Color and Light - PDF

COLOR - FIXED PROSTHETICS What is light - definition? visible light if form of electromagnetic radiation in very limited portion of overall EM spectrum Has wave and particle properties (Quantum theory) ◦ Energy of each photon is proportional to frequency of the radiation What ar...

COLOR - FIXED PROSTHETICS What is light - definition? visible light if form of electromagnetic radiation in very limited portion of overall EM spectrum Has wave and particle properties (Quantum theory) ◦ Energy of each photon is proportional to frequency of the radiation What are wavelengths of the visible light spectrum? What is colour? characteristics of human visual perception Described through colour categories (ie. red, blue, yellow, green, etc) Perception derives from stimulation of cone cells in eye by EMR in the spectrum of light Color we see is the wavelength of light reflected off of objected (based on objects physical properties such as absorption, emission spectra, etc) What are opaque surfaces? Light that hits opaque surface can be reflected specularly (mirror) or scattered (diffuse) or absorbed Objects (tend to be rough) reflect scattered wavelengths and this determines color ◦ If scatter all wavelengths equally - white ◦ If absorb all wavelengths - black Objets that reflect light specularly reflect light of different wavelengths with different efficienies look like mirrors tinted with colours determined by those differences ◦ Object that reflect some impinging light and absorbs the rest may look black but also might be faintly reflective (ie. black objects coated with layers of enamel or lacquer) What are translucent/transparent objects? transmit light  Translucent - scattering transmitted light Transparent - not scattering transmitted light Will appear tinted if absorb/reflect light of various wavelengths differently What are the different sources of light? Some objects emit light they generate from having excited elections ◦ incandescence - electrons excited due to elevated temperatures ◦ Chemoluminescence - excited electrons due to chemical reactions ◦ Floruescence- excited electrons after absorbing light of one frequencies and emitting different frequency ◦ phosphorescence - fluorescence that lasts after stimulation ◦ Light emitting diodes - from electrical contacts Sun - main source of light Describe the pathway of light entering the eye Refracted as it passes through cornea Passes trhough pupil and refracted again as it passes through lens Iris changes the pupil size and therefore controls amount of light passing through eye Cornea and lens together act as compound lens to project an inverted image onto the retina What is the retina made of that helps us see color? large photoreceptor cells which contain protein molecules called opsin. Two forms of opsin are rod opsins and cone opsins (receptor) ◦ Rods - respond black - white (gray) ‣ 20X rods than cones ‣ Peripheral areas of ◦ Cones - respond to colour the eye ‣ Long cones (L) - long wavelength, peaking 564-545 nm RED ‣ Medium cones (M) - medium wavelength, peaking 534-545nm GREEN ‣ Short cones (S) - short wavelength, near 420-440 nm. BLUE ‣ Each cone cell responds proportionally to the incident wavelength according to its sensitivity ‣ Located centrally near fovea centralist  The visual cells in eye contain Retinal (vitamin A form) which is complexed with opsins ◦ Retinal-opsin compels changes shape when it captures a photon and initated chemical chain that leads to perception of image in brain Study: individuals missing rods and cones have photoreceptive ganglion cells that act as rudimentary brightness detectors (a third way, augmented traditional visual pathway) What is tetrachromacy and types? most humans re trichromatic - have 3 types of color receptors ◦ Retinal tetrachromacy - having 4 pigments in cone cells in retina ‣ Nearly 1/2 of all women Functional tetrachromacy - having ability to make enhanced color discriminations but only have 3 different pigment receptors? Occurs when an individual receives 2 different copies of gene that codes for M or L wavelength cones, which are carried on X cchromosome. Must have two X chronometers, therefore why phenomenon only occurs in women What is monochromatic vs polychromatic light? Monochromatic - colours we see from a prison/rainbow which contains all the colour of light, each colour consisting of light on one wavelength Polychromatic - our would is much more colorful because the lightt we see is polychromatic (see many more colours) Based on light source What is luminance and how does this explain polychromatic light? rods are sensitive to low levels of light, but they are not colour Cones responsible for colour but need more light or greater luminance There are about 6 million cones in retina, few of which activated in low light conditions ◦ How we get differentiation between black and dark shade colours… What are colour spaces  have evolved and continue to grow Means of expressing colour Define Hue, Value and Chroma? hue = color Value = lightness/luminance of colour (greyscale) Chroma - intensity of colour, colour purity (saturation) What is the Munsell Colour System? a colour space that specifies colour based on three colour dimensions: hue, value and chroma ◦ Created by Professor ALbert. H Munsell in first decade of 20th denture HUE = horizontal circle divided into five principle hues and 5 intermediate hues. Each of these are then prone into 10 sub-steps (so 100 hues are given integers value). But we tend to use 40 hues in increments of 2.5 VALUE = varies vertically - colours with low value numbers are dark and high value are light. ◦ NOTE: on shade guides, the 1 has the highest value and 5 has lowest value CHROMA = measured radially from center of each slice (lower chroma is less pure and more washed out) ◦ No intrinsic upper limit to chroma ◦ Different color spaces have different maximal chroma coordinates (ie. yellow can have more potential chroma than light purples due to nature of eye and physics of color stimuli) How does the Munsell Colour system apply to tooth colour range? tooth colour located in small bounded area of mussel colour sphere What is CIEL*a*b*? colour space define by international commission on Illumination Expresses colour as 3 values: ◦ L* - perceptual lightness ◦ A* and B* = four unique colours of human vision, red, green, blue and yellow What are pigments? molecules that absorb certain wavelengths of light and reflect reminiang wavelengths Ie. chlorophyll - absorbs red and blue and reflects green wavelength What are the three primary colours of pigments? cyan, magenta and yellow Combining these is subtractive colour combining ◦ Example: ‣ Cyan absorbs wavelengths yellow to ref and lets green to blue reflect the eye ‣ Yellow absorbs other end of spectrum reflecting green and red ‣ Combining these two pigments allows green to be only reflected from paper ‣ ==> therefore paper appears green only What is additive versus subtractive colour combining? coloured LIGHT combines additively ◦ We respond to light that enters the eye and we see all the wavelengths that are in the light ◦ Therefore, addicting combinations of primary colours (red gree and blue), we make the new colour Coloured surface with PIGMENTS combine substractively ◦ Pigments are REMOVING fwavelenths ◦ So the colour we perceive is the light reflected from the surface minus all wavelengths absorbed ◦ Primary colours of pigments. - cyan, magenta and yellow selectively absorbcertain wavelengths and combine substractively What is the Ishihara colour test Test for red-green colour blindness which occurs in 7-10% of males, rare in females — its on the X chromosome, therefore women get two and the strongest is operative COLOR AND SHADE MATCHING: APPLICATION what are primary vs secondary light- colour mixtures? Primary = red, green and blue Secondary = yellow, cyan, magenta Pigments are substractive, light is additive (Note: light and pigment primary colours are different) 3D vita Master Shade Guide - how does it work? based on value first (has 0 - beaching shade (high value), 5- lower value) Once picked value, stay in this family to then pick chroma, etc. Human teeth what is Hue, value and chroma range? hue : 6YR to 9.3 Y (yellow-red to yellow) Value: 4 to 8 (towards lighter portions of scale - not many dark teeth) Chroma range: 0 to 7 (towards lower portion, not strong colours) What are shade guides? purpose - transfer information from patient to laborartory Many different shade guides - we will focus on 3D master Shade Guide They are not totally clinically referees that I’ve because: ◦ They have no metal backing (if you are making PFM) ◦ 3+ mm thick Custom shade guides are best, but expensive Digital shade guides require calibrated photos and are a talented technician… very time consuming How do you use the 3D Vita Master Shade Guide? arranged in the same value groups Then chroma (second) and hue (third) Hold shade guide in front of pts teeth at arms length 1. Determine value group (1-5) : squint because less light getting in eye, so activating more cones 2. Select chroma from 3 vertically aligned specimens within the “M” section of the best value group or linear card 3. Select Hue by determining if tooth is more yellow (L row) or red (R row) How does digital shade selection work? tooth should be clean  Hold probe perpendicular to tooth Variation in colour depending on where the probe is located can use IO scanner What is order of the three in taking shade selection and why? 1. Value first: most important of the three dimensions of colour A. Lightness and darkness differences are readily detected by individuals undtrained in colour perepction B. More easily detected at a variety of viewing distances 2. Chroma 3. Hue A. Differences in hue and chroma more difficult to quanify as viewing distance increase B. In doubt, big shade with higher value because possible with surface color ants to custom shade the completed crown to reduce value but not to increase value What components of tooth matching requir consideration/cusom shade guide: transparent Translucent Opaque Fluorescence - emission of light after it has absorbed light, will be longer wavelength Opalescence - milky iridescence of opal. Appearance of change of color as angle or light changes Characterization ◦ Adding internal color stains, or applying externally with color stains? What are guidelines for shade selection 1. Lighting A. Ideal - natural, ambient and indirect (norther exposure) B. Poor: intense and color shift 2. Metamerism A. Objects match under one light source but not another B. Want to avoid this 3. Surrounding colours A. No bright lipstick B. Neutral coloured patient bib- light blue, grey, white 4. Timing A. Beginning of appointment to reduce drying effect  A. Short duration glandes to prevent eye fatigue 1. Patient position A. Eye level and arms length 2. Tooth condition A. Clean and moist B. Dry teeth will change colo Rand usually increased in value 3. Custom shade tabs A. May be fabricated by lab with meal backing 4. Photography A. Pictures of teeth with shade tab