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INDIAN DENTAL ACADEMY Leader in continuing dental education

INTRODUCTION Esthetics is the science of sensitive perception; in a narrower sense: the science of beauty.According to Microsoft "Encarta 97" encyclopedia (1997) esthetics is a branch of philosophy concerned with the essence and perception of beauty and ugliness. A German philosopher Baumgarten introduced the term esthetics in 1753, but the study of the nature of beauty had been pursued for centuries. Albert Einstein is reported to have said, "If you cannot explain it simply, then you do not understand it well enough." This appears to be the problem regarding color matching. In a time of growing interest in cosmetic dentistry, there is a need for adequate training and communication for better and more life like results.

The first signs of man’s interest in the facial beauty were recorded more than 4000 years ago. Facial masks of "ideal" shape and proportions used to be the hallmark of royalty even in the ancient Egypt as far as from 2600 to 2000 BC (Mack, 1996). Shape and proportion, however, are not self-sufficient and they are not the only parameters of beauty. Modern concepts of esthetics in dentistry analyze this issue using a much wider approach. Dento-facial esthetics and various factors of patients’ perception and expectations have become a very important part of the prosthodontic treatment (Goldstein and Lancaster, 1984;; Bishop and Priestley, 1996. The results of an examination of Albino et al. (1984) point out that esthetics is the first demand of patients: 42% of the patients indicated that appearance "very strongly" influenced their decision to obtain treatment; 19% put forward functional problems as the major reason, while in 14% of cases the reason was pain. When asked to list 14 characteristics of a denture ranking them by importance, the patients ranked its lifelike appearance as number one.

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Lombardi (1973) described principles of visual perception and their clinical application to denture esthetics. When the term "esthetic"or "unaesthetic" is used it usually means that something is perceived as pleasant or unpleasant. The observer’s response to a physical stimuli is, in fact, his/her psychological and physiological interpretation of that what he/she perceived. The stimulus, i.e. the observed object on one hand and the response to that stimulus on the other are the elements of the science of visual perception.

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Tooth shape, size, position and color are classical determinants of esthetics in prosthodontics, and color is probably most important. A number of experts point out the outstanding need for a systematic and scientifically based approach to color science in dental (especially prosthodontic) education, and its application in clinical practice.

Prosthodontics is more concerned with color than other dental branches, so it is logical to expect that a dentist who has been trained in prosthodontics should be better in shade matching. It can also be expected that working experience exerts positive impact on the shade matching quality.

According to Sproull (1974): "The technology of color is not a simple matter that can be learned without study neither is it a complicated matter beyond the comprehension of dentists". Many authors think that certain improvements in color practice are an objective need of dentistry (Hayashi, 1967; Sproull, 1973 b; Sorensen and Tores, 1987; Sorensen and Tores, 1988 a; Sorensen and Tores, 1988 b).most of the authors think that color science study should be included in the undergraduate and postgraduate curriculum and/or in the prosthodontics training program.

There is a lot of perplexity and confusion just as there are numerous insufficiently explained questions in shade matching and reproduction procedures. However, it is neither easy nor simple to answer these questions. In spite of objective and subjective inadequacies of the shade matching and reproduction method itself, dental material manufacturers could be blamed for certain problems in this area. . The problem is that the majority of dental color standards lack a logical sample arrangement order and adequate color distribution; moreover, they do not match natural teeth color range. Since natural tooth color is not uniform, harmonization of shade guide samples, dental materials and prefabricated artificial teeth color composition with the color composition of natural teeth emerges as a yet unresolved issue.

Color disharmony was found in some manufacturers ceramic masses intended for certain ceramic layers (especially between opaque and dentin ceramic powders). Also, it cannot be positively asserted whether (and to what extent) manufacturers manage to standardize color in different batches of dental materials and whether particle size differences influence color. Color reproduction for porcelain-fused-to-metal (PFM) restorations is also a source of many questions, such as: to what extent the final color of restoration is influenced by the type of substrate, the application method, the thickness of ceramic layers, the number of firings and the firing temperature.

Color matching can be performed using visual and/or instrumental methods. Visual color matching methods are subjective, while instrumental methods are objective, but still not widespread in dental practice. Precise and objective answers to most of the questions mentioned could be obtained only by using instrumental color matching techniques, because they allow numerical expression of results. A correct interpretation of colorimetric results requires knowledge of the basic elements of the color science. Def: “ Color is light,modified by an object as percieved by an eye”.

COLOR SCIENCE A need to overcome subjectivity, as the major disadvantage of the visual shade matching method, induced the evolution of color science. Color science is multidisciplinary and it encompasses elements of physics, chemistry, physiology and psychology. In order to understand the science of color, one should be aware of some physical aspects of light, as well as of both physiological and psychological processes that enable color perception.

Webster: "Color is the sensation resulting from stimulation of the retina of the eye by light waves of certain lengths". Billmeyer and Saltzman: "Color is the result of the physical modification of light by colorants as observed by the human eye and interpreted by the brain". Color is a special type of psychophysical sensation provoked in the eye by the influence of the visible light .That incident light, or so-called colored stimulus, provokes the stimulation of high sensitive eye receptors, producing the nerve impulse, which is transported to the brain. The brain is the interpreter that recognizes those nerve impulses as a certain color. To work with color, it is necessary to be acquainted with the physical, physiological and psychological aspects of light as well as with the basic principles of colorimetry.

Physical, physiological and psychological aspects of light

Psychophysics is a scientific discipline dealing with mathematical relations between physical stimuli and the sensations they cause. Electromagnetic radiation that can provoke a sensation of color is called stimulus. Stimulus is, speaking in terms of physics, determined by the total flux of radiation, i.e. by the quantity of energy transported to the retina in the function of time and distributed onto different wavelengths (Lemiere and Burk, 1975; Prat, 1978; Birren, 1979; Billmeyer and Saltzman, 1981).

The entire process starts with the light source, which justifies the saying: "Color is light" (Saleski, 1972). What one recognizes as natural white light is daylight (not direct sunlight, which is yellow, but sunlight reflected back from the sky). The visible part of the spectrum comprises electromagnetic radiation falling between wavelengths from 380 to 780 nm. The visible spectra range, is called monochromatic light. White light can be separated into monochromatic components if it passes through prism or diffraction bars . If the wavelength of the electromagnetic radiation is less than 380 nm, it is called ultraviolet radiation and if it exceeds 780 nm, it is called infrared radiation

Light source. Light source is any area or body emitting radiation in the visible spectra range. According to one classification, light sources can be primary (emitting their own radiation) and secondary (reflecting a part of the radiation from some other light source), and according to another one, they are divided into natural and artificial light sources. The Sun is the most important natural light source. The object. One seldom looks directly at the light source. The radiation flux that reaches the eye is almost all the time reflected from some object, which indicates that observed object influences color perception. The structure of the object (type of material, texture) influences its optical properties. The eye. Color, as well as all other visual sensations, is brought to the brain through the eye. Visual perception occurs owing to the optical system in the anterior and the retina in the posterior part of the eye .

The light reflected from the object is brought to the observer’s eye. Light enters through the optical system and the image is focused onto the retina. The retina is a complex mosaic of millions of nerve endings containing a chemical substance which transforms the light stimulation into a nerve signal that is further transported to the brain. There are two types of nerve endings, rods and cones. Rods only record light, i.e. they see in black and white. They are connected together in bunches before reaching the brain, the interpretive part of the system, so that they achieve high sensitivity at the expense of fine resolution. At high levels of illumination, they play a small part in the vision process. Cones are nerve endings that enable color vision. Some seven million cones are placed in the centre of the retina, in a small pit called fovea, subtending an angle of about 2° in the visual field. Here, instead of the bunching found in the rod area, there is a "one-to-one" connection with the optical system so that their resolving power is high.

This is the area of visual acuity, lying on the visual axis of the eye. Cones require a higher level of illumination to be brought into action. This can be demonstrated by a slow increase of illumination from complete darkness, through dim illumination at which stage only shape can be distinguished (rod vision), allowing only glimpses of color, up to the stage of full intensity of light when the function of the cones is maximum. This experiment covers three stages of vision: scotopic, when only rod vision is operating; mesopic, when the cones are only initially stimulated and rods have not been flooded yet; photopic - full light color vision (Chamberlin and Chamberlin, 1980).

Trichromatic character of vision . There are many complicated theories as to how cones function, but the simplest and most commonly accepted is Thomas Young theory, supported by Helmholz. It is based on the experimental fact that a suitable mixture of three monochromatic radiations can match any color. This trichromatic theory postulates three different types of cones, which are sensitive to different bands of wavelengths. The "blue-sensitive" cones are brought into action chiefly by light of short visible wavelengths, the second type responding chiefly to light of wavelengths in the middle of the visible spectrum are called "green-sensitive", while the third type, the "red-sensitive" cones, are most affected by light of the longer visible wavelengths. The visible pigments responsible for these various functions have not as yet been positively isolated.

The distribution of rods and cones changes as one travels outward from the fovea. The central area (2째 field), which receives the image from an object, is rod free and color differentiation is the best in this area. Outwards, to a 4째 field, there is a mixture of rods and cones, the composition of which mixture can vary with individuals. Outside of this area the cone population falls off rapidly. The periphery of the eye is not color discriminating, although very sensitive to light variations, movements etc. It is because of this varying distribution of rods and cones between individuals that there arises the slight difference in color discrimination between "color normal" observers, but they are surprisingly small among more than 90% of people. Hence the statement: "Although all the people have not the same sight, the majority of them see very similar"

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The brain. Although an image may be formed on the retina, the observer cannot be said to "seeunless that image is in some way conveyed to his consciousness. A number of impulses are set in motion by the light, and these messages have to be conveyed to, and interpreted by, the brain before perception occurs.

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The electrical impulses set up in the rods and cones are programmed and sorted out somewhere on the way to the brain, but there is no general agreement as to the mechanism of sorting. There are different opinions if the commencement is made with coding in the retina itself, or in the tissues and nerves immediately adjacent to it, or at intermediate points where the nerve ganglions join to form bundles of pathways. However, some form of message is eventually conveyed by the optic nerve to the appropriate part of the brain. The messages from the rods are telling of the light or no light, while the cone messages convey information that gives rise to the sensation of color.

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On reaching the brain, the messages are decoded and refereed, as in a computer, to a bank of stored memories, which will connect the picture presented with something previously experienced, and finally sensation of something "out there in front" materializes in consciousness. All this operation is carried out at light speed. When one is waking, he is presented with an avalanche of messages from the eyes. Fortunately, the brain is selective, ignoring what is not relevant. One perceives only the things he is interested in or which the brain automatically brings to his notice of the built-in instinct for selfpreservation (Chamberlin and Chamberlin, 1980).

The most frequent complications in color perception are chromatic adaptation, metamerism and dichroism. 

Chromatic adaptation is defined as a color constancy phenomenon of the perceived color of the viewed scene. Going from daylight, into a room lit only by incandescent lamps, one is seldom aware of the fact that the color of everything has changed, although reason points out that this must be so. Metamerism which occurs when the color of two objects looks identical when observed under one light source but different under other light conditions Dichroism refers to a situation when the color of an object, viewed by transmitted light, may be different accordingto the thickness of the sample viewed. Blood is, for example, yellow if viewed in an extremely thin film but is red in greater depth.

Color defining and/or measuring Visual comparison is a comparison with some known physical standard accepted as referral. There are numerous systems of visual comparison and description of color. The easiest way is to produce some kind of systematized and precisely repeatable catalogue. Such catalogues are called color atlases or color derivation systems. The Munsell Book of Color, the Ostwald system and DIN (Deutches Institut f端r Normung) system are the most famous color catalogs.

No matter what visual method is used, light source and viewing geometry should be standardized in order to obtain valid results. In the case of instrument itself, standardization is to be done by the manufacturer, but in case when color atlases or some other samples are used, adequate conditions have to be provided. Furthermore, in all cases of visual colorimetry before any real work starts it is necessary to test whether the observer is color deficient. It has already been emphasized that there are differences among so-called "color normal" observers, but training and practice may reduce these differences to an acceptable level. If some important examination is underway, it is recommended to use more than one observer and take the mean value of their responses as a result.

Color Vision Testing Pseudo-Isochromatic Plates frequently are used by eye specialists to get an idea of one’s color efficiency or deficiency. To a color-deficient person, all the dots in one or more of the plates will appear similar or the same—“isochromatic.” To a person without a color deficiency, some of the dots will appear dissimilar enough from the other dots to form a distinct figure (number) on each of the plates —“pseudo-isochromatic.”

Light and Its Role in Dental Ceramics Just as a musician must know the scales, dentists and ceramists must know the principles of light. Without scales, there would be no music; without light, no colour. To better appreciate the importance of light in dental ceramics, we must learn some of its basic characteristics and how these, when combined with the physical and chemical composition of natural teeth, influence our visual perception of tooth colour.

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Direct Light When direct light falls upon an object, it is either absorbed, reflected, or transmitted. If all of the light is reflected, the object appears white. If the light is entirely absorbed, the object appears black. The larger the amount of light reflected by an object, the brighter the object will appear. Furthermore, the greater the intensity of the direct light source, the brighter the object will appear. The final effect depends greatly on whether the object is transparent, translucent or opaque. Teeth and porcelain have all these characteristics, however the differences in the chemical and physical properties of teeth and porcelain require that these characteristics be treated differently.

In duplicating tooth colour, we must produce a ceramic restoration that captures all the colour dimensions found in the tooth despite the opacity produced by the gold and opaque layer, rather than in conjunction with it. The opacity found in the dentin is a chemical phenomenon rather then the physical one produced by the metal in a ceramic restoration. Light can be transmitted or passed through transparent and translucent substances. A clear window glass through which an object can be seen distinctly is an example of a transparent medium; it permits maximum transmission of light.

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A frosted glass pane, through which light is visible but objects are seen indistinctly, is an example of a translucent medium; it transmits diffused light. A wooden door or brick wall is an opaque medium and permits no light transmission In both natural dentition and fabricated restorations, we are concerned with translucent and opaque qualities rather than transparent ones. Of the three, teeth have the least transparency; in a ceramic restoration, this is undesirable for it serves no constructive purpose

Reflected Light

Reflected light describes light rays that are bounced back from the surface of the object encountered instead of being transmitted through or absorbed by it. Light rays that strike the surface of an object are called incident (falling upon) rays and their point of contact is termed point of incidence. Reflected light falls into two categories: specular and diffused. Specular light travels in a single direction. When the incident light strikes a perfectly smooth surface, it rebounds from the point of impact at exactly the same angle as the incident ray. Diffused light travels in more than one direction. If light rays strike an uneven surface, they cannot be reflected at an even angle; the incident rays will be reflected at various angles, making the light diffused

Color matching and reproduction Color vision Color matching is complicated with individual differences in color perception and different color matching ability. According to Culipepper (1970), there are tooth color matching differences among dentists themselves and it happens that the same dentist may match different shades for the same tooth in different days. Hence, it turns out to be necessary for dental students, dentists and dental technicians to undergo a color vision test, particularly in view of the fact that approximately 8% of men and 0.5% of women are color deficient (Barna, 1981; Paravina et al., 1997 a).

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Color matching conditions Tooth color is in the clinical practice matched under different illuminants. Illumination for shade matching should be standardized and harmonized with the laboratory illumination (Bergen and Mccasland, 1977; Preston et al., 1978;) While performing tooth color matching, attention should be attached to the viewing distance, viewing angle as well as to the impact of such factors as background and environment. The color of the patient’s clothes, the color of the drapes, uniform, equipment, office furniture, walls and ceiling are of great importance.

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Dental color standards Hall (1991) wrote: "Shade guides of all dental restorative materials are based on the long established porcelain shade guides which evolved to represent the available shades of porcelain teeth. The shades developed by a process of popular selection by which shades perceived to be nearer tooth colour were added and the least popular eliminated. This concept has not changed since the introduction of porcelain over two hundred years ago".

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A number of authorities in dental ceramics point at inadequacies of the commercial shade guides (Sproull, 1967; Sorensen and Tores, 1987; Pizzamiglio, 1991). The shades of the samples are not logically arranged, they are not equally placed in color solid and do not cover the color range of the natural teeth (Hayashi, 1967; Sproull, 1973 b;). The absence of darker shades in the majority of dental color standards is caused by the compromise with the cosmetic demands for the "white" teeth. The samples used for PFM restoration color matching are made of fired ceramics, with no metal substrate and the anteriorposterior size of the ceramics is considerably larger than the ceramic part of the final PFM restoration (Bergen, 1985. The color of the acrylic resin samples is changeable if kept in some disinfectants, particularly in chlorine-containing disinfecting solutions (Cernavin, 1996).

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The mentioned inadequacies gave rise to various propositions for the production of new shade guides, and for the improvement of the sample arrangement order in the existing color standards, or resulted in the production of different individual (custom) shade guides

The manufacturers had ignored for decades the legitimate demands for the production of new dental color standards based on the needs of dental practice, color range of the natural teeth and the principles of the color science. Certain progress in this area, however, was made not so long ago. Vita Zahnfabrik Company (http) presented a new dental color standard, "Vitapan 3D Master". This shade guide consists of 26 samples divided into groups according to lightness and within those groups according to saturation (vertically) and hue (horizontally). Despite the fact that the improvement in relation to the previous color standard of this manufacturer (Vita "Lumin Vacuum") is obvious, certain disharmony in the sample arrangement can be noticed in shade guide as a whole.

Color matching method 

It is more than obvious that it is not simple to provide adequate shade matching conditions. As for the shade matching method, there have been significant improvements in this area, especially in the last ten years. Shade matching should be performed at the beginning of the appointment (Sorensen and Tores, 1988; Pizzamiglio, 1991) and the patient’s mouth should be at the level of the dentist’s eye. A shade guide sample should be applied parallel with the tooth whose shade is being matched, not in front of it, for it will appear lighter, not behind it because it will appear darker. Some authors suggest that the cervical part of samples should be removed because they are more saturated, which could have a negative effect on the shade matching (Miller, 1993). Spencer (http) suggests removal of the mesial and the distal third of the samples in order to enable application of two shade guide samples next to the tooth whose color is being matched.

If the sample and the tooth whose color is being matched have different surface texture, both should be wet, in order to neutralize this difference. Tooth should not be observed for more than five seconds at a time, and, in the meantime, it is desirable to observe some blue surface for one minute (Pizzamiglio, 1991) in order to increase the ability to differentiate yellow color (the dominant color of the teeth). Owing to possible occurrence of metamerism, the choice should be verified under different illuminants. Some authors’ attitude (Seluk and LaLonde, 1985, Swepston and Miller, 1985) that esthetics can be improved if the dentist and the dental technician use shade guides and relative porcelains of several manufacturers is logical and acceptable. It is also suggested that extended shade guides should be used (containing the samples of all ceramic masses used for the production of PFM restorations), such as Vita "VMK - Shade Indicator" (Pizzamiglio, 1991; Miller, 1993).

Munsell color order system Many color order systems are available, but for a variety of reasons, including worldwide recognition, consistency, flexibility, and simplicity, the Munsell Color Order System is the system of choice for color matching in dentistry. The attempt to achieve equal visual (Perceptual) spacing in this system further recommends it. The color tree (Plate I) is a representation of the tridimensional organization of the colors within the Munsell System. The Munsell color solid can be likened to a sphere or to a cylinder, as it is an irregular three dimensional figure that has characteristics of both.

Although usually described as a sphere (Munshell’s original concept), for the purpose of this article, it will be treated a a cylinder. The relationship of one color t another becomes apparent when the organization of the colors within the three dimensional solid is understood. A colorless or achromatic axis extends through the center of the cylinder, pure white at the top, pure black at the bottom A series of grays, progressing from black to white in equal visual steps, connects these extremities.

Colors (Hues) are arranged around this axis, and within each Hue, the colors are arranged in scales according to their lightness/darkness (Value) and their purity or strength (Chroma). (In the Munsell System, Hue Value, and Chroma are capitalized). Light colors are toward the top of the cylinder; dark colors are toward the bottom. The colors are purest on the outer skin of the cylinder and they become progressively grayer as they approach the gray Value axis. Within each of these scales of Hue, Value, and Chroma, the intervals were chosen to represent equal visual spacing under a standard light source.

The cylinder may be considered as a series of wheels stacked one upon the other, each wheel of ascending lightness as we progress to the tope of the cylinder. The hub of each wheel represents the Value axis. The Hues are arranged sequentially around the rim. The spokes represent the gradations of Chroma from the color less axis to the purest Hues at the rim. In actually, as can be seen by examining plate I, the Hues project unevenly beyond the surface of the solid, but this is one of the advantages of the system. As technology permits the creation of purer colors, they can easily to added to the periphery. These unequal extensions of the Chroma spokes obviously make some of the wheels flat or lopsided, but basically we have a cylinder, even if it is bent out of shape.

value scale

Dimensions of Color. Hue, Value and Chroma, the dimensions of color, are just as descriptive in describing color as length, width, and breadth are in describing form, once the language is understood by those using it. Since it is so important in working with color to understand thoroughly the three dimensional concept of color, a more explicit description of each is presented. Hue, Hue: the first dimension, is the easiest to understand, and in Munsell’s words, “it is that quality by which we distinguish one color family from another, as red from yellow, green from blue or purple.” The color wheel is a familiar form of this dimension and consists of the Hues that are arranged sequentially around the central axis of the Munsell color Solid (Plate II, C). The refer to a Hue in the Munsell system, the initials are used; R for red, YR for yellow red, Y for yellow, and so on. Each Hue is subdivided into ten segments, equally spaced visually (by psychologic criteria) from each other. The color wheel cut and placed in a horizontal strip.

Value and Chroma are more difficult to understand and are often confused with one another. Special attention must be focused on these dimensions. Value: Value “is that quality by which we distinguish a light color from a dark color”, and this is related to the achromatic (colorless) polar axis going through the Munsell color solid. The value of a color is determined by which gray on the Value scale it matches in lightness/darkness. The black of the Value scale is assigned a Value of zero, the white a Value of 10. An infinite number of gradations of gray is possible as we go from black to white, but only nine Value (gray) steps are used in the Munsell system. Pure white (10) and pure black (0) are unattainable. Fractional numbers are used when a finer evaluation is needed. “Low” values refer to dark colors : “high” values to light colors.

We perceive Value differences when we watch a black and white television picture. The actual scene is full of color, but only the lightness/darkness (Value) of a color is transmitted, a blue, red or yellow could all be transmitted as the same indistinguishable gray if they are of the same Value (a part of the same Value “wheel’). Colors of high Value would be transmitted as light grays, and those of low Value as dark grays, regardless of the Hue or chroma. It could be said that the Value of a color is the gray it would match if it were seen on a black and white television screen. Tab c in Plate II, B, and all the tabs directly to its left have the same Value and would, therefore, transmit as the same indistinguishable gray.

Chroma : Chroma, the remaining dimension, “is that quality by which we distinguish a strong color from a weak one; the departure of a color sensation from that of white or gray; the intensity of a distinctive Hue; color intensity. Chroma describes the amount of Hue in a color. The gradations of Chroma were referred to as the spokes of our wheels. The concept of painting a box will help to clarify this dimension. Suppose it is desired to paint one side of box pure red. If an amount of gray paint is added to the bucket before the second side is painted, the red on the second side will be perceived as less than a pure red; the Chroma will be reduced. If additional gray paint is added to the bucket before each additional side is painted, the paint will come closer and closer to being perceived as a gray.

Plate II, B, is from the Munsell Book of Color, and studying this illustration will aid in the understanding of these points. If the red to the extreme right at Value level 4 (tab c) is considered as the original color of the paint, the red to the left of this would represent the paints of reduced Chroma. Adding a gray always reduces the Chroma and theoretically will not affect the Hue. The change in Value of the original color depends upon the Value of the gray added to it. If a gray of higher Value than that of the original color is used, the resulting color will be of the same Hue, lessened Chroma, and higher value (tab a could represent such a result).

If a gray of the same Value is used, only the Chroma will be affected (lessened). (e.g., tab d). If a gray of a lower Value is used, only the Chroma will be lessened, and the Value will be lowered (e.g. tab b). Emphasis is placed on this point in order to dispel the confusing statements seen in some dental literature to the effect that Value depends upon the relative amount of gray in a Hue and that adding gray always lowers the Value. The need to refer to gray in describing both Value and Chroma is a major factor in the confusion concerning these two dimensions. To think of Value in relation to the television picture and Chroma in relation to the painting of the box will provide a simple, easily recalled memory aid.

SURFACE TEXTURE Matching the surface texture and outline form is an important as matching the shade of a tooth. This statement does not diminish the importance of the shade but emphasizes the importance of reproducing surface texture and outline form in establishing esthetic harmony of a ceramic restoration. Regardless of whether a tooth is flat or irregular, the surface is viewed as being rough or smooth. A smooth surface will reflect most of the incident light back to the observer. A roughened surface randomly scatters the reflection of light in many different directions. In the process of determining the character of light reflection, the surface texture of a crown must be designed to simulate the reflectance pattern of adjacent teeth. Properly blending the effects of light reflection and absorption in a crown creates a natural appearance that hides slight color differences.

Many dentists have discussed the manipulation of surface texture to conceal color differences in ceramic restorations. Obregon et al, found that increased roughness of porcelain samples decreased the Value level. Burk, in a pilot study, observed that modifying surface texture altered the appearance of porcelain in terms of Hue, Value, and Chroma, and even affected the degree of translucency. On eruption, teeth have their roughest surface texture. Undulating vertical ridges are formed by the fusion of developmental lobes transversed by fine horizontal lines. These numerous small transverse lines on the surface of enamel are perikymata produced during the incremental formation of enamel. In general, with advancing age these surface features are gradually obliterated through attrition from tooth brushing or occlusal wear.

This process of progressive enamel wear corresponding with advancing age can be characterized. Through many years of brushing and the process of natural abrasion, the lines become less defined and the tooth surface acquires more stippled appearance. As the wear process continues into the later years of life, all signs of the perikymata are lost and only the gentle undulations of the developmental lobes are observed. Finally, the definition of the developmental lobes is obliterated and the tooth appears smooth with a highly reflecting glassy surface.

The teeth with a highly reflectively glassy surface. The teeth of a younger individual will most likely have the perikymata and developmental lobes intact. Emulating the surface characteristic for a particular age group facilitates achievement of a life like restoration. Failure to reproduce surface detail accurately will result in light reflection different from that of the contra lateral teeth. This result will suggest artificially, despite correct color and contour matching.

To create the surface texture of a young individual, the developmental lobes and vertical undulations are first defined with a cone shaped diamond bur. Next, a rotating football shaped diamond bur moved mesiodistally defines perikymata. The crown is fired to a light autoglaze to hear surface flaws. Finally, diamond polishing paste on a 1 inch felt wheel creates the desired surface shine. The smooth surface of an older tooth resulting from heavy abrasion, is first prepared by defining any developmental lobes. Ridges and heights of contour are polished with a rubber wheel. The crown is held at glazing temperature for a longer period to achieve a smoother autoglaze. The final finish is accomplished by polishing with Brasso cleaner (French Household products, Rochester, N.Y.) and pumice on a high speed lathe with a large felt wheel to the desired smoothness. Wear facets can be created by further selective polishing with a rubber wheel.

Although study casts are helpful in demonstrating major features such as developmental ridges, surface texture is inadequately reproduced by a stone cast. The use of a resin replica has been suggested for better reproduction of surface detail. A tooth tab actually demonstrating surface texture provides much more detail than a written prescription or a study cast. We have developed a system of using extracted teeth with varying degrees of surface texture. The teeth are sterilized, numbered for easy identification, and retained on a ring. By having several sets of surface texture tabs available, the dentist match and record the appropriate surface texture tab and include the tab with the preparation dies. Preparation of various surface texture on porcelain tabs is an alternative to the use of extracted teeth. The identification tab, which will be discussed, can also be textured for communication with the ceramist. The identification tabs can be prepared with a range of surface texture and degrees of luster.

Although final chairside adjustment is always necessary, the ceramic restoration produced by the ceramist will require less adjustment and be closer to the desired finished result. Because the surface texture of the crown is similar to that the natural teeth to be matched, it allows rapid evaluation of suitability of color match.

SHADE SELECTION PROCEDURE: CLARK SAID, "Color, like form, has three dimensions, but they are not in general use. Many of us have not been taught neither names, nor the scales of their measurement. In other words, we as dentists are not educationally equipped to approach a color problem." This statement is, unfortunately, still true. Dentists have had little or no training in vision physiology or color science. A 1967 survey revealed that 23 out of 112 dental schools had some sort of color education in their curriculum. A survey conducted the following year, reported that 3 of 115 dental schools taught a formal course in color. Thirty years later, comprehensive color training continues to be a missing part in the dental school curriculum. If any training at all is given in dental school, it is cursory or simplistic and usually consists of presenting an incomplete explanation of three abstract concepts of the Munsell Notation:4 hue, value and chroma.

The increase in newer types of ceramic restorations and the improving quality of esthetics means the dentist of the 21st century must be trained to detect differences in color and shades in individual teeth, select a shade that reflects the color and exact shade, transmit this information to a dental technician, and then be able to make any necessary adjustments to the restoration. However, there are a number of factors that stand in the way of properly selecting a color match. Subjective faults range from differences in color perception to ocular fatigue and lack of education regarding the basic principles of color. Metamerism may occur if proper lighting is not used during shade selection in the dental office and laboratory Finally, existing shade guides are limited and require a more extensive range of shades.

Therefore, it is no surprise that color matching for crowns and dentures can be a frustrating and discouraging experience for the dentist, technician and patient. The breakdown in communication over matters ranging from shade guide to laboratory prescriptions must be addressed. This study will review the problems of color matching and will attempt to guide the reader toward enhancing his or her techniques regarding shade selection and communication with the ceramist. Tooth vs. Porcelain Prior to shade matching, the dentist must have an understanding that the human tooth and dental porcelain transmit light waves differently It is their physical composition that determines the differences in light-wave transmission, absorption, reflection, refraction, scattering and surface gloss. The manner in which light strikes an object determines the total appearance of the material. Transparent materials allow for the passage of light with little change. Translucent materials scatter, transmit and absorb light. Opaque materials reflect and absorb; however they do not transmit. Surface characteristics, such as gloss, curvature and texture, will affect the degree of light diffusion when striking the particular object.

A vital tooth is both naturally translucent and transparent. Enamel rods are transparent and therefore refract and reflect light. Light that strikes the incisal edges of an anterior tooth passes through with maximum transmission because of a high degree of translucency. Porcelain, however, is a heterogeneous material. It contains transparent properties and metallic oxides that act as opacifiers. These porcelains modify light by absorption, transmission and reflection. Absorption is largely responsible for color. It occurs when light passes through the layers of the porcelain. Scattering occurs when light encounters interfaces between the materials (i.e., pigments and glass). The smaller the pigment size, the less light that is absorbed, resulting in less detectable color. The larger the pigment size, the more reflection that occurs as light scatters at the particle surfaces. Scattering light is necessary in dental porcelains to simulate the prismatic effect of enamel. Yet, one must keep in mind that too much dispersed reflection through internal scattering will create an unnatural looking prosthesis.

Light Sources One of the questions asked when selecting a shade is, what light source should be used? Shade determination should be performed under color corrected fluorescent lighting, which contains a balance of the entire visible spectrum. The operatory should be lit using a luminous ceiling with translucent diffusing panels that are simple to maintain. Clean watt saver lamps having a color temperature of 4200K or higher is advocated. Shade selection should not be made using daylight, because daylight is subject to constant changes.

One must also be concerned with the phenomenon of metamerism, which occurs when the color of two objects looks identical when observed under one light source but different under other light conditions.Metamerism occurs only when two objects have different wavelength distribution and therefore reflect different spectra. The color of the operatory can also affect shade selection. Colors should be kept at a low saturation level. Walls and cabinets should be glossy enough to maintain brightness without causing a glare. It is recommended that the color of the walls and ceiling be white or off-white. The dentist should be concerned with "blue fatigue:' this occurs when the eye is unable to differentiate between the various shades of blue. However, blue fatigue increases sensitivity to yellow therefore, to improve shade selection in the yellow range, the operator should stare at a blue card or patient napkin between shade comparisons.

It has been suggested that dentists use natural north daylight for shade matching. Many dental offices have been designed to face the north to enhance the selection process. However, daylight is not at a constant throughout the day and therefore must not be used as the only light source for shade matching.

The Problem with Shade Guides Shade guides have become the standard for selecting shade, yet there have been many errors associated with the use of commercial shade guides. Problems that may arise include the following: 1. Porcelains do not match the shade guides that they are being compared to. 2. Shade variations occur between different die lots of porcelain from the same manufacturer. 3. Shade guide tabs are 4-5 mm thick compared to the thin 1.5 mm piece of porcelain used for the restoration. 4. Shade guides are not always made with fluorescent porcelain, which causes inconsistencies in color matching. 5. It is difficult to predict the final shade after the layering of opaque, dentin and enamel. 6. Guide tabs lack a metal backing when using porcelain-fused to-metal restorations. 7. Shade tabs are condensed differently than porcelain used for final restorations.

Now that the reader understands the potential problems that arise when selecting shade, it is imperative that the dentist have a proper education in color. However, we must assume that not every dentist will seek out the proper courses. The latter portion of this article will be a review of numerous methods for enhancing laboratory communication between the dentist and the dental technician, to assure the success of proper shade matching. The dentist must then decide for himself or herself how much information is enough to guarantee the replication of the restored teeth.

Shade Selection Guidelines The dentist must have a working knowledge of the basic principles of color. This allows for accurate shade selection. Munsell described the three dimensions of color as hue, value and chroma. Hue is the property of color that is determined by wavelength, which distinguishes one color from another. Value is a quantity of brightness. It is a qualitative term related to lightness or blackness of color and not the quantity of the color gray Chroma is the saturation of color. Matching the proper shade is not carried out just by holding up a guide tab to the tooth in question. There are a number of methods that can be employed to intensify the shade selection. They are as follows:

1. If patient is wearing bright clothing, drape him or her with a neutral colored cover. 2. Have patient remove lipstick or other make-up. 3. Clean the teeth and remove all stains and debris. 4. Have patient's mouth at dentist's eye level. 5. Determine shade at the beginning of the appointment to avoid ocular fatigue. 6. Shade comparisons should be performed at five-second intervals so as not to fatigue the cone cells of the retina. 7. Obtain value levels by squinting. 8. Compare shade under varying conditions (i.e., wet vs. dry lips; retracted lip vs. pulled down lip). 9. Use the canine as a reference for shade because of the highest chroma of the dominant hue of the teeth." 10. If unable to precisely match shade, select a shade of lower chroma and higher value. 11. Grind off the necks of the shade tabs because they tend to be darker than the rest of the shade tab.

Custom Shade Guides To properly start the shade matching process the dentist should acquire a custom shade guide. This guide is the beginning of improving communication with the laboratory Each custom shade guide should include the ceramists metal, porcelain, staining kits, equipment and techniques. It should also contain pointers as to what to look for when selecting a shade. The technician needs to send a chart along with the guide for jotting down any additional information that will allow for a better understanding of the particular shade. The dentist may choose to create a luster tab and send it to the laboratory with the prescription. The technician will then have a visual aid for what he must fabricate. Numerous techniques regarding custom shade guides have been noted in the literature.

Procedure for shade selection: The first step is to select the hue .this is a delicate step since thereis not much difference among the hues .because different chromas of the same hue are close to each other in the manufacturers arrangement of the shade guide there can be confusion.for this reason pizzamiglio used “the four hues technique�. In the vita shade guide there are only four hues ,A B C andD. The maximum chromas of each hue A4,B4,C4,andD4 are removed from the shade guide and put in a vita VMKindividualskala kit . this allows one to visualize the difference in hue more effectively because chroma is more intense . the lamp is set at a distance of 20cm from the dental arch and, with the shade guide arranged with the four hues ,two passes from the beginning to the end of the guide are quickly made close to the teeth . it is important to determine the hue by observing the shade guide against the cervical part of the tooth .

Looking toward the cervical part increases the perceived chroma where as looking toward the incisal part decreases the perceived chroma ,making it more difficult to distinguish the hues. When the canine is present ,it is the best tooth on which to choose hue because it has the highest chroma. This step should be performed within 5 sec,otherwise the ability to recognize the desired hue decreases . the eyes are then rested by gazing at a blue background. Suppose that the hue chosen is A. once this is done the other three hues (B,CandD) are set aside .next all of the different chromas of the selected hue are put in the Vita VMKIndividualskakala kit .an example that would be A1,A2,A3,A3.5andA4. At this point we have different chromas of the selected Hue in the shade guide to match with the tooth.

Again working quickly(less than 5 sec),the dentist selects the chroma by comparing the shade guide against the tooth . This is much easier because now we have only different chromas chromas of the same hue , the eyes are rested by gazing at a blue background for 1 min . Suppose that the selected chroma is A2. Through the shade indicator chart .,we know the number of the dentin (in the case of A1, it is 541). The chroma is again checked with a ring arranged by the dentin colour .it is of the necessary to make corrections . the number of the dentin chroma that has been chosen is recorded. The blue background is again used to rest the eyes . Next the enamel is chosen with enamel colours . in this case the observation should be done at the incisal part of the teeth where the enamel is thicker .

The second shade guide arranged according to the value , is used to select the value. An important part of this procedure is to squint the eyes . squinting causes the black and white sensitive rods in the eye to become more active than the colour sensitive cones. The rods are responsible for helping to determine the value. It is important to avoid consideration of the hue and chroma when selecting the value. The value that has been selected is used to choose the opaque porcelain. If the value is wrong ,the effect will be particularly unpleasant in the cervical region where the thickness of PFM is less.

Shade Guides Because an important factor in restorations is the shade determination, it is imperative that guides are available to assist in the correct shade matching. VITA Lumin Vacuum Shade Guide contains porcelains that are pre-fired set out in the colour tones that the company has available. They are arranged on porcelain pins that can be removed individually for maximum shade matching. The main tones groups are rosebrown, rose-white, greytone, and rose-grey. VITA VMK Individualised Shade Guide is a kit for the reproduction of intermediate and individual shades, and therefore demonstrates the offering of a multitude of possibilities of shade determination of the companies metal ceramics. This is the main communication method of shade determination between dentist and technician. The porcelains are layered onto a ceramic cap which corresponds in colour to the oxidised metal. These are also excellent for practice.

How do you determine the tooth shade with VITAPAN 3D-MASTER? The logical configuration of the shades makes working with VITAPAN 3D-MASTER very easy. The shade selection is a logical progression of three simplified choices - the desired shade is found very quickly:In the first step of the shade taking procedure the value (lightness) is determined. Select the value level from the five value groups (levels 1 - 5) that is closest to the value of the tooth to be compared. Pull out the medium shade sample (M) from the selected value group.

In the second step the chroma (levels 1 2,3) is determined. Select the color sample of the selected M group that is closest to the tooth to be compared. In the third step the hue (L, M, R) is determined. Check whether the natural tooth displays a "more yellowish" (L) or "more reddish" {R) shade than the color sample of the M-group that has been selected in the second step. Now the best matching shade sample is determined and the information is recorded in the color communication form.

VITAPAN 3D-MASTER divides the tooth color space into 5 levels of value.

In the medium (M) hue there are three levels of color samples for the chroma. Deviations towards the more yellowish hues (L) or more reddish hues (R) exist in 2 chromas.

A deviation of the medium hue (M) towards yellow or red can be compared with the corresponding hue groups (L,

Value (lightness) level In the first step the value or lightness is determined.

Chroma In the second step the chroma or color saturation is determined.

Hue In the third step the hue is verified.

Opaque Porcelain. Success in duplicating depends greatly on proper opaquing procedures. Reproduction of the colour tone of natural teeth is attainable with an understanding of opaque porcelain. The opaque layer is the foundation of the ceramic portion of a porcelain fused to metal restoration. This foundation provides an excellent bond and consistent and precise shade control. Opaque should be mixed with Condenser Liquid or distilled water to the consistency of heavy cream, which can be easily applied with brush or spatula. The preferable method of applying opaque is with two thin coats, fired individually to a total thickness of 0.2 - 0.3 mm. Opaque porcelain should never be allowed to dry in application

Opaque porcelain It masks the metal colour. Because teeth are translucent the body porcelain is made transparent, so the opaque porcelain is used to mask the metal colour.

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Success of the application of opaque depends of following 3 working techniques: brushing moisture control condensation of the opaque porcelain by vibration or other methods

Liquids - Opaque, Modelling & Condenser  Opaque liquid is used for mixing and remoistening of opaque porcelains  Modelling liquids are used for mixing all dentine and enamel porcelains.  The use of Condenser Liquid, which is in effect a stronger form of modelling liquid, allows the porcelain to stay wet longer, resulting in more working time. It is ideal for larger restorations. It improves stability and considerably extends working time. Some generic condenser liquids, when used with opaque powders, will result in a pastier consistency, yielding a greater ease of application

Dentine Porcelain Dentine is used to build the dental shape. It gives the opacity and the density of the natural tooth dentin to the porcelain, for use in the anatomical shading. These are the components for the build up of the crown. These are used to build up the tooth after the opaque firing. The definite shape of the tooth is constructed with dentine materials. Dentine can be mixed with stains. .

Enamel Porcelains Also known as incisal porcelains. Display a degree of opalescence that makes it comparable to natural tooth definition. Acts as a transmitter of the underlying colour found in the dentine and is made up of long rods that are surrounded by a prismatic substance and are perpendicular to the dentin. It is this fibre-optic arrangement that permits light to pass through the enamel, strike the underlying colour in the dentin and reflect off in all directions giving the opalescent appearance mentioned above. Can be applied with the dentin or separately after the dentin has been fired. Translucency of the natural enamel (in true teeth) increases with age, and therefore with age the natural tooth appears more transparent. So an understanding of the role of enamel porcelain, as well as the body and colour of the restoration, is of vital importance. It should be applied in several small portions to complete the shape of the crown or the occlusal surface. It should be modelled slightly larger than the actual tooth size to allow for shrinkage when fired.

Ceramic Stains Ceramic stains should be used sparingly as they are designed to supplement the characterisations already inserted into the restoration. Stains can be used to create root attachments, enhance the overall shaping, simulate fillings and imitate tobacco and tea stains. Stains can be used to alter shades and to add characterisation. They can be applied and baked separately or can be baked concurrently with glazes.

Cervical or Marginal Porcelains When working in metal ceramics, it is often found rather difficult to achieve satisfactory results for the cervix of the tooth. Even with a shoulder preparation, metal will still be visible as a dark rim, which will have an obtrusive and unaesthetic effect in the mouth. These materials are layered onto the dentine above the neck of the tooth extending into the approximal area to increase the illusion of depth. They are usually special dentine porcelains with a higher stability, that assists in achieving maximum marginal fit. They can also be used in corrections

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Glazes Are used to apply a soft, silky shine to the restoration Either high or low fusing glaze may be used as a last step, providing a high gloss finish to all ceramic restorations.

Laboratory Prescriptions With few exceptions, laboratory work authorizations do not request enough information from the dentist. This could be because there is not enough space on the prescription to record it. It is, therefore, important to use a laboratory that fully understands the need for shade matching. Each laboratory prescription should contain enough space to record clinical information about each ceramic component of the restoration-for example, different shades of porcelain and opaque, and where to place them on the tooth.

The authorization should include numerous diagrams of the tooth so that the dentist can draw helpful notes on them (i.e., shade, translucency, staining, glaze and surface texture). And the dentist should be in contact with the ceramist to ensure that the technician fully understands what the dentist is requesting. It is through these methods that the dentist builds a relationship with the technician. Ceramists will usually return the quality that the dentist sends to them.15

Models Along with the laboratory prescription, the technician should have a set of study models to use as a guide. Preoperative models give the ceramist information about occlusion, tooth alignment, position of soft tissue, diastema, surface texture, wear facets, and more.16 A diagnostic wax-up will aid in the occlusion and form of the restoration. Matching shade is obviously only part of the task of replicating the natural tooth.

Photography The macro lens has become an important tool in communicating with the laboratory. It has been said that, "The photograph is the cosmetic dentist's radiograph.this enables the technician to evaluate the color of a particular tooth, see craze lines, stains, surface texture and luster. Multiple pictures should be taken at different angles and under different light sources. The patient's occlusion should also be photographed.

Along with photographs of the teeth being worked on, it is best to include pictures of the patient's smile. These photographs can tell the technician about the patient, his or her age, personality and character. It is a good idea to photograph the prosthesis at the try-in stage. If color adjustments are necessary, the technician will have a visual aid to help make the proper corrections. Written instructions alone are not enough information for the technician. They leave a tremendous amount of room for interpretation.

Computers Computers have become a valuable communications tool for the dentist and laboratory Cosmetic imaging can take the place of photographs. The dentist can take a picture with an intraoral camera and send it over the Internet to the laboratory. Film developing is eliminated, saving time and money. The ceramist can use these images to fabricate the proper prosthesis. E-mail can be sent between dentist and laboratory to facilitate discussions of shade matching. The ceramist may decide to offer suggestions to the dentist based on the original images sent over the computer. E-mail can be used if the dentist is busy with a patient and cannot come to the telephone.

Computed Color Matching: Every dentist who places esthetic restorations has at one time or another been frustrated by the process of trying to match the color of natural teeth with ceramic or resin restorations. Conventional shade guides have severe limitations, both in design and in product execution. Even the latest iterations of shade selection systems do not cover the dental shade range. It would seem that in today's highly technical world we should be able to develop a computer-based shade selection device.

After all, there are spectrophotometers at the local paint store and automobile paint shops use a spectrophotometer for your car repair. Why doesn't the dentist have one for shade selection? Unfortunately, the dental color measurement problem is very complex. It has been said that the dental shade selection problem is the most difficult of all color measurement situations. Teeth have every difficulty that can be encountered: they fluoresce, are inhomogeneous and translucent, and have small, irregular surfaces.

In the past, several devices have attempted to solve the instrumental approach to dental color measurement. All failed. Today there are several devices that are presently, or soon will be, offered to the dental profession. "Pikkio", a development of a Swiss and Italian venture, briefly entered the marketplace and is currently being refined.

It is a hand-held unit that can be downloaded to a computer. The device gives the user the closest Vita速 shade guide, and the amount by which the tooth varies from it.: Wolf Industries of Vancouver, will soon market a device that provides the nearest match to both the Vita速 and Ivoclar速 shade guide, and the amount by which the tooth differs from the guide

Shofu Dental Corporation is said to be ready to offer a device researched by the group at Iwate University in Japan. The exact software behind this device has not been released as of this writing. The appearance of multiple devices attempting to solve this problem is testimony that the scientific community recognizes the need for assistance in dental shade selection, and the willingness to underwrite the development of a solution. In addition to the devices cited, several others are known to be under development.

Certainly, most restorative dentists would welcome reliable technical support in shade selection and color matching. However, the device would be most helpful if it not only correctly analyzed the tooth color, but also the optical properties such as translucency and surface gloss. Restorative materials correlated to these readings should then be developed to optimize predictable results.

Review of literature 1. Sproull, Robert C. in the year 1973 did a study to explore the 3D nature of color and the correct terminology.He explained the MUNSELL COLOR ORDER SYSTEM It’s a 3D color tree, described as a sphere or cylinder. It could be considered as a series of wheels stacked one upon the other, in order of ascending lightness. A colorless axis extends through the center of the sphere, pure white at the top, and pure black at the bottom. A series of grays connect the extremities. The three dimensions are: 1. Color (Hue)= arranged around the axis, and subdivided in ten segments. 2. Value= lightness or darkness, within each hue, arranged in scales. 3. Chroma= purity of strength. The quality by which we distinguish a strong color from a weak one.

2. Sproull, Robert C. in the year 1973 also studied the requirements for a color shade guide. He said that the ideal color space is one in which each color is the center of a sphere of color, and the closest match surrounds it. COLOR SPACE OF THE NATURAL TEETH AND SHADE GUIDES: Different studies performed by Hayashi and Clark using natural teeth , measured the ranges of Hue, Value and Chroma of natural teeth. The ranges of the Hayashi study and the spectrophotometer were used for the article. Available shade guides do not extend through the volume of color space and lack order or relationship between tabs. There is duplication of color and voids of color in other areas of color space.He concluded that increased research on color problems should be encouraged. Shade guides should be based on the Hayashi and Clark type guides ,and porcelain should be developed to match these guides.

3. Sproull, Robert C. in 1974. discuseed the perception of color and metamerism A. Perception of color 1. Light source ; incandescent, noon and average daylight. 2. Surface viewed- accomplished with a spectrophotometer, breaks down a standard light source into a series of sequential monochromatic beams. 3. Individual observer. 4. Final perception- modification of the message by the eye of the individual, creating stimulus which the brain converts into color perception. B. Metamerism: Defined as invisible spectral differences. Dependent upon: 1. Control-knowledge of metamerism, reduces potential disasters. 2. Surface viewed- dependency upon the manufacturer to use correct pigments, to simulate enamel. 3. Individual observer-elusive, since the dentist can have color vision deficiencies. 4. Light source- color match should be done under at least two sources of light.

4. Donahue J., Goodkind R., et al. 1991 did a study on Shade Color Discrimination By Men And Women. And concluded that Women do not agree with one another more than men in shade selection. No particular light source and shade guide improved agreement for men. Vita Lumin light source increased agreement with women. When a patient's teeth are to be matched with a given shade guide, there is no reason to select the clinicians according to gender; rather, clinicians should be screened for color vision.

5. Preston J.D., Ward l.C. and Mitchell B 1978. explained the importance of Light and lighting in the dental office. GENERAL CONSIDERATIONS: Visual Task: Define what is to be accomplished in the particular area, and determine what amount of light is required. Blocking Shadows: Sufficient ambient lighting to reduce shadowing. Difference in Brightness: The ideal ratio of task illumination to room illumination is 3:1. Glare: Excess light. Veiling Reflections: When a glossy surface is illuminated, reflected light may obscure the viewer's perception of the surface. Pleasantness: Sometimes an area may be illuminated for the specific purpose of being a pleasant place to pass time.

Age of the Viewer: As age advances more light is required to accomplish a task. Light and Heat: The fluorescent fixture is much more effective than the incandescent but still produces a large quantity of heat in the effort to emit light. Cost: The higher the lumens per watt, the lower the cost of the overall lighting. Lamps will last longer if burned with only one start per user day and are not turned off and on unnecessarily. DENTAL OFFICE AREAS: Reception: Conveys personality of the office. Decrease anxiety by lowering levels of illumination. Office: Ample illumination to ensure effective and efficient work. Operatory: Use fiberoptics. Place lighting units parallel to the work area and out off the direct line of the patients sight. 5500o K is best for color matching. 200 to 300 foot candles (fc) recommended light level for operatory. Powder Room: Incandescent with a pink hue works well, but this light may not exhibit the best color match of a "new" dental restoration

6. Barna, G.J., et al. 1981did a study To determine the

effect of various batches of porcelain on the shade of three porcelain-bonded-to-metal systems and concluded that:

1. No color differences were found among specimens of individual batches. 2. Discerning color changes were observed among three batches of one brand of porcelain. 3. The porcelain fired in the laboratory may not match the manufacturer's standard shade guide. 4. Batch to batch variation of porcelain may necessitate the fabrication of customized shade tabs with fresh batches of porcelain. 7. Barna, G.J., et al . 1981 Did a study on The Influence of Selected Light Intensities on Color Perception Within the Color Range of Natural Teeth . and concluded that the Intensity of office illumination is not critical for matching tooth shades. It is recommended that color corrected bulbs be used to allow the full spectrum of color to be seen. Neither the specialty of the dentist or time in practice appeared to be a factor in making color discrimination.

8.Billmeyer and Satzman 1966 defined color

as the result of the physical modification of light by colorants as observed by the human eye and interpreted by the brain.

9. Culpepper 1970 Concluded from 36 practising dentists who were invited to match the shades of 6 natural teeth using 4 shade guides & 4 different light sources , including daylight that: There was a lack in consistency between the individual dentists participating in the experiments in matching natural tooth shades . The shade guides employed in the study did not always correspond to the gradations of predominant colors observed in the natural teeth Critical color perception varied from individual to other .

CONCLUSION: CLARK SAID, "Color, like form, has three dimensions, but they are not in general use. Many of us have not been taught neither names, nor the scales of their measurement. In other words, we as dentists are not educationally equipped to approach a color problem." The increase in newer types of ceramic restorations and the improving quality of esthetics means the dentist of the 21st century must be trained to detect differences in color and shades in individual teeth, select a shade that reflects the color and exact shade, transmit this information to a dental technician, and then be able to make any necessary adjustments to the restoration. However, there are a number of factors that stand in the way of properly selecting a color match. Subjective faults range from differences in color perception to ocular fatigue and lack of education regarding the basic principles of color. Metamerism may occur if proper lighting is not used during shade selection in the dental office and Finally, existing shade guides are limited and require a more extensive range of shades.

Therefore, it is no surprise that color matching for crowns and dentures can be a frustrating and discouraging experience for the dentist, technician and patient. The breakdown in communication over matters ranging from shade guide to laboratory prescriptions must be addressed. An understanding of the science of colour and colour perception is important for the success of an esthetic restoration . for sucessful application of colour in dentistry an understanding of how light is interpreted as colour is important . errors in shade matching continue to be a problem and a source of dissatisfaction for the patient . inspite of the limitations in materials and techniques , a harmonius restoration can almost always be achieved if a methodical and organised manner is followed during shade selection.

REFERENCES 1. Sproull, R. C. Color matching in dentistry. a. Part I: The three dimensional nature of color. J Prosthet Dent 29:416-423, 1973. b. Part II: Practical applications of the organization of color. J Prosthet Dent 29:556-566, 1973. c. Part III: Color control. J Prosthet Dent 31:146-154, 1974. 2. Donahue, J.L. et al. Shade color discrimination by men and women. J Prosthet Dent 65:699-703, 1991. 3. Presswood, R. G. Esthetics and color: Perceiving the problem. DCNA 21:823-829, 1977. 4. Preston, J. D., Ward, L. C. and Mitchell, B. Light and lighting in the dental office. DCNA 22:43l-451, 1978. 5. Barna, G. J., et al. The influence of selected light intensities on color percept percep . J Prosthet Dent 46:450-453, 1981. 6. Obregon, A., Goodkind, R. J. and Schwabacher, W.

7. Schwabacher, W.B and Goodkind, R.J. Three dimensional color coordinates of natural teeth compared with . J Prosthet Dent 64:425-431, 1990. 8. O'Brien, W.J. et al. Coverage errors of two shade guides. Int J Pros 4:45-50, 1992. 9. Barghi, N., Pedrero, J. A. F. and Bosch, R. B. Effects of batch variation on shade of dental porcelain . J Prosthet Dent 54:625-627, 1985. 10. Goldstein, R. E. Esthetic principles for ceramometal restorations. DCNA 21:803-822, 1977. 11. Barghi, N. and Goldberg, J. Porcelain shade stability after repeated firing. J Prosthet Dent 37:173-175, 1977. 12. Jacobs, et al. Effect of porcelain thickness and type of metalceramic alloy on color. J Prosthet Dent 57:138-145, 1987. 13. Sorensen J. A. Improved color matching of metal-ceramic restorations. a. Part I: A systematic method for shade determination. J Prosthet Dent 58:133-139, 1987. b. Part II: Procedures for visual communication. J Prosthet Dent 58:669-677, 1987. c. Part III: Innovations in porcelain application. J Prosthet Dent 59:1-7, 1988. 14. Rosensteil, S.F. and Johnston, W.M. The effects of manipulative variables on the color of ceramic metal restorations. J Prosthet Dent 60:297-303, 1988.

15. Barghi, N. and Richardson, J. T. A study of various factors influencing shade of bonded porcelain. J Prosthet Dent 39:282284, 1978. 16. Albino J. E., Tedesco L. A., Conny D. J., Patient perceptions of dental-facial esthetics: Shared concerns in orthodontics and prosthodontics, J. Prosthet. Dent. 52: 9-13, 1984. 17. Barghi N., Alexander L., Draugn R. A., When to glaze - An electron microscope study, J. Prosthet. Dent. 35: 648, 1976. 18. Barghi N., Color and glaze: Effects of repeated firings, J. Prosthet. Dent. 47: 393-395, 1982. 19.Crispin B. J., Hewlett E., Seghi R. R., Relative color stability of ceramic stains subjected to glazing temperatures, J. Prosthet. Dent. 66: 20-23, 1991. 20.Culipepper W. D. A comparative study of shade-matching procedures. J. Prosthet. Dent. 24: 166-173, 1970 21.Ishikawa-Nagai S., Sato R., Shiriashi A., Ishibashi K., Using a Computer Color-Matching system in color reproduction of porcelain restorations. Part III: A newly developed spectrophotometer designed for clinical application, Int. J. Prosthodont. 7: 50-55, 1994 22.Ishikawa-Nagai S., Sawafuji F., Tsuchitoi H., Sato R., Ishibashi K., Using a Computer Color-Matching System in color reproduction of porcelain restorations. Part II: Color reproduction of stratiform-layered porcelain samples, Int. J. Prosthodont. 6: 522-527, 1993 a

23.Seghi R. R., Johnston W. M., O’Brien W. J., Performance assessment of colorimetric devices on dental porcelains, J. Prosthet. Dent. 68: 1755-1759, 1989 (b). 24.Seghi R. R., Johnston W. M., O’Brien W. J., Spectrophotometric analysis of color differences between porcelain systems, J. Prosthet. Dent. 56: 35-40, 1986 (a). Leader in continuing dental education

Color shade arjun/ dental implant courses by Indian dental academy  

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