Porcelain fused alloys BDS3
No description yet. This curated deck is ready for daily study.
Card preview (21)
Why do porcelain fused to metal alloy restorations exist
Porcelain has good aesthetics but poor mechanical properties The bonded alloys have good mechanical properties
What does a material with a large area between the proportional limit and fracture stress indicate
Ducility short distance between PL and FS is a brittle material
What is compressive strength
Stress to cause fracture
What is the elastic modulus
stress/strain ratio
What are porcelains mechanical properties
Hard Brittle Strong Rigid
What are Alloys mechanical properties
Hard Strong Rigid Ductile
What does an alloy do
Acts as support and limits the strain that porcelain experiences
What binds the metal and porcelain
Metal oxide
What alloys does porcelain bond to
High gold alloy Low gold alloy Silver palladium Nickel chromium Cobalt chromium
What are the required properties of an alloy
Forms good bond to porcelain Similar thermal expansion coefficient Avoid discolouration of porcelain High elestic modulus, bond strength, hardness Higher melting, recrystallisation points than porcelain to avoid creep
What is creep
Gradual increase in STRAIN (permanent) experienced under prolonged application of STRESS (< EL)
Why is Cu not used in alloys
Causes green hue imparted to porcelain
What are negatives of high gold alloys
Melting range may be too low Young’s modulus too low
What is the make-up of low gold alloys
Au - 50 Pd - 30 Ag - 10 Indium, tin - 10
What are silver palladium alloys made up of
Pd - 60 Ag - 30 In, Sn - 10
What properties do silver palladium alloys have
High melting point Care needed in casting
What are the properties of a nickel chromium alloy
High melting point High young’s modulus High casting shrinkage Low-ish bond stength
What do nickel chromium alloys consist of
Ni - 70-80 Cr - 10-25
What makes cobalt chromium alloys suitable
High melting point Casting shrinkage Lowish bond strength High young’s modulus High tensile strength High hardness
What failure modes are there
Broken in porcelain - acceptable Broken at the meet of porcelain and metal oxide Broken between the metal oxide and alloy Metal oxide is broken in 2
What alloy has the most desirable properties
Low gold alloys: Castable Low creep Elastic modulus Bonding Bio-compatability