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June 9, 2008

By Sarita Arteaga, DMD, MAGD

Light is a form of energy and is necessary to allow us to distinguish colors. When Euclid, a Greek mathematician, wrote Optica in 300 BC, he speculated that light travels in straight lines. Isaac Newton was the first to take a beam of white light and separate it into component colors or wavelengths.

Light strikes an object and is reflected, refracted, absorbed, scattered, and transmitted. As light is reflected by surfaces, including teeth, it enters the eyes and is absorbed by pigments in the photoreceptors of the retina, which sends signals via the optic nerve to the retinal ganglion fibers. These fibers terminate in the lateral geniculate nucleus that processes this information to the visual cortex of the lower cerebral cortex. The photoreceptors (the rods and cones) have photopigments that change chemically to each respective wavelength. Rods transmit no information on color, but there are three classes of cones (red, green, and blue) that do.(1)

What we see as color has been described by Munsell as hue (the property of wavelength that allows you to distinguish one color from another), value (lightness or darkness of an object), and chroma (intensity, saturation, or purity of color). A tooth's appearance is affected by its hue, value, and chroma.

Opacity is the term used to describe a tooth's "hiding power" of its internal surface, and is usually related to its thickness. Translucency is used to describe a tooth's ability to allow light to pass through its surface. Other factors that affect the color of a tooth include surface texture, size, tooth position, age, tooth wear, and extrinsic or intrinsic discolorations.

An important issue to consider when selecting tooth shades is the person selecting the shade. Fatigue of the operator can be increased late in the workday; age, nutrition, emotions, and medications can create changes in discrimination of colors. In addition, the environment, such as the ambient lighting, the color of the patient's clothing, or if the patient is wearing lipstick can change the shade chosen.

This article discusses traditional and technology-based shade selection methods available, with a brief overview of each system.

VITA shade guides

The VITA Classical Lumin Vacuum (Vident, Bad Sackingen, Germany) guide for porcelain shades has been universally accepted and in use for more than 50 years for laboratory restorations and resin composite materials. Divided into four groups, the traditional guide has an A group for the reddish-brown teeth, a B group for reddish-yellow teeth, a C group for gray teeth, and a D group for reddish-gray teeth. Within each group, there are 1 through 4 designations: 1 having the least chroma and highest value (brightness), and 4 having the most chroma and lowest value.

If placed in value based order, the tabs would be arranged as: B1 A1 B2 D2 A2 C1 C2 D4 D3 A3 B3 A3.5 B4 C3 A4 C4. The VITAPAN 3D MASTER (Vident, Bad Sackingen, Germany) shade guide has 26 tabs in five groups, where the value is selected first (groups 1 through 5), the chroma next (within the value group), and the hue last (determine if the tooth has more yellow or red cast). Recently, lighter shades have been added due to the increasing use of bleaching agents that change the tooth to higher value and lower chroma.

Rearranging the tabs from lightest to darkest can facilitate selection of a shade using these guides. Additional procedures can assist in choosing a shade:

• Clean the tooth to be matched.
• Select the shade at the beginning of the appointment.
• Align the eyes evenly to the tooth using a diffuse light source.
• Place the tabs on the same level of the tooth for five seconds only with a neutral gray card in between.
• Reduce the number of tabs quickly.
• Wet both the tooth and the tab with water.(2)

The limitations of these guides can be due to variations of the porcelain, even with the same manufacturer, and the tabs are 4 to 5 mm thick, while the restoration may only be 1.5 to 2 mm thick.

Technology-based guides

Bergen developed a technique to use a spectrophotometer and a computer to select a shade, while in the late 1990s, the Cortex Machina (Cynovad, Canada) was developed at McGill University in Montreal, Canada.(3) RGB (Red, Green, Blue) devices will capture an image with a halogen light source, provide digital shade mapping, and with specific software can be viewed with an LCD screen. The difficulty is with standardization of the different types of cameras and the cost. ShadeScan (Cynovad, Canada, $7,500), a corded unit that transfers the information to a computer screen with specific software, and various digital cameras ($3,500 and up) that save the information to memory cards are RGB devices.

Spectrophotometers will measure and record the amount of visible radiant energy (rectified or transmitted) on the surface color. These use spherical optics and monocoil fiber-optic cables with a halogen bulb, read the data to transmit to an LCD display, or can be transferred to a computer. Spectrashade (MHT Italy, $6,500), a hand-held unit with the LCD attached and VitaEasyShade (Vident, Bad Sackingen, Germany, $4,800), a hand-held unit attached to a separate tabletop LCD box, are examples of this equipment.

Colorimeters will filter light in three to four areas of the visible spectrum and measure data from the tooth under a fixed set of illuminant and observer conditions. This data can then be transferred to a computer and a laboratory. Shade vision (X-Rite, $7,500), a cordless unit that can be connected to a base that will download the information, and ShadeEyeNCC (Shofu, Japan, $7,500), a cordless item that transmits the data via infared signals to a computer, are models of colorimeters.

Shade matching lights will simulate north sky daylight with 45 degree angled LEDs for color correction and will eliminate spectral reflection. These units are battery operated and reflect light as you select a shade with the traditional guides: Optilume Trushade (Optident, UK) and Rite-lite (Addent, Danbury, Conn., $200) will use a probe to pulse a xenon flash to illuminate the teeth and averages three to five locations on the tooth.

Steps to successful shade match

There are several methods to select a shade and for more successful approaches, certain steps can be followed. For the traditional shade guides, the approach to successful shade selection includes placing the tab near the tooth. Other suggestions would be to have color-balanced fluorescent lights, remove lipstick on female patients, use the incisal edge of the tab, and wet both the tab and tooth. Technology has expanded the techniques available and continues to incorporate computer advances, but is still limited to the equipment and cost. Use computerized systems and digital images as adjuncts, since the human eye can process light and color the best.

Sarita Arteaga, DMD, MAGD, graduated from New York University's Washington Square University College with a BA degree in biology in 1986. After attending the University of Connecticut School of Dental Medicine, she received a DMD degree in 1990 and completed a general practice residency at Bronx Municipal/Albert Einstein Hospital in the Bronx, N.Y. Returning to Connecticut, she was an associate in private dental practice. After an appointment as an assistant clinical professor at the University of Connecticut, she has been teaching and seeing patients at the Health Center since 1995. In the Department of Reconstructive Sciences, she is a course director for the Operative Dentistry I course and teaches in Operative Dentistry II, III, and IV, as well as the Fixed Prosthodontics preclinical course and clinic coverage for students in the third- and fourth-year dental school classes. She attained a Mastership from the Academy of General Dentistry, and is a member of numerous dental associations. She is currently president of the Hispanic Dental Association. She is a faculty advisor for the Student National Dental Association/Hispanic Student Dental Association at the University of Connecticut School of Dental Medicine. She also serves on the Admissions Committee. Dr. Arteaga takes an active community role, performing screenings at the Head Start program in Waterbury and Meriden, the Special Olympics, and South Park Inn Homeless Shelter in Hartford. You may contact Dr. Arteaga by e-mail at Arteaga@nso2.uchc.edu.

References

1. Chu SJ. The success of color and shade selection in aesthetic dentistry. Dent Today 2002; 21(9):86-89.
2. Paravina RD, Powers JM. Esthetic Color Training in Dentistry. Elsevier Mosby. 2004.
3. Avery D. New shade-matching technology: The final piece of the shade communication puzzle. J Dent Technol 2003; 20(6):34-35.
4. Chu SJ, Devigus A, Mieleszko AJ. Fundamentals of Color: Shade-matching and communication in esthetics dentistry. Quintessence Publishing Co., Inc. 2004.
5. Sproull RC. Color matching in dentistry, part 1, The three dimensional nature of color. J Prosth Dent 1973; 29:416-424.

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