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  JADA, Vol. 137http://jada.ada.org September 2006 5S T he stage was set forexciting advances indentistry in the 1950sand 1960s when pro-totypes of computer-aided design (CAD) and computer-aided manufacturing (CAM) were introduced into in-dustrial settings. 1 In those ap-plications, the geometry of the“parts” was simpler than thatgenerally needed for dental res-torations, but the same tech-niques could be applied to creat-ing dental crowns.Early dreamers likeMörmann, 2 Duret and col-leagues 3 and me 4 were intriguedby the possibilities. But theroad was far less smooth thanany of us imagined. Computing power was limited; a gigabytedrive was unheard of, yet designof the complex geometries of crowns was computationally in-tensive. CAM systems werelarge, and the thought of having a desktop milling machine waslaughable. Equipment compa-nies perceived that dentalCAD/CAM systems would belike cameras for which revenuewould be driven by selling thematerials like film.Simultaneously, the materialcompanies perceived that thesystems were equipment andbeyond the scope of their prod-uct line. Perseverance, however,paid off. The dreamers contin-ued to work, and CAD/CAMsystems are now part of every-day dentistry.In this supplement, you willread about the success of one of the systems that emerged as aneffective in-office automatedsystem known as the CERECsystem (Sirona Dental SystemsGmbH, Bensheim, Germany),though much of what you readwill apply to any CAD/CAMsystem. The CEREC systemhas been available commercial-ly for 20 years, is used by morethan 17,000 dentists and in 28dental schools in the UnitedStates, and has produced ap-proximately 12 million restora-tions. In the first article of thissupplement, Mörmann 5 chroni-cles the evolution of his ideainto a series of increasingly ro-bust systems. At first blush, the thought of machining a brittle materiallike dental ceramics was ridicu-lous. But as Giordano 6 de-scribes in the second article of this supplement, innovations inmaterials created esthetic ma-terials that could withstand po-tential damage introduced byCAD/CAM operations. Whencreated with an in-officeCAD/CAM system, esthetic res-torations provided in a singleappointment are a reality.But can an automaticallyproduced restoration fabricatedin the dental office perform aswell and deliver the same es-thetics as those created byskilled artist technicians? In thethird article of this supplement,Fasbinder 7 reviews the litera-ture pertaining to performanceof CEREC-generated restora-tions. He provides insight intothe types of restorations thatcould be produced over time andthe successful fit, esthetics andsurvival of ceramic restorationsproduced in the dental office.While thousands of dentistshave incorporated CAD/CAMsystems into their offices, therestill are many dentists whohave not. In the fourth article of this supplement, Trost and col-leagues 8 summarize the practicemanagement considerations,providing guidance for clini-cians to make informed deci-sions about incorporating thetechnology into their own prac-tices. While this article focuseson decisions relating to theCEREC system, the same kindsof considerations will apply tofuture in-office systems. In thismonth’s issue of JADA, Struband colleagues 9 have summa-rized how CEREC’s successeshave catalyzed the developmentof other systems.Without question, the dreamsof automation have had an irre-versible impact on dentistry.With in-office systems, esthetic, Dental CAD/CAM systems A 20-year success story E. Dianne Rekow, DDS, PhD Copyright ©2006 American Dental Association. All rights reserved.  long-lasting restorations can beproduced in a single appoint-ment. Laboratory-based sys-tems expand the possibilities forrestoration type and materialselection. But clinicians must beconcerned with more than justthe initial product, whether it isproduced by CAD/CAM systemsor using traditional approaches.Ceramics, including those usedin dentistry, have interesting performance characteristics.Even when highly polished,they lose strength when subject-ed to repeated loading, like nor-mal occlusal contact. Over 1 million cycles (approximatelyfive years of clinical function),both alumina- and zirconia-based veneered structures lose50 percent of their strength. 10 Damage caused by sandblast-ing, by chairside adjustmentswith a bur or even during theCAD/CAM fabrication processcan reduce the restoration’sstrength further and compromiseits life expectancy. For some materials, researchers haverecorded as much as a 30 percentreduction in strength after sand-blasting. 11 This information is es-pecially important for posteriorrestorations, which are subject tothe highest stresses in themouth.But doesn’t sandblasting en-hance adhesion? Perhaps, but italso introduces substantial dam-age. So my colleagues and I ex-plored alternatives that can pro-vide excellent bond strengthwithout sandblasting. For alumi-na and zirconia cores, bondstrengths equal to those on particle-abraded surfaces havebeen achieved by using metalprimers in combination with ad-hesive cement formulations suchas Panavia 21 (Kuraray America,New York City) and RelyX Unicem (3M ESPE, St. Paul,Minn.) on “as-received,” etchedsurfaces. 12 The performance of ceramicscan be compromised by a mis-match between coefficients of thermal expansion of core andveneer materials. While this is not an issue for in-office–produced monolithic materials, it can play an important role incrown and bridge survival. 13 Italso may be a major factor inporcelain chipping, which is reported commonly for zirconia-based layered crowns.While much remains to belearned and many innovationsstill are possible, there alreadyhas been much success withCAD/CAM systems’ producing ceramic restorations. Innovationswill continue to affect and chal-lenge dentistry. I hope you findthis summary of 20 years of thesuccess of one dream enlightening.  Dr. Rekow is a professor and the chair,Department of Basic Science and craniofacialbiology, and the director, TranslationalResearch, New York University College of Dentistry, 345 E. 24th St., New York, N.Y.10010, e-mail “edr1@nyu.edu”. Addressreprint requests to Dr. Rekow.1. Kalpakjian S. Manufacturing engineering and technology. Addison-Wesley: New York;1989.2. Mörmann WH. The srcin of the Cerecmethod: a personal review of the first 5 years.Int J Comput Dent 2004;7(1):11-24.3. Duret F, Blouin JL, Duret B. CAD-CAMin dentistry. JADA 1998;117:715-20.4. Rekow D. Computer-aided design andmanufacturing in dentistry: a review of thestate of the art. J Prosthet Dent 1987;58:512-6.5. Mörmann WH. The evolution of theCEREC system. JADA 2006;137(9 supplement):7S-13S.6. Giordano R. Materials for chairsideCAD/CAM–produced restorations. JADA 2006;137(9 supplement):14S-21S.7. Fasbinder DJ. Clinical performance of chairside CAD/CAM restorations. JADA 2006;137(9 supplement):22S-31S.8. Trost L, Stines S, Burt L. Informed deci-sions about incorporating CEREC into a prac-tice. JADA 2006;137(9 supplement):32S-36S.9. Strub JR, Rekow ED, Witkowski S.Digital design and fabrication of dental resto-rations: current systems and future possibili-ties. JADA (in press).10. Zhang Y, Lawn BR. Long-term strengthof ceramics for biomedical applications. JBiomed Mater Res B Appl Biomater2004;69(2):166-72.11. Zhang Y, Lawn BR, Rekow ED,Thompson VP. Effect of sandblasting on thelong-term performance of dental ceramics. J Biomed Mater Res B Appl Biomater2004;71(2):281-6.12. Dias De Souza GM, Silva N, Goes M,Rekow E, Thompson VP. Effect of metalprimers on cement bonds to fully-sintered zir-conia (abstract 324). Available at: “http:// iadr.confex.com/iadr/2006Orld/techprogram/ abstract_75149.htm”. Accessed May 23, 2006.13. Filser F, Kocher P, Lüthy H, Schärer P,Gauckler L. All-ceramic dental bridges by thedirect ceramic machining process (DCM). In:Sedel L, Roy C, eds. Bioceramics. Vol 10:Proceedings of the 10thInternationalSymposium on Ceramics in Medicine. Oxford,England: Pergamon; 1997:10:433-6. 6S JADA, Vol. 137http://jada.ada.org September 2006 Copyright ©2006 American Dental Association. All rights reserved.

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Dec 16, 2018

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