Computerized Restorative Dentistry

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common digital impression systems (Figures 1 and 2). The CEREC Acquisition Center (AC) (Sirona Dental. Systems) and the E4D Dentist system (D4D ...

COVE R STORY

Computerized Restorative Dentistry By Dennis J. Fasbinder, D.D.S., and Gisele F. Neiva, D.D.S., M.S.

Imaging Systems and CAD/CAM in Dentistry A major concern we face in our clinical practice is trying to analyze and determine whether a particular technique, material or process is any different than another. Which ones have high success rates? What are the criteria needed to ensure success? How do we go about performing procedures to obtain optimal results? In this issue of the MDA Journal we will review the state of digital image scanning as it relates to the CAD/ CAM process for prosthesis fabrication. No matter how sophisticated or expensive your equipment, you still need to understand and adhere to the principles of accurate impression-making! First and foremost, if you can’t see it, the wand can’t! You cannot design and fabricate in the virtual world and hope to fit the restoration in the real world. The surface to be scanned must be clean and dry. If not, your image will be distorted due to refraction and reflection of the light beam. As the imaging devices are light emitter/collectors, all the laws of optics apply. A good review of basic intraoral photography will help in understanding these concepts. A “Clean Dry Field” is essential to successful imaging. The dentist’s worst enemy in the restorative arena is saliva. n Saliva is NOT water. n Saliva on surfaces in the mouth is NOT helpful in impression taking. n Saliva does NOT aid homeostasis. n Saliva is NOT compatible with polyvinylsiloxanes or imaging techniques. n Hydrophilic does NOT refer to saliva. Thus, when we say clean and dry, we mean nothing is covering the surface(s) to be scanned. If one keeps this principle in mind, an impression-material-free practice may be the future norm. The authors of the following two articles provide the state of the art of digital imaging techniques from the clinical and laboratory perspectives. I want to personally thank them for their time and the effort they have devoted to this issue of the Journal. — Howard A. Hamerink, D.D.S. Special Contributing Editor

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Figure 1 Lava Chairside Oral

Figure 2

Scanner (COS).

iTero system.

Introduction

Computer technology is not a new development for the dental office. Computers have had a significant impact on dental practice administrative functions from scheduling patients to processing financial records to communicating with third-party payers. However, the application of computerized dentistry for patient treatment has become a recent addition to dental practices. As with many “new” developments, they are the result of many years of research and evolution. Computerized dentistry and digital dentistry are terms generally used to describe the clinical application of Computer Assisted Design, Computer Assisted Machining (CAD/CAM). There are three features common to CAD/ CAM systems.1 The first is the ability to record the geometry of the patient’s intraoral condition to a computer system. This usually involves some sort of intraoral camera or scanning device to capture a digital file of the dentition. Once the digital file is recorded to the computer, a software program is used to manipulate the data and design the desired volume model of the restoration. This involves control of the usual restoration parameters such as proximal contacts, emergence profile, and occlusal contacts. Once the design has been completed, a machining device is used to produce the designed restoration. Most commonly, the machining device is a subtractive milling chamber that cuts or mills the final restoration from a preformed block of restorative material. Commercially available computerized dentistry systems that are used in the dental office can generally be considered either a digital impression system or a chairside CAD/CAM system. Digital impression systems focus JOURNAL OF THE MICHIGAN DENTAL ASSOCIATION • APRIL 2012

on the first step of the CAD/CAM process: to accurately record the patient’s intraoral condition. A data file is created on the system computer and the patient’s dentition is scanned or recorded to the data file. The digital data file is then electronically transmitted via the Internet to a dental laboratory. The dental laboratory downloads the patient data file to its computer system and can do two separate things with the data file. One option is to send the electronic record to a processing center to have models fabricated and mounted on an articulator. The articulated resin models are returned to the dental laboratory and the restoration can be fabricated by any conventional laboratory process, such as used for cast gold or PFM restorations. Alternatively, the lab may use a software CAD program to design and produce either a coping or full contour restoration. The articulated resin models are used to finish the case as is done for zirconia or similar restorations.2 The Lava Chairside Oral Scanner (COS) (3M ESPE) and iTero system (Cadent) are the two most common digital impression systems (Figures 1 and 2). The CEREC Acquisition Center (AC) (Sirona Dental Systems) and the E4D Dentist system (D4D Technologies) are the two available chairside CAD/CAM systems.3,4 Chairside CAD/CAM systems permit the doctor to complete all three steps of the imaging, design, and production process in the dental office, usually within the time span of a single appointment. This affords a significant improvement in efficiency and convenience for the patient as there is no need for a temporary restoration or second appointment to deliver the final restoration. Both chairside CAD/CAM systems have software programs that permit the production of single tooth ceramic or compos35

C O V E R S T O R Y (c o n t i n u e d )

Figure 3

Figure 4

CEREC AC system with MCXL mill (left) and CEREC mill (right).

E4D Dentist System and mill.

ite inlay, onlay, veneer, or crown. The concept of designing full contour restorations on a computer may seem to be a greater learning curve than a clinician may want to tackle, especially when they have been used to having laboratory technicians fabricate restorations for them. The CEREC Connect system for the CEREC AC unit and the E4D Sky network for the E4D Dentists system are recent upgrades that offer the opportunity to use the chairside systems as purely digital impression systems for cases desired to be fabricated in the dental laboratory (Figures 3 and 4).

ages are routinely captured for recording adjacent teeth, mounting opposing virtual models, or as an aid in designing the restoration. A titanium dioxide powder is sprayed on the dentition and soft tissues to create a uniform reflective surface. The shorter wavelength of the blue light compared to that of a laser allows for greater precision of the optical image.5 It also uses a telecentric beam that records the tooth surface data from all surfaces in a single view.6 The Bluecam can be used in either manual or automatic mode. The advantage of the automatic mode is that the camera is unable to record data while the camera is moving or shaking. This prevents the capture of blurred images that would be inaccurate. The E4D Dentist IntraOral Digitizer uses a red laser light, single image camera.7 It does not require the use of a reflective powder unless scanning through a thin, transparent aspect to the preparation. In that case, a reflective liquid (E4D Accent) is applied to the surface of the tooth. It is also a line-of-sight camera. The operator has the option of manual image capture or automatic image capture with Rapid Scan. A series of separate images are recorded from the occlusal, lingual, and facial views for a true 3-D capture of the preparation. Additional images are required to record adjacent teeth.6 The software immediately indicates the accuracy and usefulness of each scanned image to ensure all images are properly scanned. In addition, the ICE feature of the DentaLogic software takes pre- and post-operative pictures of the teeth and gingiva to create the ICE model, which facilitates margin detection.6,7 The iTero intraoral scanner uses a parallel confocal white light and red laser camera to record a series of im-

Computerized Systems

The first step in the CAD/CAM sequence is recording the specific teeth and soft tissues to the computer software program. A camera or scanner is the key element for a digital impression. There are significant differences in the cameras and their use to record the digital impression. The CEREC AC system has a light emitting diode (LED) camera called the Bluecam. It records a series of single images that the software combines into the 3-D virtual model of the dentition. Although a single image is the minimum required to process a restoration, additional im-

A camera or scanner is the key element for a digital impression. 36

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Figure 5

Figure 6

There is an indistinct distal margin of the crown preparation for tooth #3 in this CEREC virtual model. This is a function of inadequate soft tissue retraction for good visibility of the margins.

Low magnification of the Lava COS scanned dentition.

ages to create a 3-D model.7,8 The scanner emits a beam of light towards the tooth surface and only an object at the correct focal length will reflect light back through the filtering device.9 The scanner captures 100,000 points of laser light and focuses accurately to 300 focal depths spaced 50 microns apart.6,9 The camera can be placed in contact with the teeth and scanning powder or coating is not required for the camera to accurately record the surface. The operator is prompted to record a series of five scans from the occlusal, facial, lingual, mesio-proximal and disto-proximal angles of the prepared tooth and additional scans for adjacent teeth. The opposing dentition is scanned separately.9 In addition, angled buccal and lingual views must be taken of the remaining teeth in the arch form.7 The scan is not continuous, so individual images may be retaken until adequate data is obtained.6 A total of 15 to 30 scanned images may be required to record the preparation, opposing teeth, and occlusal relationships.9 Ultimately, the software merges common data from all scans and proposes a virtually articulated cast.7 The Lava Chairside Oral Scanner (COS) camera is the only video camera for digital impressions. It uses “active wavefront sampling” to record up to 20 3-D data sets per second and 2,400 3-D data sets per arch. Three sensors record the clinical situation from varying perspectives and use proprietary image processing algorithms to process the model.10 Unlike single image cameras, it captures 3-D data in a video process and fabricates the virtual model in real-time on the computer monitor.11 The virtual model can be switched between a 2-D and 3-D image as well as visualized with 3-D glasses to verify aspects of the recorded models. Another feature of the Lava COS video

capture is that the dentition can be recorded in strips or sections and the computer can assemble the strip scans in a real-time single 3-D virtual model.12 The operator has a field of view of approximately 10 mm by 13.5 mm and the camera must stay between 5 mm and 15 mm working depth from the surface being recorded, otherwise a fail-safe component stops capturing data, preventing poor quality data from being included in the scan.7 The most recent upgrade to the Lava COS system provides several new features. A scan/rewind function is now included that allows the user to rewind and delete 10-second portions of the scanned video rather than delete the entire scan. Smart Scan function automatically removes extraneous data that is recorded in one scan and not duplicated in successive scans. For example, if a portion of the tongue or cheek is recorded in the first strip scan, and is not recorded in the second overlapping strip scan, the computer deletes the extraneous information from the virtual model. All of the computerized systems record data files to store the digital impression. The initial versions of these systems created proprietary .stl files that could only be read and utilized by software and equipment from the same manufacturer. This is referred to as “closed architecture.” This created a significant limitation in that only equipment from the manufacturer could use the .stl file from that manufacturer’s software. Dental laboratories had the potential problem of having to acquire several different systems in order to manage all the data files from their client doctors. More recently, manufacturers of CAD/CAM systems have moved to “open architecture” with their .stl files. Multiple corporate partnerships have been developed allowing the use of a specific

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C O V E R S T O R Y (c o n t i n u e d )

Figure 7

Figure 8

Higher magnification of the Lava COS scanned data reveals an accurately recorded distal margin.

High magnification alternative contrast view of a preparation margin with the Lava COS system for critical evaluation of the margins prior to transmitting the case to the dental laboratory.

manufacturer’s .stl files across several different software programs and processing equipment. This has significantly improved things for dental laboratories as they can limit the amount of processing equipment they require to handle the .stl files from different computerized systems.

the margin areas. Traditional impressions generally require that soft tissues be retracted vertically past the margins as well as laterally. There needs to be some bulk of impression material at the margin to avoid tearing it upon removal and at least 1 mm of impression material past the margin to ensure an accurate impression of the margin. The advantage for digital impressions is that the soft tissues only need to be retracted sufficiently laterally to visualize the margins. This may be as little as 150 microns to register the margin of the tooth separate from the gingiva. For this reason diode lasers are particularly popular adjunctive instruments for digital impressions as they are useful to create lateral retraction while preventing bleeding and ensuring a dry field of view. As an example, Figure 6 (previous page) shows a low magnification image of a Lava COS scanned preparation on tooth #13. It appears that there is a void in the model at the distal margin of the preparation. However, the higher magnification image of the preparation (Figure 7) reveals that the data void is actually lateral to the margin of the preparation. Digital impressions also offer excellent immediate feedback to the clinician on the recorded preparation. This could be of even greater value in the academic setting when digital technology may be used as a learning tool. In addition, the ability to greatly magnify the scanned data on the computer monitor is a significant advantage to ensure accurate data prior to transmitting the case to the dental laboratory for processing (Figure 8). For conventional impressions, this level of magnification and critical evaluation may not be possible until the model has been poured, separated, and the die trimmed.

Digital Impressions

All computerized dentistry systems rely on the ability to accurately record the dentition. Without a precise digital recording, an accurate restoration is not possible. The margin fit and internal adaptation of the final restoration are directly related to the quality and accuracy of the recorded preparation. This concept is true for both conventional impressions and digital impressions. The final restoration can only be as good as the recorded data of the tooth. There are some guidelines that hold true for all computerized dentistry systems. One of the most important is that no matter how nice it would be to digitally record tooth preparations through saliva, blood, and soft tissues, this is not possible today. Digital recordings or scans are as sensitive to moisture contamination and soft tissue retraction as are traditional impression materials. Moisture, such as saliva or blood, obscures the preparation and prevents an accurate recording of the tooth. Similarly, inadequate retraction of soft tissues may hide the marginal areas from view (Figure 5). Digital cameras can only record what is visible and isolated. Careful control of the scanning environment ensures an accurate digital file essential to a well-fitting restoration. Digital impressions have one advantage over conventional impressions in this regard as they do not require significant retraction of soft tissues vertically beyond 38

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Figure 9

Figure 10

Quantitative information of the occlusal clearance with a digital impression from the iTero system. The red-orange areas indicate less than 1.50 mm clearance from the opposing dentition.

The dotted lines indicate the facial height of contour of the teeth. Note the flat emergence profile calculated by the CEREC software since the images recorded from the occlusal direction were not able to image data hidden by the height of contour in this angle of recording.

The digital systems also provide quantitative data on the preparation relative to the opposing dentition. This is especially helpful in ensuring adequate occlusal clearance for a case based on the specific restoration planned (Figure 9). Prompt access to high magnification images allows for the opportunity to correct preparation deficiencies and the ability to re-scan the case immediately, rather than discovering them in the final impression or stone models, which would require having them corrected at a second appointment or worked around by the dental laboratory technician. Single image cameras (CEREC AC, D4D, iTero) are lineof-sight cameras. The camera works similar to our eyes in that we can see what is directly in our line of vision but not around corners. The cameras record a series of single images of the dentition. Each single image must overlap with one or more of the other images to enable the computer to process the single images into a three dimensional virtual model on the software program. The single-image cameras must capture images from a variety of angles to accurately record the dentition below the height of contour. Figure 10 shows the facial contour of a CEREC virtual model created from a series of single images made from the occlusal aspect of the teeth. Note the straight contours of the teeth below the height of contour. To accurately record the facial and lingual contours of the teeth, the camera must be angled past the height of contour with two or three images. Note that the facial contour of the preparation has been accurately recorded as the camera can record all data within the path of insertion of the preparation. There has been considerable discussion about “calculated” image data rather than “actual” image data re-

corded by digital systems. Obviously, “real” data replicating the intraoral condition is what is required for accurate restorations. This is generally the goal with a traditional impression as well, where accuracy is evaluated upon removal from the mouth. Areas of folds, tears, and bubbles may be visible in the impression in a noncritical area relative to the planned restoration and may be considered “calculated” data. This “calculated” data may not affect the desired accurate outcome of the restoration. If it does, a new impression must be made since there is no accurate way to modify the existing impression. The evaluation of “critical” data is similar for digitally recorded data as well. Scanned data on the computer monitor can be evaluated for missing or extraneous data. Similarly, it can be judged to be critical or noncritical to the planned restoration (Figure 11). Rather than evaluating the impression, the actual virtual model is visualized on the monitor. If it is determined that there is missing data in the model, additional scans can be immediately made to correct for the missing data. This is a much more efficient process than having to remake the entire impression using conventional methods.

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Digital impressions have been shown to be equally accurate to conventional impressions. 39

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Figure 11

Figure 12

Note the small data voids on tooth #2 and #14 in the full arch Lava COS digital impression for the FPD from #4-6. These are in noncritical lateral areas of the teeth and the option to do an additional scan to fill in these data voids may be considered unnecessary for the success of the case.

Superimposition of bite registration model over the preparation model and restoration proposal to verify occlusal contacts with the E4D system.

Another critical element of a digital impression is the ability to record opposing teeth and occlusal relationships for the planned restoration. Generally, two techniques are employed. One technique is to make a bite registration of the dentition opposing the prepared teeth. The bite registration is scanned separately from the preparation model and the software program matches the two models (Figure 12). The bite registration technique can be used by the E4D and CEREC AC systems. The other technique is to digitally record the opposing models separately with the imaging camera and store them in the case file. The patient is guided into a closed centric position and the dentition is scanned from the buccal view. This is referred to as a buccal scan (Figure 13). The buccal scan records the facial contours of the teeth and soft tissues. It is used by the software program to align the opposing digital models for accurate recording of the patient’s occlusal relationship. The bite scan technique can be used by the Lava COS, iTero, and CEREC AC systems. To date, no system has the ability to digitally record functional lateral movements for mounting. Traditional lateral or protrusive check bites are required to mount the case on an adjustable articulator to simulate lateral guidance. A general concern by those unfamiliar with digital impression systems is how much longer does it take to digitally record the intraoral condition compared to traditional impressions. It may be obvious that one’s comfort with the use of an intraoral camera significantly influences the length of time required to record the images. Anecdotal reports indicate that digital image systems are

somewhat more efficient than the usual five- to sevenminute set times of polyvinylsiloxane impression materials. For example, the maximum scan time for a single arch or quadrant with the Lava COS system is seven minutes, with most quadrants requiring only two to three minutes. However, this may not be true for all digital impression systems. A recent randomized clinical trial questioned the efficacy of digital impressions by comparing crowns fabricated with either iTero or conventional impression techniques. The results showed that both impression and crown adjustment times were significantly higher when the digital method was used, even though no significant differences were found in marginal fit.13 The undisputed key issue with digital impressions is accuracy. The use of conventional impression techniques and materials is the accepted technique for fabricating well-fitting restorations. Without an accurate impression, a well-fitting restoration is not possible regardless of the fabrication process. The starting point for considering digital impression systems is an expectation of at least equally repeatable accuracy. Digital impressions have been shown to be equally accurate to conventional impressions.14,15 Several of the camera systems require the application of a titanium dioxide powder to the surface of the teeth and soft tissue to be scanned. The thin, uniform coating creates a uniformly reflective surface to the dentition for accurate data recording. A common misperception is that this thin powder layer limits the accuracy of the final restoration. However, even when used incorrectly, a small amount of excess powder does not affect the margin fit or internal adaptation any more JOURNAL OF THE MICHIGAN DENTAL ASSOCIATION • APRIL 2012

References

Figure 13 Buccal scan mounting of the scanned opposing models with the Lava COS system.

than a die spacer does on laboratory-fabricated restorations using stone casts. Each of the digital systems has been shown capable of fabricating restorations with margin fit and internal adaptation equal to conventional fabrication techniques. CEREC has more than 25 years of both laboratory and clinical research confirming the predictable outcomes possible with the chairside CAD/CAM system.16,17,18 Lava COS has laboratory and clinical research confirming the digital impression technique as a consistently accurate restoration fabrication process.10,14,15,19 In addition, the more-recently introduced systems have laboratory studies documenting the margin fit and internal adaptation of their restorations.20,21

Conclusion

Digital dentistry and CAD/CAM technology are responsible for one of the most significant developments in restorative dentistry in recent years. Dentists are no longer restricted to using conventional impression materials to fabricate well-fitting indirect restorations. Digital systems are gradually being incorporated in the work flow of many dental offices across the country with significant increases in production and overwhelming patient acceptance. However, these positive attributes may not be evident initially, as a learning curve can be expected with the incorporation of any new and emerging technology. Success with digital impressions is still dependent on mastering similar skills required for conventional impressions, such as achieving optimal soft tissue retraction and moisture control which enable accurate image acquisition and data recording. G

JOURNAL OF THE MICHIGAN DENTAL ASSOCIATION • APRIL 2012

1. Beuer F, Schweiger J, Edelhoff D. Digital dentistry: an overview of recent developments for CAD/CAM generated restorations. Br Dent J 2008;204(9):505-511. 2. Fasbinder DJ. Digital workflow for the Lava COS system. Inside Dent Oct 2009;114-117. 3. Levine N. To the sky and beyond. Dental Products Report Oct 2009;116. 4. Mormann, WH. The evolution of the CEREC system. JADA 2006; 137: 7s-13s. 5. Mehl A, Ender A, Mormann W, Attin T. Accuracy testing of a new intraoral 3D camera. Inter J Computer Dent 2009;12:11-28. 6. Birnbaum NS, Aronson HB. Dental impressions using 3D digital scanners: virtual becomes reality. Compend Contin Educ Dent 2008;29:494-505. 7. Kachalia PR, Geissberger MJ. Dentistry a la carte: in-office CAD/CAM technology. J Calif Dent Assoc. 2010;38(5):323-30. 8. Garg AK. Cadent iTero’s digital system for dental impressions: the end of trays and putty? Dent Implant Update 2008; 19(1):1-4. 9. Henkel GL. A comparison of fixed prostheses generated from conventional and digitally scanned dental impressions Comp Cont Ed Dent 2007;28(8):422-31. 10. Syrek A, Reich G, Ranftl D, Klein C, Cerny B, Brodesser J. Clinical evaluation of all-ceramic crowns fabricated from intraoral digital impressions based on the principle of active wavefront sampling. J Dent. 2010;38(7):553-9. 11. McMaster D, Cohen B, Spitz SD. Digital workflow. Dent Economics Aug 2008;30-36. 12. Fasbinder DJ. Digital dentistry: innovation for restorative treatment. Compend Contin Educ Dent 2010; 31(Spec No 4):2-11. 13. Givan DA, Burgess JO, O'Neal SJ, Aponte AA. Prospective evaluation of ceramic crowns by digital and conventional impressions. J Dent Res 2011;90 (Spec Issue A): 380. 14. Ender A, Mehl A. Full arch scans: conventional versus digital impressions - an in-vitro study. lnternatl J of Comput Dent 2011; l4:1l-21. 15. Ogledzki M, Wenzel K, Doherty E, Kugel G. Accuracy of 3M-Brontes stereolithography models compared to plaster models. J Dent Res 2011;90 (Spec Issue A):1060. 16. Martin N, Jedynakiewicz NM. Interface dimensions of CEREC-2 MOD inlays. Dent Mater 2000;16(1):68-74. 17. Estafan D, Dussetschleger F, Agosta C, Reich S. Scanning electron microscope evaluation of CEREC II and CEREC III inlays. Gen Dent. 2003;51(5):450-4. Erratum in: Gen Dent 2003;51(6):583. 18. Ellingsen LA, Fasbinder DJ. In vitro evaluation of CAD/CAM ceramic crowns. J Dent Res 2002;81(Spec Issue A):2640. 19. Kugel G, Chaimattayompol N, Perry R, Ferreira S, Sharma S, Towers J, Stark P. Comparison of digital vs. conventional impression systems for marginal accuracy J Dent Res 2008;87(Spec Issue A):1119. 20. Plourde J, Harsono M, Fox L, Hill TJ, ,Finkelman M, Kugel G. Marginal and Internal Fit of E4D CAD/CAM All-Ceramic Crowns. J Dent Res 2011;90(Spec Issue A):638. 21. Thompson VP, ReKow ED, Wolff M, Silva N. CEREC vs E4D Film thickness evaluation. NYU report E4D http://www.e4d.com/resources/nyuReports.php

About the Authors

Fasbinder

Neiva

Dr. Dennis Fasbinder is a clinical professor and the director of the Advanced Education in General Dentistry Program at the University of Michigan School of Dentistry, where he also maintains a parttime private practice. He directs the Computerized Dentistry (CompuDent) Unit at the University of Michigan that is dedicated to research and education on CAD/CAM digital dentistry. Dr. Gisele Neiva is a clinical associate professor and assistant director of the Graduate Program in Restorative Dentistry at the University of Michigan School of Dentistry, where she also practices. She has master’s degrees in restorative dentistry and clinical research design and statistical analysis. Her main research focus is on digital dentistry.

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