American Journal of Infection Control 42 (2014) 1019-21

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American Journal of Infection Control

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Microbial contamination of used dental handpieces Gordon Smith BSc Hons, MRes, PhD, Andrew Smith BDS, FDS RCS, FRCPath, PhD * Institute of Infection and Immunity, College of Medical, Veterinary, and Life Sciences, Glasgow Dental Hospital and School, University of Glasgow, Glasgow, Scotland

Key Words: Dental turbine Cross-infection Staphylococcus aureus Biofilm

Microbial contamination of used, unprocessed internal components of dental handpieces (HPs) was assessed. HPs were dismantled aseptically, immersed in phosphate-buffered saline, ultrasonicated, and cultured. A median of 200 CFU per turbine (n ¼ 40), 400 CFU per spray channel (n ¼ 40), and 1000 CFU per item of surgical gear (n ¼ 20) was detected. Isolates included oral streptococci, Pseudomonas spp, and Staphylococcus aureus. Recovery of S aureus confirms the need for appropriate HP cleaning and sterilization after each patient to prevent cross-infection. Copyright Ó 2014 by the Association for Professionals in Infection Control and Epidemiology, Inc. Published by Elsevier Inc. All rights reserved.

Dental handpieces (HPs) are routinely used to perform a variety of invasive and noninvasive procedures during dental surgery. After use, HPs may be contaminated internally from the external environment through negative pressure created by the deceleration of the turbine and from water lines that provide cooling water.1 The reprocessing of HPs to allow removal and inactivation of microbial contaminants is challenging owing to the complex internal structures, narrow lumens, and lack of disassembly after use and is frequently considered the weak link in the infection prevention chain for dentistry.2-4 It is important to determine the typical microbial contamination of used HPs before cleaning and sterilization processes to quantify the biological challenge to decontamination and ensure a sufficient safety margin. Information on likely bacterial contaminants is also useful for estimating risk after practitioners’ failure to clean and sterilize dental HPs. The present study was a quantitative and qualitative analysis of bacterial contamination from the internal components of used, unprocessed dental HPs. MATERIALS AND METHODS Instruments and components sampled HPs were obtained from Glasgow Dental Hospital and ranged in age from 1 to 8 years. No information was available on the clinical * Address correspondence to Andrew Smith, BDS, FDS RCS, FRCPath, PhD, Institute of Infection and Immunity, College of Medical, Veterinary and Life Sciences, Glasgow Dental Hospital and School, University of Glasgow, 378 Sauchiehall St, Glasgow G2 3JZ, Scotland. E-mail address: [email protected] (A. Smith). Conflict of interest: Dr. Smith was funded for a PhD scholarship by W&H. The sponsors played no role in the drafting or editing of this manuscript.

use of each HP before sampling. Three different HP components from 3 different HP models were sampled: turbines from highspeed HPs (W&H TA-98), the spray channels from low-speed HPs (W&H WA56), and the inner gear of surgical HPs (W&H S11). Instrument processing for sampling HPs were transported in sterile plastic bags to a laminar flow cabinet and sampled immediately. HPs were dismantled by hand, and internal components were removed aseptically using sterile HP disassembly tools. Sterile HPs of each type served as sterility controls. Instrument sampling: Microbial culture techniques Each component was immersed in sterile phosphate-buffered saline in a sterile Universal container and ultrasonicated (Fisherbrand 11,021; Fisher Scientific, Loughborough, UK) for 5 min at 35 kHz. Aliquots were pipetted onto Columbia blood and Sabouraud and fastidious anaerobic agar plates (Oxoid, Hampshire, UK). The blood and Sabouraud agar plates were incubated for 72 h in 5% CO2 at 37 C, and the fastidious anaerobic agar plates were incubated anaerobically at 37 C for 7 days. Each unique colony isolated was subcultured and subjected to further analysis to confirm identity. Identification of isolates Bacterial isolates were identified using a combination of Gram stain, catalase reaction, and, as appropriate, a coagulase test (STAPHaurex; Oxoid). All gram-positive and gram-negative bacteria were subjected to further speciation using a biochemical testing

0196-6553/$36.00 - Copyright Ó 2014 by the Association for Professionals in Infection Control and Epidemiology, Inc. Published by Elsevier Inc. All rights reserved.


G. Smith, A. Smith / American Journal of Infection Control 42 (2014) 1019-21

Table 1 Bacterial counts from used and unprocessed dental handpieces HP type and component TA-98; turbine WA56; spray channel S11; surgical gear

Number tested

Aerobic counts, CFU/component, median (range)

Anaerobic counts, CFU/component, median (range)

Fungal counts, CFU/component, median (range)

40 40 20

200 (0-1.9  104) 400 (0-1  104) 1  103 (0-3.7  104)

30 (0-8.5  103) 200 (0-3.3  103) 2713 (175-6  104)

10 (0-2  103) 5 (0-1.1  103) 437 (0-4.4  104)

kits (RapidID 32 Strep, 50C, 32A API strip; bioMérieux, Marcy l’Etoile, France).

Table 2 Summary of bacterial species recovered from used and unprocessed dental handpieces

Scanning electron microscopy analysis of handpiece components To confirm the origin of the bacterial contamination on the HP components, we performed scanning electron microscopy (SEM) of a selection of high-speed turbines and low-speed gears. Components were fixed in 2% paraformaldehyde, 2% gluteraldehyde, 0.15 M sodium cacodylate, and 0.15% Alcian blue for 22 hours. Each sample was coated with gold and viewed under a scanning electron microscope (JSM-6400; JEOL, Tokyo, Japan) at 12 and 100 magnifications. RESULTS A total of 40 W&H TA-98 high-speed HP turbines, 40 W&H WA56 low-speed HP spray channels, and 20 W&H S11 surgical HP gears were sampled. No bacteria were isolated from negative controls. Bacteria were isolated from 38 of the 40 turbines (median, 200 CFU per component), from 37 of 40 spray channels (median, 400 CFU per component), and from 18 of 20 surgical gears (median, 1  103 CFU per component) (Table 1). The most common organisms isolated from these components were coagulasenegative staphylococci, oral streptococci, Staphylococcus aureus, Pseudomonas spp, and Propionibacterium acnes (Table 2). Viewing HP components under SEM revealed coatings consistent with bacterial biofilms at numerous sites.

HP type and component TA-98; high-speed turbine

WA56; low-speed spray channel

S11; surgical gear

Identified organism Staphylococcus aureus Coagulase-negative staphylococci Leuconostoc spp Gamella morbillorum Propionobacterium acnes Streptococcus mutans Streptococcus gordonii Pseudomonas stutzeri Pseudomonas mendocina Candida spp Staphylococcus aureus Coagulase-negative staphylococci Streptococcus salivarius Streptococcus oralis Streptococcus mitis Propionobacterium acnes Candida species Staphylococcus aureus Coagulase-negative staphylococci Streptococcus salivarius Leuconostoc spp Streptococcous sanguinis Streptococcus gordonii Streptococcus mitis Streptococcus oralis Streptococcus mutans Propionobacterium acnes Candida spp

Count, CFU/ component, median 5 3.3 1 1 3.8 1 1 7 1 3.3 4.6 3 4.4 2 2 3 3.6 1.2 1.7 5.3 5 5.1 1.8 2.2 1.4 1 6.3 8.5


102 104 102 102 102 102 102 103 102 103 103 104 103 102 102 102 103 104 105 102 102 103 102 104 104 104 103 104

DISCUSSION Accessing internal HP parts necessitates dismantling the HP unit, a challenging task without specialist training and the proper tools. In addition to dismantling HPs, we used a sonication method to sample bacterial contamination of inner components to improve recovery rates compared with previous studies.5,6 SEM analysis of HP components confirmed the presence of bacterial biofilms. Detection of microorganisms from the viridans group streptococci and Candida spp confirms that aspiration of oral contents is the most likely source of contamination and is a common event. The presence of Pseudomonas spp suggests that contamination of HP components from the dental unit water lines is another source of contamination. Our data demonstrate that surgical HP gears had the largest quantities of microorganisms after use, although this may reflect the larger surface area of this gear. The recovery of S aureus and the use of the surgical HPs in performing more invasive procedures, such as surgical removal of alveolar bone, suggest the need for greater diligence in cleaning and sterilizing this particular HP.7-9 Of interest is the recovery of coagulase-negative staphylococci and P acnes isolates from all parts. In light of previous reports linking coagulase-negative staphylococci and P acnes with dental infections,10 this finding reinforces current guidance for appropriate cleaning and sterilization processes between patients for all dental HP types.1

In this study, we found a wider range and greater numbers of bacteria than have been reported previously,4-6 owing to the culture methods used and improved sampling methodology. The type and duration of clinical procedures undertaken before sampling will affect the quantitative and qualitative nature of bacterial contamination after use; however, this information was unavailable for this study, which should be kept in mind when interpreting our results. In addition, Glasgow Dental Hospital operates a frequent inspection and maintenance HP process (unlike most dental practices), and thus our findings are likely an underestimate of bacterial contamination. In conclusion, the numbers of microbes detected should not present a challenge to steam sterilization processes designed to penetrate lumened devices; however, the detection of such pathogens as S aureus in HP components should be considered when investigating defects in infection control precautions. The dental team also should be encouraged to submit samples for microbiological analysis from dental infections, to determine whether these findings are of clinical significance. References 1. Centers for Disease Control and Prevention. Guidelines for infection control in dental health care settings. MMWR Morb Mortal Wkly Rep 2003;52:1-61.

G. Smith, A. Smith / American Journal of Infection Control 42 (2014) 1019-21 2. Lewis DL, Arens M, Appleton SS, Nakashima K, Ryu J, Boe RK, et al. Crosscontamination potential with dental equipment. Lancet 1992;340:1252-4. 3. Hu T, Li G, Zuo Y, Zhou X. Risk of hepatitis B virus transmission via dental handpieces and evaluation of an anti-suction device for prevention of transmission. Infect Control Hosp Epidemiol 2007;28:80-2. 4. Herd S, Chin J, Palenik CJ, Ofner S. The in vivo contamination of air-driven lowspeed handpieces with prophylaxis angles. J Am Dent Assoc 2007;138:1360-5. 5. Chin JR, Miller CH, Palenik CJ. Internal contamination of air-driven low-speed handpieces and attached prophy angles. J Am Dent Assoc 2006;137:1275-80. 6. Kellett M, Holbrook WP. Bacterial contamination of dental handpieces. J Dent 1980;8:249-53.


7. Rokadiya S, Malden NJ. An implant periapical lesion leading to acute osteomyelitis with isolation of Staphylococcus aureus. Br Dent J 2008;205: 489-91. 8. Smith AJ, Robertson D, Tang MK, Jackson MS, MacKenzie D, Bagg J. Staphylococcus aureus in the oral cavity: a three-year retrospective analysis of clinical laboratory data. Br Dent J 2003;195:701-3. 9. Smith AJ, Jackson MS, Bagg J. The ecology of Staphylococcus species in the oral cavity. J Med Microbiol 2001;50:940-6. 10. Niazi SA, Clarke D, Do T, Gilbert SC, Mannocci F, Beighton D. Propionibacterium acnes and Staphylococcus epidermidis isolated from refractory endodontic lesions are opportunistic pathogens. J Clin Microbiol 2010;48:3859-69.

Microbial contamination of used dental handpieces.

Microbial contamination of used, unprocessed internal components of dental handpieces (HPs) was assessed. HPs were dismantled aseptically, immersed in...
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