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ePaper created 2015-03-06, 14:42:46 | version 1.33.01
26 I I review _ CAD/CAM _Discussion Marginal adaptation is an important factor affect- ing the longevity of all-ceramic restorations.24 Con- siderableresearchhasbeeninvestedinthemarginalfit andinternaladaptationofCAD/CAMrestorations.25–28 Softwarelimitations,aswellasaccuracyofmilling devices, may affect the fit of CAD/CAM restorations. Most clinicians agreed that marginal gap should not be greater than 100 μm. It has been reported in the literature that restorations produced by CAD/CAM systems can have marginal gaps of 10-50 μm which is considered to be within the acceptable range.29 GiannetopoulosandAlinvestigatedandcompared themarginalintegrityofceramiccopingsconstructed with the CEREC3 and the EVEREST system, employing threedifferentmarginangledesigns.Theyexploredto what extent these CAD/CAM machines can produce acute marginal angles, creating restorations with ac- ceptable margins. They found that the average chip- pingfactor(CF)oftheCERECcopingswas:2.8percent forthe0°bevelangle,3.5percentforthe30°bevelan- gle and 10% for the 60° bevel angle. For the EVEREST copings, the average CF was: 0.6 per cent for the 0°bevelangle,3.2%forthe30°bevelangleand2.0per cent for the 60° bevel angle. Univariate Analysis of Varianceandmultiplecomparisonsshowedthatthere was a statistically significant difference in the quality of margins between the two systems for the 0° and 60°bevelfinishingline.30 MjörandAlhaveevaluatedCAD/CAMrestorations and found that they have a marginal fit as good as or superior to that of traditional impressions. A further benefit found with CAD/CAM restorations has been thereducedincidenceofsecondarycaries(theleading causeofdirectrestorationfailurewithbothamalgam andcompositematerials),attributedtothehighaccu- racy of the approximal fit and the ability to ascertain that this is accurate prior to completion of the resto- rationandcementation.31 Another study evaluated the accuracy of marginal and internal fit between the all-ceramic crowns man- ufactured by a conventional double-layer CAD/CAM system and a single-layer system. Ten standardised crowns were fabricated from each of these two sys- tems: conventional double-layer CAD/CAM system (Procera) and a single-layer system (CEREC 3D). Mar- ginal discrepancies of Procera copings were signifi- cantlysmallerthanthoseofProceracrownsandCEREC 3D crowns (P > 0.05). On internal gaps, CEREC 3D crowns showed significantly larger internal gaps than Proceracopingsandcrowns(P<0.05).Withinthelim- itations of this study, the single-layer system demon- stratedanacceptablemarginalandinternalfit.32 On the other hand, depending on the preparation design, either an adhesive or a non-adhesive luting cement can be used with these materials. CAD/CAM restorative materials can be cemented with either traditional luting cements such as zinc phosphate, polycarboxylate cement, glass ionomers, or resin-modified glass ionomers. Materials that can be sealed with these include zirconia, lithium disilicate, alumina, and resin nanoceramics.33,34 With regards to resin adhesive cements, they of- fersuperioraestheticsandlowviscosity.Theychem- ically bond to the restoration surface and the tooth surface, either providing all of the retention or, for retentive preparations, improved retentive strength. They also have greater compressive strength.35 Meanwhilezirconiafixedpartialdenturesshowed good to sufficient marginal integrity in combina- tion with Panavia/ED, Compolute/EBS and RelyX Unicem.36 When evaluating the initial and the artificially agedpush-outbondstrength(PBS)betweenceramic and dentine produced by one of five resin cements, there was a significant effect of resin cement (P < 0.0001): RelyX Unicem showed significantly higher PBS than the other cements. Syntac/Variolink II showed significantly higher PBS than SmartCEM2 (P < 0.001). No significant differences were found between SpeedCEM, SmartCEM2, and iCEM. The predominant failure mode was adhesive failure of cements at the dentine interface except for RelyX Unicem, which, in most cases, showed cohesive failure in ceramic.37 _Conclusion Digitalimpressionstendtoreducerepeatvisitsand retreatmentwhileincreasingtreatmenteffectiveness. Patients will benefit from more comfort and a much morepleasantexperienceinthedentist’schair.38 The quality of adaptation of CAD/CAM-generated restorations is an area of current interest. Studies demonstrate the clinically acceptable durability of CAD/CAMrestorationsforcolourmatching,interfacial staining, secondary caries, anatomic contour, mar- ginal adaptation, surface texture, and postoperative sensitivity.39–43 Adhesive cementation seems to be the key for the long-term clinical success of CAD/CAM inlays and onlays.44_ Editorial note: A complete list of references is available fromthepublisher. CAD/CAM 1_2015 Dr Kassis Cynthia, DDS,MSc Dr Khoury Pierre, DDS,DESS Dr Tatiana Zogheib,DDS Dr Hardan Louis,DDS CES PhD head of Esthetic and Restorative Dentistry department,USJ Prof.Mehanna Carina, DDS CES PhD FICD Director of Esthetic and Restorative Dentistry Postgraduate Program USJ,President of the Continuing Education committee,Lebanese Den- talAssociation _contact: Dr Cynthia Kassis cynthiakassis@yahoo.com CAD/CAM_authors CAD0115_22-26_Kassis 02.03.15 12:47 Seite 5 CAD0115_22-26_Kassis 02.03.1512:47 Seite 5