Ceramics

Question 1

What is a ceramic?

Answer 1

Compound of metallic and non-metallic elements

Elements: oxides, nitrides and carbides
Traditional: china, porcelain, bricks, tiles, glass

Question 2

What is the building block of ceramic?

Answer 2

Silica - SiO2

Gives rise to crystalline or amorphous structure

Question 3

Give examples of crystalline and amorphous structures?

Answer 3

Crystalline - quartz, cristoballite

Amorphous - alumina-silicate glass

Question 4

What type of structure of porcelain is used in restorative dentistry?

Answer 4

Use mix of amorphous and crystallaine for end-product = glass-ceramic

Amorphous structure w/ crystalline particles

Question 5

What are core material ceramics?

Answer 5

Feldspar, quartz, kaolin (opaque)

Question 6

What are the 4 different ways of processing dental ceramic?

Answer 6

1. Sintering
2. Casting
3. Hot pressing
4. CAD-CAM

CCsH

Question 7

What are the features/ properties of feldspathic ceramic?

Answer 7

Weak
Only used in thickness up to 1mm
Must be supported

Question 8

When is feldspathic ceramic used?

Answer 8

Can be supported

1. Metal substructure - PFM
2. High strength ceramic (zirconia/ alumina)
3. Resin bonded crown - bonded to tooth (tooth support)

Question 9

How can metal-ceramic restorations be produced?

Answer 9

Metal substructure - lost wax casting

Ceramic sintering - ceramic veneer

Question 10

What are the 3 problems when producing metal-ceramic restoration?

Answer 10

1. Space
2. Aesthetic
3. Technical

Question 11

Why is space an issue when producing metal-ceramic restoration? (clinical/ technical)

Answer 11

Need 0.5mm for metal substructure and 1.0mm for ceramic

Not very conservation

Question 12

Why is aesthetic an issue when producing metal-ceramic restoration?

Answer 12

Metal substructure prevent light transmittance
Can appear opaque - tooth more transparent
Metal margins can be seen

Question 13

Why are the technical issues when producing metal-ceramic restoration?

Answer 13

Metal ceramic bond - unreliable (has weak point)
Metal ceramic junction - vulnerable - susceptible to chip
All ceramic must be supported
Metal/ceramic not compatible

Question 14

Why are metal-ceramic not compatible?

Answer 14

Different thermal coefficient
TECc > TECm - therefore ceramic shrink more
Issue w/ bonding - cause stress as ceramic placed under tension and metal under compression

Ceramic poor under tension = break (but good under compression)

Question 15

What would be ideal TEC for metal-ceramic restorations?

Answer 15

TECc < TECm - metal would shrink more
Allow ceramic to be under compression and metal under tension

Therefore TECc must be equal or slightly less than metal

Question 16

How does 3D structure affect function of ceramic?

Answer 16

Ideal is for materials to be flat

3D structure - if mismatched expansion coefficient - lead to radial tensile stress = cracked enamel

Question 17

What is the different TEC of metal and ceramic and how overcome?

Answer 17

TEC metal =13-14ppm/c

TEC ceramic = 8ppm/c w/ added leucite

Question 18

What are the indications for PFM?

Answer 18

Single unit restoration
Multiple unit bridge
Support RPDs

Question 19

What is a PJC and its adv/disadv?

Answer 19

Porcelain jacket crown - type high strength ceramic substructure (NOT MADE ANYMORE)

• Good aesthetic - opaque core (alumina reinforced core)
• Strength - 80Mpa - only anteriors
• Need significant tooth reduction
• Non-adhesive
• Foil technique = poor marginal fit

Question 20

What materials are used for high strength ceramic restorations?

Answer 20

1. Glass infiltrated materials - not made anymore
2. Alumina (rely CAD-CAM) - not made anymore
3. Zirconia - available

Question 21

How can zirconia high strength ceramic restorations be made?

Answer 21

Methods: CAD-CAM, milling, sintering

In-house milling available (need sintering after)
Stained prior to sintering
Used as monolithic materials or substructure

Question 22

What shades/ translucencies does zirconia come in?

Answer 22

Various translucencies available
Higher translucency - lower strength
Shades A1-D4

Question 23

What are the problems w/ zirconia?

Answer 23

Too tough/ hard
Initial sintering time long (large units have longer)
Bond between veneering ceramic and zirconia
Adjusting/ removing/ endo = difficult to cut through
Can be abrasive on teeth

Question 24

How to overcome problem of endo tx teeth w/ zirconia crowns?

Answer 24

Can place access cavity in softer material

Question 25

When would zirconia (high strength ceramic crowns) be indicated?

Answer 25

Strength - multiple units, tooth reduction
Aesthetic: substructure w/ veneer
Combination work- support RPD

Question 26

How to resin bonded crowns work?

Answer 26

Resin is bonded to the tooth

Therefore tooth is substructure

Question 27

How is ‘resin-bonded’ used in restorations?

Answer 27

Veneers, dentine bonded crowns, inlays, inlays, partial crowns
Need to be etched and bonded - restarting etched in lab w/ HF (neutralised before sent to clinic)

Question 28

What 3 different materials are used in resin-bonded crowns?

Answer 28

1. Feldspathic ceramics
2. Leucite glass ceramic
3. Lithium disilicate

Question 29

What are the problems in a lab w/ resin-bonded restorations?

Answer 29

1. Refractory model production
2. Dupliication of die = compound errors
3. Lack of supporting substructure = fragile restoration (Esp margins)

Question 30

What are the limitations of resin-bonded restorations?

Answer 30

Single unit only

Weak - only used on anterior teeth

Question 31

Why is lithium disilicate used?

Answer 31

Strength = 400Mpa
Can be pressed or milled
Used substructure for veneer
Monolithic 
Resin-bonded - bond to tooth

Question 32

What tooth preparation is required to resin-bonded restoration?

Answer 32

1.0-1.5mm reduction

No sharp corners

Question 33

What new materials are expected to be used?

Answer 33

1. Zirconia reinforced lithium disilicate
2. Dentsply - pressing version
3. Vita enamel - ceramic and polymer