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Dental Materials > 2PropertiesOfMaterials > Flashcards

2PropertiesOfMaterials Flashcards

1
Q

*What is the formula for stress? What is the unit of measurement?

A

S=Force/Area…1 Newton/m^2= 1 Pascal

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2
Q

*What are the 5 types of stress?

A

1.Tension 2.Compression 3.Shear 4.Torsion 5.Bending

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3
Q

*What type of stress occurs when elongation forces are directed away from each other in the same straight line and the molecules resist being pulled apart?


A

Tension

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4
Q

*Which type of stress occurs when shrinkage forces are directed toward each other in the same straight line and molecules resist being forced more closely together.

A

Compression

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5
Q

*Which type of stress occurs when forces are directed parallel to each other NOT along the same straight line and one portion resists sliding past the other.

A

Shear

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6
Q

*Which type of stress occurs when there are twisting forces?

A

Torsion

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7
Q

*Which type of stress results from a bending moment?

A

Bending..haha. lol.

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8
Q

*What is Deformation caused by stress? How is it measured? What is the formula for deformation?

A

STRAIN…Measured unitless or as a %…Deformation=Deformation/Length

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9
Q

*What is the stress at which the material begins to function in a PLASTIC manner? Limited permanent strain HAS occurred…What is the % of permanent strain?

A

Yield Strength…0.2% permanent strain

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10
Q

*Is Permanent Deformation Constructive or DeStructive in the oral cavity?

A

It can be Destructive(crowns/partials) OR Constructive(ortho wires)!

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11
Q

*Where can I find Ultimate Strength on the Strain/Stress curve?

A

Ultimate Stress=Highest point on curve

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12
Q

*What is the max. stress that a material can withstand in tension?

A

Ultimate Tensile Strength

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13
Q

*What is the max. stress a material can withstand in

compression?

A

Ultimate Compression Strength

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14
Q

What’s another word for “permanent deformation”?

A

Failure

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15
Q

*Why is Yield Strength of greater importance then Ultimate Strength in dentistry?

A

Yield strength is an estimate of when a material will start to FAIL!

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16
Q

*What is the stress at which a brittle material fractures?

A

Fracture Strength

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17
Q

What is the term for a material that elongates excessively causing a reduction in stress before permanent deformation?

A

“Necking”

18
Q

*For most dental alloys and ceramics subjected to tension, the ______ _______ and ________ _______ will be similar.

A

Ultimate Strength and Fracture Strength

19
Q

*__________ –deformation that results from the application of TENSILE FORCE. Indicates the workability of alloy. Expressed as a ___.

A

Elongation….%

20
Q

Elongation: a gold alloy with 20% elongation would be considered _______, while a material with 1% elongation would be ________.

A

20%=Ductile, 1%=brittle

21
Q

*What is the measure of elasticity and represents the stiffness of a material within the elastic region… Namely the slope of the S/S curve in the elastic portion. WHAT IS another name for it?

A

Elastic Modulus (E)..Youngs Modulus

22
Q

________/__________ forces are responsible for the property of elasticity. The stronger the forces,
the more stiff or rigid the material.

A

Interatomic/intermolecular

23
Q

What is the formula for elasticity?

A

E=Stress/Strain

24
Q

*The higher the value of the _______ _______, the more stiff or rigid the material.

A

Elastic Modulus

25
Q

*What is resistance of a material to permanent deformation AND indicates the amount of energy needed to deform a material to the proportional limit AND is the area UNDER the elastic portion? WHAT dental material is it useful to evaluate?

A

Resilience…Ortho Wires and Springs

26
Q

*What is the resistance of a material to fracture AND indicates the amount of energy needed to cause fracture AND is the area under the elastic AND plastic area?

A

Toughness

27
Q

*What three things can you increase to increase TOUGHNESS?

A

1.Yield Strength 2.Ultimate Strength 3.Strain (All increase the area under the stress/strain curve)

28
Q

*_______ generally weaken a material and may result in fractures at stresses WELL BELOW the yield stress. Occurs more in _______ materials that have no ability to deform and redistribute stresses.

A

Defects…Brittle

29
Q

*Because tensile properties of BRITTLE materials are hard to measure the _______ ________ ______ is used. It’s a good test for brittle materials – amalgam, cements, ceramics, plaster, and stone.

A

Diametral Compression Test

30
Q

*What is unique about the plastic portion of the stress-strain curve for a Brittle material?

A

The plastic response is SMALL!

31
Q

What are the two important characteristics of Endo files?

A

Flexure and Torsion

32
Q

*______ _______ – the stress at which a material fails under repeated loading. Depends on the ________ of the load and the ______ of loadings.

A

Fatigue Strength…Magnitude…..Number

33
Q

*_______ _______ – stress at which the material can be loaded an infinit of times without failing.

A

Endurance Limit

34
Q

*What is the RATE of loading measured by? Think Impression materials! Hence: Materials with mechanical properties dependent on loading rate are termed ________.

A

ViscoElasticity….Viscoelastic

35
Q

*What is the Resistance of a fluid to flow? What is the unit?

A

Viscosity…Poise

36
Q

*What is the reduction in stress in a material subjected to constant strain (ortho bands)?

A

Stress Relaxation

37
Q

*What is the increase in strain in material under constant stress?

A

CREEP

38
Q

*What is resistance to tearing forces? Important for Polymers in thin sections and depends on the RATE of loading (rapid loading=higher values)

A

Tear Strength

39
Q

What is the loss of material resulting from removal and relocation of materials through the contact of two or
more materials?

A

Wear

40
Q

How does the Linear Thermal Coefficient of Expansion of Composite compare to Human Teeth?

A

Composite= 2-6x human teeth (WANT THEM TO BE CLOSE!)

Dental Materials (11 decks)

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