Chapter 4 and 5 definitions Flashcards
Force
One body interacting with another generates a force
Constrained Force
Deformed change in shape
Free/ Non-Constrained Force
Results in movement or translation
Where are occlusal forces highest
posterior 3500 N
Force on bicuspids, canine, incisors respectively
300 N, 200 N, 150 N respectively
Good predictors of occlusal forces
low angles and square mandibular form= high occlusal forces
stress
when a force acts on a constrained body, the force is resisted by the body and the internal reaction is equal in magnitude and opposite in direction to the applied external force
All stresses can be placed into two categories
axial and shear
Tension
Results from two sets of forces being directed away from each other in the same strait line (stretch or elongate)
Compression
Result of two forces directed towards each other in the same strait line (compress or shorten)
Shear stress
two sets of forces directed parallel to each other, but not in the same strait line
(tends to resist sliding) ortho bracket
Torsion
results from the twisting of a body
Bending or Flex
results from applied bending movement
Strain
Each stress can produce a deformation in a body
Stress Strain curve
Stress X axis
Strain Y axis
stress-strain relationship= measure load and deformation and then calculate the corresponding stress strain
Elastic Deformation
from start to the proportional limit, where the material will regain its natural shape
Stress is linearly proportional to the strain
Plastic Deformation
from the proportional limit to the Failure point
failure point
where the material fails
Proportional Limit
PL = no permanent deformation of the material (elastic) (linear)
Elastic Limit
Is the maximum stress that a material will withstand without permanent deformation
Strain
Change in length (reported as percentage)
How do EL and PL differ
EL: deals with the proportionality of strain to stress in the structure
PL: describes the elastic behavior of the material
Yield Strength
The stress at which the materials begin to function in an aplastic manner
Ultimate Strength
The maximum strength something can withstand before failure (tension or Compression)
Fracture strength
Point at which a brittle material fractures (can result in necking)
Elongation
Deformation as a result of an application of tensile force
Elastic Modulus
ratio) (slope of the line is stress strain curve
The measure of elasticity of a material or the stiffness of a material within its elastic range
Poisson’s Ratio
In compressive loading, the increase in cross sectional within elastic range , the ratio of the lateral to the axial strain
Ductility
Its ability to be drawn and shaped into a wire by the means of tension
Malleability
The ability to be hammered and rolled into thin sheets without fracturing
Resilience
Resistance of a material to permanent deformation
area under elastic portion of Stress-strain
Toughness
Resistance of a material to fracture (total area under Stress strain curve)
Fracture Toughness
Ability to be plastically deformed without fracture
Viscoelastic
Materials with mechanical properties DEPENDENT on the loading rate with viscous and elastic behavior
Elastic
Materials with mechanical properties INDEPENDENT of loading rate
Viscosity
Viscous=Fluidity
the resistance of a fluid to flow
Creep Complience
Gives idea of elastic, viscous, and inelastic properties of material
Hardness
Resistance to permanent surface indentation of penetration
Friction
The resistance between contacting bodies when one moves relative to another
Wear
Loss of material resulting from removal and relocation of materials through the contact of two or more central materials
Wear types
adhesive: disruption of microjuntions
corrosive: physical removal of protective layer
surface fatigue: free particles with small areas of cont contribute to high localized stress
Abrasive: harder material cuts softer material
Colloid materials
Characterized by their high degree of microsegmentation, They consist of two or more phases
Adsorption
a liquid or gas adheres to the surface of a solid by attachment of molecules to decrease surface free energy
Absorbtion
substrate diffuses into the solid material
Surface Tension
is the contractive tendency of the surface of a liquid to resist its external force
Color
a physiological response to a physical stimulus
objective
Hue
The perceived color based on the wavelength of light
Value
The quality of lightness or darkness (white high value)
Chroma
The quality of a color’s purity
Metamerism
Have identical tristimulus values but different spectral energy distributions
Flourescence
the emission of luminous energy by a material when a beam of light is shone on it
Opacity
The property that prevents the passage of light through a material
Translucency
Property that permits the passage of light but disperses the light so objects cannot be seen through
Opalescent
Materials that are able to scatter shorter wavelength of light
Index of Refraction
the ratio of the velocity of light to its velocity in the medium
Heat of fusion
heat required to go from solid to liquid
Thermal conductivity
heat required to pass through a cross section that is 1 cm thick
Specific heat
amount of heat to raise 1 g 1 degree
coefficient of thermal expansion
The change in length per unit of length for a one degree C change in temperature
Electrical conductivity
The ability of a material to conduct an electric current
Dielectric Constant
A material that provides electrical insulation
Electromotive Force
The voltage developed by any source of electrical energy
Shear strength
Parallel opposing forces in a different plane
Torsion
shear stress and a rotation of the speciment
Fatigue Strength
Progressive fracture under repeated loading (applications to below its yield strength until fracture occurs
Fracture Toughness
Is a property which describes the ability of a material to contain a crack to resist fracture
Tear strength
The measure of the resistance of a material to tearing forces
hardness
The relative resistance of a material to denting, scratching or bending
Brinell Hardness
Circular indentation machine
Knoop Hardness Test
The diamond indentation
Height x Length
Vickers Hardness
Pyramid indenter, defined force, and measure surface area of the indentation
Nano Indentation
Smaller indenter to better test the micro structural constituents of a material (resin composite
Wear
The resistance to wear of the composite resins to abrasion depends on the nature of the filler particles
Setting Time
The time required for the reaction of the material to be completed
Working Time
Time after which the material cannot be manipulated without creating distortion in the final product
Dynamic mechanical analysis
These properties allow us to predict the strength and structure of the tested materials and their applicability to the clinic
Rheology
The study of deformation and flow of materials
Pycnometry
the technique used to determine material density
Polymerization Stress Test
Was developed to evaluate the stresses developed at the bonded interface due to resin composite polymerization while bonded to cavity walls
Composition of Dentin
50% mineralized apatite Crystals
20% water
30% collagen fibrils
Superficial Vs Deep Dentin
water content varies depending on dentin depth, deeper= more water content
