Year : 2011 | Volume
: 22 | Issue : 6 | Page : 804--809
Role of colors in prosthodontics: Application of color science in restorative dentistry
Vinaya Bhat, D Krishna Prasad, Sonali Sood, Aruna Bhat
Department of Prosthodontics and Crown and Bridge, A.B. Shetty Memorial Institute of Dental Sciences, NITTE University, Mangalore,Karnataka, India
Department of Prosthodontics and Crown and Bridge, A.B. Shetty Memorial Institute of Dental Sciences, NITTE University, Mangalore,Karnataka
Shade selection procedure depends on various factors including translucency, contour and surface texture. Tooth shade selection using a conventional means involves a high degree of subjectivity. Traditional shade guides are available that use several methods for quantifying shade. Technology-based systems provide with an advantage of natural looking restorations. They include RGB devices, colorimeters, spectrophotometers. The impact of the color science can be seen on various restorative materials ranging from ceramics to maxillofacial prosthetic materials.
|How to cite this article:|
Bhat V, Prasad D K, Sood S, Bhat A. Role of colors in prosthodontics: Application of color science in restorative dentistry.Indian J Dent Res 2011;22:804-809
|How to cite this URL:|
Bhat V, Prasad D K, Sood S, Bhat A. Role of colors in prosthodontics: Application of color science in restorative dentistry. Indian J Dent Res [serial online] 2011 [cited 2020 Jul 2 ];22:804-809
Available from: http://www.ijdr.in/text.asp?2011/22/6/804/94675
Restorative dentistry represents a significant portion of dental services encompassing on the blend of science and art. Although color may be unimportant to the physiologic success of a dental restoration, it could be the deciding factor in patient acceptance. The basis of color science is a vast subject applicable to many fields. The applied aspect of color science to the restorative dentistry includes the various factors involved for correct shade matching and its impact on the science of color. The recommended protocol for conventional and technology-based shade matching should be followed for better understanding of the complexities involved in it. This article discusses the different selection procedures involved for correct shade matching, the various systems available for the restorative dentist, and the recent developments in this field.
Shade Matching in Restorative Dentistry
Christopher  stated that the difficulty of shade selection is that clinicians must be able to interpret a multi-layered structure of varying thickness, opacities, and optical surface characteristics. This can affect the way that the eye perceives color. Teeth are often termed "polychromatic" and have the variation in hue, value, and chroma within the teeth and give three dimensional depth and characteristics. He stated that a number of related factors in selecting shades must also be understood to achieve a successful result. These factors includes (Winter 1990) translucency, contour, surface texture, luster, and fluorescence.
Generally, increasing the translucency of a crown lowers its value because less light returns to the eye. With increased translucency, light is able to pass the surface and is scattered within the restoration. The translucency of enamel varies with the angle of incidence, surface texture and luster, wavelength, and level of dehydration. 
Sulikowski et al. explained that surface texture influences aesthetics by determining the amount and direction of light reflected of the facial surface. Texture should be designed to simulate the reflectance pattern of the adjacent natural teeth. Young teeth may have a lot of characterization with stippling, ridges, striations, and lobes. These features may be worn away with age leaving smoother, highly polished surfaces. 
It is the absorption of light by a material and the spontaneous emission of light in a longer wavelength.  Vital teeth look brighter and alive as higher amount of organic material is present.
Laren stated that the more the dentin fluoresces, the lower the chroma.  These powders are added to crowns to increase the quantity of light returned back to viewer and to decrease the chroma. 
Sunder and Amber defined it as a phenomenon in which a material appears to be one color when light is reflected from it and another color when light is transmitted through it. 
After Image and Visual Distortion
Fondriest stated that after images are frequent physiologic effects of the cone receptors with normal function that cause alterations in the perception. It includes spreading effect: when light is removed from the retina, the receptors continue for a short time to be active and send signal to the brain.
Pensler defined it as the natural browning of the cornea that occurs with age. It acts as a filter and changes the appearance of colors. Hence, the age of the dentist also forms an important factor in shade determination. 
Apperception is how the mind interprets what the eye perceives. Optical illusions exemplify the perception and apperception phenomenona. Shade selection is a combination of perception and apperception, and hence involves a thought process. Teaching dentists about this phenomenon could minimize the influence of this factor on the shade selection. 
The intensity of the light conditions is also important. If the amount of light (measured in foot-candles or lumens per ft) is too small, fine details are missed and the eye has difficulty perceiving hue. The ideal luminosity for dental shade matching is 75 to 250 ft-candles.  To have 150 ft-candles intensity in the operatory at the level of the dental chair, ten to twelve 4 ft bulbs would be needed in a 10×10 ft room with 8-foot ceilings.  The diffusion panels covering the fluorescent bulbs are also important because they screen out wavelengths. As they age, the panels change what wavelengths they absorb. The best diffusers are those that do not filter out any wavelengths of the spectrum, preferably the egg-crate type. 
Requirements of Tooth Shade Guides
The prime requirements for a tooth color guide considered by Sproul (1973) are a logical arrangement in color space and an adequate distribution in color space.
A guide which did not fulfill the prime requirements in color space would pose certain problems like taking too long to decide where to begin, lack to check the chosen match for accuracy, and the volume of color space occupied by the materials to be matched may be impossible to reach within the guide. 
Shade Selection Procedure
Christopher  suggested the shade selection sequence to be as follows:
When matching teeth, the shape, surface geography, and the value are the most important characteristics. Shade selection should be completed before preparation as teeth can become dehydrated and result in higher values. Value is the most important dimension of shade rendering. nsure surgery surroundings are of neutral color so that there is no color cast onto the teeth. Remove lipstick; ask patients not to wear lurid clothing or any items that may distract the attention of the teeth. Make sure teeth are clean and unstained before attempting shade selection.Patient should be in an upright position at a level similar to the operator and the shade guide should be at arm length. This ensures that the most color-sensitive part of the retina will be used.Observations should be made quickly (5 s) to avoid fatiguing the cones of the eyes. If longer than this, the eye cannot discriminate and the cones become sensitized to complement the observed color. Fondriest  stated the use of chromatic backgrounds available: 18% reflective gray cards, Kulzer's small intraoral gray cardboards, Pensler shields screen.Use color-corrected light illumination, which should be of a diffuse nature.Viewing tabs through half-closed eyes can decrease ability to discriminate color but increases the ability to match value. Look at the other parts of the teeth, dividing the teeth into nine sections from apical to incisal, and mesial to distal.Hold the shade tab incisal edge to the incisal edges of the teeth. This effectively isolates the shade tabs from the teeth so they do not reflect onto each other reducing afterimages. Most humans have eye dominance and one eye will preferentially perceive shade.  It is wise to hold the shade guide on both sides of the tooth at each vector.Different light wavelengths reflect off a rough surface in different ways. Shades should be evaluated looking at the tooth at different angles. This re-evaluation at different angles is called vectoring. If in doubt as to the hue family, choose the A family.  Most natural teeth have more red than B.Describe surface texture and luster as heavy, moderate, and light therefore giving nine different combinations of surface characteristics. Because these surface features determine the character of light reflection and affect the amount of light that enters the tooth (opacity), the surface texture of a crown must be designed to simulate the light transmission and reflectance pattern of adjacent teeth. 
Measurement of Color
Color determination in dentistry can be divided into two categories.
Shade guide systems
Dental shade guides are shade matching tools used most commonly by the clinicians in day to day practice. Although the groups of tabs of most shade guides appear to be well arranged, the overall tab arrangements of some shade guides seem illogical because they contain light and dark tabs within each of the groups. The fact that tab arrangement can influence shade-matching results increases the importance of this issue.  For consistency, tabs can be rearranged according to increasing color difference related to the tab that appears lightest (not necessarily the tab having the highest lightness, L*). Group division of shade guides is necessary for reducing the number of potentially adequate tabs as quickly as possible. It is easier to work with fewer tabs, because the vision pigment depletes within seconds (it regenerates quickly, as well). To achieve consistent group division, the total color difference (E*) between the lightest and the darkest tab should be divided into several equal segments. Laboratory and simulated clinical conditions have demonstrated the effectiveness of this tab arrangement (small discrepancies recorded by different color-measuring devices only confirm the efficacy). 
The most popular shade guides include the vitapan classical shade guide, Vita 3D master shade guide system, and the chromascop shade guide system. The shade tabs arrangement in the Vita Classical is by hue whereas in the Chromascop guides,  the tabs are arranged in five clearly discernible value levels. VITAPAN introduced in 1956, the current American Dental Association gold standard for monitoring of tooth whitening, is supposed to correspond to decreasing lightness (from left to right). A very popular shade guide where in tabs of similar hue are clustered into letter groups A (red-yellow), B (yellow), C (grey), D (red-yellow-gray), and chroma designated with the numerical values (e.g. A1). The manufacture protocols include hue selection followed by chroma and value.
Miller  demonstrated that the classical shade guide was too low in chroma and too high in value when compared to natural extracted tooth samples. The "value scale" is inaccurate in terms of decreasing L* values, exhibiting redundancy and uneven lightness differences among neighboring tabs, which to a certain extent compromises the results of clinical studies that have been performed so far. 
The Vitapan 3D master shade guide, introduced in 1998, system reflects systematic and equidistant coverage of the natural tooth shade spectrum. The design features selection of value levels followed by the chroma and determination of hue.
Bayindir et al stated that the Vitapan 3D master shade guide system results in lower coverage errors than the Vita lumin or Chromascop shade guide systems. Ahn et al.  concluded that the color distribution of the Vitapan 3D master shade guide was more ordered than previously reported color distributions of other, traditional shade guides. However, the interval in the color parameters between adjacent tabs was not uniform.
According to the literature, the new Vita Bleached guide 3D master shade guide (Vident), designed primarily for tooth-whitening monitoring, has significant advantages over the Vitapan Classical: the tab arrangement corresponds to visual finding, it includes extra light shades, the color range is almost doubled, the color distribution is more uniform, and the chroma steps are consistent. 
The conventional visual tools used to determine shade are highly susceptible to various optical illusions and contrast effects. In 2001, Chu and Tarnow  used a clinical case report to describe the subjective deficiencies in the conventional shade selection process and compared the method to computerized aided information. Due to the errors with the use of commercial shade guides, many different devices and machine tools are used in order to make the color assessment more simple, rapid, precise, and perfect. The semi-translucent structure, small size, and irregular surface of teeth contribute to the complexity of this procedure.
Several clinical studies have confirmed that computer-assisted shade analysis is more accurate and more consistent compared with human shade assessment. The advantages are no influence of surroundings or lighting and the results being reproducible. ,
Bergon et al.  experimented with spectrophotometers and computers. Yamamoto was instrumental in the development of the Shofu eye chroma meter. In the late 1990s, a company called Cortex Machina was established in Montreal, first ones to start with technology-based shade guides system. The first measurement analysis system was the Spectroshade system from MHT Optic Research in 2001 followed by Shade vision system (colorimeter) from X-rite in 2002.
The Measurement system includes  the spot measurement systems measuring small areas on the tooth surface (e.g. Shofu Shade Eye-NCC, Chroma meter system, Vita easy shade system) or complete tooth measurement systems that measures the entire tooth surface and provide a color map of the tooth in one image.
Types of Technological Shade Systems
RGB devicesDigital camerasSpectrophotometersColorimeters
Acquire RED, GREEN, BLUE image information to create a color image. They do not control key variables associated with accurate color determination. 
Robert  in 2000 introduced Shade Scan from Cynovad which is a popular system that creates an image of the tooth with a translucency and characterization map, and then will generate a printed report.
They are efficient and easy to use and can be an ideal supplement for the clinician and lab technician in quantifying shade but alone not a very reliable method for shade analysis. 
Factors such as illumination and the angle of the photograph will alter how color is perceived by the camera. Alvin et al.  stated the use of Commercial SLR cameras when combined with the appropriate calibration protocols showed potential for use in the color replication process.
Spear stated the use of color-corrected professional quality film (e.g. Kodak EPN-100, E100-S, or EPP) and have a good photo lab to develop them, taking vector shots at 65-70° looking down with an incisal edge away from chroma and hue helps in increasing the amount of reflection thus better color accuration. 
Comparison between spectrophotometers and colorimeters
The use of the digital system that can qualify and quantify shade maps provides Delta E (E) measurements for shade comparison. Delta E is a colorimetric value that delineates the difference between two colors. To distinguish this value, three reference points are available generally CIE L*A*B* OR CIE Lch.
Chu  stated that colorimeters are tri-stimulus and can measure in either CIE Lab or CIE Lch. It is however impossible to produce precise colorimeter, since filters must be well controlled and the characteristic of light well maintained. Spectrophotometers allow the user to measure metamerism, therefore independent of filters and changing light sources.
It measures and records the amount of visible radiant energy reflected or transmitted by an object one wavelength at a time for each value, chroma, and hue present in the entire visible spectrum. , Stephen et al.  stated the disadvantage being expensive, complex, difficult to measure the color of teeth in vivo with these machines.
The various systems available are spectroshade described by Cherkes et al.  (Posey dental technology), Vita easy shade (Vident), and Shade pilot system (Degudent). The main advantage of spectroshade lies in the split screen feature encouraging the comparison of before and after images providing full face pictures on an intraoral camera. The Vita easyshade provides a prescription in both Vitapan 3D master and classic VITA shades.
Colorimeters provide measurements in CIELAB units (L*, A*, B*) that can compare the color parameters of different objects when analyzed mathematically.
Colorimeters can be of two types mainly the photoelectric tri-stimulus colorimeters (Microcolor) and silicon photodiode array (Orient Scientific Ltd). Microcolor colorimeter (a photoelectric tri-stimulus colorimeter) is a self-contained measuring system that requires no external power source while a silicon photodiode array requires both an external power source and a standard light source; it is a compact color measuring instrument that is less prone to overheating and is cost effective.
The various colorimeters available are X-Rite Shade Vision System and Shade NCC (Shofu). The shade vision system adds the advantage of shade information being sent to the dental laboratory via e-mail, disk, or by printout.
Pusateri et al.  studied the reliability and accuracy of four dental shade-matching instruments and concluded the spectrophotometers (shade vision and vita easy shade) to be more reliable and accurate compared to colorimetric devices. This is in agreement with the study by Browning et al.  where they stated the use of vita easy shade to be frequently an exact match when compared to other devices.
Dennison  described the photometric assessment of tooth color using commonly available software. He concluded that digital camera are almost an integral part of each dental office whereas the limiting factors of spectrophotometers are their cost, complexity of handling, and bulk of involved gadgets.
Stump Shade Guides
With the increasing use of all-ceramic restorations, it is important to communicate the prepared tooth or "stump" shade to the ceramist so that they can build the restoration with the right opacity/translucency. 
Chu stated the most popular stump shade guides to be used as Ivoclar, (vivadent) and Finesses guide (Ceramco).
Gingival Shade Guides
Dummet  described that the color of gingiva is variable ranging from a pale pink to deep bluish purple. Color depends on intensity of melanogenesis, epithelial cornification, and depth of epithelization. Comparisons of the imagined color of gingiva and an actual visual color measurement are of doubtful scientific value.
The findings of Nakashima  showed that imaginable color is more yellow red and higher in chroma. Fukai using a spectrophotometric technique found that free marginal gingiva in maxilla is higher in value and that female gingiva tends to be more red compared to male.
Color assessments of the attached gingiva have been evaluated using Munsell color tabs. Use of helium neon gas laser to record the reflectance of interdental papilla was documented. Dummet was the first to describe the color of intraoral soft tissues. ,
Currently, methyl methacrylate is the most frequently used resin. Thus one shade of pink for partial dentures is not acceptable for all patients, especially when the acrylic flange is adjacent to the gingiva in the esthetic zone.  Okubo et al.  stated the most popular method to be the visual shade selection with the help of shade guides. Bayindir  described the use of commonly used gingival shade guides presently i.e. Lucitone 199 shade guide system (Densply trubyte), Ivoclap plus gingival indicator set (Ivoclar vivadent), and IPS gingival shade guide (Ivoclar vivadent). 
Impact of Material Science on Colors
The importance of restorative materials and their effect on color shade cannot be overemphasized.  Mc leans -one of the leaders and innovators in dental ceramics developed a variety of present day available ceramics.  The improved characteristics are primarily in material density, which correlates directly to light transmission and color coordination.
Sulikowinski and Yoshida  proposed that the depth of tooth preparation be based on the present level of discoloration for the veneer fabrication. Greater depth of reduction is required to allow greater thickness of cosmetic restorative materials to mask the underlying tooth shade. Aoshima  stated the use of pressable ceramic restorative material for the shade matching of single veneer restoration.
Dietschi et al.  described that the use of modern fabrication of composite restorations is based on the natural layering concept. This approach embraces the typical optical and anatomic characteristics of natural teeth.
Individual color characterization is important in acceptance of an external facial prosthesis by a patient, yet it remains one of the greatest challenges faced by the clinicians (Bergstrom, 1998). Basic method by Barnhat et al. (1978) stated the use of intrinsic color characterization and extrinsic color modification. Schaaf (1970) described the tattooing method carrying some pigments below the surface for better color matching in maxillofacial prosthesis. 
Discussion and Conclusions
The study of color is one of the most integral parts of esthetic dentistry. Matching the right color leads to a pleasing appearance and satisfaction for the patient and the clinician.
The recommended protocol for conventional and instrumental shade matching should be followed to achieve esthetic and predictable results. Successful shade taking involves a combination of technology, shade tabs, and reference photograph. In spite of the limitations in materials and techniques, a harmonious restoration can almost always be achieved if a methodical and organized manner is followed during shade selection. The considerations mentioned in this article are associated with the application of color science to dentistry. Color science in fact complements the artistic talents of clinicians, dental assistants, and ceramists, providing both an appropriate foundation and a frame for their artwork.
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