DMS - Ceramics

Question 1

In comparison to non-dental ceramic; what is removed from dental ceramics and why?

Answer 1

kaolin is removed as they make the ceramic opaque

Question 2

what is kaolin replaced by in dental ceramics? (2)

Answer 2

kaolin is replaced with feldspar and silica.

Question 3

what is the function of feldspar added to the dental ceramics? (2)

Answer 3

Lowers the fusion and softening temperatures of the glass

Question 4

what is the binder used in dental ceramics?

Answer 4

starch

Question 5

what colour of ceramic does chromium and copper (metal oxides) produce?

Answer 5

green

Question 6

what colour of ceramic does cobalt (metal oxides) produce?

Answer 6

blue

Question 7

what colour of ceramic does iron and nickel (metal oxides) produce?

Answer 7

brown

Question 8

what colour of ceramic does manganese (metal oxides) produce?

Answer 8

purple

Question 9

how are conventional dental ceramics produced?

Answer 9

Sintering

Question 10

describe sintering.

Answer 10

Not a chemical reaction its just a process where the particles melt together to create a single mass of ceramic

Question 11

where can conventional dental ceramics only be used due to their low tensile, flexural and fracture toughness.

Answer 11

anterior teeth which do not load bear

Question 12

what are the properties of conventional dental ceramics. (4)

Answer 12

desirable aesthetics 
stable chemical properties 
dimensionally stable once fired (made)
High compressive strength 
High hardness 
Slow crack growth

Question 13

how much shrinkage is there of dental ceramics during firing?

Answer 13

20%

Question 14

What problems are associated with the high hardness of dental ceramics?

Answer 14

can cause abrasion to opposing teeth especially if not glazed

Question 15

describe what occurs to dental ceramics in aqueous environments - why?

Answer 15

Decrease in strength over time (even when not load bearing) this is due to hydrolysis of Si-O groups

Question 16

how do we increase the strength of conventional dental ceramics? (3)

Answer 16

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

Question 17

what copings can we used beneath dental ceramics? (3)

Answer 17

Metal coping
Alumina core
Zirconia core

Question 18

what are the advantages of alumina core ceramics? (3)

Answer 18

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

Question 19

what are the disadvantages of alumina core ceramics? (2)

Answer 19

can’t be used in posterior crowns

Requires a lot of tooth preparation to accommodate for the core and ceramic veneer on top

Question 20

what are the new alumina cores?

Answer 20

INCERAM

PROCERA

Question 21

What are the uses of the new alumina cored crowns? (1)

Answer 21

Single posterior crowns

Question 22

what is required for zirconia cored ceramics?

Answer 22

CAD CAM

Question 23

name the type of zirconia core used in dentistry.

Answer 23

Yttria stabilised zirconia

Question 24

how does Yttria stabilised zirconia prevent cracks propagating?

Answer 24

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.

Question 25

when is Yttria stabilised zirconia used? (1)

Answer 25

bridge framework

Question 26

what are the disadvantages of Yttria stabilised zirconia ? (4)

Answer 26

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

Question 27

what are the advantages of Yttria stabilised zirconia ? (2)

Answer 27

Once the equipment is purchased it is cheaper to produce the crowns - prices of metal is increasing

Crowns have an excellent fit

Question 28

what are the advantages of producing ceramics via milling instead of sintering? (3)

Answer 28

Milled is stronger
blocks will be consistent
In milled crowns the aesthetics are improving