Better Clinical Outcomes: Embracing New Technologies, Techniques and Materials

Contemporary Esthetics, January 2005

We live ins a time of rapid and continuous change. In dentistry, the changes that successfully integrate into the mainstream dental practice are those that provide the greatest benefit to patients by improving the esthetic longevity of their dentition. High-tech solutions need to fulfill different criteria to success during today's technological revolution. These new products must be durable, possess nothing less than a precision margin, and stand up to the stresses of the oral cavity. These products need to be esthetic, enhancing the individual smile, and durable, so that the improved smile will stand the test of time. Additionally, the patient experience should be as minimally traumatic as possible and accomplished in the smallest number of appointments.

Successful new products are the ones that meet these patients needs, while allowing both the practitioner and laboratory to routinely produce the most accurate fitting, esthetic restorations possible. This enhanced efficiency results in lower overhead and increases the bottom line. When it comes to machinable ceramic, the dentist simply preps with a conventional all-porcelain-margin; there is no learning curve.1, 2 The laboratory scans the die and uses the user-friendly software to design and mill the zirconia framework. When technological developments such as these make it to the dental marketplace and are easily learned, there is success.

Views on the importance of dental care have undergone extensive revision since the author graduated from dental school 24 years ago. To stay on top of the curve and deliver the best dentistry has to offer his patients, the author had to become comfortable with change and search out the systems that best meet the patient's need and would enable him to provide esthetic, easy-to-experience, time-efficient restorative care. The challenge is to do this in as cost-effective a manner as possible. Recent advances in the machining of all-ceramic restorations have helped to make these scenarios a reality.

The machining of ceramic restorative materials is coming into its own as a way to provide precision-fitting restorative components.3 The machining of implant parts is a perfect example of how this process can provide components with the best fit in dentistry.4 For example, a milled substructure implant bar, easily fabricated from an impression, fits better and more predictably than one that has been waxed and cast.5 Similarly, these principles hold true with indirect milled restorations. With the explosion of different machining systems, the milling of zirconia porcelain blocks for crown and bridge frameworks produces a more esthetic and durable restoration with outstanding fit.6 With a zirconia framework, the darker dentin color can be blocked out without having to use the opaque layer necessary with metal frameworks.

Following is a case study of a patient who had worn a maxillary removable partial denture for more than 20 years and was demanding a more esthetic, nonremovable solution. He had just retired from a 25-year career as a police officer and decided to have an "extreme dental makeover." After researching his options, implant reconstruction was ruled out, opting instead for and esthetic bridge. Additionally, he desired to correct the intrinsic yellow staining of his cuspid and bicuspid teeth.

Case Study

A 52-year-old African American man presented, desiring to replace his maxillary removable partial denture with a fixed maxillary partial denture. He also requested esthetic treatment of the deep yellow staining to achieve the best smile possible in a manner that would fit his budget, which precluded implants. Following the initial examination, a full series of digital x-rays, including a panoramic, were performed. The patient was presented with all the options of treatment of the replacement of teeth Nos. 10 and 11, using the CASEY Patient Eduction System (Patterson Dental Supply, Inc). He chose a fixed partial denture and single-appointment, machinable, ceramic veneers. Diagnostic models were made and reviewed at the consult visit to ensure that both dentist and patient expectations could be met. The use of diagnostic models was also beneficial to facilitate communication between the patient, dentist, and laboratory technician.

After achieving anesthesia, the teeth were prepared (Figure 2) using an electric high-speed handpiece. The traditional amount of reduction and retention was included in the preparations to ensure adequate thickness of porcelain and mechanical retention.

Because the bridge was a relatively long five-unit bridge, spanning teeth Nos. 9 through 13 and located in the anterior region where it would be subject to the forces of mastication, a high-strength substructure was a necessity. A traditional impression was taken and sent to the laboratory, and a CEREC inLab (Sirona Dental Systems) five-unit bridge, using high-strength zirconia material for the coping framework was prescribed. It is this author's opinion that the only other CAD/CAM system available that can produce a five-unit bridge is the DCS CAD/CAM Machining System (Popp Dental Laboratory, Inc). The key to success with a zirconia substructure is directly related to how much height can be achieved at the connectors. The connectors get their strength from the thickness; therefore a long-span bridge needs to have enough height.

Next, a model of the impression was poured at the laboratory using laser-visible stone. When hardened, the die was trimmed and placed into the CEREC inLab scanning/milling unit and scanned into the computer (Figure 3). After scanning, the "digital impression" appears on screen, ready for a framework to be designed using the CEREC inLab 3D software (Sirona Dental Systems). Using the software's automatic margin detector, the margin of each crown abutment is delineated and defined (Figure 4). Because teeth Nos. 10 and 11 were missing, the laboratory technician used the three-dimensional design software to establish and ideal margin shape for the two pontics that serve as the foundation for the porcelain buildup. After the margins are established for each abutment and pontic, the software automatically proposes the design of the entire framework (Figure 5). When the laboratory technician verified the entire framework design, a single, solid 40-mm zirconia block is placed into the CEREC inLab milling chamber, where it is precision-milled in a matter of minutes. After milling, the framework was removed from the chamber and placed on the stone preparation model to test for fit (Figure 6). Next, buildup was achieved using Vita VM7 porcelain (Vita Zahnfabrik; US Distributor, Vident) (Figure 7). A completed five-unit bridge seated on the stone model is shown in Figure 8.

The bridge was then sent back to the dentist and tried-in at patient recall. No adjustments were necessary, and the bridge was permanently seated using Panavia 21 (Kurray America, Inc) dental adhesive. The final restoration demonstrates excellent fit, finish, and natural esthetics that are common characteristics of the CEREC inLab long-span zirconia bridge (Figure 9).

Conclusion

To stay competitive in an environment where change is the only constant, dental professionals must keep an open-minded approach to the natural evolution of their practice. New technologies, techniques, and materials should be considered and - when proven practical, profitable, and clinically sound - embraced as a welcome addition to any progressive dental practice. Reluctant patients and those who do not readily accept treatment recommendations are often more accepting of treatment alternatives when they realize they have a range of options that meet their expectations. In this case, the patient was not happy with his current removable partial denture - he detested the metal and requested a metal-free restoration. His financial situation had improved because he first chose the denture, but it was not so much improved as to deem implants a likely option. Therefore, a viable alternative that met both patient's concerns for esthetics and affordability was found by choosing an all-ceramic, laboratory-fabricated, CEREC inLab, five-unit anterior bridge. As demonstrated, the high strength and impressive esthetics of a machinable zirconia substructure not only make it the ideal choice for a long-span bridge framework, but also permits ultra-thin "knife-edge" margins that allow for a fine feathering of porcelain buildup without concern about fracturing or dark lines at the margins.

References

1.	Kurbad A. CEREC goes inLab-the metamorphosis of the system. Int J Comput Dent. 2001;4(2):125-143.
2.	Fasbinder D. Utilizing lab-based CAD/CAM technology for metal-free ceramic restorations. Dent Today. 2003:22(3):100-102,104-105
3.	Various authors. Clinical efficacy of CEREC 3 all-ceramic restorations: a 20-year history of peerless performance. Sirona Dental Systems White Paper, 2004
4.	Tinschert J, Natt G, Mautsch W, et al. Marginal fit of alumina- and zirconia-based fixed partial dentures produced by a CAD/CAM system. Oper Dent. 2001;26(4):367-374.
5.	Ortorp A, Jemt T, Back T, et al. Comparisons of precision of fit between cast and CNC-millled implant frameworks for the edentulous mandible. Int J Prosthodont. 2003; 16(2):194-200.
6.	Giordano RA 2nd. CAD/CAM: overview of machines and materials. J Mass Dent Soc. 2002; 51(1):12-15.