Principles of Shade Selection Flashcards
Two crucial steps in shade selection
1) Selection of color through shade guide
2) Consequently the correct reproduction of this color in restoration
Light (without light color does not exist)
- Light is electromagnetic radiation that can be detected by the human eye. Natural white light falls between 380-770 nm along the electromagnetic spectrum, having a couple of component bands along the spectrum
- the component bands produce 6 different sensations (red, orange, yellow, green, blue, and violet).
- When a particular wavelength segment of light is reflected and enters the eye, the sensation of color is produced
-Interaction of light with an object makes color perception possible
Nature of Color
- color is all about light. for color to be seen, light is reflected from an object and stimulates the neural sensors in the eyes retina to send a signal that is interpreted in the visual cortex of the brain.
- the reflected components of incident white light determine color of an object
Perception
- occurs in the brain. Rods perceive brightness and cones perceive the hue (color)
- Receptors: rods and cones
- Rods convey shades of gray (value)
- Cones allow brain to perceive color hues and chroma
Dimensions of color
- color is usually described according to the Munsell color space in terms of HUE, VALUE and CHROMA.
- When color is determined using Munsell system, value is determined first foloowed by chroma and them hue.
Hue
the attribute of a color that enables the clinician to distinguish between different families if color
Chroma
degree of color saturation.
-intensity of the color
- low chroma = “weak”
- High chroma = “highly-saturated”
Value
- indicated the lightness of a color (gray and blacks)
-* brightness is the most important color variable in dental shade selection !!!**
Factor affecting the color perception
1) Eye (of dentist)
2) Environment (light source)
3) Object (teeth)
Factors affecting How You See Color
- color blindness
- color adaptation
- metamerism
Color Adaptation ( Negative Afterimage)
- a negative afterimage occurs because of fatigue of the cone receptors, which become less sensitive to further stimulation.
- Strong red lipstick next to the tooth being evaluated will fatigue the red receptors in the roaming eyes, while blue and green receptors remain fresh and can be fully stimulated. This can yield perception of the tooth that is too blue-green
Metamerism
- phenomenon of two objects appearing to match in color under one condition but showing apparent differences under another. In dental terms: occurs when a restoration is matched to the natural dentition under incandescent light, but when viewed under color-corrected or fluorescent light appears not to match
Illumination
- Recommended lighting for accurate shade taking in dentistry: 5500 degrees K
- replicates northern natural midday daylight balances all hues in the spectral curve
*Properties of Teeth
- enamel is translucent
- dentin is more opaque
- smooth and shiny surface reflects more light
- dry teeth appears differently than wet tooth surface
- any extrinsic or intrinsic stains affect the color
Variations in Teeth Color
1) tooth color varies from person to person, by dentition, by tooth within the same dentition and within the same tooth
2) Primary teeth are more lighter in color than permanent teeth
3) Permanent teeth are whitish-yellowish and slightly reddish
4) Permanent teeth exhibits color transitions from cervical being more darker than incisal which is more translucent
5) The variation of thickness of enamel and dentin also affect their color
6) Tooth color continuously change in persons life time based on physiological and pathological conditions
7) Tooth color varies in male and female teeth, male teeth are significantly darker, more chromatic and redder than female teeth
