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Internal contamination of air-driven
low-speed handpieces and attached prophy
angles
Judith R. Chin, DDS, MS; Chris H. Miller, MS, PhD; Charles John Palenik, MS, PhD, MBA
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Background. In an in vitro crossover study, the
authors investigated whether the interior of lowN
C
speed handpiece/prophy-angle systems becomes conU
A ING EDU 3
taminated during operation and submersion into
RT
ICLE
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 handpieces 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.
JADA 2006;137(9):1275-80.
T
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ABSTRACT
CON
he Centers for Disease
Control and Prevention
recommends that dentists “clean and heatsterilize 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
Dr. Chin is an associate professor, Oral Health Research Institute, School of Dentistry, Indiana University, 415 Lansing St., Indianapolis, Ind. 46202, e-mail “[email protected]”. 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.
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September 2006
1275
R E S E A R C H
contamination of low-speed handpiece motors and
prophy angles and their potential for patient-topatient 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.
MATERIALS AND METHODS
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 lowspeed 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
dAcclean firm cup (Henry Schein, Melville,
N.Y.);
dClassic Traditional Web (Young Dental, Earth
City, Mo.);
dClassic Twin Rib GUM (Sunstar Butler,
Chicago);
dClinpro Firm (3M ESPE, St. Paul, Minn.);
dDENSCO Firm Yellow (Waterpik Technologies,
Newport Beach, Calif.);
dNupro revolv (Dentsply, York, Pa.);
dOriginal Green regular (Denticator, Earth City,
Mo.).
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JADA, Vol. 137
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 handpiece 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 × 106 colonyforming 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.
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 handpieces 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 handpieces. 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 × 106
CFU/mL G. stearothermophilus in PBS con-
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R E S E A R C H
Figure 2. Inoculation of the single-unit handpiece motor.
Figure 1. Handpiece system wrapped with plastic barriers and
being tested for internal spread of contamination.
taining 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/handpiece 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 handpieces and prophy angles, for a total of 160 units
Figure 3. Sampling the handpiece motor.
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 handpieces. Again, we used only one brand of prophy
angle (Classic Twin Rib GUM disposable) for all
negative controls.
MICROBIOLOGICAL ANALYSIS
Experiment 1. The goal of this analysis was to
determine if the test spores had spread internally
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September 2006
1277
R E S E A R C H
TABLE 1
Number of prophy angle/handpiece units showing
spread of bacteria from the prophy angle head to the
handpiece motor gears.
TYPE OF PROPHY ANGLE
SINGLE-UNIT
HANDPIECE†
TWO-UNIT
HANDPIECE†
Acclean
Disposable
1/10
3/10
Classic Traditional Web
Disposable
0/10
8/10
Classic Twin Rib GUM
Disposable
2/10
2/10
PROPHY ANGLE*
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.
RESULTS
Experiment 1: Testing
for the spread of
microbes from the
Disposable
0/10
2/10
Clinpro
prophy angle to the
Disposable
1/10
2/10
DENSCO Firm Yellow
handpiece motor. SamDisposable
0/10
8/10
Nupro revolv
pling of the 20 uncontaminated negative control
Disposable
2/10
0/10
Original Green
handpieces did not reveal
Metal
1/10
0/10
TS2 Prophy Angle
bacterial growth. Table 1
Not applicable
7/80
25/80
TOTALS
shows the results from the
test handpiece units. Of the
* The angles’ manufacturers are as follows: Acclean firm cup (Henry Schein, Melville, N.Y.); Classic
Traditional Web (Young Dental, Earth City, Mo.); Classic Twin Rib GUM (Sunstar Butler, Chicago);
80 prophy-angle/single-unit
Clinpro Firm (3M ESPE, St. Paul, Minn.); DENSCO Firm Yellow (Waterpik Technologies, Newport Beach,
handpiece systems tested,
Calif.); Nupro revolv (Dentsply, York, Pa.); Original Green regular (Denticator, Earth City, Mo.); TS2
Prophy Angle (Young Dental).
seven exhibited test spores
† Number with positive motor gears over total number of units tested.
on the motor gears. Of the
80 prophy-angle/two-unit
handpiece systems tested, 25 exhibited test
from the prophy angle to the handpiece motor
spores on the motor gears. In total, in the 160
after the simulated use. We disassembled the
tests of handpieces contaminated at the prophy
prophy-angle/handpiece units aseptically, taking
cup end, the spores traveled into the motor gears
great care not to contaminate the internal compo32 times (20 percent).
nents. We sampled the gears of the handpiece
Experiment 2: Testing for the spread of
motor with a cotton-tipped applicator (Figure 3).
microbes from the handpiece motor to the
We then streaked the applicator onto trypticase
prophy angle. Sampling of the uncontaminated
soy agar (TSA) plates (Becton, Dickinson, Sparks,
control handpieces did not reveal bacterial
Md.), which we placed into trypticase soy broth
growth. Table 2 shows the results from the test
(TSB) supplemented with 0.25 percent glucose
handpiece units. Of the 80 prophy angle/single(Becton, Dickinson). We incubated the TSA and
unit handpiece systems tested, 30 released test
TSB media for seven days at 56 C. After incubation, we analyzed both the TSA and TSB media
spores into the PBS in which the prophy-angle
for the presence of test bacteria. The appearance
head was submerged. Of the 80 prophy angle/twoof turbidity in the TSB broth indicated microbial
unit handpiece systems tested, 45 released the
growth from the sampled site. We confirmed positest spores into the PBS in which the prophy
tive growth as G. stearothermophilus by analysis
angle head was submerged. In total, in the 160
of distinctive white colonies of gram-positive rods
tests in which the motor gears were contamion the 56 C TSA plates.
nated, the test bacterium traveled through the
Experiment 2. The goal of this analysis was
prophy cup in 75 instances (47 percent).
to determine if the test spores had spread interDISCUSSION
nally from the handpiece motor to the prophy
angle and out into the environment after the simThe results from this in vitro study substantiate
ulated use. We analyzed the PBS in which the
those of an earlier preliminary study using simprophy head was submerged for the presence of
ilar methodology with Serratia marcescens as the
test spores. To do so, we streaked an aliquot of
test microbe.9 In our study, operation of prophythe PBS onto a TSA plate, then added an equal
angle/handpiece systems in a microbial environvolume of double-strength TSB to the remaining
ment resulted in movement of those microbes
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JADA, Vol. 137
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R E S E A R C H
internally from the prophy TABLE 2
angle to the gears of the
Number of prophy angle/ handpiece units showing
handpiece motor in 9 perspread of bacteria from the handpiece motor out
cent of the single-unit
through the prophy angle.
handpiece systems studied
and in 31 percent of the
TWO-UNIT
SINGLE-UNIT
PROPHY ANGLE*
TYPE OF PROPHY ANGLE
HANDPIECE
HANDPIECE
two-unit handpiece systems
studied. These results sup- Acclean
10/10
3/10
Disposable
port the first hypothesis for
4/10
4/10
Disposable
Classic Traditional Web
this study, that microbes
5/10
3/10
Disposable
Classic Twin Rib GUM
can enter the prophyangle/handpiece system at
7/10
8/10
Disposable
Clinpro
the prophy angle end and
2/10
3/10
Disposable
DENSCO Firm Yellow
travel to the gears of the
8/10
5/10
Disposable
air-driven handpiece motor. Nupro revolv
They also support a recom- Original Green
7/10
2/10
Disposable
mendation to clean and
1/10
2/10
Metal
TS2 Prophy Angle
heat-sterilize low-speed
45/80
30/80
Not applicable
TOTALS
handpiece motors, nose
cones and reusable prophy- * The angles’ manufacturers are as follows: Acclean firm cup (Henry Schein, Melville, N.Y.); Classic
Traditional Web (Young Dental, Earth City, Mo.); Classic Twin Rib GUM (Sunstar Butler, Chicago);
angles between patients.
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.); TS2
There were differences in
Prophy Angle (Young Dental).
levels of contamination
† Number with positive motor gears over total number of units tested.
between single- and twounit handpiece systems, as well as between discontribute to cross-contamination between
posable plastic and reusable metal prophy angles.
patients unless those handpiece motors, nose
Differences between the types of handpieces may
cones and reusable angles are heat-sterilized
be attributed to the areas tested. We were able to
between uses. So decontaminating (for example,
test four areas of the two-unit handpiece system
wiping off) just the outside of these items between
versus three areas of the single-unit handpiece
patients would not prevent potential for crosssystem. The single-piece handpiece system is
contamination.
factory-sealed between the motor of the handpiece
Conditions of actual use of low-speed handpieces in the mouth differ from the simulated use
and the gears of the motor, so we could not anainvolved in this study. Such differences would
lyze this area. If we could have done so, it could
include the number and types of microbes
have shown higher levels of contamination than
involved, the degree of stress placed on the
in the two-unit handpiece system. The plastic disprophy cups, the types of prophy angles and
posable prophy angles had higher levels of contahandpieces used, and the length of time the handmination than did the reusable metal prophy
piece system is operated. A follow-up study anaangle. This may be attributed to the fact that we
lyzing the internal surfaces of low-speed handtested only one brand of reusable metal angle
piece systems actually used on patients would be
versus seven disposable plastic angles. This study
valuable. Although there could be a small chance
analyzed the more common prophy angles availfor outside contamination of the internal portions
able in the United States, and we did not test all
of the handpiece systems tested in this study, we
available prophy angles.
took great care to prevent this by using plastic
The results also supported the second hypothbarriers and other aseptic techniques. Also, we
esis in this study—that microbes on the gears of
detected no environmental contamination in the
the low-speed handpiece air-driven motor can
control handpieces.
travel to and be expelled from the prophy angle.
This release was demonstrated in 38 percent of
CONCLUSIONS
the single-unit handpiece systems tested and 56
The results of this in vitro study suggest that the
percent of the two-unit handpiece systems tested.
internal portions of some low-speed handpiece
Therefore, this suggests that the internally conmotors have the potential to become contamitaminated handpiece systems have a potential to
†
†
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September 2006
1279
R E S E A R C H
nated 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. ■
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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