Exam 1 Flashcards
Define intertubular dentin:
Structural component of the hydroxyapatite-embedded collagen matrix
Bulk of the dentin
Define peritubular dentin:
Limited to lining of the tubular walls
Little organic matrix densely packed with apatite crystals
What type of bonds at are the strongest and simplest?
Covalent bonds
What is the relationship between surface energy of a liquid and its ability spread?
A low surface energy of a liquid allows it to readily spread over a high surface energy subtrate
Define wettability:
The measure of the affinity of a liquid for a solid as indicated by the spread of a drop
Define adsorption:
Dissimilar substances in intimate contact with the surfaces of a solid adhere
Define absortion:
The uptake of a liquid by a bulk solid.
The substance absorbed diffuses into the solid material
What is the usage test in a biocompatibility test?
Usage tests are where materials are placed into a situation identical to its intended clinical use
Define microleakage:
Occurs when material may not bond with sufficient strength to resist contraction on polymerization, wear, thermal cycling
What can occur with microleakage?
Gap between tooth and restoration allows influx of materials that may irritate pulp
What is RDT and what is it’s desired value?
Remaining Dentinal Thickness; preferred 0.5 mm minimum
Define stress:
Ratio of force per area (F/A)
Define Tension:
Elongation forces directed away from each other in the same straight line
Define Compression:
Shrinkage forces directed toward each other in the same straight line
Define Shear:
Forces directed parallel to each other not along the same straight line (one portion resists sliding past another)
Define Torsion:
Twisting forces
Define Bending:
Results from a bending movement
Define Strain:
Deformation caused by stress
How do you mathematically define strain?
Deformation = deformation/length
Define proportional limit:
The greatest sustained stress without deviation from the linear proportionality of stress and strain.
What axis is stress and strain located on?
Strain is on the X axis and stress is on the Y axis
Where is irreversible strain found on a graph?
Below A
What is the elastic region (E)?
The region below A where reversible strain occurs
What is the plastic region?
The region above A where strain is irreversible or permanent
What is the elastic limit?
The greatest stress sustained without permanent deformation. Can also be termed proportional limit.
Define yield strength:
The stress at which the material begins to function in a plastic manner. Limited permanent strain has occurred. Amount of permanent strain is given by an arbitrary 0.2%.
Define Ultimate Tensile Strength (UTS):
Maximum stress that a material can withstand in tension
Define Ultimate Compression Strength (UCS):
Maximum stress that a material can withstand in compression
Define Fracture Strength (Sf):
Stress at which a brittle material fractures.
What is true of US and Sf for alloys and ceramics?
US and Sf tend to be equal for alloys and ceramics
Define Elongation:
Deformation that results from the application of tensile force. 0-A = below proportional limit = deformation not permanent A-D = plastic elongation = permanent deformation
What does elongation signify?
The workability of an alloy
Greater elongation signifies what?
Ductility
Shorter elongation signifies what?
Brittleness
Define Elastic Modulus or Young’s Modulus (E)
Measure of elasticity. Represent the measure of stiffness of a material within the elastic region. The slope of the S/S curve in the elastic region.
What forces are responsible for the property of elasticity?
Interatomic/Intermolecular forces. The stronger the forces the greater the stiffness/rigidity
What E value would you expect of Elastomers/Polymers versus Metals/Ceramics?
Low versus high
Define resilience:
Resistance of a material to permanent deformation. Area under the elastic portion that indicates the amount of energy needed to deform a material to the proportional limit.
Define toughness:
Resistance of a material to fracture. Indicates the amount of energy needed to cause fracture. Signified by the area under the elastic and plastic area.
Define fracture toughness:
Defects generally weaken a material and may result in fractures at stresses well below the yield stress. Larger the flaw the less stress is needed to cause fracture.
Define the diametral compression test
The diametral test uses compression to produce tensile forces. Load is increased until fracture occurs. Good test for brittle materials. Used because tensile properties of brittle materials are hard to measure.
Which is a smaller property in brittle material Elastic or Plastic?
Plastic
Define fatigue strength:
The stress at which a material fails under repeated loading. Depends on magnitude of the load and the number of loadings.
Define endurance limit:
Stress at which the material can be loaded an infinite number of times without failing.
Define viscoelasticity:
Rate of loading. Increasing the loading rate produces different S/S curves with higher values for E, PL, US.
Material with mechanical properties dependent on loading rate are termed what?
Viscoelactic
What two properties do viscoeleastics have?
Properties of elastic solids and viscous fluids.
Define viscosity:
The resistance of a fluid to flow. Units of viscosity = Poise or centipoise
Define stress relaxation:
Reduction of stress in a material subjected to constant strain (ortho bands)
Define creep:
Increase in strain in material under constant stress (amalgam)
Define tear strength:
Resistance to tearing forces. Important for polymers in thin sections. Depends on rate of loading. Rapid loading = Higher Values
