Shade Matching in Restorative Dentistry: the Science and Strategies

The International Journal of Periodontics & Restorative Dentistry 3

Shade Matching in Restorative Dentistry: The Science and Strategies

James Fondriest, DDS* When light rays of different colors are added together to form a mixture, the eye perceives it as lighter Closely matching natural teeth with an artificial restoration can be one of the most than the original colors that were challenging procedures in restorative dentistry. Natural teeth vary greatly in color combined to create it (additive col- and shape. They reveal ample information about patients’ background and person- oration). Mixing colors of light is very ality. Dentistry provides the opportunity to restore unique patient characteristics or different from mixing colors of replace them with alternatives. Whether one tooth or many is restored, the ability opaque pigments. Colorants like to assess and properly communicate information to the laboratory can be greatly pigments, dye, and lacquer deal with improved by learning the language of color and light characteristics. It is only possi- reflected light. When an artist or ble to duplicate in ceramic what has been distinguished, understood, and commu- dental ceramist works with pigments nicated in the shade-matching process of the natural dentition. This article will give or dental porcelains of varying opac- the reader a better understanding of what happens when incident light hits the sur- ities, the amount of light reflected is face of a tooth and give strategies for best assessing and communicating this to the dental laboratory. (Int J Periodontics Restorative Dent 2003;23:xxx–xxx.) decreased with the addition of different colors. Opaque pigments absorb or subtract the light waves of all colors except those perceived by the eye. Each subtractive mixture is darker than the original colors combined to create it. Each pigment absorbs different wavelengths and increases the absorptive ability of the mixture, decreasing the reflectance. The three primary colors of opaque pigments act differently when mixed, blending to gray or black. The primary colors of light (additive) are red, green, and blue- *Visiting Faculty, LD Pankey Institute. violet. The primary colors of opaque *Reprint requests: Dr James Foundriest, 560 Oakwood Avenue, Suite 200, Lake Forest, Illinois 60045. e-mail: [email protected] pigments (subtractive) are red, yellow, and blue. The additive primaries

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when combined yield white. The chologic interpretation of a sum of Other optical properties subtractive primaries when com- wavelengths. In dental terms, hue is bined yield black. represented by A, B, C, or D on the Translucency Every opaque object is receiving commonly used Vita Classic shade light, the three primary light colors in guide. Dental ceramics try to imitate the some ratio. Some objects reflect all appearance of the tooth as a sum of of the light they receive, and others its visual dimensions. Human teeth absorb it almost totally.1 Most Value are characterized by varying degrees “opaque” objects absorb partially of translucency, which can be and reflect the rest. The dominant Value, or brightness, is the amount of defined as the gradient between wavelength/s reflected back to the light returned from an object. transparent and opaque. Pieces of eye is the perceived color of the Munsell described value as a white- frosted glass or ice can have the object. White paper reflects almost to-black gray scale. Bright objects same chroma, hue, and value but all visible light rays; black objects have lower amounts of gray, and not look the same. Generally, absorb most of the light so nothing low-value objects have larger increasing the translucency of a is reflected back to the eyes. A per- amounts of gray and will appear crown lowers its value because less fectly black body is basically darker. The brightness of a crown is light returns to the eye. With unchanged by shining light on it. A usually increased in two ways: by increased translucency, light is able yellow object when illuminated by using lighter porcelain (lowering to pass the surface and is scattered the three primary colors will actually chroma), or by increasing the reflec- within the body of porcelain. When absorb the blue-violet and reflect tivity of the surface. Lowering value light enters enamel, it gets bounced back the red and green, which, when means diminished light returns from around the enamel. If one side of a mixed, will appear as yellow. the object illuminated; more light is tooth is illuminated with a curing being absorbed, scattered else- light, the entire crown is lighted. where, or transmitted through. Enamel is an optically dense mater- Munsell’s color theory ial bordered on either side by air or dentin, both with significantly lower Albert Munsell described color as a Chroma optical densities. Normally, increas- three-dimensional phenomenon . ing opacity or reflectivity increases He described the three dimensions Chroma is the saturation, intensity, or value. By increasing the optical den- as hue, value (brightness), and strength of the hue. Envision placing sity of dental ceramics, the fiberop- chroma (saturation). red food dye into a glass of water. tic properties of natural enamel can Each time more of the same color be replicated and the prosthetic dye is added, the intensity increases, crown can be bright and translucent Hue but it is the same red color (hue). As at the same time. With the translu- more dye is added, the mixture also cent enamel layer, the ceramist Hue is the quality that distinguishes appears darker, so the increase in achieves color depth and the illu- one family of colors from another. It chroma has a corresponding change sion of a vital natural tooth. The is specified as the dominant range of in value. As chroma is increased, the translucency of enamel is a function wavelengths in the visible spectrum value is decreased; chroma and of wavelength. The longer the wave- that yields the perceived color, even value are inversely related. Higher length, the higher the translucency. though the exact wavelength of the numbers on the Vita Classic shade Therefore, enamel is more translu- perceived color may not be pre- guide represent increased chroma. cent in light rich in yellow and red sent.2 Hue is a physiologic and psy- (eg, incandescent light) and will

The International Journal of Periodontics & Restorative Dentistry 5

Fig 1 Appearance of a tooth is the summation of reflected, transmitted, and opalesced light.12

Incident Scattered light light (opalescence)

Absorption

Reflected light Fluorescence Transmitted light

show more dentin, making the tooth cial in high-value shades, as it can appears bluish even though it is col- appear redder, with a higher chroma raise value without negatively affect- orless.1,5,10 The opalescent effects and lower value than it actually has.3 ing translucency when placed within of enamel brighten the tooth and the dentin porcelain layers. give it optical depth and vitality11 (Fig 1). Fluorescence Opalescence Ultraviolet (UV) light can have a dra- Contrast and glare matic effect on the level of vitality Opalescence is the phenomenon in exhibited by restorations. With the which a material appears to be one Contrast is caused by a difference characteristic of fluorescence, they color when light is reflected from it between the brightness or color of look brighter and more alive. and another color when light is trans- an object and its immediate back- Fluorescence is the absorption of mitted through it.9 A natural opal is ground. Object forms with high con- light by a material and the sponta- an aqueous disilicate that breaks trast are easier to pick out than neous emission of light in a longer transilluminated light down into its objects with low contrast. While wavelength.4 In a natural tooth, it component spectrum by refraction. some contrast is helpful, excessive primarily occurs in the dentin Opals act like prisms and refract contrast causes glare. An extremely because of the higher amount of (bend) different wavelengths to vary- bright object against a dark back- organic material present.1,5–7 ing degrees. The shorter wave- ground or significantly differently Ambient near-UV light is absorbed lengths bend more and require a colored objects cause discomfort and fluoresced back as light primar- higher critical angle to escape an and can interfere with percep- ily in the blue end of the spectrum, optically dense material than the tion.1,13,14 This interference is but it will occur at all wavelengths. reds and yellows. The hydroxyap- generically called glare. The illu- The more the dentin fluoresces, the atite (HA) crystals of enamel also act mination of the teeth should not be lower the chroma.1,8 Fluorescent as prisms. Wavelengths of light have significantly brighter than the ambi- powders are added to crowns to different degrees of translucency ent environment.15 With dental pho- increase the quantity of light through teeth and dental materials. tography, the use of a black back- returned back to the viewer, block When illuminated, opals and enamel ground increases impact, but it will out discolorations, and decrease will transilluminate the reds and scat- chroma.8 This is especially benefi- ter the blues within; thus, enamel

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cause glare. Thus, one constantly creates weak, Proper environment for overlapping afterimages of which color rendering one is totally unaware. If presented Color perception simultaneously with two adjacent The ability to perform shade selec- areas of different color, the eyes will tion depends on how well the eyes Color perception depends largely flick back and forth between them perceive the details of teeth. Factors on human physiology. Humans have involuntarily. The color seen for each determining the visibility of these three types of cone-shaped receptor is a combination of the true color of details include ambient light quality, cells, each sensitive to one primary the area and the afterimage of the luminance (light quantity), size, con- color. Impulses from the three types adjacent area. When holding a trast, and glare. Establishing the of receptor cones are thought to shade guide close to a tooth, it is proper environment for evaluation combine into a coded signal prior to important to decide within seconds requires an understanding of these transmission from the eye to higher because the two will soon begin to “seeability” factors. Dental-unit visual centers in the brain. The com- appear more and more alike. lights are commonly used for color bination takes place in the ganglion A negative afterimage occurs rendering. Most are incandescent cells in the retina. Changes in the because of fatigue of the receptors, and emit light high in the red-yellow color stimulus change the patterns of which become less sensitive to fur- spectrum and low at the blue end. the coded signals.13 The eye can- ther stimulation. Strong red lipstick Therefore, illuminating opaque sam- not distinguish the component next to the tooth being evaluated ples of red, yellow, and blue under wavelengths in a color sample. Two will fatigue the red receptors in the an incandescent light source shows lights of different colors when mixed roaming eyes, while the blue and that red and yellow are quite strong, produce a third color, and no human green receptors remain fresh and or highly saturated, while blue is eye can detect its composite nature. can be fully stimulated. This can yield weaker and more difficult to see. Ultimately, the perceived hue is the a perception of the tooth that is too Under an ordinary cool white fluo- dominant or average wavelength. blue-green. Give the eyes a break rescent source, which is high in the The ability to perceive color differ- with neutral gray backgrounds. green-yellow spectrum with some ences varies from person to person. Kulzer’s small intraoral gray shields strong but narrow blue-spectrum screen background color glare; 18% spikes, the reds and violets are less reflective gray cards are the photo- apparent. Some fluorescent bulbs Afterimage and visual distortion graphic industry standard achro- have full color content and render matic background.16 Blue back- color more accurately. The ambient Afterimages are frequent physio- grounds are not appropriate light quality of the operatory must be logic effects of the cone receptors because they cause afterimages and maintained with artificial lighting with normal function that cause will bias perception to its comple- (natural light conditions vary); it is alterations in perceptions. One type mentary color, orange. Some advo- commonly measured by the color of afterimage that commonly affects cate use of a blue background17–20 temperature and Color Rendering clinicians is the spreading effect that to make the eyes more sensitive to Index (CRI). occurs when light is removed from yellow-orange, but this selectively the retina; the receptors continue fatigues one type of cone and does for a short time to be active and send not make the others any more sen- Color temperature a signal to the brain.1 Under normal sitive. An 18% reflective gray card is circumstances, the eyes do not stare an excellent background for photo- When black iron is heated gradually, fixedly at a single spot, but rather graphic evaluation of hue and it will begin to glow, first with a red roam the visual field continuously. chroma.21 hue, then yellow, white, and blue.

The International Journal of Periodontics & Restorative Dentistry 7

Plotting the temperature increase of trum is present. Although the close- might look different. The closer the this black iron radiator relates tem- to-visible UV spectrum cannot be curves of the two materials to be perature with color change and seen, it is commonly absorbed and matched, the more successful the establishes a color temperature fluoresced out at wavelengths in the color match will be.23 Use of opaque scale. This scale is commonly used to visible spectrum. Fluorescent bulbs surface stains to correct mismatches index color of light sources; the ideal tend to be at 3,000 to 4,200 K. The will increase metamerism. When color temperature for color render- average incandescent dental-unit reconstructing a tooth with dental ing is 5,500 K. Light at this temper- lamp has a CRI of 75 and averages porcelain, mimicking the layers of ature can be described as having a 3,800 K.13,20,22 Theoretically, the the tooth employing materials with medium-temperature feel and is ideal light to take a shade has an the same optical properties (spectral considered “white” light. Color tem- equal energy mixture of light—a bal- reflectance curves) will minimize perature is the mean wavelength of anced, equal mixture of all the visi- metamerism. the ambient light. Because color ble wavelengths. A CRI greater than temperature is an average, not all 93 is preferred. Ideally, both the clin- wavelengths are present, nor in ician and laboratory technician Light intensity equal amounts. should have balanced full-spectrum lighting conditions. The intensity of the light conditions is also important. If the amount of Color Rendering Index light (measured in foot-candles or Metamerism lumens per foot2) is too small, fine Not all wavelengths need be repre- details are missed and the eye has sented to produce white light; it can Metamerism occurs when restora- difficulty perceiving hue. Usually, the be simply produced by mixing the tions match in one light but display ceiling lighting in the dental opera- three primary light colors. Ambient a different color in other light condi- tory is not intense enough to see light is a varying assembly of many tions.16 One object may have the everything. With teeth that have different wavelengths. Artificial light- ability to reflect more red than subtle color variations, proper inten- ing can approach white light (5,500 another. However, if there is no red sity is needed. Too great an intensity K), but the full spectrum of wave- range in the light source, they will and glare decrease the accuracy of lengths is not necessarily present. appear the same; when viewed color rendering. Dental-unit lights The reflected colors (wavelengths) under a light source containing red, should not be used for color ren- of a tooth cannot be seen if those they will appear different. The color dering; they are too bright and cause wavelengths are not present in the seen depends on the nature of the glare. Glare fatigues the eyes; ren- ambient light spectrum.2,18 If ambi- light source illuminating the object. dering shades immediately after ent conditions have only a small The color of an opaque object is the using a dental-unit light is also con- range of the spectrum of light wave- sum of the wavelengths that reflect traindicated. lengths, all that is reflected back are off it. Light spectrum reflectance The ideal luminosity for dental the wavelengths present. If red light graphs measure the percentage of shade matching is 75 to 250 foot- is not fairly represented in the spec- reflectance of all the near-UV and candles.15,17,20,24–26 To have 175 trum, the reds in the object to be visible-light spectrum off of a mate- foot-candle intensity at the level of matched will not be visible. rial. Porcelain might reflect light off the dental chair, ten to twelve 4-foot CRI is the measure of the com- its surface exactly as enamel in one bulbs would be needed in a 10 ft ϫ pleteness of the light spectrum. A part of the spectrum, but under dif- 10 ft room with 8-foot ceil- measure of 100 indicates that the ferent illumination the two objects ings.1,14,15,25 The diffusion panels entire visible and near-UV light spec- that previously looked identical covering fluorescent bulbs are also

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Fig 2 (left) Roughened surface diffuses light.33

Fig 3 (right) Smooth, polished surface produces a well-defined image and can be more translucent.33

important because they screen out istics determine how light is Reflection from a smooth, mir- wavelengths. As they age, the pan- reflected, transmitted, or scattered, ror-like surface results in a clear, well- els change what wavelengths they affecting its hue, chroma, value, and defined image. Such a “specular absorb. The best diffusers, prefer- translucency.18,30,31 The appearance reflection” returns a high percent- ably the egg-crate type, do not filter of teeth is mostly determined by age of direct, nondiffused light, and out any wavelengths of the spec- how light interacts with the curved if strongly illuminated, will be trum. Using 10 to 12 color-corrected and varied surfaces. Attractive brighter and stand out (Figs 2 and 3). bulbs on the ceiling will yield more prosthodontic replacement starts Smoothing the texture of the buccal light in the operatory than would be with a consistent silhouette and surface will make teeth appear considered comfortable. Portable shape of the buccal surface because lighter and brighter and is therefore high-quality light units, such as the these factors determine how the a primary determinant of value. [AU: Vident light, are ideal. Shade match- majority of light will be reflected. Correct as edited?] The more reflec- ing with photography lessens, but An observer only sees an object tive the surface, the more wave- does not obviate, the need for spe- when light comes from that object. lengths return to the eyes; the addi- cial lighting. The proper shade tabs Surfaces perpendicular to the viewer tive combination of more still need to be selected. send the most light back. The reflec- wavelengths yields whiter light (hue tive surfaces of a tooth will not return change). Brighter objects appear as much light to the eyes if they are closer to the viewer, so a restoration Reflections of light not perpendicular to them. Because that is too light appears to “jump out a viewer mainly sees the surfaces of at you.” Lowering the value makes It is important to realize that hue and a tooth perpendicular to him or her, objects appear further away. chroma are fifth or sixth in impor- the perceived width and length can Roughening texturally the specular tance on the list of things to match be manipulated by bending or flat- highlights of a too-bright crown will when constructing a prosthetic tening surfaces. The practitioner can make it blend better. Most teeth replacement. One must be fairly make a tooth look narrower or have irregular surfaces with convex- close to someone to detect subtle shorter by decreasing the width or ities and concavities. The convexities differences in hue; yet shape, sur- length of the direct buccal reflective tend to wear and become smooth, face morphology, value, and translu- surface.32 Another example is a max- with specular reflective characteris- cency disparities can be seen from 4 illary incisor tipped lingually: It will tics. The visual impact of a tooth or 5 feet or more. Violating confor- not reflect light directly back and will comes from these specular high- mity of the unique characteristics of appear darker. The smile can be lights that give the tooth its visual the natural dentition will cause made to appear more uniform even shape. Concavities tend to be unpol- unwanted prominence of the without realigning the tooth simply ished and collect light by reflecting restoration.18,27–29 These character- by brightening it. inward, diffusing the light and return-

The International Journal of Periodontics & Restorative Dentistry 9

Fig 4 (left) Double reflection and absorption of light in the fissures and concavities cause diminution of light coming out of these areas.

Fig 5 (right) Light is reflected more in bulging and curved areas, which are generally more worn and polished.

Fig 6 (left) Heavy vertical surface textures highlighted by specular reflections off the heights of contour.

Fig 7 (right) Heavy horizontal surface textures sit on top of the vertical textures and thus follow in and out of the concavities.

ing less to the eyes33 (Figs 4 and 5). surface textures are primarily com- in a flat to U shape (bottom of U posed of the heights of contour of toward gingiva) across the buccal the developmental lobes and mar- surfaces of the maxillary incisors. Surface texture ginal ridges (Fig 6). The specular These horizontal undulations get highlights reflecting off these heights flatter and closer together going gin- After shape and contour, surface tex- tend to form the visual outline of the givally (Aiba N, personal communi- ture and luster are the next most tooth. cation, June 2001); they never cross, important factors affecting how light Perichymata, the fine, trans- and they go circumferentially. There interplays with the tooth surface. A verse, wavelike grooves believed to tends to be more stippling of these roughened surface texture will not be external manifestations of the textures gingivally. The concentra- yield as well-defined an image and striae of retzius,7,35 are horizontal tions of dechromatized white will scatter the light; the individual textures. The striae, or lines, of retz- enamel so often found in younger, wavelengths bend differently, yield- ius are the result of the layering man- more superficial layers of enamel are ing a substantially different spectrum ner in which the deposition of often associated with horizontal tex- returning to the eye.34 Texture can enamel takes place (Fig 7). tures. Horizontal textures are formed be broken down into subgroups: Perichymata can be abraded with on top of vertical textures; the hori- vertical, horizontal, and malforma- age, often resulting in horizontal zontal patterns follow into the con- tions (Aiba N, personal communica- grooves separated by distances cavities formed by the vertical tex- tion, June 2001). [AU: Personal much greater than the original tures, but the vertical are not communications (originally refs 35, perichymata traversing the tooth. affected by the horizontal. When tex- 38, and 60) moved into text; sub- These grooves can be convexities turizing restorations, carve the verti- sequent refs renumbered.] Vertical and/or concavities, and they stretch cal textures first and then overlay the

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horizontal ones. teeth tend to have a much lower lus- these top layers wear off, the under- Malformations are the third tex- ter but still have flat areas that allow lying enamel is less opaque. The tural group and can be from cracks, for specular reflections. Polishing the chroma of a tooth, which primarily chips, and other surface aberrations. rough glaze off a porcelain restora- comes from dentin, will be lower in Surface texture can be generalized tion is a subtle way to lower value by a young tooth because of the mask- as being heavy, medium, or light. A making the porcelain clearer and ing effect of the enamel. The natural rough, or heavy, surface texture will more translucent.36 Super-polished thickness of enamel is greatest at have a lower value because it tends flat surfaces can appear bright the incisal and lowest at the cervical to diffuse light by reflecting it in because of the specular reflection, aspect; therefore, chroma is greatest many directions, and less light but they also have more translucency at the cervical and decreases toward returns to the viewer. A light surface because the light is not scattered at the incisal aspect.38 As the enamel texture has a higher value beause of the surface. When a surface defect is gets thinner with age, the dentin the increased specular reflection. At polished down approaching the becomes more obvious and the eruption, teeth have their roughest wavelength of light, it disappears. tooth becomes less monochromatic. surface texture. With age, these sur- A surface can have different Young enamel is also more perme- face features gradually wear. As the combinations of texture and luster. A able and will dehydrate quickly. The wear process continues, all signs of heavy surface texture will produce a deeper layers of enamel have fewer the perichymata are usually lost, and lower value by redirecting reflections air spaces and are more highly min- even the definition of the develop- away from the viewer or with double eralized. This deeper enamel is more mental lobes is obliterated. inward reflections, and a high surface translucent.36 luster also makes a tooth or crown When light enters a tooth, it may darker and more translucent. reflect off many surfaces within the Luster Because of the impact they have on tooth before it exits, substantially the optical properties of the tooth, changing its character. The more There is an order of magnitude or the prudent practitioner will note scattering in the enamel, the higher more size difference between luster these properties in the lab prescrip- the value.6,10 Enamel rods and the and texture. Reducing the surface tion. surrounding interprismatic sub- luster of a piece of clear window stances are positioned perpendicu- glass by wet sanding or etching will lar to the dentin layer. Light tends to produce a frosty white look. As light Tooth color characteristics travel easily down the rods but not hits the surface of the etched glass, as well laterally. This directionally de- it scatters irregularly, causing an In a newly erupted tooth, the super- pendent light transmission is called increase in opacity. The light is not ficial layers of enamel are the most anisotrophy.39,40 A highly pigmented carried off and away from the sur- opaque. These layers frequently area can sometimes be seen from face, but rather reflected. As the appear as though they have a white one angle but not another. The glass becomes less translucent, the frost. This enamel may have a higher translucency of enamel varies with value goes up. The net effect is that organic component (Eubank J, per- the angle of incidence, surface luster, more light returns to the viewer as sonal communication, 2001; and wavelength, and dehydration. the luster goes down. A decrease in Boyde37), is less mineralized, and has The hues of natural teeth tend to luster creates a similar change in more empty space between the be in the yellow to yellow-orange enamel opacity as dehydration and enamel crystals, all causing in- range. If one were to place the rain- bleaching. It is important to note creased opacity.10,37 It has a very low bow on a line, the A shade is more that surface texture, not luster, deter- luster caused by the pronounced rod toward the red end of the yellow mines specular reflection. Young endings from enamel deposition. As spectrum, and the B shade is more

The International Journal of Periodontics & Restorative Dentistry 11

to the green end of the yellow spec- begins to influence value more. To between the HA crystals, which sig- trum. Most teeth are closer to A on raise the value in a restoration that nificantly changes how light inter- the Vita Classic shade guide, but needs to be highly translucent acts with the enamel and, with pro- there is a much wider spectrum of (translucency normally drops value), longed beaching, the dentin. natural hues than most shade guides the brightness needs to be built into Common clear glass is relatively provide.17,41–46 The thickness of the dentin instead of the enamel. transparent. When crushed into dentin, size of the pulp chamber, Value is typically lowest at the cervi- smaller pieces, the glass that remains and vitality of the pulp tissue differ cal, then at the incisal, and highest in becomes opaque. If water is added during different stages of tooth the middle third of the tooth.38 Value to the pile of broken glass, it development. Teenagers generally increases going medially from the becomes more translucent again. have a larger pulp chamber that maxillary canines to the central Dehydration increases the opacity adds red. With secondary dentin for- incisors.47,48 of the enamel. Light no longer can mation, the pulp chamber decreases Translucency is greatest in lateral go from HA crystal to crystal. Less in size, causing the dentin to appear incisors; therefore, opalescence (pri- translucency causes more reflection, less red.47 Older or sclerotic dentin marily in translucent enamel) is most so the tooth is brighter.6 The hue is darker (higher chroma, lower evident in them. The mammelons changes because of a change in the value) and has more green and blue. and interproximal contact areas usu- reflectance spectrum of the Young dentin is more red-yellow.38,48 ally show the most blue opalescence enamel.52 Recently bleached teeth (CIE Lab color spaces49 a* and b* go because there is no opaque dentin are not color stable; shade matching negative with age.) There is a posi- behind them to reflect back the red should be delayed for at least 1 tive linear correlation between age and yellow wavelengths. Canines month. The rebound of bleaching is and chroma of the roots.50 Although show very little translucency. mostly due to the rehydration of the dentin undergoes a color shift Remember that the maxillary canines enamel. Bleached teeth dehydrate from red-yellow toward yellow, the are often one to two full chroma much faster than other teeth, so overall color of older teeth is red- steps higher than the maxillary shade rendering should be com- der48;less bright enamel covers the incisors and will sometimes give a pleted prior to any treatment. red dentin because of wear. Different better clue to the average hue fam- teeth in the arch can belong to dif- ily. The hue and chroma of natural ferent hue families.48 a* (red-to- teeth are not constant. If a laboratory Surface staining green gradient) is highest (most red) uses the same porcelain for all of the in canines, then central, then lateral teeth in an arch, the mouth will look There are several very good uses for incisors.47 b* (yellow-to-blue gradi- flat.36 A natural three dimensionality porcelain surface stains. The best ent) is highest (most yellow) in can be developed with chroma gra- use is to help communicate the look canines, then lateral, then central dients getting darker from the cen- of a difficult-to-match tooth to the incisors.47 The cervical hues are tral incisors tothe posterior.51 lab. Painting the surface of a shade always redder than the middle or tab or a mismatched, already com- incisal ones.48 pleted crown is very helpful to the Value is mainly determined by Bleached teeth lab and can be a great complement qualities of the enamel layer in the to photography. Tanaka Dental form of reflectivity and opacity. As Bleaching teeth will cause a change Products makes a good porcelain the superficial layers of the enamel in hue, chroma, value, and translu- stain that can be painted onto the surface are worn, the translucency cency. Bleaching causes dehydra- surface of anything. It can also be goes up and the dentin becomes tion and the brightening or removal used for enhancing the beauty of more visible and dentinal chroma of pigmented organic material from provisional restorations; stains can

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be sealed on with Palaseal (Heraeus Labs should lower value primar- els to normal light conditions. This Kulzer), a light-cured methyl ily within the dentin layers, not with light level is still too low for hue methacrylate. Painting shade tabs is superficial stains. Translucent porce- determination but is perfect for fur- a great way to convey hue and lains are less metameric than the ther value evaluations. Now view chroma, but ultimately it can encour- more opaque body porcelains. The teeth with the lips relaxed (indirect age the lab to use surface stains on addition of proximal and lingual light) and reflected (with direct light the restoration, increasing stains can reduce a monochromatic at 90 degrees). If there is a great metamerism. appearance of a restoration without value drop when shadows are cast Stains can be used for charac- directly visible stains. Visual form can on teeth by the upper lip, or with a terization and modification of a mis- also be altered by the use of stains. polarized light filter, the predomi- matched restoration. When trying to Long restorations can be “short- nant brightness source is superficial, cover an unwanted color, one can ened” by the use of darker stains caused by high surface reflectivity. use subtractive laws of color mixing cervically. Stains can be used in many After value is determined, hue and and add the complementary color. ways to darken (deemphasize) or chroma are selected. The two colors will cancel each other highlight contours. Environmental conditions are out, blending to gray.53 Caution: This critical to the proper selection of hue will lower value. Chroma can be and chroma. Create a neutral-col- increased easily with surface stain Guidelines for matching ored environment. Extraorally, bright (subtractive darkening), and to a lim- clothing and the color of the walls in ited extent it can be decreased with Clinicians can create circumstances the operatory and lab can alter color bright stains, but these will decrease to allow for better viewing of the perception. Peri- and intraorally, lip- the light coming out of the tooth. teeth. If the quality of a match is stick and the red oral tissue back- Lowering the chroma with surface judged by shape, surface morphol- ground fatigue the cones, yielding stains will limit vitality and depth of ogy, value, translucency, hue, and complementary afterimages. The color. chroma, finding superior ways to best extra- and intraoral back- Laboratories commonly lower assess these is imperative. The chro- grounds for hue and chroma selec- the value of a restoration gingivally matic portion of value and the hue tion are neutral gray.55,56 Neutral by adding surface stains. Surface and chroma require the freshest eyes gray has no complementary color stains are less preferable than inter- and should be evaluated first. and is restful to the cones. This is nal staining for permanent restora- Remember that value or brightness even more critical with aged teeth tions because they are more opaque comes from two sources, the chroma that have a glossy surface that and a light barrier, which prevents of the tooth and the surface reflec- reflects the shade of any color seeing the color from the internal tivity. The chromatic portion is eval- placed in close proximity.15,22,35,56 body of ceramic,54 of the restora- uated with a value guide in subdued Use a gray bib or towel to cover the tion. They also wear off with time. light conditions.20,30 The rods in the patient’s clothes,57 and remove, Stains increase light absorption, alter eyes are sensitive to lightness/dark- retract, or cover any lipstick. reflectivity, and decrease translu- ness, or the value scale, even with Provide the ideal lighting con- cency and opalescence.54 Opaque small amounts of light. The cones ditions while hue rendering. No mat- surface stains increase the likelihood only become activated with higher ter what technique is used, without of metamerism.23,41 Grays attained light levels. When the cones are a light source that approaches 5,500 by mixing complementary colors are functioning, the hue and chroma K and has a CRI of 93 and the proper “complex” grays, with erratic spec- seen will confuse value discrimina- luminosity, a superior match is diffi- tral reflectance curves that increase tion. Once the chromatic portion of cult for the clinician and lab. [AU: metameric problems.23 value is measured, raise the light lev- Correct?] Viewing teeth under dif-

The International Journal of Periodontics & Restorative Dentistry 13

fuse illumination will minimize the shade tabs and the natural color of pendicular to them. distortion of the reflected light. the teeth increase near the root. Translucency is best evaluated Reflection from the specular surfaces Compared to the Vita shade guide, with a black background. The best of a tooth reveals more of the color natural teeth exhibit increased red- way to evaluate translucent areas is of the illuminating light than the ness and lower translucency at the to look for the opalescent blues. The color of the tooth.3 Consider using a cervical aspect,22,38 and this must be translucent enamel transmits reds portable Vident light with a rheostat noted in the prescription. Because of and yellows and holds in blues. A that can control the light intensity later eye fatigue, first impressions black background prevents the reds and give a diffuse illumination. are the best. To prevent hue accom- from the back of the mouth from Miller44 has suggested arrang- modation, do not stare at the teeth remixing with the blues. When drawing the Vita Classic shade guide by for more than a few seconds.20 Most ing proximal translucence, ask the hue with the A and B hues at oppo- humans have eye dominance, and patient to turn from right to left, site ends and C and D in the mid- one eye will preferentially perceive which allows a better analysis. dle.42 C and D have hues in between shade.51 In addition, difficulties can Shade map in a 3-D drawing all A and B43 on the linear rainbow arise where the tooth being exam- that is seen. Use multiple views (eg, (chroma and value are manipulated ined differs considerably in size from 90-degree straight buccal, straight to yield different looks). When the specimen on the shade guide. A incisal/occlusal). Break the labial face choosing the hue family, use the A- variation in color perception can of the crown into zones. Describe 4 and B-4 or A-2 and B-2 tabs, which occur, with the larger area appearing the surface texture as vertical, hori- facilitates the process of elimination brighter and more vivid.60 zontal, or with malformations, and by using tabs with the greatest hue Different light wavelengths whether it is heavy or light. The pre- spreads.20 The chroma is very low for reflect off a rough surface in different operative models will help duplicate shades A1 and B1; it can be difficult ways. Shades should be evaluated these contours, although the luster to distinguish the proper hue family by looking at the tooth at different and texture can be better docu- using these tabs. Compare the high- angles, or vectoring.16,27,51 It is wise mented photographically. Be spe- est chroma tab in each hue family to hold the shade guide on both cific when describing the reflectance with the maxillary canines. If in doubt sides of the tooth at different vectors pattern and heights of contour on as to the hue family, choose A (Miller (Aiba N, personal communication, the prescription form. These surface L, personal communication, Feb June 2001). Because of the curved features determine the character 2001; and Smith and Wilson58). Most translucent surfaces found on teeth, and amount of light reflected35 and natural teeth have more red than the the anisotrophic properties of the amount of light that enters the B family. Perhaps as much as 80% of enamel, and the complex layering of tooth. The surface morphology of a natural teeth are a closer match to the tooth structure, vectoring will crown should be designed to simu- the A hue family.59 allow the operator to identify col- late the contralateral tooth. Hold the shade tab incisal edge orations within the layers of the tooth All shade guide selection should to the incisal edges of the teeth. This and better visualize the translucent be done before turning on the den- effectively isolates the shade tabs areas. Sometimes, the value of the tal-unit light. This light is too bright from the teeth so they do not reflect gingival and incisal thirds of a tooth and causes eye fatigue.51 Another onto each other (Aiba N, personal is seen as lower than it actually is reason to do shade selection before communication, June 2001; and because of the natural curvature of treatment is dehydration. Ray22), reducing afterimages. When the tooth.56 These are all limitations choosing the hue with a shade tab, of the new mechanical shade-taking look to the midbuccal aspect of the devices that register reflected light tooth. Differences between the predominantly from surfaces per-

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amount of reflection back at almost any angle. Note that if the pictures are taken below the incisal edge, the flash will light the back of the mouth, making it difficult to evaluate hue, chroma, and translucency without a background.62 An 18% reflective gray card is a helpful back-

Fig 8 For chroma and hue, take shots at Fig 9 Shade guides perpendicular to the ground while selecting hue and 60 to 70 degrees from surface with incisal flash have reflections rendering them use- chroma.16,21 It has no complemen- edge of tooth down and away from cam- less for hue and chroma evaluation. One tary colors (thus, no afterimages are era; keep tabs at uniform distance from never knows what reflections will appear in tooth surface; vector shots; use 18% reflec- a slide until later, so take pictures at many produced), and it is bright enough to tive gray background; include occlusal and angles. limit the contrast of brightness incisal shots; and bracket F stops. between the teeth and background. The cardboard Pensler Shields should be kept 5 to 15 mm from the teeth (Fig 10). Photos for shade rendering Surface geography and value shots It is easier to identify the translu- should be taken at 90 degrees from cent areas of a tooth with a black Many methods have been described the surface. The teeth can be wetted background behind the incisors (Fig to facilitate the transfer of shade for hue and chroma evaluation to 11). This will stop any light reflected information to the lab. It is difficult to limit the influence of surface mor- from inside the mouth from reenter- accurately describe a complex, mul- phology (Fig 8). ing the enamel (thus adding itself tilayered, multitextured, 3-D color Arrange the matching tab in the back in), which would lessen the scheme of varying opacities with a 2- middle and use the tabs one chroma visual impact of the bluing in translu- D shade guide system.43 In addition, stop higher on the right and one cent areas.63 Bracket the camera F 9.3% of male dentists have a color stop lower on the left. Note that stops. Closing down the lens vision defect, and most of them do shade guides are being used not to increases contrast and allows better not receive help with matching from measure sum total color, but rather visualization of the internal struc- someone trained in color science.61 the color of each layer of the tooth. tures. Lower light helps identify the The best way to communicate Use as many tabs as there are colors coloration within the different layers to a laboratory is with color-accurate in the tooth. If more than one hue of the tooth and better viewing of 35-mm slides. Use a color-corrected family in a tooth/arch is visible, photo translucent areas.64 A black back- professional-quality film (eg, Kodak all the tabs that seem to match. ground is not useful in hue and EPN-100, E100-S, or EPP; Eastman Suggest ratios to the lab in the pre- chroma selection, as it increases Kodak), and use a good photo lab scription. Vector shots. Try to keep glare.13 Because of the confusing for developing. An accurate clinical the tabs at the same distance as the influence of hue and chroma in the photograph can document numer- teeth from the camera; if brought shade tabs, value can be more eas- ous details that would be missed by closer, they will appear brighter. ily evaluated in low light or with the eyes. Use a color-corrected flash. The reflections produced at 90 black-and-white film.63 The teeth should be dry when degrees reduce the ability to color Remember to take incisal or evaluating value, translucency, and render the tooth and/or shade tab occlusal shots. The older the patient, surface geography to allow unre- (Fig 9). A ring flash surrounds the the higher the chroma of these stricted observation of surface. camera lens and increases the areas. Also take photos with shoul-

The International Journal of Periodontics & Restorative Dentistry 15

der and incisal porcelain tabs. Although the media image of teeth has a limited chroma gradient going gingivally, if one wants the single central to disappear, this information is needed. Distinguishing the source of value can be challenging. Use of a polarized light filter will cancel the Fig 10 Gray background is too far Fig 11 For translucency, use a black reflected light, making it easier to behind the teeth; it appears to be black, background; underexpose shots; take determine if the brightness is from which increases contrast and glare. shots from 60 degrees to surface (from Gingival necks are also partially copped, above); and vector shots. 65 low chroma or surface reflectivity. not allowing total view of the teeth. If an all-ceramic restoration is to be used, photograph the prepared teeth. Keep the prepared teeth wet for these pictures. An extension tube allows for more magnification of the charac- the proper language. Both clinician 5. Winter R. Visualizing the natural dentition. J Esthet Dent 1993;5:103–117. terizations. Take photos at 1:1 scale. and technician need to understand the nomenclature of visual effects. 6. Cornell D, Winter R. Manipulating light The technician can then use calipers with the refractive index of an all-ceramic to measure exactly where to place Clinicians should create the optimal material. Pract Periodontics Aesthet Dent characterizations. Always document environmental circumstances in the 1999;11:913–917. the shade tabs visible in the slide by shade-matching process so that all 7. Orban BJ. Oral histology and Embryology, including the tab number in the pho- that there is to see can be seen with- ed 6. St Louis: Mosby, 1976. tograph or writing it down on the out distortion. When matching 8. McLaren E. The 3D-master shade-matching system and the skeleton buildup tech- slide border. If the crown does not teeth, the shape, surface geogra- nique: Science meets art and intuition. phy, value, translucency, chroma, match, rephoto with the mismatched Quintessence Dent Technol 1999:55–68. crown in the mouth. and hue are all important character- [AU: Please list volume number.] istics. Intraoral photography is the 9. Sundar V, Amber PL. Opals in nature. J best device to communicate these Dent Technol 1999;16:15–17. Conclusion factors to the laboratory. 10. ten Bosch JJ, Coops JC. Tooth color and reflectance as related to light scattering and enamel hardness. J Dent Res Knowing how light interplays with 1995;74:374–380. References the surface and internal layers of 11. Garber DA, Adar P, Goldstein RE, Salama teeth is beneficial in the creation of H. The quest for the all-ceramic restora- 1. Overheim D. Light and Color. New York: tion. Quintessence Dent Technol an artificial replacement of tooth John Wiley, 1982. structure. Faithfully matching the 2000;23:27–36. 2. Rossing TD, Chiaverina CJ. Light Science: 12. Meyenberg K. Dental esthetics: A optical properties of each layer Physics and the Visual Arts. New York: European perspective. J Esthet Dent Springer, 1999. increases the likelihood of a good 1994;6:274–281. match and decreases the problem of 3. O’Brien W. Double layer effect and other 13. Rainwater C. Light and Color. Racine, WI: optical phenomena related to esthetics. metamerism. What the practitioner Golden Press, 1971:100–118. Dent Clin North Am 1985;29:667–673. sees is very difficult to communicate 14. Wasdyke P. The unique characteristics of 4. McLaren E. Luminescent veneers. J Esthet to the laboratory technician without lighting technology explained. CEE Dent 1997;9:3–12. News, 1/90. [AU: Is this a journal? Please

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spell out title and give volume and Quintessence, 1993. 45. Preston J. Current status of shade selec- page numbers.] 30. Glick KL. Color management of cosmet- tion and color matching. Quintessence Int 15. Preston JD, Ward LC, Bobrick M. Light ic restorations. Current Opin Cosmet 1985;16:47–58. and lighting in the dental office. Dent Dent 1995;36–40. [AU: Please list vol- 46. Schwabacher WB, Goodkind RJ, Lua MJ. Clin North Am 1978;22:431–451. ume number.] Interdependence of the hue, value, and 16. Pensler AV. Shade selection: Problems 31. Williamson RT, Breeding LC. Make luster chroma in the middle site of anterior and solutions. Compend Contin Educ tabs for use in matching texture of porce- human teeth. J Prosthodont Dent 1998;19:387–396. lain surfaces. J Prosthet Dent 1994;3:188–192. 17. Sproull R. Color matching in dentistry. 1993;69:536–537. 47. Zhao Y, Zhu J. In vivo color measurement Part I. J Prosthet Dent 1973;29:416–424. 32. Rufenacht C. Fundamentals of Esthetics. of 410 maxillary anterior teeth. Chinese J Dent Res 1998;1(3):49–51. 18. Glick K. Color and shade selection in Chicago: Quintessence, 1992. cosmetic dentistry: Part III. Establishing 33. Ubassy G. Shape and Color: The Key to 48. Goodkind RJ, Schwabacher WB. Use of a the proper environment and technique. J Successful Ceramic Restorations. fiber-optic colorimeter for in vivo color AACD 1994;Summer:14–20. [AU: Please Chicago: Quintessence, 1993:197–204. measurements of 2830 anterior teeth. J list volume number and spell out jour- Prosthet Dent 1987;58:535–542. 34. Obregon A, Goodkind RJ, Schwabacher nal name (J Am Acad Cosmet Dent?).] WB. Effects of opaque and porcelain sur- 49. Publication CIE No. 15.2, Colorimetry, ed 19. Mathews TG. A method for shade selec- face texture on the color of ceramomet- 2. Vienna: CIE Central Bureau, 1986. tion. Quintessence Dent Technol al restorations. J Prosthet Dent 50. Lackovic KP, Wood RE. Tooth root colour 1980;2:101–105. [AU: Correct volume?] 1981;46:330–340. as a measure of chronological age. J 20. Miller LL. Esthetic dentistry development 35. Ancowitz S, Torres T, Rostami H. Texturing Forensic Odontostomatol program. J Esthet Dent 1994;6:47–60. and polishing: The final attempt at value 2000;18(2):37–43. 21. Pensler AV. Photography in the dental control. Dent Clin North Am 51. McCullock AJ, McCullock RM. practice. Quintessence Dent Technol 1998;42:607–613. Communicating shades: A clinical and 1983;14:855–858. 36. Geller W. Polishing porcelain makes a technical perspective. Dent Update 1999;26:247–252. 22. Ray NJ. Some aspects of colour and crown smoother, more translucent, and colour matching in dentistry. J Irish Dent improves the color. Quintessence Dent 52. Russell MD, Gulfraz M, Moss BW. In vivo Assoc 1994;40:16–19. Technol 1983;7:384–387. measurement of colour changes in natural teeth. J Oral Rehabil 2000;27:786–792. 23. Sproull R. Color matching in dentistry. 37. Boyde A. Microstructure of enamel. Ciba Part III. Color control. J Prosthet Dent Found Symp 1997;205:19–31. 53. Friedman M. Staining and shade control 1974;31:146–154. 38. Hasegawa A, Ikeda I, Kawaguchi S. Color of dental ceramics. III. Quintessence Dent [AU: Correct and translucency of in vivo natural central Technol 1982;61:49–57. 24. Preston J, Bergen S. Color Science and volume number/journal?] Dental Art. St Louis: Mosby, 1980:31–45. incisors. J Prosthet Dent 2000;83:418–423. 54. Sieber C. In the light of nature. 25. Wozniak WT, Moser JB. How to improve [AU: 39. O’Brien WJ. Fraunhofer diffraction of light Quintessence Dent Technol 1993. shade matching in the dental operatory. Please list volume and page numbers.] Council on Dental Materials, Instruments, by human enamel. J Dent Res and Equipment. J Am Dent Assoc 1988;67:484–486. 55. Lemire P, Burk B. Color in dentistry. 1981;102:209–210. 40. Spitzer D, ten Bosch JJ. The absorption Hartford, CT: Ney, 1975. 26. Barna GJ, Taylor JW, King GF, Pelleu GB and scattering of light in bovine and 56. Jun S. Communication is vital to produce Jr. The influence of selected light inten- human dental enamel. Calcif Tissue Res natural looking metal ceramic crowns. J [AU: sities on color perception within the color 1975;17:129–137. Dent Technol 1997;14(8):15–20. Correct journal name?] range of natural teeth. J Prosthet Dent 41. Freedman G. Color communication. J 1981;46:450–453. Can Dent Assoc 1994;60:695–699. 57. Jun SK. Shade matching and communi- 27. McLaren EA. Provisionalization and the 3- 42. Miller LL. Shade matching. J Esthet Dent cation in conjunction with segmental D communication of shape and shade. 1993;5:143–153. porcelain build-up. Pract Periodontics Aesthet Dent 1999;11:457–464. Contemp Esthet Restorative Pract 43. Miller LL. Shade selection. J Esthet Dent [AU: Please list vol- 2000;May:48–60. 1994;6:47–60. 58. Smith PW, Wilson N. Shade selection for ume number.] single-unit anterior metal crowns: A 5- 44. Sproull RC. Color matching in dentistry. 28. Saleski C. Color, light, and shade match- year retrospective study of 2,500 cases. Part II: Practical applications of the orga- Int J Prosthodont 1998;11:302–306. ing. J Prosthet Dent 1972;27:263–268. nization of color. J Prosthet Dent 29. Ubassy G. Shape and Color. Chicago: 1973;29:556–566. 59. Touati B, Miara P, Nathanson D. Esthetic

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Dentistry and Ceramic Restorations. London: Martin Dunitz, 1993. 60. Schärer P, Rinn LA, Kopp FR. Esthetic Guidelines for Restorative Dentistry. Chicago: Quintessence, 1982. 61. Wasson W, Schuman N. Color vision and dentistry. Quintessence Int 1992;23:349–353. 62. Spear F. The Art of Intra-Oral Photography. Seattle: Seattle Institute for Advanced Dental Education, 1999:29–32. 63. Hall NR. Tooth contour selection: The application of colour science to dental colour matching. Aust Prosthodont J 1991;(5):41–46. [AU: Please list volume number.] 64. Polaroid Corporation communiqué: Matching tooth color, subsurface characteristics using the macro 5 SLR camera. Dent Prod Rep 2000:46–47. [AU: Is this a journal? Please list volume number.] 65. Vanini L, Mangani FM. Determination and communication of color using the five color dimensions of teeth. Pract Periodontics Aesthet Dent 2001;13:19–26.

Volume 23, Number 5, 2003