Optical, Thermal and Electrical Properties Used to Characterize Dental Materials

Question 1

physical properties

Answer 1

optical properties
thermal properties
electrical properties

Question 2

optical properties

Answer 2

color and pigmentation
opacity
refractive index

Question 3

thermal properties

Answer 3

temperature
heat of fusion
thermal conductivity
specific heat
thermal diffusivity
coefficient of thermal expansion

Question 4

electrical properties

Answer 4

electrical conductivity
dielectric constant
electromotive force
galvanism
corrosion

Question 5

light interacting with surface occurs through

Answer 5

reflection: angle of incidence equals angle of reflection, diffuse reflection
absorption: angle of incidence absorbed into material
refraction: angle of incidence different from angle of refraction

Question 6

three components of color

Answer 6

dominant wavelength: perceived color

luminous reflectance: B-W (light diffusing objects), B-Clear (transmitting objects)

excitation purity: saturation of color

Question 7

color can be measured

Answer 7

instrumentally (spectrophotometer) or visually

Question 8

pigmentation

Answer 8

esthetic process used in restorations
addition of incorporating colored pigments in non-metallic materials
observed color results from selective absorption by the pigments and reflection of certain colors

Question 9

surface roughness

Answer 9

influences how material will interact with its environment
Atomic Force Microscopy (AFM) can be used to map these areas of roughness

Question 10

surface wetting

Answer 10

the ability of a liquid to maintain contact with a solid surface
a result of intermolecular forces and determined by adhesion and cohesion forces

Question 11

cohesive forces

Answer 11

causes the liquid to ball up and avoid contact with the surface

Question 12

adhesive forces

Answer 12

interaction between liquid and solid that causes liquid to spread across the surface

Question 13

surface wetting - contact angle

Answer 13

contact angle > 90 deg - hydrophobic
contact angle < 90 deg - hydrophilic

Question 14

fluorescence

Answer 14

emission of light from a material that has absorbed light
generally has a lower energy emitted than absorbed
natural human teeth emit fluorescent light when excited by UV radiation
some restorations add fluorescing materials to reproduce natural appearance of tooth

Question 15

opacity

Answer 15

material property that prevents the passage of light

Question 16

translucency

Answer 16

permits the passage of light but disperses it

Question 17

transparency

Answer 17

permits the passage of light with little distortion

Question 18

refractive index

Answer 18

ratio of the velocity of light to its velocity in a medium
light slows from its speed in air and may change direction

Question 19

temperature

Answer 19

measured using a thermocouple or thermometer
consideration for dental work: measurement of heat during cavity shaping, increase in temperature during tooth cutting

Question 20

differential scanning calorimetry

Answer 20

used to locate transition temperatures and study effects on material
determines heats of transition and reaction

Question 21

thermal gravimetric analysis

Answer 21

can measure the mass loss as a function of temp

Question 22

thermomechanical analysis

Answer 22

measures dimensional change with or without an applied load

Question 23

glass transition temperature Tg

Answer 23

reversible transition in amorphous materials from a hard state to a more flexible state with increased temperature

Question 24

temperature of crystallization Tc

Answer 24

after a Tg, the amorphous material is less viscous, there may be a rearrangement of molecules into a crystalline state, resulting in an exothermic peak

Question 25

melting temperature TM

Answer 25

with increased temperature, the sample reaches its melting point, resulting in an endothermic peak

Question 26

differential scanning calorimetry (DSC)

Answer 26

used to locate transition temperatures and study effects on material

Question 27

heat/enthalpy of fusion

Answer 27

the quantity of heat to convert 1g of a material from solid to liquid with no temperature change

Question 28

thermal conductivity

Answer 28

the quantity of heat required per second to pass through 1 cm material with a cross sectional area of 1 cm2

Question 29

metals have much _____ thermal conductivity than non-metals

Answer 29

higher

Question 30

specific heat capacity

Answer 30

quantity of heat needed to raise the temperature of 1 gram of material one degree

Question 31

relationship of metals and specific heat capacity

Answer 31

metals have low specific heat because they require less heat to warm
also give up their heat quickly

Question 32

thermal diffusivity

Answer 32

the rate of heat transfer through a medium
significant difference between metal and ceramic values

Question 33

coefficient of thermal expansion

Answer 33

the rate at which a material expands during temperature change

Question 34

thermal expansion of restoration in tooth

Answer 34

no heat: restoration expands more than tooth, wedging and extrusion

heat applied: restoration expands less than tooth, loosening and gap formation

Question 35

electrical conductivity

Answer 35

the ability to conduct an electric current and is governed by Ohm’s Law
ceramics are not good conductors, called insulators

Question 36

electrical resistivity

Answer 36

the resistance to passing electric current
the resistivity of a homogenous conductor varies directly with its length and cross-sectional area

Question 37

resistance and resistivity are proportional based on the

Answer 37

length and size of the material

Question 38

dielectric material

Answer 38

provides electrical insulation but can be polarized in an electric field

Question 39

electromotive force emf

Answer 39

metals and alloys used in dental restorations are susceptible to corrosion
is a listing in order of their decreasing tendency to oxidize in solution

Question 40

bimetallic corrosion/galvanism

Answer 40

two dissimilar filling materials in opposing teeth have a difference in emf
the saliva can act as an electrolyte
if the flow of current goes through the patients pulp, pain is experienced and the anodic restoration may corrode