Written by Sameer Puri, DDS Tuesday, 31 March 2009 19:00
Computer-aided design (CAD)/computer-aided manufacturing (CAM) is taking over dentistry. That’s a bold opening statement, but I’m sticking to it. There’s a saying that “everything in dentistry is new for 10 years,” meaning when a revolutionary new product category is introduced to the dental market, it takes a minimum of 10 years for the industry to actually embrace it and make it mainstream. That’s not to say dental professionals are slow to adopt new and improved ways of doing something—we are just overly cautious (and rightly so) about changing our ways until we are absolutely, positively, without a doubt sure that the product or procedure is going to withstand the test of time. We want to be sure that the technology is not only practical, but that it’s also clinically sound in all respects. And to be sure, this takes a lot of time; time for clinical studies to be completed and published, and time for the materials to be proven clinically viable in real-world application.
So here I am, nearly 23 years after the first chairside CAD/CAM restorative system entered the market stating that chairside CAD/CAM dentistry has now become “mainstream” dentistry.
There are currently 4 systems in the chairside-imaging arena right now. Two of them are capable of designing and milling the restoration at the chair, while the other 2 are only digital imaging units. This is a great thing for dentists and patients alike, as competition between manufacturers usually leads to big improvements such as advancements in the speed, precision, accuracy, practicality, ease of use, and profitability of their respective products.
THE GROWTH OF CHAIRSIDE CAD/CAM
The popularity of in-office CAD/CAM has grown exponentially in the last 4 or 5 years—more than in the entire 20 years that it has been available. Again, this has to do with the fact that CAD/CAM has proven itself in the dental operatory. The process fits the way we work, it’s clinically proven, the materials have proven themselves to be viable alternatives to amalgam and composite, the aesthetics are top-notch, and patients appreciate the one-visit aspect as well as the natural-looking results.
All the chairside systems work similarly: you prep the teeth as usual, and then take a digital impression. With 2 of the systems (Lava COS [3M ESPE]) and iTero [Cadent]), the digital impressions are sent to the laboratory where the dental technicians will then fabricate traditional models from the digital data, and return the restoration of your choice within a few weeks. With the other 2 systems (E4D [D4D] and CEREC AC with Bluecam [Sirona]), the design, milling, and placement of the restoration is done chairside in just one visit. All of them—including the iTero, Lava COS, E4D, and CEREC AC—have their own version of 3-D imaging software. All of them also use a handheld acquisition camera to acquire the preparation image.
IMAGE ACQUISITION TECHNOLOGIES
One of the most important aspects of any CAD/CAM system is the optical technology employed to acquire the preparation image. Systems such as E4D use red lasers to scan the preparations. Red laser scanning for dentistry was first used in the CEREC inLab (Sirona) CAD/CAM system for laboratories starting in 2001. Red lasers provide an intense and tiny beam of light that moves across the preparation “line by line,” hence the term “laser scanning.” Lasers inherently create speckles in the acquired image, which translate into “dead spots” on the image where the laser did not strike. Dead spots are essentially missing data points that the computer software must account for. This is accomplished by taking multiple images in an attempt to “fill in the blanks.” While laser-based systems do not require an opaquing medium, that advantage is outweighed by the fact that multiple images (9 per tooth) are needed to create a virtual model. The number of images can become prohibitive when making larger quadrant models.
The Lava COS System (3M ESPE) uses video-type image acquisition, which generates a large amount of data. The files are typically several gigabytes in size because of the tremendous volume of information captured by the video in motion technology. Due to the size of the files, the information is transmitted overnight to the dental laboratory via the internet and the case is processed the following day by a central facility. A light dusting of an opaquing medium is required to capture the information on the teeth.
The iTero (Cadent) uses a combination of green laser and confocal imaging processes to acquire the image. This process takes up to 20 images per tooth to capture a virtual model but does not require an opaquing medium to be placed. The information is sent to a central processing facility where artifacts that are a function of the multiple images are removed manually and models fabricated and sent to the laboratory.
CEREC AC Powered by Bluecam (Sirona), introduced in January 2009, is the latest technological development in chairside CAD/CAM systems (Figure 1). The CEREC AC employs Bluecam LED technology for image scanning and acquisition. Bluecam LED provides consistent illumination from edge to edge, with the same intensity of light wherever it is pointed or shining upon—without speckles. Based on the same technology that powers Blu-ray DVD players, Bluecam acquires images 2X faster than infrared laser scanning, and its much shorter wavelength equates to higher precision and greater image clarity/definition. The optics in the Bluecam were specifically engineered for a greater depth of field (focal depth), which makes the camera much easier to position in the mouth because everything is in focus. Lastly, unlike other systems that require the user to take several images of a tooth from various angles, Bluecam requires just one image to acquire all surfaces of a tooth. The resulting accuracy and precision allows the clinician to fabricate highly accurate virtual models for multiunit restorations.
|Figure 1. The CEREC AC with Bluecam (Sirona) was introduced in January 2009.||Figure 2. The patient presents with wear, erosion, and caries on her existing teeth.|
Patient Presentation and Treatment Plan
The patient, a 42-year-old female presented to the office with the desire to aesthetically enhance her smile. The patient suffered from recession, abfraction, as well as erosion of the lingual portions of the maxillary teeth (Figure 2). The treatment plan was based on not only addressing the functional nature of the patient’s teeth, but also on aesthetically enhancing them. For this case, 8 maxillary teeth (Nos. 5 through 12) were prepared for all-ceramic, single-visit CAD/CAM restorations designed and fabricated with the CEREC AC Powered by Bluecam and MC XL high-speed milling unit. The treatment plan entailed preparing all 8 teeth, acquiring the full-arch preparation image, then designing, verifying, and milling each restoration in succession.
|Figure 3. A diagnostic wax-up was created in the dental laboratory to guide the procedure on the final size, shape, and contours of the teeth.|
First, a diagnostic wax-up was completed to address the proper size and shape of the teeth (Figure 3). This served as a template for the final restorations and allowed the patient to preview her new smile. Regardless of whether the case is being completed chairside with a CAD/CAM system or utilizing the creative skills of dental technicians, the basic tenets for excellence in restorative dentistry cannot be avoided. In the near future CEREC owners will have the opportunity to virtually wax-up their cases using the software. However, until that occurs, traditional wax-ups need to be completed so the case can be verified by the patient and doctor for function, aesthetics, and phonetics.
|Figure 4. The teeth were prepared for all-ceramic restorations.||Figure 5. The preparations were imaged with the CEREC Bluecam and a model preview was generated.|
|Figure 6. A putty matrix made from the diagnostic wax-up was used to transfer the wax-up to the prepared teeth.||Figure 7. The patient was allowed to preview and approve the provisionals prior to fabrication of the final restorations.|
The patient was anesthetized with local infiltration of Septocaine (Septodont) with 1:100,000 epinephrine. Once profound anesthesia was achieved, the teeth were prepared to receive the all-ceramic restorations (Figure 4). The preparations were a combination of full-coverage crowns and partial coverage veneers as dictated by the preoperative situation of the patient.
Cord was packed to isolate the tissues, and a light coating of opaquing powder (OptiSpray [Sirona]) was sprayed onto the operative field. The digital impressions were then acquired with the CEREC Bluecam (Figure 5).
Next, after all preparation images were acquired, provisionals were fabricated. These were created by using a putty matrix made from the diagnostic wax-up; filling the matrix with a bisacryl composite (Luxatemp [Zenith Dental/DMG]); and allowing the temps to self-cure on the patient’s prepared teeth (Figure 6). Once the bisacryl completely cured, it was removed, trimmed, and cemented with flowable composite (Figure 7). One reason for the care taken in the temporization process was to allow the patient to preview her new smile in her mouth.
The length of temporization will depend on each individual patient and can range from 10 minutes to 10 months, depending on the desires of the patient and clinician. By placing the provisionals, the patient’s approval for the new size, shape, and color of the teeth can be verified. If the patient is unsure of his or her new look, modifications to the temps can be made. Once the patient approves the look of the temps, only then is he or she imaged for duplication into porcelain with the CEREC AC System. As mentioned before, the basics of smile design do not change simply because one is using new technology to fabricate the restorations.
|Figure 8. Each restoration was designed with the software.||Figure 9. The occlusion and contact of each restoration was checked.|
Once all the preparation images have been acquired, the dentist need only indicate the margin line of the first restoration using the automatic margin finder and the system will automatically propose a restoration design for that tooth (Figure 8). The teeth proposals are generated within a few seconds from a comprehensive biogeneric database of tooth morphologies that is built-in to the CEREC AC software. The dentist can then confirm the occlusal and interproximal contacts (Figure 9) and send the restoration to the milling chamber. While the first restoration was being milled from the porcelain block (IPS Empress, [Ivoclar Vivadent]), the next restoration was designed, verified, and sent to the milling chamber. This process was repeated for each restoration until all 8 restorations were milled. There are 3 main manufacturers (Ivoclar Vivadent, 3M ESPE, and Vident) of blocks for the CEREC system and they all make a variety of shades and materials available that can be milled with the CEREC software.
|Figure 10. The finished restorations were verified on a model for fit and aesthetics prior to final cementation.||Figure 11. Postoperative view of the finished restorations.|
|Figure 12. Nonretracted view of the finished restorations.||Figure 13. Close-up photo (immediate post-cementation).|
Once milled, the retaining sprue was removed from each restoration, and they were tried-in for fit. Once the fit was verified, the restorations were then characterized using the stain and glaze (Ivoclar Vivadent) made specifically for the all-ceramic blocks (Ivoclar Vivadent) used. For this case, blue-colored stain was added to the incisal edges to create an appearance of incisal translucency; and a slight yellow or A3 shade was applied to the cervical to warm the cervical areas of the teeth. These colors were painted on in the usual manner and fired in a porcelain oven for final curing. Depending on the skill of the operator, and the amount of aesthetic enhancement and characterization needed, a typical 8-unit anterior case can be milled and modified in approximately one hour. A quick model of the preparations can be made to verify all contours, contacts, and aesthetics prior to trying in the restorations in the mouth (Figure 10).
Once the restorations were completed, the operative field was isolated. Then, the restorations were bonded with a light-cured resin cement. Most dual-cured cements should be avoided in the aesthetic zone as they have a tendency to discolor over time.
The patient was extremely pleased with the final results (Figure 11 to 13). Eight teeth on her lower arch were also scheduled to be restored using this same method at a later date. Fabricating the restorations in-house and at chairside allowed my practice to be profitable as well as efficient in saving the laboratory bills associated with larger cases.
Comprehensive cases can now be treated with ease using a chairside CAD/CAM system that is capable of half- and full-arch restorative dentistry. As a CEREC 3 owner for numerous years prior to owning the CEREC AC, I can say from experience that the new Bluecam LED technology offers substantial benefits and enhancements compared to the previous CEREC model. A half-arch digital impression can be acquired in about 40 seconds, and a full-arch in about 2 minutes.
In addition, based on my observations in using the CEREC AC for well over a 100 cases, the Bluecam operates more fluidly and efficiently than the previous infrared camera: simply position the camera over the teeth and system automatically begins acquiring images and also automatically stitches them together (in the case of a half- or full-arch impression) without the need to press a button or foot pedal. An antiblur and antiartifact feature (called “shake control”) is built-in to the Bluecam to ensure images are captured without distortion. This is a useful feature that is currently missing from other systems. It is a real time saver because capturing digital impressions with Bluecam does not require a special technique—the camera adapts to the way you hold it and the way you “hover” it over the impression, rather than your having to conform to the limitations of the camera, as is necessary in most other systems that don’t have real-time imaging capability.
Digital impression imaging technology is the backbone of any CAD/CAM system, since the image quality, accuracy, and precision of the acquired image is tantamount to the precision of the final restoration. Likewise, milling precision should be as close to the precision of the acquired image as possible. The CEREC AC Bluecam is capable of imaging with a precision of +/- 10 µm, and the MC XL milling unit is capable of milling to within +/- 25 µm accuracy, both of which are well within acceptable clinical tolerances.
The dental CAD/CAM landscape is constantly changing. One thing that is not going to change is that chairside CAD/CAM is an accepted and viable technique. Technological advances, like those that have been reported upon in this article, have established that fact further.
Disclosure: Dr. Puri receives financial compensation from the Sirona and Patterson companies for lectures and speaking engagements.
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