Quiz 1: Lecture 1+ 2 Flashcards
What is enamel made up of?
Rods and Interrods.
***Rod sheath= narrow space around 3/4 of each rod Keyhole shape
What is Intertubular dentin?
Structural component of the hydroxyapatite-embedded collagen matrix- bulk of the dentin
What is Peritubular dentin?
Limited to the lining of the tubular walls- little organic matrix densely packed w/ apatite crystals
What is the strongest and simplest bond within atoms?
Covalent;
Example 2 H+ bonds overlapping
What is the Biological type of properties for materials?
toxicity and sensitivity reactions that occur locally or systemically within associated tissues.
What is surface energy ?
A LOW surface energy liquid will readily spread over a HIGH surface energy substance
What is Wetability?
The measure of the affinity of a liquid for a solid as indicated by the spreading of a drop
What is Adsorption?
Dissilimar substance in intimate contact with the surface of a solid= adhere
**HIGH energy surfaces will adsorb molecules more readily than LOW energy surfaces
What is Absorption?
The uptake of a liquid by a bulk solid. The substance absorbed diffuses into the solid material
Describe the Biocompatibility usage test?
Material is placed in a situation identical to its intended clinical use. In animals or humans (clinical trials)
What is Microleakage?
Materials may not bond with sufficient strength to resist contraction on polymerization, wear, thermal cycling
What does the gap between the tooth and restoration allow?
Allows influx of materials that may irrigate the pulp
Acids used to remove smear layer are potential source of irritation.. Depends on:
1) ****Remaining Dental Thickness (RDT) - 0.5mm min
2) Strength of the acid
3) Degree of etching
How is stress measured?
The force & the area to which it is applied are measured and stress is calculated from the
RATIO OF FORCE PER AREA* (F/A)
What are the types of stress? Specifically Tension?
**Elongation!
Forces are directed away from each other in the same straight line
(Axial- Molecules resist being pulled apart)
What is Compression force?
***Shrinkage!
Forces directed toward each other in the same straight line
(Molec. resist being forced more closely together)
What is a Shear force?
Forces directed parallel to each other **NOT along the same straight line
(One portion resists sliding past the other)
What is a Torsion force?
Twisting forces
What is bending forces?
Results from a bending moment
What is Strain?
*****Deformation CAUSED by STRESS **
Deformation = deformation/length
What is the proportional limit?
The greatest stress sustained without deviation from the linear proportionality of the dress and strain
What is Elastic limit?
The greatest stress sustained without permeant deformation
Elastic deformation is __________?
***NON-permanent
Plastic deformation is __________?
**PERMANENT
What is Yield Strength?
The stress at which the material begins to function in a plastic manner. Limited permanent strain has occurred
Is Permanent Deformation a good or bad thing?
BOTH***
Destructively: filings, crowns, bridges, can be deformed casing improper occasion
Constructively: Ortho appliances adjustment to fix bite..etc
What is Ultimate Strength?
-Max stress that a material can withstand in tension or compression.
-Greatest stress occurs at the HIGHEST POINT
(center of graph (C)
What is Fracture Strength?
- Stress at which a brittle material fractures
- At the END of graph where it FAILS (BREAKS) (D )
What is Elongation?
-Deformation that results from the application of TENSILE FORCE
-Takes in the WHOLE CURVE
(***Indicates the workability of alloy)
What is Elastic Modulus? (Young’s Modulus)
- **The measure of elasticity
- **The HIGHER the value of E, the MORE STIFF/RIGID the material
(Represents the stiffness/rigid/flexible of a material within the elastic region)
What is Resilience?
- **Resistance of a material to permeant deformation
- The amount of energy needed to deform the material to theproportional limit
(Area under the Elastic portion)
What is Toughness?
- **The resistance of material to fracture
- **Indicates the amount of energy needed to cause fracture
- ** Combination of yield strength, ultimate strength, strain INCREASING any of these, INCREASES TOUGHNESS!
(-Area under the elastic & plastic area )
What is Fracture Toughness?
Fracture Mechanics- Characterizes the behavior of materials with cracks or flaws
What do Defects generally do to material ?
**Weaken material and may result in fractures at stresses well below the yield stress.
(larger the flaw, less stress need to create flaw)
What is Tensile properties of Brittle Materials ?
Tensile properties of brittle materials, hard to measure so **Diametral Compression Test
When creating “Compression strength” of brittle material, what is the pastil response like?
The plastic response is small
What is Fatigue strength?
The stress at which a material fails under repeated loading
***DEPENDS OF MAGNITUDE of the LOAD & the # of LOADINGS
What is Endurance Limit?
Stress at which the material can be loaded an infinite number of times WITHOUT FAILING
What is Viscoelasticity?
***RATE of LOADING is important for many materials. (alginate, elastomeric immersion materials, waxes, amalgam, polymers)
Materials with mechanical properties dependent on loading rate are termed?
***Viscoelastic
What is Viscosity?
-The resistance of a fluid to flow
***time and temp DEPENDENT
What is CREEP?
Increase in strain in material under constance stress (amalgam)
What is Tear Strength?
Resistance to tearing forces
rapid loading = higher value (less likely to tear
What kind of bonds to Ceramics have?
-Ionic bonds - crystalline (leucite) and amorphous (glass)
What kind of bonds do Metals have?
Metallic bonds- crystalline
What kind of bonds do Polmers have?
Molecular solids -covalent and secondary bonds
