February 2012, Volume 8, Issue 2
Published by AEGIS Communications
How to get back to basics to ensure a predictable result.
By Chad J. Anderson, MS, DMD
Current technology in shade matching, although interesting, has not had any significant changes in a number of years. The author is often asked how the general practitioner can get the best shade-matching results without a significant investment in a shade-matching device such as the VITA EasyShade® (Vident, A VITA Company, www.vident.com) or the CrystalEye (Olympus America, Inc., www.olympusamerica.com). These systems can cost thousands of dollars and yet their use does not guarantee a perfect or, in some cases, even a good color match.1 Very often getting a good or great result consistently will not require any more investment in materials than what the clinician most likely already has in the office. What will be needed is a little color science background and the time to diagnose specific problems with a shade-matching protocol, and just get back to the basics.
In this article the author will be limiting the discussion to a few of the most often overlooked areas affecting clinicians’ ability to accurately match a standard shade guide in the operatory setting, focusing on the receptor and direct and indirect lighting sources. To address the receptor, the author will start with a refresher in color science and human physiology.
The most delicate and sensitive instrument in the whole shade-matching process is the observer’s eye.2 It is composed of approximately 120-million-plus light-recepting structures, called rods and cones (Figure 1). The rods see on a gray scale and are responsible for the amount of light allowed to enter the eye by regulating the pupillary constriction.2 The cones are specialized color receptors with three specific types relating to the frequency of light they absorb: red, blue, and green. The combination of these three frequency-specific cone receptors allows for the brain to interpret the color images humans see.2 The brain uses the information from the cones and rods in a process referred to as the “opponent-process theory.” It interprets information by processing signals from cones and rods antagonistically. There is some overlap of the three types of cones in the wavelengths of light to which they respond, providing a more efficient visual system to record differences between the cones’ responses, rather than each cone’s individual response.
The cones and rods produce an electrical signal and, much like muscles in the body, these structures must restore the chemicals used to send a signal to the brain. The chemical is a photo-pigment called rhodopsin. This mechanism can fatigue or become attenuated if we look for too long at an object without averting our gaze. The rule of thumb is not to stare at an object for more than 5 seconds.2,3
To prove this point, look at Figure 2. Stare at the image intently without blinking or diverting your eyes for 30 seconds. After the 30 seconds, close your eyes and tilt your head back, as if you are going to look at the ceiling, but do not open your eyes. What do you see? The Italian flag—green, white, and red? You should see the image you were staring at with complementary colors appearing to replace the colors of the image. This is the opposite of what you were looking at, as you have caused the cones and rods associated with the image to be fatigued, leaving an after-image. The author finds that when taking his own shades or teaching students, clinicians tend to stare at the teeth with a shade tab next to it for far too long, in the hope that it will become clear to them which shade is the best match, only to become more conflicted as time passes. The relationship of the tab to the teeth should be assessed quickly, taking no longer than 5 seconds in concentrated focus.4 If it cannot be determined during this time, avert your eyes to a neutral back ground or just simply look around for a few seconds before reassessing the best match. It is also helpful to have more than one individual take the shade.
One of the most overlooked areas in shade matching is the light source and, specifically, conflicts caused by indirect lighting sources. It is critical that the main light source being used to illuminate the teeth is a full-spectrum source. Many dental operatories in the United States use fluorescent lighting. With the advent of some new energy-saving regulations, incandescent light bulbs may become harder to purchase. Fluorescent bulbs are an energy efficient source of light but they are not ideal for rendering color accurately; however, this type of light can be optimized for color-matching. There are several light-bulb manufacturers that produce fluorescent bulbs that can do an adequate job of reproducing color. These bulbs all have a CRI (Color Rendering Index, a range of 1 to 100) above 90. A standard “cool white” fluorescent lamp, for example, will have a CRI near 62, whereas natural sunlight has a CRI value of 100. This score represents the light source’s ability to reproduce the full spectrum of visible light. The higher the CRI number, the better it will be for shade matching.
The author is currently using a 5,500K fluorescent lamp with a CRI of 91. These lights can be found easily at numerous retailers. If you cannot find these lights or you want to use your local hardware store such as Lowes or Home Depot, make sure to verify that the light is between 5,200K and 6,000K with a CRI above 90.5 The total amount of light is also important, but too much can be as bad as too little. Light intensity and volume is a little harder to quantify, but 200 footcandles is considered to be ideal. If putting in more lighting or modifying operatories for proper light intensity is not possible, there are some handheld sources of light that can be a good adjunct to existing lighting and are not too expensive. The Rite-lite™ (AdDent, Inc., www.addent.com) is a 5,500K handheld LED light that can provide a good source of light for those who cannot adjust their lighting environment. It gives the practitioner a full-spectrum light source in the palm of their hands (Figure 3). The Rite-lite is held between the observer and the teeth, and has a window that you can look through much like a magnifying glass, or you can look from the side and shine the light on the subject teeth. The author prefers the latter method. When it comes to light, it ideally should have all the color of the spectrum in equal amounts. If the light has more yellow, the object being viewed will appear more yellow. If the light source is too orange, the object will appear more orange. These yellow and orange spectrum lights, lower in Kelvin number, will cause the observer to select teeth in the VITA Classic A and B shade ranges (Figure 4).
Nearby color interferences also can cause shade assessment difficulties.2 Bright make-up, such as red lipstick, or bright-colored bibs and clothing can cast colors onto the teeth that are not present in a neutral color setting. Also, indirect light sources can have a profound effect. Some of these indirect light sources are operatory windows, hall lighting, and the overhead operatory light. These light sources can provide light that has been filtered and are of a narrow spectrum of color. Also, adjacent colors such as the paint color of the operatory can create challenges. If the operatory is painted in a bright color, this color will be reflected to the teeth and it can conflict with a proper shade match. All energy-efficient windows have a coating to reflect solar emissions. These tinted windows can have a profound effect on the available light in an operatory and, thus, can affect the color selected especially because most of these tints are brown or gray in color. Subsequently, the light transmission will lead the clinician to select a VITA Classic shade in the D or C range (Figure 5). As an example, the author took over ownership of a practice that had very large tinted sliding glass windows composing the entire north-facing wall of the operatory. This glass wall had a platinum energy-conserving film on its exterior surface. On the other side of the window was a row of tall green shrubs that filtered the majority of the natural light from this northern-facing exposure. As one could imagine, the author was perplexed when reviewing the patient charts and lab slips that a VITA Classic C shade tab was selected in more than 70% of the cases yet in his own private practice it was very rare for this tab to be selected.
Shade matching is a process that is often taken for granted and where success is often based on whether the patient accepts the outcome or rejects it. This article identified three basic rules to follow: 1) verify and possibly change overhead light bulbs; 2) make sure the shade is taken in a neutral color environment; and 3) do not stare too long (more than 5 seconds) when matching the subject tooth to the shade guide. For a relatively inexpensive investment in time and materials, clinicians can give themselves the best opportunity to match the shade correctly the first time.
1. Goodacre CJ, Paravina RD, Bergen SF, Preston JD. A Contemporary Guide to Color and Shade Selection for Protsthodontisits. American College of Prosthodontists. 2009.
2. Chu SJ, Devigus A, Paravina RD, Mieleszko A. Fundamentals of Color: Shade Matching and Communication in Esthetic Dentistry. Chicago, Ill: Quintessence; 2010.
3. Clark EB. The color problem in dentistry. Dent Dig. 1931;37:499-509.
4. Miller LL. A Scientific Approach to Shade Matching. Chicago, Ill: Quintessence; 1988.
5. Commision Internationale de l’Eclairage. Colorimetry, Official Recommendations of the International Commision on Illumination [Publication CIE No. 15 (E-1.3.1)]. Paris: Bureau Central de la CIE, 1971.
About the Author
Chad J. Anderson, MS, DMD
Tufts University School of Dental Medicine