Optical, Thermal and Electrical Properties Used to Characterize Dental Materials Flashcards
physical properties
optical properties
thermal properties
electrical properties
optical properties
color and pigmentation
opacity
refractive index
thermal properties
temperature
heat of fusion
thermal conductivity
specific heat
thermal diffusivity
coefficient of thermal expansion
electrical properties
electrical conductivity
dielectric constant
electromotive force
galvanism
corrosion
light interacting with surface occurs through
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
three components of color
dominant wavelength: perceived color
luminous reflectance: B-W (light diffusing objects), B-Clear (transmitting objects)
excitation purity: saturation of color
color can be measured
instrumentally (spectrophotometer) or visually
pigmentation
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
surface roughness
influences how material will interact with its environment
Atomic Force Microscopy (AFM) can be used to map these areas of roughness
surface wetting
the ability of a liquid to maintain contact with a solid surface
a result of intermolecular forces and determined by adhesion and cohesion forces
cohesive forces
causes the liquid to ball up and avoid contact with the surface
adhesive forces
interaction between liquid and solid that causes liquid to spread across the surface
surface wetting - contact angle
contact angle > 90 deg - hydrophobic
contact angle < 90 deg - hydrophilic
fluorescence
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
opacity
material property that prevents the passage of light
translucency
permits the passage of light but disperses it
transparency
permits the passage of light with little distortion
refractive index
ratio of the velocity of light to its velocity in a medium
light slows from its speed in air and may change direction
temperature
measured using a thermocouple or thermometer
consideration for dental work: measurement of heat during cavity shaping, increase in temperature during tooth cutting
differential scanning calorimetry
used to locate transition temperatures and study effects on material
determines heats of transition and reaction
thermal gravimetric analysis
can measure the mass loss as a function of temp
thermomechanical analysis
measures dimensional change with or without an applied load
glass transition temperature Tg
reversible transition in amorphous materials from a hard state to a more flexible state with increased temperature
temperature of crystallization Tc
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
melting temperature TM
with increased temperature, the sample reaches its melting point, resulting in an endothermic peak
differential scanning calorimetry (DSC)
used to locate transition temperatures and study effects on material
heat/enthalpy of fusion
the quantity of heat to convert 1g of a material from solid to liquid with no temperature change
thermal conductivity
the quantity of heat required per second to pass through 1 cm material with a cross sectional area of 1 cm2
metals have much _____ thermal conductivity than non-metals
higher
specific heat capacity
quantity of heat needed to raise the temperature of 1 gram of material one degree
relationship of metals and specific heat capacity
metals have low specific heat because they require less heat to warm
also give up their heat quickly
thermal diffusivity
the rate of heat transfer through a medium
significant difference between metal and ceramic values
coefficient of thermal expansion
the rate at which a material expands during temperature change
thermal expansion of restoration in tooth
no heat: restoration expands more than tooth, wedging and extrusion
heat applied: restoration expands less than tooth, loosening and gap formation
electrical conductivity
the ability to conduct an electric current and is governed by Ohm’s Law
ceramics are not good conductors, called insulators
electrical resistivity
the resistance to passing electric current
the resistivity of a homogenous conductor varies directly with its length and cross-sectional area
resistance and resistivity are proportional based on the
length and size of the material
dielectric material
provides electrical insulation but can be polarized in an electric field
electromotive force emf
metals and alloys used in dental restorations are susceptible to corrosion
is a listing in order of their decreasing tendency to oxidize in solution
bimetallic corrosion/galvanism
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
