Table of Contents

Periodontics

Inside Dentistry

July/August 2006, Volume 2, Issue 6
Published by AEGIS Communications

PFM and All-Ceramic Restorations: Examining the Trends in Clinical Practice

Allison DiMatteo, BA, MPS

Today’s discussions about porcelain-fused-to-metal (PFM) or all-ceramics—specifically today’s higher strength zirconia core options—are not about whether either is better or worse than the other. Rather, they’re about preference, confidence, and convenience.

“The PFM is the gold standard of crown and bridge,” comments Roger Levin, DDS, the CEO of Levin Group. “They hold up well; they’re easy to prescribe and place; and they’re predictable. At the same time, the PFM has always had one limitation, and that’s esthetics.”

In the last 5 years, the dental industry has changed significantly with the advent of CAD/CAM and zirconia substructures, says Kerri M. Sebring, director of marketing for DENTSPLY Prosthetics Division. Clinicians are increasingly moving from single-unit PFMs toward single-unit all-ceramic zirconia restorations because they enable similar chairside cementation and preparation options, and the biocompatibility, fit, and esthetics of these restorations are appealing to clinicians, she says.

“What’s happened is that as the opportunity to create better-looking restorations and prosthetics developed, dentists jumped on it,” Levin observes. “We experienced the same excitement when composites were introduced; it was something new to restore teeth with that was attractive and tooth-like, and it was a phenomenon for the profession as well as the patient.”

Though the numbers of clinicians prescribing all-ceramics instead of PFMs is increasing, it’s a slow-moving tide. According to Jim Shuck, vice president of sales and marketing for Glidewell Laboratories, only about 5% to 7% of the laboratory’s dentists are routinely using zirconia-based all-ceramics.

“It’s still a very small part of the marketplace, but it’s where the area of interest is,” Shuck says.

Within the various all-ceramic categories—densely-sintered aluminum-oxide, reinforced pressed ceramics, silica-based ceramics, glass-infiltrated aluminum-oxide, and zirconium-oxide—there are more options available today than 10 years ago. With more options being widely advertised and promoted, clinicians are paying more attention to all-ceramics as a restorative option, notes Bob Vartanian, vice president of sales and marketing for Trident Dental Laboratories.

“There has been a synergy of attention by all-ceramic companies,” Vartanian explains. “The more all-ceramic brands available for patients, the more demand we’ll see being created for them.”

To that end, genuine interest in the all-ceramic opportunities available has been fostered in part by heavy advertising from manufacturers and laboratories alike, Shuck says. All of the “all-ceramic” messages are making dentists more aware of the possibilities.

“The all-ceramic restoration has gone from being an incipient, new, disruptive technology to a mainstay, and I think that trend is going to continue to the point where we probably won’t do a lot of PFMs,” predicts Levin. “The materials are better; the fracture rates are lower; and they are beautiful. The more companies that introduce all-ceramic restorations and apply pressure to the marketplace, the more we’ll begin adopting all-ceramic restorations. I think we are well into the adoption curve at this point.”

According to Norman Hammer, DMD, a clinical professor of postgraduate pros­thodontics at Tufts University School of Dental Medicine, the all-ceramic restoration has become the well-accepted treatment modality for teeth in the anterior part of the mouth and often in the posterior as well. With the all-ceramic restoration, optimal esthetics that closely resemble the natural tooth can be achieved, he says. Also, in the hands of a competent laboratory technician, often the all-ceramic restoration becomes indistinguishable from the natural dentition, he adds.

However, the PFM restoration still has a place in the dentist’s armamentarium, advises Hammer. Although over the past 20 years there has been a shift from metal-ceramic restorations to all-ceramic restorations, the dental practitioner may still prefer to prescribe a PFM as a predictable, functional restoration for the posterior segment of the mouth, particularly if esthetics is not a critical issue, he says.

DRIVING TOWARD CHANGE

The movement toward all-ceramics is, again, about esthetics. Levin explains that esthetic dentistry is shifting from being a niche area offered to a limited number of patients to being something incorporated into the bulk of dental work performed on a daily basis.

Additionally, Hammer says, patients are becoming more concerned about the biocompatibility issues surrounding different materials used in medicine and dentistry.

“Although there is no evidence to substantiate a biocompatibility problem with the currently, commonly used alloys in metal-ceramic restorations, patients feel better when they know they are receiving an esthetic, functional, and metal-free restoration,” Hammer explains.

The two most significant advances in the all-ceramic restoration, he says, have been the constant improvements in the marginal integrity and strength of these restorations.

“Twenty-five or 30 years ago, accurate and predictable margins could only be achieved with a gold crown, which has become the ‘gold’ standard that we compare to,” Hammer observes. “Today, the all-ceramic restoration, through improvements in laboratory technology, has become a clinically acceptable restoration because the marginal integrity is now accurate. Additionally, with improvements in ceramic technology and the introduction of zirconia—the ‘ceramic steel’ of the dental profession—all-ceramic crowns can now be fabricated that have strength and physical properties that are greater than the metal-ceramic restoration.”

Vartanian comments that some clinicians believe they need the strength of a PFM in the posterior, where there are biting forces and mastication issues, so they’re more willing to put an all-ceramic restoration in the anterior. However, he says, “Zirconia now has been proven to be as hard as any metal out there, so it’s just a matter of dentists experiencing it and seeing for themselves that patients won’t come back with chipped or broken down crowns.”

Sebring echoes that observation, noting recent trends in the marketplace and the advent of CAD/CAM systems that use zirconia substructures. Those substructures, she says, are in many cases equivalent in strength to a metal substructure.

Additionally, clinicians want to cement all-ceramic restorations the same way they would a PFM, says Arlo H. King, CDT, director of laboratory services for DENTSPLY Prosthetics Division. Today’s zirconia restorations enable conventional cementation as opposed to adhesive bonding.

“This is one of the major reasons that zirconia is being accepted so well in the marketplace—ease of cementation,” King observes.

Shuck explains that with the advent of the new zirconia-based all-ceramics, which are stronger than earlier all-ceramic materials and the closest thing to the PFM that dentistry’s seen to date, the industry finally has a material for single-unit crowns anywhere in the mouth, as well as three-unit bridges. There are still some limitations on size for some of the zirconia systems (ie, green state), he says, but future technological advancements—such as ultrasonic milling—could make the use of pre-processed, super-hard zirconia a more realistic option for certain indications.

CLINICAL & MATERIAL CONSIDERATIONS IN THE DECISION PROCESS

Whether the restoration is a fully pressed all-ceramic porcelain veneer or a zirconia-based all-ceramic restoration, clinicians choose all-ceramics for esthetic reasons because there is no metal involved, explains Sebring. All-ceramic restorations also offer the benefit of patient comfort when there may be sensitivity or allergy issues related to the metals contained in PFMs, she says.

Jim Buchanan, the US sales and marketing manager for 3M ESPE, explains that with today’s higher-strength, glass-free, all-ceramic materials—like zirconium dioxide—there is also the potential for less tooth reduction. Restorations fabricated from this material require thinner copings or walls than traditional all-ceramic materials, which could potentially enable clinicians to leave more natural tooth structure intact, he says.

When faced with the decision to select a PFM or an all-ceramic restoration, King encourages clinicians to prescribe a material or restoration based on its indications. Pressable ceramics, he says, typically are indicated only for the anterior region for single units only (eg, laminate veneers). When bridges are required—regardless of whether anterior or posterior—then zirconia would be the all-ceramic material of choice, he says.

“If we are comparing conventional ceramics, feldspathics, and pressables directly to a PFM, then there are definite limitations because these materials don’t demonstrate the strength requirements that the new glass-free all-ceramics do,” notes Buchanan. “With polycrystalline zirconium oxide materials, that limitation has been significantly reduced.”

However, there are clinical circumstances for which choosing a PFM may be a matter of selecting the most appropriate restorative option for the indication, King emphasizes.

“Large-span bridges containing more than two floating pontics between the abutments would be better suited for a PFM based on the strength and material properties of those restorations,” explains Sebring. “There just is not sufficient clinical history yet with the zirconia material to feel confident that it would be a good long-term choice for long-span bridges with more than two pontics.”

Or, consider cases of patients with a strong bite, who have lost vertical dimension over time, and may even have generated a posterior group function. “In these instances, I would most likely prescribe a metal-ceramic restoration for the posterior, possibly one that even has a metal occlusal component, to be a predictable restoration—one that will function over time,” explains Hammer.

Additionally, if a patient presents with an existing PFM restoration for which the tooth has already been prepared and there isn’t sufficient tooth structure remaining to perform the correct preparation for an all-ceramic restoration (ie, chamfer/shoulder margin), then perhaps a replacement PFM would be indicated based on the limitations of some ceramic systems, says Buchanan. Also, if a patient presents with a very short gingival/incisal height, a standard PFM may be more appropriate, but the decision regarding restorative options should be based on the particular case and the limitations of the materials being considered, he points out.

“If you’re considering a weaker type of ceramic material, then more aggressive preparations are required compared to what’s necessary for higher-strength all-ceramic materials,” Buchanan explains. “So, clinicians must assess the limitations of the ceramic options they’re considering, the particular tooth to be restored, and the patient’s case overall to determine the best restorative treatment.”

Levin adds that as a clinician, dentists select the best solution for the clinical problem. When it comes to PFMs or all-ceramics, the decision is between a long-standing, very well-proven, and established methodology and a newer, proven, and established methodology.

“There may be a situation where a PFM is a better choice, and there may be a case where an all-ceramic restoration is the better choice,” Levin comments. “In either case, we know that we have to use clinical judgment to the best of our ability.”

It’s understood that clinicians must balance a patient’s esthetic desires with their functional needs. In the anterior area of the mouth, esthetics is often the main concern when prescribing a restoration, Hammer says. With all-ceramic restorations, the esthetic desires of the patient can be satisfied and, with the improvements to physical properties reflected in today’s all-ceramic materials, function is not compromised, he explains.

“The metal-ceramic restoration has certainly improved over the years, mostly through advancements in the porcelains that are fused to the metal substructure,” Hammer says. “These advances have led to improvements in the esthetic quality of these restorations.”

However, in the posterior segment of the mouth, function must be the primary concern; esthetics is less important. Despite the advancements in all-ceramic restorations, for patients presenting with occlusal considerations, the metal-ceramic or even all-metal restoration is still the restoration of choice, Hammer notes.

Shuck recalls that early all-ceramic alternatives—not zirconia—were not necessarily the best option when discolored teeth or preparations were present. Such circumstances would require subopaquing which, he says, sometimes wouldn’t work well. In those cases, the PFM was a better choice for masking a metal post or discolored tooth.

When questions arise regarding material indications and optical properties, Shuck encourages clinicians to discuss their case needs with their laboratory. For example, if there are limitations on how much tooth structure can be prepared (eg, a younger patient with a large pulp chamber), one all-ceramic product may be preferable over another because desirable esthetics and predictable function can be achieved with thinner dimensions.

“I think consultation with a laboratory about what products they work with, what their experiences have been, what the indications are, and what the feedback has been from other customers can provide dentists with a good amount of information,” Shuck believes.

THE QUESTION OF COST

“There are materials out there that can give you the same strength and better esthetics,” Vartanian says. “Whether it [an all-ceramic restoration] costs more or not remains to be determined depending on what type of PFM you would have otherwise prescribed.”

According to Sebring, laboratories may incorporate into their all-ceramic fees anywhere from a 10% to 20% premium for a zirconia restoration compared to a PFM restoration for two reasons. First, in order to fabricate these restorations, the laboratory must first invest heavily in the CAD/CAM technology necessary to design and manufacture the all-ceramic zirconia coping. Secondly, if the laboratory chooses to outsource the fabrication of the zirconia coping, the charges it incurs for that service must be recovered.

“There is generally not a daily fluctuation,” Sebring explains, “but there is a premium charge for the accuracy, consistency, and fit of the CAD/CAM zirconia restoration.”

Shuck explains that pure zirconia as a material is more expensive, as are the machinery and equipment necessary to process it. Premiums that laboratories pay for these restorations could range from $30 to $40, which is essentially the material cost paid to a manufacturer, he says, and doesn’t include the costs associated with the processing tools that the laboratory needs. Therefore, it’s possible for a porcelain-to-zirconia restoration to cost an estimated average of $175 per unit in the United States, Shuck says.

For this reason, dental laboratories are beginning to introduce their own brands of 3% yttrium-stabilized, high-strength zirconia restorations at a lower cost in order to provide their PFM customers with a less-expensive opportunity to try this option. By reducing the cost, more dentists may be willing to try higher-strength all-ceramics and fit them into their practices.

However, Dan Krueger, professional relations manager for 3M ESPE, points out that doctors may experience some confusion when it comes to identifying and prescribing “zirconia” restorations. Within the zirconia category itself are variations of zirconia content.

“When doctors ask for zirconia, they can get anything from a restoration that is pure zirconia with a very high strength to something that is glass ceramic with zirconia added into it,” Krueger explains. “So, it’s not so much a premium that is being charged; you are actually talking about two different product materials all together, each with different strengths and different translucencies.”

Affecting the cost of PFM restorations, on the other hand, are various factors, not the least of which is the sky-rocketing price of precious metals. In early May, gold prices reached their all-time 25-year high of over $712 (US) per ounce (www.goldprice.org). On May 17, the price had dropped to $692 (US) per ounce.

Regional location plays a factor in PFM costs as well. As a result, it’s not unheard of to see a PFM restoration fabricated with precious metal substructures that costs more than an all-ceramic restoration.

“With the price of gold going up constantly and laboratories needing to add surcharges, precious-metal PFMs are like a runaway train,” Vartanian says. Therefore, clinicians are left to “wait and see” what the surcharges will be before they can put a price together for the patient of what their precious metal-based PFM restoration will cost.

The price of a PFM fluctuates on a daily or weekly basis, depending on the precious metal content of the restoration prescribed. So, if dentists prescribe a PFM coping with a very high gold or palladium content, a significant surcharge could be paid for the quality of metal involved in the restoration. If a non-precious metal PFM is prescribed, then that would be subject to a flat rate price.

However, Shuck sees an opportunity in the fluctuating precious-metal pricing for more dentists to try to the stable, flat-rate priced zirconia restorations.

“We may find more dentists prescribing a trial crown or two fabricated from the more competitively priced zirconia products because at least they will have price consistency,” Shuck explains. “The price of zirconia doesn’t fluctuate the way gold does, so dentists would have an opportunity to evaluate zirconia’s benefits—metal-free, better light transmission and illumination, natural-looking esthetics—for themselves.”

THE INFLUENCE OF INSURANCE

Vartanian explains that most patients today—especially those with HMO dental insurance plans for whom a set fee is established for certain types of restorations—don’t know or have a say in what type of restorations are placed in their mouths. Whatever is approved by the insurance company for the set fee allowed is what will be placed. The dentist will determine—based on that limitation and the economic constraints of the patient—what can be placed restoratively, he says.

Patients paying on a fee-for-service basis, however, may present with other expectations and be willing to pay for them, Vartanian explains. In those in­stances, clinicians will likely discuss a range of restorative options.

King elaborates that different insurance plans will pay for PFMs but may not have the same universal rate for all-ceramic restorations. Sebring explains that the American Dental Association provides annual recommendations to insurance companies regarding appropriate reimbursement for dental procedures that are constantly being updated and modified.

“With the advent of new materials and research findings that support clinical predictability, it is conceivable that, at some point in the future, the reimbursement rate for all-ceramic restorations could become comparable to that for PFMs,” Sebring says. “In some cases, depending on the insurance company, they already are comparable today.”

King points out, for example, that based on clinical research started in 1998, high-strength zirconia restorations have been shown to have the same success rates as PFM restorations. He suggests that as the industry becomes more accustomed and comfortable with these success rates—and similar results are increasingly reported—insurance reimbursement for all-ceramic restorations will be adjusted.

CONCLUSION

When it comes to deciding between PFMs and higher-strength, all-ceramic restorations, clinicians are no longer faced with as many limitations as in years past, emphasizes Krueger. In fact, all things being equal, clinicians can look at either type and confidently select the high-strength, all-ceramic alternative.

“With the high-strength zirconia, clinicians have the flexibility to use conventional cementation using glass ionomers, resin-modified glass ionomers, or resin cements,” Krueger says. “They have a lot of flexibility, and they really don’t have the limiting factors any more.”

Prompting increased interest in zirconia, Shuck says, is the tremendous amount of ongoing research taking place that is validating its long-term use and function for specific indications.

“Researchers are really putting zirconia through its paces and, from what I’ve seen, there has been more worldwide research conducted on zirconia than any other restorative product in the last 25 years,” Shuck admits. “And I think it was needed, because we’ve had some restorative systems in the past that didn’t live up to their expectations, but so far, zirconia is doing well.”

Levin notes that deciding between a PFM restoration and an all-ceramic rest­oration is not about choosing one over the other because there’s a problem. Rather, it’s about the opportunity that’s created because all-ceramics are more esthetic. And, he says, there may be times when you want to give the patient the choice.

“We are an evolving profession,”Levin explains. “We are becoming much more of a profession for which esthetics is tied directly into our work, not considered as an adjunct to it.”