The Art of Matching Select Porcelain Restorations to Anterior Teeth in Bellevue,WA
Friday, November 9th, 2007Introduction
Matching a single central incisor is challenging but possible if the dentist and ceramist understand the principles of natural oral esthetics; good tissue health and perfectly reflected tooth contours at the midline are just as important as the actual color of the teeth. If the teeth are rotated or the roots are misaligned, the match can become far more challenging because the ideal contours of the porcelain must, by necessity, be transitioned into the poorly aligned contours of the malpositioned tooth. Some of our color-matching illusions stem not just from matching a color, but also from where that color reflects light. Just by changing the position, of a tooth it is possible to alter the
appearance of a color. Sometimes it is necessary to alter the color of a tooth to match its position, in order to change how that color is perceived by the eye and then interpreted by the brain.
Just by changing the position of a tooth it is possible to alter the appearance of a color.
Ocular Perception and Brain Interpretation
Most experienced cosmetic dentists are familiar with the basic three dimensions of color: Hue, value, and chroma (saturation). In addition to the three dimensions of color, there are other factors that must be managed for a successful shade-matching experience. One significant factor is the color property of metamerism (in which either of two colors of different spectral composition appear identical to the eye of a single observer under some lighting conditions but different under others; or that, under constant lighting conditions, they appear identical to some observers and different to others).1,2 Metamerism occurs when two objects are the same color but are molecularly different in structure. As with two different fabrics, for example, wool and silk, dyed with exactly the same dye—the two colors may match in natural daylight, but may not match in a different type of light (e.g., incandescent).
Interpreting Color Based on Context
Other factors that influence color are the effects perceived by the eye and interpreted by the brain. One example is the way that the brain interprets a color based on its context. In Figure 1, the light gray square in the shadow cast by the cylinder is exactly the same color as the dark gray square in direct light, but our mind probably refuses to “believe� it.3 This is because we have learned to interpret colors based upon their context. A color that is perceived to be in the shade will appear to be much brighter than the exact same color if it appears to be in direct light. Because of this perception, brighter teeth will generally appear to be larger and closer.4,5 Conversely, a prominent tooth that is the same shade as its neighbors that are in the shadows will appear to be darker.
This fact is significant when matching the central incisors, especially if they happen to be prominent. In Figure 2, the two central incisors appear to be lower in value than the lateral incisors. When the lateral incisor is digitally cut and pasted directly onto the adjacent central incisor, teeth #9 and #10 appear to be the same color (Fig 3). The reason for this discrepancy is that our eyes interpret the central incisors as being prominently placed in the light, and the surrounding teeth as being more lingually placed back in the shadows. The brain then interprets the central incisors as being lower in value based upon their context, just as in the example of the gray shadow in Figure 1.
Figure 2: The new all-porcelain restorations are an improvement over the porcelain-fused-to-metal crowns. The hard and soft tissue contours, margins, and translucency look healthy and realistic.
Figure 3: When the left lateral is digitally positioned over the central incisor, the value of the two teeth appears to be the same. This is similar to Figure 1, in which the color of the green dot is affected by its context. The color of these teeth is being influenced by context, not by value of the porcelain. We expect the more prominent central incisors to appear lighter than the lateral incisors.
Figure 4: The color of the porcelain on these central incisors is actually lighter than the adjacent lateral incisors. In spite of this fact, the restorations appear to match because of the inherent expectation that these two teeth will appear slightly lighter than the lateral incisors.
The porcelain restorations on the two centrals shown in Figure 4 appear to match better than the previous set of veneers. In this case, the central incisors are slightly lighter than the adjacent teeth. To achieve the greatest colormatching accuracy with photographic color communication, it is important to place the shade tab in the same plane as the tooth being matched. In my experience, the most ideal shade tab position for color matching is sitting adjacent to and in the same plane as the tooth being matched (just like a bridge pontic). This ideal shade tab position also can be recreated using image manipulation software. This can be done by photographing the shade tab placed in a position incisal-edge-to-incisal-edge in the ex-act same plane with the tooth that is being matched. The photograph of the shade tab can then be digitally manipulated to place that shade tab into the “pontic� position adjacent to the tooth being matched for more precise color comparison (Fig 5). This enables the laboratory to visualize the subtle differences between the shade tab and the actual tooth, and to modify the color of the porcelain accordingly.
Figure 5: Trial shade tabs photographed and manipulated with software to position the shade tabs in the same plane and position as the adjacent tooth.
Successfully matching central incisors involves more than simply choosing the correct hue, value, and chroma.
Conclusion
Successfully matching central incisors involves more than simply choosing the correct hue, value, and chroma in order to match a porcelain restoration to a natural tooth. It requires an understanding of other factors, such as tooth contours and tissue health. It also requires an understanding
of other dimensions of color such as metamerism, visual context, and lighting. Understanding and managing these properties of color, lighting, and perception can help to increase the success of color-selecting appointments and assist with identifying and trouble shooting particularly challenging shade-matching situations.
References
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1. MedlinePlus. Merriam-Webster Medical Dictionary.
Definition of metamerism. Accessed
August 23, 2007, at http://www2.
merriam-webster.com
2. Magne P, Belser U. Bonded Porcelain Restorations
in the Anterior Dentition: A Biomimetic
Approach (p. 230). Hanover Park, IL: Quintessence
Pub.; 2002.
3. Adelson E. Checkershadow illusion. Accessed
August 22, 2007, at http://web.mit.edu/
persci/people/adelson/checkershadow_illusion.
html
4. Magne and Belser, op cit., p. 84.
5. Chiche G, Pinault A. Esthetics of Anterior
Fixed Prosthodontics (p. 31). Hanover Park,
IL: Quintessence Pub.; 1994.
Reprinted by Permission, The Journal of Cosmetic Dentistry Fall 2007, Volume 23, Number 3.
