As you scan a current dental journal, you cannot avoid being confused as you see numerous ads for tooth-colored, non–metal-containing crowns and fixed prostheses, most of which proclaim to the dental world their superiority over other brands. Some brands even challenge the venerable porcelain-fused-to-metal, or PFM, crown or fixed prosthesis.
Are you behind in your clinical practice if you are still using PFMs? Is it time to change to all-ceramic or resin-based composite crowns as a routine procedure? A discussion and comparison of the new materials was published recently.1 How do these new crowns and fixed prostheses compare with the state-of-the-art PFM crown?
This article includes an overview of the available types of tooth-colored, non–metal-containing crowns and fixed prostheses and makes suggestions about the most appropriate clinical situations for their use.
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CURRENT USE PATTERNS
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A recent discussion I had with one of the administrators of a major U.S. dental laboratory (oral communication, Jim Schuck, vice president of sales and marketing, Glidewell Laboratories, June 2003) showed the following characteristics in the approximately 363,000 crowns the laboratory made from January to June 2003:
- – PFM, 65 percent;
- – all-ceramic, 23 percent;
- – gold alloy, 8 percent;
- – resin-based composite, 4 percent.
Compared with activity at the same laboratory three years ago, use of PFM units is down a few percentage points; use of all-ceramic units is up several percentage points; gold alloy use is about the same as before; and resin-based composite use is down a few percentage points. In other words, there has not been an enormous change in use of the categories of crowns and fixed prostheses. However, numerous new types of tooth-colored crowns and fixed prostheses appear to have promising potential and should be considered.
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WHY CHANGE?
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Are you satisfied with the service your patients receive from PFM restorations? Are you satisfied with the esthetic result of PFM restorations? If the answer to both questions is yes, you have only a few reasons to consider any change from PFM.
Esthetic results.
It is well-known that pressed-ceramic restorations have the potential to create excellent esthetic results. Most technicians and clinicians agree that on a day-today basis, the esthetic result obtained with pressed-ceramic restorations is better than the result obtained from PFM crowns made by a typical dental technician. However, the strength of pressed-ceramic restorations is significantly less than that of PFM crowns. In my opinion, if a patient needs a single crown in the anterior portion of the mouth, the odds of creating an optimal esthetic result are better with a pressed-ceramic restoration than with a PFM. If a number of single crowns are needed in the anterior portion of the mouth, and ceramic margins are placed on the PFM crowns, an optimum overall esthetic result may be obtained with PFM crowns.
A popular brand of pressed-ceramic restoration is IPS Eris (Ivoclar Vivadent, Amherst, N.Y.). There are other brands of pressed ceramic that provide similar high-level esthetic results, including OPC 3G (Pentron Laboratory Technologies, Wallingford, Conn.), Cerinate Porcelain (DenMat, Santa Maria, Calif.), Cerpress SL (Leach & Dillon Products, Cranston, R.I.) and Finesse (Dentsply Ceramco, York, Pa.).
Allergies to metals used in dentistry.
Fortunately, patients who have allergies to metal usually are aware of the fact. Often, they cannot wear metal jewelry without it causing skin irritation. All patients should be asked about this potential problem. Although the all-ceramic restorations have trace components of metal in them, including aluminum, the possibility of the small quantity of these trace elements’ escaping from the fired material and causing an allergic reaction is small. If you are relatively convinced that the person has a legitimate allergy to dental metals, you have several alternatives for both anterior and posterior restorations.
Any of the all-ceramic materials discussed in this article probably would be acceptable for single-unit anterior or posterior restorations for patients with metal allergy. Some all-ceramic products that have had several years of successful use should be considered. One such all-ceramic product is Vita In-Ceram (Alumina or Zirconia versions) (Vident, Brea, Calif.). Restorations of this material have been recognized as strong and esthetic, and Vita In-Ceram’s success is well-documented for single crowns and selected fixed prostheses. These crowns have been especially well-suited to block the dark color of endodontically treated root stumps in a similar manner to that demonstrated by PFMs.
Procera Zirconia (Nobel Bio-care, Yorba Linda, Calif.) is well-known to be strong and is supported by several years of successful use for single crowns. The rapid growth in popularity it experienced after its introduction and continued acceptance is indicative of its potential and usefulness. Resin cements, required by some of the all-ceramic and resin restorations, caused postoperative tooth sensitivity and occasional pulpal death.2 One of the desirable characteristics of Procera Zirconia that contributed to its rapid acceptance by the profession has been its ability to be cemented with standard cements.
If multiple-unit fixed prostheses are needed, the relatively new zirconia-substructure, porcelain-fused-to-ceramic restorations would be good choices. These restorations are beginning to win the confidence of dentists, since some have been observed in clinical research projects for as long as five or six years. They have more strength than previous all-ceramic restorations, and their esthetic potential is good to excellent when compared with that of PFM restorations.
In this category of materials, the product that has motivated the profession to change and has caused significant interest in porcelain-fused-to-ceramic restorations is Cercon (Dentsply Ceramco). This all-ceramic material provides more strength for multiple-unit all-ceramic restorations than has been available before in all-ceramic restorations, and the laboratory procedures required to place fired ceramic on the milled ceramic substructures are similar to techniques used for PFM restorations.
Other similar products are Cerec In-Lab (Sirona USA, Charlotte, N.C.), Lava (3M ESPE, St. Paul, Minn.) and Wol-Ceram (Glidewell Laboratories).
This entire area is evolving rapidly, as companies attempt to achieve the esthetic result of PFM without having the underlying white color of the zirconia understructure show through the fired porcelain. Pigmented internal structures are present in some brands and probably will be available in all brands.
Patients with or without metal allergies and presence of bruxism or clenching.
Placing all-ceramic restorations in patients who have abusive occlusion—regardless of whether they have metal allergy—is inviting premature failure of the restorations and significant wear on the teeth of the opposing arch. In such situations, resin-based composite is a good choice. Fiber-reinforced resin-based composite restorations have been successful on an intermediate longevity basis for treating patients who cannot have metal in their mouths and who have abusive occlusion.
Many brands of resin-based composite have struggled to stay in this marketplace. Only a few have survived the test of time. Two products that have achieved the confidence of practitioners for single and short, multiple-unit clinical situations are belleGlass (KerrLab, Orange, Calif.) and Sculpture/FibreKor (Pentron Laboratory Technologies). Two products that are successful in single units are Cristobal+ (Dentsply Ceramco) and Sinfony (3M ESPE). Other resin-based composite products are available. You should ask your technician which products are available from his or her laboratory and what long-term research or clinical experience is available on them.
It is well-known among experienced practitioners that gold alloy is the best choice for restorations for bruxers or clenchers, but that most patients will not accept the display of metal in their mouths. In my opinion, resin-based composite crowns or fixed prostheses satisfy the need for nonmetal, occlusally kind restorations in the few patients who are allergic to metals and who need tooth-colored restorations. Patients should be advised of the restorations’ potential for wear, as well as of the potential fracture of pieces of the polymer from the underlying fiber-reinforced structure. If bruxers and clenchers demand all-ceramic crowns or fixed prostheses, they should be required to wear a resin nightguard each night and during times of psychological stress.
Fees for all-ceramic and resin-based composite crowns and fixed prostheses.
Premature failure of expensive restorations in dental practice is a considerable problem. Patients should be advised of the relative lack of information on the longevity of some of the non-metal restorations, and they should have reasons (as discussed above) to select these restorations instead of PFM. In my opinion, dentists should set fees at a level that have a "cushion" of income in them to allow occasional replacement of fractured restorations for a minimal fee, or for no fee.
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SUMMARY
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The venerable PFM crown or fixed prosthesis still dominates the tooth-colored restoration market. However, use of PFMs is declining slightly, as the many new all-ceramic and resin-based composite crowns and fixed-prosthesis products flood the market.
Several situations may indicate the use of materials other than PFM. They include patients requiring a high level of esthetic acceptability, patients with proven or perceived allergies to the metals used in dentistry and bruxing or clenching patients with metal allergies or desire to eliminate metal from their mouths.
PFM restorations have been proven during 40 years of successful use. They provide acceptable esthetics for most situations, minimal fracture during service, proven ability to serve in multiple-unit situations and excellent fit, and the profession has detailed knowledge of these restorations’ advantages, disadvantages and physical characteristics. PFM restorations have only a few well-known negative characteristics. Be cautious as you elect to move from the reliability and positive history of PFM to relatively unknown types of restorations.
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CURRENT USE PATTERNS
WHY CHANGE?
