50 TEAMWORK Vol.5-No.3 - March 2012

Dental Asepsis

John A. Molinari, Ph.D. is currently Director of Infection Control for THE DENTAL ADVISOR in Ann Arbor, Michigan. Previously, heserved for 32 years at the University Of Detroit Mercy School Of Dentistry as Professor and Chairman of the Department of BiomedicalSciences and Director of Infection Control. He has published over 350 scientific articles, text chapters, and abstracts in the areas ofmicrobiology and immunology, and lectures nationally and internationally on topics dealing with infectious diseases and infection control.Dr. Molinari is also co-author of the text Cottone’s Practical Infection Control in Dentistry, with the 3rd edition published in 2009. Hecontinues serving as a consultant for the CDC, ADA Council on Scientific Affairs, Council on Dental Practice, and hospitals in the Detroit areain the areas of infectious disease and infection control. He is currently a member of the Michigan Board of Dentistry. In addition, he writes amonthly column for Dental Economics. In recognition of his efforts, Dr. Molinari was inducted as an honorary member of the Michigan dentalassociation, the International College of Dentists, the American College of Dentists, and is a 2009 recipient of the ADA Golden Apple Award.

Dental Water Asepsis: Rationale, Challenges,and Infection Control Strategies

Author:

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The demonstration of high concentrations ofmicrobial accumulation in coolant water for highspeed dental handpieces was first reported by Blake

in 1963.1 This initial study served as the trigger forsubsequent investigations into the mechanisms ofcolonization, potential health problems for dental healthcare providers and their patients, and possible approachesfor resolution. As a result, numerous studies have shownthat dental unit waterlines can be rapidly contaminated byorganisms that thrive in aqueous environments, leading tothe formation of biofilms inside the lumens of colonizedwater lines. Researchers have further identified multipleclasses of organisms in collected water samples, ranging fromnonpathogenic to pathogenic species. These include:Bacterionema spp.; Corynebacterium spp.; gram negative bacilliand cocci; Klebsiella spp.; Neisseria (N. catarrhalis);Pseudomonas spp., including P. aeruginosa, P. pyogenes, andBurkholdaria capacia; Staphylococcus epidermidis; Streptococcusmutans, Streptococcus salivarius, and Streptococcus mitis;Actinomyces spp.; Enterococcus spp.; a-hemolytic streptococci;Staphylococcus aureus; B. subtilis; E. coli; Flavobacterium;nonhemolytic streptococci; Legionella pneumophila;Mycobacterium spp.; Aspergillus niger; Cladosporium;Achromobacter; and Alcaligenes faecalis.2-7

Although municipal water coming into the system from anexternal source is of potable quality (<500 colony formingunits/milliliter [cfu/mL] of bacteria and <1 coliform), watercoming out of dental units used in clinical facilities may becolonized with microbial concentrations ranging from 1,000to 10,000 cfu/ml. Some units have even shown to harbor 1million cfu/mL. This contamination occurs because a

number of dental unit water line factors (e.g., narrow hollowbore design of plastic tubing, flow rates, materials) promotebacterial growth and development of biofilm over time. Previously, there wasn’t any documented evidence of

individual cases or outbreaks or serious health problems foreither patients or dental health care professionals (DHCP)resulting from contact with dental water. Recently, however,investigators reported in the medical journal The Lancet thefirst case of a fatal patient infection from exposure tobacteria in dental waterlines. The patient was an elderlywoman who succumbed to fulminant Legionnaires’ diseasein February 2011. The source of the Legionella pneumophilainfection was ultimately traced to the high speed handpiecewaterline in the dental practice where she had been treatedduring 2 appointments. This unfortunate case serves to reinforce the importance of

ongoing efforts to implement and utilize effective infectioncontrol precautions during provision of patient care. Inaddition, when one considers universally accepted infectioncontrol principles and the high level of asepsis routinelyexhibited in most dental facilities, exposing patients or DHCWto water of poor microbiological quality is inconsistent withcurrent infection prevention practices. As a result, healthprofessional associations and governmental agencies continueto respond to concerns by developing guidelines and, in someinstances regulations, to address this issue. The followingsections will attempt to discuss the area of dental water asepsisby using a question/answer format to review, among others,health implications of microbial colonization, governmentalrecommendations and regulations for health care facilities, andevolution of infection control strategies.

Fig. 5

Fig. 1: Corynebacterium

Fig. 2: Klebsiella

Fig. 3: Neisseria

Fig. 4: Pseudomonas

Fig. 5: Streptococcus mutans

Fig. 4Fig. 2Fig. 1 Fig. 3

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52 TEAMWORK Vol.5-No.3 - March 2012

Have there been reported incidents of cross-infectionassociated with contaminated water in healthcarefacilities?Prior to the recent Legionnaires’ disease report occurring in adental patient, there have been published clinical investigationsdocumenting waterborne infections and disease in hospitalsettings.8-10 Waterborne pathogens, especially Pseudomonas, non-tuberculous Mycobacterium species, and Legionella species were themost commonly cited etiologic agents. Medical devicesassociated with these infections include nebulizers, endoscopes,otologic equipment, and hemodialysis units. With specific regard to dental facilities, the overwhelming

majority of microbes isolated from dental waterlines originatefrom the local municipal water supply. These microbes do nottypically pose a high risk of disease for healthy persons.However, Pseudomonas, Klebsiella, Legionella, and non-tuberculousMycobacterium species and other potential pathogens have beenisolated from dental water supplies. In addition, two publishedreports in the 1980’s suggested increased exposure of dentalhealth care workers to legionellae from aerosolized dentalwater.11-12 As more people with weakened immune systems seekdental treatment, more questions arise about the potential rolewaterborne organisms could play as “opportunistic pathogens”in a similar manner as described with hospital outbreaks.13

What are biofilms and how do they populate dentalunit waterlines?Microbial biofilms are found virtually anywhere that moistureand a suitable solid surface for bacterial attachment exist.Biofilms consist primarily of naturally occurring slime-producingbacteria and fungi that form microbial “communities.” This

bacterial film tightly adheres and lies flat against the walls of thesmall-bore plastic tubing in dental units that deliver coolantwater to high-speed handpieces and air/water syringes. As waterflows through the microbial matrix, microorganisms mayoccasionally be released into the effluent water.

Biofilms are characterized by cells that are: 1. irreversiblyattached to a substratum or interface with each other; 2.embedded in a matrix of extracellular polymeric substancesthat they have produced; and 3. grow as a distinct communityof bacteria and other microorganisms acting as a self-perpetuating and self-protecting unit. As mentioned above,they can harbor numerous waterborne bacteria, fungi,protozoa, even nematodes. While at first glance biofilms mayappear as merely amorphous masses on water-laden surfaces,they have a surprisingly complex structure.13

Of particular importance to both possible infectiousexposure and the public’s perception of microbial exposure,some clumps of biofilm may be dislodged and come out assolid material as water flows through the lines.

What is the evolution of statements by professionalorganizations and governmental agencies regardingaddressing dental waterline challenges?In response to growing concerns about the quality of dentalwater used in patient treatment the American DentalAssociation convened an expert panel in 1995 to discuss andaddress the issue. A subsequent statement was publishedestablishing goals for improving dental unit water. Thisstatement also encouraged the industry and researchers toprovide dental equipment with the ability to deliver treatmentwater with 200 colony forming units (cfu)/mL or less of

Fig. 10

Fig. 6: Enterococcus

Fig. 7: E. coli

Fig. 8: Legionella pneumophila

Fig. 9: Mycobacterium

Fig. 10: Aspergillus niger

Fig. 9Fig. 7Fig. 6 Fig. 8

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unfiltered output from water lines.5 In 2003, the U.S.Centers for Disease control and Prevention (CDC) publishedcomprehensive updated infection control guidelines.14 Theserecommendations include a limit of no more than 500 cfu ofheterotrophic bacteria per mL in dental water, the flushing ofdental waterlines at the beginning of the day and betweenpatients, and the use of sterile water or saline for irrigation ofsurgical sites where bone is exposed. The CDC recommendsthe same level of standard that exists for safe drinking water. The Canadian Dental Association (CDA) Committee on

Clinical & Scientific Affairs published similar guidelines in2006. In part, their recommendations stated: “The potential risk ofinfection from dental unit waterlines (DUW) microorganisms can beeffectively reduced to counts to potable water standards (i.e. less than 500cfu/mL) following regular waterline maintenance procedures”.15 Thesewere subsequently expanded in the development of the mostrecent Alberta Dental Association and College (ADA) provincialstandards and Royal College of Dental Surgeons of Ontario(RCDSO) recommendations, respectively.16,17 Both documentscontain essentially the same procedures for waterlinemaintenance. Statements from the ADA Infection Preventionand Control Standards published in 2010 are provided below:• The dental clinic must use a water supply, which is tested for,and is free of contaminants, such as from a monitoredmunicipal water supply; unless there is a boil water advisory.Non-monitored water supplies should be tested bi-annually.

• Waterline heaters should not be used in a dental unit or indental equipment, as these heaters encourage waterlinemicroorganism growth.

• All waterlines must be purged at the beginning of eachworkday by flushing the lines thoroughly with water for atleast two minutes. This purging should not be done withhandpieces, air/water syringe tips and ultrasonic tipsattached to the waterlines.

• Handpieces utilizing water coolant must be run for at leasttwenty seconds after patient care, in order to purge allpotentially contaminated air and water. A sterilizedhandpiece can then be attached, following regular clinicalcontact surface management.

• Sterile water or saline must be used when irrigating openvascular sites and whenever bone is cut during invasivesurgical procedures. Conventional dental units do notreliably deliver sterile solutions, even when equipped withindependent water reservoirs or microfilters, due to theformation of biofilm along the water pathway. Deliverysystems, such as a bulb syringe, should be used to deliversterile irrigation solutions.

• When closed water systems are used, DHCP should becareful not to touch the tubing with the fingers or glovedhand when changing the water coolant, as this easilycontaminates the entire system.

• Manufacturers’ instructions of the dental units and dentalequipment must be followed for daily and weeklymaintenance whenever closed water systems or otherspecial water delivery systems are utilized.

What kinds of commercial products are availableto assist clinicians in their efforts to improve thequality of dental water?A common approach used by practices for many years involvedflushing water through waterlines for variable intervals. Whilethis procedure is able to remove free-flowing (i.e. planktonic)organisms suspended in waterline fluids, the beneficial effectsof mechanical flushing have been shown to be transient.18-19

Recommendations from the CDC, ADA, and the RCDSO doinclude flushing waterlines between patients to eliminate anypatient material that may have been retracted into handpiecesand air water syringes during dental procedures, however, theydo not consider this procedure to be an effective means forreliably improving dental water quality.A range of engineering and work-practice controls have

been evaluated for this purpose. As a result, a variety ofcommercial products are currently available to the professionto control microbial contamination in dental waterlines.These choices are as follows:1. An alternate water supply that bypasses community waterand dental water systems by providing sterile or distilledwater directly into water line attachments (i.e. separatereservoir) combined with chemical treatment.

2. Filtration involving in line filters to remove bacteriaimmediately before dental unit water enters instrumentattachment.

3. Chemical germicides or cleaners that inactivate or removemicrobial contamination (sometimes described asintermittent “shock” treatment).

4. Chemical germicides or cleaners that prevent microbialcontamination in new or cleaned systems (sometimesreferred to as “continuous” treatment). These products maybe added to or used as the irrigating solution for clinical use.

5. Thermal inactivation of facility water at a centralized source.6. Reverse osmosis or ozonation using units designed foreither single chair or entire practice water lines.

7. Ultraviolet irradiation of water before entrance intoindividual unit water lines.

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A number of features should be considered when dentistsand staff evaluate any of these types of products for possibleuse in their practice. These are summarized in Table 1. Products claiming many of the attributes listed in Table 1

are now being marketed. Before introducing any chemicalagent into a dental water system, the user must seekassurance from the manufacturer that the product is non-toxic, will not damage the dental unit and—if continuouslypresent in treatment water, that it will not harm the patientor dental healthcare professional or interfere withrestorative bonding agents. The keys for accomplishing DUWL asepsis remain the same

as for other infection control goals. Contaminated waterlines,like contaminated hands, instruments, and environmentalsurfaces, should first be cleaned to remove accumulatedmicrobial and extracellular material. This should be doneprior to working to maintain low microbial levels. Compliancewith a manufacturer’s step-by-step procedures foraccomplishing initial removal of accumulated material isessential. Minimizing subsequent DUWL colonization mayrequire another series of protocols, some of which may bemore time consuming than anticipated. Thus, the entiredental team should be aware of the necessity for compliance,and the time required to attain the recommended DUWLmicrobial concentrations. Research developments in recent years have led to both

greater individual product options for dental practitioners,but also the availability of combination systems which

Non-toxic to equipment or patients

Non-pyrogenic

Non-allergic

Non-corrosive to metals

No damaging effects on rubber or synthetic materials

Does not interfere with performance of restorative or therapeutic agents

Rapid “cidal” (i.e. lethal) antimicrobial action

Broad-spectrum anti-microbial activity

Ability to disrupt/disperse accumulated biofilms

Environmentally friendly or “green”

Table 1

Desirable Properties for DUWL Treatment Strategies contain separate waterline cleaning agentsand maintenance chemicals. Thisapproach minimizes the necessity andpossible confusion that can arise fromevaluating, purchasing and using multipletypes of products from differentmanufacturers. Remember to ask theappropriate questions when discussingavailable product choices withmanufacturers’ representatives, and thenbe certain to evaluate what approach willwork best in your specific facility.

References1. Blake GC. The incidence and control of bacterial

infection of dental units and ultrasonic scalers. BritMed J 1963; 115:413-416.

2. Abel LC, Miller RL, Micik RE, et al. Studies ondental aerobiology: IV. Bacterial contamination ofwater delivered by dental units. J Dent Res 1971;50:1567-1569.

3. Gross A, Devine MJ, Cutright DE. Microbial contamination of dental units andultrasonic scalers. J Periodontol 1976; 47:670-673.

4. Bagga BSR, Murphy RA, Anderson AW, et al. Contamination of dental unitcooling water with oral microorganisms and its prevention. J Am Dent Assoc1984; 109:712-716.

5. Shearer BG. Biofilm and the dental office. J Am Dent Assoc 1996; 127:181-189.6. Barbeau J, ten Bokum L, Gauthier C, et al. Cross-contamination potential of

saliva ejectors used in dentistry. J Hosp Infect 1998; 40:303-311.7. Mills SE. The dental unit waterline controversy: defusing the myths, defining

the solutions. J Am Dent Assoc 2000; 131:1427-1441.8. Bolan G, Reingold AL, Carson LA, et al. Infections with Mycobacterium

cheloni in patients receiving dialysis and using processed hemodialyzers. JInfect Dis 1985; 152:1013-1019.

9. Arnow PM, Chou T, Weil D, et al. Nosocomial Legionnaire’s disease causedby aerosolized tap water from respiratory devices. J Infect Dis 1982;146:460-467.

10. Breiman RF, Fields BS, Sanden GN, et al. Association of shower use withLegionnaire’s disease: possible role of amoebae. J Am Med Assoc 1990;263:2924-2926.

11. Fotos PG, Westfall HN, Snyder LS, et al. Prevalence of Legionella-specific IgG andIgM antibody in a dental clinic population. J Dent Res 1985; 64:1382-1385.

12. Renthaler FF, Mascher F, Stunzner D, et al. Serological examinations for antibodiesagainst Legionella species in dental personnel. J Dent Res 1988; 67:942-943.

13. Mills S. Dental unit water and air quality challenges. In: Cottone’s PracticalInfection Control in Dentistry, 3rd ed. Philadelphia: Wolters Kluwer/LippincottWilliams & Wilkins, 2010:63-75.

14. Kohn WG, Collins AS, Cleveland JJ, et al. Guidelines for infection control indental healthcare settings – 2003. Morbid Mortal Wkly Rpt 2003; 52:1-66.

15. Canadian Dental Association. Infection prevention and control in the dentaloffice: an opportunity to improve safety and compliance. 2006.

16. Alberta Dental Association and College. Infection prevention and ControlStandards and Risk Management for Dentistry. 2010; 1-106.

17. Royal College of Dental Surgeons of Ontario. Infection Prevention andControl in the Dental Office. 2009; 1-50.

18. Williams HN, Baer ML, Kelley JI. Contribution of biofilm bacteria to thecontamination of the dental unit water supply. J Amer Dent Assoc 1995;126:1255-1260.

19. Santiago JI, Huntington MK, Johnston AM, et al. Microbial contamination of dentalunit waterlines: short- and long-term effects of flushing. Gen Dent 1994; 48:528-544.

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