Written by Sameer Puri, DDS Monday, 09 May 2011 14:23
For more than 25 years, clinicians have realized the benefits of using computer-aided design and computer-aided manufacturing (CAD/CAM) technology for the restoration of their patients' dentition. The pioneering system with this technique has been the CEREC (Sirona Dental Systems), which has been successfully fabricating one-visit restorations for more than a quarter of a century. The protocol to image, design, and mill restorations chairside in one visit is represented by over 30,000 systems in use in the world and approximately 11,000 systems in the United States.
While the current number of CAD/CAM users is still a relatively small portion of the total dental market, dentistry is coming to a tipping point in terms of clinician and patient perception with regard to chairside milling, and digital dentistry as a whole. As is often the case, it takes a critical mass of users before a particular technology becomes mainstream. Now that there are additional digital systems (such as E4D [D4D Technologies]; Lava C.O.S [3M ESPE]; and iTero [Cadent]) that can either be used for digital impressions or chairside milling, as with CEREC (E4D cannot be used for digital impressions—they are working on it, but it is not yet released and there is no indication it will be anytime soon), it seems logical that this technology which has already been embraced by the innovators and early adopters will eventually be accepted and implemented by the majority of dentists. In the author's opinion, there is no doubt where the future of dentistry is headed.
EVOLUTION OF HARDWARE AND SOFTWARE
One of the driving forces behind the increased adoption of digital dentistry is the evolution of the hardware and software systems. These advances have allowed clinicians to utilize the technology in more clinical indications than early generations would allow. For example, initial versions of the CEREC system allowed clinicians to fabricate only simple inlays and onlays. More complex restorations were either too difficult for the average practitioner to design and fabricate, or were simply not possible with the newly introduced technology at the time. For mass adoption of this concept of digital dentistry to occur, users should be able to utilize the technology with a minimum amount of training and computer knowledge. Again, with the original machines and software, this was not the case.
As the hardware became more robust and the software became more sophisticated, the technology allowed the users to increase the range of indications for the use of their machines. Technological evolution has now allowed posterior full-coverage crowns, while some early adopters also ventured into treating anterior teeth. It was not until the creation of the CEREC 3D (Sirona Dental Systems) in the early 2000s that the software was sophisticated enough to allow mass-market treatment of anterior restorations in one visit.
The software-hardware advancements and the increased range of indications dictated that material evolution needed to occur so that the aesthetics of a restoration created from a milled block of porcelain could be improved. Early generations of materials were monochromatic which, for the indicated use at the time, was adequate. However, limitations in the technique meant that detailed anatomy and morphology were not possible so, historically, material aesthetics was the least of the practitioners' worries. Then, with the eventual increased range of indications, users realized that they needed more robust and aesthetic materials to allow for increased use of this technology.
One of the evolutions in materials was the introduction of blocks manufactured with multilayered translucencies of porcelain. One of the more popular multilayered blocks introduced, fabricated in layers with increasing translucency from one end of the block to the other, was the Vita Triluxe block (Vident); still a popular choice for aesthetic areas (Figure 1). Multilayered blocks allow the restorations to be positioned spatially within the block via the design software, so that the desired level of translucency can be created in the final milled restoration (Figure 2). As a result, the limitation of having a single translucency choice was no longer an issue. However, the one critique that clinicians did have about the layered blocks was that the distinction (in certain clinical situations) between the layers was sometimes noticeable. The incisal edge position, instead of a natural and random layer of enamel, gave the appearance of a straight line in its depiction of the natural incisal edge translucency.
|Figure 1. The Vita Triluxe block (Vident) has layers of varied translucencies built into the premanufactured block.||Figure 2. The software gives the doctor the ability to select the level of translucency desired in the incisal/occlusal area.|
|Figure 3. The VITABLOCS RealLife (Vident) has a spherical dome of dentin built into it, allowing for 3-dimensional positioning of the restoration to optimize aesthetics.|
These observations led to the latest generation of blocks for the aesthetic zone (VITABLOCS RealLife [Vident]) (Figure 3). Instead of a conventional layered approach to the porcelain in the block, the user instead custom positions the restoration to be milled within a spherical dome of "dentin" that is surrounded by "enamel." By eliminating the conventional layer design previously used in machinable blocks and using the spherical dentin dome, the clinician is able to avoid the distinct transition from the cervical to the body, to the incisal edge. In addition, one can create a more natural incisal edge position without having to cut back any porcelain. While the actual porcelain itself is the same chemistry and composition (fine structure feldspar ceramic) as the Vita Triluxe block, the ability to position it 3-dimensionally within the dentin and enamel core allows the clinician to precisely fine tune the aesthetics of the final restoration.
The following clinical case reports will demonstrate how these innovative new blocks, along with the improved software, give the clinician the ability to realize better aesthetic outcomes than previously possible with CAD/CAM dentistry.
A patient presented to the office after suffering a traumatic fall in the middle of the night. Clinical examination revealed that the 2 central incisors suffered fractures of the mesial portions of both teeth (Figures 4 and 5). The patient was given the different treatment options and it was mutually decided to restore the teeth with chairside CEREC CAD/CAM restorations.
|Figure 4. (Case 1) The patient presented with traumatic fractures in the central |
|Figure 5. A close-up view of the fractured teeth.|
|Figure 6. A digital system (Vita EasyShade [Vident]) was used for shade taking.||Figure 7. Endodontic therapy was performed on tooth No. 9.|
|Figure 8. After root canal therapy, the access area was built up with composite resin.||Figure 9. Retration cord (Ultrapak [Ultradent Products]) was placed to expose the margins on the preparation.|
|Figure 10. The CEREC software (Sirona Dental Systems) was used to manipulate multiple restorations.||Figure 11. The restoration was virtually positioned in the block (VITABLOCS RealLife). Instead of a conventional layered approach to the porcelain in the block, now the user can custom position the restoration to be milled within a spherical dome of "dentin" that is surrounded by "enamel."|
|Figure 12. The final restorations were etched, silanated, and bonded in place using a dual-cured resin cement (NX3 [Kerr]).||Figure 13. (Case 1) Final view of the seated restorations, demonstrating very |
First, a preoperative shade was taken using a digital shade-taking system (Vita Easyshade [Vident]) (Figure 6). The shade is taken prior to the start of the dental procedure, as it is important to record the shade before the teeth become dehydrated. Once dehydrated, the ability to capture the correct shade is much more difficult. The Easyshade not only gives an accurate color rendition of the patient's dentition; the latest version of this device is designed to tell the user which CEREC block should be used for the restoration in order to achieve the chosen shade.
Clinical and radiographic examination revealed that tooth No. 9 needed root canal therapy to remove the apical lesion that had formed from the exposed pulp (Figure 7). The root canal therapy was completed and both teeth were prepared for all-ceramic restorations after building up the endodontic access area on tooth No. 9 with a direct composite restoration (Premise Composite [Kerr], used with etch and Optibond Solo Plus [Kerr] as the bonding agent) (Figure 8).
While it's advisable to offer complete cuspal coverage for any tooth after a root canal procedure in the posterior of the mouth, anterior teeth can be treated with a more conservative approach. With anterior teeth, every effort should be made to preserve the cingulum of the tooth. In his book, Bonded Porcelain Restorations in the Anerior Dentition: A Biomimetic Approach, Pascal Magne makes a compelling argument to not violate the cingulum of an anterior restoration whenever possible. Were it not for the extent of the fractured tooth structure, the ideal treatment for the restoration of the endodontic access would have been a simple direct composite to close the access opening, instead of a full-coverage crown.
Whenever possible, CEREC preparations should be kept supragingival at all times for ease of imaging and cementation of the final restoration. If the margins go subgingivally, then retraction of the tissues should be accomplished with either laser troughing of the sulcus or with retraction cord. In this case, after final preparation, a 000 cord (Ultrapak [Ultradent Products]) was placed in the sulcus to help expose the margins for imaging with the digital CAD camera (Figure 9).
The preparations were then imaged and designed utilizing the CEREC software. Advances in the software permit the manipulation of multiple restorations at once, allowing the user to achieve maximum aesthetics and symmetry (Figure 10). Once the restorations were designed, the restorations were positioned in the RealLife blocks to obtain the proper amount of translucency in the incisal portion (Figure 11) and then milled in the CEREC MC XL (Sirona Dental Systems) milling unit. The milling process typically takes 6 to 8 minutes to fabricate each restoration.
After verification of the fit and aesthetics in the mouth, the restorations were stained and glazed with the appropriate materials and prepared for final cementation in the mouth (Figure 12). The inner surfaces of the porcelain restorations were prepared for bonding via an acid-etch technique with hydrofluoric acid for 60 seconds. As the assistant applies fresh silane to the internal etched porcelain to enhance the resin cement-to-porcelain bond, the doctor can prepare the tooth structure for the bonding procedure. A dual-cured resin cement (NX3 [Kerr]) was used to permanently bond the restorations into place. The final restorations blended in well with the surrounding tooth structure, providing excellent aesthetics and restoring the teeth to proper form and function (Figure 13).
A 32-year-old male with an existing porcelain veneer presented to the office on an emergency basis after suffering a traumatic fracture of the incisal edge playing basketball (Figure 14). Typically, the CEREC software will use the adjacent teeth as a guide to give a proposal in the software that is highly accurate. In this particular case, the clinical decision was made to use the biogeneric reference mode of the software. This allows the clinician to copy the adjacent central incisor and uses its morphology and contours for the final restoration (Figure 15).
The preoperative shade was once again taken digitally prior to starting any dental care to capture the true color of the surrounding teeth. The patient was then given local anesthesia, the fractured porcelain veneer was removed, and the final preparation was made on the affected tooth. As with case 1, once the preparation was complete, a single 000 cord was placed in the sulcus to retract the tissue and to allow for the digital impression to be accurately taken (Figure 16). The images of the prepared tooth were captured in the CEREC software the restoration was designed (Figure 17).
|Figure 14. (Case 2) Preoperative view of the fractured restoration.||Figure 15. The CEREC software in the Biogeneric Reference mode was used to copy tooth No. 8 and place its mirror image on tooth No. 9.|
|Figure 16. The preparation, ready to be imaged for the CAD/CAM restoration.||Figure 17. The designed |
restoration was virtually placed within in the RealLife block in the desired position to achieve optimal aesthetics.
|Figure 18. Retracted view of the seated restoration.||Figure 19. (Case 2) The final restoration. (Note how it blends in with the surrounding teeth.)|
Next, the designed restoration was positioned in the VITABLOCS RealLife block to allow for the optimal amount of translucency and enamel to show through and milled. Once the clinician and patient confirmed the fit and aesthetics of the restoration, it was stained and glazed in a porcelain oven and prepared for bonding to the tooth structure. Finally, the porcelain and tooth structure were prepared, as described in case 1, and the restoration was seated using resin cement.
The patient received an acceptable restoration that blended in with the surrounding tooth structure and accurately mimicked the adjacent central incisor (Figures 18 and 19).
Digital dentistry with CAD/ CAM technology is becoming more and more routine, and the successful treatment of both posterior and anterior teeth is now possible. With the advances in materials as well as advances in the software and hardware, clinicians now have the tools needed to fabricate a wider variety of aesthetic restorations.
Disclosure: Dr. Puri lectures for Sirona and Patterson Dental and receives compensation from both for running cerecdoctors.com.