greater difference between the groups compared, therefore indicating that one decontamination procedure was more effective than 364 JADA, Vol. 126, March 1995

Figure. Comparison of relative mean blood scores. (Mean blood scores correspond to the colorimetric strip readings of 0 through 5, 5 being high.)

CIUNICA[ PRACTICE cleaner-in combination with the chemical activity of a specifically formulated detergent (IMS)-proved effective (the method used for Group 5). This was comparable to the mechanical force of the highpressure water jet in the household dishwasher (the method used for Group 6) after the initial presoak. Least effective methods. The agents least effective in decontaminating dental instruments were the ultrasonic cleaner with water only (as used with Group 2) and a presoaking agent at a concentration of 1 oz/gal (as used with Group 3). The relative ineffectiveness of the Group 2 method may be due to the neutral pH of the water bath. A previous study indicated that ultrasonic cleaners are more effective with either acidic or alkaline cleansing solutions.'6 Meraner6 evaluated a cassette system used in a school of dentistry and found that the cavitation energy in the ultrasonic bath may be reduced significantly by the presence of a plastic cassette. (Plastics, by their nature, may absorb the ultrasonic energy.'0) The relative ineffectiveness of the Group 3 method may be due to the solution's low concentration of enzymes. Less effective methods. The methods that were less effective included those used for Group 1 (dishwasher with water only), Group 4 (presoaking in a concentration of 4 oz of presoak per gal of water) and Group 7 (presoaking in a concentration of 4 oz/gal of water followed by ultrasonic cleaning using the same presoaking solution). The jet action of the dishwasher may 366 JADA, Vol. 126, March 1995

account for the Group 1 method's being more effective than the Group 2 and Group 3 methods. The enzymatic presoak may have been rendered ineffective by the ultrasonic cleaner because the cleaner's operating temperature may have denatured the proteolytic enzymes. The enzymatic presoak used reacts optimally at a temperature of 140 F (not to exceed 150 F), but the cavitational activity of the ultrasonic unit may cause a rise in temperature of the solution within the bath to temperatures greater than 140 F."7 The presoak also had a neutral pH of 7.7, which may make it an ineffective detergent in the ultrasonic unit. Walmsley and Williams' research suggested that when acidic or alkaline chemicals are used, their cleaning effectiveness is enhanced by the cavitational activity produced by the ultrasonic energy within the

bath.'6 The role of water. Water plays a significant role in decontamination. The jet action in the dishwasher was very effective; "dip" rinsing of the contaminated cassettes in premeasured water baths (as done with Groups 2,

Dr. Sanchez Is a recent graduate of

the advanced

pediatric dentistry program, University of Southern California, School of Dentistry, Los Angeles, and now is in private practice in the Los Angeles area.

Dr Macdonald Is director of safety *and Infection

control, University *of Southern California, School of Dentistry, Loa *Angelesa 90089*0641. Address

*reprint requests to Dr. Macdonald.

3, 4 and 7) was relatively ineffective. Rinsing the contaminated cassettes under running tap water for a measured length of time may be a more effective method of rinsing in the methods used for these four groups. The role of the cassette design. In this study, the cassette design may have prevented any decontamination method from eliminating all detectable blood. Instruments were placed such that the contaminated ends had to make contact with the flexible rack that stabilizes instruments in the cassette. When closed, the cassette secured the instruments against the rack tightly enough to trap blood and prevent its adequate removal. The blood also dripped and dried along hidden areas beneath the flexible rack, preventing its adequate removal by dip rinsing. This result was in agreement with Meraner's6 conclusions regarding the cassette's rail system and its need for improvement. The effects of handle design. Many of the instruments had working ends and handles with serrations (for better grip), which allowed the accumulation of blood. The dressing pliers had holes, hinges and serrations that trapped blood and presented the greatest difficulty in decontamination. The results indicated that although an instrument may appear visually clean, it still was contaminated with blood (which was removed later with the brush). This residual blood was present in all of the experimental groups in amounts significant enough to be detected.

CLINICAL PRACTICE Colorimetric strips. Although the blood-indicating strips used in this study are intended for use in urinalysis, they have been used in previous studies to test for the presence of blood in water.10 The minimum amount of blood required to produce colorimetric changes was previously quantified in Miller and Hardwick's study.10 The trace categories in their study using these indicating strips were below the threshold level considered significant for the transmission of hepatitis. Based on Miller and Hardwick's findings, only Groups 5 and 6 had trace levels below the level for hepatitis transmission. However, this method of detecting blood in water using colorimetric bloodindicating strips requires further investigation so that a definitive quantitative analysis can be made and threshold levels for transmission of disease be established. Limitations of the dishwasher. It should be noted that the household dishwasher used in this study is not approved by the U.S. Food and Drug Administration as a medical device. This preliminary study is not intended to endorse the use of household dishwashers in the health care setting. Research for these machines' potential in this environment should be pursued.

368 JADA, Vol. 126, March 1995

CONCLUSIONS

Based on our methods of decontamination and our interpretation of blood analysis in washings, we present the following conclusions: - None of the methods we tested completely decontaminated the instruments in any of the experimental groups. This clearly indicates that, to ensure the safety of patients and personnel, it is critical to follow instrument decontamination with instrument sterilization using steam, dry heat or chemicals. - The dishwasher appears to be an effective alternative to and/or adjunct for decontamination because it reduces the exposure of potential bloodborne pathogens by not creating aerosols. It also reduces the potential for injury to personnel by accommodating safer cassette systems. Future studies should consider the dishwasher's water consumption and operating costs. - Enzymatic presoaking agents are effective in their initial attack on blood contamination but are ineffective as the only agent in the ultrasonic cleaner. - An effective detergent is needed in the ultrasonic cleaner to optimize the use of ultrasonic energy. - Decontamination methods

can and should be used in combination to yield the most effective results. . 1. Miller CH. Sterilization: disciplined microbial control. Dent Clin North Am 1991;35(2):339-55. 2. Gerber PC, Asa RW. Infection control through instrument management. Dent Manage 1989;29(11):34-7. 3. Miller CH. OSHA regulations protect employers and employees. RDH 1989;9(8):17-8. 4. Department of Labor, Occupational Safety and Health Administration. 29 CFR Part 1910.1030, Occupational exposure to bloodborne pathogens, final rule. Federal Register

1991;56(235):64004-64182. 5. Miller CH. Instrument cleaning involves multiple steps. Dentist 1990;68(4):23-5.

6. Meraner M. The IMS cassette: A new system for the management of instruments in the dental office. Gen Dent 1989;37(4):326-9. 7. Miller CH. Instrument recirculation prevents infection transfers. RDH 1989;9(4):18,20-1. 8. Miller CH, Palenik CJ. Infection control and management of hazardous materials for the dental team. St. Louis: Mosby;1994. 9. Kneedler JA, Darling MH. Using an enzymatic detergent to prerinse instruments. A research study. AORN J 1990;5:1,326-32. 10. Miller CH, Hardwick LM. Ultrasonic cleaning of dental instruments in cassettes. Gen Dent 1988;36(1):31-6. 11. Eames WB, Bryington SQ, Suway NB. A comparison of eight ultrasonic cleaners. Gen Dent 1982;30:242-5. 12. Palenik CJ, Miller CH. Use of an ultrasonic cleaner in the dental office. J Indiana Dent Assoc 1980;59(3):11-2. 13. Crow S. Washer-decontaminator: an evaluation. Infect Control Hosp Epidemiol 1989;5:220-1. 14. Jette LP, Lambert NG. Evaluation of two hot water washer disinfectors for medical instruments. Infect Control Hosp Epidemiol 1988;5:194-9. 15. Miele & Cie. Miele Professional Critical Cleaning Systems brochure. Federal Republic of Germany: Miele & Cie; 1993. 16. Walmsley AD, Williams AR. Measurement of cavitational activity within ultrasonic baths. J Dent 1991;1:62-6. 17. Houke HF. Ultrasonic cleaning. Presented at Fifth Annual Conference of the Office Sterilization and Asepsis Procedures Research Foundation; June 1990; San Francisco.