Disinfection procedures: Their efcacy and effect ondimensional accuracy and surface quality of an irreversiblehydrocolloid impression materialA. Rentziaa, D.C. Colemanb, M.J. ODonnellb, A.H. Dowlingc, M. OSullivana,*aDivision of Restorative Dentistry and Periodontology, Dublin Dental University Hospital, University of Dublin, Trinity College Dublin, Dublin2, IrelandbMicrobiology Research Unit, Division of Oral Biosciences, Dublin Dental University Hospital, University of Dublin,Trinity College Dublin, Dublin 2, IrelandcMaterials Science Unit, Division of Oral Biosciences, Dublin Dental University Hospital, University of Dublin, Trinity College Dublin, Dublin 2,Ireland1. IntroductionThe increased awareness of infectious diseases and therecognitionof the potential for transmissionof infectiousmicroorganisms during dental procedures has led to anincreasedconcernfor, and attentionto, infectioncontrolandpreventionindental practice.1It has beensuggestedintheliterature that dental impressions which become contaminat-j o ur na l o f d e nt i s t r y3 9( 2 0 1 1 ) 1 3 3 1 4 0a r t i c l e i n f oArticle history:Received 21 October 2010Received inrevised form10 November 2010Accepted 10 November2010Keywords:DentalimpressionsAlginateIrreversiblehydrocolloidDisinfectionDimensional accuracyHypochloriteOrtho-phthalaldehydePseudomonas aeruginosaa b s t r a c tObjectives: This studyinvestigatedtheantibacterial efcacyandeffect of 0.55%ortho-phthalaldehyde(CidexOPA1)and0.5%sodiumhypochlorite(NaOCl)onthedimensionalaccuracyandsurfacequalityofgypsumcastsretrievedfromanirreversiblehydrocolloidimpression material.Methods: Asimulatedclinical castandtechniquewasdevelopedtocomparethedimen-sional accuracy andsurface quality changes of the test gypsumcasts withcontrols.Dimensional accuracy measurements were completed between xed points using a travel-lingmicroscopeunderlowangleilluminationat amagnicationof 3. Surfacequalitychangesofsmoothandroughareasonthecastwereevaluatedbymeansofopticalprolometry. The efcacy of the disinfectionprocedures against Pseudomonas aeruginosa wasevaluatedby determining the number of colony forming units (cfu) recovered after disin-fection of alginate discs inoculatedwith1 106cfu fordened intervals.Results: The dimensional accuracy of the gypsum casts was not signicantly affected by thedisinfectionprotocols. Neither disinfectantsolution nor immersion time had an effect onthe surface roughness of the smooth area on the cast, however, a signicant increase insurface roughness was observed with increasing immersion time for the rough surface.Complete elimination of viable Pseudomonas aeruginosa cells fromalginate discs wasobtained after 30 and 120 s immersion in Cidex OPA1and NaOCl, respectively.Conclusions: Immersion of irreversible hydrocolloid impressions in Cidex OPA1for 30 s wasproved to be the most effective disinfectionprocedure.# 2010 Elsevier Ltd. All rights reserved.* Corresponding author. Tel.: +353 1 612 7312; fax: +3531 612 7297.E-mail address: michael.osullivan@dental.tcd.ie (M. OSullivan).avai l abl eat www. sci encedi r ect . comjournal homepage: www.intl.elsevierhealth.com/journals/jden0300-5712/$ see front matter # 2010 Elsevier Ltd. All rights reserved.doi:10.1016/j.jdent.2010.11.003ed with patients saliva and/or blood can cross-contaminatestone casts poured against them.2The subsequent handlingoftheimpressions, followingremoval fromtheoral cavityalsohaspotential formicrobial transmission.3Until 1991,rinsing under running tap water was the recommendedprocedurefordisinfection of dental impressions.4How-ever,ithasbeenshownthatwashingimpressionmaterialswith water alone removes as little as 40% of bacteria, virusesand fungi5and therefore is totally inadequate as a means toreduce potential infectionrisks.5Best practice advocatesthat chemical disinfection of impressions is the mosteffective means of minimizing infectionrisks.4,6Awidevariety of disinfectants are commercially available, butspecic recommendations about which one to use areprimarily based on the disinfection characteristics ofindividual disinfectants.1Chemical disinfectants can bebroadly classiedintothree categories7: high-level disin-fectants namely, ethylene oxide gas or glutaraldehydesolutionswhichareabletoinactivatesporesandall othermicrobial forms8; intermediatelevel disinfectantsnamely,formaldehyde, chlorine compounds, iodophors, andalco-holsphenoliccompoundswhichmaynotinactivatesporesbut will destroy other microbes, in particular tuberclebacilli7; and lowlevel disinfectants namely, quaternaryammoniumcompounds, simplephenols, detergentswhichareunacceptablefordisinfectionofcontaminatedimpres-sions.7Chemical agents suitable for the disinfection ofdental impressions routinely used in dentistry include:sodiumhypochlorite, glutaraldehyde, iodophor, andphe-nol.810However,notallimpressionmaterialsarecompati-ble with all types of disinfectant and the potential fordisinfectants to modify the properties of the impressionmaterial(surfaceroughness,anddimensionalstability)area distinct possibility.11Controversy exists in the dentalliterature as to whether the disinfection process causesdegradation or distortion of dental impressions and to whatextent.8,12Importantfactorstobeconsideredwhenadisinfectionprotocol for dental impressions is being consideredincludetheeffectivenessofthedisinfectionprocedure,thechemical stability of the disinfecting solution and theinuence of the disinfectant procedure on thedimensional stability and surface reproduction of theimpressionmaterialsandresultant casts.1,13Inthedentalliterature, numerous studies investigating different disinfec-tionproducts, disinfectionprocedures, contact times, anddisinfectant agents suggest that there are nouniversallyrecognized disinfection protocols for dental impres-sions.1,14,15Therefore, individual analysis of impressionmaterials is required.Theaimofthecurrentinvestigationwastoevaluatetheeffect of twodifferent disinfectionsolutions (a highleveldisinfectant: ortho-phthalaldehyde(CidexOPA1; Johnson&Johnson, East Windsor, NJ, USA) andanintermediateleveldisinfectant: sodiumhypochlorite(NaOCl)) atsevenimmer-siontimes on (1) the dimensional accuracy and surface qualityof gypsum casts retrieved from disinfected irreversiblehydrocolloidimpressionsand(2) theantimicrobial efcacyofthedisinfectingsolutionsusedinrelationtodisinfectionimmersion time.2. Materials and methods2.1. Part I. Evaluation of dimensional accuracy andsurface qualityA stainless steel master model made froma maxillaryDentoformmould(ColumbiaDentoformCorporation, LongIsland City, NY, USA) with edentulous polished surfacesparalleltothehorizontalplane(Fig. 1)similartothatusedpreviously by Byrne etal.16was used in the current study. Theteeth were marked with 100 mmwide cross lines in thehorizontal planewithtwoindentationsonthemesial anddistal side of the prepared surfaces for measuring purposes.16Theedentuloussurfaceontherightsideofthemastercastwaspolishedtocreateasmooth areaandtheedentuloussurface on left side was roughened using an acrylic polishingbur (Tungsten Carbide Cutter; Edenta AG, Heidelberg,Switzerland) to create a rough area.Topreparethehydrocolloidimpressions, onesizestockplastic impression trays (O-tray Upper No 3; Dentaurum,Ispringen, Germany) were used with a new tray used for eachimpression.Alginateadhesive(Pegasustrayadhesiveliquid;Pegasus Dental Supplies Ltd, Altrincham, England) wasappliedtotheimpressiontrayinathinlayer5 minbeforethe impression was made. The irreversible hydrocolloidimpressionmaterial(Hydrogumthixotropic; ZhermackSpA,BadiaPolesine, Italy; BatchNo. A078B) wasmanipulatedinaccordance with the manufacturers recommended powder toliquid mixing ratio of 1 g to 2 mL, respectively. To prepare theHydrogum impressions, 0.9 g of powder was measured into amixing bowl using a balance accurate to 1 mm(SartoriusExpert; Sartorius AG, Goettingen, Germany) and 18 mL ofdistilled water was dispensed on top using a disposablesyringe. The powder and liquid constituents were hand-mixedtogether using a spatula for 10 s and thenmechanically-mixedunder vacuumfor 20 s using an automated mixer (Alginator II;Cadco, Oxnard, CA, USA). To standardize the impressiontechnique, a positioning device consisting of a base and threeparallel guidepostssimilartothat describedpreviouslybyStaufferet al.17wasused(Fig. 2). Toensureaccurateandreproducible positioning of the trays to the positioning device,

Fig. 1 The stainless steel master model cast from amaxillary Dentoform mould with edentulous polishedsurfaces parallel to the horizontal plane.j our na l of d e nt i s t r y3 9( 2 0 1 1 ) 1 3 3 1 4 0 134twoindexeswerefabricatedusingPatternResin(GC,DentalProducts Corporation, Japan), one was used to accurately openthe screw hole on the stock trays and the other to position thestocktrayonthemetal plate. Beforeeachimpression, themastercastwassteamcleanedfor10 s. Therecommendedsetting time of Hydrogum was increased from 130 to 300 s, tocompensatefor adelayedsettingof thematerial at roomtemperature (21 2 8C) compared with closed mouth temper-ature(37 8C).18Aftersetting,eachimpressionwasrinsedfor10 s under cold tap water and immersed in 0.55% (v/v) ortho-phthalaldehyde (Cidex OPA1) or 0.5% (w/v) sodium hypochlo-rite(NaOCl) for30, 60, 90, 120, 180, 240, and300 swiththecontrol groupundergoingnodisinfectionimmersionproce-dure. Ten impressions were made for each group underinvestigation.After the immersiontime had elapsed, eachimpressionwasrinsedfor 10 sunder coldtapwater andsealedinaplasticbagfor7 min (at room temperature). All impressions were cast usinggypsum(JadestonetypeIV; WhipMix, Louisville, KY, USA; BatchNo. 18597) preparedusingapowder toliquidmixingratioof 4.5 gto 1 mL, respectively. Distilledwater (15.5 mL) was placedinto avacuummixing bowl and70 gof gypsum powder wasslowlyaddedandhand-mixedusing a spatula for 10 s until the powderwascompletelywettedbytheliquid.Thepowderandliquidwerethenvacuum-mixedfor20 susing anautomated mixer(Vac-U-Vestor; Whip Mix, Louisville, KY, USA) and poured intothe impression using vibration (Vac-U-Vestor). The casts wereallowedtoset for 45 minbefore separationfromthe impressionand none of the casts were mechanically trimmed. The modelswerestoredat roomtemperaturefor48 hpriortoanalysis.Cross-arch (AB), antero-posterior (BC) and cross-arch antero-posterior (AC) dimensions(mm) (Fig. 3) weremeasuredoneachcast usingatravellingmicroscope(NikonMeasuringMicroscopeMM-40; Inspection Equipment Co. Ltd., Dublin, Ireland) with anaccuracyof 0.001 mmunderlowangleilluminationat 3magnication. Ten measurements of AB, BC and ACdimensionswereperformedfor eachgroupunder investigation.To assess the surface quality of the retrieved gypsumcasts,thesurfaceroughnessof thecastswasassessedusinganopticalprolometerconsistingofanon-contact3 mmrangechromatic length aberration gauge (Talysurf CLI 2000; Taylor-Hobson Precision, Leicester, England). Three prolometrictraceswereperformedoneachof thepolishededentuloussurfaces (smooth and rough) at a speed of 200 mm/s withmeasurements taken every 2 mm intervals and a 2 mm spacingbetween traces. The roughness (Ra) of each prole (thearithmetic mean deviation of the roughness prole) wasdetermined in accordance with ISO 4287:199719using aGaussian lter and a 0.25 mm cut-off.Statistical analyses(twoandthree-wayanalysesofvari-ance (ANOVAs), Tukeys post hoc tests and regressionanalyses) were made in software (SPSS 12.0.1; SPSS Inc.,Chicago, IL, USA) at a signicance value of p = 0.05.Individualtwo-wayANOVAs (disinfectantsolution ximmer-sion time) and Tukeys post hoc tests were conducted for eachdimension measured (AB, BC and AC). Athree-way ANOVA(disinfectant solution immersion time roughness area)was performed for the Ra data. Tukeys post hoc testsemployed to determine signicant differences betweengroups. Individual regression analyses were conducted whererequiredtocheckforgeneraltrendswithinthedimensionalaccuracy and Ra data with increasing immersion time.2.2. Part II. Evaluation of antimicrobial efcacyDisc-shapedHydrogumspecimens(15 mmdiameter, 4 mmheight) were prepared (n = 10) using the manipulation proce-dure outlined previously and placed into individual wells of a24well cell cultureplate. Thetest organism, Pseudomonasaeruginosa246wildtypeenvironmental isolatewhichwasrecovered froma dental chair unit suctionsystem20wasculturedinBrainHeart Infusion(BHI; Oxoid, Basingstoke,England) broth at 37 8C for 15 h in a shaking incubator(Gallenkamp, Leicester, England) at 150 rpm. Pseudomonasaeruginosa246producesgreenpigmentedcoloniestypicalofthespeciesonBHI agarfollowing15 hincubationat 37 8C.Using a fresh 15 h BHI agar culture, the bacterial cell densitywasadjustedtoapproximately1 107colonyformingunits(cfu)permLbydilutioninsterilephosphatebufferedsaline(PBS). An inoculum of 1 106in a nal volume of 100 mL was

Fig. 2 Positioning device with a base and three parallelguide posts to standardize the impression makingtechnique.

A BCFig. 3AschematicrepresentationshowingthemeasurementsAB, BCandCAperformedonthetestcasts.j o ur na l o f d e nt i s t r y3 9( 2 0 1 1 ) 1 3 3 1 4 0 135applied to discs using a sterile pipette tip tted to a Gilson P200laboratory pipette (Gilson, Middleton, WI, USA). Inocula werelefttoairdryinaClass2laminarairowsafetycabinetfor20 min. Inoculatedandcontrol discs were completelyim-mersed in disinfectant solution contained in a sterile 90 mmPetri dishes for the desired time, removedwitha sterileforceps and rinsed thoroughly with sterile PBS. The disinfec-tion protocol applied was: (1) immersion in Cidex OPA1for 30,45 or 60 s; (2) immersion in NaOCl for 60, 120 or 180 s; or (3) nodisinfection (control group). Duplicate disinfected discs wereimmersed aseptically in 5 mL of sterile BHI broth in separate50 mLFalcontubes(BectonDickinson,Oxford,England)andvortexed thoroughly for 1 min, after which time 1 mL aliquotswere removed in 1.5 mL Eppendorf Safelock tubes andcentrifugedat 3000 ginabenchtopmicrofugefor5 minto recover bacterial cells. Following centrifugation, pelletswere resuspended in0.1 mL PBS supplementedwith0.5%(w/v)sodiumthiosulphatetoneutralizeresidual disinfectantandplateddirectlyonfreshBHI agarmediumandincubatedat37 8Cfor 15 hinastaticincubator (Gallenkamp, Leicester,England). Following incubation, plates were examined and thenumber of green bacterial colonies present, if any, werecountedandrecorded. The number of colonies was thenmultiplied by 5 to obtain the total number of bacterial cfu permL recovered from the disinfected discs.3. Results3.1. Dimensional accuracyThemeandimensions andassociatedstandarddeviationsmeasured between points AB, BC and AC on the retrievedgypsumcastsareshowninTable1.Theindividualtwo-wayANOVAs (disinfectant solution immersion time) showedthat there was no signicant effect of disinfectant solution onthe dimensions measured between points AB ( p = 0.912), BC( p = 0.056) and AC( p = 0.844). In addition, no signicant effectof immersion time was shown for the dimensions measuredbetweenpointsAB( p = 0.417)andAC( p = 0.593),however,therewasasignicanteffectforthedimensionsmeasuredbetweenpointsBC( p = 0.029).Regardlessoftheimmersiontime, the mean dimensions measured between points AB, BC and CA for the groups immersed inCidex OPA1and NaOClsolutions did not differ signicantly ( p > 0.250) compared withthe control group.3.2. Surface quality (roughness)The mean Ra values of the smooth and rough surfaces ontheretrievedgypsumcasts for thecontrol groupandthegroupsimmersedinCidexOPA1andNaOCl forimmersiontimes ranging from 30 to 300 s are shown graphically in Fig. 4.Thethree-wayANOVAofdisinfectantsolution immersiontime roughness area for the Ra data showed that thedisinfectant solution did not have a signicant effect( p = 0.087),howevertherewasasignicanteffectofimmer-sion time ( p = 0.006) on the Ra data. As a result, the Ra data foreach roughness area (smooth and rough) was pooled andindividual regressionanalyseswereconductedtocheckforsignicant trends within the Ra data with increasing immer-sion time. There was no signicant effect of immersion timeon the Ra data for the smooth surface ( p = 0.551), however, astatisticallysignicant increaseinRa( p < 0.0001) was ob-served with increasing immersion time for the roughsurface.3.3. Microbiological evaluationTheresultsshowedthatnobacterialgrowthwasrecoveredfromtheirreversiblehydrocolloiddiscsimmersedinCidexOPA1for at least 30 s or in NaOCl for at least 120 s.Furthermore, the results conrmed the asepsis of thetechnique withno bacterial growthrecoveredfromthe controlTable 1 The mean measurements of the cross-arch (AB), antero-posterior (BC) and cross-arch antero-posterior (AC)dimensions for the control group and the groups exposed to Cidex OPAWand NaOCl for immersions times ranging from30to 300 s (standard deviations are shown in parenthesis).Disinfectant Immersion time (s) Measured dimensionsAB (mm) BC (mm) CA (mm)Control group 46.31 (0.03) 20.39 (0.03) 48.14 (0.09)Cidex OPA130 46.28 (0.09) 20.35 (0.03) 48.12 (0.28)60 46.32 (0.07) 20.45 (0.09) 48.14 (0.10)90 46.34 (0.03) 20.39 (0.03) 48.12 (0.07)120 46.32 (0.02) 20.38 (0.04) 48.12 (0.23)180 46.33 (0.03) 20.41 (0.02) 48.08 (0.05)240 46.32 (0.09) 20.36 (0.08) 48.07 (0.15)300 46.34 (0.02) 20.39 (0.05) 48.04 (0.04)NaOCl 30 46.31 (0.05) 20.39 (0.04) 48.07 (0.06)60 46.33 (0.05) 20.38 (0.03) 48.12 (0.06)90 46.33 (0.05) 20.40 (0.04) 48.13 (0.05)120 46.35 (0.05) 20.43 (0.03) 48.09 (0.03)180 46.34 (0.07) 20.41 (0.02) 48.13 (0.10)240 46.36 (0.02) 20.41 (0.06) 48.10 (0.05)300 46.32 (0.04) 20.42 (0.03) 48.14 (0.05)j our na l of d e nt i s t r y3 9( 2 0 1 1 ) 1 3 3 1 4 0 136PBS inoculum discs as well as before contamination with theinoculum. No bacterial growth was observed on the negativecontrolagarplatesused, indicatinganasepticexperimentalenvironment. The positive results observed with the positivecontroldemonstratedthevalidityoftheassaymethod.ThecfupermLforthetest, control, andnegativecontrol speci-mens are presented in Table 2.4. DiscussionIncreased emphasis continues to be placed on infectioncontrolandpreventioninthedentalsurgerybecauseofthepotentialthreatpresentedbyarangeofovertandopportu-nistic microbial pathogens. Awide variety of disinfectingsolutions are available in the dental market, but a universallyrecognized disinfectionprotocol for dental impressions islackingbecauseof thevaryingresponseof eachbrandofimpressionmaterialandgypsumproducttodifferentdisin-fection procedures.11A number of studies3,2124have investi-gatedawidevarietyof brandsof irreversiblehydrocolloidimpression materials, disinfecting solutions, and dentalstones using a variety of different disinfectionprotocols,whichhasledtoinconclusiveresultsreportedinthedentalliterature regarding the most efcient protocol for disinfectionofdental impressions.Thepresent studywasundertakentoevaluate the disinfectionprotocol applied in the Dublin DentalUniversity Hospital for the brands of irreversible hydrocolloidimpression and dental stone currently used.NaOCl is one of the original and most widely useddisinfectants.25The literature shows that it is effective againsta broad spectrumof micro-organisms including humanimmunodeciencyvirus,26,27hepatitis Bvirus28as well asnumerous other bacterial species3,2124andtheir spores,29viruses5,22and fungi.23Cidex OPA1, a relatively newhigh leveldisinfectant, was introduced to the market as a saferalternativetoglutaraldehydeeventhoughtherewas littleevidenceat that timetosupport suchclaims.30Alimitednumber of studies31,32have shownfavourable results forCidex OPA1solution as a viable alternative to glutaraldehydefor high level disinfection of endoscopes. However, to date nostudies have evaluated the effect of Cidex OPA1on thephysical properties of dental impression materials.In the present study, the two-way ANOVAs of thedimensional accuracydatafor theretrievedgypsumcastsshowed no signicant difference betweenthe two disinfectantsolutions investigated. For the dimensions measured betweenpoints BC a statistically signicant effect of immersion timewas found ( p = 0.029), however, this was not considered to beclinicallysignicantsincethegreatestmeandeviationfromthe control group was 0.061 mm after 60 s immersion in CidexOPA1and0.042 mmafter120 simmersioninNaOCl overadistance of 20.387 mm. Initially it was expected that exposureofirreversiblehydrocolloidimpressionmaterialtodisinfect-ing solutions would adversely affect the dimensional accuracydue to the hydrophilic nature of the material and thephenomenonof imbibition. The dimensional stability ob-servedinthisstudymaybeattributedtoinitial syneresiswhichcauses contractionof the impression material, counter-

00.020.040.060.080.10.120.140.160.180.20 30 60 90 120 180 240 300Immersion time (s)Surface roughness (Ra) (m)Rough Cidex OPA Rough NaOCl Smooth Cidex OPA Smooth NaOClFig. 4 The meanRa values of the smooth and rough surfaces onthe retrieved gypsumcasts for the control group (0 s) andthe groups immersed in Cidex OPAWand NaOCl for immersion times ranging from 30 to 300 s (error bars indicating standarddeviations are omitted for clarity).Table 2 The cfu per mL for the test, control, andnegative control specimens.Test disc Recovered bacterialdensity (cfu/mL)Sample 1 Sample 2Blank disc(no inoculum) Nil NilBlank disc + PBS inoculum Nil NilDisc + inoculum1 106cfu 12,000 10,500Disc + inoculum60 s NaOCl 1500 500Disc + inoculum120 s NaOCl Nil NilDisc + inoculum180 s NaOCl Nil NilDisc + inoculum60 s Cidex OPA1Nil NilDisc + inoculum120 s Cidex OPA1Nil NilDisc + inoculum180 s Cidex OPA1Nil NilAgar plate(no inoculum) Nil Nilj o ur na l o f d e nt i s t r y3 9( 2 0 1 1 ) 1 3 3 1 4 0 137actedbyimbibitionduringdisinfectionand/orlinearexpan-sion of the dental stone during setting.10The results reportedinthepresentstudywithrespecttotheeffectofNaOCl onalginateimpressionsareinagreement withother publica-tions9,10,3336where the same conclusions were drawn.However, dimensional changes following disinfection ofirreversiblehydrocolloidimpressionusingarangeof con-centrations of NaOCl have been reported in the litera-ture.12,21,37Rueggeberg et al.21examined the effects ofalginatedisinfectionusinga0.525%NaOClsprayorimpres-sionimmersionin0.525%NaOCl solutionfor 10 min. Theresultsshowedthatimmersiondisinfectioncreateddimen-sional distortionoftheresultantcasts. Nevertheless, directcomparisonof resultsisnot possibleduetothevarietyofmaterialstested, thedisinfectionprotocolsapplied, andthemeasuringtechniquesusedineachstudy. Thisemphasizesthe needfor compatible studies to ensure that the mostappropriate disinfection protocol is used for each givenimpression material.Surfacequalityofgypsumcastsretrievedfromirrevers-iblehydrocolloidimpressionmaterialshasbeenproposedas an indicator of the compatibility of the impressionmaterial and dental stone.38The results of this studydemonstratedthattheRaofgypsumcastswereincreasedafterimmersionof HydrogumimpressionsinCidexOPA1for60 sorinNaOClfor300 s.Thiswasparticularlytrueforthe rough surface but it is unclear whether the increasedRa observed would have a clinically signicant effect on thesurfacequalityof thecasts. Inaddition, forthesmoothsurface, it is not known if its quality remained the same, orif aclinicallysignicant distortionoccurredwhilst main-tainingthesmoothnessof thesurface. It maybethat thesmoothsurfacewasrapidlydegradedbythedisinfectingsolutionsbutremainedsmoothastheconcentrationofthesolutiononthe surface was more equal thanwould befoundonanirregular surface. ImmersioninCidexOPA1increased the rough Ra at an early stage (90 s) which mayindicate a chemical reaction of the solution with theimpressionmaterial orthedental stone. However, duetothe fact that this effect of Cidex OPA1was observed only forthe roughsurface, it may be possible that anadditionalchemical reactionoccurredbetweenthedental stoneandthe residual disinfecting solutionwhichremainedintheirregularitiesof theroughsurfaceevenafter rinsingwithwater.Additionally,thelowwatersolubilityofCidexOPA1could also explain the early stage (90 s) increase in Raobservedonthegypsumcasts.Thismaybeduetothefactthat 10 srinsingwasnot adequatetoremovethedoseofCidex OPA1retained on the porous impression surfaceresultinginsurfacedistortion. Furtherlaboratoryresearchis requiredto explainthe mechanismandthe chemicalreactionbetweenCidexOPA1andbothalginateanddentalstonematerials.The antibacterial efcacy of Cidex OPA1and NaOClsolutionsagainst Pseudomonasaeruginosa inoculated irrevers-ible hydrocolloid discs was also evaluated. The Association ofOfcial Analytical Chemists39detailed recommended testorganisms, includingPseudomonas aeruginosa, Staphylococcusaureus, Salmonella cholearusuis, which may be used to classify adisinfectant as bactericidal, tuberculocidal, or sporicidal. TheADArecommendation40suggestsuseof at least amediumlevel disinfectant for dental impressions, which indicates thatthe disinfecting solution must be bactericidal and tuberculo-cidal. Bothdisinfectingsolutionsusedinthepresentstudysatisfytheserequirements;NaOClisclassiedasainterme-diateleveldisinfectant, whileCidexOPA1isusedasahighlevel disinfectant.31,32,41It has been suggested that for adisinfectingsolutiontobeeffectiveitmustproduceconsis-tently high kill levels on every impression and not just a highaveragethatincludessomelowvalues.42Theresultsofthisstudyconrmedtheasepticenvironment underwhichtheexperimentwasconductedandprovedthatbothtestdisin-fectingsolutionswereeffectiveagainst Pseudomonasaerugi-nosa. Complete elimination of viable bacteria from the samplewas observed after immersion of inoculated irreversiblehydrocolloid discs in Cidex OPA1for 30 s and in NaOClsolution for 120 s. However, comparison of these ndings withthoseofsimilarstudieswouldnotreinforceourconclusionsduetothevariabilityofthematerialsandmethodsapplied.Additionally, the efcacy of a disinfecting solutionis notnecessarilythesameforall impressionsdependingonthetexture and thickness of the impression material. Forirreversible hydrocolloid impression material a uniformcross-sectional thicknessof46 mmwasproposedbyRuddand Morrow43to provide maximumaccuracy. In this study thealginatediscsusedtotesttheantibacterialefcacyofCidexOPA1andNaOCl solutionswereof auniformthicknessof4 mm. However, denitiveconclusions donot exist intheliterature as to whether organisms are present inthe body ofirreversible hydrocolloid impressions and theextent to whichdisinfectant solutions can penetrate impressions.44Someauthors considered the chemical composition of someirreversiblehydrocolloidimpressionmaterials as havingasignicant role ininhibiting the efcacy of certaindisin-fectants.3Taylor et al.10reported that brands of irreversiblehydrocolloidimpressionmaterial whichshowedtheleastpenetrationofdisinfectingsolutiondemonstratedsuperiorsurfacereproduction. However, impressionmaterialsthatdonotabsorbdisinfectingsolutionsmaynotbeadequatelydisinfected if micro-organisms become entrapped withinthe material when the impression is taken. Individualresponses of dental impression materials to immersionprotocolsforaparticulardisinfectingagentmayexplaininpart the conicting reports in the dental literature.35In thisstudy, thenegativendingspresentedfor NaOCl solutioncould be attributed to either a reaction between thehypochloriteabsorbedintotheimpressionandthedentalstone or a direct effect of the hypochlorite on the alginate inrelationtosurfacequality. NaOCl visiblysmoothenedthesurfaceoftheimpressions,andalmofdisinfectantcouldbefelt onthematerial evenafter rinsingwithwater. Inaddition, the surface of the retrieved stone discs wasextremelysmoothandeasilyabraded, lackinganyrepro-ductionofnedetail.TheseobservationsareinagreementwithastudyconductedbyBlair et al.,15wheresurveyeddentallaboratoriesreportedsoftenedsurfacesonthecastsretrievedfromsome,butnotall,alginatematerialsfollow-ing immersion in glutaraldehyde, NaOCl, and sodiumdichloroisocyanuratemade.15j our na l of d e nt i s t r y3 9( 2 0 1 1 ) 1 3 3 1 4 0 1385. ConclusionsBased on the ndings of this study it can be concluded that:1. The dimensional accuracy of Hydrogumirreversible hydro-colloid impression material was not affected by immersionin either Cidex OPA1or NaOCl solutions for up to 300 s.2. The disinfecting solution or immersion time did not have asignicanteffectintermsofRaonsmoothareasontheimpressions. However the immersiontime signicantlyincreasedthedistortionofirregularareasoftheimpres-sions for both disinfection solutions. Changes wereobserved after 30 and300 s immersioninCidex OPA1and NaOCl solutions, respectively.3. ThecompleteeliminationofPseudomonasaeruginosacolo-nies was obtained after 30 s immersion in Cidex OPA1and120 s in NaOCl solution.4. Based on botheffectivenessofdisinfectionandeffects ontheresultantgypsumcaststhebestresultsinthisstudywereobtainedafter immersioninCidexOPA1for 30 s.NaOCl was effective only after longer immersion times.5. 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