Bright, beautiful smiles are much in demand these days, and not just among celebrities. Inspired by glossy magazine covers and television shows such as “Extreme Makeover,” more and more ordinary people want extraordinarily attractive teeth. They even consider them essential to social and business success. When their smiles fall short, however, they turn to cosmetic dentists. These dentists often recommend porcelain veneers to enhance esthetics, restore tooth structure and function, and even correct some orthodontic problems. Since veneer technology has improved a great deal during the last 20 years, predictability and success rates have improved as well. This has stimulated even more demand. Hence, esthetic dentistry is booming.
For a long time, ceramic veneers were fabricated in a specific way from feldspathic porcelain. About 15 years ago, labs began to use a new fabrication technique, which produced a type of veneer made from a different kind of porcelain. “Pressed ceramic” veneers now compete with the traditional feldspathic variety in the marketplace, and dentists and patients must choose between them.
Which veneer works best? If popular opinion is a guide, pressed ceramics, according to manufacturers and leading labs. The majority of cosmetic dentists now choose pressed ceramic veneers for the majority of cases. Yet some dentists still use feldspathic systems exclusively, and many others prefer them in certain situations. I suspect that the former simply haven’t explored pressed ceramics, which can be clearly superior for many purposes. But the latter select different systems in different situations precisely because they’ve done their homework, and have good reasons for their choices. This article will address some of these reasons. I admit that I’m a devotee of pressed ceramics, specifically MAC Veneers by MicroDental. Although I’ve placed many feldspathic veneers in my career, I now consider them outdated. I respect the opposing point of view, however, and would like to spark a productive debate.
Fabrication
Feldspathic veneers are fabricated from a quartz-type porcelain on a platinum foil or refractory die. Ceramicists use a wet brush and a jar of porcelain powder to essentially paint layers onto a model and then bake it in a porcelain oven. Since each application of porcelain is very thin and shrinks when heated, the process is repeated many times to obtain the proper contour. Ceramicists can lay in different colors at each stage to create the patient’s desired look.
Technicians fabricate pressed ceramic veneers by waxing a tooth to the desired contour, investing it, and melting out the wax. They then inject a leucite-based molten porcelain and apply constant hydraulic pressure to press in additional material as the porcelain cools and shrinks. The process is very similar to fabricating gold, and results in a porcelain ingot that fills out the desired contour in a single color. Ceramicists then can create more natural, less-uniform coloration by cutting back the ingot and painting different colored porcelains in various areas of the tooth.
Advantages of pressed ceramics
Why might ceramic restorations be considered a better choice? Here’s a list of major advantages:
• Strength - Pressed ceramic porcelains are at least two times stronger than feldspathic. This is because the material is cast under heat and constant pressure, which increases the tightness of the particles and makes the material much denser. Hence, pressed ceramic restorations are far more durable and resistant to fracture.
•Versatility - The inherent strength of pressed ceramic porcelain supports a much larger range of treatments and restorations than feldspathic material. For example, dentists can use it, as well as Zirconia materials, in bridges without a metal substructure. Indeed, whereas feldspathic porcelain usually requires a metal substructure for posterior restorations, dentists can use pressed ceramic material in full-mouth reconstruction without any metal at all. Since it is generally more difficult to match porcelain-fused-to-metal crowns with feldspathic veneers elsewhere in the mouth, the all-ceramic option allows dentists to create a far more natural looking uniformity of optical properties among the teeth. Patients are more informed these days and are demanding metal-free restorations; pressed ceramic systems allow dentists to provide these for the entire mouth.
• Wearability - Pressed ceramic porcelain is less abrasive to opposing teeth than traditional feldspathic porcelain. Numerous studies show that many feldspathic materials are far more aggressive against natural dentition and causes far more wear and damage. Pressed ceramic restorations which utilize lower-fusing porcelains are much closer in abrasiveness to natural tooth enamel.
•Fit- Pressed ceramic veneers generally fit better than feldspathic. When fabricating a feldspathic veneer, the technician repeatedly adds layers and fires it in the oven, which causes the porcelain to shrink and often warp. On the other hand, pressed ceramic veneers are waxed to ideal at the very beginning and then pressed, so it is easier to obtain a much tighter marginal integrity and fit.
•Predictability of results - Technicians trained in ceramic waxing, pressing, and cut-back techniques can apply their skills with very consistent results. However, feldspathic methods can be less predictable and more susceptible to human error. The results depend largely on the artistic abilities of the ceramicist and can be less precise. (In either case, it is very important that dentists choose a laboratory with highly qualified technicians. Technician feedback can be invaluable; experienced technicians work on far more restorations than individual dentists and understand how teeth should be prepared to achieve a certain look.)
Disadvantages?
Given all of the advantages of pressed ceramic restorations, why would a dentist choose feldspathic? The reasons cited usually involve “natural beauty” or tooth preparation, and often both.
Some dentists believe that feldspathic porcelain and traditional layering techniques allow artistic ceramicists to create veneers that are more “natural” in their beauty than even the finest pressed porcelains. The reason probably derives from the thinness of feldspathic material. Since the layers are very thin, ceramicists can allow what’s attractive in existing teeth to shine through, and then mask flaws where necessary and enhance colors without creating a painted-on look. On the other hand, technicians using pressed ceramics usually can’t exploit the natural appearance of an existing tooth. They must start with a fully contoured ingot in a uniform shade, and then render the ingot more natural with cut-back techniques and exte`rnal staining. Some dentists believe that this disadvantage can’t be overcome, and recommend feldspathic veneers when natural beauty is the primary concern.
Here are three points to consider that are contrary to the view of dentists who favor feldspathic veneers:
1) The “disadvantage” that the natural appearance of feldspathic porcelains can’t be matched by pressed ceramic veneers is questionable. Virtually any color or optical property that can be achieved through feldspathic layering can be mimicked as well or better by pressed ceramic cut-back methods. While ceramicists can’t use these techniques to exploit the actual color of existing teeth, they can match that color, if that’s what the dentist and patient really want.
2)But, oftentimes, that isn’t what dentists and patients want. To the extent that the traditional layering techniques exploit the color of existing teeth, the veneers can be quite a bit darker than what most patients envision when they ask for the bright white smile on the cover of People magazine. Although they often say they want a “natural” smile, they also want a smile that is generally whiter than their natural teeth. What they tend to mean by “natural” (or youthful) is something like “alive,” i.e., not artificial or “painted on.” They want teeth with the same range of gradations and optical properties - fluorescence, opalescence, opacity, translucency, etc. - but a range that starts farther up the scale of brightness and whiteness.
3)Finally, one should distinguish between the initial results of veneer placement, and what those results might look like in five years. Insofar as a feldspathic placement lets the color of an existing tooth shine through, the veneer is subject to a “shade shift” as time passes. Human teeth change color as people age. If feldspathic veneers allow the existing tooth structure to shine through, the veneers will darken as well - so much so that patients may need to have them redone in five years. Hence, the putative virtue of feldspathic veneers, their inherent “translucency,” can turn into a vice over time. Patients pay considerable money for veneers, and they don’t want to spend it again soon. They won’t need to with pressed ceramics, which almost never change shade.
Another “advantage” of feldspathic veneers is that they require dentists to remove less tooth structure than pressed ceramics. While this is only half true, because even with feldspathic materials the clinician still needs to create more room for the technician (i.e., remove more tooth structure), if they want to change the color of the teeth. The difference - .3 mm vs. .8-1.0 mm - is not as great as feldspathic proponents often claim. Generally, skilled dentists need not remove more than .5-.6 mm when prepping for pressed ceramic veneers.
In dental school, we all learn to respect a conservative principle: Remove only as much tooth structure as necessary, and no more. This is certainly sensible, but “necessary” is a relative term. In one sense, much - if not most cosmetic dentistry - could be considered unnecessary. People can survive with perfectly functional teeth without it. But, in our business, what’s necessary is determined by what is required to satisfy the patient - as long as that’s possible and doesn’t do harm. What patients usually want are bright, lively smiles with well-formed teeth that look real. They also want their expensive restorations to last for a reasonable period of time, ideally the rest of their lifetimes. Judged by these standards, .3 mm represents no critical limit. Indeed, overly cautious dentists, observing this limit, can easily under-prep for feldspathic veneers. For example, if a dentist only removes .3 mm, and the technician then applies extra layers of porcelain to mask yellow in existing teeth, the veneers may look and feel bulky and artificial. But if the dentist anticipates the problem by slightly removing more tooth structure, he or she might as well use pressed porcelain, which is superior in many other ways.
Indeed, it’s not clear that saving a minimal amount of tooth structure ever justifies selecting feldspathic veneers - especially since the alternative is stronger, less abrasive, fits and looks better, keeps its shade, and lasts longer. So the conservative maxim should be liberalized: Remove as much tooth structure as necessary, no more but no less. Dentists should then select the material that will best support their patient’s vision of an ideal smile. This brings us back to where we began: I can’t imagine choosing anything other than pressed ceramic porcelain for veneers.
Dr. Christopher Pescatore lectures worldwide on topics such as state-of-the-art esthetic procedures, techniques, and materials. A graduate of the University of Medicine and Dentistry of New Jersey-New Jersey Dental School, he holds a U.S. patent for a nonmetallic post system to restore endodontically treated teeth. He is the former clinical co-director and current featured speaker at the Las Vegas Institute for Advanced Dental Studies. Dr. Pescatore has a full-time practice in Danville, Calif., that is dedicated exclusively to esthetic dentistry. He can be reached by phone at (925) 362-9330 or via email at [email protected].
