DMS - Ceramics Flashcards
In comparison to non-dental ceramic; what is removed from dental ceramics and why?
kaolin is removed as they make the ceramic opaque
what is kaolin replaced by in dental ceramics? (2)
kaolin is replaced with feldspar and silica.
what is the function of feldspar added to the dental ceramics? (2)
Lowers the fusion and softening temperatures of the glass
what is the binder used in dental ceramics?
starch
what colour of ceramic does chromium and copper (metal oxides) produce?
green
what colour of ceramic does cobalt (metal oxides) produce?
blue
what colour of ceramic does iron and nickel (metal oxides) produce?
brown
what colour of ceramic does manganese (metal oxides) produce?
purple
how are conventional dental ceramics produced?
Sintering
describe sintering.
Not a chemical reaction its just a process where the particles melt together to create a single mass of ceramic
where can conventional dental ceramics only be used due to their low tensile, flexural and fracture toughness.
anterior teeth which do not load bear
what are the properties of conventional dental ceramics. (4)
desirable aesthetics stable chemical properties dimensionally stable once fired (made) High compressive strength High hardness Slow crack growth
how much shrinkage is there of dental ceramics during firing?
20%
What problems are associated with the high hardness of dental ceramics?
can cause abrasion to opposing teeth especially if not glazed
describe what occurs to dental ceramics in aqueous environments - why?
Decrease in strength over time (even when not load bearing) this is due to hydrolysis of Si-O groups
how do we increase the strength of conventional dental ceramics? (3)
Produce a coping that is resistant to fracture and then cover with ceramic
Press a block of harder ceramic
Mill a laboratory prepared block of ceramic
what copings can we used beneath dental ceramics? (3)
Metal coping
Alumina core
Zirconia core
what are the advantages of alumina core ceramics? (3)
Double the flex strength > 120Mpa of conventional ceramic
Alumina particles act as crack stoppers and prevent cracks propagating through the material - more alumina increases strength
Cheap
No specialist equipment required
what are the disadvantages of alumina core ceramics? (2)
can’t be used in posterior crowns
Requires a lot of tooth preparation to accommodate for the core and ceramic veneer on top
what are the new alumina cores?
INCERAM
PROCERA
What are the uses of the new alumina cored crowns? (1)
Single posterior crowns
what is required for zirconia cored ceramics?
CAD CAM
name the type of zirconia core used in dentistry.
Yttria stabilised zirconia
how does Yttria stabilised zirconia prevent cracks propagating?
When a stress at the crack tip occurs
causes the crystal structure to transform to the monoclinic structure
which causes the material to slightly expand and closes the crack tip.
when is Yttria stabilised zirconia used? (1)
bridge framework
what are the disadvantages of Yttria stabilised zirconia ? (4)
Expensive equipment required - CAD CAM
The veneer can debond differential rates of expansion and contraction during firing and there can be chip off when the crown is subjected to load.
Since the core is opaque = same aesthetics as MC crowns
Cannot etch the tooth to allow bonding to the surface have to using luting agent = conventional cement
what are the advantages of Yttria stabilised zirconia ? (2)
Once the equipment is purchased it is cheaper to produce the crowns - prices of metal is increasing
Crowns have an excellent fit
what are the advantages of producing ceramics via milling instead of sintering? (3)
Milled is stronger
blocks will be consistent
In milled crowns the aesthetics are improving
