DMS for fixed pros

Question 1

What type of gold is used for gold crowns?

Answer 1

Type III gold alloy
16 karat (>60% gold)

Question 1

What are the key properties of precious metal alloys for crowns?

Answer 1

Mechanical strength
Ductility (able to be shaped without losing toughness)
Corrosion resistance

Question 2

What are the main constituents of gold alloy, and what purpose do they serve?

Answer 2

Gold - corrosion resistance and malliability
Silver - Hardness and durability
Copper - Hardness and durability
Platinum - Corosion resistance
Tin - Improves cast ability

Question 3

What is the main distinction between decroative ceramic and dental ceramic?

Answer 3

Low kaolin content
High feldspar content
Higher glass content

Question 4

What is dental porcelain?

Answer 4

A type of ceramic
Feldspathic aluminium silicate

Question 5

What is the purpose of metal oxides in porcelain?

Answer 5

Convey different colours to the ceramic

Question 6

Describe the aesthetic properties of feldspathic dental porcelain.

Answer 6

Best of any restoriative material
Stable colour
Smooth surface
Less long term staining
Good optical properties (reflectance, opacity, translucency etc)

Question 7

Describe the thermal properties of feldspathic dental porcelain.

Answer 7

Similar to tooth subtance
Thermal expansion similar to dentine
Low stresses to restoration during use
Low thermal diffusivity

Question 8

Describe the dimensional stability of feldspathic porcelain.

Answer 8

Very stable once fired
Shrinkage can happen during fabriction

Question 9

Describe the mechanical properties of feldspathic porcelain.

Answer 9

High compressive strenght
High hardness (leads to abrasion of opposing teeth)
Very low tensile and flexural strength
Fracture toughness very low

Question 10

What about the mechanical properties of feldpathic porcelin indicate its use?

Answer 10

Low tensile/flexural strenght and low fracture toughness indicate that it can only be used in low stress areas.

Too brittle for posterior crowns and patients with heavy contacts/bruxsim.

Question 11

What steps can be taken to improve the undesirable mechanical properties of porcelain?

Answer 11

Metal coping (PFM)
Aluminia core
Zirconia core
Advanced materials
Milled/monolithic crowns

Question 12

Why are alumina core crowns no longer as desriable as they once were?

Answer 12

Low flexural strength
Still not used posterior crowns or bridgework

Question 13

What are zirconia core crowns?

Answer 13

Porcelain crowns with a zirconia core

The zirconia is yttria stabilised, which gives good mechanical properties, strong enough to use as bridge framework.

Question 14

Why is pure zirconia not used in for dental crowns?

Answer 14

It can crack on cooling if not stabilised with yttria.

Question 15

What is the process of prodcuing a monolithic zirconia crown?

Answer 15

CAD/CAM
Milling from a single block

Question 16

What are some of the drawbacks of ziroconia cored crowns?

Answer 16

Expesnive equipment
Cannot etch or bond fitting surface
Porcelain can debond from core
Similar aesthetics to PFM crown

Question 17

What are the two main types of ceramic milled crown?

Answer 17

Zirconia
Lithium disilicate (E-Max)

Question 18

Why do layered ceramic crowns have better aesthetics than milled crowns?

Answer 18

Layered porcelain rather than just a single monolithic block.

Lack of sintered layer on the core of the crown.

Question 19

What are the differences between the aesthetics and strength of zirconia and lithium disilicate crowns?

Answer 19

Zirconia is general stronger than LiDiSi

LiDiSi have better translucency, and hence better aesthetics

Question 20

Which types of porcelain crown can be used for posterior teeth and short span bridges?

Answer 20

Monolithic Zirconia

Question 21

What type of porcelain crown can be used for anterior teeth with high aesthetic demand?

Answer 21

LiDiSi, can use as far back as first premolar

Question 22

What type of porcelain can be used for short span anterior bridgework?

Answer 22

LiDiSi as long as no parafunction

Question 23

What type of porcelain can be used for longer span bridgework, or those with heavier occlusions?

Answer 23

Zirconia cored with additional zirconia where occlusal contacts meet.

Question 24

What luting agents can be used for zirconia and LiDiSi crowns?

Answer 24

Conventional cement (GI, RMGIC)
and
Resin cements (dual, self)

Question 25

How can you make a silica containing cermaic core more retentive?

Answer 25

Etching using HF acid, which can then be bonded to with a silane coupling agent.

Question 26

Why can zirconia cored crowns not be bonded to?

Answer 26

The core does not contain any silica, and are not effected by acid or bonded to.

However, they are strong enough to be self supporing and can be luted with a conventional cement.

Question 27

How can you make a zirconia cored crown more retentive?

Answer 27

Air abrasion (sand blasting)

Question 28

What layers are present in a PFM crown?

Answer 28

Porcelain
Metal oxide
Metal alloy

Question 29

What metals can be used in a PFM crown?

Answer 29

Ni-Cr
Co-Cr
Gold alloys

Question 30

What can you do to make a PFM crown more retentive?

Answer 30

Sandblasting
Acid etch with HF

Question 31

What is the purpose of using a metal coping in a PFM?

Answer 31

Utilises the great aesthetic qualities of porcelain, with the good mechanical propeties of a metal alloy.

The alloy acts as a support and limits the strain the porcelain experiences.