Download - Mechanical Properties of Dental Materials
![Page 1: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/1.jpg)
Mechanical Properties of
Dental Materials
Resilience
AB
Str
ess
(Pa)
Strain
Resilience
AB
Str
ess
(Pa)
Strain
![Page 2: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/2.jpg)
Occlusal forces
• Average occlusal forces for fully dentate patients :
150 Newton in the anterior region to 500N in posterior region
• Maximum occlusal forces: different reports in the literature up to 3500N.
• The occlusal forces for edentulous patients 15% of dentate patients.
![Page 3: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/3.jpg)
Bulk Properties
![Page 4: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/4.jpg)
Stress
Force per unit area; a force exerted on one body
that presses on, pulls on, pushes against, or tends to invest,
compress another body; the deformation caused in a body by such a force;
an internal force that resists an externally applied load or
force. 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. GPT 2005, J Prosthetic Dentistry
Stress: Internal resistance to applied external force.
Stress= Force/Area
![Page 5: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/5.jpg)
Types of stresses
• Axial
Compressive
Tensile
![Page 6: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/6.jpg)
Types of stresses
• Non Axial Shear
Torsion
Bending
![Page 7: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/7.jpg)
Strain
• Strain: change in length per unit length when stress is applied; the change in length/original length
GPT 2005, J Prosthetic Dentistry
• Strain(ε)= Deformation/Original length
![Page 8: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/8.jpg)
Stress-Strain curve
Strain
Res
ilien
ceA
B
Str
ess
(Pa) Toughness
C D
![Page 9: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/9.jpg)
Resilience: the resistance of a material to permanent deformation
A: Proportional limit
Elastic limit
A
Str
ess
(Pa)
Strain R
esili
ence
A
Str
ess
(Pa)
Strain
![Page 10: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/10.jpg)
A: Proportional limit
• The greatest stress that a material will sustain without a deviation from the proportionality of stress to strain, below which no permanent deformation happens.
![Page 11: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/11.jpg)
Elastic limit
• The maximum stress that a material will withstand without permanent deformation.
![Page 12: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/12.jpg)
AB
Str
ess
(Pa)
Strain
Res
ilien
ce
AB
Str
ess
(Pa)
Strain
![Page 13: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/13.jpg)
B:Yield strength(YS)
• The stress at which a material exhibits a specified limiting deviation from proportionality of stress to strain
* YS indicates a degree of permanent deformation (usually 0.2%)
YS indicates a functional failure!!!
![Page 14: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/14.jpg)
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
AB
Str
ess
(Pa)
Strain R
esili
ence
AB
Str
ess
(Pa)
Strain
![Page 15: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/15.jpg)
Poisson’s ratio
• Ratio of lateral to axial strain within the elastic range
![Page 16: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/16.jpg)
Ductility and malleability
• Ductility: The ability of a material to be plastically deformed.
• Malleability: The ability of a material to be hammered or rolled into thin sheets without fractureing.
![Page 17: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/17.jpg)
Plastic deformation
Strain
AB
Str
ess
(Pa) Toughness
C D
![Page 18: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/18.jpg)
C: Ultimate strength
• Tensile or Compressive.
• The Ultimate strength: The maximum that a material can withstand before failure (tension or compressive).
it does give an indication of the needed thickness (cross section) of the restorations before failure.
![Page 19: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/19.jpg)
D: fracture strength
• The stress at which the material fractures.
![Page 20: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/20.jpg)
Toughness
• The resistance of a material to fracture
So what does yellow area under curve represent?
![Page 21: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/21.jpg)
Fracture toughness
• The amount of energy required for fracture.
![Page 22: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/22.jpg)
• Bond strength:
the bond strength between two dental materials.
Either tensile or shear
Fatigue bond strength?
![Page 23: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/23.jpg)
Bending and torsion
• Endodontic files and reamers
![Page 24: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/24.jpg)
Transverse strength
• Modulus of rupture or flexural strength
3- point bending test
![Page 25: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/25.jpg)
Fatigue strength
• Fatigue: Progressive fracture under repeated loading
• The importance of endurance limit?
Str
ess
(Pa)
Strain Cycles
Str
ess
![Page 26: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/26.jpg)
Fluid behaviour and Viscosity
• Viscosity: the resistance of a fluid to flow
• Viscosity= Shear stress/shear strain rate.
![Page 27: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/27.jpg)
Viscous fluids
She
ar s
tres
s
Newto
nian
Str
ess
(Pa)
Strain Shear rate
Pseduplasti
c
Dilata
nt
She
ar s
tres
s
The importance of thixotropic impression materials
![Page 28: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/28.jpg)
Creep and stress relaxation
• Creep is the increase in strain in a material under constant pressure.
Creep test is used for study of new amalgam materials
![Page 29: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/29.jpg)
Surface mechanical properties
![Page 30: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/30.jpg)
Indentation hardness
• Brinell hardness test. Ball,(steel or T carbide),
• Knoop hardness: Microindentation, pyramid shape.
• Vickers: 136 degrees diamond pyramid.
• Rockwell:metal cone.
• Shore A hardness for rubber
![Page 31: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/31.jpg)
Stress analysis
• Lab based studies.
• Photoelasticity
• Finite Element Analysis.
![Page 32: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/32.jpg)
Wear
• Loss of material due to contact between two surfaces
![Page 33: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/33.jpg)
Surface phenomena
• Atoms or molecules at surface different to bulk
Stainless steel Vs steel
Oxide layer
![Page 34: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/34.jpg)
Colloidal systems
• Two or more phases with one highly dispersed on the other.
Types:
* Sols and Gels
* Emulsions
![Page 35: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/35.jpg)
Gels
• Entangled framework of solid colloidal praticles in which liquid is tapped in the intestices in which liquid is trapped
![Page 36: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/36.jpg)
Emulsions
• A uniform dispersion of minute droplets of one liquid into another with the aid of emulsifier.
![Page 37: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/37.jpg)
![Page 38: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/38.jpg)
Surface tension and wetting
Θ Θ
High contact angle= less wetting
Low contact angle= better wetting
![Page 39: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/39.jpg)
Adhesion
• The bonding of dissimilar materials by either:
^ Chemical bonding (True) OR
^ Mechanical bonding (retention).
![Page 40: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/40.jpg)
Optical properties
• Basic colours:Red, Green and Blue.
Why only three??
HueChromaValue
Munsell colour system
![Page 41: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/41.jpg)
![Page 42: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/42.jpg)
Hue
• Basic colour
![Page 43: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/43.jpg)
Chroma
• Colourfulness OR saturation
![Page 44: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/44.jpg)
Value
• lightness
![Page 45: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/45.jpg)
Metamerism
When two colour samples match when viewed under one light source but not another.
Any significance in dentistry?
![Page 46: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/46.jpg)
Flouresence
• The emission of luminous energy by a material when a beam of light is shown on it.
What impact does this have in anterior restorations.
![Page 47: Mechanical Properties of Dental Materials](https://reader033.vdocuments.net/reader033/viewer/2022061604/56815968550346895dc6a6d2/html5/thumbnails/47.jpg)
Thermal properties
• Heat of fusion: melting or freezing heat.
• Coefficient of thermal expansion: of paramount importance in clinical dentistry, why???
• Glass transition temperature??? For non metallic structures; glasses and polymers