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Journal of Dentistry and Oral Care
Review Article Open Access
1Specialist Prosthodontist, Private dental practice, Dubai2Senior Lecturer, Department of Prosthodontics, Bangalore Institute of Dental Sciences, Bangalore
Abstract
CAD/CAMisafieldofdentistryandprosthodonticsusingCAD/CAM(com-puter-aided design and computer-aided manufacturing) to improve the design and creationofdentalrestorations,especiallydentalprostheses,includingcrowns,crown,veneers,inlaysandonlays,fixedbridges,dentalimplantrestorations,dentures(remov-ableorfixed),andorthodonticappliances.ThereexistsamisconceptionthattheCAD/CAMprocessiscomplicatedandtime-con-suming.However,theCAD/CAMsystemissimpletooperate,versatile,andprecise.All-ceramicrestorationscanbedesignedandmilledchairside,withtheaddedadvan-tage of elimination of traditional impressions and temporaries, and the patient leaves theappointmentinaboutanhourwiththefinalrestorationinplace.DentalCAD/CAMis approaching20yearsof clinical experienceandhas aproven track recordonallrelevant aspects of clinical performance, including fit, longevity and survival rates,sensitivity,strength,andwear.
*Corresponding author: Smitha Annie Jacob, Specialist Prosthodontist, Private dental practice, DubaiE-mail: dr.smitha.jacob@gmail.com
Keywords:CADCAM;Ceramics;DigitalDentistry;DigitalWorkflow;CEREC
Citation:SmithaA.J.,etal.CADCAM- Understanding the Basics: A Review.(2016)JDentOralCare2(2):50-55.
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Aim TheapplicationofdentalCAD/CAMsystemsispromising,notonlyinthefieldofcrownsandFPDs,butalsoinotherfieldsofdentistry.ThereisnodoubtthattheapplicationofCAD/CAMtechnologyindentistryprovidesinnovative,state-of-artdentalservice,andcontributestothehealthandQualityofLiving(QOL)ofpatients.Thepurposeofthispaperistogiveanin-depthknowledgeofCADCAMtechnologytothereadersastoday’sdentistryhasenteredintothedigitalera.
Introduction
ThetermCAD/CAM,whichcomesfrommachine-tool technologyandstandsfor“Computer-Aided-Design/Comput-er-Aided-Manufacturing”,designatesthethree-dimensionalplanningofaworkpieceonthescreenofacomputerwithsubsequentautomatedproductionbyacomputercontrolledmachinetool[1,2].In1971,FrancoisDuretintroducedCAD-CAMtechnologytothefieldofdentistry.Hisideawasbasedupontheassumptionthatthetechnologiesestablishedinindustrycouldbeeasilytransferredtodentistry. Thoughcastingprocedurehasadvancedoverthepastyears,eachofitsstepscouldinduceerrorinthefinalcasting.Until1988,indirectceramicdentalrestorationswerefabricatedbyconventionalmethods(sintering,castingandpressing)andneitherwaspore-free.Machiningblocksofpore-freeindustrialqualityceramiccanalternatelyproducepore-freerestorations[3-5].Thetre-mendousadvancesincomputersandroboticscouldalsobeappliedtorevolutionizedentistryandprovidebothprecisionandreducetimeconsumption.With thecombinationofoptoelectronics,computer techniquesandsinter technology,computerizeddentistry
CAD CAM - Understanding the Basics: A Review
Copyrights: ©2016SmithaA.J.ThisisanOpenaccessarticledistributedunderthetermsofCreativeCommonsAttribution4.0InternationalLicense.
50
Smitha Annie Jacob1*, Savitha P.N2
Received date: August 10, 2016Accepted date: August 29, 2016 Published date: September 02, 2016
SmithaA.J.,etal.
DOI: 10.15436/2379-1705.16.1046
haspavedthewayforanewgenerationdentalceramicwithanunprecedentedhighstrengthanddurability,derivedfromdevel-opmentsinNano-ceramictechnologiesinthelastdecades.
What is CAD CAM?ThecontemporaryCAD/CAMsystemsconsistofthreecompo-nents: 1.Thescanner,whichscansthedentalpreparationpro-videdbythedentisteitherintra-orallyorextra-orallybyrefer-ence to toothmodels (Figure 1). For inlays and single crownframeworks,justthesurfacedataofthepreparedteethneedtobedigitized.ForFPDframeworksoradditionalocclusalcharacter-ization, further data from the neighboring teeth and antagonists, aswellasfromthespatialrelationofthepreparedteethtooneanother,arerequired[6-9].
Figure 1:CERECScanner.
2.ThesoftwareCADconsistsofacomputerunitusedfor the three-dimensional planning and design of restorations on thecomputerscreen(Figure2).Thesoftwareprogramsavailabletodayoffer a high level of intervention andpermit thedesignandproductionofanindividuallyadaptedrestoration.SystemsnotofferingafullCADcomponentarenotconsideredasCAD/CAMsystemsbutjustasCAMsystems[10].
Figure 2 : Softwaredentaldesigner.
3. The hardware CAM covers different productiontechnologies for converting the virtual restoration into a den-talmaterial(Figure3).Atpresent,computer-controlledmillingorgrindingmachinesaremainlyused.Theymachinetheresto-ration from the fullmaterial block consistingof prefabricatedmetal or ceramic[11,12].Asarule,aftertheCAMproduction,somemanual corrections and final polishing or individualization ofthe restorationwith staining colors or veneeringmaterials arerequiredtobecarriedoutbythedentaltechnician(Figure4).
Figure 3 :SironaMillingUnit.
Figure 4 :CycleofCAD/CAM.
Scanning of Preparation Since1971,anumberofattemptstodentalCAD/CAMhavebeenreported.Themostprominentare
1. Holodontography by altschuler : Areportdated1971claimsthatdevelopmentoflaserholographycansignificantlyinfluencetheproceduresusedindentalcare.Itmentionstheuseoftoothprints recorded bymeans of a combination of computers andlaser holography. Such tooth print could serve for diagnosticand forensic purposes, but also applicable to prosthetic and re-storativework[13].Aspecifictaskwouldbecomputer-controlledmillingofdentalcrownsbasedoncontourholograms.
2. The Duret/ Hennson/ Sopha system :TheoriginofFrench
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approachdatesbacktotheearlyseventies.Goalofthisendeav-oristhecomputer-aidedrestorationanddentistryinthebroad-estsense.Theprimaryapplicationofthesystem,however,wasthefabricationofcrowns.Theoriginalscanningprinciplewasbasedonlaserholography.DrFrançoisDuret’smethodrequiresasetofdifferentviewsofthepreparation.Theindividualviewsarecorrelatedbythecomputertoproduceathree-dimensionalrecord.Tofacilitatethealignment,thedentistplacesreferencebracketswithin thefield of view.Thedesign is accomplishedbymanually tracing thecervicalmarginof thepreparationbymeans of a large screen color monitor and a digitizing tablet[14].Theprogramusesaselectiveshrinkagealgorithmtoproduceanoptimumcementationgap.Themachineisequippedwiththreeaxesandhastheadditionalcapabilitytoturntheworkpieceup-sidedown.
3. Active triangulation:Thisprincipledoesnotrelyonanim-agepairasobtainedbytwo-eyedvision.Insteadoneopticalpathisconvertedfromreceptortotransmitteror,moreaccurately,apatternprojector.Duetothephysicalseparationofthetwochan-nelsacertainamountofparallaxisintroduced.Sincetheparal-laxisaknownconstant,theresultingrange-dependentshiftofthepatternprojectedontotheobjectcanbeaccuratelyconvertedinto depth values[15].
Data Acquisition Thefirstelementofthedataacquisitionchainisasolidstateimagesensor.Thisdeviceaccuratelyconvertslightinten-sitytovoltagewhenreadinalinebylinemode.Thealternatingregionsofdarkandlighttranslateintohigherandlowervoltag-es.Whenreadingasensorline,whichrunsmesio-distally,sinu-soidal pattern is observed[16,17].Whilethereticlefeaturesasquarepattern (bands are either transparent or totally opaque), limit-edresolutionofthedetectedsignalapproximatesasinewave.Justliketheindividualline,everylineofthepatternisshiftedproportionallytoverticaldistances.Inmathematicalterms,thephaseofthespatialfrequencyismodulated. Oncetheparticularphasewhichcorrespondstoaref-erencelevelhasbeenestablishedbycalibration,theelevationofanypointoftheobjectcanbecalculatedfromthephaseshift.Amorecarefulanalysisofthesinusoidalpatternrevealssomeadditionaldifficulties:theshapeofthispatternisnotverywellbehaved.Itexhibitslargelocalvariationsinbothamplitudeandoffseti.e.thedistancefromthebaseline.Thelatterarecausedbythevariousamountsofstraylightandsensordarkcurrent.Theformerarecausedbythefact,thattheamountoflightpickedupbythesensorisafunctionoftheslopeofthepreparationwallsat any point.An additional difficulty arises from the non-uni-formityintheresponseoftheindividualsensorelements.Duetolimitationsintheartofsemiconductorfabrication,atypicalsensorwillevencontainacertainamountofblindcells.Inordertoisolatethethreevariables–phase,magnitudeandoffset-atleast three images are required, all takenwith the exact sameorientation,buteachusingadifferentphaseoftheprojectedpat-tern[18,19]. Asequenceoffourimages(Figure5),provedtobeamoreefficientapproachinourparticularapplicationandhard-wareimplementation.Thereticleisphysicallytranslatedduringaperiodof4times40millisecondsfromanarbitrary0˚initialpositionover 360˚, i.e., one entire line period.For reasonsofclarity, the illustration shows a fixed position for each frame,
whileinrealitythepatterniscontinuouslysweptacrosstheim-age. Various levels of intensity, reflecting the actual positionofpattern,aredetected.Thesignalisasteppedapproximationof theactual intensitypatternsince theelementsof thesensorhave finite dimensions (period of pattern 200µ divided into a22µelementpitchofthesensorarrayyieldsapprox.9samplesperperiod),whilethemodulatedpartofthesignalisshiftedinphase,theoffset,representedbytheaverageintensity,remainsconstant[20,21].Thisobservationsuggestsadifferentialoperation.Subtractingthe180˚imagefromthe0˚imagecancelstheoffsetportion off the signal. Since this subtraction is achieved by areactionofmodify-writeoperation in the imagememory, it isexecutedinstantaneously.The90˚-270˚subtractionisaccom-plishedinthesameway.
Figure 5:Sequenceoffourimages.
At the endof the 160millisecond exposure,we thusfindthetwodifferentialdatasetsintheframebuffer.Thechar-acterizationfeaturesofthemodulationhavebeenunaffectedbythe subtraction, the amplitudes have been doubled and the sig-nalsarenowbiasedatthezerolevel.The90˚phasebetweenthetwosignalshasbeenpreserved.Wearenowleftwithadatapaircorrespondingtoeachpicturecell-orpixel-oftheimage.Datapairsmustbetransformedtoyieldthedesireddepthinformation.Thetwo-dimensionalarrayofthedepthvaluesisreferredtoastheprofile.A second setofvalues, representing local contrastamplitudecanbeobtainedfromthisconversion;inourcontextwecallthissecondsetofdatathehill-shadedimage[22-24]. Priortomakinganopticalimpressionwiththesensor,it isnecessary topowder the toothsurfaceandtheentirefielduniformly.Thedetectionof thepattern cast onto anuntreatedpreparationisnotpossibleforthefollowingreasons:ontheonehandthedifferentslopesofthepreparationandthedifferencesinsurfacequalityyieldadynamicrangeofintensities,whichistoolargetobeaccommodatedbythesensorandtheassociated
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circuitry.Thesteepwallsappearasvirtuallyblackregions.Thecuspwhichreflecttheincidentlightinaspecularfashiontendtoglaretherebycausingsmearingartifactssimilartothehumanretinawhenwelookdirectly intoapowerful lightsource[25,26].Ontheotherhandthedentinandenamelistranslucentwherebyit absorbs at least partially, the pattern projected onto its sur-face.Toalleviatebothproblems,thesurfaceofthetooth,andforthatmatter,theentirefieldofviewmustbecoatedwithathinopaquerlayer.Afinecoatoftitaniumdioxideproducesahighlyuniformscatteringofthelight.Theremainingvariationininten-sity is verydesirable since it enhances the three-dimensionalfeaturesofthepreparation.
Milling of the Ceramic Restoration Therestorationismilled(4-7minutes)withadiamondwheelfromapremanufacturedandstandardizedceramicblockinthemillingchamberoftheCAMunit.Factorystandardized,preformeddentalporcelainblocksarehomogenousandalmostpore-free(VitaCerecblocks,DicorCerecblocks).
The Cam UnitApumpsystemwithanattachedwaterreservoirlocatedatthebaseofthemobilecartmaintainsthewaterpressurerequiredfor thehydraulicdrivenwater turbine in themillingchamber.Duringmillingabout5litersofwateriscycledinternally,whicheliminatestheneedforexternalwatersupplyanddrainage.Thewater reservoirsystemalsocontainsamicroporousfilter thattrapsanyofthelooseneddiamondparticlesseparatedfromthewheelforfutureretrieval[27,28](Figure6).
Figure 6:Themillingunit.
Procedure[29,30]: •Theappropriateceramicblockisselectedfromase-riesconsistingofdifferentsizesandshade •Theceramicblockismountedonametalstub(retain-er), inserted into the milling unit and the grinding operation is initiated. •Grindingoftheceramicrestorationisdonebyadia-mond–coateddisk/wheelinconjunctionwithahighvelocitywater-spray,whichsimultaneouslycoolsandcleansthemillingdisk.Therestorationismilledfromthemesialtothedistalprox-imalsurfaceswiththeblockrotatingalongitscentralaxisandbeingsteadilyadvancedforwardduringthemillingprocess.Inaddition,thediamondwheelnotonlyrotatesbutalsotranslates
upanddownovertheporcelainblockbeingmilled.Aseriesofstepsorcuts(200–400)arerequiredformillingaceramicres-toration.
The Computer program associated with the milling process has additional interesting features such as[31]: • Before themilling process, the screen displays thedimensionsoftherestorationfromoneproximalsurfacetotheotherin1/900thofanmm. •Duringthemillingoperation,thescreencontinuouslyinformstheoperatorofthepercentageofcompletion. • A continuous readout is displayed concerning thecuttingefficiencyofthediamondwheel,therebyindicatingtheprobableneedforreplacement.
Advantages of CAD CAM[32-35]
1.Theconceptthatadentistcan,inasingleappointment,admin-isteranestheticinpreparationfor,preparethetoothfor,makeanimpression for, design, mill, customize and place a restoration isdesirableformanycliniciansandpatients.Thecommandof“one-appointment”dentistryispowerfulnotonlyforthepatient,butalsofortheentiredentalteamandtheoffice’sproductivity.Single-appointmentdentistryhasavarietyofbenefits:theneedforonlyoneadministrationofanesthetic,theabsenceofneedfortemporaryorprovisionalrestorations(therefore,nolosttempo-rariesorre-cementations),theabsenceoflaboratoryfeesandareductioninsecond-chairset-upcosts.Thesefactorsultimatelyequatetofewerinstrumentsneedingtobesterilized, lessneedforchairtimeset-up/breakdownandimprovedofficeefficiency. 2.Another, oftenoverlookedadvantage is thedisposable sup-plies that can be eliminated (from impression material, wax,stone, temporarybridge resin andcement to cottonandpaperdisposables)by institutionofaCAD/CAMsystem.Clinicianscangainotherintangibleadvantagesinthelongtermbyintro-ducing CAD/CAM technology into their already-busy dentalpractices.WithCAD/CAMtechnology,cliniciansmaintaintotalproduct and artistic control of the restorations to be fabricated and seated. It allows clinicians to spend themajority of theirtimeontoothpreparationandonseatingofthefinalrestoration;thesoftwareprograms’optionsdeliveraproductthatmayneedonlyendpointcharacterization,stainingorglazing.Thecomput-er and milling processes diminish potential inaccuracies result-ingfromthehand/laboratoryfabricationprocessandareabletoprovide a restoration that fitswithin the 50-micrometer rangeestablishedbytheAmericanDentalAssociation.
3.When thedentist implementsCAD/CAMtechnology,heorshe must create a schedule that supports single-appointment treatment.This schedule arrangement can both save time andincrease efficiency. Dentists can complete most CEREC sin-gle-unitcrownswithinoneandone-halfhours.Dentistscantreatquadrantswithintwoortwoandone-halfhours.Withthistypeofdentistry,thesecond“seating”appointmentnowisfreedupand can be re-designated for an additional productive appoint-ment.Givenatraditionaltwo-appointmentprocedureandtimeallotment, this single-appointment treatment approach becomes practical.Moreover, a practitioner seasoned in using CERECcanperformadditionalprocedureswhiletherestorationisbeingmilled,againenhancingthepractice’sefficiencyandproductiv-ity.
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4. Patients often experience irritation in, sensitivity in and/ordifficultyincleaningtemporizedteeth.Single-appointmentden-tistryavoidsthesecomplaints.Also,cliniciansmustconsiderthediminished chance of bacterial invasion during this phase; de-creasedpulpalstressresultingfromexcessivecleaning,dryingor trauma; and decreased need for the additional tooth manipu-lationthatoftenisexperiencedatasecondappointment.Giventhe fact that veneers represent a significant portion of labora-tory-fabricated restorations today and that veneer temporarieseasily can be displaced and are time-consuming to fabricate,dentistsshouldfindtheconvenienceofsingle-appointmentden-tistrysignificant.
5. Furthermore, theCEREC veneer software program is easytouseandwillenhance the implementationofsingle-appoint-ment dentistry.Dentists have the ability to include their teammembersbydelegatingsomeofthetasksintheCERECprocess.In sucha scenario, assistantsmaybe included in introductoryCERECtrainingandcanbettertheirskillsbytakingadditionaltrainingcoursesspecificallydesignedforassistants.Inpractice,the team approach flows thus: the dentist prepares the tooth,powdersitandmakestheopticalimpression.Thentheassistantdesigns the restoration, mills it, polishes it and prepares it for bonding.Finally,thedentistcompletestheprocedurebybond-ingtherestoration.
Disadvantages of CAD CAM[36-38]
Intheimplementationofanynewtechnology,discus-sions arise that require critical thinking. The primary consid-eration in a CAD/CAM purchase is the length of the learning curve,whichmayrangefromafewdaystoseveralmonthsandmay result in the lossofofficeproduction, the lossofpatienttreatmenttimeandanincreaseintheclinician’sfrustration.Oth-er obstacles to incorporating this system into practice are thecostof the equipment, thepotential for thedental team to re-sist the system’s use, the clinician’s lack of confidence in us-ingacomputerizedsystem,andperhapstheclinician’slackofwillingnesstolearnanewconceptthatwillrequiretrainingandpractice.Dentistswhohavedifficulty integrating this technol-ogyintotheirpracticesusuallyaredentistswhodonotwanttochangethewaytheyarepracticing. However,theadvantagesofthissystemoutweighthesedisadvantages listed and so it is emerging as a successful treat-mentoption.
Summary During the past decade, computer-aided design/ manu-facturing(CAD/CAM),whicharewell-knownprocessesintheindustrialworld,havefoundtheirwayintodentistry.Interestinthis designing and manufacturing process occurred because of itspotentialasanalternativetothelost-waxtechniquethathasbeenusedformanydecadesforfabricatingdentalrestorations.Anumber of reports in the literature[39-42]inrecentyearsdetailtheCAD/CAMmethods thathavebeenused indentistry.Equallyimpressive is the number of articles reporting on the clinical suc-cess and the improved characteristics of restorations fabricated bytheseCAD/CAMmethods.
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