26 Dent. Tech. N° 117 Dent. Tech. N° 117 27

In our first article on cross-contamination in the dental laboratory,we discussed the risks associated with contamination and where theresponsibility for disinfection of dental devices should lie. In thissecond article, the author will examine steps that can be taken toprevent contamination from occuring in the lab.

HEALTH & SAFETY

By Marilla Hunter

Health & Safety PART 2

““Clinical DentalTechnicians whohave direct contactwith patients mustfollow the sameprocedures asdentists.

Dental laboratories are frequentlyoverlooked when providing control measuresand guidance for infection prevention. This is despite the fact that dentaltechnicians are as at risk as other dentalhealthcare professionals of acquiring atransmissable infection, unless adequateinfection control precautions areimplemented and adhered to.

The lack of current guidance is furthercomplicated by the fact that there isambiguity as to how a dental laboratoryshould be classified; this will directly affectthe level and type of precautions required, asthese are based on risk assessment of theagents that staff routinely come into contactwith and the level of risk these present.

Whilst most dental laboratories do notgenerally have direct clinical contact withpatients, this can occur. Clinical dentaltechnicians and labs that provide shadetaking services must follow the samehygiene procedures as dentists in order toprevent cross contamination.

Even when not in contact with patients,potential routes for the transmission ofinfection do still exist via direct contact withblood or saliva through cuts and abrasionson the skin, accidental percutaneousexposure when using sharp instruments,slurry spatter and airborne infection fromaerosols created during laboratoryprocedures.

Items that have been contaminated with theblood, saliva or respiratory secretions of apatient must be disinfected prior to handling.In the UK, dentists are responsible for thedisinfection of all dental impressions anddental prostheses. Effective communicationbetween the lab and the dental surgery isessential in order to ensure that appropriatedisinfection procedures are followed. Inother countires, dentists may not have anobligation to disinfect items prior to sendingthem to the lab.

This article will explore other potentialsources of infection that exist within thelaboratory and the measures that can betaken to minimise these risks.

Infection Control inthe Dental Laboratory

Original article published in Dental Technologies Magazine, issue 117. For more information about subscribing to the journal please contact:crg.paris@wanadoo.fr or call 0800 028 4529 (UK freephone)or 0033 146 516059 (overseas).

Standard InfectionControl Precautions Standard Infection ControlPrecautions (SICPs) underpin alltreatment within healthcare and areused in all healthcare settings, forthe treatment of all patients,regardless of the infection status ofthe patient undergoing treatment.This would therefore dictate that alllaboratory work is handled in thesame way and treated as ifcontaminated or infectious. Thisensures that the risk of transmissionof infection from a patient who maybe unaware of their infection statusor has not wished to divulge this tothe dental team is minimised, as thesame procedures will be carried outfor all patients, regardless of their

medical history. There are ten SICPs(see Box A).As is evident from the list of SICPs inBox A, whilst al l of theseprecautions are applicable in allhealthcare settings, they are not allrelevant to dentistry due to thenature of our work. This isparticularly true in the laboratory,where there is no direct patientcontact.

Routine ImplementationThose SICPs that are of relevancehowever, must be implementedroutinely such as hand hygiene,which is considered the single mostimportant action to minimise the riskof transmission of infection (fig. 1).Hand hygiene can be carried out

using soap and water or an alcohol-based hand rub, which providesrapid hand disinfection and can beused in all situations as long ashands are not visibly contaminated,in which case hands must bewashed with soap and water toremove the contaminant.

PPE, control of the environment, safesegregation, disposal of waste andoccupational exposure managementare also of relevance, and localpolicies regarding these must beadhered to by all laboratory staff. Inaddition, all dental technicians mustbe aware of their immune status,including Hepatitis B, as immunisationwill substantially reduce both thenumber of staff susceptible tovaccine-preventable diseases and thepotential for disease transmission toother staff and patients.

Disinfection Impressions, prosthesesand appliances The principal route for transmissionof infection from patient totechnician is via contaminatedimpressions, prostheses andappliances as these items frequentlybecome contaminated with blood,saliva, respiratory secretions and / orfood debris, which may containbacteria, viruses and fungi.

Responsibility for ensuring all itemssent to the laboratory areappropriately disinfected lies with thedental practice or clinic and can becarried out using a variety ofmethods and disinfectant solutions.

The issues relating to thedisinfection of dental impressionsand communication with the dentistwere discussed in length in our firstarticle on Cross Contamination inthe Dental Lab (Dental Technologiesissue 115, page 12).

One important issue that was raisedrelated to the disinfection methodsused.

Dent. Tech. N° 117 29

Standard Infection Control Precautions

Box A:

When considering methods ofdisinfection, two factors are ofimportance: the effect thedisinfectant will have on thedimensional stability and surfacedetail of the impression and thedeactivating effect the impressionmaterial may have on thedisinfectant, thereby reducing theefficacy of the process.

Disinfection by immersion isgenerally preferred to spraying. Thismethod is more likely to ensure thatall surfaces of the impression,prosthesis or appliance, and inparticular any undercuts, are fullyexposed to the disinfectant solutionfor the recommended time. It hasconversely been suggested thatspraying disinfectant may reducethe risk of distorting the impression.From a Health and Safety

perspective, one benefit thatimmersion disinfection has to offeris the reduction of risk to staff frominhalation of chemicals whencarrying out the disinfectionprocess.

Whilst the method and type ofdisinfectant used is of importance,rinsing the impression, prosthesis orappliance before and afterdisinfection is also necessary.

Rinsing prior to disinfection willremove any blood, saliva or debrispresent that may prevent exposureof all surfaces of the impression,prostheses or appliance to thedisinfectant. Rinsing afterwards isnecessary to remove any residualdisinfectant that may affect thestone surface of the cast after it hasbeen poured.

As the dental practice andlaboratory are frequently not in thesame physical facility, there is a riskof cross-contamination betweenthe two settings and effectivecommunication between the two isrequired. A laboratory shouldclearly articulate their infectioncontrol requirements for submissionof work which the dental practiceor clinic must comply with andclearly identify, with a writtenrecord, that this has been carriedout to the requested standard. Allprostheses and appliances deliveredto the patient must be free ofcontamination and disinfection istherefore also required, prior tofitting a prosthesis or appliance, toreduce the risk of transmission ofinfection to the patient. Again,effective communication betweenthe laboratory and dental practice

11Extract from the WHO Poster “How to Handwash”

…

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ll HHaanndd hhyyggiieennee

ll RReessppiirraattoorryy hhyyggiieennee aanndd ccoouugghh eettiiqquueettttee

ll PPeerrssoonnaall pprrootteeccttiivvee eeqquuiippmmeenntt ((PPPPEE))

ll MMaannaaggeemmeenntt ooff ccaarree eeqquuiippmmeenntt

ll CCoonnttrrooll ooff tthhee eennvviirroonnmmeenntt

ll SSaaffee mmaannaaggeemmeenntt ooff lliinneenn

ll MMaannaaggeemmeenntt ooff bblloooodd aanndd bbooddyy fflluuiidd ssppiillllaaggeess

ll SSaaffee ddiissppoossaall ooff wwaassttee

ll OOccccuuppaattiioonnaall eexxppoossuurreemmaannaaggeemmeenntt iinncclluuddiinngg sshhaarrppss

28 Dent. Tech. N° 117

HEALTH & SAFETY

The WHO provides clear guidelines on hand hygiene

post-exposure management wouldnot be necessary, as no exposureto blood or body fluid hasoccurred. Similarly, if a sharpsinjury is sustained during the repairof a prosthesis or appliance thesame principle would apply, aswhilst in this instance the devicewill have been in contact with thepatient, assuming laboratory staffare satisfied that the device hasbeen disinfected satisfactorily priorto handling, there will again beminimal risk of blood or body fluidcontamination and subsequenttransmission of a blood-borne

virus, although risk assessment ofeach individual case and thecircumstances surrounding itshould be carried out as per local

procedure. It is necessary to ensurethat lab equipment is kept cleanand that it is steri l ised ordisinfected where appropriate.

or clinic is necessary to determinewho is responsible for the finaldisinfection process as this willensure no confusion arises as towho has final responsibility for this.

Pumice Slurry and brushesAnother major source of cross-contamination in the dental labcomes from pumice slurry andbrushes used to polish a denturebefore returning it to the dentist forfitting in the patient’s mouth. Onestudy found that slurry sampleswere heavily contaminated withpathogenic micro-organisms, andthat adding disinfectant loweredthe bacterial count (1).

This means that slurry, polishinginstruments and the dentalappliances being polished are allpotential sources of cross-contamination. The techniciandoing the polishing is at risk, aswell as the dentist who will handlethe appliance and above all thepatient who will wear it. Anotherstudy associated contaminatedslurry with the high level of eyeinfections amongst dentaltechnicians observed , due tospatter(2).

There are several preventivemeasures, which are very efficientat reducing the risks of cross-contamination; these includedisinfecting the pumice pan andchanging pumice slurry regularly,making up the slurry using anappropriate disinfectant (fig. 2),soaking brushes and rag wheelsafter each use in disinfectant toensure they are not contaminated(fig. 3) and wearing theappropriate proctective clothing(such as eye protection and a dustmask to protect from spatter).

Disinfecting surfacesWork benches, model trimmersand sinks also need to be cleanedregularly, ideally in-between casesif possible, but at least on a twice-a-day basis. All-purposedisinfectants are suitable for this .

Sharps Injuries Healthcare workers in general are atan increased risk of blood bornepathogens because of occupationalexposure to blood and other bodyfluids, although dental techniciansdo not generally come into contact

with items that present the highestrisk, such as hollow bore needlescontaining blood. Dental techniciansdo handle sharp items such as burs,cutters and screws on a daily basis(fig. 4), although the exposure riskfrom a sharps injury sustained fromthese items during the manufactureof a prosthesis or appliance wouldbe minimal as they have not havebeen in contact with a patient ortheir blood or saliva and wouldtherefore not be consideredcontaminated. In such an instance,whilst first aid must stil l beadministered as required (fig. 5),

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Pumice made up with an appropriate disinfectant reduces the risk of bacteria and fungi inthe slurry thereby limiting the risk of cross infection, as well as reducing bad smells

Brushes should be soaked in disinfectant

…

5544

Sharps injuries also present a risk of cross-contamination, though there is less riskof this in a dental lab where the instruments are not contaminated

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References

First aid must be administered as required and the risk of cross-contamination must beassessed according to each situation.

…HEALTH & SAFETY

PPEPersonal protective equipment(PPE) is designed to protect thewearer from injury or hazards thatmay be present within theenvironment (figs. 6 and 7). In thedental laboratory this wouldinclude spatter, chemicals, dust andairborne particulate matter. PPE,such as gloves, goggles and masksprovide a physical barrier betweenthe wearer and the workingenvironment. It is the responsibilityof the employer to ensure that theappropriate PPE is provided andreplaced when necessary. PPEshould always be used inconjunction with other controlmeasures that minimise exposuressuch as local exhaust ventilation(LEV) and disinfection, as PPE onlyprotects the wearer when worn.

Local exhaust ventilation(LEV)As laboratory procedures generateaerosols containing dust andchemicals such as methylmethacrylate which can be absorbedin the body by inhalation, throughthe skin and by ingestion, alllaboratories should have local exhaustventilation (LEV) to control airbornecontaminants at the point at whichthey are generated or released.Mechanical removal of these beforethey can be inhaled will minimise staffexposure to such agents and the risksassociated with these.

It is of note however, that it is notonly essential, but a legal requirementunder the Health and Safety at WorkAct 1974 and the Control ofSubstances Hazardous to HealthRegulations (COSHH) 1992, that LEVequipment is regularly maintainedand the airflow monitored at leastannually. Further guidance regardingthis can be obtained from the Healthand Safety Executive (HSE) who haveproduced guidance on therequirements of employers andemployees in relation to LEV.

(1) Jagger D. C., Haggett R., Harrison A.,(1995) Cross Infection in DentalLaboratories, British Dental Journal, 179 (3), 93-96 (2) Blair F. M., Wassell R. W., (1996) Asurvey of the methods of disinfection ofdental impressions used in Dental Hospitalsin the UK British Dental Journal, 180 (10),369-375 (3) Almortadi N., Chadwick R. G., (2010)Disinfection of dental impressions BritishDental Journal, 209, 607-611 (4) Powell G. L., Runnells R. D., Saxton B. A.,Whisenant B. K., (1990) The presence andidentification of organisms transmitted todental laboratories The Journal of ProstheticDentistry, 64 (2), 225-237 (5) How to Handwash Poster, World HealthOrganisation, 2009(6) Infection Control Recommendations forthe Dental Office and Dental Laboratory(1996) Journal American Dental Association,127 (5), 672-680 Health Protection Scotland, National InfectionPrevention and Control Manual, Chapter 1.2Hand Hygiene, Chapter 1.10 OccupationalSafety: Prevention and ExposureManagement (inlcuding sharps)(7) Cross-infection hazards associated withthe use of pumice in dental laboratories, WithS. and Hart P. J Dent, 1990

ConclusionProtective measures need to betaken by the lab manager andensuring that specific hygieneprocedures are put in place willmean that the risk of cross-contamination is minimised. SICPsmust be followed whereapplicable, but obviously these arenot al l relevant to a dentallaboratory setting. Good organinsation of theworkflow and effectivecommunication with the dentalsurgery are important for this, as itis through organisation andcommunication that appropriatedisinfection and protectionmeasures are ensured. u

By Marilla HunterSenior Dental Nurse for Infection Control

and Honorary Teaching FellowDundee Dental Hospital

Original article published in Dental Technologies Magazine, issue 117. For more information about subscribing to the journal please contact:crg.paris@wanadoo.fr or call 0800 028 4529 (UK freephone)or 0033 146 516059 (overseas).