Materials Chapter 3 Flashcards
Define Mechanical Properties
mechanical properties describe a material’s ability to resist forces.
They are dependent on the amount of material and on the size and shape of the object
Ex. strength and stiffness
Define Chemical Properties
chemical properties describe the setting reactions as well as the decay of degradation of materials.
Ex. gypsum products set by a precipitation process, whereas dental composite polymerize
Biologic properties
the effects that the materials have on living tissue
What is density as it relates to dental materials?
the amount or mass of a material in a given volume
What does density depend on?
the amount of atoms that are present;
the higher the atomic number and more closely the atoms are packed together, the heavier an object will feel
Boiling and melting points are _______ properties of materials
physical
What is vapor pressure
a measure of a liquid’s tendency to evaporate and become a gas
as the temperature of a liquid increases, the vapor pressure also increases
Define thermal conductivity
the rate of heat flowing through a material
the measurement of thermal conductivity depends on the distance the heat travels
Define specific heat capacity
the amount of energy needed to raise the temperature of one unit of mass of that material by 1 degree celsius
What is heat of fusion
amount of energy required to melt a material
What is heat of vaporization
amount of energy required to boil a material
Define coefficient of thermal expansion
a measure of the change in volume in relation to the change in temperature
Define percolation
process of heating/cooling, and accompanying opening and closing of the gap
What does percolation result in?
micro-leakage, tooth sensitivity, and recurrent decay
What is galvanic shock?
it is why a new amalgam filling will hurt when its is touched with a metal fork
Define Viscosity
materials ability to flow;
it is temperature dependent
Define wetting
doing this to a surface with an adhesive material, such as a sealant, brings the material into intimate association with the surface so that chemical and micro-mechanical bonding can occur
How is hardness measured?
Hardness is measured based on the size of the indentation measured
What are Durometer measurements?
measures how deep a steel ball will sink into a soft material; used to measure the hardness of impression material
What is abrasion resistance?
the wear resistance of dental restorations to food, opposing teeth, and other dental materials
Goldilocks Principle
material that is not too hard, not too soft, but just right
Define solubility
the amount of a material that dissolves in a liquid, such as water
Define water sorption
materials that absorb water; many polymers absorb water over time and slightly swell as a result
Define force
the weight or load applied to an object
Define the color response.
a complex phenomenon that is a psychological response (brain processing stimulus) to a physical stimulus (light reaching rods and cones of eye)
Define elasticity
a measure of push or pull that changes the shape of an object
What is stress?
force divided by the area on which the force has been applied
Define strain
the change in length divided by the original length
(the longer an object is, the more it must be stretched)
stress= load/area
Modules of elasticity
characteristic of a material and its atomic bonds. The higher the modules of elasticity, the stiffer the material
the load (stress) and the length (strain) are proportional and always occur together
Example: Enamel’s modulus of elasticity is high, and a rubber band is low
What is elastic deformation
When a stress is removed and the object returns to its original length, the initial change in length is called elastic deformation
What is plastic deformation or permanent deformation
this occurs when an ortho wire bent to fit a patients mouth, force is placed on the wire beyond the point where it can return to its original shape
Define elastic limit, proportional limit, yield point
the point on the stress-strain plot at which the line starts to curve and plastic deformation begins
Define ultimate strength
the point at which the strength of the spring has been exceeded
What are the types of stress?
Compression- pushing or crushing
Tension- pulling
Shear- slip stress occurs when parts of an object slide past each other
Torsion- twisting force
Bending- combination of different types of stress
To function properly, a restoration must be hard, strong, and stiff enough to _______
withstand the forces of mastication
What is Poisson’s ratio?
the mechanical property that is the ratio of the strain in the direction of stress to the strain in a direction perpendicular to the stress
Define resilience
the ability to absorb energy and not become absorbed
Define toughness of materials
the energy absorbed up to the failure point on the stress-strain diagram
Define fracture toughness
the measure of the energy required to fracture a material when a crack is present
glass and porcelain have a low fracture toughness value whereas metals have a high fracture toughness value
Define fatigue
the failure of an item after repeated use
Define creep
it is the small change in shape that results when an object is under continuous compression
a very slow flow; amalgam or composite
Define stress relaxation
slow decrease in force over time
A drop of water on a popsicle is an example of
a. poor wetting (low contact angle)
b. Good wetting (high contact angle)
c. Good wetting (low contact angle)
d. Poor wetting (high contact angle)
c. Good wetting (low contact angle)
Good wetting indicates that the adhesive is in very close contact with the adhered, forming a low contact angle.
Poor wetting “stays as a drop: and a big contact angle is formed
The tightening of a guitar string is an example of which of the following stresses?
a. compression
b. torsion
c. Shear
d. Tension
d. Tension
Tension is a pulling or stretching stress, which many times is referred to as tensile stress.
Compression is a crushing or pushing force.
Torsion is a twisting stress
Shear is a sliding stress
The modulus of elasticity is an indication of what property of a material?
a. resilience
b. strength
c. stiffness
d. tension
c. Stiffness
The higher the modulus of elasticity, the stiffer the material.
The modulus is a measure of flexibility. A rubber band has a low modulus, a mouth mirror has a high modulus
Resilience is the ability of a material to absorb energy without deforming, whereas toughness is the ability of a material to absorb energy up to and include failure or fracture.
Cooled Materials will contract and heated materials will expand. A measurement of this change in volume in relation to change in temperature is called the coefficient of thermal expansion.
a. there first statement is true, the second it false
b. the first statement is false, the second statement is true
c. both statements are true
d. both statements are false
c. .Both statements are true
Nearly all materials will contract when called and expand when heated. Measuring this change in size in relation to the change in temperature is called the coefficient of thermal expansion. In dentistry, this property holds importance because, ideally, the tooth structure and the restorative material should expand and contract by the same amount
When a stress is induced in a material that is greater than the material’s yield strength, the stress is ______________ proportional to the strain, and the material does not return to it’s original shape.
a. always
b. no longer
c. equally
d. None of the above
b. no longer
remember that you cannot have stress without strain. They occur together
when they are proportional, as illustrated on a graph, it is a straight line
As we increase the load, eventually, the spring will not go back to the original length. This stress is no longer proportional to the strain
we have reached the yield strength on the graph and the line begins to curve
Which formula defines the modulus of elasticity?
a. stress/strain
b. stress 2/strain
c. strain/stress
d. 2 x stress/strain
a. stress/strain
the modulus of elasticity is defined as the stress divided by the strain in the linear portion of the stress strain graph
An example of a physical property is:
a. density
b. strength
c. stifness
d. setting reaction
a. density
other examples of physical properties are color and thermal conductivity
strength and stiffness are mechanical properties, and setting relations are chemical properties
A twisting force is termed
a. compression
b. shear
c. tension
d. Torsion
e. Bending
d. torsion
torsion is twisting stress, such as turning a door knob
shear stress occurs when parts of an object slide past each other
tension is pulling stress
bending is a combination of compression, tension, and shear stresses
The ability of a material to dissolve in liquid is termed:
a. viscosity
b. water sorption
c. solubility
d. wetting
c. solubility
solubility is calculated as the amount of material that dissolves in a given time.
viscosity is the ability of a material to flow.
water sorption is the ability of a material to absorb water
wetting is the interaction of a liquid with the surface
Elasticity is an example of which of the following properties?
a. physical
b. mechanical
c. chemical
d. biological
b. mechanical
Mechanical properites include stress, strain, resilience, toughness, fatigue, and elasticity, to name a few
physical properties include thermal conductivity, heat capacity, vapor pressure, viscosity, hardness, and many more
chemical properties describe setting reactions and decay and degradation.
biologic properties are the effects materials have on living tissue
Elasticity is an example of which of the following properties?
a. physical
b. mechanical
c. chemical
d. biological
b. mechanical
Mechanical properties include stress, strain, resilience, toughness, fatigue, and elasticity, to name a few
physical properties include thermal conductivity, heat capacity, vapor pressure, viscosity, hardness, and many more
chemical properties describe setting reactions and decay and degradation.
biologic properties are the effects materials have on living tissue
Jennifer is a practicing hygienist who goes to a nearby restaurant each day for lunch. She often orders a cola with ice and a bowl of homemade soup. As she eats and drinks her composite restorations (tooth colored) and tooth structure are expanding and contracting at different rates. This change in volume or length of these materials due to the hot food and cold drink is referred to as?
a. heat of fusion
b. coefficient of thermal expansion
c. heat capacity
d. thermal conductivity
b. coefficient of thermal expansion
Fingernal polish remover has “solvent” properties as it will remove the polish from our fingernails. Another property polish remover has is it’s tendency to evaporate. Fingernail polish remover can be said to have:
a. high vapor pressure
b. a low vapor pressure
c. no vapor pressure
d. an intermitten vapor pressure
a. high vapor pressure
14-16:
Match the properties listed below with the procedure or situation in question:
a. solubility
b. compression
c. stress concentration
d. viscosity
14. ________________ is the force used to condense an amalgam in a preparation
15. A hardened cement having “low” _________ can firmly hold a patient’s gold crown in place for years in a wet environment
16. _________ is the term given to the incerase of stress around defects within an object
- b. compression
- a. solubility
- c Stress concentration
