Materials
What Can We Offer Patients With Today’s Advancements in Dental Materials?
Christopher B. Marchack, DDS
Christopher B. Marchack, DDS, is an associate clinical
professor in the Department of Continuing Education at the University
of Southern California.
Copyright 2003 Journal of the California Dental Association.
The dental materials and techniques used in the treatment of patient "A.K."
25 years ago have historical significance. The use of metal-ceramic restorations
was the norm and considered state of the art. Since their introduction
by Weinstein and colleagues in the early 1960s, porcelain-bonded-to-gold
alloys have been a breakthrough in dental esthetics and porcelain restorations.1,2
This patient’s treatment with metal-ceramic restorations was the evidence-based
treatment of its day and the standard of care. It still is. As new techniques
have evolved, many other restorative options have established a growing
body of evidence of success.
All-ceramic restorations have evolved from the porcelain jacket crowns of the 1960s to the CAD/CAM restorations of today, using high-alumina-reinforced ceramics or zirconium-reinforced ceramics as cores instead of metal or gold. The first breakthrough in all-ceramic restorations, without a significant sacrifice of strength, is the In-Ceram restoration. In-Ceram is an infiltrated high-alumina core material. A diffusion of glass fills the spaces between the alumina particles creating a 72 percent concentration of alumina in the core, which is then veneered with feldspathic porcelain.2,3 A prospective clinical trial study shows the three-year survival rates of In-Ceram restorations to be 98 percent for anterior crowns and 94 percent for premolars or molars. The reasons for lost crowns were core fractures, porcelain fractures, and removal without failure.3
The difficulty with any of the high-alumina systems is control of shrinkage.2 In 1993, Andersson and Odén developed a manufacturing process to fabricate copings with a dense sintered high-purity alumina of 99.9 percent. The technique uses a contact scanner and a copy-milling machine to develop a 12 percent to 20 percent enlarged die of the tooth preparation. In a manufacturing center, high-alumina powder is compacted against the die, and the unsupported coping is sintered at 1,550 degrees Celsius for one hour, resulting in a highly dense sintered alumina coping that is the core for a Procera AllCeram crown.4 The coping is returned to the local dental laboratory for the technician to apply the porcelain veneer. A prospective multicenter study of 12 clinicians looked at the cumulative survival rates of these crowns over a period of five to 10 1/2 years. The survival results were 97.7 percent and 93.5 percent respectively, with a cumulative success rate of 97.7 percent.5 Their results were similar to other all-ceramic alumina core studies.
The later years of A.K.’s treatment show the placement of two dental implants restored with a metal-ceramic fixed partial denture. Studies have shown that this treatment requires a passive-fitting restoration to help prevent unstable or loose gold screws, implant fractures, and other mechanical complications.6,7 Creating a passive-fit implant prosthesis by the lost-wax technique has a wide range of variables, which starts with the fabrication of the impression, creating the master cast, making the casting, and soldering techniques, and ends with the application of porcelain.6,8 With the use of the computer numeric-controlled milling technique, it is possible to fabricate a solid one-piece titanium framework (Procera Implant Bridge) that is milled to shape instead of a cast-gold framework.9 This process eliminates the casting and soldering problems and the possible distortion after the firing of dental porcelain to the framework. Studies have compared the computer numeric-controlled-milled frameworks to conventional castings on master-cast replicas and found no significant differences. Therefore, the advantage of this technique is to eliminate the multiple problems with distortion inherent in the lost-wax casting technique, soldering, and dental porcelain application.10
As the years pass, there is an ever-increasing number of technological advances in dentistry, especially in materials. The use of all-ceramic restorations instead of metal-ceramic restorations is increasing, with new ceramic restorations on the horizon, such as zirconium copings. The longest studies, however, are only 10.5 years, whereas metal-ceramic restorations have been used since the late 1960s and have more than 25 years of treatment success, as seen with A.K. All these new techniques and materials have provided great advances in esthetics, precision, and time savings; but it will take time and research to develop evidence-based treatments for the predictable, successful restoration.
References
1. Weinstein M, Katz S, Weinstein AB, Fused porcelain-to-metal teeth. US patent 3052, 982, 1962.
2. McLean J, Evolution of dental ceramics in the 20th century. J Prosthet Dent 85:61-6, 2001..
3. McLaren E, White S, Survival of In-Ceram crowns in a private practice: A prospective clinical trial. J Prosthet Dent 83:216-22, 2000.
4. Andersson M, Odén A, A new all-ceramic crown. A dense-sintered, high-purity alumina coping with porcelain. Acta Odont Scand 51:59-64, 1993.
5. Odman P, Andersson B, Procera AllCeram crowns followed for 5 to 10.5 years: A prospective clinical study. Int J Prosthodont 14:504-9, 2001.
6. Goodacre CJ, Kan JY, Rungcharassaeng K, Clinical complications of osseointegrated implants. J Prosthet Dent 81:537-52, 1999.
7. Skalak R, Biomechanical considerations in osseointegrated prostheses. J Prosthet Dent 49:843-8, 1983.
8. Goll GE, Production of accurately fitting full-arch implant frameworks: part 1 -- clinical procedures. J Prosthet Dent 66:377-84, 1991.
9. Jemt T, Three-dimensional distortion of gold alloy castings and welded titanium frameworks. Measurements of the precision of fit between completed implant prostheses and the master casts in routine edentulous situations. J Oral Rehabil 74:284-93, 1995.
10. Jemt T, Bäck T, Petersson Anders, Precision of CNC-milled titanium frameworks for implant treatment in the edentulous jaw. Int J Prosthodont 12:209-15, 1999.
To request a printed copy of this article, please contact: Christopher B. Marchack, DDS, 301 S. Fair Oaks Ave., Suite 408, Pasadena, CA 91105-2536.
Legends
Figure 1. Internal aspect of a Procera Zirconium core crown.
Figure 2.Solid milled titanium framework, prior to metal finishing.
Figure 3. Procera implant bridge framework, prior to porcelain application.
