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Mechanical properties of dental biomaterials 2
To Compare the properties of two materials:
Elastic Modulus of material (A) is higher than that of material (B)Elastic Modulus of material (A) is higher than that of material (B)
#Strength = Height of the curve
#Stiffness (Rigidity) = Slope of the curve
A
A
B
B
#Ductility & Flexibility
A B
X Y Z X Y Z
X Y Z X Y Z
# Resilience & Toughness = Area under the curve
#Ductility & Flexibility
A B
X Y Z X Y Z
X Y Z X Y Z
# Resilience & Toughness = Area under the curve
Question?
• Is rubber a rigid or a flexible material?
• Which is stronger? Glasswaxstainless steel
Testing compressive strength of a material:
• Specimen shape: Cylindrical
• Type of force used: compression
•Tester: Universal Testing Machine
Tensile strength testing:
• Specimen shape: Dumble-shape
• Type of force: Tension
• Tester: Universal Testing Machine
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)
Fig 15: A drawing to illustrate how compression force develops tensile stress in brittle material
Fig 15: A drawing to illustrate how compression force develops tensile stress in brittle material
Diametral compression test of brittle materials:
• Specimen shape: Disk-shaped
• Type of force applied: Compression
• Resultant force: Tension
• Tester: Universal Testing Machine
Stress = 2P Load π D T Diameter X Thickness
Compression
Tension
Shear
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
Fig 16-a: Diagrammatic representation of a 3-point bending test or transverse test bending of the beam introduces both
tensile and compressive stresses.
Fig 16-a: Diagrammatic representation of a 3-point bending test or transverse test bending of the beam introduces both
tensile and compressive stresses.
Impact strength
Materials such as glasses,
ceramics, cements and amalgam
have low resistance to breakage
when a load is applied by
impact. (dynamic load).
Denture mid-line fracture Porcelain bridge fracture
The impact strength is defined
as the energy required to
fracture a material under an
impact force.
Impact strength (Charpy tester)
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.
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.
1. Brinell hardness test• 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
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.
3. Vickers Hardness Test
• Shape of indentor: Pyramid-shaped• Indentor material: 136 degree Pyramid• Type of indentor: Micro-indentor• Measurement: Diagonal of indentation
4. Knoop hardness test
• Shape of indentor: Pyramid-shaped• Indentor material: Diamond• Type of indentor: Micro-indentor• Measurement: The longer diagonal of indentation.
Shore A test• Shape of indentor: Blunt pointed• Indentor material: Steel• Type of indentor: For rubber materials.• Measurement: The depth of indentation.
Why do we need to know the mechanical properties of the materials? Human Dentin
Density 2.1 ~ 2.2E-9 Mg/mm3Modulus of Elasticity 12 ~ 14000 MPaYield Stress 240 MPa
Cementing Agents – Zinc PhosphateDensity 3.94E- 09 Mg/mm3Modulus of Elasticity 13400 MPaYield Stress 6.9 MPa
Aluminum OxideDensity 3.72E- 09 Mg/mm3Modulus of Elasticity 14000 MPaYield Stress 352 MPa