Mechanical Properties of Dental Materials

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Questions and Answers

What type of stress occurs when two forces are directed away from each other in a straight line?

  • Tensile stress (correct)
  • Flexural stress
  • Compressive stress
  • Shear stress

Which type of stress is characterized by forces directed toward each other?

  • Flexural stress
  • Compressive stress (correct)
  • Tensile stress
  • Shear stress

What mechanical property describes the internal reaction to an external force?

  • Stress (correct)
  • Strain
  • Strength
  • Stiffness

Flexural stress is associated with which type of loading?

<p>Bending loading (C)</p> Signup and view all the answers

Which material would have the highest compressive strength based on the provided examples?

<p>Amalgam (B)</p> Signup and view all the answers

Shear stress is primarily associated with which kind of forces?

<p>Forces directed parallel to each other (C)</p> Signup and view all the answers

Which property of a dental material is essential for it to withstand forces during its use?

<p>Mechanical properties (A)</p> Signup and view all the answers

Which type of stress involves sliding of molecules over each other due to the applied forces?

<p>Shear stress (D)</p> Signup and view all the answers

What is the term for the ability of a material to return to its original shape after the stress is removed?

<p>Elastic region (A)</p> Signup and view all the answers

What happens when stress is applied beyond the proportional limit?

<p>The material undergoes plastic deformation (D)</p> Signup and view all the answers

Which point on the stress-strain curve represents the maximum stress a material can withstand before failure?

<p>Ultimate strength (C)</p> Signup and view all the answers

What is Poisson's ratio for most materials?

<p>0.3 (B)</p> Signup and view all the answers

How is the modulus of elasticity calculated from a stress-strain curve?

<p>Stress / Strain (C)</p> Signup and view all the answers

Which material is likely to have the highest ultimate strength mentioned in the content?

<p>Co/Cr (A)</p> Signup and view all the answers

What does ductility refer to in terms of material properties?

<p>Ability to undergo permanent deformation under tensile stress (C)</p> Signup and view all the answers

What is the elastic region defined by on the stress-strain curve?

<p>Between points 0 and A (C)</p> Signup and view all the answers

What type of stress is exhibited on the outer surface of a metal piece being bent?

<p>Tensile stress (B)</p> Signup and view all the answers

Which of the following describes strain?

<p>The change in dimensions per unit length due to applied force (B)</p> Signup and view all the answers

What type of strain occurs when a material is returned to its original length after the applied force is removed?

<p>Temporary strain (A)</p> Signup and view all the answers

At which point on the stress-strain curve does the material reach the maximum stress without permanent deformation?

<p>Elastic limit (A)</p> Signup and view all the answers

What is the term for the shortening of a body in the direction of loading under compressive stress?

<p>Contraction (C)</p> Signup and view all the answers

Which statement is true regarding the proportional limit and elastic limit of a material?

<p>Both limits are identical in theoretical terms (C)</p> Signup and view all the answers

Which of the following materials has the highest percentage of strain mentioned in the examples?

<p>Stainless steel (B)</p> Signup and view all the answers

What is the definition of torsion stress?

<p>Force per unit area due to twisting of a body (C)</p> Signup and view all the answers

What property describes a material's ability to withstand permanent deformation under compressive stress without fracture?

<p>Malleability (A)</p> Signup and view all the answers

How is toughness defined in materials?

<p>Total work or energy required to break the material (B)</p> Signup and view all the answers

What does fatigue in materials refer to?

<p>Constantly applied stress below the proportional limit causing cracks (D)</p> Signup and view all the answers

Which of the following materials is considered the most malleable?

<p>Gold (A)</p> Signup and view all the answers

What does resilience measure in a material?

<p>Energy needed to deform the material to its proportional limit (B)</p> Signup and view all the answers

Transverse strength is particularly important for which application?

<p>Dental bridges (A)</p> Signup and view all the answers

Which testing method is used to measure the hardness of a material?

<p>Vickers test (A)</p> Signup and view all the answers

What type of material typically exhibits low impact strength?

<p>Brittle materials (C)</p> Signup and view all the answers

Flashcards

Stress

The force per unit area within a material caused by an external force.

Tensile Stress

Pulls a material apart.

Compressive Stress

Pushes a material together.

Shear Stress

Causes layers of the material to slide past each other.

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Flexural Stress

Bends a material, causing tensile stress on one side and compressive stress on the other.

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Torsional Stress

Twists a material.

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Strain (ε)

The change in a material's dimensions caused by an applied force. It has no units of measurement.

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Elastic Strain

Temporary, reversible deformation. The material returns to its original shape.

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Plastic Strain

Permanent, irreversible deformation. The material does not return to its original shape.

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Stress-Strain Curve (S-S Curve)

A plot of stress versus strain, which demonstrates a material's mechanical properties.

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Proportional Limit (Point A)

The maximum stress a material can sustain before its stress-strain relationship becomes non-linear.

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Elastic Limit (Point A)

The maximum stress a material can withstand before permanent deformation occurs.

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Elastic Region (0 to A)

The region where the material is elastic (reversible deformation)

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Plastic Region (A to D)

The region where the material deforms permanently.

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Ultimate Strength (Point C)

The maximum stress a material can withstand before failure.

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Fracture Strength (Point D)

The stress at which a material breaks.

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Modulus of Elasticity (Elastic Modulus)

A measure of a material's stiffness. Represents the slope of the linear (elastic) region of the S-S curve.

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Flexibility

The ability of a material to withstand elastic strain.

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Ductility

The ability of a material to withstand permanent deformation (plastic strain) under tensile stress without fracturing.

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Malleability

The ability of a material to withstand permanent deformation under compressive stress without fracturing.

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Brittleness

Opposite of ductility. Materials that fracture easily.

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Resilience

The amount of energy a material absorbs before reaching its elastic limit.

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Toughness

The amount of energy a material can absorb until fracture. Represents the area under the stress-strain curve.

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Fatigue

Fracture caused by repeated application of small stresses below the proportional limit.

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Transverse Strength

The strength of the middle of a beam supported at its ends. Important for dental bridges.

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Impact Strength

A material's ability to withstand sudden shock.

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Hardness

Resistance to scratching or indentation. Measured using a steel ball or diamond tip (Brinell, Rockwell, Vickers, Knoop). Higher numbers indicate harder materials.

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Brinell Hardness Test

A standardized test for hardness. Uses a steel ball, a diamond tip, or a Vickers pyramid indenter.

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Knoop Hardness Test

A standardized test for hardness. Uses a small diamond-tipped indenter.

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Study Notes

### Mechanical Properties of Dental Materials

  • Mechanical properties describe how dental materials respond to applied forces.
  • Important factors: stress, strain, strength, and stiffness
  • Stress is the force per unit area within a material caused by an external force.
    • Tensile Stress: Pulls a material apart. Examples: enamel (10 MPa), dentin (106 MPa), amalgam (32 MPa)
    • Compressive Stress: Pushes a material together. Examples: enamel (384 MPa), dentin (297 MPa), amalgam (388 MPa)
    • Shear Stress: Causes layers of the material to slide past each other.
    • Flexural Stress: Bends a material, causing tensile stress on one side and compressive stress on the other.
    • Torsional Stress: Twists a material.
  • Strain (ε) is the change in a material's dimensions caused by an applied force. It has no units of measurement.
    • Elastic Strain: Temporary, reversible deformation. The material returns to its original shape.
    • Plastic Strain: Permanent, irreversible deformation. The material does not return to its original shape.
  • Stress-Strain Curve (S-S Curve): Plot of stress versus strain, which demonstrates a material's mechanical properties.
    • Proportional Limit (Point A): The maximum stress a material can sustain before its stress-strain relationship becomes non-linear.
    • Elastic Limit (Point A): The maximum stress a material can withstand before permanent deformation occurs.
    • Elastic Region (0 to A): The region where the material is elastic (reversible deformation).
    • Plastic Region (A to D): The region where the material deforms permanently.
    • Ultimate Strength (Point C): The maximum stress a material can withstand before failure. Examples: acrylic (8000 PSI), Co/Cr (100000 PSI), stainless steel (15000 PSI).
    • Fracture Strength (Point D): The stress at which a material breaks.
    • Modulus of Elasticity (Elastic Modulus): A measure of a material's stiffness. Represents the slope of the linear (elastic) region of the S-S curve. Examples: enamel (84 GPa), dentin (17 GPa).
  • Flexibility: The ability of a material to withstand elastic strain.
  • Ductility: The ability of a material to withstand permanent deformation (plastic strain) under tensile stress without fracturing. Examples: gold (highly ductile).
  • Malleability: The ability of a material to withstand permanent deformation under compressive stress without fracturing. Examples: gold (highly malleable).
  • Brittleness: Opposite of ductility. Materials that fracture easily.
  • Resilience: The amount of energy a material absorbs before reaching its elastic limit.
  • Toughness: The amount of energy a material can absorb until fracture. Represents the area under the stress-strain curve.
  • Fatigue: Fracture caused by repeated application of small stresses below the proportional limit.
  • Transverse Strength: The strength of the middle of a beam supported at its ends. Important for dental bridges.
  • Impact Strength: A material's ability to withstand sudden shock.
  • Hardness: Resistance to scratching or indentation. Measured using a steel ball or diamond tip (Brinell, Rockwell, Vickers, Knoop). Higher numbers indicate harder materials. Examples: Brinell hardness number - acrylic (22), dentin (65), gold (250); Knoop hardness number - enamel (343), dentin (68), Co/Cr (391).

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