TheOptimalSmile
Porcelain Crowns & Veneers
A closer look at two innovative techniques and strategies to improve your
Whether porcelain crowns or veneers are used to enhance your smile, the truth of the matter is no one should know that you have had any work done, just that you look great. Admirers should perceive only a subtle change, something they can't quite put their finger on. In the end, it is you who will be exuding improved self-confidence.
Nevertheless, from a patient's perspective, it is both helpful and important to know what modern dentistry has to offer. This article will focus on two innovative techniques and strategies to improve a person's smile. In many instances these two restorative techniques can produce nearly identical esthetic results, even though they are structurally different. When pushing the envelope to satisfy esthetic dilemmas, it is necessary to incorporate the latest in ceramic technology in both porcelain laminate veneers and porcelain crowns.
Similar Yet Different
Dental porcelains are used to create replicas of natural looking teeth for both veneers and crown fabrication. Although they share similar visual characteristics with natural teeth, one technique will be more suitable than the other, depending on the situation. As both a healthcare professional and artist, a dentist must take several factors into account when selecting which technique will provide an ideal restoration.
Veneers of Excellence
Porcelain laminate veneers are composed of thin ceramic layers that essentially replace tooth enamel. Similar to a contact lens for the eye, a veneer adheres to the outer surface of a tooth. Natural tooth structure must first be reduced by a minimal amount, approximately 1 mm or less of tooth enamel. This will allow room for the veneer to work its magic and restore natural tooth form, enhancing brilliance and exceptional beauty. Porcelain veneers are an excellent solution for many esthetic imperfections such as poor color, shape or contours, fractured teeth, tooth position, as well as some minor bite related problems [Figure 1 and 2]. They are also an excellent option for managing superficial stains in teeth not amenable to bleaching.
Crowns to Cap it Off
Much like a monarch's headdress draping over the head, a crown almost, if not entirely, replaces the enamel “cap” of a tooth. The term “cap” is used synonymously with crown. A crown replaces the entire external form of a tooth, down to the gum level [Figures 3, 4 and 5]. Whatever inner core of tooth remains, “crowning” a tooth re-establishes its natural form, as well as its function (how it contacts other teeth). Whether from the ravages of tooth decay or from trauma, replacing large amounts of tooth structure is part of crown design. Crowning teeth can also create dramatic improvements for patients whose teeth have been worn by bruxism (grinding habits) or by enamel erosion.
Like veneers, crowns are also excellent for changing tooth color and shape; in some cases they can facilitate this change more easily. Porcelain crowns are generally necessary when more tooth structure has been lost and therefore more material is needed to replace it. Conversely, if more tooth structure needs to be lightened (because of deeper staining) and/or strengthened, a crown will serve as the restoration of choice. For back teeth that receive greater biting force, newer and stronger “all-ceramic” crowns may be a better alternative.
A Material Difference
The primary difference between a porcelain veneer and a crown is the amount of natural tooth structure that needs to be replaced. Generally speaking, greater thickness of porcelain is needed for a crown. In order to place the porcelain crown, at least 2 millimeters (mm) of tooth structure thickness is needed.
For these two different restorative applications, the porcelain itself, a glass-like ceramic material has necessitated modification to strengthen it, particularly if used for back teeth, which are subject to higher biting forces.
Figure 1: A pre-treatment photograph showing two upper front teeth having surface imperfections that had been previously repaired with composite bonded restorations.
Figure 2: A post-treatment photograph showing two veneer restorations reestablishing the natural beauty, form and function of the two upper front teeth.
Figure 4: A photograph showing an all-porcelain crown.
Figure 3: A photograph showing the top of an implant abutment that will need to be restored with a new crown.
Figure 5: A photograph showing a porcelain crown cemented on top of the implant abutment restoring the natural appearance of the patient's smile.
Making Them Stick
The insertion or cementation of laminate veneers and crowns may be similar. They are placed with a light-sensitive resin and hardened with the use of a blue or ultraviolet light source. The ultra-thin porcelain veneer achieves its optimal strength when it is adhesively bonded to the underlying tooth enamel. In addition, the overall retention of an “all-ceramic” crown is increased especially when bonded to enamel rather than to dentin.
Back to Basics — Smile Analysis and Other Tools of the Trade
A comprehensive assessment and diagnostic evaluation are often critical prior to any restorative procedure. These elective procedures not only ensure proper esthetics and functional capabilities, but also allow individuals to assess the end result prior to any permanent change. Remember, you always want to look at the car before you buy it. This conservative approach will involve you in the decision-making and will enhance your comfort with the process and outcome.
Making a “Mock-up” — Can Really Be a Good Idea
Envisioning the end result before it is finalized is a tool almost unique to dentistry. Whether to improve the appearance of one front tooth or a larger group of front teeth, a “mock-up” in association with a thorough dental examination is a critical tool.
What is a diagnostic mockup? You may go to see your dentist with one or
more issues to solve. A few examples may include tooth decay, small or large
spaces between teeth, broken edges or corners of teeth, unsightly stains or
discolorations of teeth, severely rotated or twisted teeth, or unleveled gum
lines impairing your smile line.
A mock-up is the creation of a “trial smile” — allowing you the exciting prospect
of actually being part of your own smile transformation [Figure 6]. This simple
procedure allows your dentist to apply tooth-colored filling materials to
temporarily improve the shape and form of your teeth, to close spaces
between teeth, or to simulate the ideal balance between the gum line and
the teeth. In turn it allows you time to try out the newly created tooth shapes,
with lips at rest and at full smile. This also gives you time to decide how the
changes appeal to you and those viewing your new look. This approach is
the most realistic way of experiencing the whole host of improvements
that you and your dentist have envisioned.
After photographing your dental appearance before and after the “mockup,” your dentist can easily remove the tooth-colored material returning the teeth to their original condition [Figure 7].
At the next office visit, you can examine and compare the photographs of these transformative changes. By actively participating in your own treatment, you can discuss and evaluate the proposed changes and make further recommendations and possible improvements. After all — it's all about you, so with this knowledge and awareness you can and should be your own best advocate.
Figure 6: A photograph showing a “trial smile” which is created by applying tooth colored materials on top of the patient's teeth for them to see their “new look.” Figures 7-10 show the patient's veneer makeover from start to finish.
More About Choices — Shades of Grey
There may be a fair amount of judgment necessary when determining whether to place porcelain veneers or crowns. For example, your dentist may feel that circumstances dictate that a porcelain veneer needs to be made thicker than normal to cover a larger percentage of a tooth to align it with a neighboring or adjacent tooth. Additionally, more tooth preparation may be required to achieve a desired effect in a severely stained tooth [Figure 8]. Other circumstances may present a sort of compromise between a veneer and a crown — where more than just the face of the tooth needs enhancing. Indeed, porcelain “veneer” restorations have been prescribed where the whole surface of the tooth is “veneered” [Figure 9 and 10].
What Crowns and Veneers Can't Do
These techniques cannot fully correct poor tooth position, poor bite relations, or a poor profile. They may, however, correct minor alignment problems, depending upon the individual case. Many situations may first require some form of orthodontic treatment (braces) to move the teeth into proper position — for both function as well as esthetics. Ceramic restorations may serve as an excellent restorative solution, but like most other techniques, they have both advantages and disadvantages.
Beginning to See the Light?
A talented ceramic artist can sculpt dental porcelain into spectacular tooth imitations that mimic tooth enamel. Properties associated with porcelains include glass-like whiteness and translucence — most important from an optical or visual standpoint. It is these particular nuances that allows light to penetrate and/or scatter, making the restoration life-like.
Porcelains are a form of inorganic, non-metallic ceramic material formed by the action of heat. Dental porcelains are made in many colors and shades; they are manufactured in a powder form corresponding to the primary colors of basic tooth structure. These are mixed with water and placed in an oven for “firing” — hence their ceramic nature. Porcelains are built up in layers to mimic the natural translucency, staining and contours of the enamel of teeth.
Figure 7: After the “trial smile” is removed the patient is back to his original appearance.
Figure 8: The dentist will reduce a small amount of the surface of the patient's teeth creating adequate space for the new veneers.
Figure 9: The laboratory technician creates porcelain veneers on a model following the dentist's prescription.
Figure 10: The final result creating a new smile which closed spaces and replaced worn, uneven teeth.
New Ceramic Materials
Problems with porcelain restorations in the past have been in those composed of high concentrations of glass particles. They were brittle and had low tensile strength, and like glass, they were prone to fracture. One way of overcoming this has been to incorporate a core or substructure material made out of metal, i.e. cast gold, with porcelain facings. Unfortunately, while strengthening the crown, the metal tends to detract from the glass-like translucence of the porcelain and from its life-like appearance — not so bad for back teeth but not so great for front teeth.
Recently, the newest category of all-ceramic crowns make use of an internal ceramic “core” made from “Zirconia” which adds significant strength as well as esthetic beauty. This polycrystalline ceramic core (poly – many, crystalline – a crystal-structure which imparts greater strength) is the same material that forms the basic structure of fake diamonds.
CAD-CAM (Computer Aided Design – Computer Aided Manufacturing) technology is another innovation in dentistry which allows extraordinary accuracy of fit and contour of crown restorations. Using a special wand to scan a tooth that has been modified for a new crown, information is beamed from a computer to a milling machine that sculpts an exact fitting “ceramic core” of the crown [Figure 11]. Porcelain is then baked on top of this core to mimic tooth form and color as well as impart its traditional brilliance and translucence. The result of this computer-aided system is a crown composed of a strengthened core which is permanently cemented to the remaining natural tooth.
Secrets of Success — Veneers or Crowns?
In many instances porcelain veneers and crowns can produce pleasing and excellent results but these two types of dental restorations do have different structural characteristics. Ultimately, the precise terminology is unimportant. The secret to a successful outcome is to know what to use and when to use it. This is the province of the dental professional, who combines knowledge, skill and experience. Whether veneers or crowns are used to enhance your smile, the truth of the matter is that no one should know that you've had anything done, just that you look great!
Figure 11: A milling machine sculpturing a restoration from CAD-CAM technology.