Physical Properties

Graciously from Alexis

what are optical properties

properties related to the light interacting with the optical aspects of an object and recognized by a sensor (observer)

what is incident light

light emitted from a source that strikes an object

what is reflected light

light that bounces off an object and that the observer perceives

what are 2 sources of light?

artificial or natural

what is perception of the color of an object determined by

the radiation from the light source as modified by the object and received by the human visual system

color is the result of what kind of response to what kind of stimulus?

the result of a physiological response to a physical stimulus in human beings

what 2 things determine appearance properties

1) reflected light intensity

2) combined intensities of the wavelengths present in incident and reflected light

what are the 3 dimensions of color

1) hue (the color itself)

2) value (brightness)

3) chroma (intensity of the color)

what is light?

electromagnetic radiation (or photon) that can be detected by the human eye

red light has ________ wavelength and ________ energy

longer wavelength and lower energy

blue light has _________ wavelength and ________ energy

shorter wavelength and higher energy

what are the 6 colors and corresponding wavelengths of the visible light spectrum

1) violet: 400-450 nm

2) blue: 450-495 nm

3) green: 495-570 nm

4) yellow: 570-590 nm

5) orange: 590-620 nm

6) red: 620-700 nm

the spectrum is __________ and there are no _______ __________ between one color and the next that can be detected by the human eye

continuous; there are no clear boundaries between one color and the next

what is the range of the visible spectrum

400 nm (violet) - 700 nm (red)

the hue or the dominant wavelength is the wavelength in ______

nm (nanometers)

what is the visible spectrum

the wavelengths of visible light which can be perceived by the human eye

what does hue describe

the dominant color of an object

hue is the visual quality that distinguishes what

one color family from another

what are the 3 major bands of color on the visible light spectrum

red, green, and blue

why are the RGB primary (additive colors) significant

RGB color model is based on principle of additive color mixing; colors are created by combining light of these 3 primary colors in varying intensities

what are tristimulus values

set of 3 numerical values that represent the color of an object based on the human visual system's response to light; these values correspond to the 3 primary colors in sensitivities of the human eye: red, blue, green

what is the dominant wavelength of grass

green; 550 ish nm

what are 2 other terms for chroma

excitation purity or saturation

chroma is only present when?

when there is hue

chroma depends on the _______ or ________ of the hue

concentration or strength

the higher the chroma —> the _____ _______ the color

the more intense the color

value or luminance reflectance is a measure of what

relative lightness OR darkness of a color

the luminous reflectance of a color permits an object to be classified as equivalent to what

to a member of a series of achromatic objects

what are achromatic objects

objects that reflect or transmit light without selectively absorbing specific wavelengths of visible light; no distinct hue and typically appear as shades of black, white, gray

what is the range of achromatic objects

black to white for light-diffusing objects and from black (complete absorption) to perfectly clear/colorless for complete reflection or transmitting objects

what does value or luminance reflectance reflect?

the subjective brightness perception of a color

what is spectral energy distribution

a pictorial representation of the radiant power emitted by a light source at each wavelength or band of wavelengths in the visible region of the electromagnetic spectrum (300 to 750 nm)

radiant power of incandescent light

radiant power of cool white fluorescent light

examples of artificial light sources and how they look

what is metamerism

a phenomenon that occurs when colors change when viewed in different light sources

what are colors that match under one light source called

metamers

general explanation of metamerism

under some lights, the color pairs appear to match, but under other lights, they would be different

metameric colors are color stimuli of identical tristimulus values under a particular light source but with ?

but with different spectral energy distributions

what 3 things contribute to metamerism

1) spectral energy distribution of the light source

2) material reflectance

3) human vision response

because of metamerism, shade matching should be done in conditions where ?

where patient's activity will occur mostly

what is the best light source for shade matching

natural diffuse light

what is the worst light source for shade matching

harsh/direct dental chair light

what are optical effects caused by

light given off via transmitted, emitted, or reflected reactions

comparison of transmitted, emitted, and reflected lights

complete reflection: white color

complete absorption: black color

selective reflection/absorption: colored but will appear the color that it reflects bc absorbed wavelengths are usually converted into other forms of energy and are not visible to us

what determines the appearance properties of objects?

the combined intensities of the wavelengths present in incident and reflected light

what is opalescence

optical phenomenon characterized by a milky/pearly appearance seen in some materials when light scatters through them; this occurs when particles in a medium are small enough to scatter shorter wavelengths of visible light (like violet or blue) while allowing longer wavelengths (like red and yellow) to pass through, creating a bluish/iridescent appearance when viewed against light and the transmitted light that passes through may appear red/orange

what is the tyndall effect

the scattering of light by particles in a colloid or very fine suspension that favors the scattering of shorter wavelengths; opalescence is a specific visual manifestation of the tyndall effect

what happens in direct light in the tyndall effect

shorter wavelengths (blue and violet) are reflected/scattered (by dentin or porcelain) and the longer wavelengths (red and yellow) are absorbed

what happens in transillumination (light passing through a medium and being observed from opposite side) in the tyndall effect

longer wavelengths are reflected at the surface and the shorter wavelengths are absorbed

opalescent materials (such as enamel and dentin) can _______ and ______ shorter wavelengths of light

scatter and reflect shorter wavelengths of light

an opalescent object will appear what color in transmitted light?

yellowish-red

an opalescent object will appear what color in the reflected light perpendicular to the transmitted light?

blue

what is fluorescence

the emission of visible light by substances or minerals that have absorbed light (UV) or other electromagnetic radiation

the wavelength of the emitted light in fluorescence usually is ________ than that of exciting radiation

longer (this is because emission occurs as the energy is released and will be at a lower energy)

what is exciting radiation

electromagnetic radiation (usually UV, visible, or near-infrared light) that provides energy to a system and raises it to a higher energy state —> the system becomes unstable in this excited state and will release the absorbed energy (ex: fluorescence)

the most striking examples of human teeth fluorescence occur when the absorbed radiation is in the _____, and thus invisible to the human eye, and the emitted light is in the _______ region - blue

UV; visible region

what kind of oxides such as cerium oxide are added to the dental porcelain and composite that cause them to look blue under UV lights

rare earth oxides

why does surface texture matter in the perception of the color of an object

a rough surface will look dull due to scattering light in many directions

what does transparency mean

light will fully pass through an object

what does translucency mean

light will pass through a little but will also be dispersed

what does opacity mean

light will not pass through at all

what is translucency as a property

it is the property of a material that indicates the degree of light transmission or disperses the light

what is opacity as a property

it is the property of the material that prevents the passage of light or light is totally reflected

what is the refraction of light

the bending or change in direction of light when it travels from one medium to another

what is the index of refraction

the speed of light in vacuum / the speed of light in medium (n = c/v)

the amount of bending of light depends on the change in ___

the index of refraction

what is the clinical application of the index of refraction

dentists should control the IR component of restorative materials to match the translucent appearance of tooth structure

materials with low refractive indices allow light to pass through with minimal bending, making them appear?

transparent

materials with high refractive indices scatter or absorb more light, making them appear more?

more opaque or translucent

when light enters a medium, it ______ from its speed in air and may change ____________

slows; may change direction

indices of refraction of various materials

white opacity on teeth are created by differences in what

differences in the refractive index (for example enamel has IR of 1.65 but composite has IR of 1.6)

a perfect match in the IR results in what

a translucent solid

what might white lines on teeth indicate (4)

1) gaps

2) discontinuous voids

3) micro fractures in the tooth substance

4) micro fracture in the restorative materials

what is the munsell color system

color is compared with a large set of color tabs and is then identified by its hue, value, and chroma (HV/C)

shade guides used in clinic are designed to match which classical shade guide

VITA classical shade guide

A1-A4 on the shade guide are what colors

reddish brown

B1-B4 on the shade guide are what colors

reddish yellow

C1-C4 on the shade guide are what colors

gray

D2-D4 on the shade guide are what colors

reddish gray

to measure color of teeth, you may use __________ technique

instrumental

what is the function of instrumental technique

it evaluates the chromaticity and illuminance of light sources or objects by reflected or transmitted light

what is a relevant instrumental technique

CIELab Method: uses 3 coordinates to define color to find the color difference metric (deltaE)

- L (lightness): 0 (black) to 100 (white)

- a (green-red axis): +a (red) to -a (green)

- b (blue-yellow axis): +b (yellow) to -b (blue)

- delta E: 0 (perfect color match), < or equal to 1 (not noticeable to human eye), >3 (noticeable difference)

how does the CIELab Method work

1) the sample is illuminated with a standard light source

2) a color measurement device captures the light reflected or transmitted by the sample

3) the instrument converts the spectral data into L, a, and b values on mathematical models

4) the measured color can be compared to target standard using the calculate deltaE, which represents the difference between 2 colors

what are the perceptibility and acceptability ranges of the CIELab Method

no perceptible color difference (match): 0-2.6 deltaE

perceptible and acceptable color difference (mismatch): 2.6-5.5 deltaE

perceptible and unacceptable color difference (mismatch): 5.5+ deltaE

what are thermal properties related to

related to the thermal changes of the materials during manufacturing

what are the 3 states of matter

solid, liquid, gas

states of matter table

what is the melting temperature

the temperature in which a solid transforms from a solid to a liquid

a pure element most likely has one melting/freezing _______

one melting point

an alloy (mixture) most likely has a melting/freezing _______

melting range

melting curve picture

what is the cooling temperature

the temperature at which a liquid transforms from a liquid to a solid

cooling curve picture

what are the importances in dentistry of melting temperature

1) casting alloy melting temperatures determine types of investments and flame source

2) porcelain addition and staining requires close observance of firing temperatures to avoid melting of metal substrate

what is latent heat

the heat/energy required for a material to undergo a change of phase or state rather than to increase its temperature

latent heat is retained for what?

for maintaining the kinetic molecular motion of molecules in the liquid and gas state

there is ___ temperature change in latent heat

NO

in other words, latent heat is the heat input required to change what

to change from a solid to liquid or liquid to gas