DMS Properties Flashcards
What are some examples of mechanical properties?
- tensile strength
- compressive strength
- shear strength
- young’s modulus (rigidity)
- hardness
- ductility
What are some examples of chemical properties?
- setting mechanism
- setting time
- corrosive potential
What are some examples of physical properties
- viscosity
- viscoelasticity
- thermal conductivity
- thermal diffusivity
- thermal expansion
- colour
- translucency
- surface texture
- density
- radiodensity
What is stress defined as?
force per unit area that is acting on a material
What is strain defined as?
fractional change in dimensions caused by force
What are the 3 principle types of stress?
- compressive
- shear
- tensile
What is compressive stress?
What is shear stress?
What is tensile stress?
What can compressive strength be defined as?
the compressive strength is the compressive stress required to fracture a material
What can tensile strength be defined as?
the tensile strength is the tensile stress required to fracture a material
What can shear strength be defined as?
The shear stress required to fracture a material
What region of this stress/strain curve is the linear elastic region?
The red region
This is the range that elastic deformation occurs - in this region, removal of the stress will result in the material returning to its original shape
What is Young’s Modulus?
Young’s Modulus is stress/strain in the linear region and is a measure of a material’s rigidity
What is the yield stress?
This is the stress at which plastic deformation begins (blue region)
It is when the curve begins to deviate from its linear path and has exceeded its elastic limit
What is the fracture strength?
This is the stress required to break the material
What is the ultimate tensile strength?
The maximum stress that the material can withstand (highlighted in yellow)
What is ductility and how is it calculated from a stress strain diagram?
- Ductility is the amount of plastic strain produced at fracture
- It is measured by drawing a line from the point of fracture which is parallel to the elastic region
What is the hardness test?
The hardness test measures the resistance of a material to an indenter or cutting tool
It provides an indication of the resistance of a materail to scratching or abrasion
What is creep?
Under the influence of a constant stress, materials can deform permanently if the load is applied for a long time, even though the stress on the material may well be below its elastic limit
This time dependent deformation of materials is known as CREEP and will eventually lead to the fracture of the material
What is viscoelasticity?
The property of a substance of exhibiting both elastic and viscous behaviour, the application of stress causing temporary deformation if the stress is quickly removed but permanent deformation if it is maintained
This is why we need to try to remove impression materials quickly
What is thermal conductivity?
The ease with which heat is transferred through a material
What is the thermal expansion?
How the material absorbs energy and expands when heated
Want it ideal to enamel and dentine because otherwise it can result in marginal gap formation and the breakdown of adhesive bonds –> microleakage
What is the clinical significance of thermal properties?
They can influence the sensation of hot and cold food
Can cause mechanical failure due to different expansion and contraction
What is corrosion?
Corrosion in the oral environment is either by chemical or electrochemical process through which a metal is attacked by natural agents, such as air and water, resulting in partial or complete dissolution, deterioration, or weakening of any solid substance
Which material has the greatest compressive strength?
Amalgam (500)
Composite after (300)
Glass ionomer the least (80-110)
Which material has the greatest tensile strength?
Amalgam (60)
Composite after (50)
GIC least
Which material has the greatest rigidity?
Amalgam (30)
Composite after (14)
GIC has a low modulus
Which material has the greatest hardness?
Amalgam (100)
Composite after (90)
GIC least
Which material has the greatest thermal expansion coefficient?
Amalgam and Composite are similar but composite has a much greater RANGE
- Amalgam = 22-28
- Composite = 25-68
- GIC = 10-11
- Ceramic = 8-14
- Gold alloy = 12-15
Which material has the greatest thermal conductivity?
Amalgam but this is NOT GOOD - metals genearlly have high thermal conductivities. Amalgam requires a LINING
Composite is LOW
