A Comparison of Fixed Prostheses Generated from Conventional vs Digitally Scanned D... Page 1 of 8
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`Issue: August 2007
`A Comparison of Fixed Prostheses
`Generated from Conventional vs
`Digitally Scanned Dental Impressions
`
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`Gary L Henkel, DDS, MAGD
`Private Practice
`Horsham, Pennsylvania
`
`Abstract
`For many years, mechanical and laser-based scanning
`technology has been used with computer-aided design
`and computer-aided manufacturing applications in the
`field of dentistry, but most have been limited to the
`dental laboratory. For the past 20 years, only 1 intraoral scanning device has been available to
`the dentist for in-office use. Recently, a new kind of intraoral scanning technology was
`introduced to the dental market. This technology, based on a laser scanning protocol called
`"parallel confocal," allows the dentist to take electronic impressions intraorally. This technology
`is coupled with traditional laboratory protocol for the construction of fixed dental restorations,
`providing the dentist with an accurate and efficient system to produce high-quality fixed dental
`restorations of all types. In a blind study, crowns developed using this technology were
`preferred over crowns generated using conventional impressions and criteria of marginal fit,
`contacts, occlusion, and time of adjustment in nearly 70% of cases. This article introduces
`scanning technology including a discussion of its clinical applications and an overview of the
`benefits.
`
`Since its introduction to the dental arena, computer-aided design and computer-aided manufacturing
`(CAD/CAM) technology has been largely limited to the realm of the dental technician. Many systems have
`been used for the design and fabrication of fixed dental prostheses by the dental technician, but for the past
`2 decades, only 1 system that is capable of direct intraoral impression taking (CEREC 3Da) has been
`available to the dental practitioner.l Recently, another system (iTerob) has been introduced. The 2 systems
`are very divergent in their development. CEREC emphasizes 1 visit, in-office scanning and milling of ceramic
`prostheses from prefabricated ceramic monoblocks; whereas, iTero has been developed as an office-based
`intraoral scanning system, connected by the internet to a centralized milling center and to the traditional
`dental laboratory technician.2 In this article, the author will introduce the reader to this new scanning
`technology, discuss its use and clinical applications, and provide an overview of the benefits of such a
`system in the clinical setting.
`
`The fabrication of a high-quality fixed dental
`prosthesis requires the expertise of the dentist all
`along the clinical pathway. The dentist must provide
`adequate axial and coronal reduction, establish
`proper draw to create a path of insertion for the
`prosthesis, establish a properly designed finish line,
`manage soft tissue, and record the results of these efforts in a dimensionally accurate and stable impression
`and bite registration, which is then presented to the dental technician.J,4 The technician depends on the
`dental impression to accurately duplicate the dentition and occlusal relationships. If the occlusal relationship
`is not accurate, all subsequent efforts on the part of the technician are rendered moot.
`
`a Sirena Dental Systems, Charlotte, NC 28273;
`www.sirona.com
`b Cadent, Inc, Carlstadt, NJ 07072;
`vvvvvv.cadent.Qiz
`
`................................................
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`Unfortunately, a tour of virtually any commercial dental laboratory will reveal
`that most dental impressions presented to the technician are inadequate,
`missing areas of the finish lines, and containing pulls and voids. In 2005
`Christensen stated that 50% of conventional dental impressions do not show
`the entire preparation margin to fabricate an indirect dental prosthesis, and
`surveys of laboratory technicians have indicated that as high as 90% of
`conventional dental impressions have incomplete registration of finish lines.5,6
`
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`A Comparison of Fixed Prostheses Generated from Conventional vs Digitally Scanned D... Page 2 of 8
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`Without the accurate duplication of finish lines, the prosthesis becomes little
`more than an approximation of the properly fitted prosthesis.
`
`Clearly, there was a need in the dental profession to improve on this
`questionable record, which was recognized over 2 decades ago by some of the
`pioneers who began the search for a better way to record the dental
`impression. Duret and colleagues, Mormann and colleagues, and others began
`working on electronic impression taking in the mid 1980s.7,8 Their work
`evolved into the modern day CEREC 3D system. In the past decade, Taub,
`Kopelman, Babayoff, and other engineers at the Tel Aviv engineering
`laboratory of Cadent began laying the foundation for the newest electronic
`impression device, Cadent iTero.
`
`Development of the Electronic Impression Device
`First attempts at developing an electronic impression device (EIDs) began over
`2 decades ago. Despite multiple advances in CAD/CAM technology during that
`time and active development efforts by several research groups, 1 intraoral
`device, the CEREC 3D, was successfully brought to market.9 In 1996,
`engineers at Cadent developed a scanning system called OrthoCADb. This
`digitizing system is for conventionally taken and poured models for various
`orthodontic applications such as digital model fabrication, virtual tooth setups,
`and indirect bonding and bracket-placement applications.lO
`
`Figure 1-The iTero
`Electronic Impression
`Device.
`
`The company realized that OrthoCAD technology might
`have application in the area of prosthodontics. As a result,
`Cadent began the development of an intraoral EID.ll
`Initial prototypes were cumbersome and unwieldy,
`suspended from a cable system, and were large and
`heavy. However, they were able to register accurate
`digital optical impressions from which fixed dental
`prostheses could be produced. After 18 months of initial
`testing and analysis of the suspended system, a handheld
`version was developed, and in the fall of 2004, this author
`took possession of the first Cadent handheld scanner. The
`author and his staff began a double-blind clinical
`evaluation in a private office setting in Horsham,
`Pennsylvania, of crowns made on EID scans and compared them with crowns made on conventional
`quadrant impressions of the very same preparations. This evaluation continued to the summer of 2006,
`when the data was tabulated and analyzed.
`
`Figure 2-iTero scanner disposable sleeve.
`
`The iTero Electronic Impression Device
`Before discussing the results of the evaluation, a discussion of the iTero EID technology and its use are in
`order, as this is a unique and novel technology. The goal of an electronic scan is the same as the
`conventional impression: the dentist wants to accurately record the tooth preparation, emphasizing the finish
`line, the remaining teeth in that quadrant, the opposing dentition, and the occlusal relationship between
`them.
`
`The iTero device consists of a mobile cart 29.33 inches tall, 26.13
`inches wide, and 15.6 inches deep (Figure 1). It is mounted on
`caster type wheels for movement from operatory to operatory. A
`handheld scanner is attached to the cart by way of a proprietary
`data cable. The cart houses a personal computer optimized for the
`processing of video data and a 19-inch liquid crystal display (LCD)
`monitor. There is an uninterruptible power supply, which allows the
`unit to be unplugged for short periods and relocated from
`operatory to operatory. A small air compressor and regulator are
`incorporated that provide a flow of air over the lens of the scanner
`to prevent fogging and provide some cooling.
`
`The device uses a wireless Internet connection for transmission of
`scanned data to Cadent for processing. Wireless mouse technology
`and a sealed keyboard in the top of the cart aid in data entry and
`the maintenance of asepsis for the unit. The scanning process is
`controlled by a wireless foot pedal so that once the initial patient data is entered into the system, the
`clinician need not touch anything other than the scanner head and the foot pedals while recording an
`electronic impression.
`
`Figure 3-Triangulation-based device
`scan with opaque powder.
`
`The scanner head houses sensors, light sources, focusing
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`motors, analog-to-digital converters, and video cameras for
`aiming and recording a scan. In early beta testing, the scanner
`head was 3x the size, much heavier, and more difficult to
`control than the current unit. Miniaturization of many of the
`components was a technical challenge but resulted in a scanner
`that is better balanced, easier for the operator to handle, and
`more comfortable to the patient. Also, it provides easier access
`to second molar regions that are more difficult to reach. The
`scanner head uses disposable sleeves that are changed
`between patients to prevent cross contamination (Figure 2).
`
`Much of the scanner technology is proprietary, but this much is
`known- in many optical scanning devices, a theory known as
`"the triangulation of light," the intersection of 3 linear beams of Figure 4-Triangulation-based device scan
`light, is used to locate a given point in 3-dimensional space.
`without opaque powder.
`This theory has been used in a variety of industrial measuring
`devices, but surfaces that disperse light irregularly and do not reflect it evenly (eg, curved surfaces) and
`surfaces that are not continuous adversely affect the accuracy of scans based on triangulation.12 The CEREC
`3D intraoral scanning device currently available is based on triangulation. It uses a thin coating of an opaque
`powder to provide uniform light dispersion to enhance the accuracy of its scans.13 Figures 3 and 4 show
`scans taken with a scanning device based on triangulation both with and without opaque powder application.
`Note the difference in quality of the scan when powder is not applied.
`
`While the principle of triangulation is widely used in industry
`and technology, the iTero scanner is based on an entirely
`different concept, a range finder technique by focus finding. It
`is described by Cadent engineers as "parallel confocal," making
`use of the confocal light theory found in microscopy (Figure 5).
`Confocal roughly translates as "having the same focal point."
`Briefly described, a light source is "filtered" by passing it
`through a small filtering pinhole. That light passes through the
`optics of the system, focuses on the target object, then reflects
`off of the object. Only an object at the proper focal length will
`reflect light back through the filtering device. Points above or
`below the confocal plane will direct light along a path that will
`not pass through the pinhole but will be blocked instead. Only
`those rays that are in focus will return through the filtering
`device.
`
`·Q ... ··v~t:o:::::~l~
`'f'bc·<>
`
`Confocal microscopes have significant advantages over
`conventional types including notably better imaging by rejecting
`out-of-focus information and the ability to control depth of
`field.14,15 The iTero device expands on this concept by
`projecting 100,000 beams of parallel red laser light in a 14 x 18
`mm2 pattern, providing a 13.5-mm scan depth, and converting the reflected light into digital data through
`the use of analog-to-digital converters, all of which happens in one third of a second. The registration of the
`surfaces of the oral structures is accurate to within 15 ~m. These rays of laser light act as tiny optical
`probes, surfing the surface of the oral structures and recording the anatomic surfaces by detecting the
`confocal points.
`
`Figure 5-IIIustration of a confocal dual
`disk microscope.
`
`This technology is able to capture all of the materials
`found in the mouth in their native form. The more
`diffusive dentin, the more translucent enamel, amalgam,
`gold, ceramics, resins, and soft tissue are recorded with
`equal accuracy and without the need for a coating to
`produce uniform light dispersion. All finish line designs
`such as feather edges, chamfers, shoulders, or bevels can
`be recorded. As long as proper tissue management allows
`the scanner to visualize the finish line, both supragingival
`and subgingival positions can be recorded with accuracy.
`Having a telecentric (the rays of light are parallel to the
`optical axis) aperture is important because this maintains
`a constant field of view and the clinician does not need to
`be concerned with distance from the cusp tip. This property and the absence of a powdered surface allow
`the clinician to place the device directly on the teeth, which enhances stability and allows for the image
`capture of steeper slopes. This in turn results in fewer incomplete scans because of undercuts. Before each
`individual scan, the system provides the clinician with a true color video image, magnified SOx, with an
`overlaid crosshair for aiming. After the one third of a second individual scan period, a 3-dimensional colored
`model of a single scan is presented on the LCD screen (Babayoff, Noam, Cadent, personal communication,
`
`Figure 6-Treatment information screen of the
`iTero system. Yiewim<Jgein<JI;ar:gersi;c.:;.
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`A Comparison of Fixed Prostheses Generated from Conventional vs Digitally Scanned D... Page 4 of 8
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`June 12, 2006).
`
`Taking an Electronic Impression
`The EID is user friendly despite the previous discussion of
`technology because most of the sophisticated processing
`occurs in the background, transparent to the user. To
`demonstrate the device's ease-of-use, the following is a
`simple posterior single unit crown case from start to
`finish. The ensuing discussion assumes that the iTero unit
`has been installed along with a wireless router in the
`dentist's office and that the dentist has chosen and been
`paired with 1 or more of the several iTero-certified dental
`laboratories around the United States. The laboratory and
`dentist information will have been preinstalled into the
`database of the iTero software.
`
`After the patient is seated in the dental chair, local
`anesthesia is administered in the clinician's usual manner,
`and while waiting for anesthesia to take effect, shade
`Figure 7-iTero active scanning screen view.
`selection is completed. The first step in the electronic impression process is to fill in the necessary data on
`the initial screen, an electronic counterpart of the dental laboratory instruction sheet (Figure 6).
`
`Information such as type of restoration, material to be
`used, finish-line design, shade chosen, and any special
`instructions are entered using either the keyboard or by
`clicking drop-down boxes with the wireless mouse.
`Missing teeth are marked as missing, including whether
`an edentulous space remains. The abutment tooth or
`teeth are marked as such. This allows the iTero software
`to correctly provide visual and audio prompts to the
`clinician during the scanning process, which requires a
`few minutes to accomplish.
`
`Figure 8-Screen view of articulated virtual
`models.
`
`Although the software allows the clinician the option of
`scanning both arches and the bite registration after
`completion of preparations, it is the author's preference to use the "scan opposite arch first" option in most
`cases. There are several advantages to this approach. First, the time between administration of anesthesia
`and the start of dental preparations is effectively used. The patient is given an opportunity to get used to
`what is likely to be a new experience and at the same time, it allows the software to initially process digital
`renditions of the opposing arch while tooth preparations are completed. In some locations, the dentist may
`be able to delegate this responsibility to the dental assistant.
`
`The flat panel display has 3 windows (Figure 7). The upper left window is a visual prompting window,
`showing the proper position of the scanner for the current scan. The bottom left window displays the results
`of the last individual scan taken a few seconds after it is recorded, which allows the clinician to evaluate it
`for completeness in near real time. The largest window on the right side of the screen is in real time and
`provides an aiming crosshair graphic to assist the clinician in proper positioning of the scanner. There also is
`an audio prompt to provide additional assistance.
`
`A typical series of scans can range from 15 to 30 scans.
`Generally more scans are needed in the anterior because
`esthetic needs require the recording of data from the
`contralateral and the ipsilateral side. Typically, fewer
`scans are required in the posterior.
`
`Preparations are completed in the manner preferred by
`the clinician. The scanner is capable of recording virtually
`any dental preparation; therefore, veneers, crowns,
`bridges, inlays, onlays (essentially any fixed prosthesis
`that can be recorded by conventional impression
`techniques) can be recorded electronically. However, it
`should be mentioned that electronic impressioning will not Figure 9-iTero laboratory technician working
`with an iTero scan.
`compensate for inadequate preparation and tissue-
`management techniques. As conventional impression
`material must be able to "see" the entire margin of a preparation, so too must the electronic impression
`device. In the clinical data presented here, a double-corded technique was used, but any technique including
`expansive materials, laser or electrosurgical troughing, curettage diamonds, and others preferred by the
`individual clinician may be used.
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`Once the preparation is completed, scanning of the arch containing the abutment preparations can proceed.
`The process is initiated by a simple actuation of the foot-pedal control. The software will then prompt for a
`series of 5 scans per abutment that target the abutment, followed by additional scans for recording the
`remainder of the quadrant. The final 2 scans are for bite registration. The patient is guided into a fully closed
`position, and 2 scans are taken at 90° to the long axis of the teeth at the level of the occlusal plane.
`
`When all scans have been completed, another press of the foot pedal begins an assimilation process, and in
`less than 1 minute, 3-dimensional magnified virtual models of both arches appear on the flat screen. These
`models will be virtually articulated by the software, which finds overlapping points in common between the
`final bite registration scans and the arch modeling scans (Figure 8).
`
`The models can be rotated and manipulated in virtual space to any desired viewing position. Utilities
`included in the software allow the finish line to be marked and evaluated and occlusal clearance to be
`judged. If anything is found to be unacceptable, additional scans can be taken or the preparation can be
`modified and rescanned. If the clinician should move excessively during a scan, the software will reject the
`scan and prompt the clinician to rescan. It should be noted that the visual representation presented on the
`flat screen is not a full resolution final view, but it is a preliminary view that allows the clinician to evaluate
`his or her work while further processing of the scans occurs in the background.
`
`When the clinician is satisfied with the results, a mouse
`click on the "send" icon starts a process of packing and
`organizing scan data for transmission to Cadent's servers.
`The case is digitally stamped with the name, date, and
`time of scan, so even if the same tooth is scanned a
`second time, one can identify distinct files. Provisional
`restorations can then be fabricated for the patient in the
`clinician's preferred manner, and the patient is dismissed.
`
`The completed scan file will then appear in a second
`software program, the iTero case manager. This can be
`thought of as a digital laboratory work progress log. All
`cases transmitted will appear in the case manager, and as
`the case progresses, the dentist can look at the case
`manager to determine the production sequence of every
`scan.
`
`Figure 11-Dies and models are being milled
`from polyurethane blocks.
`
`The Cadent Processing Sequence
`After completing a successful scan sequence, the clinician clicks the "send" icon, and the data files are
`forwarded to Cadent's servers. On arrival, the data files undergo a process called "modeling." The scans will
`receive a "cleanup" process where artifacts and nonessential structures are eliminated. After modeling, the
`virtual models seen on the computer screen will look very much like the final physical models generated
`from the data file. The modeled files are then transmitted to a highly trained iTero dental technician who will
`do the initial design of the case, identify finish lines, and determine the path of insertions not only for the
`prosthesis, but also for the abutment dies in relationship to the arch models.
`
`The data file is then transmitted to the iTem-certified
`dental laboratory with which the practitioner is paired.
`The laboratory technician can approve of the design as is
`or make corrections or modifications before transmitting
`the case back to Cadent for model milling (Figure 9). The
`model-milling process is accomplished on a computer
`numerical control (CNC) s-axis milling machine at Cadent
`(Figure 10). The patient's iTero data file is translated into
`"g code," a language the milling machines understand.
`The upper model, lower model, and dies are milled from 3
`separate blocks of a proprietary polyurethane material
`made in Germany to Cadent's specifications for this
`purpose (Figure 11 ).
`
`Figure 12-Models and dies are assembled on
`proprietary iTero articulator.
`
`Cadent has developed a proprietary die system that allows
`easy removal of a die for finish work by the technician, while holding the die with no discernable movement
`when placed into the model. These milling machines are accurate to within 2 ~m. The upper and lower
`models are milled with special modifications that allow the models to be quickly and easily articulated on a
`proprietary simple-hinge articulator, which maintains the occlusal relationship between the arches that were
`captured in the scanning procedure (Figure 12).
`
`The finished models and dies are physically shipped to the clinician's partner laboratory for fabrication of the
`prosthesis. If a metal coping or full-cast metal crown is requested, a wax pattern can be milled from a
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`A Comparison of Fixed Prostheses Generated from Conventional vs Digitally Scanned D... Page 6 of 8
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`special proprietary plasticized burnout wax and sent to the laboratory with the models and dies. The
`laboratory then proceeds with the case as it would to create a conventional poured i rnpression case, and the
`final prosthesis is returned to the dentist for insertion.
`
`It is assumed that this process would result in longer fabrication time
`than conventional techniques, but it may make the entire process
`more efficient. In preparing this article, the author visited and toured
`the Cadent facility and a partner laboratory located within a 2-hour
`drive from his office. During the visit to Cadent, a scan was
`transmitted in the morning. By the time the author arrived at the
`laboratory that afternoon, modeling and the design phase by Cadent
`technicians had been completed, and the laboratory had received
`the electronic transmission. At that point, the laboratory technician
`and the author were able to make a few modifications to the design
`and transmitted the case back to Cadent. The next morning, the
`author visited Cadent headquarters and within 30 minutes of his
`early-morning arrival, he was presented with the physical dies and
`models. Less than 24 hours had passed since the initial scan was
`transmitted and dies and models were on their way to the
`laboratory. (Note: These results are not typical. Standard processing
`time for Cadent milled models is 3-5 days.)
`
`· ........ , .... :.::-.··.•,•·.
`:.; ...... ,"". :~=·.·:~:·'
`
`Comparing Conventionally Fabricated Prostheses
`with E!D-Generated Prostheses
`In Fall 2004, the author received a prototype that would later evolve into the iTero. He was asked to
`critically evaluate the unit and conduct a comparative assessment of crowns fabricated on conventional
`quadrant impressions vs crowns fabricated only from iTero scans. If it were determined that iTero-produced
`prostheses were inferior to conventionally fabricated cases, there would be little need to develop the unit.
`
`Figure 13-iTero study evaluation
`form. View image in a larqer size.
`
`A protocol was developed where each clinical case was both electronically and physically impressed. Early
`on, the scanner was optimized for scanning single units of posterior teeth, so it was decided to take physical
`impressions using one piece triple trays (Polybitec) and vinyl polysiloxane impression material (light and
`heavy body Correct VPSd), providing models that would extend from second molars to canines in both
`instances. Eventually, the study was expanded to include multiple single units, bridges, and anterior crowns
`and veneers. The finished crowns were returned to the author from the dental laboratory labeled as "A" and
`"B," without dies or models. At the insertion visit, an evaluation form was filled out for each crown, assessing
`clinical parameters such as marginal fit, retention, contact points, occlusion, and adjustment time, if
`necessary, to make the prosthesis clinically acceptable (Figure 13).
`
`A master list of the origin of each crown was
`maintained by one individual at Cadent headquarters,
`and only after insertion, was the author notified as to
`their origin.
`
`c Dentamerica, City of Industry, CA 91744;
`www.d<Of1tamerica.cQm
`d Pentron Clinical, Wallingford, CT 06492;
`v.v.vv.pentron.com
`
`Discussion
`The evaluation involved 117 patients over 18 months. A few patients were dropped from the evaluation
`because conditions developed that adversely influenced the results for either type of prosthesis including
`fracture of core buildups and premature loss of provisional restorations.
`
`After data tabulation, certain patterns emerged. The most notable of these is that in 68% of the cases, Em(cid:173)
`processed crowns were identified as the crown of choice for insertion based on the clinical acceptability
`criteria. The second notable finding was 85% of EID-produced crowns were judged to be clinically
`acceptable compared with 74% of conventionally produced crowns. Also, the iTero-scanned crowns
`averaged 2.4 minutes to adjust to clinical acceptability compared with 3.2 minutes for the physically
`impressed cases. It should be noted that a second dental laboratory was introduced during the latter part of
`the study, and the results were essentially unchanged from the early data. This suggests that the
`advantages identified of EID impression taking were, to some degree, independent of the dental laboratory
`and laboratory technician.
`
`Encouraged by these findings, additional scanners were made available to a larger group of dentists for their
`evaluation in a second phase of beta testing. Many of these dentists took impressions both digitally and
`conventionally for a short time and did their own comparisons, but because the cases were not returned
`blindly, their data is not included here. It is interesting to note, however, that in all instances, the preference
`for scanner-based crowns held true. As of this writing, 4691 restorations have been fabricated using iTero
`technology.
`
`Through exit polling of patients and round-table discussions with participating dentists and participating
`laboratory technicians, some other interesting observations emerged:
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`A Comparison of Fixed Prostheses Generated from Conventional vs Digitally Scanned D... Page 7 of 8
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`1. Laboratory technicians commented that they perceived an improvement in the quality of the crown
`preparations of their partnered clinicians after electronic impression taking was introduced. They
`attributed the difference to the magnified image that the dentist had of his or her preparation,
`making deficient areas in a preparation scan much more obvious, along with the analytical tools built
`into the iTero software.
`2. Patients found scanning more comfortable than conventional impression taking. Phobic patients
`commented that the ability to stop or rest between scans, which cannot be done with the
`conventional technique, was important to them.
`3. Dentists using the EID commented that the chair-side time allotted to adjustments decreased
`significantly.
`
`Conclusion
`In this article, the development, use, and benefits of the EID have been discussed. Its ease of use, coupled
`with multiple benefits perceived by dentists, laboratory technicians, and patients, led the author to conclude
`that this technology is here to stay. It is the author's opinion that the application of such technology will
`rapidly increase over the next decade. The dental profession has seen a rapid growth in the areas of digital
`radiography and in laboratory-based scanning technologies in recent years. Intraoral digital recording is
`taking a logical next step. This technology has significant potential beyond the arena of fixed prosthetics.
`Envision the orthodontist using the EID for evaluation and appliance fabrication. Imagine capturing virtual
`models and using them to treatment plan cases more accurately, less invasively, and less work intensively
`than before. Visualize the results of preprosthetic surgery and esthetic alteration done in a noninvasive,
`virtual manner. Then, picture what can be accomplished when digital impressioning is coupled with other
`advanced technology currently being developed. It is a wonderful time to be involved in the field of
`dentistry.
`
`Disclosure
`Dr Henkel has actively consulted with Cadent during the development of the iTero Electronic Impression
`Device and has received honoraria from Cadent for his participation.
`
`References
`
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