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JADA, Vol. 140 http://jada.ada.org October 2009 1301

P E R S P E C T I V E S O B S E R V AT I O N S

Digital dental impres-sion devices havebeen introduced tothe profession, poten-tially eliminating the

need for taking conventionalimpressions for crowns and fixedprostheses. I have discussed thisconcept in previous columns inthis journal.1,2 However, addi-tional changes to the concept areemerging, creating confusionamong dentists and causingthem to wonder whether there isa need to change their impres-sion techniques. The many ques-tions I hear about this topicfrom dentists attending contin-uing education courses can bedistilled into the following four. d“Should I continue to makeimpressions in the conventionalmanner using conventionalmaterials?” Both scientific evi-

dence and clinical observationhave shown that currently avail-able impression materials—vinyl polysiloxane, polyether,the newer material vinylsilox-anether and the older revers -ible hydrocolloid—provide excel-lent reproduction of toothpreparations.3-9

d“Should I purchase a devicethat makes digital impressions?”With a digital impression device,the clinician creates the impres-sion digitally and sends the datato a laboratory capable ofworking with this technology;the laboratory then creates therestorations and sends them tothe dentist for placement. Twopopular digital impressiondevices now competing on themarket are the iTero (Cadent,Carlstadt, N.J.) and the LavaChairside Oral Scanner C.O.S.

(3M ESPE, St. Paul, Minn.).Both of these devices limit thedentist to the use of laboratoriesthat have, and are trained touse, the laboratory devices asso-ciated with the respectiveimpression devices. Thesedevices and this technical con-cept are proving themselves tobe viable alternatives to conven-tional impression making.10-14

d“Should I purchase a devicethat makes digital impressionsand also provides the ability tomill some types of restorationsin the clinical office?” The twocompeting devices are CEREC(Sirona Dental Systems GmbH,Bensheim, Germany) and theE4D Dentist System (D4D Tech-nologies, Richardson, Texas).The ability of computer-aideddesign/computer-aided manufac-turing (CAD/CAM) devices toproduce clinically acceptablerestorations has been reportedmany times in the dental litera-ture.15-27 Other companies soon

Impressions are changingDeciding on conventional, digital or digital plusin-office milling

Gordon J. Christensen, DDS, MSD, PhD

Copyright © 2009 American Dental Association. All rights reserved. Reprinted by permission.

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P E R S P E C T I V E S O B S E R V A T I O N S

will enter the market and becompetitive with the CERECand E4D milling devices. d“Should I purchase a devicethat enables me to make digitalimpressions now and upgrade toin-office milling later if I like?”At this point, only the entry-level CEREC and E4D devicesoffer the initial ability to makedigital impressions only and anoption to upgrade to in-officemilling down the road. However,it is rumored that other compa-nies will provide this option inthe future.

Although research reportsand clinical comparisons con-tinue to come forth regardingthe acceptability of the aboveconcepts and devices, in myopinion and clinical experience,the accuracy of properly accom-plished impressions—whetherconventional or digital—is nolonger a question with any ofthe concepts.

There are other questionsdentists should ask about thesefour choices: d“Are there major advantagesto making digital impressionsinstead of conventional impressions?” d“Should I purchase a digitalimpression device at this pointin the concept’s development,and will digital impressionsdominate impression making inthe future?”d“Would a device that makesdigital impressions and alsomills restorations in the dentaloffice fit into my practice?”d“Am I sure I want to investthis amount of money in adevice that still is being devel-oped and refined?”

I will discuss these questionson the basis of both scientificresearch and clinical observa-tion, and I will make sugges-tions for clinicians who are con-

sidering changing to the use ofdigital impression techniquesand to the in-office milling ofrestorations. The predictionsincluded below are opinionsbased on my significant experi-ence with all of the devices andconcepts discussed and on myglobal contacts with practicingdentists in continuing educationcourses.

USING CONVENTIONALIMPRESSION TECHNIQUES

Most dentists are comfortablewith conventional impressionmaterials and techniques asused for crowns and fixed pros-theses. It is difficult for anyoneto change from a successful andrelatively moderate-cost tech-nique to an unknown and expen-sive one. As I noted previously,current impression materialsare excellent. I often have iden-tified elastomer impressionmaterials as among the mostadequate of all dental materialsin fulfilling their intended pur-pose. However, digital impres-sions have advantages, asdescribed in the next section.Dentists must consider whetherthe advantages of the digitalimpression technique outweightheir familiarity with conven-tional impression proceduresand their clinical success withconventional impression tech-niques. There appears to be nourgency to change from the useof conventional impressionsunless practitioners areimpressed with the positivecharacteristics of digital impres-sions outlined below. I predictthat digital impression tech-niques will grow in use gradu-ally and, eventually (many yearsfrom now), will dominate theimpression procedures forinlays, onlays, crowns and fixedprostheses.

PURCHASING A DEVICETHAT MAKES DIGITALIMPRESSIONS ONLY

In my opinion, many dentists donot enjoy or have interest in thelaboratory aspects of dentistry.These dentists are satisfied tomake tooth preparations andimpressions, send the impres-sions to a competent laboratorytechnician and seat the restora-tions a few days later. If you arepositive that you do not want tobe involved with any of the stepsin the milling procedure, andyou have made the decision tomake digital impressions, youmay purchase any of the fourdevices described in this columnat roughly similar prices tomake digital impressions only.The approximate price of a dig-ital impression device rangesfrom $25,000 to $30,000 (J.Denney, western regional salesmanager, Cadent, oral commu-nication, Aug. 27, 2009; E.Neuenfeldt, professional rela-tions manager, 3M ESPE,written communication, Aug. 27, 2009).

Why change from conventional impressions to digital impressions? Dig-ital impressions have severaldesirable characteristics:dThe mess that occurs whenmaking conventional impres-sions is eliminated. Dentalassistants are pleased with theresultant elimination of mixingand cleanup.dPatients prefer the simplifieddigital impression concept, andthey express relief at not havingto endure the uncomfortableexperience of having a conven-tional impression made in themouth.dShipping the impression tothe laboratory is merely a dig-ital transfer via one of manymethods such as e-mail, disk or


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JADA, Vol. 140 http://jada.ada.org October 2009 1303


flash drive.dBecause there is no actual,tangible impression, there is noneed for disinfection or threat ofdisease transfer from thepatient to the technician.dThe tasks of pouring theimpression, making the baseand trimming the dies are eliminated.dAssuming that the digitalimpression and the digital interocclusal record have beenobtained accurately, the need toarticulate the casts also is eliminated.

Are these advantages impor-tant enough to convince you tomake the change to digitalimpressions? Additionally, areyou sure you want to send thedigital impression to a labora-tory and not mill the restorationin your own office?

Some dentists do not knowwhether they want the responsi-bility of in-office milling withthe attendant potential need tomodify restorations and to stainand glaze them before they areready to be seated. If you areone of those dentists, perhapsyou should enroll in a CERECcourse, an E4D course or both tohelp you make the decision.

If you still are undecided aftertaking such a course, you mayelect to purchase the entry-levelCEREC or E4D device, with thepotential to upgrade if youdecide to add in-office milling inthe future.

PURCHASING A DEVICETHAT MAKES DIGITALIMPRESSIONS AND MILLSRESTORATIONS

There are now about 25,000CEREC users worldwide(Michael Dunn, director ofCAD/CAM Marketing, CEREC,oral communication, Aug. 13,2009) and, although the E4D

was released on the market onlyrecently, there are a growingnumber of dentists using thatdevice as well. There is minimalindependent research comparingthe two devices; however, arecent comparative project con-ducted by the staff of CliniciansReport showed that both deviceswere similarly capable of pro-ducing acceptable milled restorations.28

Advantages of in-officemilling of restorations. Den-tists can gain from milling resto-rations in their offices in severalways:dRestorations can be placed inone appointment, an aspectmany patients regard as a sig-nificant advantage.dThe patient receives feweranesthetic injections becausethere is no second appointment.dPractitioners report that thein-office milling concept encour-ages the use of conservativetooth preparations such asonlays, three-quarter crownsand conservative full crowns.dIn-office milling eliminatesthe need for provisional restora-tions, with their accompanyingnegative characteristics.dThe clinician controls theentire procedure; the processinvolves no laboratory component.dSeveral steps in the pro-cedure—including imaging,milling and initial fitting of therestoration—can be delegated toqualified staff members whilethe dentist treats other patients.dAccording to experiencedusers, the in-office milling con-cept can be financially accept-able and even can produce sig-nificant income.

Disadvantages of in-officemilling of restorations. Notevery aspect of in-office restora-tion milling is positive.

dThe equipment requires aninitial investment of about$120,000. Various financialplans and potential add-ons (atadditional cost) exist. dLearning to use the deviceand fit it into the office routinerequires time and effort.dTo become and remain profi-cient in using the software andhardware, the clinician and staffmembers must use the devicesfrequently.

After assisting many dentistsin learning about and using in-office milling, I conclude that itis a viable concept for some, butnot all, dentists. I advise inter-ested dentists to enroll incourses on in-office milling ofrestorations before making adecision about purchase ofeither of the two devices.

SUMMARY

Some dentists face the dilemmaof wanting to keep up with thetechnological advances in theprofession while feeling unsureabout embracing the digitalimpression technique and therelated in-office milling of resto-rations. This column provides,on the basis of scientific evi-dence and clinical observation, acandid appraisal of the severalimpression options available todentists: conventional impres-sions, digital impressions anddigital impressions accompaniedby the ability to mill restora-tions in-office.

After considering all options,dentists must make the decisionthemselves concerning whetheror not these concepts fit wellinto their practices at this time.All of the devices and techniquesI have described here, includingconventional impressions, areproducing clinically acceptablerestorations, but the digitaloption also can provide signifi-


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cant advantages for both den-tists and patients. ■

Dr. Christensen is the director, PracticalClinical Courses, and a cofounder and seniorconsultant, CR Foundation, Provo, Utah. Healso is the senior academic advisor, ScottsdaleCenter for Dentistry, Scottsdale, Ariz.; anadjunct professor, Brigham Young University,Provo, Utah; and an adjunct professor, Uni-versity of Utah, Salt Lake City. Addressreprint requests to Dr. Christensen at CRFoundation, 3707 N. Canyon Road, Suite 3D,Provo, Utah 84604.

The views expressed are those of the authorand do not necessarily reflect the opinions orofficial policies of the American Dental Association.

1. Christensen GJ. The challenge to conven-tional impressions. JADA 2008;139(3):347-349.

2. Christensen GJ. Will digital impressionseliminate the current problems with conven-tional impressions? JADA 2008;139(6):761-763.

3. Cox JR. A clinical study comparing mar-ginal and occlusal accuracy of crowns fabri-cated from double-arch and complete-archimpressions. Aust Dent J 2005;50(2):90-94.

4. Jamani KD, Harrrington E, Wilson HJ.Rigidity of elastomeric impression materials. JOral Rehabil 1989;16(3):241-248.

5. Clancy JM, Scandrett FR, Ettinger RL.Long-term dimensional stability of three cur-rent elastomers. J Oral Rehabil 1983;10(4):325-333.

6. Endo T, Finger WJ. Dimensional accuracyof a new polyether impression material. Quin-tessence Int 2006;37(1):47-51.

7. Shafa S, Zaree Z, Mosharraf R. The effectsof custom tray material on the accuracy of

master casts. J Contemp Dent Pract2008;9(6):49-56.

8. Shetty P, Rodrigues S. Accuracy of elas-tomeric impression materials on repeatedpours. J Indian Prosthodont Soc 2006;6(2):68-71.

9. Wöstmann B, Rehmann P, Balkenhol M.Accuracy of impressions obtained with dual-arch trays. Int J Prosthodont 2009;22(2):158-160.

10. Birnbaum NS, Aaronson HB. Dentalimpressions using 3D digital scanners: virtualbecomes reality. Compend Contin Educ Dent2008;29(8):494, 496, 498-505.

11. CRA Foundation. Digital impressionschallenge conventional impressions. CRANewsletter 2007;31(11):3-4.

12. Garg AK. Cadent iTero’s digital systemfor dental impressions: the end of trays andputty? Dent Implantol Update 2008;19(1):1-4.

13. Pieper R. Digital impressions: easier than ever. Int J Comput Dent 2009;12(1):47-52.

14. Leifert MF, Leifert MM, Efstratiadis SS,Cangialosi TJ. Comparison of space analysisevaluations with digital models and plasterdental casts. Am J Orthod Dentofacial Orthop2009;136(1):16.e1-16.e4.

15. Bindl A. Mörmann WH. Marginal andinternal fit of all-ceramic CAD/CAM crown-copings on chamfer preparations. J OralRehabil 2005;32(6):441-447.

16. Beuer F, Schweiger J, Edelhoff D. Digitaldentistry: an overview of recent developmentsfor CAD/CAM generated restorations. Br DentJ 2008;204(9):505-511.

17. Christensen GJ. In-office CAD/CAMmilling of restorations: the future? JADA2008;139(1):83-85.

18. Christensen GJ. Successful use of in-office CAD/CAM in a typical practice. JADA2008;139(9):1257-1260.

19. Fasbinder DJ, Dennison JB, Heys DR,Lampe K. The clinical performance of

CAD/CAM–generated composite inlays. JADA2005;136(12):1714-1723.

20. Heymann HO, Bayne SC, Sturdevant JR,Wilder AD Jr, Roberson TM. The clinical per-formance of CAD-CAM–generated ceramicinlays: a four-year study. JADA 1996;127(8):1171-1181.

21. Miyazaki T, Hotta Y, Kunii J, KuriyamaS, Tamaki Y. A review of dental CAD/CAM:current status and future perspectives from 20years of experience. Dent Mater J 2009;28(1):44-56.

22. Nakamura T, Dei N, Kojima T, Wak-abayashi K. Marginal and internal fit ofCEREC 3 CAD/CAM all-ceramic crowns. Int JProsthodont 2003;16(3):244-248.

23. Nakamura T, Tanaka H, Kinuta S, et al.In vitro study on marginal and internal fit ofCAD/CAM all-ceramic crowns. Dent Mater J2005;24(3):456-459.

24. Otto T. Experience with CEREC in aSwiss practice. In: Mörmann WH, ed.CAD/CIM in Aesthetic Dentistry: CEREC 10Year Anniversary Symposium. Chicago: Quintessence; 1996:601.

25. Otto T, De Nisco S. Computer-aideddirect ceramic restorations: a 10-year prospec-tive clinical study of Cerec CAD/CAM inlaysand onlays. Int J Prosthodont 2002;15(2):122-128.

26. Reiss B. Clinical results of CEREC inlaysin a dental practice over a period of 18 years.Int J Comput Dent 2006;9(1):11-22.

27. Sjögren G, Molin M, van Dijken JW. A10-year prospective evaluation of CAD/CAMmanufactured (CEREC) ceramic inlayscemented with a chemically cured or dual-cured resin composite. Int J Prosthodont2004;17(2):241-246.

28. CR Foundation. Making in-officeCAD/CAM work for your practice. CliniciansRep 2009;2(6):1-3.


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