JADA Continuing Education
Internal contamination of air-driven low-speed handpieces and attached prophy angles
Judith R. Chin, DDS, MS,
Chris H. Miller, MS, PhD and
Charles John Palenik, MS, PhD, MBA
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ABSTRACT
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Background. In an in vitro crossover study, the authors investigated whether the interior of low-speed handpiece/prophy-angle systems becomes contaminated during operation and submersion into Geobacillus stearothermophilus.
Methods. This study involved two types of handpieces attached to eight brands of prophy angles. The researchers operated angles attached to sterile handpieces for 60 seconds. They then analyzed the inside surfaces of the angle, nosecone and motor. They tested each prophy angle and handpiece 10 times.
Results. In the 160 tests of handpieces contaminated at the prophy cup end, the spores traveled into the motor gears 32 times (20 percent). In the other 160 tests in which the motor gears were contaminated, the test bacterium traveled through the prophy cup in 75 instances (47 percent).
Conclusions. The in vitro data suggest that low-speed handpiece motors can become contaminated internally during use with prophy angles. Also, internal contaminants appear to have been released from the handpiece.
Clinical Implications. The results suggest that low-speed hand-pieces can become contaminated internally during use. Unless low-speed handpieces are sterilized properly between patients, they may become cross-contaminated.
Key Words: Infection control; handpiece; prophy angle; Geobacillus stearothermophilus; equipment contamination; sterilization
The Centers for Disease Control and Prevention recommends that dentists "clean and heat-sterilize handpieces and other intraoral instruments that can be removed from the air and waterlines of dental units between patients."1 Several studies have recommended heat sterilization of high-speed handpieces because of the potential for internal contamination during use.2–9 The justification for the heat sterilization of the low-speed handpiece system is less clear. Pressurized air is needed to operate the air-driven low-speed handpiece. This air must escape or be reduced to eliminate excessive heat buildup. All disposable and reusable types of prophy angles have a vent or opening to reduce or eliminate excessive heat buildup. This vent may allow internal contamination of a low-speed handpiece system because it is not a sealed system. This could lead to subsequent cross-contamination unless the handpiece is heat-sterilized between uses. However, there is only preliminary information concerning the internal contamination of low-speed handpiece systems during use.10
Thus, we conducted a study to determine the potential for internal contamination of low-speed handpiece motors and prophy angles and their potential for patient-to-patient transmission of organisms. We tested two hypotheses. The first was that microbes can enter the prophy-angle/handpiece system at the prophy angle end and travel to the gears of the air-driven handpiece motor. The second hypothesis was that microbes on the gears of the low-speed handpiece air-driven motor can travel to and be expelled from the prophy angle.
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MATERIALS AND METHODS
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Study design.
This study was conducted at a single center, with an eight-by-two crossover design using two types of low-speed handpieces attached to seven different brands of disposable and one brand of reusable prophy angle. In a crossover design, an object receives all treatments in sequence. By contrast, in a parallel-groups design, some objects get the first treatment and different objects get the second treatment. The crossover design represents a special situation in which there is not a separate comparison group. In effect, each object serves as its own control. Also, since the same object receives both treatments, there is no possibility of covariate imbalance.
Low-speed handpieces.
Two different styles of air-driven low-speed handpieces were used for this study. One was the Prophy Star single piece low-speed handpiece (Star Dental, Lancaster, Pa.), and the other was the Titan 3 two-piece low-speed handpiece (Star Dental). Both were connected to the dental unit using a four-line swivel attachment (360 Quick Connect Swivel, Star Dental). We cleaned and sterilized the handpieces in a steam autoclave at 1,210 C for 30 minutes before use and after testing with each type of prophy angle.
Prophy angles.
We used eight types of prophy angles, seven disposable and one reusable. The seven disposable angles we used were
- – Acclean firm cup (Henry Schein, Melville, N.Y.);
- – Classic Traditional Web (Young Dental, Earth City, Mo.);
- – Classic Twin Rib GUM (Sunstar Butler, Chicago);
- – Clinpro Firm (3M ESPE, St. Paul, Minn.);
- – DENSCO Firm Yellow (Waterpik Technologies, Newport Beach, Calif.);
- – Nupro revolv (Dentsply, York, Pa.);
- – Original Green regular (Denticator, Earth City, Mo.).
The reusable metal prophy angle we used was the TS2 Prophy Angle (Young Dental), with a disposable screw-type prophy cup (Classic Traditional Web, Young Dental).
Experiment 1: testing for the spread of microbes from the prophy angle to the handpiece motor.
We covered a sterile hand-piece with a disposable plastic sleeve (Lowspeed Handpiece Sleeve, Denticator) and attached a prophy-angle with a cup. We then partially wrapped the prophy angle/handpiece unit with plastic wrap to further prevent contamination from the outside. The prophy angle’s vent was not covered. We submerged the prophy angle head aseptically in 12.5 milliliters of a suspension of sterile phosphate-buffered saline (PBS, Sigma Chemical, St. Louis) containing 2.0 x 106 colony-forming units per mL of Geobacillus stearothermophilus spores (ATCC 7953, Ethox International, STS Life Sciences Division, Rush, N.Y.) and 10 percent by volume of sterile defibrinated sheep blood (Colorado Serum, Denver). The spore/blood suspension was contained in a sterile 60-mL Pyrex centrifuge tube (No. 8540, Corning, Corning, N.Y.) (Figure 1
). We covered the tube with a sterilized piece of aluminum foil to prevent external aerosol contamination.
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Figure 1. Handpiece system wrapped with plastic barriers and being tested for internal spread of contamination.
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We turned on the handpiece and pressed the prophy cup against the inside walls of the tube and ran it 30 times within 60 seconds to simulate use. We then blotted the prophy angle/handpiece with a paper towel to remove excess external liquid and removed the plastic wraps aseptically. We donned fresh sterile gloves, separated the handpiece components, and carefully sampled and cultured the gears of the handpiece motor as described in the following section (Microbiological Analysis). We repeated each of the 16 combinations (eight types of prophy angles and two types of handpieces) 10 times with new sterilized hand-pieces and prophy angles, for a total of 160 units tested. As a negative control, we tested and sampled 20 uncontaminated handpieces to detect any microbial contamination from the environment. The negative controls tested consisted of 10 single-unit handpieces and 10 two-unit hand-pieces. We used only one brand of prophy angle (Classic Twin Rib GUM disposable) for all negative controls.
Experiment 2: testing for the spread of microbes from the handpiece motor to the prophy angle.
We placed 0.1 mL of 2.0 x 106 CFU/mL G. stearothermophilus in PBS containing 10 percent sheep blood on the motor gears of a sterilized handpiece (Figure 2). We covered the handpiece with a plastic sleeve and attached a prophy-angle with cup. We partially wrapped the prophy angle/handpiece unit with plastic wrap to further prevent outside contamination. The prophy angle’s vent was not covered. We submerged the prophy angle head in 12.5 mL of sterile PBS contained in a sterile 60-mL Pyrex glass centrifuge tube. We covered the tube with a sterilized piece of aluminum foil to prevent external aerosol contamination. We turned on the handpiece and pressed the prophy cup against the inside walls of the tube and ran it 30 times within 60 seconds. We removed the prophy angle/hand-piece from the tube and cultured the PBS as described in the section below (Microbiological Analysis). We tested each of the 16 combinations (eight types of prophy angles and two types of handpieces) 10 times with new sterilized hand-pieces and prophy angles, for a total of 160 units tested. As a negative control, we tested 20 uncon taminated handpieces and sampled them to detect any microbial contamination from the environment. The negative controls tested consisted of 10 single-unit handpieces and 10 two-unit hand-pieces. Again, we used only one brand of prophy angle (Classic Twin Rib GUM disposable) for all negative controls.
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MICROBIOLOGICAL ANALYSIS
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Experiment 1.
The goal of this analysis was to determine if the test spores had spread internally from the prophy angle to the handpiece motor after the simulated use. We disassembled the prophy-angle/handpiece units aseptically, taking great care not to contaminate the internal components. We sampled the gears of the handpiece motor with a cotton-tipped applicator (Figure 3). We then streaked the applicator onto trypticase soy agar (TSA) plates (Becton, Dickinson, Sparks, Md.), which we placed into trypticase soy broth (TSB) supplemented with 0.25 percent glucose (Becton, Dickinson). We incubated the TSA and TSB media for seven days at 56 C. After incubation, we analyzed both the TSA and TSB media for the presence of test bacteria. The appearance of turbidity in the TSB broth indicated microbial growth from the sampled site. We confirmed positive growth as G. stearothermophilus by analysis of distinctive white colonies of gram-positive rods on the 56 C TSA plates.
Experiment 2.
The goal of this analysis was to determine if the test spores had spread internally from the handpiece motor to the prophy angle and out into the environment after the simulated use. We analyzed the PBS in which the prophy head was submerged for the presence of test spores. To do so, we streaked an aliquot of the PBS onto a TSA plate, then added an equal volume of double-strength TSB to the remaining PBS and incubated it at 56 C for seven days. Turbidity indicated positive growth, which we analyzed on TSA plates for G. stearothermophilus as described above.
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RESULTS
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Experiment 1: Testing for the spread of microbes from the prophy angle to the handpiece motor.
Sampling of the 20 uncontaminated negative control handpieces did not reveal bacterial growth. Table 1 shows the results from the test handpiece units. Of the 80 prophy-angle/single-unit handpiece systems tested, seven exhibited test spores on the motor gears. Of the 80 prophy-angle/two-unit handpiece systems tested, 25 exhibited test spores on the motor gears. In total, in the 160 tests of handpieces contaminated at the prophy cup end, the spores traveled into the motor gears 32 times (20 percent).
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TABLE 1 Number of prophy angle/handpiece units showing spread of bacteria from the prophy angle head to the handpiece motor gears.
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Experiment 2: Testing for the spread of microbes from the handpiece motor to the prophy angle.
Sampling of the uncontaminated control handpieces did not reveal bacterial growth. Table 2 shows the results from the test handpiece units. Of the 80 prophy angle/single-unit handpiece systems tested, 30 released test spores into the PBS in which the prophy-angle head was submerged. Of the 80 prophy angle/two-unit handpiece systems tested, 45 released the test spores into the PBS in which the prophy angle head was submerged. In total, in the 160 tests in which the motor gears were contaminated, the test bacterium traveled through the prophy cup in 75 instances (47 percent).
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TABLE 2 Number of prophy angle/handpiece units showing spread of bacteria from the handpiece motor out through the prophy angle.
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DISCUSSION
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The results from this in vitro study substantiate those of an earlier preliminary study using similar methodology with Serratia marcescens as the test microbe.9 In our study, operation of prophy-angle/handpiece systems in a microbial environment resulted in movement of those microbes internally from the prophy angle to the gears of the handpiece motor in 9 percent of the single-unit handpiece systems studied and in 31 percent of the two-unit handpiece systems studied. These results support the first hypothesis for this study, that microbes can enter the prophy-angle/handpiece system at the prophy angle end and travel to the gears of the air-driven handpiece motor. They also support a recommendation to clean and heat-sterilize low-speed handpiece motors, nose cones and reusable prophy-angles between patients.
There were differences in levels of contamination between single- and two-unit handpiece systems, as well as between disposable plastic and reusable metal prophy angles. Differences between the types of handpieces may be attributed to the areas tested. We were able to test four areas of the two-unit handpiece system versus three areas of the single-unit handpiece system. The single-piece handpiece system is factory-sealed between the motor of the handpiece and the gears of the motor, so we could not analyze this area. If we could have done so, it could have shown higher levels of contamination than in the two-unit handpiece system. The plastic disposable prophy angles had higher levels of contamination than did the reusable metal prophy angle. This may be attributed to the fact that we tested only one brand of reusable metal angle versus seven disposable plastic angles. This study analyzed the more common prophy angles available in the United States, and we did not test all available prophy angles.
The results also supported the second hypothesis in this study—that microbes on the gears of the low-speed handpiece air-driven motor can travel to and be expelled from the prophy angle. This release was demonstrated in 38 percent of the single-unit handpiece systems tested and 56 percent of the two-unit handpiece systems tested. Therefore, this suggests that the internally contaminated handpiece systems have a potential to contribute to cross-contamination between patients unless those handpiece motors, nose cones and reusable angles are heat-sterilized between uses. So decontaminating (for example, wiping off) just the outside of these items between patients would not prevent potential for cross-contamination.
Conditions of actual use of low-speed hand-pieces in the mouth differ from the simulated use involved in this study. Such differences would include the number and types of microbes involved, the degree of stress placed on the prophy cups, the types of prophy angles and handpieces used, and the length of time the hand-piece system is operated. A follow-up study analyzing the internal surfaces of low-speed hand-piece systems actually used on patients would be valuable. Although there could be a small chance for outside contamination of the internal portions of the handpiece systems tested in this study, we took great care to prevent this by using plastic barriers and other aseptic techniques. Also, we detected no environmental contamination in the control handpieces.
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CONCLUSIONS
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The results of this in vitro study suggest that the internal portions of some low-speed handpiece motors have the potential to become contaminated during use with prophy angles. They also show that there is a potential for internal contaminants to be released through the prophy angle into the mouth of a patient. This could contribute to transmission of organisms between patients if low-speed handpiece motors, components and prophy angles are not heat-sterilized between uses. Future clinical trials analyzing the internal surfaces of low-speed handpiece systems actually used on patients are recommended.
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FOOTNOTES
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Dr. Chin is an associate professor, Oral Health Research Institute, School of Dentistry, Indiana University, 415 Lansing St., Indianapolis, Ind. 46202, e-mail "jchin{at}iupui.edu". Address reprint requests to Dr. Chin.
Dr. Miller is the executive associate dean and a professor of oral microbiology, School of Dentistry, Indiana University, Indianapolis.
Dr. Palenik is the sponsored research manager, School of Dentistry, Indiana University, Indianapolis.
The authors would like to thank Kenneth Burgess, Huong Vu, Richard Le and Sharon Gwinn for their expertise and assistance with this study.
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S. Herd, J. Chin, C. J. Palenik, and S. Ofner
The in vivo contamination of air-driven low-speed handpieces with prophylaxis angles
J Am Dent Assoc,
October 1, 2007;
138(10):
1360 - 1365.
[Abstract]
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ABSTRACT
MATERIALS AND METHODS
