Chairside All-Ceramic CAD/CAM Veneers With Lab-Assisted Cutback and Aesthetic Porcelain Buildup: Case Report

Dentistry Today, May 2006

Recently, one of my technology-savvy patients told me about how he enjoys being able to "timeshift." The first thing I thought was maybe he invented some sort of time machine. Turns out, that is not too far from the truth. Timeshifting, he says, is a new buzzword to describe the function of digital video recorders (DVRs) that connect to television sets. Say you have a favorite TV show that airs at 10 PM but won't be around to watch it. Not a problem when you can simply "timeshift" the show to fit your own viewing schedule. In other words, these programmable DVRs will, at the press of a button, record TV shows onto a hard drive and allow you to view them at a later time. This technology is really nothing more than a convenience item, and some would say a frivolous luxury. But I say give it time. It is amazing how rapidly life's luxuries become so pervasive and routine that they shift from "cool new tech toys" to absolute "cant-live-without-it" necessities. Look what happened with the Internet, cell phones, Blackberries (the mobile computing devices, not the fruit!), and iPods. They have become ubiquitous, and most who own and use them say they have become necessities of daily living.

This got me thinking about technologies in dentistry that many in the profession initially wrote off as gimmicky, faddish or just a nonessential high-tech item. Digital radiography comes to mind, and so does in-office CAD/CAM. I enjoy new technology and am often one of the first to incorporate new devices, tools, and techniques into my practice. I've got lasers, digital radiography, and CEREC 3D (Sirona Dental Systems). All of these have become an integral part of my treatment armamentarium-so much so that I have come to rely on their practical application in everyday dental practice. In a way, these high-tech tools have enabled me to incorporate my own brand of timeshifting.

With digital radiography, radiographs are viewable within seconds, not minutes. Plus, digital radiography gives us the ability to recognize changes over time by superimposing a radiograph of a certain tooth over a radiograph of that same tooth taken weeks, months, or years earlier. Because it is digital, the computer can highlight and display only those areas that differ between the two images, resulting in a snapshot of any physiologic or pathologic changes that occurred over time. How's that for timeshifting?

Chairside CAD/CAM restorations also allow me to timeshift by completing most cases in one appointment rather than the 2 or 3 required with lab-involved procedures. As for soft-tissue lasers, they're easier to use than a blade, and due to their ability to produce immediate hematosis and tissue cauterization, we've shifted healing time from a few weeks to just a few days. But I digress. Let us move on to a case report in which all of these technologies and more were utilized to provide the patient with what I call "good, old-fashioned, state-of-the-art treatment."

CASE STUDY

CAD/CAM Restoration Design
CEREC software allows the dental professional to select the design technique that is most appropriately suited to the clinical situation. Deciding which one to use is influenced by the preoperative condition of the teeth and the restorative goals. For teeth that are intact and possess a pleasing, anatomically correct form that the clinician wishes to copy, Correlation Mode is most often employed. Correlation uses 2 optical impressions and allows the clinician to copy an existing tooth and all of its morphological characteristics and replicate it on the restoration. The contour of the original tooth will be kept as well as height information. Another mode, Dental Database, taps anatomical data for the tooth to be restored. Dental Database is ideal when replacing cusps, as it will automatically design the cusp in the buccal-lingual, mesial-distal and cervical-occlusal dimensions, as well as allow the development of custom embrasures, marginal ridges, contacts, and and contours for that specific clinical situation. Lastly, Replication Mode allows the clinician to copy an image of the contralateral tooth, which is converted into a mirror image, thus resulting in a restoration with perfect morphological symmetry.

For this particular case, Correclation Mode was chosen, and although the patient's existing teeth would not function as ideal correlates, this was easily remedied with a diagnostic wax-up that would later serve as a correlate model. Dental Database was not used because there were no cusps involved with these veneers, and Replication was not used because the case did not call for a simple duplication of the patient's existing anatomy.

Pateint Presentation
Several existing factors were taken into consideration and serves as an impetus for using the CEREC Correlation technique. First, the patient's natural teeth were too small, resulting in diastemas between the central incisors, both maxillary lateral incisors, and cuspids. Additionally, her teeth were too short, which created a "gummy" smile appearance. So, in this patient's case we were dealing with several pre-existing conditions that were less than ideal. An orthodontic solution to her cosmetic goals was presented first, but the patient declined this option. Therefore, I decided to have my dental laboratory technician (Tony Ingalls of Dental Compositions) create a diagnostic wax-up of ideal tooth morphologies for each of the patient's 8 teeth that showed when she smiled and thus were to be restored.

Treatment Planning
Performing a diagnostic wax-up is an integral part of any cosmetic restorative treatment plan. It allows the clinician predictability of end results by controlling the many restorative factors leading to a successful cosmetic and restorative outcome. It enables the clinician to know where the incisal edge position for the anterior teeth will need to be, where the protrusive and lateral excursions will function, how large and long the teeth will be when inserted, and what the contours and line angles will be in order to meet aesthetic and restorative goals.

Using the CEREC system, these wax-up serve well as the correlative models. The CEREC computer will superimpose these correlative images over the images of the preparations. The marriage of these perfectly proportioned wax-up teeth and the preparations of her natural teeth will come together to form the design of the patient's veneers. Now, some may say, "Why get the lab involved-doesn't that defeat the purpose of chairside-fabricated CEREC restorations?" My answer to that is "No, it does not." As I have gained confidence and experience using my chairside CAD/CAM computer, the desire and ability to perform more complex cases has increased; incorporating the services of a ceramist merely adds to the process. This approach still benefits the patient with reduced chair time and optimal results. The overarching function of CEREC is to create restorations that are milled from single, solid blocks of extremely strong, aesthetic, and long-lasting all-ceramic material. Not only did we accomplish that, was also completed the case within 2 short visits over a time span of 3 days. Of course, that is not the same as a single-visit, same day case completion, which is what 99% of CEREC-generated restorations represent, but we did manage to complete this rather complex case in a remarkably brief time frame with excellent results. The patient's initial appointment was on a Monday, and her final restorations were placed Wednesday morning. In dentistry, where time is of the essence, fast is good. But faster and better is best. This case falls under that principle and gives new meaning to the phrase "best-case scenario."

Following is a review of the veneer fabrication procedure from preparation to placement and all steps in between.

Veneer Fabrication Procedure
First, extraoral photographs were made of the patient's smile, resulting in a record of her preoperative facial, left and right smile conditions (Figures 1 and 2). These were used to help the doctor and the patient evaluate her smile, the lip line, and how broad it was, which helps determine the correct number of veneers necessary to achieve the desired cosmetic outcome. Additionally, it helps the patient gain understanding and motivation to move forward to the next step of treatment. Before-and-after pictures allow patients to see the difference themselves and can also be shown to new and existing patients to help market the practice.

Next, preliminary alginate impressions were taken and poured up into lab stone. The lab technician then performed a full diagnostic wax-up using mounted casts on a Combi Articulator (Denar). The articulated wax-up ensured that we were able to lengthen each of the patient's teeth to an aesthetically pleasing size, making the centrals 10.5 to 11 mm, in order to achieve the desired aesthetic, biomechanical, functional, and dento-facial results. 1

After a consultation appointment was completed and the patient accepted the treatment plan, minimal gingival recontouring was performed using an Oddysey Diode Laser (Ivoclar Vivadent; Figure 3). This had the result of increasing crown length on some of the shorter teeth and also established an improved aesthetic contour of the gingiva. As previously described, the patient's teeth were too small, which required her restorations to be lengthened in order to produce an aesthetic appearance with balanced and symmetrical proportions. The soft-tissue diode laser (Oddysey) was used to remove and reshape overgrown gum tissue at the crown of the teeth. Minimal crown lengthening was necessary to reduce the "gumminess" of her smile and, at the same time, create harmony in her gingival contours. The patient was then appointed to return 10 days later for veneer preparations.

At the veneer prep appointment, a full-arch impression was taken of the patient's preoperative dentition to be used for provisional veneers that would be worn for about 48 hours. After anesthesia was initiated, 2 full-arch putty wash impressions of the patient's preoperative dentition were prepared using Provil Novo fast-set PVS impression material (Heareaus Kulzer). Next, an OptraGate (Ivoclar Vivadent) was used to retract both upper and lower lips. Then teeth Nos. 5 through 12 were conservatively prepared with only 0.7 mm of facial reduction and a 1 mm to 1.5 mm incisal reduction necessary to accommodate the all-ceramic CEREC veneers. With this conservative preparation technique, approximately 70% to 100% of her natural enamel remained intact in the preps. The 2 PVS wash impressions were finalized and and poured up in CAM-base stone (Garreco; Figure 4). Rather than immediately taking separate optical impressions of all 8 of the prepared teeth, I injected an acrylic temporary material (EXACTA Temp Xtra [EXACTA Dental Products]) into a PVS impression of the patient's preoperative dentition. The patient's temporary veneers were made using EXACTA Temp Xtra and cemented in place; the patient was then dismissed.

Next, the optical impressions of the patient's prepared teeth were taken from on of the CAM-base stone models of the preparations. This is an example of timeshifting in action. Instead of taking individual optical impressions of the patient's actual 8 veneer preparations in her mouth, which would have required her to sit for an extra 15 to 20 minutes, I let her go and took the optical impressions from the stone preparation model. This saved time for her and shaved time off the total procedure. Once the optical impressions of the preps were taken, another CAM-base stone model was fitted with and EXACTA Temp Xtra copy of the diagnostic wax-up teeth. This EXACTA Temp Xtra model was used as the correlate model, because the CEREC computer will design the veneers based on this model. The model was sprayed with IPS Contrast Spray (Ivoclar Vivadent), which enables the CEREC to capture an accurate image of each tooth (Figure 5). Once the preparation image was captured for for one tooth, an optical impression of the correlate was taken (Figure 6).

Next, the CEREC software combined the preparation images and the correlate images to form the basis of the veneer designs (figure 7). The computer proposes a veneer design (Figure 8) for each of the 8 teeth, which will require minimal to no adjustments since they are based on data obtained from both the ideal diagnostic wax-up and the preparation models. Once satisfied with the veneer designs, each tooth is virtually separated from its mesial and distal neighbors (Figure 9), and they are now ready to be milled out of separate blocks of all-ceramic materials (ProCAD 100 [Ivoclar Vivadent]) by the CEREC milling machine (Figure 10). This material was selected due not only to its aesthetic properties, but also for its inherent strength and fracture resistance that has been shown to increase after oven-glazing, which is a process these veneers would undergo during the porcelain cut-back and characterization phase at the lab. 2

Upon completion of milling, the veneers were tried-in on a stone model of the preparations (Figure 11) and then taken to the lab for finalization. This included beveling back the incisal one third to incisal one half depending where we wanted enamel characterization. A putty index was used to transfer the incisal edge position from the diagnostic wax-up (Figure 12). We were able to create dentinal structure form by adding porcelain using add-on porcelain kit containing color modifiers (Ivoclar Vivadent) and IPS Style shade and stain kit used for ProCAD blocks (Ivoclar Vivadent). After they were fired in a vacuum furnace (QEX [Ney]) for 15 minutes, and additional enamel porcelain layer was placed over that modified veneer, vacuum fired, and glazed. They were then shipped back to the dental office via courier.

Wednesday morning, just 2 days after her prep appointment, the patient returned to the dental office for placement of the final restorations. Upon anesthesia with a single palatal injection for her maxillary 6 anterior teeth and a buccal infiltration for her bicuspids, her temporaries were removed and the preps were cleaned and readied to accept the veneers (Figure 13). Before cementation, the underside of each veneer was gently air-abraded with a 50-µm alpha-aluminum particle using a Danville Micro Etcher. This created a roughened texture and increased the surface area to enable maximum adhesion with the bonding agent. Next, the undersides of the veneers were treated with 5% hydrofluoric acid-etch, followed by the application of Clearfil Porcelain Bond (Kuraray Dental). Each tooth was etched with 32% phosphoric acid etchant (UNI-ETCH [Bisco]) for 15 seconds and then washed for 20 seconds using water. Nexus 2 base clear enameling cement (Kerr) and OptiBond Solo Plus bonding agent (Kerr) were used; the bonding agent was light-cured using the Blue-phase curing light (Ivoclar Vivadent), excess cement was removed with a hand scaler and No. 12 Nard-Parker, and adjustments were made using a red stripe finishing diamond. The veneers were polished using Ceraglaze polishing cups and points (Axis Dental).

The patient's teeth were examined at a recall appointment 2 weeks later. She reported no problems or functional issues, and loved her new smile (Figures 14 and 15). Her gingival tissue also demonstrated excellent healing.

Conclusion
Incorporating the use of proven, high-tech tools and equipment in complex procedures assists the clinician in achieving favorable outcomes. Some of this success can be attributed to the nature of computers and their ability to simulate real-world conditions in a controlled, digital environment, an environment where we can shift time to the future, allowing us to see end results on-screen before we apply the "digital steps" taken to get those results into practice reality. Computers allow us to ask "what if?" and then test - and verify - our theories in virtual simulation. If the results are not what we anticipated, we hit the "undo" button and try again until the results are right. This degree of end-result predictability can lead to a higher level of treatment acceptance and patient satisfaction by way of streamlined, efficient, and more confident approaches to treatment, with demonstrable outcomes.

References

1.	Kois J, McGowan S. Diagnostically generated anterior tooth preparation for adhesively retained porcelain restorations: rationale and technique. J Calif Dent Assoc. 2004; 32:161-166.
2.	Chen HY, Hickel R, Setcos JC, et al. Effects of surface finish and fatigue testing on the fracture strength of CAD/CAM and pressed ceramic crowns. J Prosthet Dent. 1999:82:468-475.