1. Mechanical properties of dental biomaterials 2

2. To Compare the properties of two materials:
Elastic Modulus of material (A) is higher than that of material (B)

3. # Strength = Height of the curveA B
# Stiffness (Rigidity) = Slope of the curve A B

4. # Ductility & FlexibilityA X Y Z X Y Z
# Resilience & Toughness = Area under the curve X Y Z X Y Z

5. # Ductility & FlexibilityA X Y Z X Y Z
# Resilience & Toughness = Area under the curve X Y Z X Y Z

6. Question?
Is rubber a rigid or a flexible material?
Which is stronger?
Glass
wax
stainless steel

7. Testing compressive strength of a material:
Specimen shape: Cylindrical
Type of force used: compression
Tester: Universal Testing Machine

9. Tensile strength testing:
Specimen shape: Dumble-shape
Type of force: Tension
Tester: Universal Testing Machine

11. Brittle materials:
They are materials which undergo fracture or rupture with little or no prior permanent deformation.
They are stronger under compression rather than tension.
Their tensile strength can be calculated using:
Diametral compression test. (Indirect tensile test)

12. Fig 15: A drawing to illustrate how compression force develops tensile stress in brittle material

13. Diametral compression test of brittle materials:
Specimen shape: Disk-shaped
Type of force applied: Compression
Resultant force: Tension
Tester: Universal Testing Machine
Stress = P Load
π D T Diameter X Thickness

15. Compression
Shear
Tension

16. Transverse strength - Modulus of Rupture: (3 point bending test)
It is the ability of a material to bend before it breaks.
Stress= 3 Load X Length
2 X Width X Thickness2
Strain= Load X Length3
4 Elastic Modulus X Width X Thickness3

17. Fig 16-a: Diagrammatic representation of a 3-point bending test or transverse test bending of the beam introduces both tensile and compressive stresses.

18. Impact strength
Materials such as glasses, ceramics, cements and amalgam have low resistance to breakage when a load is applied by impact. (dynamic load).

19. Denture mid-line fracture
Porcelain bridge fracture

20. The impact strength is defined as the energy required to fracture a material under an impact force.

21. Impact strength (Charpy tester)

22. Hardness:
It is defined as the resistance of a material to surface penetration or indentation.
There are four common standard test methods for expressing the hardness of a material: Brinell, Rockwell, Vickers, and Knoop.

23. HARDNESS
The property of hardness is of major importance in the comparison of restorative materials.
Hardness is defined as to resistance to permanent surface indentation or penetration.

24. 1. Brinell hardness test Indentor material: Tungestun or carbide
Shape of indentor: Sphere
Indentor material: Tungestun or carbide
Size of indentor: 1.6 mm in diameter
Type of indentor: Macro-indentor
Measurement: Depth of indentation

26. 2. Rockwell hardness test
Shape of indentor: Cone shaped
Indentor material: Tungestun or carbide
Size of indentor: 1.6 mm in diameter
Type of indentor: Macro-indentor
Measurement: Depth of indentation
Limitation:
Can not be used to test the hardness of brittle materials.

27. 3. Vickers Hardness Test Shape of indentor: Pyramid-shaped
Indentor material: 136 degree Pyramid
Type of indentor: Micro-indentor
Measurement: Diagonal of indentation

29. 4. Knoop hardness test Indentor material: Diamond
Shape of indentor: Pyramid-shaped
Indentor material: Diamond
Type of indentor: Micro-indentor
Measurement: The longer diagonal of indentation.

30. Shore A test Indentor material: Steel
Shape of indentor: Blunt pointed
Indentor material: Steel
Type of indentor: For rubber materials.
Measurement: The depth of indentation.

31. Why do we need to know the mechanical properties of the materials?
Human Dentin Density ~ 2.2E-9 Mg/mm3 Modulus of Elasticity 12 ~ MPa Yield Stress MPa
Cementing Agents – Zinc Phosphate Density E- 09 Mg/mm3 Modulus of Elasticity MPa Yield Stress  MPa
Aluminum Oxide Density E- 09 Mg/mm3 Modulus of Elasticity MPa Yield Stress   MPa

32. Questions:
1) If material (A) has a lower elastic modulus than material (B), then this means that:
Material (A) is more flexible than material (B)
Material (A) is less flexible than material (B)
Material (A) is more elastic than material (B)
Material (A) is less elastic than material (B)

33. Questions:
2) ____________ measures the resistance of a material to indentation
Tensile testing
Compressive testing
Hardness testing
Diametric compression

34. Thank you