Compound Structures

Question 1

What is a tooth to a bioengineer?

Answer 1

Highly sophisticated functional microstructure not yet fully understood
Damaged structure = cannot be properly repaired with today’s technology

Question 2

What is a tooth to a dentist?

Answer 2

Block of enamel sitting on dentine

Can be filled

Question 3

What is the elastic modulus, fracture strength and compressive strength for enamel?

Answer 3

Elastic module (high = brittle) = 85GPa
Fracture strength = 10MPa
Compressive strength = 400MPa

Question 4

What is the elastic modulus, fracture strength and compressive strength for dentine?

Answer 4

Elastic module = 15GPa
Fracture strength = 50MPa
Compressive strength = 300MPa

Question 5

What to restore?

Answer 5

Structure
Form and colour/shade
Resist functional/parafunctional forces
Resist wear and degradation
Resist static and dynamic fatigue

Question 6

Mechanical properties of enamel?

Answer 6

Hard
Brittle
Crystalline = translucency

Question 7

Mechanical properties of dentine?

Answer 7

Porous
Tough
Softer
Absorbs load from enamel

Question 8

Mechanical properties of PDL?

Answer 8

Visco-elastic
Active suspension system = will harden or soften depending on the situation BUT fails in bruxism and epilepsy = large loads of teeth, exceeds structural strength

Question 9

How to restore the compound structure of teeth?

Answer 9

Using compound systems made up of components with desirable properties
Make bio-mechanical design considerations
Use effective and reliable adhesive interface assembly

Question 10

What are the relevant properties of restorative materials?

Answer 10

Elastic modulus
Compressive strength
Flexural strength
Fracture toughness
Coefficient of thermal expansion
Wear behaviour
Fatigue behaviour

Question 11

Coefficient thermal expansion of enamel and dentine?

Answer 11

10ppm degrees C

Question 12

Coefficient thermal expansion of composite? Relevance of this?

Answer 12

50ppm degrees C= pushes tooth apart = enamel fractures

Question 13

Define a composite material

Answer 13

Single entity containing 2 or more constituent phases

Question 14

What does composite structure of composite filler alter the properties and behaviour of the material?

Answer 14

Reduces polymerisation shrinkage
Limits fracture propagation
Increases wear resistance
Improves optical properties

Question 15

Why are compound structures needed?

Answer 15

To restore compound structures
Compensate for inadequate properties in otherwise useful materials
Utilise materials with different properties
Create a system which utilises the most desirable property

Question 16

Types of compound systems?

Answer 16

Enamel bonded to dentine
Composite bonded to ionomers
Beta quartz inserts in composite
Porcelain bonded to metal
Porcelain bonded to alumina
Glass infiltrated ceramic crowns
Porcelain acrylic metal dentures

Question 17

How to join materials in a compound system?

Answer 17

Specific adhesion
Micromechanical adhesion
Mechanical interlocking

Question 18

Joining materials in a compound system?

Answer 18

Moulding around base materials
Casting against 2nd material
Welding
Soldering
Adhesives

Question 19

Interactions between materials in a compound system?

Answer 19

Desired benefits of the compound structure

Unavoidable drawbacks of materials interactions

Question 20

What are the useful interactions between materials in a compound system?

Answer 20

Complementary properties - aesthetic vs strength
Mechanical protection
Adhesion

Question 21

What are the unwanted interactions between materials in a compound system?

Answer 21

Electromechanical corrosion
Mismatched thermal expansion interface damage
Unstable dimensional form

Question 22

What are the constitutional forms used in restorative dentistry?

Answer 22

Block form e.g. restoration (filling)
Shell form e.g. crown
Laminate form

Question 23

How to achieve success with compound systems?

Answer 23

Match the restorative system to the remaining substrate by means of:
1. Appropriate choice of compound system
2. Appropriate choice of restorative design construct
Compensate for inadequacies of materials by design construct
Effective and reliable adhesive assembly

Question 24

Features of gold shell crown?

Answer 24

Ductile and easily deformed

360 degree wrap prevents deformation

Question 25

Features of adhesive porcelain crown?

Answer 25

Brittle and easily fractured if deformed

Adequate bulk prevents deformation

Question 26

What to take into account to achieve an effective and predictable adhesive assembly?

Answer 26

Strength of bond to restorative substrate
Strength of bond to tooth
Durability of the chemistry
Cohesive strength of the component materials
Resistance of the lute to surface degradation and wear

Question 27

Desirable properties of an enamel replacement?

Answer 27

High elastic modulus
Tooth coloured
Reliable bonding
High strength
Resistant to mechanical fatigue

Question 28

Desirable properties of a dentine replacement?

Answer 28

Low elastic modulus
Adhesive
Resilient to absorb shocks
F releasing
Resistant to degradation