Structure And Properties Flashcards
Dental composite definition
Combination of materials in which the individual retain their identity and which possess different properties to the components acting alone
What are fibre reinforced materials?
Type of composite consisting of fibres of a high strength and modulus bonded/embedded to a matrix
The medical devices directive says that u must offer to a patient receiving dental appliance what?
Statement of manufacture
Statement of manufacture must contain 5 things
- Patients name and confirmation appliance is for them
- Prescribers name and registered address
- Technicians name and registered address
- Description of appliance
- Confirmation that is meets legal requirements
Dental materials must meet standards from? 2
BSI - British standards institute
ISO - international standards organisation
The Instron universal testing machine tests which mechanical properties? 4
Tensile strength
Compressive strength
Diametral tensile strength
Flexural strength
How is tensile strength tested?
Pulling force applied to elongate rod, rod is stretched till it breaks at a force F newtons
Why is the compressive strength test not recommended for some materials?
Causes premature cracks leading to premature failure in brittle materials
Draw diametral tensile strength test using instron universal testing machine
What material is the diametral tensile strength test used for?
Brittle materials
Draw the flexural strength test using instron universal testing machine
What is this point?
Yield
Point at which the specimen begins to get disrupted, the specimen can withstand everything up until this point
What is this point?
Fail
After it has failed as the mechanism isn’t fast enough to record fail
What is this point?
Ultimate tensile strength
The specimen fails
What does modulus mean?
The stiffness of a material
How do u calculate modulus using the graph?
Stress/strain (in the linear region of graph)
What is ductility?
The ability of the material to be drawn out into a wire
How do you calculate ductility using the graph?
Extend the linear line and move across till it touches F
What is resilience?
Energy absorbed by the material in undergoing plastic deformation up to the elastic limit
How do you calculate resilience using the graph?
What is toughness?
Total amount of energy a material can absorb up to the point of fracture
High value = tough
Low value = brittle
How do u calculate toughness on this graph?
What is fatigue?
Application of cyclical on/off loading for a defined number of cycles
Do you understand this graph showing fatigue?
What is used to measure the surface hardness of a material?
Hardness microscope
How does the hardness microscope measure surface hardness?
Apply and indent or under a load onto a material
Measure the height and width
Look up in book to get hardness number
A large hardness number means?
A small hardness number means?
Large = low hardness
Small = high hardness
What hardness microscope makes this shape?
Vickers
What hardness microscope makes this shape?
Brinell
What hardness microscope makes this shape?
Knoop
How does the shear bond strength test work?
2 materials stuck together
Try to separate by shearing (sliding) them apart
In the shear bond strength test what does adhesive failure mean?
The two materials are separated completely
In the shear bond strength test what does cohesive failure mean?
The union remains intact but the force has caused one of the materials to fracture separating them
How does the impact strength test work?
Pendulum swings and fractured the specimen, the pendulum continues its swing round
The lower the pendulum swings after fracture the greater the impact strength as more energy is consumed by the specimen
How does the surface roughness test work?
Profilometer runs along the surface
Measures the Ra (mean deviation of the surface profile)
Higher Ra means rougher material
What three things r calculated in the thermal properties test?
Thermal conductivity (K)
Specific heat capacity (Cp)
Thermal diffusivity (D)
What is thermal conductivity (K)?
Rate of heat transfer through a material
What is specific heat capacity (Cp)?
Energy required to heat up a material
What is thermal diffusivity (D)
The rate that temperature will rise within a material when heat is applied to its surface
What is the rheological properties test?
Study of viscosity and how it varies with
Rate of shear ( how fast push plunger down)
And time
For rheological properties test
Viscosity is proportional to what? 2
Pressure / speed
What is this type of material?
Dilatant material
What is this type of material?
Newtonian material
What is this type of material?
Pseudoplastic material
What happens to viscosity in dilatant material?
Viscosity increases with applied pressure
What happens to viscosity in Newtonian material?
Viscosity remains constant with applied pressure
What happens to viscosity in pseudoplastic material?
Viscosity decreases with applied pressure and, unless setting, increases when pressure decreases
Remember this
Thermal expansion and contraction of a material must match as closely as possible to tooth surface being replaced
What are the 2 chemical properties that are tested for a material?
Corrosion
Solubility parameter
What is corrosion?
Chemical reactivity of metals and alloys
An electrolytic property (conducts electricity)
What is Solubility parameter
Solutions used to simulate various foods in a laboratory
To test biological properties
Testing occurs at what 3 levels
Laboratory screening
Limited laboratory in Vivo usage testing
Human randomised controlled clinical trial
What does laboratory screening assess? 3
Acute systemic toxicity
Irrational potential
Carcinogenic potential
