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Mechanical Properties of Dental Materials -- Part 1

Mechanical Properties of Dental Materials -- Part 1. Dr. Raghuwar D Singh Associate Professor. Prosthodontic Department King George’s Medical University UP, Lucknow. Dental Materials:. Properties of Dental Materials – Physical, Mechanical Biocompatibility

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Mechanical Properties of Dental Materials -- Part 1

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  1. Mechanical Properties of Dental Materials --Part1 Dr. Raghuwar D Singh Associate Professor Prosthodontic Department King George’s Medical University UP, Lucknow

  2. Dental Materials: • Properties of Dental Materials – Physical, Mechanical • Biocompatibility • Micro structure of metal alloys • Impression materials • Gypsum product • Dental Resins – Denture base and Restorative Resin • Dental Amalgam • Dental Cements • Direct filling Gold • Dental casting alloys • Finishing and polishing materials • Dental Ceramics

  3. Mechanical Properties of DM • Mechanical Properties: • Stress • Strain • Mechanical Properties based on elastic deformation: • Stress- Strain diagram/ curve • Modulus of elasticity • Poisson’s ratio • Flexibility • Resilience

  4. Strength Properties: • Proportional limit • Elastic limit • Yield strength • Diametral tensile strength • Flexural strength • Fatigue strength • Impact strength

  5. Other Mechanical properties: • Toughness • Fracture toughness • Brittleness • Ductility and Malleablility • Hardness

  6. STRESS • Force per unit area; Stress= Force/Area • It is normally defined in terms of mechanical stress, which is the force divided by the perpendicular cross sectional area over which the force is applied.

  7. Stress: Internal resistance to applied external force.

  8. Types of stresses:

  9. Types of stresses.... • Axial Compressive Stress- Tensile Stress-

  10. ....Types of stresses • Non Axial • Shear – Tends to resist the sliding of one portion of a body over another. • Torsion • Bending

  11. Flexural Stress: Bending forces

  12. STRAIN • Strain: change in length per unit original length when stress is applied; = Length / Original length • Strain(ε)= Deformation/Original length

  13. Elastic Strain • Plastic Strain

  14. Mechanical Propertied based on Elastic deformation • Stress- Strain diagram/ curve • Modulus of elasticity • Poisson’s ratio • Flexibility • Resilience

  15. D C B A Toughness Stress (Pa) Resilience Strain Stress-Strain curve

  16. B B A A Stress (Pa) Stress (Pa) Resilience Strain Strain

  17. B B A A Stress (Pa) Stress (Pa) Resilience Strain Strain ELASTIC MODULUS • Is a measure of elasticity of the material: how stiff the material is in the elastic range. • Elastic modulus= Stress/Strain • The slope of the curve

  18. ...ELASTIC MODULUS

  19. POISSON’S RATIO • Ratio of lateral to axial strain within the elastic range. • For an ideal isotropic material of constant volume the ratio is 0.5. • Most material have values of 0.3.

  20. FLEXIBILITY • Ability of a material to return to its original form indicates its elasticity, but the strain taking place at elastic limit is known as flixibility. • Flexibility is bending capacity. • It can be defined as the strain that occurs when the material is stretched to its proportional limit.

  21. RESILIENCE • Defined as the amount of energy absorbed within a unit volume of a structure when it is stressed to its proportional limit. • The property if often described as “springback potential.”

  22. A A Stress (Pa) Stress (Pa) Resilience Strain Strain • Resilience: • The resistance of a material to permanent deformation. • Proportional limit • Elastic limit

  23. STRENGTH PROPERTIES • Proportional limit • Elastic limit • Yield strength • Diametral tensile strength • Flexural strength • Fatigue strength • Impact strength

  24. Strength properties: • Strength is the stress that is necessary to cause fracture or a specified amount of plastic deformation.

  25. PROPORTIONAL LIMIT • It is defined as the greatest stress that a material will sustain without a deviation from the linear proportionality of stress to strain.

  26. ELASTIC LIMIT • The maximum stress that a material will withstand without permanent deformation.

  27. YIELD STRENGTH • Defined as the stress at which a material exhibits a specified limiting deviation from proportionality of stress to strain. • It is the amount of stress required to produce a predetermined amount of permanent strain usually 0.1% or 0.2% which is called the Percent Offset.

  28. For brittle materials such as composites and ceramic – Yield strength can not be measure. • YS indicates a degree of permanent deformation (usually 0.2%) Continue……

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