Colour science in dentistry Flashcards
- Define photon
- State its property
- Define the electromagnetic wave
Photon:
• It is a bundle of electromagnetic energy
• It is the basic unit that makes up all light
Property:
• Property: it can be absorbed or emitted
Electromagnetic wave:
• Electromagnetic (EM) radiation is a form of energy that is all around us and takes many forms, such as radio waves, microwaves, X-rays and gamma rays
• Sunlight is also a form of EM energy, but visible light is only a small portion of the EM spectrum
State the 2 types of light
- Polychromatic light: consists of a variety of wavelengths
* Monochromatic light: a single wavelength
Define:
- Phase difference
- Coherent waves
- Incoherent waves
- Phase difference between two waves tells us how much a wave is in front or behind another particle
- Coherent waves: Two beams oflightarecoherentwhen the phase difference between theirwavesis constant
- Incoherent waves: does not contain photons with the same frequency and does not have wavelengths that are in phase with one another
State the two things that determine tooth colour
- Intrinsic effects: Interaction of light with enamel (reflects most light) and dentin (gives tooth natural colour)
- Extrinsic effects: absorption of materials/stains, pellicle coating
List the 6 factors that affect the appearance of the tooth colour (vision)
- Lighting conditions
- Translucency
- Opacity
- Light scattering
- Gloss
- Human eye and brain etc
List and describe the components of the eye
- Cornea: Transmits and focuses light into eye
- Pupil & iris: control the amount of light reaching the eye
- Lens: Transparent structure that focuses the light rays onto the retina
- Retina: Nerve layer that lines the eye. It contains photoreceptors
- Macula: small central area in the retina that contains special light-sensitive cells and allows us to see fine details clearly
- Vitreous: clear jelly like substance
List 7 risk factors for cataract formation
- Age related
- Diabetes
- Drugs ie corticosteroids
- UV radiation
- Smoking
- Alcohol
- Nutritional deficiency
Describe the role of the retina in vision sensation
- The retina contain two types of photoreceptors cones and rods
- Cones contain photosensitive pigment opsins. This is for colour vision
- Rods: contain photosensitive pigment rhodopsin. This is for night vision
- A visual stimuli will cause changes in membrane potential. This will cause neurotransmission along the CN II Optic nerve which will travel to the brain to be interpreted
State the sensitivity of rhodopsin and opsin
- Rhodopsin: Sensitive to 498 nm, light sensitivity (blue)
* Opsin: Sensitive to 564-570nm, 534-540 nm, 420-445 nm. It is colour sensitive (red/ orange)
Define hue, value and chroma
- Hue: Distinguish one group of similar colours from another. It is the he name of a colour (eg, red, green, blue, etc)
- Value: How light or dark the colour is
- Chroma: Distinguishes saturated colours from weak, pastel ones (intensity of a colour)
Describe how shade selection should be undertaken in dentistry
- The patient should be viewed at the eye level so that the most colour sensitive part of the retina will be used
- The patient is taken to a window and the colour is confirmed in natural daylight after initial selection under incandescent and fluorescent lightening
- The teeth to be matched should be clean
- Brightly coloured clothing should be draped and lipstick should be removed
- The eye should be rested by focusing on a gray-blue surface immediately before a comparison since this balance all the colour sensors of the retina and re-sensitises the eye to the yellow colour of the tooth
- If tooth and shade tab have different surface characteristics, wetting the surface helps remove the difference
Define Chubb illusion
An error in visual perception in which the apparent contrast of an object varies substantially to most viewers depending on its relative contrast to the field on which it is displayed.
Explain the mechanism of retinal fatigue
- Retinal fatigue causes complementary colours to be seen in after-images
- The photoreceptors in the retina that respond to colour come in just three varieties, which we call ‘red’, ‘green’ and ‘blue’
- If looking at a red rectangle, a rectangular patch of the retina is illuminated with (only) red light, while the surrounding retina receives a mix of red+green+blue light from the three available colours in the screen
- In that patch, the ‘red’ photoreceptor cells gradually become fatigued, while the ‘green’ and ‘blue’ cells are rested
- After 30s, the screen goes white, so now the patch with the fatigued ‘red’ cells is illuminated equally by red, green and blue light
- The ‘green’ and ‘blue’ photoreceptors respond strongly, but the ‘red’ cells only weakly, thus a mix of green and blue, i.e. cyan is seen
