Color Matching & Shade Determination PDF

Summary

This document presents a lecture on color matching and shade determination, focusing on factors affecting color perception, different color systems (like RGB, Munsell, and CIE), optical properties of natural teeth, and various shade determination techniques. The lecture is likely from a university setting, targeting undergraduate students in dentistry.

Full Transcript

# Color Matching and Shade Determination ## A Presentation By Dr. Mohamed Hussein ### A. Professor of Conservative Dentistry - Master in Adhesive and Restorative Dentistry - PHD In Digital Smile Design and porcelain laminate veneers ## Lecture Outline: 1. Introduction 2. Color perception 3. Col...

# Color Matching and Shade Determination ## A Presentation By Dr. Mohamed Hussein ### A. Professor of Conservative Dentistry - Master in Adhesive and Restorative Dentistry - PHD In Digital Smile Design and porcelain laminate veneers ## Lecture Outline: 1. Introduction 2. Color perception 3. Color description 4. Optical Properties of the natural tooth 5. Shade determination techniques 6. Principles of proper Shade determination ## I. Introduction - The color phenomenon is a psychophysical response to the physical interaction between the luminous energy and an object, associated with the subjective experience of an observer. - Visible light is a form of electromagnetic radiation, with wavelength range between 390 and 770 nm, which is detected by the light-sensitive photoreceptor cells of the human eyes. - Each wavelength corresponds to a specific color. - A light source can emit a single wavelength (monochromatic) or multiple wavelengths (polychromatic). - The light waves pass through the composite hit the filler particles of different sizes and shapes of a composite, its scattering give the color and translucency effects. ## II. Color perception ### Factors affecting color perception (color triplet): - **Light source:** The light source can emit luminous energy on a broad wavelength range on the visible spectrum. - **Object:** its spectral reflectance or light transmission characterizes its color. - **Observer (human eye):** Perception of color at the retina depends on cone cells. ### Mechanism of color perception: - **Color of light:** When the light source is observed directly, the color that human vision detects is a result of the emitted wavelengths, which is the color of the light by itself. - **Color of Object:** When the light hits an object, it can be transmitted through it, absorbed, or reflected, and this last one is responsible for the color perception that the humans have about the object. The more the incident light is absorbed by the object with less light reflection, the darker it is perceived by the observer. The less incident light is absorbed by the object with more light reflection, the whiter it appears to the observer. - **a:** Every wavelength is absorbed resulting in the black color. - **b:** every wavelength is reflected, resulting in a white color. - **c-e:** prevalence reflection of a certain wavelength.(red-yellow-blue) ## III. Color description ### Color systems and dates of their development - **1. RGB System: 1860** - **2. Munsell Color System :1905** and took its final form at 1945. - **3. CIE system: 1931** - **4. CIELAB system: 1976** - **5. CIEDE 2000 system: 2001** - **6. CMC Color Tolerance System: 1994** #### 1- RGB (Red-Green-Blue) Color System - Most chromatics consider red, green, and blue as the primary colors. They think that the other colors originate from their interaction. - It describe colors within three-dimensional space with coordinate axes red, green, and blue. - In the system, each hue, color intensity, and color brightness can contain different values increasing from 0 to 255. ((255*255*255)(16.7 million possible combinations)) - This system is used in devices such as computer monitors, scanners, and cathodic television tubes. RGB values can be easily converted to CIELAB values after being converted to XYZ values. #### 2- Munsell Color System - The Munsell color system is recommended by the American Dental Association (ADA) for defining color guides, which is a three-dimensional model based on: Hue, Value, and Chroma. 1. **Hue (5 + 5 colors)** is the actual color. 5 principle hue: Red (R), Yellow (Y), Green (G), Blue (B), and Purple (P), along with 5 intermediate hues (YR, GY, BG, PB, RP). 2. **Value (0-10)** indicates the lightness of a color, ranging from for pure black (0) (low value) to pure white (10) (high value). 3. **Chroma (0-12)** is the intensity or purity of a color. When the chroma is low, the color is weak (low chroma), while when it is high, the color is strong or vivid (high chroma). - The combination between the three-color dimensions gives the shade or tone of a color. #### 3. CIE (Commission Internationale de l'Eclairage) XYZ Color System - The CIE XYZ color system is a color space defined by the International Commission of Illumination (CIE) in 1931. - used to describe the color of light using three numerical coordinates. #### 4-CIELAB Color System (Commission Internationale de l'Eclairage LAB axes) - It is one of the most used systems. It used to define lightness, hue, and chroma and to draw graphs to understand their relationship to each other. Also, used to control expressions such as color tolerance, color stability, metamerism. - Calculation of the the spatial distance between two colors is defined as the color difference (ΔΕ). CIELAB color space is defined in 3 different axes. In these three axes, - ΔL: differences in black-white direction. - Δa: differences in red-green direction. - Δb: differences in yellow-blue axis. - The color difference formula is defined as thus: > $ΔΕab = √AL*2 + Δα*2 + Δb*2$ - If the color difference in a material is ΔΕ=0 after test applications, the color is defined as stable. #### 5. CIEDE 2000 Color Difference Formulation - The formula defining the CIEDE 2000 color difference was developed by the CIE technical committee in the year 2001. - The CIEDE 2000 formulation is much more complex than the CIELAB color difference formula > $ΔΕ00 = (\frac{AL'^2}{KL*SL} + \frac{AC'^2}{KC*SC} + \frac{AH'^2}{KH*SH} + R_T * \frac{AC'*AH'}{KC*SC * KH*SH})^{1/2}$ - AL' defines lightness, AC' chroma, and AH' the difference between hue values. - Rris the rotation function of the color differences in the blue region. St, Sc, and Share weighting functions. Parametric factors KL, Kc, and Khare correction terms that describe the effect of experimental imaging conditions. #### 6. CMC Color Tolerance System - CMC is a color tolerance expressed by a single numerical value. The Delta E formula was developed in 1994 by the Color Measurement Committee in Great Britain. Its formulation is as follows: > $ΔΕcmc (1:c) = (\frac{AL'^2}{IS*L} + (\frac{AC' ab}{CS*C})^2 + (\frac{AH'ab}{SH})^2)^{1/2}$ - The components St, Sc, and Share special basis weighting factors. The values "l" and "c" are additional weighting factors and are chosen to provide appropriate weighting for differences in lightness and chroma. ## IV. Optical Properties of the natural tooth - Tooth color is the result of the inter-action of enamel, dentin and pulp with light. ### 1- Translucency & Opacity - A material is considered translucent when part of the light that hits its surface is transmitted through it. The opposite property is called opacity. - The dental enamel is more translucent than the dentin, which is almost opaque. - For the proper restoration of the tooth structure, the use of composites with optical characteristics close to the natural tooth is necessary to obtain excellence on the esthetic results. The translucency of a composite is as relevant as its color, since it affects the final restoration appearance. - The overlapping of the enamel over the dentin on different thickness, according to the region of the tooth, is the responsible for the polychromatic effect observed on the natural teeth. - The dentin is thicker and the enamel thinner on the cervical region of the teeth, which gives a general opaquer aspect to this region. The shade is more saturated, with a greater influence of the dentin color. - The enamel translucency is not only due to its [high] degree of mineralization, but also because of its internal mineral organization of [low] refractive index, which allows the transmission of most of the incident light. The enamel prisms act similarly to the optical fibers. - The light that enters the prisms is reflected by its crystals and remain on its interior, running through it. ### Biomimetic approach according to translucency - **A. High-translucency composite resin restoration**, namely incisal shade, are indicated for restorations of the enamel on the highly translucent incisal edges. - **B. Medium translucency composite resin restoration**, namely enamel shade, are indicated for restorations of the enamel on most situations. They are also called by some manufacturers as universal or body shade composites. - **C. low translucency composite resin restoration**, nemely dentin shade, are used to restore the lost dentin tissue. They are referred by some manufacturers as opaque shade composites. - **HVT:** High value – Translucent - **T:** Translucent - **LVT:** Low value - Translucent - **AM:** Amber ### 2- polychromatic - As a result of several shades found on enamel and dentin, influenced by the different thickness of those structures along the crown. - The enamel color varies from white to gray, while the dentin has variable amounts of yellow, orange, and red. - The enamel is thicker on the incisal edge and thinner in the cervical region. - When the incisal edges are not worn, frequently have blue, violet, or gray tones, due to the enamel translucency and absence of the dentin. ### Biomimetic approach According to Chroma: - **1- Monochromatic composite resin (used with single shade technique)** - Couldn’t match the perfect shade specially in large composite restoration. - Could be used with small cavities producing the same tooth shade. - Need less technical skills. - Take less working time (just one shade used). - Less cost (use only one syringe of shaded composite) - **Monochromatic composite resin with chameleon effect** - This smart composite depend on "chameleon effect" (blending effect) illustrates the capability of material to attain a shade identical to adjacent tooth structure. - No pigments present, color matching depend on light reflection. - No step of shade selection before work. - Could be used with small cavities. - **Disadvantages:** couldn't match the perfect shade specially in large composite restoration. - **Monochromatic Single shade Composite:** Can be **conventional** or **Monochromatic composite (with Chameleon effect).** - **2- Polychromatic composite resin (used with Multishaded technique)** - Produce perfect color matching. - Could be used with large cavities producing the same tooth shade. - Need higher technical skills. - Take more working time (to build up each layer with its color, translucency & opacity - Enamel & Dentin). - **Higher cost** (use many syringes with different shades). - **Example:** (If Tooth with color A1, it will be restored with composite A1 shade in monochromatic system or E1& D1 shades in polychromatic system) ## 3- Opalescence - Due to its similar optical characteristics of the opal stone. - When the enamel receives white light, which is a combination of different wavelengths, it is capable to reflect the shorter wavelengths, specially the blue, and transmit the longer wavelengths, such as the yellow and the red. (teeth appear bluish in reflected and orange in transmitted color) - **Importance:** The enamel opalescence increases the lightness of the tooth and creates effects of optical depth and vitality (Opalescence Halo effect). - Orange: Opaque halo - Blue: Opalescence. - Yellow: dentin Mamelons ### Types of Opalescence: - **Type 1:** Found in incisal edges that have opalescent halo closely related to the dentinal mamelons. It kind of opalescence presented by 58% of individuals - **Type 2:** In this type of opalescent halo mamelons not penetrate between the dentin, extending over the incisal edge. It kind of opalescence presented por17% of individuals - **Type 3:** Found in incisal edges showing diffuse halo opalescent, distributed randomly throughout the incisal edge. It kind of opalescence presented by 4% of subjects - **Type 4:** In this type of opalescence opalescent halo presents mixed with some kind of pigmentation or characterization. It kind of opalescence presented by 25% of subjects. ## 4- counter-opalescence - some people have the dentin on the tip of the developmental lobes of anterior teeth with intense white opaque shade. - This does the dentin in this area to have higher light reflection capacity than the rest of the tooth. - Therefore, in this specific region, the reflection of yellow and red light which crossed the enamel and hit the dentin will be higher, resulting in an orange appearance to the area. ### Opalescence and counter-opalescence. - **a.** Whitish dentin on the tip of the developmental lobes; - **b.** incidence of white light on three different areas of the labial surface (1, incisal edge without dentin; 2, tip of the whitish dentin lobules; 3, rest of the tooth structure); - **c.** reflection of the blue light (shorter waves) by the enamel on the three areas and transmission of the orange light (longer waves) toward the dentin; - **d.** complete transmission of the yellow light through the incisal edge without dentin (1) and reflection of the light by dentin, more intense on the tip of the whitish lobules (2 - counter-opalescence) and less intense on the rest of the structure (3) ## 5- Fluorescence. - It is a phenomenon of spontaneous emission of radiation by some atoms and molecules inside the tooth structure composition, being considered a kind of photoluminescence. - The fluorescence turns the natural teeth whiter and brighter under daylight, seeming as they are internally illuminated. - fluorescence can be noticed with ultraviolet light. This wavelength is part of white light emitted by the sun, or generated by ultraviolet light bulbs - ultraviolet wavelength is almost invisible. However, when absorbed by the tooth structure, results in the emission of visible light of whitish-blue color, which does the tooth, appear brighter. - Dentin three times more fluorescence than enamel. - The enamel seems to act as a filter, attenuating the intense fluorescent emissions that come from the dentin. - So it is surface phenomenon. So, it is important that the composite has fluorescence, similar to the natural tooth structure ## 6- Metamerism - It is defined when two objects appear to be the same color under one illuminant but different color in another source. (In the dental office, when the teeth of a patient and a selected shade guide tab matching its color are illuminated under natural sunlight they can match perfectly. However, when the same teeth and shade tab are illuminated by an incandescent light bulb, such as the one in most of the overhead chair lights, the teeth and the shade tab atoms will not interact on the same way with the incident light, because they are made by different materials. This will result on different shades from those observed under the natural light, making the initial shade determination to appear incorrect). - So, shade determination must be performed with 2 light sources. under the natural day light and confirmed by under artificial light that simulates the daylight (fluorescent light bulb) ## 7- Thickness of Enamel and Dentin - On the incisal third, there is more enamel than dentin. - On the cervical third, the amount of dentin increases and of enamel decreases, resulting on a darker shade. - The dentin chroma increases from incisal edge toward the cervical area and from DEJ toward the pulp. - Therefore, the incisal third has a higher value and translucency than the cervical third, while the middle third is a mixture of the incisal and cervical shades. - The dentin shade must be taken looking directly to the dentin, whenever it is exposed, or in the cervical region of the tooth, where the enamel is thinner and more translucent, which allow the best comparison with the underlying dentin chroma. - The enamel shade of a composite can be better taken on the middle third of the tooth to be restored, where the thickness of the enamel is larger than in cervical area and there is less influence of the chromaticity promoted by the dentin. - The enamel translucency can be evaluated on the incisal third. - In natural teeth, the value is characteristic for the enamel, while the chroma and hue characterize dentine. - A basic factor when studying tooth color is the variation in thickness of these tissues due to aging. - The younger individuals, less exposed to the wear caused by the acids in the diet and brushing, present enamel thicker than older individuals, and consequently lighter teeth. (high value, low chroma & hue) - Older individuals: As wear is accentuated and the thickness of the enamel layer decreases, the translucency of the enamel increase, enabling chroma and hue, characteristics concerning the dentine, become more obvious. (darker tooth)(low value, high chroma & hue) ## V- Shade determination techniques ### Shade Determination - **I- Conventional (manual)** - A- Classical vita shade guide - B- 3D vita shade guide - C- Customized shade guide (ready made - hand made) - D- Non vita shade guide - **II- Digital** - A- Digital spectrophotometer - B- Digital imaging - 1- Digital camera- Camera phone - 2- Intraoral scanner - **First step** is to select a restorative material with similar shade to the remaining tooth structure and/or the adjacent teeth. - Different types of shade guides were produced, related to the shades of their respective products. (composite - ceramics) - However, with the time, most of the dental materials manufactures started to match the shade of their product with the VITA shade guide (VITA, Bad Säckingen, Germany) which is specialized mainly for ceramics. ### I- Conventional shade determination #### A- Classical shade guide - **1st Hue:** - A varies from reddish to brownish. - B varies from reddish to yellow. - C grayish shades - D family has the reddish - gray shades. - **2nd Chroma:** 1, 2, 3, 3.5,4 - **3rd Value:** Degree of darkness & whiteness - **Example:** - A2: reddish brownish hue with chroma 2 - **This shade guide is used with direct composite restoration with same shades based on this type** #### ND: Natural Die series - Dentin shade, Specialized mainly for ceramics, but some composite manufactures use it. (ND1, ND2, ND3, ......) (D1,D2, D3, .......) - For example (tooth shade needed is A2. The tooth after preparation with enamel removal, the exposed dentin has shade ND3, so it need A1 enamel to mask the Dentin shade (ND3) to have overall A2 shade.) #### Tooth whitening shad guide - Used to communicate and discuss with the patient the effect before and after bleaching ( the degree of shade changes occurs). - For example: patient come with shade 9 degree, after bleaching it become 4 degree, this means it become whiter by 5 degree. #### B- 3D Master shade guide - It uses Yes/No decision. 1. **1st determine value.** Arranged by lightness (0, 1, 2, 3, 4, and 5), starting with the darkest shade. 2. **2nd determining the Chroma.** Vertically arranged (1,1.5, 2, 2.5, 3) based on the middle (M) 3. **3rd determine Hue.** determine 1st (M) Middle hue, then detect more (R) Reddish hue or (L) Yellowish hue. - **This shade guide is used most commonly with indirect restorations with same shades based on this type** ### II- Digital shade determination #### A- Spectrophotometer - INSTANTLY DETERMINE AND VERIFY SHADE WITH THE ALL-NEW VITA EASYSHADE V #### Advantages: - Fast Precise and reproducible tooth shade determination. - Objective and reliable measurements. - reliable shade reproduction. - Simple and intuitive. - Efficient, digital communication. #### B- Digital imaging - **1- Digital DSLR camera - Mobile phone cameras:** - Digital images can be captured and saved, in JPG format typically prefer RAW format (with minimally processed data). - Photography enables magnify a tooth image, discriminate subtle transitions of color and use black-and-white contrast adjustments to study translucency patterns, and is an essential tool for communicating color to the dental laboratory technician for indirect restorations. ### Steps of digital imaging for shade determination: 1. a photo can be taken of a tooth with a shade tab with a standard black/white/gray standard card. 2. An attachment arm (Shade Arm) is available for fixing the distance, angle, and position of the color reference in the photo. 3. Under day light, day light flash or flash light with cross polarizing filter (polarized light). ### Cross Polarized - light - Cross-polarization is a two-step filtering process using two linear polarizer filters-one on the flash oriented either horizontally or vertically, and one on the lens oriented 90 degrees off the axis of the flash filter. - This causes the light illuminating the teeth to be filtered for one direction of light wave; then the reflected light is organized in the contrasting direction as it passes through the filter/lens combo and is recorded by the DSLR sensor. - The result is a filtered photo that has absolutely no glare or reflection ... a photo that allows for much more objective assessment of shade (Hue - chroma) and translucency. - Software can provide a "Color Map" of the target tooth. example of this type of dental shade matching software is (eg.: Shade Wave, Rayplicker, Adobe Photoshop, corel photo paint) - The software will mathematically normalize, or color correct, the image to compensate for color imbalances that occur when the image is taken and will cross-reference the standard card to generate "Shade Map," "Value Map," and "Translucency Map." - Mobile apps are becoming increasingly popular for color management. #### 2- Intraoral scanner: - Intraoral scanners are highly repeatable for shade matching (Color mapping), and outperformed visual shade matching. - Setting intraoral scanners to the Vita classical or 3D Master shade guide improve both accuracy and precision. - Disadvantages: Shade matching with intraoral scanners may be influenced by external factors such as ambient light sources and incorrect use or manipulation, so it should be verified with visual shade matching. ## VI- Principles of proper Shade determination 1. The dentin shade selection should be done taking the shade tab close to some exposed dentin area, whenever it is possible, or close to the cervical region of the tooth (especially done at the canine, High chroma). 2. The enamel shade of a composite can be better taken on the middle third of the tooth to be restored whrere then enamel thickest. 3. The incisal or translucent shade is observed in the incisal third of the tooth, where the enamel is the thickest and there is little dentin opacity. (In most anterior teeth the translucent zone is not limited to the incisal edge but also to the transitional line angle zones.) 4. One Tooth may have different color differs from incisal to cervical, so it is important to detect the proper **color mapping** of the tooth. The color map is a picture or prescription to be used as a guide throughout the fabrication of the direct restoration. 5. The shade guides better to be made with the same composite to be used for the restoration and kept hydrated by immersion in a water container. 6. The shade guide should be hold it at least one arm's length (25-35 cm ) far from the patient's mouth. (working distance) 7. The teeth should be viewed along a line of sight perpendicular to the tooth surface. 8. The teeth should be viewed 45° angle to the light source. 9. The teeth should be cleaned & polished with pumice and water. 10. The shade tab should be placed parallel to the tooth being matched and in the same plane. 11. The shade determination must be performed before the rubber dam isolation. (wetted Hydrated tooth ??) (It must be done before the teeth undergoes any long drying period, because the dehydration makes the teeth lighter higher value, as the result of the translucency reduction. This way, if the shade was correctly selected before the rubber dam isolation, immediately after its removal, the restoration will appear darker than the dehydrated tooth remaining. If the restoration shade is similar to the dehydrated tooth remaining, it is probably that the shade selection was incorrect and with the hydration, after the contact with saliva, it will appear lighter. The complete hydration of the teeth may take several hours). 12. The walls and furniture of the dental office must have neutral colors (Black, white, Brown, Gray). (As, The walls and other object in dental office reflect the light in the wavelength corresponding to its color. This will influence the color of the other objects observed in the same room, such as the teeth). 13. The patient is asked to remove the red lipstick. (it affect the color determination through the contrast, some parts stick to the tooth changings its color, it has greasy material that affects bonding & dental procedure) 14. If the patient is wearing colorful clothes, it is advisable to cover them with a bib with a neutral color, such as white or gray. 15. For anterior: A black cardboard as a background may be used to help confirm that translucency & color. 16. Shade taking must be performed quickly (less than 5 sec.),. In long time shade determination, the photoreceptor cells of retina become saturated by the wavelengths reflected from the teeth, creating a visual fatigue (seeing different incorrect colors). 17. When taking too much time looking to the tooth to choose the right shade, it is convenient that the clinician relaxes the eyes looking to neutral color (neutral gray) for a 3-5 seconds, to recover the eyes from fatigue. (balance all the colour sensors of the retina) 18. The shade selected must be registered on the dental records of the patient, as well as the composite brand that will be used. 19. If dental bleaching is planned on the patient's treatment plan, it must be performed before any restorative procedure with composites. - Shade determination should be done under the natural light or under artificial light that simulates the daylight (fluorescent light bulb) (polarized light) (5500°K and 6500°K). To confirm the shade selection, small amounts of composite can be applied and cured over the tooth without adhesive, and mock-up restoration can be performed. - If one concentrates on a solid color red target, for example, the red cones gradually respond less strongly to that reflected red signal. If one switches his or her gaze to a solid white target, now all colors are reflected to the retina and cones will send a strong green signal and a strong blue signal, but a weak red signal. One will see a cyan color afterimage, cyan being the complementary color of red ## Thank You!

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