Materials for crowns and bridgeworks

Question 1

🏗️ What is an indirect restoration?

Answer 1

It’s a restoration made outside the mouth and cemented in place to replace failed tooth structure.

Question 2

❌ Why can’t direct materials be used for all restorations?

Answer 2

They often lack the physical properties required for strength, fit, and longevity.

Question 3

🎯 What are the goals when choosing a material for indirect restorations?

Answer 3

Meet cosmetic expectations, preserve sound tooth tissue, and ensure optimum tissue response.

Question 4

🧩 What should you consider when choosing a material?

Answer 4

Contact with opposing/adjacent teeth
Technical ease of use
Compliance with standards

Question 5

What are the main material requirements?

Answer 5

Accurate fit
Strength against occlusal forces
Rigidity
Thermal expansion similar to teeth
Plaque resistance
Biocompatibility

Question 6

🔧 What types of materials are used for crowns and bridges?

Answer 6

Metals
Ceramics
Metal-ceramics (PFM - Porcelain Fused to Metal)

Question 7

🧠 Why is it important to know the properties of these materials?

Answer 7

For effective communication with patients and dental labs.

Question 8

⚙️ What are noble metal options?

Answer 8

Type III Gold alloys
Silver-Palladium
Palladium-Silver-Gold
Gold-Silver-Copper-Palladium

Question 9

🧪 What are base metal alloys?

Answer 9

Nickel-Chromium
Nickel-Chromium-Beryllium
Titanium

Question 10

💸 How do we choose between metals?

Answer 10

Consider cost,
corrosion resistance,
strength,
stiffness
, ductility, and
clinical application (e.g. inlay vs. bridge).

Question 11

🌟 What’s the composition of a gold crown from Leeds Dental Institute?

Answer 11

1-star medium gold casting alloy, extra hard, 60% gold.

Question 12

🧬 What are the roles of alloy elements in gold crowns?

Answer 12

Gold: Tarnish resistance, malleability, density
Copper: Strength and reddish color
Silver: Balances copper’s red, can cause greenish tint
Palladium: Strengthens and stiffens alloy

Question 13

🛡️ What is a key advantage of base metals?

Answer 13

Higher rigidity (modulus of elasticity) — ideal for long-span bridges.

Question 14

⚠️ What are the risks of base metals?

Answer 14

Toxic casting fumes
Nickel can cause conjunctivitis, dermatitis, bronchitis
Nickel = carcinogenic & allergenic (contact dermatitis)

Question 15

🔄 What is a PFM restoration?

Answer 15

A metal core with a ceramic outer layer, combining strength and aesthetics.

Question 16

📏 What’s key to successful PFM bonding?

Answer 16

Mechanical retention (roughness)
Chemical bonding
Compatible thermal expansion (tangential compressive stress)

Question 17

🧪 What does indium do in PFM alloys?

Answer 17

Strengthens and hardens, raises thermal expansion, lowers melting range, and forms bonding oxide.

Question 18

🚫 What are aesthetic drawbacks of PFM restorations?

Answer 18

Lack of light transmission
Less translucency
Grey gingival margins
Allergy to metal

Question 19

👑 What are the benefits of all-ceramic crowns?

Answer 19

No metal
Better aesthetics
Natural translucency and light transmission

Question 20

🧱 Why are ceramics brittle?

Answer 20

No ability to bend
Governed by flaws (Griffith’s theory)
Catastrophic failure at a fixed strain point

Question 21

🦾 What is aluminous porcelain?

Answer 21

Porcelain with 50% fused alumina crystals to stop crack propagation.

Question 22

🧊 What are glass ceramics?

Answer 22

Heat-treated glass that forms fine crystals — this increases strength and crack resistance.

Question 23

💎 What is IPS e.max made of?

Answer 23

60% lithium disilicate (framework)
Lithium orthophosphate
Fluorapatite (layering)

Question 24

💅 What are indications for IPS e.max?

Answer 24

Posterior/anterior crowns
Inlays/onlays
Thin veneers
3-unit anterior bridges
Excellent aesthetics

Question 25

What is the CAD/CAM process?

Answer 25

CCD camera captures images Design on software Milling machine creates crown May be heat-treated before fitting

Question 26

🧩 What is CEREC 3?

Answer 26

A CAD/CAM system with a wand for imaging and automated milling process.

Question 27

🧨 What is transformation toughening in zirconia?

Answer 27

Stress-induced phase change from tetragonal to monoclinic, increasing volume and creating compressive stress to stop cracks.

Question 27

⚙️ What core ceramics are commonly used?

Answer 27

Alumina, Zirconia, Lava, Cecon, IPS.

Question 28

📈 How strong are lithium disilicate and zirconia?

Answer 28

Lithium disilicate: 360–400 MPa Zirconia-veneered: 80–120 MPa

Question 29

🔬 What’s the current status of research in digital workflows for fixed prosthodontics?

Answer 29

Promising but lacks high-quality RCTs; industrial progress is outpacing clinical research.

Question 30

What is the Role of Gold

Answer 30

- Adds to the colour, tarnish and corrosion resistance, and malleability of an alloy - Also increases density of an alloy

Question 31

What is the Role of Copper

Answer 31

- Strengthener and colour enhancer in Au-Ag-Cu alloys - tend to have a "reddish"

Question 32

What is the Role of Silver

Answer 32

- Balance the reddening effect of the copper Au-Ag-Cu alloys = greenish color - used to control the strength and hardness of crown and bridge alloys

Question 33

Why is the affects of reducing gold content in alloys

Answer 33

- reducing Gold content reduces density - making casting more unreliable - Palladium and silver absorb oxygen when molten which can result in porous castings

Question 34

What is the definition of Material Biocompatibility

Answer 34

Question 35

Name some biocompatibility issues with base metals

Answer 35

Question 36

Name different choices of metal ceramic alloy

Answer 36

Question 37

How is a good bon achieved for PFM

Answer 37

Question 38

Answer 38

ALL ceramic are new gold standard

Question 39

Who found Porcelain in dentistry

Answer 39

Question 40

Describe Aluminous porcelain

Answer 40

Question 41

Why are Ceramics better than Glasses

Answer 41

- Ceramic consists of crystalline material in a glassy matrix - Crack starts to propagate in the glass, the crystalline domains deviate the propagation -Thus the progression of the crack is hindered - Hopefully the crack will stop before complete failure

Question 42

What is transformation toughening

Answer 42

- Strength and toughness comes from transformation toughening - Zirconia nickname is ceramic steel - See that zirconia exists in different crystal phases - Pure zirconia as you cool it is monoclinic Take advantage of this that you can play with the composition

Question 43

Zirconia can see toughness and bend strength are higerh than others Aesthetics good but nto as good as glass ceramics Zirconia has excellent mehcncial properties and good aesthetics but glass ceramics have even better aesthetics for translucnecy Material used in unit bridges particularly posteriorly … zirconia

Question 44

What is the nickname for zirconia and why?

Answer 44

Zirconia is nicknamed "ceramic steel" due to its high strength and toughness, similar to that of metals.

Question 45

What are the three main crystal phases of zirconia?

Answer 45

Monoclinic (low temperature), Tetragonal (high temperature), and Cubic (even higher temperature).

Question 46

What phase is pure zirconia in at room temperature?

Answer 46

Monoclinic phase.

Question 47

How can the tetragonal phase of zirconia be stabilized at low temperatures?

Answer 47

By adding stabilizing dopants like yttria (Y₂O₃), producing yttria-stabilized zirconia (Y-TZP).

Question 48

What is transformation toughening in zirconia?

Answer 48

A mechanism where stress at a crack tip causes tetragonal zirconia to transform into monoclinic, expanding slightly and generating compressive forces that hinder crack propagation.

Question 49

What causes the phase transformation from tetragonal to monoclinic in zirconia?

Answer 49

The energy/stress from an advancing crack tip.

Question 50

What effect does the phase transformation have on a crack?

Answer 50

It creates compressive forces that oppose tensile forces at the crack tip, slowing or preventing crack growth

Question 51

Why is volume expansion important in transformation toughening?

Answer 51

Because the ~3–5% expansion during phase change exerts compressive stress, which resists crack propagation.

Question 52

Why is transformation toughening considered beneficial in dental ceramics?

Answer 52

It improves the fracture toughness of ceramics like zirconia, making them more durable and suitable for load-bearing applications.

Question 53

How does adjusting zirconia’s composition affect its mechanical properties?

Answer 53

It allows stabilization of the tetragonal phase at room temperature, enabling transformation toughening to occur when needed.