Haute Pursuit

Mentor explores the latest clinical technologies that are elevating the art of indirect restorations to high fashion.

Oral enhancements aren’t just sought after by movie stars, models and other celebrities who make their living on their looks. An attractive smile can boost self-esteem and, by extension, career success for the millions of us with less-than-perfect teeth. And despite the fact insurance companies typically do not reimburse for elective cosmetic procedures, a recent report notes the demand for esthetic treatment is increasing, and growth in the global cosmetic dentistry market will reach $27.9 billion by 2024. That’s up from $15.8 billion in 2015.1

Cosmetic dentistry encompasses a wide range of procedures that, beyond esthetics, can also improve function. Yet, cosmetic (or esthetic) dentistry is not among the nine specialties recognized by the American Dental Association (ADA). Rather, as the ADA puts it, “Cosmetic dentistry has become a common denominator of the general practice of dentistry.”2 Nonetheless, clinicians who choose to focus on the “art of the smile” often receive additional training, and many are accredited through the American Academy of Cosmetic Dentistry (AACD) or American Academy of Esthetic Dentistry (AAED). These practitioners will typically talk in terms of “smile design.” This is a concept — often presented using photos, video and digital programs — that takes into account facial symmetry, as well as alignment, shape and shade of dentition, as well as gingival contour — and even the patient’s personality.

While there are many kinds of procedures a cosmetic/esthetic dentist might perform — from gum grafting to orthodontics — among the most prevalent are indirect restorations. These prostheses, including crowns, bridges, inlays, onlays, partial dentures, full dentures and veneers, are created in the lab or chairside via in-office computer-aided design/computer-aided manufacturing (CAD/CAM) systems. The prostheses are subsequently cemented (or “luted”) into place via an adhesive system. And, thanks to improvements in design and fabrication technologies, today’s dentists can tailor custom-made prostheses that fit better than a custom couture gown.

Among the numerous forms of indirect restorations, crowns are perhaps the most common. These replicas of the visible portion of a tooth are called for in the case of single-unit dental implants. And when posterior caries, such as a large Class II case, demands preparation that doesn’t leave sufficient tooth structure to retain a direct restoration (or “filling”), a full-contour crown is likely the best answer. In such cases, especially when there is more than one such restoration, recommending a prosthesis may save practices time and money. This is because attempting to directly fill such preparations is both difficult and time consuming.

When cusps are damaged in posterior teeth and a portion of one or two of a tooth’s walls are compromised, inlays (which are cemented between cusps) or onlays (which replace damage that includes cusps) can be used. These restorations have a better chance of withstanding compressive forces than would directly placed composite. In addition, inlays and onlays allow more conservative preparations than would be needed for a crown.

Another option that supports the concept of minimally invasive dentistry — while boosting both strength and esthetics — is the “vonlay,” a term coined by Ed McLaren, DDS, director of the Center for Esthetic Dentistry at the University of California, Los Angeles. “I got to thinking that when we restored the occlusal surface of a tooth, we would often restore the facial aspect for esthetics, and the lingual and interproximal surfaces just got included for retention and resistance for a crown,” explains McLaren. “The vonlay is a combination of an onlay on the occlusal surface and a veneer on the facial surface — an approach that leaves alone that which doesn’t need to be repaired.”

Of all the materials used for indirect restorations, gold alloy is still thought to be the best as far as longevity in the oral cavity. But gold is pretty much unaffordable these days and in no way resembles natural dentition — which is what patients want. For that, ceramics fit the bill. The most traditional of these materials is feldspathic porcelain, which is still favored by many for anterior applications. This material is typically hand layered in the lab by a ceramist who builds in shadings, colors and translucencies to create a lifelike prosthetic. Indeed, layered porcelain is considered as possibly the highest art in restorative work.

Though beautiful, porcelain tends to be brittle, however, and it lacks the properties needed to withstand compressive forces. Therefore, it is used only in anterior cases (where this isn’t an issue), or it’s underlain with a substrate, such as metal, for posterior applications. In this case, it is known as a porcelain-fused-to-metal restoration. The downside to this arrangement is that it’s not uncommon for the metal to show around the margins, or even cast a graying shadow through the porcelain.


POINT OF SALE | INDIRECT RESTORATIONS

  • Demand for esthetic indirect restorations is growing, which is creating sales opportunities and industry growth worldwide.
  • Although many dentists send cases to labs for fabrication, in-office design and milling technology allow fabrication of indirect prostheses chairside.
  • Today’s ceramic materials offer excellent esthetics and strength; the latest restorative materials are indicated for anterior or posterior applications.
  • Because the most recent ceramic materials are strong enough to be used in thin layers, more tooth structure can be conserved during preparation.
  • Zirconia, the strongest ceramic used in dentistry, is becoming increasingly esthetic thanks to improvements in its color and translucency.

Among the numerous forms of indirect restorations, crowns are perhaps the most common. These replicas of the visible portion of a tooth are called for in the case of single-unit dental implants. And when posterior caries, such as a large Class II case, demands preparation that doesn’t leave sufficient tooth structure to retain a direct restoration (or “filling”), a full-contour crown is likely the best answer. In such cases, especially when there is more than one such restoration, recommending a prosthesis may save practices time and money. This is because attempting to directly fill such preparations is both difficult and time consuming.

When cusps are damaged in posterior teeth and a portion of one or two of a tooth’s walls are compromised, inlays (which are cemented between cusps) or onlays (which replace damage that includes cusps) can be used. These restorations have a better chance of withstanding compressive forces than would directly placed composite. In addition, inlays and onlays allow more conservative preparations than would be needed for a crown.

Another option that supports the concept of minimally invasive dentistry — while boosting both strength and esthetics — is the “vonlay,” a term coined by Ed McLaren, DDS, director of the Center for Esthetic Dentistry at the University of California, Los Angeles. “I got to thinking that when we restored the occlusal surface of a tooth, we would often restore the facial aspect for esthetics, and the lingual and interproximal surfaces just got included for retention and resistance for a crown,” explains McLaren. “The vonlay is a combination of an onlay on the occlusal surface and a veneer on the facial surface — an approach that leaves alone that which doesn’t need to be repaired.”

Of all the materials used for indirect restorations, gold alloy is still thought to be the best as far as longevity in the oral cavity. But gold is pretty much unaffordable these days and in no way resembles natural dentition — which is what patients want. For that, ceramics fit the bill. The most traditional of these materials is feldspathic porcelain, which is still favored by many for anterior applications. This material is typically hand layered in the lab by a ceramist who builds in shadings, colors and translucencies to create a lifelike prosthetic. Indeed, layered porcelain is considered as possibly the highest art in restorative work.

Though beautiful, porcelain tends to be brittle, however, and it lacks the properties needed to withstand compressive forces. Therefore, it is used only in anterior cases (where this isn’t an issue), or it’s underlain with a substrate, such as metal, for posterior applications. In this case, it is known as a porcelain-fused-to-metal restoration. The downside to this arrangement is that it’s not uncommon for the metal to show around the margins, or even cast a graying shadow through the porcelain.


LEXICON

  • Class II: A restoration involving a tooth’s proximal surfaces.
  • Cusp: Projection or projections on a tooth’s chewing surface.
  • Direct Restoration: A restoration placed directly into the tooth, without fabricating a prosthesis (in layman’s terms, a filling).
  • Full-Contour Crown: An indirect prosthesis that covers all surfaces of a tooth.
  • Indirect Restoration: A toothlike prosthesis — such as a crown, bridge, onlay or inlay — created outside of the oral cavity.
  • Inlay: A restoration that lies within the cusps.
  • Luting: Use of mechanically retentive cement.
  • Onlay: A restoration that covers the cusps.

The New Ceramics

IPGGUTENBERGUKLTD/ISTOCK/THINKSTOCK

IPGGUTENBERGUKLTD/ISTOCK/THINKSTOCK

To remedy some of these issues, other ceramic materials continue to gain ground. “Clearly, the most significant innovation in 10 years is the advent of good-looking, stronger esthetic materials,” says McLaren. “While the traditional materials looked pretty good, they just didn’t have the strength or the ability to function well over time.”

But these stronger materials — many of them available in ingots or blocks for reductive manufacture via in-office CAD/CAM technology — have long had the opposite problem of feldspathic porcelain. Used monolithically as all-ceramic restorations, they offer the strength needed for posterior placement, but, due to their opacity, they haven’t been used as much in the anterior region. This is changing. No longer looking as if they fell out of a box of Chiclets, today’s all-ceramic indirect restorations offer both strength and anterior-worthy beauty, courtesy of toothlike gradations in color, shading and improved translucency.

At the heart of the three primary groups of dental ceramics are their microstructures. Feldspathic porcelain is glass- or silica-based. Manufactured using feldspar, quartz and kaolin, it is less dense than other ceramics, but it offers high levels of translucency, so is considered highly esthetic. As a result, feldspathic porcelain is often used in anterior applications, such as veneers. Other systems, such as leucite or lithium disilicate, are composed of silica that’s reinforced with crystalline fillers. Says McLaren, “Probably the No. 1 indirect material with these improvements — that an average general dentist can use without major changes in technique — is lithium disilicate.”

Grand Rapids, Michigan-based cosmetic dentist Betsy Bakeman, DDS, agrees. Although she uses all types of ceramics — including leucite-reinforced ceramic and feldspathic porcelain — as an examiner and mentor for the AACD, she believes the advent of lithium disilicate has significantly impacted dentistry.

Bakeman explains the new ceramics offer clinical advantages — whether layered with porcelain for anterior placement or used monolithically in posterior applications. “The great thing is that because they are stronger, new ceramics can be used to create restorations that are thinner than earlier iterations. This means they don’t require as much accommodative tooth structure removal as did past materials,” she says. “In addition, they are now more translucent, which means they are more optically acceptable.”

The third category of ceramics, crystalline materials, includes alumina and zirconia. These are the strongest of the ceramics and are less likely to chip or fracture than other materials — but they contain no glass, and, due to their high density, tend to be more opaque and less esthetic than their glass-containing counterparts. This has been an issue, particularly for zirconia restorations — until recently, that is.

“Continuous development of zirconia formulas has increased translucency, resulting in more natural-looking restorations,” reports Ronald Goldstein, DDS, a general and cosmetic practitioner based in Atlanta. An author, educator and cofounder of the AAED, Goldstein considers continuous development in materials, such as zirconia, to be critical to the growth of cosmetic dentistry.

Goldstein and Bakeman both note, however, that though zirconia is now available with degrees of translucency, there’s a trade-off. “With translucency, you give up some strength. A lot of clinicians don’t know that,” says Bakeman. But Goldstein observes that while translucent zirconia is not as strong as monolithic zirconia, it is still slightly stronger than lithium disilicate. It can also better match tooth shades than its monolithic counterpart, making it a candidate for anterior or posterior esthetic restorations.


THAT NATURAL LOOK

ALEKSANDARNAKIC/ISTOCK/THINKSTOCK

ALEKSANDARNAKIC/ISTOCK/THINKSTOCK

To look like natural teeth, restorations must exhibit characterizations — such as the appearance of hairline cracks and faint grooves, as well as translucence. In addition, teeth are not monochromatic, so gradations in color must be layered in for a natural look.

Betsy Bakeman, DDS, a Grand Rapids, Michigan-based cosmetic dentist, notes that most labs mill or press restorations from blocks. “Some manufacturers are now making multilayered blocks that offer changes in opacity, translucency and color from one part of the block to the other — because teeth are not one color,” she says. “This helps minimize the need for cut backs; this is where the labs make the restoration a little bit smaller in order to layer in extra color or translucencies to make it appear more lifelike.”

Joe Ontiveros, DDS, a professor in the Department of Restorative and Prosthodontics, and head of Esthetic Dentistry and the Oral Biomaterials Division at the Houston Center for Biomaterials and Biomimetics at the University of Texas School of Dentistry, still regards color as a significant challenge for clinicians. “While color and optical properties of dental materials continue to improve, the complexities of color still confound our profession,” he says. “To address this, a fairly young consortium of dental professionals and other experts have recently formed the Society for Color and Appearance in Dentistry. This group is bringing researchers and clinicians together to collaborate on the various aspects of color in dentistry.”


Crystal Math

According to McLaren, the translucency/strength trade-off boils down to how molecules or crystals are aligned. “Generally, materials that are more translucent have a microstructure of glass,” he says. “Glass is a loose arrangement of molecules in no particular order that light can easily pass through. Contrast this with a crystalline structure, which is what makes up zirconia. Because of the order of its tetragonally shaped crystals, and their edges and boundaries, it’s like a brick wall — light can’t easily pass through it. There are some crystals, like cubic zirconia (CZ), whose molecules are not misaligned, and it is possible to make them fairly translucent.”

In fact, McLaren notes that in an effort to compete with patented lithium disilicate products, some manufacturers began to add CZ — which is used to make imitation diamonds — to zirconia to increase translucency. “The whole push the last few years has been to find that balance between strength and translucency, adding in the right amount of CZ for increased translucency and enhanced esthetics, while maintaining strength. Adding 10% to 30% CZ, you give up about 50% strength — but it’s still stronger than lithium disilicate, and with a comparable medium level of translucency,” he explains.

Nonetheless, McLaren says there’s still a demand for hand-layered porcelain for anterior applications — but at a premium. “You tend to see the higher-end ceramists and dentists resurfacing with feldspathic porcelain as veneers, or even microlayering zirconia with it just because it has that extra esthetic touch you can’t get with monolithics. But like anything else, you’re going to have 5% of the people go for a Mercedes and 95% go for Yugos. It depends on how much a patient is willing to pay for esthetics.”

Looking Forward

In Goldstein’s estimation, a primary challenge for clinicians is treatment planning. “The quick fix is not always the best fix,” he emphasizes. “A quick fix may be choosing to use no-preparation porcelain veneers in patients with bite problems, such as bruxism or clenching, which may potentially cause debonding or, worse, porcelain fracture.” Goldstein says it’s also crucial to know when to refer a case. “Too many times, money has dictated that a dentist take on a case that he or she was not prepared or qualified to treat, leading to what I call ‘esthetic failure’ — which is a potential disaster, and costly, for both the patient and practitioner.”

Bakeman stresses the importance of good communication between clinicians and labs, and ensuring they are on the same page. “The partnership is like a marriage,” she says. “Dentists and ceramists must have the same vision. I can do the best dentistry, but if the lab work is not what I want, it won’t matter.”

As clinicians pursue dentistry’s latest versions of haute couture down the runway to restorative nirvana, their paths are not without trip hazards. For beauty in its truest form must not only be strong and durable, it must also be as affordable as off-the-rack wear and available to everyone.

Featured Photo Courtesy of EGORR/ISTOCK/THINKSTOCK 

References

  1. Grand View Research. Cosmetic Dentistry Market Analysis. Available at: grandviewresearch.com/industry-analysis/cosmetic-dentistry-market. Accessed April 6, 2017.
  2. American Dental Association. Cosmetic Dentistry 3rd edition. Available at: ada.org/en/search-results#q=cosmetic%20dentistry&t=all&sort=relevancy. Accessed April 6, 2017.

 

From MENTOR. May 2017;8(5):22-24, 27-29.

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