Crowns And Other Extra Oral Restorations Flashcards
What are the categories of materials available for crowns and other extra coronal Restorations
All metal
Ceramics
Metal ceramics
Resin composites
What are the different types of cement?
Conventional or adhesive
What are all metal Restorations
These include crowns onlays and shims
Do onlays rely solely on adhesive retention?
Yes
What alloys are used in all metal Restorations
Low conc of noble metals or entirely base metals
What factors influence alloy selection
Cost Castability and handling Physical properties Resin binding Corrosion and tarnish Biocompatibility
What is palladium
Palladium is a silvery white metal used to form a cheaper white gold. It was the fist noble metal used to form precious alloys Palladium silver Palladium silver gold Gold silver copper palladium Palladium copper Palladium tin
What does palladium look like
Palladium has a strong whitening effect which means that most of these alloys will have a silvery appearance unless the gold content is greater than 40% and the palladium less than 6%
What is the disadvantage of using palladium?
Unfortunately palladium and silver absorb oxygen with molten which can result in porous castings especially if casting buttons are reused
What effect does reducing the gold content have on the alloy
Owners the specific gravity (density) which may make casting less reliable than with high gold alloys
Why?
Because Less dense alloys have lower kinetic energy during casting which in turn reduces the penetration of moten metal into the mould.
Advantages of high gold alloys
High gold alloys have excellenr Corrosion resistance which implies that few metal ions are eluted from Restorations
Allergies are rare
Gold and palladium alloy key points:
Porous castings can result from _____
Some alloys especially those of low noble metal content are prone to ______
The potential for cheap alloys to cause a ____ reaction is unknown but must be kept in mind
Porous castings can result from reusing casting buttons
Some alloys especially those of low noble metal content are prone to Corrosion
Lichenoid
What base metal alloys are used to make indirect Restorations
Nickel chromium
Nickel chromium beryllium
Titanium
Pro gold
What are the most commonly used alloys
Nickel chromium and nickel chromium beryllium
Why is beryllium added
To improve the alloys physical properties: it’s used as a hardner grain structure refiner and to reduce the alloys fusion temperature
Why might some alloys contain molybdenum instead of beryllium
The concerns over health
All the base metal alloys have a higher modulus of elasticity than noble alloys?
True
What are the base metal alloys
Nickel chromium
Nickel chromium beryllium
Titanium
Pro gold
Is nickel chromium a base metal alloy used to make indirect restorations
Yes
What is the advantage of using base metal alloys over the precious metal alloys given the higher modulus of elasticity?
The advantage of using base metal alloy given the higher modulus of elasticity than noble alloys means they are more rigid
Which is helpful in preventing flexion of long span bridges
Why is rigidity in thin section necessary?
For adhesive Bridge frameworks and for adhesivelh retained shims used to restore the palatal surfaces of worn incisors
What advantage do base metal alloys with high modulus of elasticity have in resin bonded bridgework
It is possible with selected resin adhesives to obtain high bond strengths to the surface of the sandblasted alloy
Eg nery et Al reported a bond strength of 22 Mpa for a nickel chromium alloy bonded to dentine with AllBond2
True or false precious metal alloys have a lower bond strength than base metal alloys
True base metal alloys have a higher bond strength
True or false a good bond strength can be achieved between Ni Cr alloys and resin luring cements
True
Can Ni Cr alloys achieve a good bond strength with resin luring cements
Yes
Are Ni Cr alloys stuffer than most notable alloys
Yes
Why can Ni Cr alloys be used in slightly thinner section than other alloys
Ni Cr alloys are stigger than most noble alloys so can be used in thin section
Why is there a health concern with using some base metal alloys in fabricating indirect restorations?
Technicians and dentists possibly inhaling Ni Cr casting fumes or grindinf dust especially if the alloy contains beryllium
If the pt is sensitive to nickel what should be avoided
Using Ni Cr alloys should be avoided on pts 2ith hypersensitive to Ni
What is the concern with using nickel as a base metal alloy
Nickel is known to cause contact dermatitis
What are the health risks associated with beryllium
Acute: conjunctivitis dermatitis bronchitis
Chronic beryllium disease may not express itself for several years after exposure
What are the health risks of nickel
Dermatogical and lung problems
High levels of nickel or nickel compounds are carcinogenic
Tumous: rhabdomyosarcoma nasopharyngeal and lung carcinoma
What precautions can technicians and dentists take when working with beryllium and nickel
Ensure adequate exhaust and filtration system. So the grinding and cast fumes of beryllium are removed.
And when fitting a Ni Cr restoration use adequate aspiration during adjustment
What is the technical difficulty technicians have with base metal alloys
Basse metal alloys are hard to adjust and difficukt to finjsh
What is the percentage in the population of sensitivity to nickel
10-20% women
1-2% men
Titanium key points
Specialised casting requires what?
Restorations can alse be ____________ using spark erosion
Specialised casting requires an argon arc under vacuum
Restorations can also be electroformed using spark erosion
Cast post and cores key points
Avoid cheap alloys which may _________ or ________ _________
The alloy needs to have a high modulus of elasticity and high yield strength
Proper heat treatment ensures ________________________________
Cast post and cores::
Avoid cheap alloys which may corrode and cast poorly
The alloy needs to have a high modulus of elasticity and high yield strength
Proper heat treatment ensures a stiff post which is less likely to bend
What qualities are needed for materials used as cast post and cores
High modulus of elasticity
High yield strength
Proper heat tx to ensure stiff post less likely to bend
Corrosion resistant
What properties does titanium have?
Biocompatibility
Restorations can be either cast or electro formed (milling of titanium blank by spark erosion)
Casting requires high temp (1650¢) and a special magnesium investment
Must be cast under vacuum to prevent oxidation of titanium
What is required in the casting of magnesium
Hugh temperature 1650 degrees
Magnesium investment
Argon arc
What is ‘progold’
Like brass
Consist largely of copper zinc
So tarnishes easily
Does progold tarnish easily? Why
Yes because progold is an alloy like brass made from copper and zinc so tarnishes
What are the material requirements for cast post and cores
High hardness, proportional limit, ultimate tensile stength
Affordable
Easy Castability
Corrosion resistant
What allows a more rigid casting, capable of resisting distortion from occlusal forces
Proper alloy selection
Heat tx
Porosity within a cast post can result in
Post fracture with unfortunate consequences
Thin posts are more likely to suffer critical porosity than thicker ones
True or false: many gold alloys used for post and cores can be either soft or hard depending on heat tx
True
A soft post will ______&______ more easily under occlusal load than a hard one
Bend and break
How may labs unwittingly make a soft post
Quenching the hot casting ring to allow the investment to be easily removed
If this is done the casting must be heat treated according to manufacturers specifications
What is the usual temperature for heat treating gold alloys
400 degrees for 40 minutes
How can the need to heat tx be avoided
Allowing the casting ring to bench cool
Slowly to room temperature
True or false
Some of the alloys used for all metal Restorations can also be used as metal ceramic Restorations
True
What are dental ceramics
Porcelains consisting of oxides largely of metals and silica, and are essentially inert materials
Have a composite structure
Consist of a crystalline phase or phases within a glassy matrix
Can dental ceramics be affected by APF gel
Yes can be attacked by acidulated phosphate fluoride gel
Can ceramic Restorations break under occlusal load
Yes
Ceramics are susceptible to stress Corrosion
Slow crack growth
