40 I I feature _ interview _IDS2009showcasedtheimpressiveadvancements inCAD/CAMdentistry.Forprivatedentists,however,there is much uncertainty regarding response to these devel- opments. cosmetic dentistry spoke with Prof Albert Mehl, currently Guest Professor at the Centre for Den- tistryandOralMedicineattheUniversityofZürich,about whetherinvestinginCAD/CAMpaysoffandforwhom. _cosmetic dentistry: Most failures with conven- tional technology occur during impression preparation (insufficient illustration of the preparation margins, insufficient drainage). What advantages do CAD/CAM systemsofferforthedentalpractice? Prof Mehl: Most importantly, treatment times are reduced because the dental restoration can be manu- facturedinthesamesessionasthepreparation(chairside method).Temporariesbecomeobsolete,thusmakingun- comfortable and unaesthetic transition times a thing of thepast.Owingtoadhesivetechnology,sufficientreten- tionforatemporaryisinsomecasesnotavailablebecause of the minimally invasive preparation. Furthermore, the latest studies demonstrate improved bonding to teeth with freshly cut dentine and enamel. Computer-aided millingandpolishingallowstheuseofhigh-qualityma- terials, which are manufactured industrially under opti- mal conditions, resulting in longer-lasting restorations comparedtoconventionallymanufacturedrestorations. Thishasalreadybeendocumentedinnumerousscientific studies. Through the combination of time saving, cost reduction and increased quality, the chairside method offers an interesting perspective for modern dentistry. Thispertainsmainlytosingle-toothrestorationsbutwe can expect new possibilities in the production of fixed partialdentureswithsmallspanwidthsinthenearfuture. _Howdoesthesignificantinvestmentindigitalim- pressiontechnologypayoff? Whenconsideringconceptsthatentailthesendingof dataofadigitalimpressiontoadecentralisedproduction site via the Internet, one can say that the time-frame equals that of conventional impression techniques. The extenttowhichtheaccuracyofdigitaltechnologyiscom- parable to conventional impression techniques (includ- ingpreparationofmodels)hasnotyetbeendetermined, particularly in larger span widths. Comparative studies arenowbeingconducted,anditisuponthisissuethatthe furtherexpansionoftheseconceptsisdependent.How- ever,firstexperiencessuggestthatthisisindeedpossible. Digitalisationwouldthenenablethesameadvantagesin other areas. The virtual 3-D model is important not only for the computer-aided fabrication of dental restora- tions, but also for every other kind of diagnostic, such as the exact 3-D determination of tooth movements, archiving of virtual models and the documentation of 3-D changes to the tooth and surrounding soft tissue. Accordingtotheindustry,amortisationcouldbeachieved throughthecostsavingsofcomputer-aidedproduction inproductioncentres,softwareupdatesandsystemsfor thechairsideproductionofsingle-toothrestoration,and extensiontodiagnosisandtreatmentplanningsoftware. The enormous potential of digital scanning has been recognisedbytheindustryandthusiscurrentlyinheavy development. As soon as quality and practicability have been demonstrated within clinical environments, amor- tisationwillnolongerbeanissue. _Howcantheaestheticdisadvantagesofthesingle- sessiontreatment(CEREC/E4D)besolvedinthefuture? Sophisticated, aesthetic single-session treatments in the anterior region are difficult and achievable only withmuchexperience.Hence,mostdentistswillproba- blyprefertheconventionalveneerlayeredcrowns.How- ever,aestheticallypleasingresultscanbeobtainedusing multi-coloured blocks. It is expected that these blocks will be improved by optimising the form and position of the layers and that the software will position the restorationwithintheblockforoptimumcoloureffects. In order to standardise this process, the use of tooth colourmeasurementsystemsmayalsoberelevant. _Are you referring to integrating digital colour measurementsystemswithCAD/CAM? This is an interesting aspect. This kind of integration islikelytobeavailablesoon.Inmyopinion,thisisanother majoradvantageofCAD/CAMtechnology.Throughthe means of standardised calculation processes, the ideal layerthicknessofframesandveneersforeveryrequired shade can be obtained individually for each combina- tion of materials and type of restoration. A systematic analysisofthesecombinationsandtheresultingcolour effects through large test series are essential though. Suchtestshavenotbeenavailablethusfar. _Does the extended workflow—from practice to centre to laboratory and back to the practice—offset thetime-savingfactor? Thisisthecaseandcertainlyadisadvantageofacen- tralisedproductionprocess.Theadvantage,however,is thatsuchcentrescaninvestinhigh-qualityandhighly precise production technologies. These machines are maintainedbyspecialistsandensurehighcapacity.The storageofmanydifferentmaterialsincludingavariety cosmeticdentistry 2_2010 Does CAD/CAM pay off? An interview with Prof Albert Mehl, University of Zürich, Switzerland Prof Dr Dr Albert Mehl