Intro
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What is a CE mark
A mark indicating the material is safe
What restorative materials will we use
Amalgam Composites Glass ionomer cements Porcelain Compomers
What are the impression materials
Impression Compound Impression Paste Hydrocolloids -alginate Elastomers: -polysulphides -polyethers -silicones
What materials are metals and alloys
Amalgam Cobalt chromium Titanium Gold Stainless steel
What types of force are there
Compressive (down) Tensile (pulled) Shear (pushed from side)
What is the equation for stress
Force/unit area units = pascal
How is strain calculated
Change in length/original length x 100
What are the mechanical properties of enamel
Brittle Hard Strong Rigid
What is the typical biting force
500-700N
What are the retention properties of amalgam and composite
Amalgam - mechanical Composite - adhesive
What is abrasion resistance
ability to withstand surface layers being removed, so compromising surface integrity
What does hardness within a dental material allow for
Ability of surface to resist indentation
When a material gradually changes dimensions when forces are aapplied…
Creep
What causes fatigue within a material
Repetitive ‘small’ stresses causing the material to fracture
What is the difference between creep fatigue and deformation
Deformation is caused by stress alike fatigue however it results im permanent change to dimensions instead of fracture Creep also results in dimensional change but gradually due to repetitive small forces
What is DE-BOND
applied forces sufficient to break material-tooth bond
What is impact
Large sudden force which causes fracture
What causes most fractures
Fatigue- repeated loads are applied causing small flaws/cracks resulting in the risk of fracture under a small force
When is debonding used in dentistry
To remove orthodontic appliance, shear force is applied to separate bracket/bonding material from tooth surface
What are classed as mechanical properties
Hardness Brittle/ductile Flexible/rigid Stength
What are chemical properties
setting mechanism setting time corrosive potential
What are physical properties
viscosity thermal conductivity thermal expansion density radiodensity
Why is there little evidence for the performance of dental materials in vivo
Time-consuming Costly Limited in scope: retrospective/prospective