Dental Biomaterials I - Mechanical Properties
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Questions and Answers

What role does rigidity play in the design of partial dentures?

  • It reduces the risk of material fatigue under stress.
  • It controls the stability of the entire design by influencing major connectors. (correct)
  • It enables more intricate designs to be employed effectively.
  • It allows for thicker sections to be used without compromising stability.

    • Which property best describes a material that exhibits large elastic strain under slight stress?

  • Flexibility (correct)
  • Hardness
  • Brittleness
  • Rigidity

    • What is ductility primarily associated with in materials?

  • Ability to resist shear forces
  • Ability to undergo permanent deformation under tensile stress (correct)
  • Ability to conduct heat efficiently
  • Ability to maintain shape under compression

    • Which method is NOT commonly used to measure ductility?

    <p>Tensile strength measurement</p> Signup and view all the answers

    Flexibility is crucial for which type of dental material?

    <p>Elastic impression materials</p> Signup and view all the answers

    How is percentage elongation calculated to measure ductility?

    <p>(Increase in length / Original length) × 100</p> Signup and view all the answers

    What is the primary characteristic of a stiff or rigid material?

    <p>Minimal elastic strain under applied stress</p> Signup and view all the answers

    What effect does a rigid base under a restoration have?

    <p>Improves the fracture resistance of the filling</p> Signup and view all the answers

    What does yield strength indicate in a material?

    <p>The stress at which a material starts to exhibit permanent deformation.</p> Signup and view all the answers

    Which property is most affected by the composition of the material?

    <p>Elastic modulus</p> Signup and view all the answers

    How is Young's modulus defined?

    <p>The ratio of stress to its corresponding strain.</p> Signup and view all the answers

    Which material property is considered more critical in dental restorative materials?

    <p>Yield strength</p> Signup and view all the answers

    What is the significance of the proportional limit in stress-strain relationships?

    <p>It shows the limit of elastic behavior before yielding begins.</p> Signup and view all the answers

    Which of the following best describes the nature of ultimate strength?

    <p>It signifies the maximum stress a material can withstand before fracture.</p> Signup and view all the answers

    What does a high value of elastic modulus indicate about a material?

    <p>It has strong interatomic or intermolecular forces and is rigid.</p> Signup and view all the answers

    Why is yield strength often prioritized over ultimate strength in functional applications?

    <p>Because it measures the stress before the ultimate failure point.</p> Signup and view all the answers

    What is the SI unit for force as defined in the content?

    <p>Newton (N)</p> Signup and view all the answers

    What does stress (σ) quantify in terms of mechanical properties?

    <p>Internal reaction to the external force</p> Signup and view all the answers

    Which of the following is NOT a characteristic of force?

    <p>Duration of application</p> Signup and view all the answers

    What type of stress occurs when forces act towards each other along the same straight line?

    <p>Compressive stress</p> Signup and view all the answers

    What is the formula to calculate stress (σ)?

    <p>σ = F/A</p> Signup and view all the answers

    Which of the following units is commonly used to report stress?

    <p>Mega Pascal (MPa)</p> Signup and view all the answers

    Which mechanical property is defined as the amount of force per unit area?

    <p>Stress</p> Signup and view all the answers

    What type of materials must withstand forces during restoration and mastication?

    <p>Restorative materials</p> Signup and view all the answers

    What does malleability specifically refer to in materials?

    <p>Ability to be shaped without breaking</p> Signup and view all the answers

    Which of the following statements correctly describes ductility?

    <p>Ductility impacts the workability of a material.</p> Signup and view all the answers

    In what way are brittle materials characterized?

    <p>They fracture at or near their proportional limit.</p> Signup and view all the answers

    Which dental material is mentioned as an example of a brittle material?

    <p>Ceramics</p> Signup and view all the answers

    How is resilience defined in the context of materials?

    <p>Ability to return to original shape after deformation.</p> Signup and view all the answers

    What distinguishes a tough material from a resilient material?

    <p>Tough materials can absorb energy without breaking.</p> Signup and view all the answers

    Which statement best describes the relationship between ductility and toughness?

    <p>Ductile materials are always tough materials.</p> Signup and view all the answers

    Which best describes the behavior of dental amalgam in terms of its mechanical properties?

    <p>It exhibits high compressive strength compared to tensile strength.</p> Signup and view all the answers

    What is the consequence of using softer surface materials for crown and bridge wax patterns?

    <p>They may lead to inaccuracies in the final restoration.</p> Signup and view all the answers

    Which hardness value indicates a natural tooth that should not be opposed by porcelain teeth?

    <p>KHN=340</p> Signup and view all the answers

    What is fracture toughness in the context of brittle materials?

    <p>The amount of energy required to break a material with pre-existing flaws</p> Signup and view all the answers

    What is the typical cause of mechanical wear in dental materials?

    <p>Aggressive tooth brushing.</p> Signup and view all the answers

    Which type of wear is specifically caused by excessive stresses in the cervical region during occlusal loading?

    <p>Pathological wear</p> Signup and view all the answers

    How do glass particles in composite resins affect fracture toughness?

    <p>They increase fracture toughness by preventing crack propagation</p> Signup and view all the answers

    What effect does high hardness in co-cr denture-base materials have on its surface?

    <p>It retains a mirror-like surface.</p> Signup and view all the answers

    What is the primary clinical significance of hardness in dental materials?

    <p>It influences the resistance to surface scratches and penetration</p> Signup and view all the answers

    Which type of wear is considered desirable during finishing and polishing procedures?

    <p>Wear in restorative materials</p> Signup and view all the answers

    What is a potential disadvantage of high hardness in co-cr denture-base materials?

    <p>It complicates the finishing and polishing processes</p> Signup and view all the answers

    Which of the following substances is an intrinsic cause of erosion?

    <p>Gastric acid</p> Signup and view all the answers

    What should denture-wearing patients avoid when cleaning their dentures?

    <p>Using hard bristle brushes</p> Signup and view all the answers

    What is the definition of friction as described in the content?

    <p>The resistance to the motion of materials over each other.</p> Signup and view all the answers

    What is the effect of adding zirconia particles to porcelain materials?

    <p>They increase fracture toughness by absorbing energy during crack propagation</p> Signup and view all the answers

    What can excessive hardness in dental materials lead to when opposed by softer materials?

    <p>Increased risk of abrasion of the opposing teeth</p> Signup and view all the answers

    Which of the following statements about surface mechanical properties is true?

    <p>They include hardness, wear, and friction properties</p> Signup and view all the answers

    Study Notes

    Dental Biomaterials I - Mechanical Properties

    • Mechanical properties deal with forces and their effects on dental materials.
    • Restorative materials must withstand forces during fabrication and mastication.

    Key Concepts

    • Force: An external action causing or tending to cause motion.

      • Unit: Newton (N), Kilogram (Kg), or Pound (Ib)
      • Characterized by magnitude, direction, and point of application
      • Can be static or dynamic

    • Stress (σ): Internal reaction to an external force, equal in intensity but opposite in direction.

      • Unit: MPa (megapascals) or GPa (gigapascals).
      • Calculated as force per unit area (σ = F/A).
      • Different types:
        • Compressive: Forces pushing together
        • Tensile: Forces pulling apart
        • Shear: Forces acting parallel but in opposite directions

    • Strain (ε): Change in length per unit length due to stress.

      • Unitless
      • Calculated as (change in length / original length)
      • Types:
        • Elastic strain: Temporary, material returns to original shape after stress removal
        • Plastic strain: Permanent, deformation remains after stress removal

    • Stress-Strain Curve: Graph of stress vs strain, showing material behavior under increasing load.

      • Proportional Limit (PL): Maximum stress where stress is directly proportional to strain.
      • Elastic Limit (EL): Maximum stress where material still returns to original shape. Above this point, permanent deformation occurs.
      • Yield Strength (YS): The stress at which a material starts to deform.
      • Ultimate Strength (US): The maximum stress a material can withstand before failure.
      • Fracture Strength (FS): Stress when a material fractures.

    • Elastic Modulus (Young's Modulus, E): Measures stiffness (rigidity) of a material in the elastic region.

      • Ratio of stress to strain in the elastic region (E = σ/ε)
      • Unit: MPa or GPa
      • High values indicate stiff materials, low values indicate flexible materials

    • Resilience: Energy absorbed by a material to the proportional limit, represented by the area under the elastic portion of the stress-strain curve.

      • Measured in energy/unit volume.

    • Toughness: Total energy absorbed by a material up to fracture, including the elastic and plastic areas in the curve.

      • Measured in energy/unit volume.

    Mechanical Properties (Detailed)

    • Flexibility: Large elastic strain with small stress.
    • Ductility: Ability to undergo permanent deformation under tensile force without fracture, measured by percentage elongation and reduction in area after fracture.
    • Malleability: Ability to undergo permanent deformation under compressive force without fracture.
      • Important in material shaping (e.g., metal forming).
    • Brittleness: Opposite of ductile, material fractures at or near the proportional limit with little or no permanent deformation.
      • Ceramics often display this characteristic; Dental amalgam has high compressive strength.

    Testing Methods

    • Diametral compression test: Used for brittle materials under compressive loading to determine tensile strength.
    • Transverse (3-point) bending test: Used for materials such as denture base resins and long span bridges to determine flexural strength.
    • Fatigue test: Used to determine fatigue behavior by exposing a specimen to alternating stresses. A stress- vs time curve (S-N) shows how material fails over repeated stress
    • Impact test (Charpy or Izod): Measures ability of material to withstand sudden impact. Useful for complete dentures.
    • Fracture toughness: Measuring a material's resistance to crack propagation.

    Clinical Significance

    • Material properties dictate their function in the oral environment.
      • Flexibility important for impression materials
      • High hardness prevents excessive wear.
      • Yield strength important for restorative materials and bridges.

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    Related Documents

    Dental Biomaterials I Lectures 3 & 4 PDF

    Description

    This quiz explores the mechanical properties of dental biomaterials, focusing on the impact of forces during their use. Key concepts include force, stress, and strain, along with their types and units. Test your understanding of these essential principles crucial for restorative dentistry.

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