A Randomised Controlled Trial of complete denture impression materials

A

Randomised

Controlled

Trial

of

complete

denture

impression

materials

T.P.

Hyde

*

,

H.L.

Craddock

,

J.C.

Gray

,

S.H.

Pavitt

,

C.

Hulme

,

M.

Godfrey

,

C.

Fernandez

,

N.

Navarro-Coy

,

S.

Dillon

,

J.

Wright

,

S.

Brown

,

G.

Dukanovic

,

P.A.

Brunton

a

LeedsDentalInstitute,UniversityofLeeds,LeedsLS29LU,UK

b

UniversityofAberdeenDentalSchool,CornhillRoad,AberdeenAB252ZR,UK

c_{ClinicalTrialsResearchUnit,LeedsInstituteofClinicalTrialsResearch,UniversityofLeeds,LeedsLS29JT,UK}

d_{AppliedHealthResearch,LeedsInstituteofHealthSciences,UniversityofLeeds,LeedsLS29LJ,UK}

e_{AcademicUnitofHealthEconomics,LeedsInstituteofHealthSciences,UniversityofLeeds,LeedsLS29LJ,UK}

f_{HealthandSocialCare,LeedsInstituteofHealthSciences,LeedsLS29LJ,UK}

g

LeedsInstituteofClinicalTrialsResearch,UniversityofLeeds,LeedsLS29JT,UK

h_{DentalTranslationalClinicalResearchUnit(DenTCRU),LeedsDentalinstitute,UniversityofLeeds,LeedsLS29LU,UK}

i_{FacultyofDentistry,UniversityofOtago,Dunedin,NewZealand}

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received2October2013 Receivedinrevisedform 7February2014

Accepted11February2014

Keywords:

Prosthodontics Quality-oflife Patientoutcomes Impressionmaterials Edentulous

Removableprosthodontics

a

b

s

t

r

a

c

t

Objectives:Thereiscontinuingdemandfornon-implantprosthodontictreatmentandyetthereisa paucityofhighqualityRandomisedControlledTrial(RCT)evidenceforbestpractice.Theaimof thisresearchwastoprovideevidenceforbestpracticeinprosthodonticimpressionsbycomparing twoimpressionmaterialsinadouble-blind,randomised,crossover,controlled,clinicaltrial.

Methods:Eighty-fivepatientswererecruited,usingpublishedeligibilitycriteria,tothetrialatLeeds DentalInstitute,UK.Eachpatientreceivedtwosetsofdentures;madeusingeitheralginateor siliconeimpressions.Randomisationsdeterminedtheorderofassessmentandorderof impres-sions.Theprimaryoutcomewaspatientblindedpreferenceforunadjusteddentures.Secondary outcomeswere patientpreferencefortheadjusteddentures,ratingofcomfort,stability and chewingefficiency,experienceofeachimpression,andanOHIP-EDENTquestionnaire.

Results:Seventy-eight(91.8%)patientscompleted theprimaryassessment. 53(67.9%)patients preferreddenturesmadefromsiliconeimpressionswhile14(17.9%)preferredalginate impres-sions.4(5.1%)patientsfoundbothdenturesequallysatisfactoryand7(9.0%)foundbothequally unsatisfactory.Therewasa50%differenceinpreferencerates(infavourofsilicone)(95%CI32.7– 67.3%,p<0.0001).

Conclusion: Thereis significantevidencethatdenturesmadefromsiliconeimpressionswere preferredbypatients.

Clinicalsignificance: Giventhestrengthoftheclinicalfindingswithinthispaper,dentistsshould considerchoosingsiliconeratherthanalginateastheirmaterialofchoiceforsecondary impres-sionsforcompletedentures.

TrialRegistration:ISRCTN01528038.

Thisarticleformspartofaprojectforwhichtheauthor(TPH)wontheSeniorClinicalUnilever Hatton Awardof theInternational Assocation forDentalResearch, Capetown, SouthAfrica, June2014.

#_{2014TheAuthors.PublishedbyElsevierLtd.ThisisanopenaccessarticleundertheCC}

BY-NC-SAlicense(http://creativecommons.org/licenses/by-nc-sa/3.0/).

*Correspondingauthor.Tel.:+441133438515.

E-mailaddress:[email protected](T.P.Hyde).

Available

online

at

www.sciencedirect.com

ScienceDirect

journalhomepage:www.intl.elsevierhealth.com/journals/jden

http://dx.doi.org/10.1016/j.jdent.2014.02.005

1.

Introduction

Although the treatment of edentulous patients has been transformedbytheintroductionofimplants,thebarriersto implanttreatmentareknownandhavebeenexploredinthe literature.1,2Thebarriersarerelatedtothecostoftreatment, the fear ofsurgery andageism. Even when implants were offeredfree,morethan athirdofthepatientsrejectedthis option.3 _{28% of edentulous patients were not suitable to} receive implants in a clinical trial.4 _{Although the best} treatmentoptionforpatientsofteninvolvesimplants,5,6_the currentrealityisthatamajorityofpatientsareunsuitablefor implantsoroptfornon-implanttreatmentduetocostorfear ofsurgery.Theoptionoftraditionalprosthodonticsremains thestapleprovisionfortoothreplacementformanypatients. Given the high incidence in the use of non-implant treatment,thereisacontinuingneedforhighqualityresearch evidence to inform the dentist and patients of the best methodsofproducingtherequiredprosthesis.Thesystematic reviewsofJokstad7_andofHarwood8_{showthatitisinthisarea} ofclinicaltechniquefortraditionalprosthodonticsthatthere remains a particular paucity of high quality Randomised Controlled Trial’s (RCTs). This lack of research has been highlightedbyCarlsson.9–11_{Muchofourknowledgeofcurrent} ‘‘bestpractice’’inprosthodonticsisbasedonexperienceand traditionarguedfromapositionoffirstprinciplesratherthan highqualityevidencefromRCTresearch.Asaresultourbelief inwhatconstitutes‘‘bestpractice’’canvaryfromoneteaching tradition,onedentalschool,oneculture,toanother.

Asurveyofimpressionmaterialsforcompletedenturesin theUK12_{demonstratedthatthemajorityofdentistsreportthe} use ofalginate as the material of choicefor the definitive secondaryimpression material forcompletedentures. This contrastswiththepositionbothpracticedandtaught13,14_in USA dental schools and found in UK private denture laboratories.15 _{It is implied by these surveys that experts} use alternatives to alginate. Dentists have a choice of materialsformakingdentalimpressionsbutthereisadearth ofRCTevidencetoinformtheirchoice,highlightingtheneed forrobustRCTresearch.

TheprimaryaimforthisRCTistoestablishwhetherthere isapatientpreferencefordenturesproducedfromalginateor siliconeimpressions.Thesecondaryobjectivesare

1. Toassesstheimpactofdenturesproducedfromalginate andsiliconeimpressionsonoralhealthrelatedqualityof life.

2. To assess comfort, stability and chewing efficiency for denturesproducedfromalginateorsiliconeimpressions. 3. Toassesspatients’experienceofhavingimpressionsmade

usingalginateandsiliconeimpressionmaterials.

2.

Method

This research was carried out in the Dental Translational ClinicalResearch Unit (DenTCRU) at LeedsDental Institute, UniversityofLeedsundertheauspicesoftheLeedsClinicalTrial Research Unit (CTRU). It was a single centre, double-blind,

randomised,controlled,crossoverclinicaltrialofalginateand siliconeimpressionsforcompletedentures.Fulldetailsofthe trial protocol can be found in the pre-published protocol paper.16_{Therewerenomajordeviationsfromthepublished} protocol. Ethical approval was obtained through the UK IntegratedResearch Application System(IRAS)systemfrom Leeds(West)ResearchEthicsCommitteeinFebruary2010and writteninformedconsentwasobtainedfromallpatients.

Eligibleparticipantswereedentulousadultsaged18orover who required new complete dentures, were available for follow up and able and willing to complete the informed consentprocess.Patientswereexcludediftheyhadanoral tumour,requiredanobturator,hadextremexerostomia,hada knownhypersensitivitytosiliconeoralginateorwouldbenefit fromselectivepressureimpressions.

Asample sizecalculationrevealedthat 76patientswould have80%powertodetectadifferenceinpreferenceratesof30% betweenthetwodentures(30%versus60%)atasignificancelevel of5%,assumingthat10%ofpatientsexpressnopreference.A totalof85patientswererecruitedoveralltoallowforadropout rateof10%,consistentwithpreviousstudies.

All85patientswererecruitedfromprimarycarereferralsto the Leeds Dental Institute. Patients received two sets of dentures,onesetofdenturesmadefromimpressionstaken withsiliconetheothersetmadefromalginateimpressions.

Two setsof acrylic,spaced, and customised impression trayswithstubhandlesandacrylic‘‘stops’’wereconstructed for eachpatient. Thespacing ofthe customised trays was achievedintheusualwayofadaptingalayerofdenturewax overtheprimarycastandconstructingthecustomisedtrays overthewax.17_{Wheretherewasdeephardtissueundercuton} thecaststhiswasreducedbyblockingouttheundercutinwax priortolayingdownthespacer.Thetrayswereidenticaland labelledAandB.Duringimpressionmaking,thetrayswhich wereusedfirst(AorB)andtheimpressionmaterialwhichwas usedfirst(alginateofsilicone)wasrandomised. The rando-misationwasblockedbyvariableblocksizestoensurebalance between groups and concealed in sequentially numbered sealedenvelopesbytheCTRUstatisticianandsecurelystored in the randomisation locker at DenTCRU. The envelope containingthetrayrandomisationswasopenedbyauthorised membersoftheresearchteamafterthe‘blind’adjustmentof bothsetsofimpressiontraystoremoveoverextensions.

Thetraystobeusedforthealginateimpressionwereborder mouldedwithgreenstickimpressioncompound(Kerr)inthe usual way17_{and the alginate impressionstaken(Xantalgin,} Heraeus).Thetraysusedforsiliconeimpressionswereborder mouldedinsilicone,usingheavybodiedfortheupper(Extrude, Kerr)andregularbodiedforthelower(Express,3MESPE)andthe impressiontakenwithlightbodiedsilicone(Express,3MESPE). Thebordermouldingmaterialsselectedwerethoseadvocated byexpertopinion foreachimpressionmaterial.17,18_A retro-spectiveauditbyDrago19_{wasunabletodetectadifferencein} theuseofthesematerialsforbordermoulding.Thequalityof theimpressionswasassessedbytheclinicianandbyasecond independentinspector. If either the clinician or thesecond independent assessor felt an impression was below an acceptablestandard,theclinicianre-tooktheimpression.

Thecasts wereallocated a number (blind to the clinician) whichallowedthelateridentificationofthedentures.Atall subsequentstagesofdentureconstructiontheclinicianwas blindtotheimpressionmaterialused.

The completed unadjusted dentures were labelled by randomallocationwithblueandreddots.Therandomisation wasblockedbyvariableblocksizestoensurebalancebetween groups and concealedin sequentiallynumbered envelopes created by the statistician and securely stored in the randomisationlockeratDenTCRU.Halfthereddotdentures were from alginate impressions and half from silicone; similarlyforthebluedotdentures.Patientsweregivenboth setsofunadjusteddenturesandaskedtofollowastructured programmeofalternatewearingofthedentures,startingwith thereddentures,foratwo-week‘HabituationPeriod’.Thus thedentureswornfirstduringthisperiodwasdeterminedby therandomisationdefinedbythecolourcodeallocation.The ‘HabituationPeriod’allowedpatientstobecomeaccustomed to the new dentures and assess their preference for the unadjusteddentures(primaryoutcome).

Followingtheinitialassessmentofthedentures(primary outcome) the dentures were relabelled by green or yellow coloured dots by randomised allocation. It was blocked (variable block sizes) and balanced for order of testing in the initial ‘Habituation Period’. This was administered centrallyby the CTRU usingan automated24-h telephone system. Patients then wore the newly coded dentures sequentially in 2 periods of 8 weeks each (‘Adjustment Period’), during which time, the patients returned to the DenTCRUforanyadjustmentstheyrequired. All necessary adjustments were made by a second independent, blind clinician.The1:1randomisationcodedbytheyelloworgreen dotsestablishedtheorderoftestingduringthe‘Adjustment Periods’.Thepatientsandtheclinicalteamwereblindtothese allocations.Finally,patientstookbothsetsofdenturesfora finaltwo weekperiod (‘ConfirmationPeriod’) at theend of whichtheyreturnedforthefinalassessment.

Theprimaryoutcomeassessedwas:

1. The patients’ preference for the unadjusted dentures followingthe2weeks‘HabituationPeriod’.

Secondaryoutcomeassessmentswere:

1. Patientperceptionofdenturecomfort,stabilityandchewing efficiencyofthedenturesusing5-pointLikertscales. 2. Patients’preferencefortheadjusteddenturesfollowingthe

2week‘ConfirmationPeriod’.

3. OHIP-EDENT questionnaires assessing the patient oral healthrelated quality oflife following eachAdjustment Period.

4. Patientperceptionofcomfortandtasteofeachimpression materialusing5-pointLikertscaleattheimpressionstage. 5. Patientpreferencefor the impressionofmaterialsat the impressionstageBaselineOHIP-EDENTquestionnaireswere completedbythepatientspriortodentureconstruction.

2.1. Statisticalmethods

The comparison of the proportions of patients preferring denturesmadefromalginateimpressionstothosepreferring

denturesmadefromsiliconeimpressionswaspresentedina 22tableforpaireddataandanalysedusingMcNemar’stest. Thisanalysiswasusedatboththeprimaryendpoint(afterthe habituationperiod,fortheunadjusteddentures)and atthe endofthetrial(fortheadjusteddentures).OHIP-EDENTscores wereanalysedusingaWilcoxonRankSumtesttocompare scores between dentureimpression materials (dueto non-normalityofthedata).Theperiodandcarry-overeffectswere alsotestedusingWilcoxonRankSumtests.Assessmentsof the Likert scale assessments of the dentures used the Wilcoxontestformatchedpairs.

3.

Results

Eighty-five patientswererecruitedfromApril 2010toApril 2012; follow-up finished January 2013. 59 (69.4%) of the patientswerefemale,77(90.6%)white,withameanage of 69.4(SD 10.87). Fig. 1 shows a flow diagram of patients’ progression through the trial. There were no serious unexpected adverseeventsthatwererelatedtotrial proce-dures.

3.1. Primaryoutcome

78 (91.8%) patients completed the primary assessment. 53 (67.9%) patients preferred dentures made from silicone impressionswhile14(17.9%)preferredalginateimpressions. 4(5.1%)patientswhofoundbothdenturesequallysatisfactory and 7(9.0%)foundbothequallyunsatisfactory. Therewasa 50%differenceinpreferencerates(infavourofsilicone)(95% CI32.7–67.3%,p<0.0001McNemar’stest)Table1.

3.2. Secondaryoutcomes

1. After the ‘Habituation Period’ (i.e. before substantial dentureadjustment),the patientreportedassessment of the ‘Comfort’, ‘Stability’ and ‘ChewingEfficiency’ of the dentures showed significant evidence that unadjusted dentures made fromsilicone impressionswere ratedas morecomfortable(p=0.0039),morestable(p=0.0047)and more efficient for chewing (p<0.0001) than unadjusted denturesmadefromalginateimpressions(Table2). 2. Aftertheconfirmationperiodtherewasa33.8%difference

inpreferenceratesfortheadjusteddentures(infavourof silicone)(95%CI14.3–53.3%,p=0.0016)(seeTable1). 3. After the ‘Confirmation’ period, the patient reported

assessment of the ‘Comfort’, ‘Stability’ and ‘Chewing Efficiency’ of the dentures showed there was again no evidenceofadifferenceincomfortratingbetweensilicone and alginate impression materials (p=0.5417). However, there wassignificant evidencethat denturesmadefrom siliconeimpressionswereratedasmorestable(p=0.0066) and moreefficient(p=0.0010)thandenturesmadefrom alginateimpressionsafteradjustment(seeTable2). 4. Afterwearingthedenturesforthetwo8weekAdjustment

(p=0.0014)(seeTable3).Therewasnoevidenceofaperiod effect(p=0.2105)orcarry-overeffect(p=0.5295).

5. Therewassignificantevidencefromthepatientreported Likertscoresthatsiliconeimpressionsweremore comfort-ablethanalginateimpressions(p=0.0021)butnoevidence of a difference in taste between the two impression materials (p=0.1128). An additional post hoc statistical analysisusingMcNemar’stestshowedtherewasa28.9% difference in patient preference rates for having their impressiontakeninsilicone(95%CI11.1–46.8%,p=0.0027).

4.

Discussion

This trial has produced definitive answers to a pertinent clinical question. Previous attempts at RCTs for dental impression materials have been scarce20,21 and have not yielded definitiveanswerstotheirresearchquestions.Thus thelackofRCTsofimpressionmaterialsiscompoundedbythe inability of previous RCTs to find a clinically significant differencebetweentheimpressionmaterials.Thisinabilityof Excluded (n=1, 1.2%)

Withdrawn from treatment and follow-up (n=1, 1.2%)

Excluded (n=30)

Not meeting inclusion criteria

Registered(n=85, 100.0%) Excluded (n=2, 2.4%)

Lost to follow-up (n=1, 1.2%) Withdrawn from treatment and foll ow-up (n=1, 1.2%)

Inial randomisaon

(n=83,

Habituaon randomisaon(n=80, 94.1%))

Excluded (n=3, 3.5%) Withdrawn from treatment and follow-up (n=2, 2.4%)

Died (n=1, 1.2%)

Adjustment randomisaon(n=78, 91.8%) (n=85) Excluded (n=1, 1.2%)

Withdrawn from treatment (n=1, 1.2%)

Excluded (n=2, 2.4%) Lost to follow-up (n=1, 1.2%)

Withdrawn from treatment and follow-up (n=1, 1.2%)

Excluded (n=1, 1.2%) Withdrawn from treatment and follow-up (n=1, 1.2%)

Excluded (n=2, 2.4%) Withdrawn from treatment and follow-up (n=2, 2.4%)

Excluded (n=1, 1.2%) Withdrawn from treatment and follow-up (n=1, 1.2%)

Alginate (yellow)/ Silicone (green) (n=22, 25.9%)

Silicone (yellow)/ Alginate (green) (n=18, 21.2%)

Silicone (yellow)/ Alginate (green) (n=20, 23.5%)

Alginate (yellow)/ Silicone (green) (n=18, 21.2%)

Completed treatment (n=20, 23.5%)

Completed treatment (n=16, 18.8%)

Completed treatment (n=18, 21.2%)

Completed treatment (n=17, 20.0%) Tray A first Alginate,

Tray B second Silicone (n=22, 25.9%)

Tray B first Silicone, Tray A second Alginate (n=21, 24.7%) Tray B first Alginate,

Tray A second Silicone (n=20, 23.5%) Tray A first Silicone, Tray

B second Alginate (n=20, 23.5%)

Silicone (red)/Alginate (blue) (n=41, 48.2%)

Alginate (red)/Silicone (blue) (n=39, 45.9%)

Assessed foreligibility

Confirmaon period(n=72, 84.7%)

Excluded (n=1, 1.2%) Lost to follow-up (n=1, 1.2%) ♦

♦

♦

♦

♦ ♦

♦

♦ ♦ ♦ ♦

♦

♦

Table1–Patientpreferenceofthedenturesbeforeandafteradjustment.

Silicone

Prefer/satisfactory Notprefer/unsatisfactory Total

Patientdenturepreferencebeforedentureadjustment(afterHabituationPeriod) Alginate

Prefer/satisfactory 4(5.1%) 14(17.9%) 18(23.1%)

Notprefer/unsatisfactory 53(67.9%) 7(9.0%) 60(76.9%)

Total 57(73.1%) 21(26.9%) 78(100.0%)

Silicone

Prefer/satisfactory Notprefer/unsatisfactory Total

Patientdenturepreferenceafterdentureadjustment(afterConfirmationPeriod) Alginate

Prefer/satisfactory 7(9.9%) 17(23.9%) 24(33.8%)

Notprefer/unsatisfactory 41(57.7%) 6(8.5%) 47(66.2%)

Total 48(67.6%) 23(32.4%) 71(100.0%)

Table2–Differencesincomfort,stabilityandchewingefficiencyofdenturesbyLikertscores.

Atotalof80patientsreachedHabituation ComfortN(%) StabilityN(%) EfficiencyN(%)

Beforedentureadjustment(afterHabituationPeriod): Differenceinscore(Silicone–Alginate)

4to 2 19(23.8%) 15(18.8%) 18(22.5%)

1 21(26.3%) 16(20.0%) 16(20.0%)

0 25(31.3%) 38(47.5%) 40(50.0%)

1 4(5.0%) 3(3.8%) 0(0.0%)

2–3 9(11.3%) 6(7.5%) 4(5.0%)

Missing 2(2.5%) 2(2.5%) 2(2.5%)

Total 80(100.0%) 80(100.0%) 80(100.0%)

Atotalof72patientsreachedConfirmation ComfortN(%) StabilityN(%) EfficiencyN(%)

Afterdentureadjustment(afterConfirmationPeriod): Differenceinscore(Silicone–Alginate)

4to 2 10(13.9%) 10(13.9%) 12(16.7%)

1 12(16.7%) 16(22.2%) 12(16.7%)

0 30(41.7%) 35(48.6%) 39(54.2%)

1 12(16.7%) 7(9.7%) 6(8.3%)

2–3 7(9.7%) 3(4.2%) 2(2.8%)

Missing 1(1.4%) 1(1.4%) 1(1.4%)

Total 72(100.0%) 72(100.0%) 72(100.0%)

Table3–OverallanddomainOHIP-EDENTscoresbyimpressionmaterial.

Alginate Silicone

N=78 N=78

OverallOHIP-EDENTscore

Overallscore: Median(range) 38.5(2,75) 27.0(0,69)

Missing 6 6

DomainOHIP-EDENTscore

Functionlimitation: Median(range) 9.0(0,12) 7.0(0,12)

Missing 5 5

Pain: Median(range) 11.0(0,16) 8.0(0,16)

Missing 6 5

Psychologicaldiscomfort: Median(range) 3.0(0,8) 2.0(0,8)

Missing 5 5

Physicaldisability: Median(range) 7.0(0,12) 5.0(0,12)

Missing 6 6

Psychologicaldisability: Median(range) 2.0(0,8) 2.0(0,8)

Missing 5 6

Socialdisability: Median(range) 2.0(0,12) 0.0(0,11)

Missing 5 6

Handicap: Median(range) 0.0(0,8) 0.0(0,8)

prosthodontic RCTstodetecta differenceextends toareas beyondRCTsofimpressionmaterials.

Inadditiontothetrialsofimpressionmaterials,therehave beenanumberofprospectiveRCTswhichhaveaddressedthe issueof‘simplified’dentureimpressiontechniquescompared toconventionaltechniques.22–25_{The‘simplified’singlestage} impressioninastocktraycomparedwithvarioustwostage impression techniques showed no significant difference between the trialarms. Of coursethe inability to detect a differenceshouldnotautomaticallyleadtotheassumptionof equivalence;absenceofevidenceisnotevidenceofabsence.26 Noneofthesetrialsweredesignedasanequivalencestudy (which have particular design issues to avoid establishing equivalence through poor adherence and underpowering amongst other issues27_{). It may alsobe that the protocols} used were incapable of detecting a clinically significant difference. Protocolsfor prosthodontic trials would benefit fromawiderdiscussioninacademicliterature.

Currently,thereareanumberofissueswithprosthodontic protocolsthatmayprovideunderlyingreasonswhyclinically significantdifferencesarenotproducedinRCTs.Prosthodontic trialscanhavenumerousspecificconfoundingvariablessuch aspatientrelatedfactors(e.g.ridgeform,salivaflow,mucosal quality,patient expectation, psychological profile, perceived aesthetics),technicalconstructionfactors(e.g.occlusalform, impressiontechnique,processingmethods,different techni-cians/technicalprocedures,thefulluse,ornot,oftherecorded sulcusdepth)anddentistrelatedfactors(e.g.ability,education, numberofclinicians,velocityofseatingoftheimpression).

Randomisation by minimisation will usually reduce the potential impact of these variables, however the particular natureandvolumeofpotentialprosthodonticconfoundersdoes meanthisproblemismorepronouncedinthisfieldandparallel groupRCTswillneedverylargenumbersofpatientstoeliminate theproblem.Alternatively,acrossoverprotocol(wherepatients effectivelybecometheirowncontrol)usingaverycarefuldenture duplicationprotocol28_{willeliminatemanypotential} confoun-ders,ensuringthattheonlydifferencebetweenthetwosetsof denturesisthesingleissueunderinvestigation.

Theresultsreportedwithin thispaper have shown that patients’perceptionsoftheirdenturesinrelationtocomfort werechangedaftertheadjustmentofthedentures;thiswas anticipatedasa potentialeffectofadjustment.Theresults showthatbeforeadjustmentthepatientsratedthesilicone dentures as more comfortable than the alginate dentures, whereas after adjustment the trial was unable to detect a significantdifferenceinthepatients’assessmentofcomfort. Adjustingthedentureseffectivelyeliminatedadifferencein comfortratingsbetweenthe dentures.Inother trials,22,24,25 theuseofassessmentatthepost-adjustmentstagealone(e.g. at 3 months and 6 months) coincides with a failure to differentiatebetweengroups. Postadjustmentassessments whenreportedontheirownmaynotadequatelydescribethe clinicalsituation.Itisappropriatetoreportassessmentsboth pre and postadjustment since both areclinicallyrelevant. Where post adjustment assessments are reported on their own,itwouldbegoodpracticetoalsoreporttheextentofthe adjustmentsrequiredoneachsideofthetrial,toallowthe readertoassessifanypreferentialadjustmentofthedentures hastakenplace.

Useofexpertopinionand/orexpertassessmentofthequality of dentures in RCTs have been ineffective23,29 and may be inappropriate.Thereisaparadoxhereinusingexpertopinion (whichisregardedashavinglowevidencevalue)todeterminean outcomeofanRCT(whichisregardedashavinghighevidence value). Instead,itis proposed thatblind,patient derivedand patient centred outcome measures (for example, patients preferreddenture,orOHIPs)areusedasamoreselectiveand clinicallyrelevantprimaryoutcomeinfuturecrossovertrials.

Theissueofsimplifiedversusconventionaldenturesmay be usefullybroken down into two separate areas;the first relatedtosimplified impressionsand thesecondrelatedto simplifiedocclusion.Doingsoisusefulsincethetwoissues canandshouldbeaddressedseparately.Forinstanceitmaybe thatseparateinvestigationsfindthatsimplifiedocclusionsare superiorbutsimplifiedimpressionsarenot(orviceaversa).If the ‘simplified technique’ improves one aspect of denture constructionbutmakesanotheraspectworse,theeffectswill canceloutandinvestigatingbothissuessimultaneouslyina singlestudywillleadtoconfoundedresults.Thisisanareaof potentialfutureinvestigations andwhencorrectlypowered the protocols, from Heydecke30 _{(for occlusion), Gray}16 _and Hyde31_{provideapotentialwayforward.}

In summary, there are problems designing effective protocolsinthefieldofprosthodonticresearch.Theauthors ofthispapertaketheviewthattheinabilityofprosthodontic RCTstodetectaclinicaldifferencecanbelimitedbyacareful protocoldesignwhichincludes:

1. acrossoverrandomisation,

2. acarefuldentureduplicationprocess, 3. theblindingofcliniciansandpatients,

4. thereportingofbothpreandpostadjustmentassessments and

5. aprimaryoutcomemeasurecentredonpatientpreference.

Following these principles this trial has differentiated betweendenturesconstructedonsecondaryimpressiontaken witheithersiliconeoralginate.Thisprotocolhaspotentialtobe ausefultooltolookatotherareasofprosthodontictreatment.

4.1. Clinicalimplications

Inviewofthestrengthoftheoutcomesofthistrial,dentists shouldconsiderreplacingalginatewithsiliconeasthematerial ofchoiceforsecondaryimpressionsforcompletedentures.

5.

Conclusions

1. Denturesmadefromsiliconeimpressionswerepreferred by patients over dentures constructed from alginate impressions, both before and after the dentures were adjusted.

2. Overallpatientspreferredtheexperienceofhaving impres-sionstakeninsilicone,findingsiliconeimpressionsmore comfortable;howevertherewasnopreferenceforthetaste ofeithermaterial.

4. Unadjusteddenturesmadefromsiliconeimpressionswere morecomfortable,stableandefficientforchewing. 5. Afteradjustment,thedenturesmadefromsilicone

impres-sions remained more stable and efficient for chewing. However, theadjustment ofthe denturesresultedinno detectabledifferenceincomfortbetweenthedentures.

Funding

FundedbyNIHR-RfPBgrantnumberPB-PG-0408-16300.

Acknowledgments

This paper presents independent research funded by the National Institute for Health Research (NIHR) under its ResearchforPatientBenefit(RfPB)Programme(Grant Refer-ence Number PB-PG-0408-16300). The views expressed are thoseoftheauthor(s)andnotnecessarilythoseoftheNHS,the NIHRortheDepartmentofHealth(UK).

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