Current perspectives on the evolution of techniques and materials.
Dennis J. Wells, DDS
Porcelain veneers have had a rich history in dentistry over the past 30 years, obtaining overwhelming success from the perspective of both the consumer and the dental industry. In fact, it is difficult to imagine our world today without this wonderful restoration that allows dentists to enhance the appearance, the health, and, ultimately, the entire lives of our patients. The techniques and materials continue to evolve, albeit very slow, and many aspects that were introduced relatively early in the evolution still remain “state of the art” today. New does not necessarily mean better in the dental world, and caution is always in order when considering a change in a proven technique or material. This article will briefly summarize some of the current concepts and trends in the area of ceramic veneers.
Just as the plastic surgery community has generally moved away from the initial days of over-corrected and unnatural-appearing facelifts, dentistry is moving away from smile designs that are over-corrected and too perfect. Designing a smile with small, manmade pieces of porcelain is a complex process that can produce an infinite number of outcomes—everything from practically undetectable to replicas of Chiclets gum. The evolution in smile design with porcelain veneers in the United States has been toward a higher degree of emulating nature and less toward the over-corrected “Hollywood Smile,” as it is often labeled. Likewise, there seems to be a trend in the European community and other countries toward less compromised esthetics and more toward straighter, brighter smiles. Nature presents in both beautiful and not so beautiful forms, and just because it is natural does not make it necessarily desirable. It is the author’s opinion that dentists across the world are beginning to unite in a common goal to emulate nature that is fairly uncompromised in terms of alignment, wear, color, etc. In the author’s practice, the clinical staff is constantly searching for beautiful, natural smiles that our culture would view as beautiful that can be used as blueprints for ceramic smile designs. Figure 1, Figure 2, and Figure 3 show such a natural smile, with whitening and orthodontics being the only two treatments rendered for this 20-year-old woman.
In attempting to follow these blueprints, dentists have become far less concerned about perfect contralateral symmetry, and to this end note the subtle differences in the lateral incisors in Figure 2. Even the central incisors are rarely “mirror images” in nature as we have been taught traditionally, but often have slight variances in axial rotation, etc.1 Also, incisal embrasures are generally far more open than we have tended to create in our ceramics (Figure 4, Figure 5, and Figure 6 ).
Color is also very complicated in nature with an abundance of polychromatic effects present, and often porcelain veneers were too consistent in color. It is no longer the author’s goal to have each tooth the same exact same color as the adjacent tooth, but to rather emulate nature with the centrals being slightly brighter than the laterals and the laterals brighter than the cuspids. This step in color is less pronounced in bleached teeth, but it is still present on some level. Natural teeth that respond well to the whitening process can sometimes exceed the brightest porcelain shade guides, and thus brightness is generally not the enemy in creating natural-looking smiles. Some cultures will be more attracted to white teeth than others, but at least here in the United States bright white color is generally desirable if it emulates the optics found in nature, and even more importantly, has the proper architecture.
With these concepts in mind, the author and his staff refer to nature’s blueprint and in many cases will attempt to copy the form at some level in the design phase, in fabrication, and even in post cementation, where slight alterations can make a profound difference. Note the influence of the natural teeth in Figure 6 to the porcelain veneers in Figure 5, although it was not copied precisely due to patient input and other factors. It is becoming a trend in the author’s practice to create a smile design by copying a specific natural smile from the practice’s personal library (both in architecture and color) rather than referring to a “default mode” or manmade design.
Conservation of Enamel
In the early days of porcelain veneers, very little enamel was removed, in part because dentists were never sure if the adhesion process would hold up. The adhesion techniques proved to be quite reliable and dentistry enjoyed several years of success with conservatively prepared teeth veneered with feldspathic porcelain, although the strength of the porcelain was a concern in some cases. Dentistry then entered into an era driven primarily by pressed ceramics that offered more strength but also required more ceramic thickness and, thus, more preparation. Although some beautiful results were achieved, clinicians began to see more complications and side effects from the increased preparation, including micro-cracks, craze lines, debonding, and increased endodontic treatment.2 In addition, patients were oftentimes emotionally traumatized upon seeing their prepared teeth and so there were some psychological negatives as well. In the mid 2000s a “back to the future” movement began with a return to conservation of enamel and minimally invasive dentistry. This prevailing philosophy is changing everything, and it goes hand in hand with the idea of not “overcorrecting” smiles. For example, in the past teeth would often be aggressively prepared to achieve absolute perfect symmetry of contralateral teeth, whereas now clinicians might consider leaving a slight rotation or asymmetry in order to conserve enamel and produce a more natural-looking smile. This conservative movement is also aligning more closely to the literature in regard to strength and durability. Studies show that porcelain veneers have the longest track record when bonded to a maximum amount of enamel that has been acid-etched.3
The popularity of no-preparation veneers has surged in recent years, as it is the ultimate in minimally invasive dentistry. Many doctors and ceramists struggle to see beyond visions of over-contoured teeth with unhealthy gum tissue when they hear the term “no-prep” veneers, but new techniques and materials allow additive-only ceramics to be a reality for many patients.4 Examples of potential cases for no-preparation veneers include: microdontia; loss of enamel volume due to wear, abrasion, and erosion; an excessively large frame (lips) that creates an imbalance between the frame and the teeth; and bicuspid extraction orthodontic cases where the teeth have a narrow arch form and are lingually inclined.5
The author’s practice has found these types of cases to comprise roughly 50% of its patient population, and thus about 50% of the practice’s cases are minimal- to no-preparation. Of this 50%, a considerable amount will be “hybrid” cases where some of the teeth will perhaps require preparation while others in the arch will not. Figure 7 represents an ideal case for no-preparation veneers, followed by Figure 8, Figure 9, Figure 10, and Figure 11 showing final porcelain veneers on teeth Nos. 5 through 12 accomplished with no-preparation veneers.
Although manufacturers have introduced a variety of new products and materials over the last 30 years, it is remarkable how many of the early materials remain relevant in today’s world of porcelain veneers. In the area of adhesion, self-etch adhesives continue to grow in popularity and they are certainly improving rapidly. However, when adhering porcelain veneers, the etch-and-rinse systems that have been around for years continue to be the material and technique of choice.6 As mentioned already, preparation designs are moving toward conservation of enamel and so it is critical that a system is used that will etch the remaining enamel in the most effective way.
Very little has changed in the area of composite cements, and there are several great products on the market that are closely ranked. One technique that has gained popularity is to use a restorative hybrid composite to bond porcelain veneers. This requires heating the composite to temporarily lower the viscosity, and in doing so the veneer is readily seated with reasonable pressure and the clean up is minimized as the composite begins to cool. The author has found this to be an effective system to bond porcelain veneers to achieve maximum strength of the restoration while minimizing clean up time.
In the area of porcelains, several innovations have been introduced through the years that offer the clinician multiple options—especially in strength. The four main categories7 that are currently applicable to porcelain veneers are:
- Glass-based systems (powder liquid)
- Glass-based systems with fillers (typically leucite)
- Glass-based systems with lithium-disilicate and high crystalline content
- Fine-grain machinable blocks (used with CAD/CAM systems)
In the author’s opinion, the glass-based powder/liquid porcelains continue to be the “gold standard” in producing nature-like optics, and these basic powders have been used in porcelain veneer fabrication from the start. The other systems can produce beautiful optics as well, and with the added benefit of increasing strength when needed. In the author’s opinion, the ultimate in strength presently is the lithium-disilicate systems (ie, IPS e-max®, Ivoclar Vivadent, www.ivoclarvivadent.com). This material has a variety of benefits from its high flexural strength (about 3x that of IPS® Empress, Ivoclar Vivadent) to the fact that it can be pressed or milled.8 Like all pressed restorations, the monochromatic nature of the material requires a strategic plan to create polychromatic color. If a cutback approach is taken with lithium disilicate, then the add-on ceramic is more in the strength range of traditional powder/liquid ceramics, thus losing the high flexural strength in the incisal zone. One way to combat this issue is to create thin restorations from relatively translucent ingots that allow the underlying tooth structure to shine through somewhat, assuming the underlying color is good and that little to no enamel must be removed.
The remarkable strength of the lithium-disilicate material does allow ceramists the opportunity to press the restorations very thin, making it a good candidate in many cases for a minimum- to no-preparation case. Figure 12, Figure 13, and Figure 14 represent a case accomplished using IPS e.max on teeth No. 5 through 12. Other than removing the old composite on tooth No. 8, no further enamel reduction was required.
The machined blocks used for CAD/CAM restorations are a stronger ceramic than its comparable powder/liquid porcelain due to the efficient and controlled way machined blocks are fabricated. The CAD/CAM restorations have continued to improve and offer a relatively fast way for the clinician to provide porcelain restorations. Although creating natural optics has been challenging with milled restorations, new developments such as the multicolored blocks coupled with more sophisticated software holds great promise for the future.
Dentists and patients alike are forever indebted to the pioneers and innovators of the dental industry who brought porcelain veneers to the forefront of cosmetic dentistry. The next 30 years should be as equally exciting as the past, and one can only imagine the advancements that are yet to come. As dentistry marches into the future, our goals will undoubtedly be: follow nature’s beautifully imperfect guidelines, conserve as much tooth structure as possible, and choose materials that are well tested and match the strength requirements of the individual case.
The author is the co-developer of DURAthin veneers.
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About the Author
Dennis J. Wells, DDS