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CAD/CAM Magazine

preparation for a ZrO2 crown framework. (Figs. 3 & 4 courtesy of Wöstmann) Fig. 5_ITero is equipped with a laser camera. It is the third intraoral scanner on the European market. Fig. 6_ITero scans the tooth at several levels using laser triangulation. Figs. 7a & b_The virtual “prep-check” checks the preparation margins and the occlusal reduction against the antagonist tooth. (Photo courtesy of Lauer) Fig. 8_The full-arch scan for an FDP construction using the iTero system. (Figs. 5, 6, 8 & 10 courtesy of Straumann) Fig. 9_SLA resin model using the C.O.S. Lava system. (Photo courtesy of 3M ESPE) Fig. 10_Digitally milled resin model using the iTero system. Fig. 11_Construction of an FDP. I 39 trends _ digital datasets I CAD/CAM 2_2011 Nowthatproducingall-ceramicrestorationswith- out CAD/CAM has become almost unthinkable, the next step has already been taken towards complete digitisationoftheprocessfrompreparationtoseating the prosthesis: optical scanning to create a digital, intraoral impression. In terms of clinical use, the de- vices—CEREC AC (Sirona), C.O.S. Lava (3M ESPE), iTero (Cadent-Straumann)—are similar, but they function according to different principles. Technically, the systems are similarly constructed, but the procedures foracquiringthe3-Ddatasetsdiffer. The acquisition unit of CEREC AC uses short-wave blue light and functions according to the principle of structured-light projection (Fig. 1). The scanning procedurecapturessingleimages;theangledimaging function acquires tooth areas below the equator and thus increases accuracy. Through matching, several images are computed of a quadrant or whole arch (Fig.2),asaretheantagonistdentitionandbiterecord. The wavefront sampling of C.O.S. Lava captures the tooth shape by moving the video camera over the teeth. The distance to the camera can be calculated fromthechangingpositionofindividualpixelsduring filming, giving rise to a 3-D image of the dental arch (Figs.3&4). The functioning of the iTero scanner is based on theprincipleoflasertriangulation.Theimagecaptures the tooth and vertically scans 300 levels, each 50 µm deep(Figs.5&6). According to Prof Wöstmann, the scanning ac- curacy of CEREC AC and C.O.S. Lava corresponds to a conventional hydrocolloid or polyvinyl-siloxane im- pression. The differences were not significant.1 Meas- urements of crown copings fabricated with C.O.S. Lava yielded an average of 33 µm (± 16 µm) for all marginal gaps. Copings produced using the conventional im- pression-takingtechniquehadameanmarginalgapof 69 µm (± 25 µm). Syrek etal. found comparable results in a clinical study.2 The mean marginal gap of conven- tionallymanufacturedcrownswas71µm,ascompared with 49 µm for the C.O.S. Lava crowns. For CEREC 3D, theliteraturecitesatoleranceof40µm(±21µm).3 Anotheradvantageofdigitalimpressionsisthatthe scanned preparation can be checked directly on the screen, where imperfections can also be immediately corrected (Figs. 7 & 8). For patients with an easily trig- gered gag reflex, these scanning methods greatly im- prove treatment comfort. Further benefits result from fewerworkingstepsinvolved,especiallyinthepractice. Choosinganimpressiontray,mixingtheelasticimpres- sioncompound,waitingduringsettinganddisinfection, aswellasproducingamodelarenolongernecessary. Fewertreatmentandworkingstepsalsomeanfewer sources of error and better standardisation, which in turn can improve the predictability of treatment out- come.ProfWöstmanncautionedthatwithcrownmar- gins that are clearly subgingival, the optical systems reachtheirlimits;thus,conventionalimpression-taking techniquesarestillusedinsuchcases. Fig. 7a Fig. 8 Fig. 7b Fig. 9 Fig. 11Fig. 10