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ePaper created 2015-03-06, 14:42:46 | version 1.33.01
I 23 review _ CAD/CAM I CAD/CAM 1_2015 is followed by the pouring of stone models and dies prior to laboratory fabrication of the definitive fixed restoration.Takinganaccurateimpressionisoneofthe mostdifficultproceduresindentistry,requiringcareful retractionorremovalofsofttissuearoundpreparation margins, haemostasis, and selection of an appropriate impressionmaterialandtrayforthetechniqueused. By using a CAD/CAM restorative technique, a numberofstepscanbesimplifiedoreliminated.7 Digitalsystemsnowoffertheopportunitytoavoid traditional,analogueimpressions,includingtheusual impression materials, time, and handling limitations associated with them. Intraoral scanners have the potentialtoofferexcellentaccuracywithamorecom- fortable experience for the patient and more efficient workflow for the office. But care must be taken to ensurethatthewholepreparationisscanned,toavoid introducingerrors. TwotechniquescanbeusedforCAD/CAMrestora- tions:thechairsidetechniqueortheintegratedchair- side-laboratoryprocedure. _Chairside technique The development of CAD/CAM technologies for dental applications has enabled clinicians to prepare and indirectly restore tooth tissue with an aesthetic all-ceramicrestoration,manufacturedatthechairside inasinglepatientvisit. Chairside CAD/CAM techniques offer advantages to the patient, including eliminating the laboratory procedure and the requirement for intra-visit tempo- risationofthepreparedtoothstructure.8 It eliminates several cumbersome dental office tasks, such as selecting trays, preparing and using materials, disinfecting and sending impressions to the laboratory. It also removes a source of discomfort andgagging.Moreover,itenablesthecliniciantotake a digital impression, design and mill the restoration in-office, and fabricate cosmetic crowns, onlays and veneers, with full management over contours and tooth shade. Finally, it enhances the accuracy of adaptationoftherestorationtothepreparation.9 In summary, with these systems, final restorations areproducedinmodelscreatedfromdigitallyscanned data instead of plaster models made from physical impressions. There are three main sequences to this workflow. Thefirstsequenceistocaptureorrecordtheintraoral condition to the computer. This involves the use of ascannerorintraoralcamera. During scanning, the clinician must ensure that all margins of the cavity are captured by the scan and visualised. The accuracy of CAD/CAM restorations depends on the scanner’s ability to visualise the mar- gin. A true laser scanner/digitiser takes precise digital images of the preparation, including the margin, the undercuts, the contours, the adjacent dentition, and the gingiva. It captures hundreds of thousands of points of reference with each image, and then utilises a million data points to create an exact replica of the preparedtoothandneighbouringdentition. Dependingonthesystem,alightandrapiddusting of an opacifier may be required prior to capturing the digital scans of the preparation arch, opposing arch, and buccal bite registration. Once the data has been recorded to the computer, a software programme is usedtocompletethecustomdesignoftherestoration. The preparation is shown on the monitor and can be viewed from every angle to focus or magnify areas of thepreparation.Inadequateimagesareautomatically detected. The “die” is virtually cut on the virtual model, and the finish line is delineated by the dentist directly on the image of the die on the monitor screen. Then, aCADsystem,called“biogeneric”,providesaproposal Fig. 3_Designed molar restorations using dental designer software. Lingual view. Fig. 4_Designed molar restorations using dental designer software. Occlusal view. Fig. 4Fig. 3 CAD0115_22-26_Kassis 02.03.15 12:47 Seite 2 CAD0115_22-26_Kassis 02.03.1512:47 Seite 2