THE DENTAL UNIT WATERLINE CONTROVERSY - MAE … · JADA, Vol. 131, October 2000 1427 THE DENTAL...

JADA, Vol. 131, October 2000 1427

THE DENTAL UNIT WATERLINE CONTROVERSY:DEFUSING THE MYTHS, DEFINING THE SOLUTIONS

In recent years, few issues in the field of dentalinfection control have been more controversial than

the phenomenon of dental unit waterline, or DUWL,contamination. While few dentists now seem willing todispute the existence of microbial contamination in den-tal treatment water, many dentists remain unsure asto what to do about it. A number of factors probably

contribute to their confusion, including the absenceof well-documented links to health problems in

dental health care workers and patients and alack of consensus among the experts about thebest approaches to solving the problem.

This article will address this topic by tryingto answer the following most frequently askedquestions, or FAQs, about the nature of DUWL

contamination, its possible health effects andthe technologies that exist to address it.

FAQ 1. HOW LONG HAS DENTISTRY BEENAWARE OF THIS ISSUE?

The existence of contaminated water in dental unitsappears to have first been reported in 1963 in GreatBritain by Dr. G.C. Blake,1 after installation of newhigh-speed air-rotor handpieces. Since dental units ofthat era were not equipped with systems to provide

coolant water, the handpieces were equipped withseparate water reservoirs. What led Dr. Blake toinvestigate the quality of dental treatment water isnot clear.

Background andOverview. This article reviews theliterature on the subject of dental unitwaterline contamination. It has beenexpanded from the text of a lecturegiven at the Scientific Frontiers inDentistry program sponsored by theNational Institute for Dental andCraniofacial Research in Bethesda, Md., inJuly 1999. The author examines the underly-ing biological causes of waterline colonization bymicroorganisms, the evidence of potential healthconsequences and possible means of improvingthe quality of dental water. He also describesexamples of devices currently marketed toimprove and maintain the quality of dentaltreatment water.Conclusions. Microorganisms colonizedental units and contaminate dental treat-ment water. While documented instancesof related illness are few, water thatdoes not meet potable-water standardsis inappropriate for use in dentistry.Clinical Implications.Exposure to water containing high num-bers of bacteria violates basic principlesof clinical infection control. Dentistsshould consider available options forimproving the quality of water used in den-tal treatment.

SHANNON E. MILLS, D.D.S.

A B S T R A C T

C O V E R S T O R Y

Copyright ©1998-2001 American Dental Association. All rights reserved.

However, his finding—thatlarge numbers of bacteria (somepotentially pathogenic) werepresent in water and aerosols—has been confirmed by dozens ofpublished articles during thelast 37 years. He also was thefirst to test the effectiveness ofchemical germicides as a possi-ble solution to the problem.1

Since Blake’s landmark pub-lication, dozens of articles haveappeared in dental journalsworldwide describing the exis-tence of microbial contamina-tion in dental water systemsand investigating methods tocontrol it. Most of the approach-es currently in use (flushing,chemical treatment, filtration)were evaluated in some formbefore 1980.2 There is presentlylittle evidence that these arti-cles have had a significantimpact on the practice of dentistry.

Nevertheless, by the early1990s, a profession sensitized toinfection control issues becauseof the worldwide humanimmunodeficiency virus, orHIV, epidemic began to showmore interest in the topic.Reports of waterline contamina-tion by Legionella and otherpotential pathogens probably

increased overall awareness.3

Research also began to eluci-date the role that biofilmsplayed in the presence and per-sistence of the phenomenon.4

This awareness led the Centersfor Disease Control andPrevention to first address thetopic of water quality in its1993 infection control guide-lines.5 The American DentalAssociation Council onScientific Affairs6 followed suitby convening an expert panelon DUWLs in 1995; the panel’swork culminated in a formalstatement published in JADAin 1996.

Gaining a basic understand-ing of the nature of microbialcontamination of dental wateris a crucial step in seeking asatisfactory resolution of thiscontroversial issue. To accom-plish that, we first must answera few questions, starting withFAQ 2 below.

FAQ 2. WHAT IS ABIOFILM?

Biofilms are microbial commu-nities that adhere to solid sur-faces wherever there is suffi-cient moisture (including plantand animal tissues). Consistingprimarily of bacteria, biofilms

often exhibit astonishingly com-plex communal architecture.Most biofilms are heteroge-neous in species and morphol-ogy and are enveloped in a poly-saccharide slime layer knownas a glycocalyx. The glycocalyxprotects the organisms withinfrom desiccation, chemicalinsult and predation, as well asfrom attacks by plant and ani-mal immune systems. The rela-tionship between biofilm organ-isms is often symbiotic, withone species providing key cofac-tors required by another. Somespecies apparently communi-cate with others in the biofilmcommunity using a variety ofsignaling compounds. Depend-ing on environmental condi-tions, these chemical signalscan initiate slime formation ororder the breakup of thebiofilm. Biofilms also providean environment conducive tothe proliferation of a wide vari-ety of other microscopic life,including fungi, algae, protozoaand nematodes.7 Absent thealgae and nematodes, thisdescription of biofilms shouldsound familiar to dentists, asdental plaque is a classicbiofilm.8 Figure 1 shows a scan-ning electron micrograph of abiofilm inside a DUWL and aschematic representation of typ-ical aquatic biofilm architec-ture, including channels thatallow convective flow within thecommunity.

The formation of biofilms onwater-bearing surfaces in den-tal units results in fouling ofthe water that passes throughthe unit with high levels of sus-pended bacteria. Most organ-isms recovered from dentalwater systems are gram-negative noncoliform water bac-teria.4,9-11 Although most of thespecies recovered have limited

1428 JADA, Vol. 131, October 2000

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Figure 1. Biofilm architecture. A. Dental unit waterline magnified ×5,000,showing the polysaccharide slime layer and typical biofilm surfacearchitecture. (Photo courtesy of the USAF Dental Investigation Service.)B. An artist’s conception, revealing the presence of complex featuressuch as channels for convective flow within the biofilm. (Illustrationused by permission of the Center for Biofilm Engineering, MontanaState University, Bozeman.)

A B


pathogenic potential inimmunocompetent people, theSafe Drinking Water Act sets astandard for noncoliform bacte-ria in drinking and recreationalwater at 500 colony-formingunits per milliliter, or CFU/mL.12

(This is a standard measure formicrobial contamination thatrepresents a single colonygrown on solid media. A CFUmay consist of a single cell ormany bacterial cells clumpedtogether.) The American PublicHealth Association andAmerican Water WorksAssociation recommend thesame standard for recreationalwaters such as swimming poolsand spas.13 By comparison,DUWL contamination inuntreated systems often exceeds1,000 CFU/mL. Counts rangingbetween 10,000 and 100,000CFU/mL may be commonplace.14

FAQ 3. IF DRINKINGWATER IS SAFE, WHY ISDENTAL UNIT WATER SOBAD?

Despite high-profile incidentssuch as the Cryptosporidiumoutbreak that sickened thou-sands in Milwaukee in 1994,15

most drinking water in theUnited States meets estab-lished standards for biologicalcontamination on a day-to-daybasis. Many clinicians are puz-zled as to how dental units canbecome so heavily contaminatedwhen they are supplied by well-maintained municipal watersystems. The answers lie in aconvergence of biology, physicsand geometry that can be sum-marized into three components:surface colonization, laminarflow and surface:volume ratio.

Surface colonization.Many materials commonly usedto deliver water to dental hand-pieces and air/water syringesprovide excellent substrates for

the initial attachment of bacte-ria and the subsequent prolifer-ation of biofilm. Moreover, mosttreated drinking water containsminerals—principally calciumcarbonate—that are depositedon water-bearing surfaces.Organic molecules subsequentlyconcentrate on these surfacesand promote adhesion of bacte-ria suspended in water suppliedby the municipal water system.7

Figure 2 demonstrates a typicalsequence of biofilm formationon calcium carbonate depositedon a polyurethane DUWL. Overtime, individual cells attachedto the surface multiply to formmicrocolonies that ultimatelycoalesce to form a continuoussheet of bacteria protected bythe glycocalyx. Figure 3 showsa biofilm in a DUWL formedafter only six weeks of exposureto tap water.

Laminar flow. Fluids mov-ing through narrow-bore tubing

characteristically assume ahydrodynamic pattern knownas laminar flow. Closer to thetubing surface, frictional forcesslow the movement of fluidsuntil flow at the surface is sta-bilized; this creates an environ-ment conducive to the forma-tion of biofilm.16 In laminar flowsystems, biofilm can flourishwith minimal risk of being dis-lodged. This is one of the princi-pal reasons that flushing ofwaterlines can eliminate sus-pended (planktonic) microor-ganisms, but usually is noteffective in removing biofilms.17

Figure 4 presents a highly sim-plified representation of a lami-nar flow pattern in a DUWL.

Surface:volume ratio.Although understanding thebiology (attachment and prolif-eration of biofilms) and physics(laminar flow) operating in den-tal water systems is crucial inanswering this FAQ, it is geom-


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Figure 2. Biofilm colonization sequence on dental unit waterline sur-face. A. Carbonate deposits (which resemble ice floes). B. Initialattachment. C. Division of cells into microcolonies. D. Formation ofbiofilm.

A B

C D


etry that ultimately explainswhy dental unit water is morecontaminated than water froman adjacent faucet. After all,biofilms also are present in thewater mains and lines that linkthe faucet to the municipalwater system, and the samehydrodynamic principles applyas well.

As the diameter of a cylin-der—in this case, the water-line—decreases, an increasinglylarger surface area becomesavailable for colonization. Thetotal combined volume of water-line tubing in most dental unitsis somewhat less than 100 mL.To understand the effect of tub-ing diameter on surface area, I

will describe a hypothetical100-mL volume of water as itflows from the city water mainto the end of the handpiecehose. Figure 5 demonstrateswhat happens when 100 mL ofwater is confined in a section of10-inch diameter water main.In this case, there are only foursquare inches of surface areaavailable for biofilm formation(the size of a 2-in. × 2-in. gauzesponge). As the water entersthe dental office, it is channeledinto a pipe roughly one-half in.in diameter. The same 100-mLvolume of fluid is now in con-tact with a surface area equiva-lent to the faces of six creditcards (roughly 42 square in.).On entering the 1⁄16-in.–diametertubing that courses through amodern dental unit, the bacte-ria suspended in our watersample now find more than 400square in. of surface availablefor colonization (equivalent toone and one-half pages of adaily newspaper). The juxtapo-sition of large quantities oforganic material with verysmall quantities of water alsoaccounts for the almost totalconsumption of residual chlo-rine observed in colonized den-tal water systems.18,19 The netresult of all of these phenomenais treatment water that fre-quently is contaminated withhigh levels of microorganisms.

FAQ 4. WHAT ORGANISMS ARE PRESENT AND WHEREDO THEY COME FROM?

Now that we have some ideahow and why there are so manyorganisms in dental treatmentwater, it is reasonable to ask,“What are they, and where dothey come from?” Many earlyresearchers assumed that mostof the organisms they found indental water were retracted


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Figure 3. Biofilm formation on dental unit waterline tubing after sixweeks of exposure to tap water. (Photo courtesy of Richard Karpay,D.D.S.)

Figure 4. Laminar flow. Arrows represent the relative velocity of fluidthrough a dental unit waterline, which decreases as the fluid travelsbecause of frictional forces along the tubing walls. The relatively sta-ble region below the hydrodynamic boundary layer is conducive tobiofilm proliferation.

HydrodynamicBoundary

Laminar Flow


from the oral cavity. On thebasis of this assumption, theyoften used culture media andincubation methods designed torecover human flora.2,20 This didnot always give an accurate pic-ture of the true nature of themicrobial communities residingin dental units. While organ-isms consistent with oral floraare recovered, the majority ofmicrobes living in the biofilmcommunities are gram-negativewater bacteria of the same vari-eties that survive in small num-bers in municipal water sys-tems.20

Older dental units that weredesigned to retract water (toprevent water dripping fromhandpieces and air/watersyringes) can, in fact, retractoral flora.21 Since these organ-isms usually are well-adaptedto the warm, nutrient-rich oralenvironment, they typically donot compete well with the waterflora that predominate inwaterline biofilms. Someexperts, however, conjecturethat heating dental water toensure patient comfort actuallymay increase the prevalence ofbacteria “pre-adapted” to life ina warm-blooded host, includingLegionella bacteria (W.W. Bond,M.S., former deputy chief,Hospital EnvironmentLaboratory Branch, HospitalInfections Program, NationalCenter for Infectious Diseases,Centers for Disease Control andPrevention, oral communica-tion, April 30, 2000).

As biofilms mature, they pro-vide a hospitable environmentfor fungi, protozoa and otherorganisms that survive indrinking water systems.7 Whilemost of these organisms haveminimal pathogenic potential inimmunocompetent hosts, someprotozoa serve as hosts for pro-

liferation of parasitic bacteria,including Legionella.22,23

Although independent reser-voirs can be effective in improv-ing DUWL quality, lax hand-washing discipline and carelesshandling of bottles and feedertubes can result in contamina-tion of the water systems withenteric or skin organisms. Thesame thing can happen whendental water systems arerepaired. A case of coliform con-tamination in dental units hasbeen reported.24

Worrisome organisms.Although most of the organismsrecovered from dental units arewater bacteria with littledemonstrated potential to causedisease in immunocompetenthosts, potential pathogens dofind their way into dental watersystems. Pseudomonas aerugi-nosa has been reported as beingpresent in dental units9

(although many organismsreported as “Pseudomonasspecies” in older articles mightactually be bacteria that havesince been assigned to othergenera). This gram-negative rodis associated with a wide range

of opportunistic infections andis a cause of pneumonia in hos-pitalized patients. Pseudomonasand related species in the genusBurkholderia also are associat-ed with pneumonia in patientswith cystic fibrosis, or CF. Astudy conducted in Denmark,however, found that the risk forpatients with CF who wereundergoing dental treatmentwith contaminated units wasequal to the yearly “naturalbackground” incidence (1 per-cent to 2 percent) of acquisitionof P. aeruginosa in that clinic.25

Legionella pneumophila andrelated species also have beenisolated in dental treatmentwater. These weakly stainingbacteria thrive as intracellularparasites of protozoa (principal-ly amoebae). They are thecausative agents for legion-naires’ disease and a relatedcondition known as Pontiacfever. Outbreaks and sporadiccases of legionnaires’ diseaseoccur in both hospital and com-munity environments and mayaccount for as many as 10,000to 15,000 cases of pneumoniaeach year in the United States,


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Figure 5. Surface:volume ratio.The surface area available for col-onization for a fixed volumevaries with a waterline’s interiordiameter. The surfaces picturedrepresent the internal surfacearea provided for 100 milliliters offluid by each of the lines pic-tured. A. A newspaper. B. Creditcards and a piece of 2-in. × 2-in.gauze.

BA


with an estimated mortalityrate of 5 percent to 15 percent.Risk factors that increase sus-ceptibility to this diseaseinclude smoking, pre-existingrespiratory disease and age.26

Aquatic nontuberculous My-cobacterium species associatedwith pulmonary disease andopportunistic wound infectionsalso have been recovered indental unit water.27 All of thisbrings us to the next FAQ.

FAQ 5. ARE YOU CERTAINALL DENTAL UNITS(INCLUDING MINE) ARECONTAMINATED?

This question has the shortestanswer of all: unless proceduresspecifically designed to prevent,eliminate, trap or kill biofilmsare performed, there is littlereason to believe that anydental unit can avoid beingcolonized by bacteria.

If the bacteria are there,the next logical question—because we know that someof the bacteria have beenshown to produce disease—should be FAQ 6.

FAQ 6. IS THERE ANYPROVEN HEALTH RISK?

Epidemiologic studies. Thefirst part of the evidence basisfor answering this question lieswith three epidemiologic stud-ies. In 1974, Clark28 recoveredthe same species of gram-negative bacteria (Pseudomonasspecies) from dental units andthe nasal flora of 14 of 30 den-tists he evaluated. While noclinical symptoms were report-ed, seeding of the respiratorytract with gram-negative bacte-ria has been identified as anantecedent event in the devel-opment of gram-negative pneu-monia in hospitalized patients.29

Studies have demonstrated thatdental health care workers

show evidence of increasedexposure to Legionella bacteriaas evidenced by elevated anti-body titers when compared withdemographically similar controlpopulations. Although thesestudies suggest a possibleincreased risk of experiencingillness among dental healthcare workers, no clinical casesof legionellosis were reported ineither study.30,31

Clinical case reports.Martin32 published a case reportdescribing P. aeruginosa woundinfections in two immunocom-promised patients. The organ-

ism isolated from the infectedsites was matched by pyocintyping to bacteria recoveredfrom the dental unit. In bothinstances, the patients weretreated and recovered.32 In anarticle describing the preva-lence of Legionella contamina-tion in dental unit water, Atlasand Williams22 mentioned thecase of a 65-year-old dentistwho died after developinglegionnaires’ pneumonia.

Although several species ofLegionella bacteria were isolat-ed in high numbers from a den-tal water source in his office, aswell as in low levels fromsources in his home, theauthors were unable to estab-lish a conclusive dental associa-tion.22 As previously mentioned,a small-scale study in Denmarkfailed to identify exposure tocontaminated water as a riskfactor for increased incidence ofrespiratory infection in patientswith CF who were undergoingdental treatment.25

Legal cases. A 1990 civilsuit against a dental unit man-ufacturer was reported anecdo-tally by Dr. Robert Runnels (R.Runnels, D.D.S., written com-munication, October 1999). The

plaintiff claimed that bacteri-al endocarditis and the needfor subsequent prostheticheart valve surgery resultedfrom dental treatment withcontaminated water. Thesame strain of gram-negative water bacteria

(Moraxella) was isolated fromthe patient and the dentalunit. The plaintiff intended toargue that the organismentered the unit as a result ofretraction of oral flora thatoccurred because the dentalunit was not equipped with anantiretraction valve. AlthoughDr. Runnels was asked to pro-vide an expert opinion in thecase, he was not required tosign a nondisclosure statementand therefore was free to dis-cuss the case. Subsequently, thecase was settled out of court foran undisclosed sum (R. Run-nels, D.D.S., written communi-cation, October 1999).

Dr. Edward Zinman, a den-tist and lawyer, disclosed a sec-ond legal case during a two-part “CBS Morning News” seg-


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Unlessprocedures

specifically designed toprevent, eliminate, trap orkill biofilms are performed,

there is little reason tobelieve that any dental unit

can avoid being colonized by

bacteria.


ment on DUWLs that wasbroadcast on Oct. 11 and 12,1999.33 The plaintiff, who suf-fered a brain abscess afterundergoing dental treatment,claimed that her illness result-ed from exposure to contami-nated dental treatment waterand won an out-of-court settle-ment against her dentist. Theplaintiff also was interviewedby ABC News, in a nationallybroadcast segment on “20/20”that aired originally on Feb. 18,2000.34

Unfortunately, the clinicalparticulars of these cases areunknown since no scientificinvestigation has been pub-lished to date.

Environmental investiga-tions. Endotoxins are lipopoly-saccharides in the cell wall ofgram-negative bacteria that canproduce a wide range of physio-logical responses, includinglocalized inflammation, feverand even toxic shock.35 Sincemany of the organisms recov-ered in dental treatment waterare gram-negative bacteria,some researchers have specu-lated about the presence of bac-terial endotoxins in dentaltreatment water. Recently,Puttaiah and Cederberg36

reported that contaminateddental treatment water indeedmay contain levels of endotoxinas high as 500 endotoxinunits/mL, or EU/mL, with anaverage of about 80 EU/mL. Incomparison, the United StatesPharmacopeia, or USP, sets alimit for endotoxin in sterilewater for irrigation at only 0.25EU/mL.37 At present, thereappear to be no standards forendotoxin in drinking or recre-ational waters.

Unanswered health ques-tions. While the clinical effectsof endotoxin in treatment water

are unknown, Mathew and col-leagues38 found a significantdecrease in lung function in 15percent of 57 children aged 6years through 18 years whounderwent dental treatment.Although the authors did notsuggest an association with res-pirable contaminants from den-tal handpiece coolant spray,bacterial endotoxin is a recog-nized trigger for asthma.35,39

Further investigation may helpclarify whether such an associa-tion exists.

Most investigations of dentalwater have focused on bacterialcontamination. As previouslynoted, however, fungi and proto-zoa also are present and mayhave health consequences. Forexample, Cladosporium is anaquatic fungus recovered fromDUWLs4,10,40 that has been asso-ciated with hypersensitivitypneumonitis.41 In addition totheir ability to serve as a host forreplication of bacteria, some ofthe protozoa identified as inhabi-tants of water systems also arepotentially pathogenic.42-44

There also has been specu-lation on the issue of disinfec-tant byproducts such as tri-halomethanes resulting fromchemical treatment of biofilm-colonized dental unit watersystems.19 This problem maybe most acute when chemicalagents are introduced continu-ously into systems that stillharbor residual biofilm matrix.

Whatever the true nature ofhealth effects associated withmicrobially contaminated den-tal treatment water, there islittle evidence of a major pub-lic health problem—at leastnot in terms of the “dead bod-ies” that some people seek asproof. Nevertheless, the evi-dence suggests reason for con-cern. As a result, the issue has

come to the attention of regu-latory agencies and advisorybodies at both state and feder-al levels.

FAQ 7. WHAT RECOMMENDATIONS ORREGULATIONS ADDRESSTHE QUALITY OF DENTALTREATMENT WATER?

Recommendations. TheCenters for Disease Control andPrevention RecommendedInfection Control Practices forDentistry, 1993, urged dentiststo install and maintain anti-retraction valves to prevent oralfluids from being drawn intoDUWLs. They also recommend-ed flushing waterlines daily forseveral minutes and for 20 to 30seconds between patients to dis-charge oral fluids that mayhave entered the lines duringtreatment. Furthermore, theystated that only sterile solutionsshould be used for proceduresthat involve the cutting of bone.5

The 1996 American DentalAssociation6 statement onDUWLs challenged the dentalmanufacturing industry todevelop methods to controlbiofilms in dental unit watersystems. The statement estab-lished a goal for dental water tocontain no more than 200CFU/mL of heterotrophic bacte-ria in unfiltered output.6 TheOrganization for Safety andAsepsis Procedures45 issued astatement in 1996 supportingboth the CDC and ADA guide-lines, but containing moreexplicit guidance on waterlinemonitoring and the use of ster-ile irrigants in surgery.

The ADA waterline panelreconvened in early 1999 toreview the progress made inpursuit of the 1996 goal. Thepanelists concluded thatindustry had responded with awide range of potential solu-


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tions and that the goal ofimproved dental treatmentwater is achievable.46 TheADA Seal of Acceptance pro-gram now includes productsintended to maintain dentalwater quality.

Regulations. At present,there appear to be no state orlocal laws or regulations thatspecifically address the den-tist’s obligations to ensuredental treatment water quali-ty. Existing rules for drink-ing water quality, however,may be enforceable in dentalclinics, especially those per-taining to coliforms orLegionella contamination.12

(The Safe Drinking WaterAct sets limits for hetero-trophic water bacteria, aswell as these specificorganisms, in drinkingwater.12) While the topicwas not specificallyaddressed by an Occupa-tional Safety and HealthAdministration rule, theagency’s compliance officersrecently were advised of thepotential for occupationalexposure to bacteria fromcontaminated DUWLs.47

Manufacturers of dentalunits and products intendedto improve the quality of den-tal treatment water are obli-gated to comply with a num-ber of federal laws and regu-lations enforced by the U.S.Food and Drug Administra-tion, or FDA, and the U.S.Environmental ProtectionAgency, or EPA. Theserequirements will be dis-cussed later in this article(see page 1437).

In 1997, the CaliforniaState Board of DentalExaminers held hearings onthe subject of dental watercontamination. The board has

established a requirement forthe use of sterile irrigatingsolutions for invasive pro-cedures and accepted an adhoc DUWL committee reportrecommending no additionalaction before 2000.48 InFebruary 1999, a bill wasintroduced into the CaliforniaState Assembly (AssemblyBill 498) that would haveestablished the ADA goal of200 CFU/mL as an enforce-able standard after January1, 2001.49 Failure to provide

water meeting this standardwould have constituted unpro-fessional conduct under thestate Business andProfessions Code. Althoughthe 1999 assembly did notpass the bill, a revised versionwas introduced for 2000 thatwould direct state healthauthorities to investigate thepotential health consequencesof the presence of pathogenicbacteria in water in a varietyof public settings, includingdental offices.50

FAQ 8. WHY SHOULD WE DO ANYTHING ABOUT WATERLINE CONTAMINATION?

For those not yet persuaded toaction by the evidence provided,I offer the following rationale:clinical infection control pro-cedures concentrate on break-ing the chain of infection thatconsists of potential pathogensin sufficient numbers, a suscep-tible host and a portal of entry.The susceptibility of the host(patient or health care worker)and the pathogenicity of theorganisms are the links overwhich we have the least control.For this reason, most efforts tobreak the chain concentrate onreducing the numbers oforganisms in the clinical envi-ronment. Indeed, most dentalpractices expend consider-able effort and expense toaccomplish this goal as aneveryday matter throughsurface disinfection, instru-

ment sterilization, hand-washing and use of antimicro-bial mouthrinses.

As with recommendations toimprove the quality of dentaltreatment water, few of theaforementioned procedures arebased on strong epidemiologicevidence. Nevertheless, reduc-ing the numbers of microbes inwater from dental units isabsolutely consistent with long-accepted infection control prin-ciples. Does it make sense tosterilize a dental handpiece,store it in an impervious pack-age designed to ensure itssterility, and then use it tointroduce into the oral cavitywater that fails to meet accept-ed microbiological standards fordrinking or recreational water?

The reader also may wish toconsider the issue in light of thedoctrine of informed consent. As


COVER STORY

Atpresent, there

appear to be no stateor local laws or

regulations that specificallyaddress the dentist’s

obligations to ensure dentaltreatment water quality.

Existing rules for drinkingwater quality, however,may be enforceable in

dental clinics.


do all health care professionals,dentists have an ethical obliga-tion to provide patients andemployees alike with a safeclinical environment. Patientsmust be informed of potentialrisks associated with treatmentand provide their consent. Simi-larly, employees may need to beinformed of potential hazardsas defined under statutesdirecting the “right to know.”While the incidence of infec-tions associated with contami-nated dental treatment waterappears to be low, would mostpatients consent to treatmentwith water contaminated withthousands or even millions ofbacteria?

If the reader accepts that theanswer to each of these ques-tions is “no,” the next questionthat must be answered is FAQ 9.

FAQ 9. WHAT MEANS ARE NOW AVAILABLE TOIMPROVE AND MAINTAINTHE QUALITY OF WATERUSED ON DENTAL TREATMENT?

Current approaches. Re-searchers beginning withBlake1 in 1963 have investigat-ed treatment options intendedto maintain the quality of den-tal treatment water. Thelargest number of studies ofwaterline treatment publishedover the last 37 years haveinvestigated various chemicalagents intended to inactivatemicroorganisms, induce detach-ment of biofilms or both. Thesecond largest group of studiesexamined the flushing of water-lines; the use of filters hasreceived the least attention inthe peer-reviewed literature.2

On the basis of this researchand other work in the relatedfields of microbiology and engi-neering, a number of products

have been developed. Moststrategies to improve the quali-ty of water provided by conven-tional dental units employ theuse of chemical treatmenteither alone or in combinationwith other technologies, includ-ing microfiltration. Anotheralternative is to entirely bypassthe conventional dental waterdelivery system and use eitherautoclavable or disposable pathways.

Waterline flushing. Theefficacy of mechanical flushingalone to control microbial con-tamination in dental unit wateris not well-supported by the sci-entific literature.10,11,17,51,52 Al-though flushing can temporari-ly reduce the number of organ-isms suspended in DUWLs,there is no predictable effect onadherent biofilm. Bacterialaggregates breaking free fromthe biofilm have been shown torecontaminate dental unitwater during the course of sub-sequent clinical treatment.17

Flushing for several secondsbetween patients, however, mayremove materials that mayhave entered the water systemduring patient treatment.

Independent reservoirs.Independent reservoir systemsare available as original equip-ment or as after-market acces-sories for most dental units. Byisolating the dental unit fromthe municipal water supply, theclinician can control the qualityof water introduced into thesystem. But without treatmentwith chemical agents to inacti-vate or detach biofilm or instal-lation of point-of-use filters,independent reservoirs are oflittle value in improving thequality of treatment water.Independent reservoirs are rel-atively inexpensive to installcompared with other devices.

Some dental manufacturersnow ship independent reser-voirs as standard equipment,and after-market units can beinstalled for as little as $100per unit. Recurring costs willdepend on the source water and treatment agents selectedfor use.

Chemical treatment. Anideal agent for control of biofilmwould be bactericidal but nottoxic or irritating to humans. Itwould detach biofilm and dis-courage subsequent reforma-tion, while protecting the dentalunit’s internal components fromcorrosion or degradation. Ifdelivered continuously in treat-ment water, it would have noeffect on enamel or dentinbonding agents. And, of course,to be truly ideal, it would beinexpensive and easy to use.Although such an agent doesnot appear to exist, there areproducts that possess some ofthese desired characteristics.

Intermittent chemical release.Chemicals may be introducedinto water systems either inter-mittently or continuously. Mostintermittent treatment regi-mens use potentially biocidalconcentrations of germicide thatalso may remove biofilm. Bor-rowing terminology from theswimming pool industry—whichmust also deal with biofilm—some experts refer to thisapproach as “shock treatment.”The usual practice is to deliverthe agent for a specified contacttime and frequency using anindependent water reservoirthat isolates the unit from themunicipal water supply. Thisalso permits the use of water ofknown microbiological qualityfor subsequent therapeutic pro-cedures. A major advantage ofintermittent chemical use isthat the active agent is purged


COVER STORY


from the system before patienttreatment. Disadvantagesinclude the potential for surviv-ing biofilm organisms torebound between treatments;potential staff exposure tochemicals; and the potential foradverse impact on metal, rub-ber and synthetic dental unitcomponents.

Continuous chemical treat-ment. Continuous treatmentuses either lower concentrationsof potentially biocidal agents orless toxic (biostatic) substancesin the water used for patienttreatment (just as municipalwater systems rely on residualchlorine to maintain the safetyof drinking water). Continuoustreatment regimens also mayemploy initial shock treatmentto inactivate or eliminatebiofilms. Although continuoustreatment offers less poten-tial for recolonization ofwaterlines, it still may dam-age equipment. Since theagent is always present andmay be aerosolized, the effectsof chronic exposure on thehealth care worker must be con-sidered. Enamel and dentinbond strength of dental adhe-sive materials also may beaffected.53,54

Chlorine compounds havebeen studied more extensivelythan any other class of chemicalagents intended to control oreliminate biofilm in dental unitwater systems. Although mostinvestigators have used sodiumhypochlorite (usually in theform of diluted householdbleach in varying concentra-tions),11,19,55-59 chloramine T40 andelemental chlorine3 also havebeen evaluated. Sodiumhypochlorite is a potent germi-cide with broad-spectrumantimicrobial action that isused widely to treat both

potable and recreational watersand has shown promisingresults as a means to improvethe quality of treatment waterin numerous clinical trials.Several manufacturers of den-tal equipment—including A-dec,DCI International, DentalEZand Proma—now authorizeweekly treatment of water sys-tems with household bleachdiluted 1:10 to control biofilmaccumulation and improve thequality of treatment water.However, no sodium hypochlo-

rite–based solution has beensubmitted to the FDA for clear-ance or registered with the EPAspecifically as a waterline biocide.

Although some investigatorshave voiced concern about theformation of potentially carcino-genic disinfectant byproducts,such as tri-halomethanes, as aresult of chlorine’s reactingwith biofilm organic polymers,the use of intermittent protocolsminimizes the exposure risk forpatients and staff. However, the

use of chlorinated treatmentwater in the presence of resid-ual biofilm may increase thisrisk. Although Karpay and col-leagues19 detected tri-halometh-anes when rechlorinated tapwater with three parts per mil-lion, or ppm, free chlorine wasused in independent reservoirs,none of their samples exceededEPA limits.

While household bleach isinexpensive and readily avail-able, the relative complexity ofthe treatment protocols mayresult in noncompliance byoffice staff and subsequent re-establishment of biofilm (aproblem not unique to the use

of bleach).55 As an oxidizingagent, sodium hypochloritecan corrode metal compo-nents and damage rubberor synthetics. Nevertheless,these effects can be limitedby following the manufac-turer’s recommendation.56

Other agents that havebeen proposed or evaluated

for improving dental waterquality include chlorhexidinegluconate, hydrogen peroxide,iodophors and commercialmouthrinses. Recently, severalproprietary agents havereceived FDA clearance formarketing as waterline clean-ers. These include a glycerin-based bur lubricant (introducedcontinuously) that contains 0.12percent chlorhexidine glu-conate, 12 percent ethanol andflavoring agents (Bio 2000,Micrylium Laboratories), ahydrogen peroxide–based solu-tion used intermittently(Sterilex Ultra, Sterilex Corp.),and a citric acid–based product(Bioclear, Waggoner ProductDevelopment Corp.). Dentacide(Frio Technologies) is an iodine-based solution sold as a periodicwaterline cleaner and thereby


COVER STORY

Sodiumhypochlorite is a

potent germicide withbroad-spectrum

antimicrobial action that isused to treat both potable

and recreational waters andhas shown promising results

as a means to improvethe quality of

treatment water.


is exempted from EPA or FDArequirements.

The table presents, as exam-ples, four of the proprietarysolutions available for improv-ing and maintaining the qualityof dental treatment water.

As a result of an agreementbetween the FDA and the EPA,waterline treatment agents thatare not part of a device (such asbleach protocols used withFDA-cleared dental units) nowmust be registered by the EPA.Agents that are continuouslypresent in dental water systemsare considered therapeuticagents and also must be clearedby the FDA. At present, neitherthe FDA nor the EPA will per-mit the marketers of chemicalwaterline agents to makeclaims either for germicidal effi-cacy or biofilm removal in den-tal unit water systems. There-fore, all FDA-cleared productsin this category must be labeledas cleaners rather than germi-cides. Before they will be able

to make germicidal claims,makers of chemical agents alsomust register their productswith the EPA as required bythe Federal Insecticide,Fungicide and Rodenticide Act.To provide standard evaluationmethods for this application,the ADA and the AmericanNational Standards Institute,or ANSI, have joined forcesthrough the Accredited Stand-ards Committee MD 156 andhave initiated a work project todevelop a national specificationfor DUWL antimicrobial agents.

Although it may be temptingto experiment with variouschemicals and to invent newtreatment protocols, the poten-tial for unintended conse-quences is real. The conceptthat “if a little bit of somethingis good, a lot more would bebetter” can result in damage toequipment and harm topatients or staff. The prudentclinician always will seekadvice from the equipment

manufacturer or supplierbefore using any chemicalagent or device.

Automated treatmentdevices. Devices to introducechemical agents into the watersystem automatically also areavailable. This approach poten-tially could reduce the effect ofcompliance variables on clinicalsuccess. Devices such as theOdyssey I (Tuttnauer USA)generate an ozone and silvergermicide via electrolytic actionon incoming water. Periodictreatment regimens also can beautomated using devices suchas the Clean Source 1 (Aquar-ius Technologies) or the PortaPurge (Micrylium Labora-tories). DentaPure iodinatedresin cartridges (MLRBInternational) continuouslyrelease 2 to 6 ppm free iodineinto treatment water to controlbiofilm; their use life rangesfrom one week to one year.These cartridges may be usedeither with municipal water


COVER STORY

TABLE

A COMPARISON OF PROPRIETARY WATER TREATMENT CHEMICALS.

Bio 2000

Bioclear

Dentacide

SterilexUltra

MicryliumLaboratories

Waggoner ProductDevelopmentCorp.

Frio Technologies

Sterilex Corp.

Glycerin-based bur lubricant (chlorhexidinegluconate 0.12 percent, alcohol 12 percent) usedcontinuously and/orovernight

Citric acid (0.224 percent)used continuously

Iodine-based cleaning solu-tion used daily (overnight)

Alkaline peroxide-based,used weekly; is hydrolytic,oxidative and lipid- andwater-soluble

Kills Pseudomonasaeruginosa

Eliminates andprevents attach-ment of biofiolms

Is safe for mostdental equipmentcomponents

Eliminates andprevents attach-ment of biofiolms

Is safe for mostdental equipmentcomponents

Breaks up biofilms

PRODUCTNAME

MANUFACTURER MANUFACTURER’SCLAIMS

DESCRIPTION


connections or in independentwater reservoirs.

The source water dilem-ma. Irrespective of the methodused to control or eliminatebiofilm in the water system, thequality of unfiltered output canbe no better than that of thewater entering the system.Some independent water sys-tems are equipped with abypass switch that allows theclinician to switch back andforth from independent reser-voirs to municipal water. Otheroffices refill reservoirs withwater from the tap. Althoughtap water may meet drinkingwater standards, it usually con-tains some viable bacteria andorganic molecules that accumu-late on waterline surfaces andcan quickly initiate new biofilmformation. Using water ofknown microbiological qualityis the best way to eliminateuncertainty and ensure consis-tent delivery of high-qualitytreatment water.

An excellent source of waterfor use in dental water systemsis bottled sterile water for irri-gation, as it not only is free ofviable microorganisms but alsohas very low levels of mineralsand organic compounds thatcan encourage re-establishmentof biofilm. No conventional den-tal unit, however, can deliversterile irrigating solutionsunless the water pathway issterile as well.

If an autoclave with a fluidsterilization cycle is available,the office can prepare sterilewater for use in independentreservoirs. Heating water toboiling also can produce waterfree from viable vegetative bac-teria. However, minerals andorganic compounds still will bepresent in sterile or boiled tapwater.

Continuous ultraviolet ger-micidal irradiation, or UVGI, ofincoming tap water may reducethe numbers of viable microbesin incoming water. The OdysseyI (Tuttnauer USA) and theWater Purifier System (DCIInternational) both employUVGI for this purpose. How-ever, bulbs must be replaced atspecific intervals, since theylose germicidal efficacy overtime.

While distillers and deion-izers can reduce mineral ororganic content, they are lessreliable in eliminating bacterialcontamination. Distiller hosesand holding tanks must becleaned on a regular basis toensure water of acceptablequality. The membranes andresin columns used to deionizewater actually may become col-onized with biofilm them-selves.60 Alternatively, thesource water may be treatedwith chemicals or replaced al-together with alternative solu-tions.

Filtration. While relativelyfew studies in peer-reviewedjournals have evaluated theefficacy of filtration in dentalunits,57,61,62 micropore membranefilters are used to removemicroorganisms from water andsolutions in a wide range ofmedical and industrial applica-tions. Filtration is even used tosterilize heat-labile sterilepharmaceutical solutions.63 Inthe dental clinic setting, howev-er, the carefully controlled con-ditions and sterility assuranceprograms found in pharmaceu-tical plants and research labo-ratories are impractical. If theunits are connected to munici-pal water supplies, the wateralso may contain impurities—including minerals, organiccompounds and endotoxin—that

are not always removed by fil-ters. Therefore, even whenwater produced by filtration inthe dental clinic is bacteria-free, it should not be used inplace of sterile water in surgicalprocedures.

Nevertheless, studies con-ducted to date suggest that fil-ters can produce water thatmeets or exceeds the 200CFU/mL goal established bythe ADA for nonsurgical pro-cedures when used according tothe manufacturer’s recommen-dations. Two independent eval-uations of microfiltered waterused in dentistry found that 80percent of output water sam-ples were bacteria-free, andnone of the remaining speci-mens exceeded 200 CFU/mL ofheterotrophic plate count bacte-ria.63,64 Murdoch-Kinch and col-leagues57 found that use of 0.22-µm filters resulted in fewernumbers of organisms observedon scanning electron microscopyin postfiltration tubing sectionsthan in prefiltration sections.Mayo and Brown62 found nodetectable organisms in watersamples taken immediatelydownstream from 0.2-µm pro-prietary filters; however, whenthey increased the distance atwhich the filter was placedfrom the air water syringe, lev-els of bacteria in effluent waterincreased—probably owing tothe formation of biofilm in thepostfiltration waterlines.

Among the potential advan-tages of filters are the reductionor elimination of reliance onchemicals, the potential fordamage to dental units and pos-sible staff exposure to chemicalresidues. Installation usuallycan be performed at minimalcost; it requires only the place-ment of a filter housing on eachwater-bearing line as close as


COVER STORY


possible to the handpiece orwater syringe. In addition,units may remain connected tothe municipal water supply.

While filters have beenshown to be effective in remov-ing suspended bacteria fromdental treatment water, theywill have no effect on thebiofilm that continues to flour-ish in the prefiltration seg-ments of waterlines unless con-comitant treatment to removethem is performed. Persistenceof biofilm in the dental unitwater system carries the atten-dant risk of biofouling, cloggingand elution of endotoxin intreatment water. Someexperts have speculated thatultramicrobacteria—extremely small but viablebacterial cells that developunder conditions of nutrientdeprivation16—may passthrough membrane filtersmore easily than typical veg-etative bacterial cells.Testing by the manufacturerthat validates the use-life of fil-ters using worst-case testorganisms can help preventsuch problems in the clinicalsetting. As with all therapeuticinterventions, conscientiouscompliance with the manufac-turer’s instructions will helpensure optimal performance.

At least three companies arecurrently marketing filter sys-tems. SciTech Corp. providestwo products, including Clear-line One-Day (a disposable0.22-µm filter changed daily)and Clearline Plus (a 0.22-µmdisposable filter with a built-inantiretraction valve and a one-week use-life). SciTech recom-mends periodic cleaning thepostfilter waterline to preventbiofilm accumulation. PallCorp. markets the AquasafeDental Water Filtration

System, which consists of a sin-gle reusable filter housing withtwo different 0.2-µm filter ele-ments. The standard filterremoves bacteria and has a one-day use-life. The high-performance filter element alsoremoves endotoxin and has anoptimal performance durationof one patient. The DentaPurepoint-of-use filter from MLRBInternational Inc. employs aniodinated resin in combinationwith a 0.22-µm point-of-use fil-ter. The release of small

amounts (5 ppm) of iodine pur-portedly retards the growth ofbiofilm formation in the postfil-tration tubing segment.

Sterile water delivery sys-tems. Since conventional dentalunits cannot be sterilized, theycannot reliably provide sterilewater for use in surgical pro-cedures—even when they aretreated with chemical agents orfiltration. Sterile water deliverysystems bypass or replace thedental unit water system to pro-vide sterile irrigants for powered

surgical instruments. Examplesof sterile water delivery systemsinclude a variety of oral surgeryand implant handpiece systems.Other devices bypass the dentalunit water delivery systems invarious ways. The Sterile WaterPump (Biotrol) uses an electricperistaltic pump and a speciallymodified International Stand-ards Organization, or ISO, con-nector to deliver water from astandard intravenous bag andIV tubing to air-driven hand-pieces. The AXCS SterileIrrigation System (DentalEZ)system also uses bagged solu-tions but relies on a pressurizedcuff to drive the solutions. Anair-powered pinch-valve assem-bly attached to a second ISOconnector controls the flow offluids through a standard IVset connected to the hand-piece by an adapter. TheAquaSept device (LaresDental) uses an autoclavablereservoir and handpiece tub-

ing assembly to replace eachwater-carrying line. The reser-voirs can be filled with clean orsterile solutions depending onthe application. The SteriWatersystem (Veltek Associates) pro-vides an entire miniaturizeddental unit assembly including acontrol block, handpiece linesand a fluid reservoir that can besterilized between patients in atabletop autoclave.

FAQ 10. SHOULD I TESTMY WATER?

Although clinicians may becurious as to whether specificorganisms with greater path-ogenic potential are present indental units, routine testing forspecific organisms such asLegionella or Pseudomonasrarely is indicated because cur-rent treatment methods targetthe entire biofilm, rather than


COVER STORY

Sinceconventional

dental units cannotbe sterilized, they

cannot reliably providesterile water for use in

surgical procedures—evenwhen they are treatedwith chemical agents

or filtration.


specific organ-isms. A nega-tive test for adifficult-to-cul-ture pathogensuch asLegionella at agiven time maygive falseassurance ofthe safety ofdental treat-ment water.Unless a differ-ent treatmentregimen will beused when spe-

cific organisms are recovered,there is no need for such testingexcept when directed by localhealth authorities as part of aninvestigation of a suspectedwaterborne illness. The docu-mented isolation of pathogenicorganisms from dental watersystems also may havemedicolegal implications fordental practice. For these andother reasons, current CDCguidelines do not recommendroutine microbiological cultur-ing of environmental and med-ical device surfaces.66

Monitoring. Some research-ers have suggested that compli-ance may play an importantrole in the success of clinicalefforts to maintain the qualityof dental treatment water.19,55

Monitoring is a process distinctfrom environmental samplingthat can help identify tech-nique errors or noncompliance;it also can provide positivereinforcement for the dentalstaff. Clinical monitoring is aquality assurance process, how-ever, not a validation of processefficacy. The manufacturermust perform adequate tests toensure the safety and efficacyof products before they aremarketed. These studies also

should determine the need for,and frequency of, monitoring inthe clinical setting. In general,test methods used to enumer-ate noncoliform bacteria indrinking water should be ade-quate to ensure compliancewith water management procedures.

DECIDING WHAT TO DO

In the final analysis, the deci-sion to take measures toimprove and maintain the qual-ity of water used in dental prac-tice lies with the dentist. Pru-dent clinicians who choose totake this issue seriously shouldconsider the following recom-mendations. dReview the scientific litera-ture to keep current on newdevelopments and be preparedto answer questions frompatients and staff. dUse only sterile fluids forsurgical procedures.dContact the equipment man-ufacturer or dealer to obtaincurrent recommendations forimproving and maintainingwater quality. dWhen purchasing new equip-ment, select products that canreliably and economically main-tain good water quality.

SUMMARY

DUWL cleanliness is not a pub-lic health crisis. Nevertheless,water that is unfit to drink asdefined by nationally recog-nized standards is unsuitablefor therapeutic use in dentistry.Continued inaction on the partof the dental profession canserve only to undermine publicconfidence in our commitmentto quality dental care. ■

The opinions expressed in this article arethose of the author and do not reflect the offi-cial policy of the U.S. Department of Defenseor other departments of the U.S. government.

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2. Mills SE, Karpay RI. Critical comparisonof peer-reviewed articles on dental unitwaterline treatment methods. Paper present-ed at: Organization for Safety and AsepsisProcedures Annual Symposium; June 27,1997; Portland, Ore.

3. Pankhurst CL, Philpott-Howard JN,Hewitt JH, Casewell MW. The efficacy ofchlorination and filtration in the control anderadication of Legionella from dental chairwater systems. J Hosp Infect 1990;16:9-18.

4. Williams JF, Johnston AM, Johnson B,Huntington MK, Mackenzie CD. Microbialcontamination of dental unit waterlines:prevalence, intensity and microbiologicalcharacteristics. JADA 1993;124(10):59-65.

5. Centers for Disease Control andPrevention. Recommended infection controlpractices for dentistry, 1993. MMWR1993;42(No. RR-8):1-12.

6. Shearer BG. Biofilm and the dentaloffice. JADA 1996;127:181-9.

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8. Marsh PD, Bradshaw DJ. Dental plaqueas a biofilm. J Ind Microbiol 1995;15:169-75.

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11. Williams HN, Baer ML, Kelley JI.Contribution of biofilm bacteria to the con-tamination of the dental unit water supply.JADA 1995;126:1255-60.

12. U.S. Environmental Protection Agency.National primary drinking water regulations,1999. Available at: “www.epa.gov/safewater/mcl.html”. Accessed Jan. 31, 2000.

13. American Public Health Association.Standard methods for the examination ofwater and wastewater. 20th ed. In: EatonAD, Clesceri LS, Greenberg AE, eds.Washington: American Public HealthAssociation; 1999.

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15. MacKenzie WR, Hoxie NJ, Proctor ME,et al. A massive outbreak in Milwaukee ofCryptosporidium infection transmittedthrough the public water supply. N Engl JMed 1994;331:161-7.

16. Costerton JW. Overview of microbialbiofilms. J Ind Microbiol 1995;15(3):137-40.

17. Santiago JI, Huntington MK, JohnstonAM, et al. Microbial contamination of dentalunit waterlines: short- and long-term effectsof flushing. Gen Dent 1994;48:528-44.

18. Nemeth JF, Sherman LR, Mills SE,Plamondon TJ. The measurement of chlorineactivity in biofilm contaminated dental unitwater lines. Microchem J 1997;55:134-44.

19. Karpay RI, Plamondon TJ, Mills SE,


COVER STORY

Dr. Mills is a colonel,

U.S. Air Force Dental

Corps, and the den-

tal program manag-

er, Office of the U.S.

Air Force Surgeon

General, Bolling Air

Force Base,

Washington. Address

reprint requests to

Dr. Mills at 12312

Dendron Place, Fort

Washington, Md.,

20744, e-mail

“[email protected]”.

Dr. Mills is a coinventor of the AXCSSterile Irrigation System, which has beenlicensed by the U.S. Air Force to DentalEZInc. He is eligible to receive a percentage ofroyalties collected by the Air Force. Heholds no other proprietary interest in anycommercial products or services.


Dove SB. Combining periodic and continuoussodium hypochlorite treatment to controlbiofilms in dental unit water systems. JADA1999;130:957-65.

20. Williams HN, Quinby H, Romberg E.Evaluation and use of a low nutrient mediumand reduced incubation temperature to studybacterial contamination in the water supplyof dental units. Can J Microbiol 1994;40:127-31.

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25. Jensen ET, Giwercman B, Ojeniyi B, etal. Epidemiology of Pseudomonas aeruginosain cystic fibrosis and the possible role of con-tamination by dental equipment. J HospInfect 1997;36:117-22.

26. Centers for Disease Control andPrevention. Legionellosis: legionnaires’ dis-ease and Pontiac fever. Available at: “www.cdc.gov/ncidod/dbmd/diseaseinfo/legionellosis-g.htm”. Accessed Feb. 1, 2000.

27. Schulze-Robbecke R, Feldmann C,Fischeder R, Janning B, Exner M, Wahl G.Dental units: an environmental study ofsources of potentially pathogenic mycobacte-ria. Tuber Lung Dis 1995;76(4):318-23.

28. Clark A. Bacterial colonization of dentalunits and the nasal flora of dental personnel.Proc R Soc Med 1974;67:1269-70.

29. Penn RG, Sanders WL, Sanders CC.Colonization of the oropharynx with gram-negative bacilli: a major antecedent to nosoco-mial pneumonia. Am J Infect Control1981;9:25-34.

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33. [Dental unit waterlines]. “CBS MorningNews.” CBS television, Oct. 11-12, 1999.

34. Dirty dental water. “20/20.” ABC televi-sion, Feb. 18, 2000.

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(AADR abstract 1257). J Dent Res 1998;77:263.

37. United States Pharmacopeial Conven-tion. Sterile water for irrigation. In: UnitedStates Pharmacopeial Convention. UnitedStates pharmacopeia and national formulary(USP 24-NF19). Rockville, Md.: United StatesPharmacopeial Convention; 1997:1753.

38. Mathew T, Casamassimo PS, Wilson S,Preisch J, Allen E, Hayes JR. Effect of dentaltreatment on the lung function of childrenwith asthma. JADA 1998;129:1120-8.

39. Kline JN, Cowden JD, HunninghakeGW, et al. Variable airway responsiveness toinhaled lipopolysaccharide. Am J Respir CritCare Med 1999;160(1):297-303.

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42. Bottone EJ. Free-living amebas of thegenera Acanthamoeba and Naegleria: anoverview and basic microbiologic correlates.Mt Sinai J Med 1993;60(4):260-70.

43. el-Fakahany AF, Fahmy RR, MohamedAS. Free living amoebae as opportunistic par-asites in immunocompromised hosts. J EgyptSoc Parasitol 1997;27(2):515-27.

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45. Organization for Safety and AsepsisProcedures. OSAP statements on dental unitwaterlines 1996. Annapolis, Md.: Organi-zation for Safety and Asepsis Procedures;1996. Available at: “www.osap.org/water/pp-duwl.htm”. Accessed Aug. 23, 2000.

46. ADA Council on Scientific Affairs.Dental unit waterlines: approaching the year2000. JADA 1999;130:1653-64.

47. Occupational Safety and HealthAdministration. Legionnaires’ disease. In:OSHA technical manual TED 1-0.15A [manu-al online]. Washington: Occupational Safetyand Health Administration; 1999. Availableat: “www.osha-slc.gov/dts/osta/otm/otm_iii/otm_iii_7.html”. Accessed Aug. 23, 2000.

48. Dental unit waterline ad hoc committeeconsensus report. Sacramento, Calif.:California Board of Dental Examiners; 1997.

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Lilge C. Influence of biofilms on microbialcontamination in dental unit water. J Dent1991;19(5):290-5.

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65. Piche JE, Mills SE, Plamondon TJ.Decontamination of coolant water from ultra-sonic scalers using a proprietary 0.22 micronfilter. Paper presented at: Organization forSafety and Asepsis Procedures AnnualSymposium; June 13, 1996; Las Colinas,Texas.

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