nized potential danger is microbial contamination of the
Microbial Contamination of Dental Units and Ultrasonic Scalers
water system in dental units and accessories. Several investigators
5-8
studying bacterial colonization of dental
units have reported concentrations of microorganisms in water samples from air-turbine handpieces and air-water syringes of up to 10,000,000/ml. Yet little information is available on the presence and extent of microbial contamination of ultrasonic scalers. This report provides such information and additional data on microbial levels
by
in the water system of dental units.
ARTHUR GROSS, D.D.S., M.S.* MATERIALS
M A R Y J . DEVINE D U A N E E . CUTRIGHT, D.D.S., PH.D.
AND METHODS
Water samples from 12 dental units at two A r m y dental clinics were tested for microbial contamination. During the periods of nonuse (overnight and weekends) the orifices of the equipment to be tested were covered
T H E R E IS I N C R E A S E D evidence that in modern dental practice both patients and dentist are subjected to health hazards of varying degrees of severity. Use of dental equipment has been shown to be responsible for the production of aerosols containing high concentrations of microorganisms. Although definite proof of transmission of infectious diseases by aerosols in dental operato-
with sterile gauze to prevent contamination by microorganisms that may have been suspended in the environment. Approximately 2-ml water samples from highspeed
1-4
TABLE I. Microbial
Concentration
in Ultrasonic
engine lines
with or without
the
handpieces
attached, air-water syringes and ultrasonic scalers with no tips attached were aseptically obtained prior to regu-
Scaler
Water Lines before and after 2 Minute
Flushing
M i c r o b i a l counts (cfu/ml) Day A*
Bt Flushing time (minutes)
3
1.5
4
1.6
x x x x
1.1
x
1 2
5.1 3.2
10
10
4.9
x x x x
8.0
x
10
4.3
5
10
4
1.1
10
6
2.3
10
6
10
5
2.6
2
10
3
1.8
10
4
2.2
10
3
1.1
2
9.4
5 6 7
2
0
2
0
6.8
x x x x
10
x x
10
5
1.5
10
4
2.0
6
1.5
10
4
5.4
10
5
1.2
6
3.5
10
8
x x x x
10
x x
10
3
10
3
4
10
3
10
5
10
1
x x
10
3
2.4
2
1.7
5
5.5
4
3.0
10
2
5.5
10
3
5.3
x x
10
4
x x
10
10
x x
10
3.6
10
3
12
2.8
x
10
5
4.0
x
10
1
1.6
x
10
5
1.3
x
10
Mean
50.9
x
10
4
0.39
x
10
4
58.7
x
10
4
2.3
x
9 10
7.4
11
l
10
3
4
* After weekend, t Another weekday.
lar use early in the morning both following the weekend and on another week day. After sampling, all tested lines were flushed immediately with dental unit main line water for 2 minutes, and approximately 2-ml samples were again collected. Water samples from faucets in the dental clinics were also obtained before daily use. These lines were flushed for 5 minutes and another 2-ml sample was collected to determine the possible microbial
ries is still lacking, their infectious potential should not be disregarded. The elimination of possible sources of microbial infection in dental operatories should be of primary importance. One such source of a frequently unrecog* Division of Basic Sciences, United States A r m y Institute of Dental Research, Walter Reed A r m y M e d i c a l Center, Washington, D . C . 20012.
670
Volume 47 Number 11
Microbial
Contamination
671
contamination in water mains. A l l samples were serially
indicated by the lowest count of 35 cfu/ml (unit 4) and
diluted, using sterile tap water as a diluent. Aliquots
the highest count of 120,000 cfu/ml (unit 3). Comparison
(0.1 ml) of dilutions were plated on trypticase soy agar
of the means of 3,900 cfu/ml for 8 devices and 23,000
and incubated aerobically at 3 5 ° C for 7 days. Colony
cfu/ml for 9 devices points to the variability in microbial
forming units (cfu) were counted after 48 hours and 7
reduction on different days.
days. High-speed Handpieces RESULTS
Microbial contamination of high-speed handpiece lines (Table II) did not differ significantly from that of
The results of 48-hour and 7-day incubations have shown great difference in cfu counts. The majority of
ultrasonic scaler lines. Microbial concentrations before
samples showed cfu counts 2 to 10 times higher after 7
daily use ranged from 5,700 (unit 10) to 3.3 million
days than after 48 hours. Differences
cfu/ml (unit 3). Longer periods of nonuse (weekends)
among some
samples were smaller, but in others 100- to
did not appear to increase bacterial levels in water from
1,000-fold
increases were observed upon prolonged incubation. This
these lines. Most handpiece lines showed slightly greater
was particularly evident in samples which after a 48-hour
contamination after overnight nonuse than after weekend
incubation period appeared to be sterile, but upon fur-
nonuse as indicated by means of 929,000 cfu/ml and
ther incubation were shown to yield 1,000 or even more
285,000 cfu/ml respectively, but this is probably due to
c f u / m l . The morphology of the colonies which appeared
daily variations as stated above. The means of 10,000 and
after prolonged incubation was markedly different from
98,000 cfu/ml on two different days indicate that 2
that present after 48 hours. The samples from the water
minutes flushing did not significantly reduce microbial
faucets yielded 0 to 63 cfu/ml and 0 to 3 cfu/ml before
concentrations of the line water.
and after flush respectively. Water Syringe Lines
The results shown in Tables I to III represent counts
Water samples from water syringe lines (Table III) showed much lower microbial counts than samples from ultrasonic scaler and high-speed handpiece lines. N o bacteria or fungi were recovered from one water syringe (unit 4), which is in contrast to a sample from another unit with 190,000 cfu/ml (unit 7). Counts from the majority of the 12 units, however, ranged from 1,000 to 10,000 cfu/ml. Because of the very high count in one unit, as indicated above, the mean count reached a value
after 7 days of incubation. Ultrasonic Scalers Microbial levels in water from ultrasonic scaler lines (Table I) ranged from 5,500 to 2.6 million cfu/ml with means of 509,000 and 587,000 on two different days. A two-minute flushing of the scaling devices reduced the bacterial contamination, but complete decontamination was not achieved. The effectiveness of flushing varied, as TABLE II. Microbial
Concentration
in High-Speed
Handpiece
Lines before and after 2 Minute
Flushing
M i c r o b i a l counts (cfu/ml) Day A*
Bt Flushing time (minutes)
0
2
2
0
1 2 3
2.4
4
1.3
5
2.0
x x x x x
10
5
1.6
10
4
2.2
10
5
3.0
10
5
1.3
10
5
4.3
x x x x x
10
4
1.6
10
3
2.7
10
4
5.7
10
3
4.6
10
3
10
4
10
4
3.3
10
3
4.4
10
3
8.8
x x x x x
10
6
5.7
10
5
7.5
10
6
1.0
10
5
2.6
10
5
6.6
x x x
10
3
10
4
x x
10
5
10
3
10
2
10
5
6 7
2.5
8
4.3
9
9.6
x x x
28.5
x
10
1.0
11
3.2
12 Mean * After weekend, †Another weekday.
10
6
1.6
10
5
4.0
10
4
9.6
x x x
10
4
1.0
x
10
3
2.8
x x x
10
4
9.8
x
10
4
10
3
6.0
10
5
7.7
4.8
x x x
10
5
92.9
x
10
4
672
J. Periodontal November, 1976
Gross, Devine, Cutright
TABLE III. Microbial Concentration in Air- Water Syringe Water Lines before and after 2 Minute Flushing M i c r o b i a l counts (cfu/ml) Day A*
B† Flushing time (minutes) 2
0
10
5.0
11
9.0
12
7.3
x x x x x x x x x x x x
Mean
2.0
x
1
5.1
2
1.1
3
1.1
4
2.3
5
1.3
6
73
7
1.9
8
3.0
9
1.0
10
3
7.0
10
5
1.0
10
3
2.0
10
4
1.0
10
3
2.3
10
3
4.1
10
3
9.7
x x x x x x x x x x x x
10
4
0.04
x
2.2
10
3
10
3
1.0
10
3
5.0
10
3
2.0
10
3
1.0
2
0 10
3
7.3
10
3
8.7
10
1
5.2
10
1
x x x
2
10
3
2.3
10
3
2.6
x x
10
3
2.0
x
10
0
10
1
1.5
10
2
2.1
10
2
6.0
10
2
2.1
10
2
1.3
10
2
1.2
10
2
2.4
10
4
0.36
x
1.9
2
10
3
10
3
10
1
0
0
x x x x x x x x
10
10
0
10
3
10
4
10
1
1.0
10
3
4.0
10
3
1.0
10
2
10
2
1.0
4
0.04
0
x x x
10
1
10
1
10
1
x
10
1
x
10
4
0
* After weekend, †Another weekday.
of 20,000 cfu/ml on one day of sampling but fell to 360 cfu/ml on another. The reduction of microbial concentration in water syringe samples following 2 minutes flushing as evidenced by the identical means of 400 cfu/ml on two different days, was much greater than that for other lines tested. Also, it should be pointed out that two minutes flushing resulted in complete elimination of bacterial contamination in water syringe lines of 5 out of 12 units on one day of testing. DISCUSSION
The results of this study confirm the findings by others of unusually high levels of microorganisms in water hoses to high-speed handpieces and water syringes. The quantitative differences between our determinations and those of others may be due to several factors such as length of nonuse, chlorination of water, daily fluctuations in levels of contamination, and the length of incubation of inoculated culture media. Growth of fungi and of many water bacteria cannot be detected after 48 hours incubation. Therefore longer incubation periods are necessary for accurate and reliable detection of microbial contamination of the water supply. 5-8
Since all ultrasonic scalers tested received their water supply from the water systems of the dental units to which they were attached, the finding of extremely high contamination similar to that of high-speed handpiece lines was not surprising. Simultaneous flushing of the tested supply lines for 2 minutes reduced the microbial population up to 99.2, 96.5 and 98.0% for ultrasonic devices, high-speed handpieces and water syringes, respectively. The percentage of reduction, however, should not be considered an indication or proof of the effective-
ness of this decontamination method since the mean microbial counts remained high, ranging from 400 to 98,000 cfu/ml. Even counts of 400 cfu/ml should be considered excessive, especially when irrigation or use of water-cooled rotary instruments and ultrasonic scalers is necessary during surgical procedures. Pelleu and Wachtel reported reduction of bacteria to less than 10 cfu/ml in most units following 2 minutes flushing and therefore recommended daily flushing of all dental units for at least 2 minutes before regular use. They stated, however, that persistently contaminated dental units required prolonged flushing time. 5
Our results indicate that 2-minute flushings failed to reduce microbial concentration of water samples to similar levels. This may be attributed to the different procedures employed and to a more persistent colonization of our dental unit water system. Spraying the contaminated water into the patient's mouth with the associated production of aerosols is potentially hazardous both for the patient and dental personnel. Ultrasonic scalers have been shown to be responsible for formation of aerosols containing indigenous and transient organisms of the oral cavity as well as other microorganisms, probably water contaminants. tn another study some of the bacteria from air-rotor water systems have been identified as Pseudomonas species (probably Pseudomonas aeruginosa and Pseudomonas cepacia) and Klebsiella species. These organisms, possibly originating from contaminated water, have been shown to be constituents of the abnormal nasal flora of dentists and dental assistants. Although in our study definite identification of all microorganisms was not attempted, it was observed that water samples from 1
8
Volume 47 Number 11
Microbial
several units were heavily contaminated with Pseudomonas spp. and fungi which were not further identified. Some Pseudomonas species are known to have a pathogenic potential, particularly in debilitated patients and those overtreated with broad spectrum antibiotics or corticosteroids. 9
The possibility of transmission of infections by aerosols to dental personnel through the respiratory route has been repeatedly pointed out. Less attention has been focused on another potential hazard, namely, bacteremia that may be caused by forcing microbial water contaminants through gingival crevices or periodontal pockets during scaling with ultrasonic devices, or during surgical procedures requiring water irrigation and use of watercooled high-speed handpieces. Caution is especially advised when treating patients undergoing immunosuppressive or prolonged antibiotic and/or corticosteroid therapy since it has been shown that these patients are susceptible to infections caused by microorganisms that are considered to be nonpathogenic to healthy individuals. It has been shown that microbial levels in water systems of dental units and accessories are very high and that even after a 2-minute flushing exceed the safety limits for human consumption. Obviously there is a need for control of bacterial contamination of dental unit water lines either through modification of design or other means that would guarantee the sterility of the water introduced into the patient's mouth. Solutions of this problem are currently being sought. Until this is accomplished, it is recommended that dental units and accessories such as ultrasonic units be flushed for a period in excess of 2 minutes prior to the start of daily procedures. One should realize, however, that this procedure will, at best, reduce microbial concentrations in water systems to levels that should still be considered unacceptable.
Contamination
673
SUMMARY
Microbial contamination of the water system in 12 dental units and nine ultrasonic scalers was investigated. Water samples from ultrasonic scalers,
high-speed
handpieces and water syringe lines showed microbial concentrations of up to 2.6 million, 3.3 million and 190,000 colony forming units/ml respectively. Flushing the lines for 2 minutes reduced the microbial levels, but complete elimination of all bacteria was not achieved. The infectious potential of contaminated water, to the dentists and patients, particularly the compromised host is discussed. REFERENCES
1. Larato, D. C , Ruskin, P. F., and Martin, A.: Effect of an ultrasonic scaler on bacterial counts in air. J Periodontal 38: 550, 1967. 2. Micik, R. E., Miller, R. L., Mazarella, M . A., and Ryge, G.: Studies on dental aerobiology: I. Bacterial aerosols generated during dental procedures. J Dent Res 48: 49, 1969. 3. Williams, G . H . Ill, Pollok, N . L . Ill, Shay, D. E., and Barr, C. E.: Laminar air purge of microorganisms in dental aerosols: Prophylactic procedures with the ultrasonic scaler. J Dent Res 49: 1948, 1970. 4. Nixon, G. S.: Occupational hazards in dentistry. Community Health (Bristol) 3: 221, 1972. 5. Pelleu, G. B. Jr., and Wachtel, L. W.: Microbial contamination in dental unit warm water systems. NDS-TR-009. Naval Dental School, National Naval Medical Center, Bethesda, Md., 1969. 6. Abel, L . C , Miller, R. L . , Micik, R. E. and Ryge, G.: Studies on dental aerobiology: IV. Bacterial contamination of water delivered by dental units. J Dent Res 50: 1567, 1971. 7. McEntegart, M . G . , and Clark, A.: Colonization of dental units by water bacteria. Br Dent J 134: 140, 1973 8. Clark, A. Bacterial colonization of dental units and the nasal flora of dental personnel. Proc R Soc Med 67: 1269, 1974. 9. Davis, B. D., Dulbecco, R., Eisen, H . N . , Ginsberg, H . E., and Wood, W. B. Jr.: Microbiology, ed 2, p 783. Hagerstown, Harper & Row, 1973.
Announcement INTERNATIONAL
CONFERENCE ON PERIODONTAL
purpose of the investigation, materials and methods, and results (if available) should be submitted to:
RESEARCH Stockholm, Sweden
DOCTOR JAN LINDHE Department of Periodontology
June, 1978
University of Goteborg A 3-day international conference on periodontal research will be held in Stockholm, Sweden June 26-28,
1978. The conference is
sponsored by the Periodontal Research G r o u p of the I . A . D . R . Support for
the conference has been obtained from the Proctor & Gamble
by July 1, 1977. The
conference will cover travel expenses based on economy jet
excursion fare and per diem for expected speakers.
Company. Individuals wishing to present original research, relative to periodontology
400 33 Goteborg 33, Sweden
and not
previously published, are invited to submit
A l l reports and summary discussions will be published in the Journal of Periodontal Research during 1978. Each speaker will be requested to
abstracts for consideration by the program committee. Abstracts of
submit a final abstract (maximum 500 words) no later than immedi-
approximately 200 words giving title, author's name and affiliation,
ately before the presentation of his/her paper.
Microbial Contamination of Dental Units and Ultrasonic Scalers
water system in dental units and accessories. Several investigators
5-8
studying bacterial colonization of dental
units have reported concentrations of microorganisms in water samples from air-turbine handpieces and air-water syringes of up to 10,000,000/ml. Yet little information is available on the presence and extent of microbial contamination of ultrasonic scalers. This report provides such information and additional data on microbial levels
by
in the water system of dental units.
ARTHUR GROSS, D.D.S., M.S.* MATERIALS
M A R Y J . DEVINE D U A N E E . CUTRIGHT, D.D.S., PH.D.
AND METHODS
Water samples from 12 dental units at two A r m y dental clinics were tested for microbial contamination. During the periods of nonuse (overnight and weekends) the orifices of the equipment to be tested were covered
T H E R E IS I N C R E A S E D evidence that in modern dental practice both patients and dentist are subjected to health hazards of varying degrees of severity. Use of dental equipment has been shown to be responsible for the production of aerosols containing high concentrations of microorganisms. Although definite proof of transmission of infectious diseases by aerosols in dental operato-
with sterile gauze to prevent contamination by microorganisms that may have been suspended in the environment. Approximately 2-ml water samples from highspeed
1-4
TABLE I. Microbial
Concentration
in Ultrasonic
engine lines
with or without
the
handpieces
attached, air-water syringes and ultrasonic scalers with no tips attached were aseptically obtained prior to regu-
Scaler
Water Lines before and after 2 Minute
Flushing
M i c r o b i a l counts (cfu/ml) Day A*
Bt Flushing time (minutes)
3
1.5
4
1.6
x x x x
1.1
x
1 2
5.1 3.2
10
10
4.9
x x x x
8.0
x
10
4.3
5
10
4
1.1
10
6
2.3
10
6
10
5
2.6
2
10
3
1.8
10
4
2.2
10
3
1.1
2
9.4
5 6 7
2
0
2
0
6.8
x x x x
10
x x
10
5
1.5
10
4
2.0
6
1.5
10
4
5.4
10
5
1.2
6
3.5
10
8
x x x x
10
x x
10
3
10
3
4
10
3
10
5
10
1
x x
10
3
2.4
2
1.7
5
5.5
4
3.0
10
2
5.5
10
3
5.3
x x
10
4
x x
10
10
x x
10
3.6
10
3
12
2.8
x
10
5
4.0
x
10
1
1.6
x
10
5
1.3
x
10
Mean
50.9
x
10
4
0.39
x
10
4
58.7
x
10
4
2.3
x
9 10
7.4
11
l
10
3
4
* After weekend, t Another weekday.
lar use early in the morning both following the weekend and on another week day. After sampling, all tested lines were flushed immediately with dental unit main line water for 2 minutes, and approximately 2-ml samples were again collected. Water samples from faucets in the dental clinics were also obtained before daily use. These lines were flushed for 5 minutes and another 2-ml sample was collected to determine the possible microbial
ries is still lacking, their infectious potential should not be disregarded. The elimination of possible sources of microbial infection in dental operatories should be of primary importance. One such source of a frequently unrecog* Division of Basic Sciences, United States A r m y Institute of Dental Research, Walter Reed A r m y M e d i c a l Center, Washington, D . C . 20012.
670
Volume 47 Number 11
Microbial
Contamination
671
contamination in water mains. A l l samples were serially
indicated by the lowest count of 35 cfu/ml (unit 4) and
diluted, using sterile tap water as a diluent. Aliquots
the highest count of 120,000 cfu/ml (unit 3). Comparison
(0.1 ml) of dilutions were plated on trypticase soy agar
of the means of 3,900 cfu/ml for 8 devices and 23,000
and incubated aerobically at 3 5 ° C for 7 days. Colony
cfu/ml for 9 devices points to the variability in microbial
forming units (cfu) were counted after 48 hours and 7
reduction on different days.
days. High-speed Handpieces RESULTS
Microbial contamination of high-speed handpiece lines (Table II) did not differ significantly from that of
The results of 48-hour and 7-day incubations have shown great difference in cfu counts. The majority of
ultrasonic scaler lines. Microbial concentrations before
samples showed cfu counts 2 to 10 times higher after 7
daily use ranged from 5,700 (unit 10) to 3.3 million
days than after 48 hours. Differences
cfu/ml (unit 3). Longer periods of nonuse (weekends)
among some
samples were smaller, but in others 100- to
did not appear to increase bacterial levels in water from
1,000-fold
increases were observed upon prolonged incubation. This
these lines. Most handpiece lines showed slightly greater
was particularly evident in samples which after a 48-hour
contamination after overnight nonuse than after weekend
incubation period appeared to be sterile, but upon fur-
nonuse as indicated by means of 929,000 cfu/ml and
ther incubation were shown to yield 1,000 or even more
285,000 cfu/ml respectively, but this is probably due to
c f u / m l . The morphology of the colonies which appeared
daily variations as stated above. The means of 10,000 and
after prolonged incubation was markedly different from
98,000 cfu/ml on two different days indicate that 2
that present after 48 hours. The samples from the water
minutes flushing did not significantly reduce microbial
faucets yielded 0 to 63 cfu/ml and 0 to 3 cfu/ml before
concentrations of the line water.
and after flush respectively. Water Syringe Lines
The results shown in Tables I to III represent counts
Water samples from water syringe lines (Table III) showed much lower microbial counts than samples from ultrasonic scaler and high-speed handpiece lines. N o bacteria or fungi were recovered from one water syringe (unit 4), which is in contrast to a sample from another unit with 190,000 cfu/ml (unit 7). Counts from the majority of the 12 units, however, ranged from 1,000 to 10,000 cfu/ml. Because of the very high count in one unit, as indicated above, the mean count reached a value
after 7 days of incubation. Ultrasonic Scalers Microbial levels in water from ultrasonic scaler lines (Table I) ranged from 5,500 to 2.6 million cfu/ml with means of 509,000 and 587,000 on two different days. A two-minute flushing of the scaling devices reduced the bacterial contamination, but complete decontamination was not achieved. The effectiveness of flushing varied, as TABLE II. Microbial
Concentration
in High-Speed
Handpiece
Lines before and after 2 Minute
Flushing
M i c r o b i a l counts (cfu/ml) Day A*
Bt Flushing time (minutes)
0
2
2
0
1 2 3
2.4
4
1.3
5
2.0
x x x x x
10
5
1.6
10
4
2.2
10
5
3.0
10
5
1.3
10
5
4.3
x x x x x
10
4
1.6
10
3
2.7
10
4
5.7
10
3
4.6
10
3
10
4
10
4
3.3
10
3
4.4
10
3
8.8
x x x x x
10
6
5.7
10
5
7.5
10
6
1.0
10
5
2.6
10
5
6.6
x x x
10
3
10
4
x x
10
5
10
3
10
2
10
5
6 7
2.5
8
4.3
9
9.6
x x x
28.5
x
10
1.0
11
3.2
12 Mean * After weekend, †Another weekday.
10
6
1.6
10
5
4.0
10
4
9.6
x x x
10
4
1.0
x
10
3
2.8
x x x
10
4
9.8
x
10
4
10
3
6.0
10
5
7.7
4.8
x x x
10
5
92.9
x
10
4
672
J. Periodontal November, 1976
Gross, Devine, Cutright
TABLE III. Microbial Concentration in Air- Water Syringe Water Lines before and after 2 Minute Flushing M i c r o b i a l counts (cfu/ml) Day A*
B† Flushing time (minutes) 2
0
10
5.0
11
9.0
12
7.3
x x x x x x x x x x x x
Mean
2.0
x
1
5.1
2
1.1
3
1.1
4
2.3
5
1.3
6
73
7
1.9
8
3.0
9
1.0
10
3
7.0
10
5
1.0
10
3
2.0
10
4
1.0
10
3
2.3
10
3
4.1
10
3
9.7
x x x x x x x x x x x x
10
4
0.04
x
2.2
10
3
10
3
1.0
10
3
5.0
10
3
2.0
10
3
1.0
2
0 10
3
7.3
10
3
8.7
10
1
5.2
10
1
x x x
2
10
3
2.3
10
3
2.6
x x
10
3
2.0
x
10
0
10
1
1.5
10
2
2.1
10
2
6.0
10
2
2.1
10
2
1.3
10
2
1.2
10
2
2.4
10
4
0.36
x
1.9
2
10
3
10
3
10
1
0
0
x x x x x x x x
10
10
0
10
3
10
4
10
1
1.0
10
3
4.0
10
3
1.0
10
2
10
2
1.0
4
0.04
0
x x x
10
1
10
1
10
1
x
10
1
x
10
4
0
* After weekend, †Another weekday.
of 20,000 cfu/ml on one day of sampling but fell to 360 cfu/ml on another. The reduction of microbial concentration in water syringe samples following 2 minutes flushing as evidenced by the identical means of 400 cfu/ml on two different days, was much greater than that for other lines tested. Also, it should be pointed out that two minutes flushing resulted in complete elimination of bacterial contamination in water syringe lines of 5 out of 12 units on one day of testing. DISCUSSION
The results of this study confirm the findings by others of unusually high levels of microorganisms in water hoses to high-speed handpieces and water syringes. The quantitative differences between our determinations and those of others may be due to several factors such as length of nonuse, chlorination of water, daily fluctuations in levels of contamination, and the length of incubation of inoculated culture media. Growth of fungi and of many water bacteria cannot be detected after 48 hours incubation. Therefore longer incubation periods are necessary for accurate and reliable detection of microbial contamination of the water supply. 5-8
Since all ultrasonic scalers tested received their water supply from the water systems of the dental units to which they were attached, the finding of extremely high contamination similar to that of high-speed handpiece lines was not surprising. Simultaneous flushing of the tested supply lines for 2 minutes reduced the microbial population up to 99.2, 96.5 and 98.0% for ultrasonic devices, high-speed handpieces and water syringes, respectively. The percentage of reduction, however, should not be considered an indication or proof of the effective-
ness of this decontamination method since the mean microbial counts remained high, ranging from 400 to 98,000 cfu/ml. Even counts of 400 cfu/ml should be considered excessive, especially when irrigation or use of water-cooled rotary instruments and ultrasonic scalers is necessary during surgical procedures. Pelleu and Wachtel reported reduction of bacteria to less than 10 cfu/ml in most units following 2 minutes flushing and therefore recommended daily flushing of all dental units for at least 2 minutes before regular use. They stated, however, that persistently contaminated dental units required prolonged flushing time. 5
Our results indicate that 2-minute flushings failed to reduce microbial concentration of water samples to similar levels. This may be attributed to the different procedures employed and to a more persistent colonization of our dental unit water system. Spraying the contaminated water into the patient's mouth with the associated production of aerosols is potentially hazardous both for the patient and dental personnel. Ultrasonic scalers have been shown to be responsible for formation of aerosols containing indigenous and transient organisms of the oral cavity as well as other microorganisms, probably water contaminants. tn another study some of the bacteria from air-rotor water systems have been identified as Pseudomonas species (probably Pseudomonas aeruginosa and Pseudomonas cepacia) and Klebsiella species. These organisms, possibly originating from contaminated water, have been shown to be constituents of the abnormal nasal flora of dentists and dental assistants. Although in our study definite identification of all microorganisms was not attempted, it was observed that water samples from 1
8
Volume 47 Number 11
Microbial
several units were heavily contaminated with Pseudomonas spp. and fungi which were not further identified. Some Pseudomonas species are known to have a pathogenic potential, particularly in debilitated patients and those overtreated with broad spectrum antibiotics or corticosteroids. 9
The possibility of transmission of infections by aerosols to dental personnel through the respiratory route has been repeatedly pointed out. Less attention has been focused on another potential hazard, namely, bacteremia that may be caused by forcing microbial water contaminants through gingival crevices or periodontal pockets during scaling with ultrasonic devices, or during surgical procedures requiring water irrigation and use of watercooled high-speed handpieces. Caution is especially advised when treating patients undergoing immunosuppressive or prolonged antibiotic and/or corticosteroid therapy since it has been shown that these patients are susceptible to infections caused by microorganisms that are considered to be nonpathogenic to healthy individuals. It has been shown that microbial levels in water systems of dental units and accessories are very high and that even after a 2-minute flushing exceed the safety limits for human consumption. Obviously there is a need for control of bacterial contamination of dental unit water lines either through modification of design or other means that would guarantee the sterility of the water introduced into the patient's mouth. Solutions of this problem are currently being sought. Until this is accomplished, it is recommended that dental units and accessories such as ultrasonic units be flushed for a period in excess of 2 minutes prior to the start of daily procedures. One should realize, however, that this procedure will, at best, reduce microbial concentrations in water systems to levels that should still be considered unacceptable.
Contamination
673
SUMMARY
Microbial contamination of the water system in 12 dental units and nine ultrasonic scalers was investigated. Water samples from ultrasonic scalers,
high-speed
handpieces and water syringe lines showed microbial concentrations of up to 2.6 million, 3.3 million and 190,000 colony forming units/ml respectively. Flushing the lines for 2 minutes reduced the microbial levels, but complete elimination of all bacteria was not achieved. The infectious potential of contaminated water, to the dentists and patients, particularly the compromised host is discussed. REFERENCES
1. Larato, D. C , Ruskin, P. F., and Martin, A.: Effect of an ultrasonic scaler on bacterial counts in air. J Periodontal 38: 550, 1967. 2. Micik, R. E., Miller, R. L., Mazarella, M . A., and Ryge, G.: Studies on dental aerobiology: I. Bacterial aerosols generated during dental procedures. J Dent Res 48: 49, 1969. 3. Williams, G . H . Ill, Pollok, N . L . Ill, Shay, D. E., and Barr, C. E.: Laminar air purge of microorganisms in dental aerosols: Prophylactic procedures with the ultrasonic scaler. J Dent Res 49: 1948, 1970. 4. Nixon, G. S.: Occupational hazards in dentistry. Community Health (Bristol) 3: 221, 1972. 5. Pelleu, G. B. Jr., and Wachtel, L. W.: Microbial contamination in dental unit warm water systems. NDS-TR-009. Naval Dental School, National Naval Medical Center, Bethesda, Md., 1969. 6. Abel, L . C , Miller, R. L . , Micik, R. E. and Ryge, G.: Studies on dental aerobiology: IV. Bacterial contamination of water delivered by dental units. J Dent Res 50: 1567, 1971. 7. McEntegart, M . G . , and Clark, A.: Colonization of dental units by water bacteria. Br Dent J 134: 140, 1973 8. Clark, A. Bacterial colonization of dental units and the nasal flora of dental personnel. Proc R Soc Med 67: 1269, 1974. 9. Davis, B. D., Dulbecco, R., Eisen, H . N . , Ginsberg, H . E., and Wood, W. B. Jr.: Microbiology, ed 2, p 783. Hagerstown, Harper & Row, 1973.
Announcement INTERNATIONAL
CONFERENCE ON PERIODONTAL
purpose of the investigation, materials and methods, and results (if available) should be submitted to:
RESEARCH Stockholm, Sweden
DOCTOR JAN LINDHE Department of Periodontology
June, 1978
University of Goteborg A 3-day international conference on periodontal research will be held in Stockholm, Sweden June 26-28,
1978. The conference is
sponsored by the Periodontal Research G r o u p of the I . A . D . R . Support for
the conference has been obtained from the Proctor & Gamble
by July 1, 1977. The
conference will cover travel expenses based on economy jet
excursion fare and per diem for expected speakers.
Company. Individuals wishing to present original research, relative to periodontology
400 33 Goteborg 33, Sweden
and not
previously published, are invited to submit
A l l reports and summary discussions will be published in the Journal of Periodontal Research during 1978. Each speaker will be requested to
abstracts for consideration by the program committee. Abstracts of
submit a final abstract (maximum 500 words) no later than immedi-
approximately 200 words giving title, author's name and affiliation,
ately before the presentation of his/her paper.
