Fundamentals of Materials Science

Question 1

what is light?

Answer 1

• electromagnetic radiation resulting in changes of the state of electron cover
• includes ultraviolet, infrared, and x-ray radiation

Question 2

what is dual character?

Answer 2

• stream of material particles
• photons widespreading as electromagnetic waves

Question 3

what is visible light?

Answer 3

• has wavelength in a range from 380-760nm
• frequency range of 405-790THz

Question 4

what happens when light is refracted by a prism?

Answer 4

the dispersion causes the separation of colors

Question 5

white light is polychromatic. what does that mean?

Answer 5

it is a mixture of wavelengths

Question 6

how are hue, value, and chroma determined?

Answer 6

reflected light intensity and combined intensities of wavelengths presented in incident and reflected light

Question 7

what is reflection and brightness?

Answer 7

• reflection: either specular or diffuse, depending on the nature of the interface
• brightness: color property, expressed mainly in metals; depends on quality of reflected light. high brightness occurs when nearly all incident light is reflected

Question 8

how can mirror-like reflection of ceramics construction occur?

Answer 8

opaque layer is backed by temperature higher than recommended

Question 9

what is refraction?

Answer 9

change in direction of a wave due to change in its speed

Question 10

what is absorption?

Answer 10

the property of material to let light pass through it

Question 11

what is opacity?

Answer 11

object does not let incident light pass through it

Question 12

what is the difference between transparency and translucency?

Answer 12

• in transparency, nearly all light passes through an object
• in translucency, only some light passes through an object

Question 13

what is metamerism?

Answer 13

properties of materials to appear to have different colors when illuminated by different light sources

Question 14

what is a metameric pair?

Answer 14

a pair of objects whose colors match under a certain illumination, but do not match if illumination conditions are changed

Question 15

what is opalescence?

Answer 15

• origination of a rainbow inside a material with little opacity due to the interference of light waves owing to the inside defects and microstructural inhomogeneity
• teeth opalescence is the result of the interaction of light with enamel prisms - refraction, reflection, and interference

Question 16

what is luminescence?

Answer 16

property of materials to absorb energy and emit it as visible light

Question 17

what are the 2 types of luminescence?

Answer 17

• fluorescence: emission of light by a substance that has absorbed light of other electromagnetic radiation of a different wavelength
• phopshorescence: does not immediately re-emit the radiation it absorbs

Question 18

describe the VITA classical A1-D4 shade guide

Answer 18

• A1-A4: reddish brown
• B1-B4: reddish-yellowish
• C1-C4: greyish shades
• D1-D4: reddish grey

chroma increases and value decreases as shades move from 1-4

Question 19

describe the chromascop shade guide

Answer 19

• 5 color groups: 100, 200, 300, 400, 500
• increase in chroma and decrease in value and shade numbers increase

Question 20

what is the scattering coefficient?

Answer 20

the fraction of incident light flux lost by reversal of direction in an elementary layer

Question 21

what is the absoprtion coefficient?

Answer 21

the fraction of incident light flux lost by absorption in an elementary layer

Question 22

what is light reflectivity?

Answer 22

the light reflectance of a material of infinite thickness

Question 23

what is masking ability?

Answer 23

• dental restorations are often used to restore esthetic problems
• the ability of masking depends on optical constants and thickness of the dental materials used

Question 24

why is temperature important in dentistry?

Answer 24

temperature produced during procedures can affect other tissues and produce pain or irreversible pulpitis

Question 25

name 3 transition temperature techniques

Answer 25

• differential thermal analysis (DTA)
• thermo-mechanical analysis (TMA)
• dynamic mechanical analysis (DMA)

Question 26

what is the heat of fusion?

Answer 26

the heat required to convert 1g of material from solid to liquid state at the melting temperature

Question 27

what is thermal conductivity?

Answer 27

the quality of heat per second passing through a body 1cm thick with cross section of 1cm² when the temperature difference is 1*C

Question 28

what is specific heat?

Answer 28

the quality of heat needed to raise the temperature of 1g of a substance by 1*C

Question 29

what is thermal diffusivity?

Answer 29

a measure of transient heat-flow

Question 30

what is the coefficient of thermal expansion?

Answer 30

the change in length per unit length of material for a 1*C change in temperature

Question 31

what is zeta-potential?

Answer 31

the potential difference existing between the surface of a solid particle immersed in a conducting liquid and the bulk of the liquid