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Shade selection

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shade selection seminar
Yasir A. alnakib
supervised by : prof. Dr. ammar A. ali
department of conservative dentistry
college of dentistry
university of al-mustansiriya

Published in: Health & Medicine

Shade selection

  1. 1. SHADE SELECTION Done by: Yasir A. Alnakib M.Sc. student Under supervision of: Prof. Dr. Ammar A. Ali 2015
  2. 2. Shade Selection Page: 1 of 40 Table of Contents 1 INTRODUCTION ........................................................................................ 3 2 THE PRINCIPLES OF COLOR...................................................................... 5 2.1 TRANSMISSION AND ABSORPTION....................................................................5 2.2 REFLECTION AND ABSORPTION .......................................................................5 2.3 THE ADDITIVE AND SUBTRACTIVE SYSTEM ..........................................................6 2.4 THE MUNSELL SYSTEM.....................................................................................7 2.4.1 Hue............................................................................................... 8 2.4.2 Chroma........................................................................................ 8 2.4.3 Value............................................................................................ 9 2.4.4 Translucency ............................................................................... 9 2.5 COLOR (HUE) RELATIONSHIP................................................................10 2.5.1 Primary Hues.............................................................................. 11 2.5.2 Secondary Hues........................................................................ 11 2.5.3 Complementary Hues .............................................................. 11 2.6 CIELAB COLOR SYSTEM.............................................................................12 2.6.1 Color Differences...................................................................... 13 2.7 THE COLOR OF HUMAN TEETH......................................................................13 3 ELEMENTS AFFECTING COLOR............................................................... 15 3.1 ILLUMINATION.............................................................................................15 3.1.1 Standard illuminants ................................................................. 15 3.1.2 Metamerism .............................................................................. 16 3.2 COLOR PERCEPTION BY HUMAN EYE............................................................17 3.2.1 Color blindness.......................................................................... 17 3.2.2 Age............................................................................................. 17 3.2.3 Fatigue....................................................................................... 18 3.2.4 Binocular Difference in Color Perception............................... 18 3.3 CONTRAST EFFECTS.....................................................................................18 3.3.1 Value contrast........................................................................... 18 3.3.2 Hue contrast.............................................................................. 19 3.3.3 Chroma contrast ...................................................................... 20 3.3.4 Areal contrast............................................................................ 20 3.3.5 Spatial Contrast ........................................................................ 21 3.4 FLUORESCENCE ..........................................................................................21 3.5 OPALESCENCE ...........................................................................................21 3.6 REFLECTIONS OF LIGHT ................................................................................22 3.6.1 Surface Texture ......................................................................... 22 3.6.2 Luster .......................................................................................... 23 3.7 BLEACHING................................................................................................23 4 CONVENTIONAL SHADE MATCHING .................................................... 24 4.1 SHADE GUIDE SYSTEMS .................................................................................24 4.1.1 Vita Classical ............................................................................. 25
  3. 3. Shade Selection Page: 2 of 40 4.1.2 Chromascop ............................................................................. 26 4.1.3 Vita 3D-Master shade guides .................................................. 26 4.2 COMMUNICATION......................................................................................29 5 TECHNOLOGY-BASED SHADE MATCHING ........................................... 30 5.1 DEVELOPMENT OF TECHNOLOGY-BASED SHADE SYSTEMS ...............................30 5.2 SPOT VERSUS COMPLETE-TOOTH MEASUREMENT..............................................31 5.3 TYPES OF TECHNOLOGY-BASED SHADE SYSTEMS ............................................32 5.3.1 RGB devices .............................................................................. 32 5.3.2 Spectrophotometers ................................................................ 33 5.3.3 Colorimeters .............................................................................. 35 5.4 RELIABILITY AND ACCURACY .......................................................................35 5.5 INTERPRETATION METHODS OF DIFFERENT TECHNOLOGIES ...............................36 6 REFERENCES............................................................................................ 38
  4. 4. Shade Selection Page: 3 of 40 1 INTRODUCTION Many have long pondered the question: If a tree falls in the woods and there is no one there to hear it, does it make a sound? In color theory the question becomes: If the petals of a rose are pink and there is no one there to view them, are they actually pink? According to color theorists, the answer is no!! . The reason for this surprising answer is that in order for a color to exist, there needs to be an interaction between three elements: light, an object, and a viewer (Fig. 1). If all three elements are not present, color as we know it does not exist. Figure 1 perception of color (pink) by the viewer Color is best described as an abstract science. Color appeals to the visceral and emotional senses. Color is personal; each individual will view the same object differently, Take, for example, the apple shown in (Fig 2). Most would define its color as red; others might take it a step further and describe it as cranberry red or vibrant ruby red. It is often difficult to come to a consensus based on visual assessment alone. Figure 2 red apple
  5. 5. Shade Selection Page: 4 of 40 There are numerous factors that influence an individual’s color perception, including lighting conditions, background effects, color blindness, binocular differences, eye fatigue, age, and other physiologic factors. But even in the absence of these physical considerations, each observer will interpret color differently based on his or her past experiences with color and resulting color references. Each individual also verbally defines an object’s color differently. However, there are quantifiable aspects of color that are important for the dental practitioner to understand. Basic knowledge of how color is perceived and reproduced will aid the clinician in evaluating and matching shades in the dental practice.
  6. 6. Shade Selection Page: 5 of 40 2 THE PRINCIPLES OF COLOR In 1666, Sir Isaac Newton observed that white light passing through a prism divided into an orderly pattern of colors now termed the spectrum. He also discovered that these colors produced white light when passed back through the prism, proving that all spectral colors were in the original beam. (R.Waltke, 1977) Color, as the eye interprets it, is either a result of absorption or reflection. In absorption, a white light is passed through a filter. The colors that pass through the filter and reach the eye are perceived as the color of the filter. In reflection, as with solid objects, the perceived color is the portion of the spectrum that is reflected back to the eye. Light perceived by the three types of color receptors (called cones) in the human eye as variations of red, green, and blue light. Light entering the eye stimulates the photoreceptor rods and cones in the retina. The energy is converted through a photochemical reaction into nerve impulses and carried through the optic nerve into the occipital lobe of the cerebral cortex. The rod cells are responsible for interpreting brightness differences and value. The cone cells function in hue and chroma(saturation) interpretation. 2.1 TRANSMISSION AND ABSORPTION Transmission occurs when light passes through a transparent or translucent material, such as a slide or film. If light encounters molecules or larger particles in the material, some wavelengths of light will be absorbed. The number of light rays and the specific wavelengths (colors) that are absorbed are determined by the density and makeup of the material the light travels through; the wavelengths that are transmitted (referred to as spectral data) compose the color that is perceived. If the material is completely transparent, all light is transmitted, and the color white is perceived. If the material is completely opaque, all light is absorbed, and the color black is perceived. In most cases, however, some of the wavelengths (colors) are absorbed and others transmitted. If this occurs, the color that is perceived corresponds to the wavelengths that are transmitted. For example, if a material absorbs red wavelengths and transmits green and blue wavelengths, a combination of green and blue (referred to as cyan) is perceived (Stephen J. Chu, 2011) 2.2 REFLECTION AND ABSORPTION Reflection occurs when light rays strike a solid object, such as an apple or a photograph, and then bounce off of it. Depending on the molecular structure or density of the object or medium, certain wavelengths (colors) may be absorbed rather than reflected. The wavelengths that are reflected compose the color that is perceived . Theoretically, an object that reflects all light would be perceived as
  7. 7. Shade Selection Page: 6 of 40 white , and an object that absorbs all light would be perceived as black . In most cases, however, the object absorbs some wavelengths (colors) and reflects others (Fig. 3).If this occurs, the object is perceived to be the color of the wavelengths that are reflected. For example, an object that absorbs green wavelengths but reflects red and blue wavelengths is perceived as a combination of red and blue (referred to as magenta) (Stephen J. Chu, 2011) Figure 3 reflection and absorption 2.3 THE ADDITIVE AND SUBTRACTIVE SYSTEM The additive system consists of three primary colors: red, green, and blue. All other colors are made up of combinations of these three unique or “primary” colors. Knowledge of this system (the so-called “additive” system of color) has enabled the creation of such devices as the color television. Using only three phosphors, one each of the three primary colors, the color television is able to produce a seemingly unlimited range of shades. One such television monitor boasts a palette of 16,777,216 colors that are available on the screen. In the additive system, white is the balanced mixture of all the colors, and black is the absence of color. Yellow is a balanced mixture of red and green (Freedman, 2012). In the subtractive system, black is the result of a mixture of the three primaries (cyan, magenta, and yellow), and white is the absence of color (Fig. 4). This system is popular because it is perhaps the easiest to use when dealing with pigments(Reflective and transmissive media). Because dentists work with pigments when dealing with porcelain, the easiest system for clinicians to use is the subtractive system (Freedman, 2012)
  8. 8. Shade Selection Page: 7 of 40 Figure 4 In the subtractive system, black is the result of a mixture of the three primary colors. 2.4 THE MUNSELL SYSTEM In 1915, Albert Henry Munsell created an orderly numeric system of color description that is still the standard today. In this system color is divided into three parameters—hue, chroma, and value (AH.Munsell, 1969) The Munsell system is not unique. Numerous other color wheels are available. Each is of different national origin, with versions from Britain, France, Germany, Argentina, and Sweden. Naturally enough, each system finds its greatest usage in its country of origin. Unfortunately, although such systems provide a good way to describe color, they actually do little to teach how to manipulate and control color in a clinical situation. In other words, rather than the Munsell system being a method used to control color, it merely serves as a relatively precise “language” to verbalize what is being done. In fact, it is even of limited value in describing tooth color, because it is primarily involved with surface reflection. It does not make any distinction between one color that is relatively translucent and one that is opaque (Freedman, 2012). The Munsell color solid can be described as follows. The hues are uniformly spaced around the central axis of the color wheel. The center of the wheel – or axle – is the achromatic or value portion. Each spoke of the wheel represents the gradations in chroma occurring within a hue (Fig.5 ) demonstrates one wheel with the hues designated around the periphery of the wheel, the center value axle, and the spokes representing increased chroma going from the center of the wheel toward the rim (AH.Munsell, 1969).
  9. 9. Shade Selection Page: 8 of 40 Figure 5 The Munsell color system, showing: a circle of hues, and levels of value and chroma. 2.4.1 Hue The term "hue" is synonymous with the term "color", and it is used to describe the color of a tooth or dental restoration, Roy G. Biv (Red, Orange, Yellow, Green, Blue, Indigo, Violet) is an acronym for the hues of the spectrum. In the younger permanent dentition, hue tends to be similar throughout the mouth. With aging, variations in hue often occur because of intrinsic and extrinsic staining from restorative materials, foods, beverages, smoking, and other influences (Aschheim, 2015). Figure 6 HUE 2.4.2 Chroma Chroma (Fig. 7) is the saturation or intensity of hue; therefore it can only be present with hue. For example, to increase the chroma of a porcelain restoration, more of that hue is added. Chroma is the quality of hue that is most amenable to decrease by bleaching. Almost all hues are amenable to chroma reduction
  10. 10. Shade Selection Page: 9 of 40 Figure 7 Chroma 2.4.3 Value Value is the relative lightness or darkness of a color. A light tooth has a high value; a dark tooth has a low value. It is not the quantity of the “color” gray, but rather the quality of brightness on a gray scale “colorless distinction”. That is, the shade of color (hue plus chroma) either seems light and bright or dark and dim. It is helpful to regard value in this way because the use of value in restorative dentistry does not involve adding gray but rather manipulating colors to increase or decrease amounts of grayness. Value is the most important factor in shade matching. If the value blends, small variations in hue and chroma will not be noticeable (Preston JD, 1980). To compare the color match between a restoration and tooth, value is generally considered the most challenging of the three dimensions of color. One reason is that value differences are readily detected, even by an untrained eye, and restorations with improper value are frequently described by patients as being too dark or too white. In addition, value differences are more easily detected both close-up and at a distance, whereas differences in hue and chroma become less noticeable as the viewing distance increases (Goodacre, et al., 2011). Figure 8 Value 2.4.4 Translucency Many authors regard translucency as the fourth dimension of color, Human teeth are characterized by varying degrees of translucency.It can be defined as the gradient between transparent and opaque. Pieces of frosted glass or snow can have the exact same chroma, hue, and value but not look the same. Generally, increasing the translucency of a crown lowers its value because less light returns to your eye (Fig. 9 left). With increased translucency, light that enters is scattered
  11. 11. Shade Selection Page: 10 of 40 within the body of porcelain. When light enters enamel it gets bounced around the enamel like a fiber-optic cable. If you illuminate one side of a tooth with a curing light, the entire crown is lighted. Similar to the fiber-optic cable, enamel is an optically dense material bordered on either side by air or dentin, both with significantly lower optical densities. (Fondriest, 2003) The translucency of enamel varies with the angle of incidence, surface texture and luster, wavelength and level of dehydration (Fondriest, 2003). More opaque teeth allow less light transmittance; they are more reflective in nature and, therefore, appear brighter. The characteristic of translucency must also be present in the restorative materials in order to achieve a natural appearance and avoid the opaque, dead-in-appearance restorations (Fig 9 right). Translucency and value are the most important characteristics in shade selection, since hue is not easily detectable, and since there is a lack of chroma in the lighter shades (e.g. A1, B1). (Curel, 2003) Figure 9 (left) Highly translucent teeth tend to be lower in value {darker}, (right) The opaque, dead appearance teeth allow less light transmittance; they are more reflective in nature and, therefore, appear brighter. 2.5 COLOR (HUE) RELATIONSHIP Hues, as used in dentistry, have a relationship to one another that can be demonstrated on a color wheel. The relationships of primary, secondary, and complementary hues are graphically depicted by the color wheel (Fig. 10). Figure 10 The color wheel.
  12. 12. Shade Selection Page: 11 of 40 2.5.1 Primary Hues The primary pigment colors are very similar to the subtractive primaries, but they are referred to as red, yellow, and blue, rather than magenta, yellow, and cyan (Stephen J. Chu, 2011) In dentistry, the metal oxide pigments used in coloring porcelains are limited in forming certain reds; therefore pink is substituted. The primary hues and their relationships to one another form the basic structure of the color wheel (Aschheim, 2015). 2.5.2 Secondary Hues The mixture of any two primary hues forms a secondary hue. When red and blue are mixed they create violet, blue and yellow create green, and yellow and red create orange. Altering the chroma of the primary hues in a mixture changes the hue of the secondary hue produced. Primary and secondary hues can be organized on the color wheel with secondary hues positioned between primary hues (Aschheim, 2015). 2.5.3 Complementary Hues Colors directly opposite each other on the color wheel are termed complementary hues. A peculiarity of this system is that a primary hue is always opposite a secondary hue and vice versa. Because the pigments used in dentistry are poorly saturated and imperfect, the mixture of the stains usually cancel each other and produces some shade of grey instead of black (subtractive system) (Freedman, 2012) Figure 11 Complementary Hues This is the most important relationship in dental color manipulation. The additive principle of complementary colors may be used to alter the value of restorations. For instance, if we want to lower the value (increase gray or darkness) of a restoration, the complementary color can be added to that hue (i.e. A3 shade contains: orange hue + blue stain = lower value). Adding gray stain to lower the value will only make the restoration look dull and unclean. Adding violet (purple) stain to a B shade (yellow hue) restoration will also appropriately
  13. 13. Shade Selection Page: 12 of 40 lower the value. Therefore, adding the complementary color to a restoration will effectively alter the value (Curel, 2003). When a portion of a crown is too yellow, lightly washing with violet (the complementary hue of yellow) produces an area that is no longer yellow. The yellow color is canceled out and the area will have an increased grayness (a lower value). This is especially useful if the body color of a crown has been brought too far incisaly and if a more incisal color is desired toward the cervical area. If a cervical area is too yellow and a brown color is desired, washing the area with violet cancels the yellow. This is followed by the application of the desired color, in this situation brown (Aschheim, 2015). Complementary hues also exhibit the useful phenomenon of intensification. When complementary hues are placed next to one another, they are each intensified and appear to have a higher chroma. A light orange line on the incisal edge intensifies the blue of an incisal color. (Curel, 2003) 2.6 CIELAB COLOR SYSTEM Color research continued to evolve based on the Munsell color model. In 1976, The Commission Internationale de l’Eclairage (CIE), an international color research group founded in 1931, published the CIELAB color system. In this 3-dimensional color system, L* refers to brightness (0 to 100), a* represents red (+a*) vs. green (-a*) and b* indicates yellow (+b*) vs. blue (-b*). When a* and b* are zero, the L value represents the continuum of black to white. The CIELAB model offers some advantages over other color models. The L*a*b* color space was designed to correlate with perceptions of color. This allows the CIELAB system to measure color differences that are meaningful in industrial applications. Since the development of the original 1976 CIELAB color system, several refinements have been made to make the color space more visually uniform. These versions are known as the CIELAB94 and CIEDE2000 models.
  14. 14. Shade Selection Page: 13 of 40 Figure 12 CIELAB color space 2.6.1 Color Differences CIELAB is often used to measure changes in color, including changes in tooth color from use of whitening products. Color difference equations are used to quantify the color change. ΔL*, the change in brightness, is calculated as L *2 -*L1 w here L*1 represents the initial L* value and L*2 is the end of treatment measure. The change in a* and b* is calculated similarly. ΔE* represents overall color change. ΔE* is defined as ( ΔL*2 + Δb*2 + Δa*2 )1/2. Extreme care must be used when interpreting ΔE* because it gives no information about the quality or direction of color change. For example, a unit negative change in L* (- ΔL*) means a sample became darker while a unit positive change in L* means a sample became brighter. Both situations, however, yield the same value for a change in E*. 2.7 THE COLOR OF HUMAN TEETH The color of teeth encompasses only a small portion of the total color space. The color ranges of human teeth have been measured by different researchers at different times and using different methods and color notation systems. Using the Munsell color notation system, Dr. E. B. Clark, a dentist, produced the first data in 1931.10 He indicated the Hue ranged from 6 YR (yellow-red) to 9.3 Y (yellow), the Value ranged from 4 to 8, and the Chroma ranged from 0 to 7. Lemire and Burk found a Hue range from 8.9 YR to 3.3 Y, a Value range of 5.8 to 8, and a Chroma range from 0.8 to 3.4 Goodkind and Schwabacher identified the Hue range as 4.5 YR to 2.6 Y, the Value range as 5.7 to 8.5, and the Chroma range from 1.1 to 5 (Goodkind, et al., 1987)
  15. 15. Shade Selection Page: 14 of 40 There are several other studies that used spectrophotometers and the findings were expressed in different color notation systems. However, all of the studies indicate that human teeth are in the yellow-red to yellow portion of the spectrum, they are relatively high in Value (light or bright), and they have a relatively low Chroma (not too much color intensity). (Goodacre, et al., 2011) Objective measurements of tooth color have also been performed using the CIELAB system under Daylight 5000K lighting. Values for L*, where 0=black and 100=white, typically fall in the 60-95 range. On the b* scale, which measures yellow-blue, tooth values typically range from 8 to 25. Finally, standard values range from -2 to 10 on the red-green scale (a*). The CIELAB color space is also used to characterize changes in tooth color. For example, when teeth are whitened with hydrogen peroxide, the teeth become brighter (L* increases), less red (a* decreases) and less yellow (b* decreases). (Goodacre, et al., 2011)
  16. 16. Shade Selection Page: 15 of 40 3 ELEMENTS AFFECTING COLOR There are many variables that affect how a color is perceived. For example, the color of the ocean cannot carry a blanket description of blue. The ocean appears to be a different color at night than it does at midday, with varying hues at different levels of relative lightness and brightness. The surrounding scenery, such as the sky, beach, and vegetation, can create contrasts that affect the perceived color of the waters. Moreover, different viewers may perceive the ocean as being different colors even when viewing it under the same conditions. The same rules apply in the dental operatory during shade-matching procedures. The lighting conditions, the environment, and the viewer all play vital roles in color perception and evaluation (CP., et al., 2001). 3.1 ILLUMINATION Color can be neither accurately perceived nor correctly evaluated without proper illumination. It is not only crucial to have enough lighting to evaluate color properly, but it is also essential to achieve the proper quality of lighting. This is accomplished by using the correct light intensity and the proper illuminants (Stephen J. Chu, 2011). The intensity of light is the most common regulator of pupil diameter, which is a crucial factor in accurate shade matching. Therefore, the most accurate color reading is obtained by the human eye when the pupil is opened enough to fully expose the cones in the fovea. This is achieved by maintaining a lighting intensity of 150 to 200 foot-candles, as verified by a light meter which facilitates accurate shade analysis and matching. (Carsten, 2003) 3.1.1 Standard illuminants The type of illuminant used can significantly impact the perception of color. A system created in 1931 by the Commission Internationale de l’Éclairage (CIE; translates to International Commission on Illumination) categorized illuminants based on their effect on color perception: A: A tungsten light source with a correlated temperature of about 2,856 K, producing a yellowish-red light. Generally used to simulate incandescent viewing conditions (eg, household light bulbs). B: A tungsten light source coupled with a liquid filter to simulate direct sunlight with a correlated temperature of about 4,874 K (Fig 3-6). Rarely used today. C: A tungsten light source coupled with a liquid filter to simulate indirect sunlight with a correlated temperature of about 6,774 K. illuminant C is not a perfect simulation of sunlight because it does not contain much ultraviolet light (required when evaluating fluorescence).
  17. 17. Shade Selection Page: 16 of 40 D: A series of illuminants representing different daylight conditions, as measured by color temperature. Illuminants D50 and D65 (so called because their correlated color temperatures are 5,000 and 6,500 K, respectively) are commonly used as the standard illuminants for graphic arts viewing booths and correspond to bluish daylight reflectance . E: A theoretical light source with equal amounts of energy at each wavelength. This illuminant does not actually exist, but is a useful tool for color theorists. When performing shade matching, clinicians should use D50 illuminants, which provide the closest lighting rendition to natural sunlight in respect to illumination quality and quantity and therefore present the best opportunity to see and select the correct shade (Stephen J. Chu, 2011). The dental operatory is not free from conflicts in lighting. Light coming in through a window mixes with the fluorescent light coming from the hallway and the color-corrected lighting in the dental operatory. Amid these various lighting conflicts, it is the job of the clinician to analyze the opposing teeth and to determine an accurate shade match. The following tips will aid in that process (Curel, 2003). 1. If the clinician or the lab technician has access to a natural light source, it is best to perform shade matching at 10 am or 2 pm on a clear, bright day when the ideal color temperature of 5,500 K is present. 2. Color-corrected lighting tubes that burn at about 5,500 K (D50 illuminants) should be installed when only artificial lighting is available (i.e., when there is no natural light). 3. A lighting intensity of 175 + or - 25 foot-candles must be maintained (verified by color temperature meter). 4. A color temperature meter should be used periodically to verify that a color temperature of 5,500 K is achieved in the shade-matching area. 5. Dust and dirt should be cleaned from lighting tubes and diffusers routinely, since the presence of dust may alter the quantity and quality of emitted light. 3.1.2 Metamerism Metamerism is a phenomenon where the color of an object appears different, depending upon the light source. When viewed together under the same light source, two objects may appear to have the same color; however, each appears to have a different color when viewed under different light sources. For instance, a crown may be matched under incandescent light; however, when the crown is viewed under color-corrected or fluorescent light, the crown will appear different in color. In dentistry, this phenomenon occurs predictably and frequently if the shade selection environment is not controlled and neutral. To
  18. 18. Shade Selection Page: 17 of 40 avoid or minimize metamerism, it is of utmost importance to control the lighting conditions when shade is being determined. (Curel, 2003) Figure 13 Shade under varied lighting conditions looks completely different in hue, chroma, and value: (left) restoration is viewed under color corrected light. (Middle) same restoration viewed under fluorescent light, looks completely different in hue, chroma, and value. (Right) same restoration tabs, viewed under incandescent light, 3.2 COLOR PERCEPTION BY HUMAN EYE Color perception is the psychophysiological reality of color. The light waves in themselves are not colored butColor arises in the human brain, with the cones in the eyes as the color receptors. Colors arise from qualitative differences in photosensitivity. The eye and the mind achieve distinct perception through comparison and contrast (Curel, 2003). In a study Fifty-four volunteering dentists were asked to match the shade of an upper right central incisor tooth of a single subject ,the Vita 3D-Master shade guide was used for the protocol, results indicate that dentists perform insufficiently regarding reliability and repeatability (11.1%) in visual shade matching, but they are able to select clinically acceptable shades. (Özat, et al., 2013). 3.2.1 Color blindness A person with color blindness has trouble seeing red, green, blue, or mixtures of these colors. Although the condition might be perceived as rare, approximately 10% of US males (but only 0.3% of US females) are affected by color blindness. 3.2.2 Age Aging is detrimental to color-matching abilities because the cornea and lens of the eye become yellowed with age, imparting a yellow-brown bias and causing the differentiation between white and yellow to become increasingly difficult. This process begins at age 30, becomes more noticeable after age 50, and has clinical significance after 60 years of age. After age 60, many people have significant difficulties in perceiving blues and purples. (Stephen J. Chu, 2011)
  19. 19. Shade Selection Page: 18 of 40 3.2.3 Fatigue Tired eyes cannot perceive colors as accurately as alert eyes can. Compromised visual perception is the consequence of systemic, local, and/or mental fatigue. The inability to accurately determine hue and chroma is most evident during times of fatigue; in addition, color may be perceived as faded or blurry. Successive shade observations (i.e., treating many patients requiring shade assessment during a single workday) can be one of the primary causes of fatigue. Fatigue is the most common cause of an inaccurate shade match (Stephen J. Chu, 2011). 3.2.4 Binocular Difference in Color Perception Binocular difference is a perception variance between the right eye and the left eye. Such color perception disparity between the eyes of an individual is small; however, when it is present, there must be a compensation for it. When two objects of the same shape and color are juxtaposed (arranged side by side), they may appear to be different (i.e. one seems to be slightly lighter than the other) (Curel, 2003). Binocular color differences cause disharmony in shade selection and color matching. Placing shade tabs on the same side of the tooth to be matched will help to eliminate error and compensate for this effect (Fig. 14). (Curel, 2003) Figure 14 avoiding binocular difference 3.3 CONTRAST EFFECTS The phenomenon of contrast effect can alter the perception of color considerably, as well as the ability to evaluate color in a clear, concise, and objective way. These effects create optical illusions that are difficult to decipher unless the observer is prepared for them. 3.3.1 Value contrast Visual judgment of lightness is not dependable, primarily because the relative lightness of an object is affected by the lightness of the contrasting background or surroundings. For example, if the surrounding background is dark, an object will appear light. However, if the same object is placed against a lighter
  20. 20. Shade Selection Page: 19 of 40 background it will appear darker, this illustrates is that the perceived lightness can vary, even though the reflectivity of the object is constant. This is due to the fact that the retina is very sensitive to light. It expands and contracts in response to varying light intensities as they are interpreted by the brain. (Curel, 2003) A practical dental example of this phenomenon is when a restoration is viewed adjacent to inflamed gingival tissues (Fig. 15). The redness (darkness) of the gingiva (background) distorts color perception, making the restoration (object) appear lighter than it actually is. As a result, a crown that is too low in value (ie, dark) may be chosen. The mistake becomes apparent when the tissues heal and the crown appears darker than the adjacent teeth. (Curel, 2003) Figure 15 excessively inflamed gingival tissues lead to value contrast effects 3.3.2 Hue contrast A color will be perceived differently when viewed in conjunction with various background or adjacent colors with contrasting hues. When a color is viewed simultaneously with another color, the perceived hue of the first color will appear more similar to the complementary color of the second color.For example, a tooth or restoration will appear bluish against an orange background and purplish if the background is yellow. (Stephen J. Chu, 2011) A majority of tooth shades fall into the orange hue family (Sproull, 1973). To view the orange tones with a more critical eye, dental professionals can precondition their eyes by looking at a light blue shade immediately prior to the shade selection process. The closer the tooth shades are to the complementary color (ie, light orange), the more vibrant they will appear (Fig. 16). (Stephen J. Chu, 2011)
  21. 21. Shade Selection Page: 20 of 40 Figure 16 The closer the tooth shades are to the complementary color (ie, light orange), the more vibrant they will appear 3.3.3 Chroma contrast This contrast follows the same effect as the value and the hue contrasts. An object will appear more intense against a background low in chroma, and less intense against a more chromatic background. In addition, the closer the object is to the hue and chroma of the surrounding background, the less visible it becomes. This is important to remember during shade matching; using backgrounds of similar hue and chroma to the teeth will make it more difficult to distinguish the shade (Fig. 17). (Stephen J. Chu, 2011) Figure 17 Chroma contrast. The closer the color of the orange tooth is to the orange background, the more muted it becomes. 3.3.4 Areal contrast Visual color perception is also influenced by the size of the object. Optical illusion is present even though the object reflects the same wavelength of light in the visible spectrum. For instance, a large object will appear brighter, while one of a smaller size will appear darker, even though they both are of the same color. Conversely, a brighter object will appear to be larger, while a darker object will appear smaller (Figs 18). (Curel, 2003)
  22. 22. Shade Selection Page: 21 of 40 Figure 18 objects of an equal size, a brighter object will appear larger 3.3.5 Spatial Contrast An object that is more recessed will appear to be smaller in size and not as bright; an object closer to the observer will appear larger and brighter. This phenomenon is frequently seen with rotated and overlapped teeth. (Curel, 2003) 3.4 FLUORESCENCE We live in a world of UV light. UV light can have a dramatic effect on the level of vitality exhibited by our restorations. With the characteristic of fluorescence, our restorations look brighter and more alive. Fluorescence by definition is the absorption of light by a material and the spontaneous emission of light in a longer wavelength”blue” (Fig. 19 b) (McLaren, 1997). Fluorescence in a natural tooth primarily occurs in the dentin due to the higher amount of organic material present (Cornell, et al., 1999). The more the dentin fluoresces, the lower the chroma. Fluorescence is considered a subset of reflectivity. Fluorescent powders are added to crowns to increase the quantity of light returned back to the viewer, to block out discolorations, and to decrease chroma. This is especially beneficial in high-value shades as it can raise value without negatively affecting translucency when placed within the dentin porcelain layers. (Fondriest, 2003) 3.5 OPALESCENCE Opalescence can be described as a phenomenon where a material appears to be one color when you observe light reflected from it and looks another color when you see light transmitted through it (Sundar, et al., 1999). A natural opal is an aqueous di-silicate that breaks trans-illuminated light down into its component spectrum by refraction. Opals act like prisms and refract (bend) different wavelengths to varying degrees. The shorter wavelengths bend more and have a higher critical angle needed to escape an optically dense material than the reds and yellows. The hydroxyapatite crystals of enamel also act as prisms. (Fondriest, 2003).
  23. 23. Shade Selection Page: 22 of 40 When illuminated, opals and enamel will trans-illuminate the reds and scatter the blues within its body. This is why enamel appears bluish at the incisal edge even though it is colorless (Fig. 19 c ) (Bosch, et al., 1995). The opalescent effects of enamel brighten the tooth and give it optical depth and vitality (Garber, 2000) . Figure 19 In vitro examples of light effects exhibited by a natural tooth. Natural light effects (a), fluorescence (b), opalescence (blue [c] and orange [d]) 3.6 REFLECTIONS OF LIGHT It is important to realize that matching the hue and chroma is sixth or seventh in importance on the list of things to match when constructing a prosthetic replacement. You have to be fairly close to someone to detect subtle differences in hue; yet shape, value, surface texture, luster, and opacity disparities can be seen from four or five feet away or more. Violating conformity of the unique characteristics of the natural dentition will cause an unwanted prominence of your restoration. (Glick, 1994) These characteristics determine how light is reflected, transmitted, or scattered thus affecting its hue, chroma, value, and translucency. The appearance of teeth is mostly determined by how light interacts with the curved and varied surface. (Glick, 1994) 3.6.1 Surface Texture A roughened surface texture will not yield as well defined an image and will scatter the light and the individual wavelengths will all bend differently yielding a substantially different spectrum returning to the eye. (Obregon, 1981) Texture can be broken down into subgroups: vertical, horizontal, and malformations. Vertical surface textures are primarily composed of the heights of contour of the marginal ridges and the developmental lobes. Perichymata, the fine transverse wavelike grooves believed to be external manifestations of the striae of retzius are horizontal textures. The striae or lines of retzius are the result of the layering manner in which the deposition of enamel takes place. Malformations are the third textural group and can be from cracks, chips, and other surface aberrations (Fondriest, 2003).
  24. 24. Shade Selection Page: 23 of 40 Surface texture can be generalized as being heavy, medium, or light. A rough or heavy surface texture (Fig. 20) will have a lower value because it tends to diffuse light by reflecting it in many directions and less light returns to the viewer. A light surface texture has a higher value due to the increased specular reflection. At eruption, teeth have their roughest surface texture. With age, these surface features gradually wear. As the wear process continues into the later years of life, all signs of the perikymata are lost and even the definition of the developmental lobes is obliterated and the tooth appears smooth with a highly reflective glassy surface. (Fondriest, 2003) Figure 20 teeth with heavy surface texture 3.6.2 Luster Reducing the surface luster of a piece of clear window glass by wet sanding or etching will produce a frosty white look. As light hits the surface of the etched glass, it scatters or bends irregularly. This scattering of the light at the surface causes an increase in opacity. The light isn’t carried off and away from the surface but rather reflected. As the glass becomes less translucent, the value goes up. The net effect is more light returns to the viewer as the luster goes down. (Fondriest, 2003) It is important to note that surface texture and not luster determines specular reflection. Although the surface luster has been roughened the glass remains flat and has low texture so it will remain a specular reflector. Polishing the rough glaze off of a porcelain restoration is a subtle way to lower value by making the porcelain clearer and more translucent. (Geller, 1983) 3.7 BLEACHING Most people say they want white teeth. However, the color white is scientifically described as being completely reflective of all visible wavelengths of light, which implies an opacity that is undesirable in the dentition. In the context of esthetic dentistry, white as an ideal tooth color refers to the lightness or translucency of a tooth or restoration. When teeth are bleached, the relative lightness (value) of the teeth is increased, making them appear whiter. Therefore, bleaching does not necessarily involve making the teeth more opaque and reflective; rather, intrinsic colored pigments are removed, allowing a tooth to become whiter yet remain highly translucent (Stephen J. Chu, 2011).
  25. 25. Shade Selection Page: 24 of 40 4 CONVENTIONAL SHADE MATCHING For nearly a century, dental professionals have relied on tooth shade guides for an “accurate” shade match. Shade guides are sets of physical standards that are routinely used in dentistry for visual comparison with natural teeth in order to match color and other optical properties of the target tooth or restoration. The value of this method depends on the education and training of the clinician performing shade matching, the quality of the shade guide used, and the quality of the shade-matching method and conditions. Traditional shade taking involves matching one or more selected colors from a range of shade tabs to the teeth adjacent or contralateral to the teeth to be restored. This serves as a guide to the lab technician fabricating the crown or the bridge. The more information (and accuracy) that the dentist can provide in the prescription, the more lifelike the technician’s output can become. Thus the dentist who provides a drawing of a tooth color map, indicating the various shades within the tooth and their borders, is more likely to have a positive result than the dentist who describes the shade as a single generic color (Freedman, 2012). 4.1 SHADE GUIDE SYSTEMS Tooth shade matching is most frequently performed visually using dental shade guides. The first shade guide was introduced on the market in 1956 by Vita Zahnfabrik for the measurement of the color of ceramic systems. Although still imperfect, it introduced some visual parameters that with some minor modifications are still routinely used by dental practitioners. The Vitapan Classical Shade Guide consists of 16 tabs arranged into four groups based on hue and within the groups according to increasing chroma (also known as A-to-D arrangement) (Paravina, 2009). The most important issues are related to the need for and lack of a logical and adequate distribution in part of the color space encompassed by human teeth. Another quite popular shade guide not systematically arranged is the Ivoclar-Vivadent Chromascop. As with the Vitapan Classical, the Chromascop is arranged in groups based on the hue (1=White, 2=Light Yellow, 3=Dark Yellow, 4= Grey and 5=Brown) and within the groups according to increasing chroma (from 10 to 40). Dental color science then developed in a manner that minimized the errors in visual color selection (Miller, 1993 and 1994). In the late 1990s the Lab* system was adopted by dentistry and one of the first clinical results was the development of the Vita 3D Master Shade Guide.
  26. 26. Shade Selection Page: 25 of 40 4.1.1 Vita Classical In the Vita Classical shade guide, the tabs are arranged alphabetically according to hue:  A = Orange  B = Yellow  C = Yellow/Gray  D = Orange/Gray (Brown) The chroma and value for each hue are communicated by a system of numbers: 1 = Least chromatic, highest value 4 = Most chromatic, lowest value Vita Classical (Fig. 21) has been the gold standard for shade matching in dentistry since it was introduced in 1956. Indeed, the majority of restorative materials, particularly composite resins, are keyed to it. However, the criticism of its empiric conception, especially regarding the arrangement of the tabs and the color distribution, persists even today. The tabs can be arranged according to value (light to dark) in addition to hue and chroma. While this adds to the shade guide’s versatility, studies have found inconsistencies as a result of using the value scale (Paravina, et al., 2001). Before the VITAPAN Classical Shade Guide system is used for shade matching, the color tabs should be rearranged from their alphabetic order (which is how they are packaged) into the indicated value-based order that is included with every kit and goes from B1 to C4 The patient is asked to smile, and the VITAPAN Classical Shade Guide is passed in front of the teeth from the darker shades through the middle of the range to the lighter shades. The tabs of this shading group are brought edge to edge with the tooth in question in order to narrow down the actual color. The most appropriate color tab is pulled from the guide. Several readings are necessary to create a color map of a tooth. (Freedman, 2012) Figure 21 Vita Classical shade guide system
  27. 27. Shade Selection Page: 26 of 40 4.1.2 Chromascop The Chromascop system (Fig 4-6), developed by Ivoclar Vivadent, is another viable shade guide. Like the Vita Classical shade guide, the tabs are initially divided based on hue, and then further intra-group selections are made. Chromascop differs in the use of a three-digit numbering system and the use of five groups of four tabs, as follow:  Group 100 = White  Group 200 = Yellow  Group 300 = Orange  Group 400 = Gray  Group 500 = Brown Chroma and value are communicated by a system of numbers: 10 = Least chromatic, highest value 40 = Most chromatic, lowest value 4.1.3 Vita 3D-Master shade guides The Vitapan 3D-Master color system (Fig. 22) consists of 11 sets of fired porcelain tooth-shaped samples built up with cervical, dentinal and incisal powders and composed of feldspar nepheline and high-temperature ceramic pigments from the Vita family of ceramic porcelains. The 11 sets consist of 26 samples ranging from lightest to darkest value, from lowest to highest intensity and from yellow to red. Samples are arranged in groups of two or three that form five sets (numbered 1 through 5). Each set represents a single value, 1 being the lightest tooth color and 5 the darkest. Chroma and hue are represented within each value set. The distance between each of the pairs of adjacent colors is approximately 2 AE units. Each of the five lightness levels differs from the next by a ΔE of approximately 5. Each chroma level differs from the next by a ΔE of approximately 6. Hues are separated into middle, or M; yellow, or L; and red, or R (JADA., 2002)
  28. 28. Shade Selection Page: 27 of 40 Figure 22 Toothguide VITA 3D-Master shade system The VITA 3D-Master Shade Guide is based on a color classification principle in which 3 dimensions of color, value (brightness), chroma (intensity of the color), and hue (the color itself), are considered equally so that the determination of shade can be easily carried out using systematic, consistent criteria (Paravina, 2009). The VITA 3D-Master Shade Guide addressed the most important elements of tooth shade measurement: a scientific color distribution, having a systematic arrangement of shades within the natural tooth color space and an objective, numerical measure of color, according to the colorimetric CIELab* order principle, rather than on the mere observation of the natural tissue aspects , that can be written as a clear prescription for the laboratory technicians. Figure 23 Shade tabs distribution in color space: (left) VITA classical, (right) VITA 3D master
  29. 29. Shade Selection Page: 28 of 40 4.1.3.1 Steps of Using the Vita 3D-Master The first step in using the Vita 3D-Master system is to make sure the tabs are aligned vertically. Misaligned tabs can be distracting to the operator. The patient is asked to smile then the Toothguide Vita 3D-Master is used in 3 steps as follows: 1. Value determination: Shade guide is passed adjacent to the teeth, going from the darker shades through the intermediate to the lighter shades. The user selects the value level (from 0 to 5, with 0 being the lightest [high value] and 5 being the darkest [low value]) that is closest to the value of the tooth to be matched, and then takes the medium (M) shade sample from the selected value group 2. Chroma determination: The user selects the color sample from the M group with the chroma level (from 1 to 3, with 1 being the least chromatic and 3 being the most chromatic) that is closest to that of the tooth to be matched. 3. Hue determination: shade than the color sample of the M group selected in the second step. Now the best-matching shade sample can be determined and the information recorded in the color communication form. Several readings are necessary to create a color map of a tooth. Typically at least three readings per tooth are suggested, one each for the gingival, middle, and incisal thirds. The Linearguide Vita 3D-Master (Fig. 24) has the same shade tabs as the Toothguide but a different design, and shade matching is reduced to two steps: 1. Value selection: A dark-gray holder, containing only 6 middle tabs (0M2 to 5M2) is used. The small number of tabs with large color differences and the linear tab arrangement simplify group selection. 2. Chroma and hue selection: A final selection based on chroma and hue is made from the initial value group selected. Figure 24 Linearguide VITA 3D-Master shade guide system
  30. 30. Shade Selection Page: 29 of 40 Its relative simplicity makes Linearguide recommended for a “pick the best match” approach, while Toothguide is recommended for a “dimension-by- dimension” approach. It was also found that, overall, Linearguide enables better shade-matching results and was found to be superior in a subjective evaluation compared to Toothguide. Linearguide and Toothguide were both found to enable significantly better (closer) matches compared to Classical. (Paravina, 2009) The Bleachedguide Vita 3D-Master is the only shade guide developed specifically for visual evaluation of tooth whitening. Bleachedguide exhibits a wider color range and more consistent color distribution than the Vita Classical and other shade guides, such as Trubyte Bioform (Dentsply). In one study, the progression of lightening in natural teeth was found to be identical to the order suggested by Bleachedguide (Ontiveros, et al., 2009) 4.2 COMMUNICATION In the conventional shade-matching system the lab technician takes the basic information about value and chroma provided by the shade tabs and applies that information to the ceramic system and effect powders being used. Effective communication between the lab technician and the clinician is therefore critical to achieving a successful shade match. (Stephen J. Chu, 2011) It is recommended that the clinician send photographs along with the shade tabs as reference. Photography is a valuable means of communication between the clinician and the lab technician and adds credibility to the shade tab selection. Once the gingival, body, and incisal shade tabs are selected, photographs of each of the tabs should be taken next to the tooth to be matched, together with an aggregate photograph of all three tabs near the dentition. It also makes sense to photograph the matched tooth next to the two extreme shades (one lighter than the perceived shade and one darker); this allows the lab technician to get a concrete sense of the shade and value variation. Finally, photographs should be taken of the patient’s face and full smile to allow the technician to envision how the restoration will fit into the patient’s overall appearance. (Avery, 2003)
  31. 31. Shade Selection Page: 30 of 40 5 TECHNOLOGY-BASED SHADE MATCHING Precise color communication is integral to the development of esthetic harmony and overall restorative success. While traditional shade-taking procedures enable some degree of shade information transfer, contemporary shade-analysis devices allow for standardized, repeatable shade determinations by placing technology in the role of “observer” in the light-object-observer triad required for color perception Several clinical studies have confirmed that computer-assisted shade analysis is more accurate and more consistent compared with human shade assessment (Paul, et al., 2002) (Judeh, et al., 2009) The need for improvement in the accuracy of shade matching was highlighted by a study that showed that 80% of patients notice a difference in the shade of their natural teeth compared with their restored teeth (Ishikawa-Nagai, et al., 1992). Such a widespread lack of accuracy should not be accepted as the standard; rather, clinicians should strive to improve the esthetic quality of restorative work. Advantages of computer-aided shade determination include: 1. No influence of surroundings 2. No influence of lighting 3. Results are reproducible 4. Easy documentation 5. Reliable data transmission 5.1 DEVELOPMENT OF TECHNOLOGY-BASED SHADE SYSTEMS Advances in technology in the areas of computers, the Internet, and communication systems have greatly influenced and shaped modern society. Commensurate with these strides are the advances in contemporary dentistry: During the past half-decade, the dental profession has experienced the growth of a new generation of technologies devoted to the analysis, communication, and verification of shade (Stephen J. Chu, 2011). The earliest color-measuring device designed specifically for clinical dental use was a filter colorimeter. The Chromascan (Sterngold) was introduced in the early 1980s but enjoyed limited success because of its poor design and accuracy (Goodkind, et al., 1985). Further development was hindered primarily by a lack of resources and commitment on industry’s side—the market was too small. In the late 1980s and early 1990s, Seghi and Ishigawa-Nagai published experimental research using both colorimeters and spectrophotometers (Ishigawa-Nagai, 1994). Several prominent color science experts also tried to objectively quantify color. Bergen experimented with spectrophotometers and computers in an effort
  32. 32. Shade Selection Page: 31 of 40 to standardize analysis in the profession (Bergen, 1985). Miller used a single- point-source spectrophotometer in his research for correlating the shades of extracted natural teeth to those of available shade guide tabs (Miller, 1988). Preston made a major contribution to the field by identifying the quantity and quality of lighting required to analyze shade properly and pointing out inconsistencies in the manufacturing of shade guides and tabs (Preston, 1985). Yamamoto was instrumental in the development of the Shofu ShadeEye Chroma Meter and subsequently the Shofu NCC (Natural Color Concept) System (Yamamoto, 1998). Chu and Tarnow reported the clinical use and application of the Cortex Machina prototype, which employed RGB digital camera technology that inferred color properties (Chu, et al., 2001). The authors found that the more accurate data provided by technology-based systems allowed technicians at all levels of skill and experience to produce well-matched restorations. In 2001 and 2002, the first two measurement analysis systems mapping the whole surface of the tooth were developed: the SpectroShade System (a spectrophotometer) from MHT and the ShadeVision system (a colorimeter) from X-Rite. Recently, the development and integration of light-emitting diode (LED) technology into various dental fields has allowed for more portable, battery-powered devices. This development has also lowered the cost of shade analysis systems, making them more readily available. 5.2 SPOT VERSUS COMPLETE-TOOTH MEASUREMENT Spot measurement devices measure a small area on the tooth surface. The size or diameter of the optical device aperture (generally 3 mm2) determines how much of the tooth surface and subsequent shade is measured. The average central incisor is 80 to 100 mm2; therefore, spot measurement cannot deliver all of the information necessary to create an overall image. Spot measurement devices generally require three points of reference each for the gingival, body, and incisal areas of the tooth (a total of nine reference measurements). This increased number equates to greater sources of error during image capture as well as increased time for shade information data capture. Examples of spot measurement devices are the Vident EasyShade Compact system and the X-Rite Shade-X. (Stephen J. Chu, 2011) Complete-tooth measurement systems measure the whole tooth surface area and provide a topographic color map of the tooth (Fig. 25). The measurement of the complete surface gives the operator more consistent and reproducible information of the tooth structure. A drawback of complete-tooth measurement systems, however, is that their use is limited to anterior teeth because of the size of the sensor, which does not allow access to the molar region. Examples of these devices are the MHT SpectroShade Micro, X-Rite ShadeVision, and the Olympus CrystalEye. (Da Silva, et al., 2008)
  33. 33. Shade Selection Page: 32 of 40 Figure 25 Complete-tooth measurement devices measure the entire surface of the tooth and provide a detailed color distribution map 5.3 TYPES OF TECHNOLOGY-BASED SHADE SYSTEMS 5.3.1 RGB devices Most consumer video or digital still cameras acquire red, green, and blue image information that is utilized to create a color image and are commonly referred to as RGB devices. Digital cameras and other RGB devices represent the most basic approach to electronic shade taking and require a certain degree of subjective shade verification with the human eye. (Stephen J. Chu, 2011) Various approaches to the translation of this data into useful dental color information have been used. The problem inherent in the use of these systems is that they do not control some of the key variables associated with accurate color determination. Typically, color is synthesized from RGB data according to various assumptions about the camera and the use of reference materials within the captured image. The information accuracy (reliability) of RGB devices is questionable since they are not measurement instruments; rather, they infer color properties of the captured image. These systems are more helpful for providing lab technicians with a starting reference point than for visually determining the shade of a tooth. The ShadeVision system from X-Rite is an example of an RGB device (Fig. 26) . (Stephen J. Chu, 2011) Figure 26 The ShadeVision system from X-Rite
  34. 34. Shade Selection Page: 33 of 40 5.3.2 Spectrophotometers Spectrophotometers are highly precise and accurate instruments that are relatively simple and easy to use. They measure light wavelengths reflected from an object at many points along the visual spectrum (approximately every 10 nanometers), and these measurements produce spectral color data. A spectrophotometer measures and records the amount of visible radiant energy for each value, chroma, and hue present in the entire visible spectrum. These instruments typically divide and measure the visual spectrum into multiple parts, resulting in 16 to 32 data points across that range. The extensive data obtained from spectrophotometers must be manipulated, and a data reduction strategy employed, to translate the data into a useful form (eg, a spectral curve) (Freedman, 2001) There are two basic optical light geometries that are used in reflectance spectrophotometer instruments: (1) illumination at 0 degrees and observation at 45 degrees (0/45), and (2) illumination at 45 degrees and observation at 0 degrees (45/0) Because of the limited access afforded by the oral cavity, only the 45/0 option is suitable for clinical use One example of a spectrophotometer developed for clinical use is the SpectroShade (MHT) (Fig. 27), which uses dual digital cameras linked through optic fibers to measure the color of the tooth (polarized picture). There is a multimodal dual-light mechanism to illuminate the tooth and allow readings of its translucency and reflectivity. This permits the SpectroShade to provide consistent shade measurements regardless of the environmental lighting conditions. Figure 27 MHT SpectroShade system The VITA Easyshade (Vident, Brea, California) is a hand-held spectrophotometer that has been designed for quick and accurate shade determination and is capable of accurately measuring a very varied range of
  35. 35. Shade Selection Page: 34 of 40 VITAPAN Classical and VITAPAN 3D-Master shades. Easyshade simplifies the shade-matching procedure, providing high-quality, predictable, dependable, totally objective shade determination, resulting in fewer re-shades, fewer color alterations, and an overall superior esthetic product. (Freedman, 2012) The Vita Easyshade is one of the latest spectrophotometers available for clinical use. The instrument's software is programmed to give absolute CIELab* color values only for natural teeth. Conversely, when assessing the color of a ceramic, the spectrophotometer provides the differences (Δ values) from color value presets in the instrument's database. The spectrophotometer data acquisition is different when reading natural tooth and ceramic also because the instrument applies different scanning methods on the two diversely structured substrates (JJL Technology, 2003). Ceramic restorations are generally less than 1.6mm in thickness and the color layers (dentin and opaque) are from 0.2-0.4 mm under the enamel porcelain layer. Conversely, inside the teeth, the dentin layer is generally 1.0-1.5 mm from the outer surface (Shillingburg et al., 1991). Furthermore, the enamel thickness causes a scattering of the penetrating light. Moreover, the overall thickness of a natural tooth is greater than that of a ceramic tooth. In 2009 Vita Zahnfabrik comapny introduced onto the market a new shade taking device, the Easyshade Compact (Fig. 28), which represents an evolution of the previous one. Thanks to the use of LED technology, the new device became smaller, wireless and easier to handle. The most important difference between the two devices is that the Compact has a single spectrophotometer rather than the two ones belonging to Easyshade standard. In the standard Easyshade the difference in color reading between natural teeth and ceramic restorations is due to two different spectrophotometers embedded in the instrument. In the Easyshade Compact's tip there are two different sets of LEDs that provide different light according to what is being measured and the reflected light converges in a single Charge Coupled Device (CCD). Figure 28 VITA Easyshade Compact (Vident).
  36. 36. Shade Selection Page: 35 of 40 5.3.3 Colorimeters These instruments approximate the spectral function of the standard observer’s eye and are engineered to directly measure color as perceived by the human eye. A colorimeter filters light in three or four areas of the visible spectrum to determine the color of an object. Properly designed colorimeters such as X- Rite’s ShadeVision system (Fig. 24) can provide greater data efficiency because they store only the necessary 3 data points of hue, value, and chroma instead of the 16 or more data points of reflectance. A colorimeter can deliver color information accuracy similar to that of spectrophotometers and reduce the data load time by avoiding the unnecessary color mapping associated with spectrophotometers. The ShadeVision system provides simple, reliable shade measurement information for precise, quantifiable communications between the dental office and laboratory. The assurance of an accurate shade match is significantly improved compared with traditional techniques (Stephen J. Chu, 2011). 5.4 RELIABILITY AND ACCURACY Recent study tested 4 commercially available digital shade matching devices demonstrated that the Accuracy of devices was as follows: VITA Easyshade, 92.6%; ShadeVision, 84.8%; SpectroShade, 80.2%; and ShadeScan, 66.8%. (Seungyee, et al., 2009)
  37. 37. Shade Selection Page: 36 of 40 Table 1 Specifications for currently available technology-based shade systems 5.5 INTERPRETATION METHODS OF DIFFERENT TECHNOLOGIES As discussed previously, the surface of the tooth has significant impact on the perceived value of the shade. The smoother (more reflective) the surface is, the brighter the surface will appear. To overcome this problem, some systems use filters to adjust for the surface gloss. Shade-matching systems that do not use such filters often record shades at a value that is too high, which can be very problematic. Accuracy of color measurement is also affected by the phenomenon of edge loss, which occurs because of light lost primarily through the translucent tooth and ceramic enamel layers. Although algorithms are incorporated into the software to accommodate for the different light-scattering properties of teeth, crowns, and shade tabs, it is difficult to fully compensate for these differences, and this can be a significant source of error.
  38. 38. Shade Selection Page: 37 of 40 Translucency mapping is inadequate in all of the systems. Replication of tooth translucency remains the most challenging aspect of matching the appearance of a natural tooth. The transfer of this three-dimensional quality to a two-dimensional map provides little benefit. Systems that incorporate digital imaging have the best chance because a high-quality visual is the best that is currently available. Positioning of the probe or mouthpiece seems to be critical to the repeatability of the measurement. In addition, any device that uses a small- diameter contact probe is limited because it cannot give detailed mapping of color on the surface and provides only a general base shade of the limited area measured. The larger mouthpieces are limited to measurements of anterior teeth because of access. (Brewer, et al., 2004)
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