usually strong, conduct electricity and heat well and are opaque to light
forces of ceramics
positive or negative ions, coulomb forces
composition of ceramics
combinations of metals or semiconductors with oxygen, nitrogen, or carbon
examples: glass, porcelain, minerals, diamonds
forces of polymers
covalent, van der waals, H-C bonds
Weight of polymers
examples of polymers (4)
light weight
plastics, rubber, polyester, elastomers
the mixture of a metal, ceramic and polymer is a
composite
Stress equation
Example:
According to the Centers for Disease Control, the average weight of an American man and woman in 2010 was 195.5 and 166.2 pounds, respectively. Imagine a typical American man wearing shoes with a heel area of 10 square inches and a woman wearing high heels with an area of .25 square inches (1/4 inch per side). When walking, a man’s foot exerts a force of 19.5 pounds per square inch on the surface he is walking on while a woman’s heel would exert a force of 2,659 pounds per square inch.
Stress= Force/ Area
Stress = Force / Area 195.5/10 = 19
166.2/.0625 = 2659
A and B?
P
A= compression
B= tension
P= pressure or force?
the measure of heat transfer or heat flow
thermal conductivity
True/False: metals have lower values of conducting heat than plastics and ceramics
FALSE; they have higher values
Enamel and dentin are ___ conductors of heat and cold
poor
____ ____ and their components have the largest coefficient of thermal expansion of any material used in restorative dentistry
dental waxes
the generation of electrical currents that the patient can feel
Galavinism
a surface reaction of metals in the mouth from components in saliva or food
tarnish
the dissolution of metals in the mouth
corrosion
True/False: computerized systems are the best way to color match for restorative dentistry
FALSE; they offer great hope for the future but visual shade selection with the human eye is still the most predictable method available
the visible spectrum ranges from ___ to ___ nm
400 to 700
what are the 4 wavelengths shorter than the visible light
ultraviolet, x-rays, gamma, and cosmic rays
what the 5 waves above the visible spectrum
infrared
microwaves
television
radio
electrical waves
degree of saturation of a shade; light yellow to dark yellow
chroma
sensation induced from light of varying wavelengths reaching the eye
color
the property of light source to influence color of objects
color rendition
dominant color of an object; dominant color: red, yellow, green, blue, etc
Hue
phenomenon in which the color of an object under one type of light appears to change when illumination by different light source
metamerism
relative lightness or darkness of a color; white to dark
amount, location, and quality varies w person and age
determines the amount and direction of light reflected off the facial surface; wears with age; develop texture from adjacent natural teeth
surface texture
the property of materials that prevents the passage of light
opacity
A property that allows the passage of light so little distortion takes place and objects may be seen clearly through them.
transparency
Is a property of substances that permits passage of light but disperses the light so objects cannot be seen through the materials
translucency
The same object, without changing color may appear different in color under different lighting conditions
metamerism
strain equation
strain= deformation (change in length)/ original length
the ratio of stress to strain in the linear or elastic portion of the stress-strain curve
elastic modulus
the stiffness of a material and is a constant
elastic moduli of dental materials
elastic moduli of:
human enamel:
gold alloy:
83,000
96,600
the stress at which the material no longer functions as an elastic solid and is higher than the elastic modulus
proportional limit
used to designate a certain permanent deformation or offset, usually 0.2% (slightly higher than proportional limit)
used because proportional limit is difficult to determine
yield strength
indicates that stress and strain are no longer proportional
plastic deformation
higher than plastic deformation on graph
the strength at which fracture occurs
ultimate strength
higher forces applied to a material will cause fracture or rupture
ultimate tensile strength
indicates the energy absorbed up to the proportional limit
resilience
indicates the energy absorbed up to the ultimate tensile strength
toughness
on graph under the elastic modulus until proportional limit
resillence
on graph between proportional limit to ultimate tensile strength along plastic deformation curve
toughness
the resistance of a material to indentation
hardness
knoop hardness scale goes from what to what?
hardest material
softest material
0-600
softest: acrylic resin
hardest: dental porcelain
a measure of the consistency of a fluid and its inability to flow. it is a function of time that can be used to measure the working time of a material that undergoes a liquid-to-solid transformation
viscosity
the percentage of shrinkages or expansion of a material
