Compound structures

Question 1

As a bioengineer, how do they see teeth?

Answer 1

A highly sophisticated functional microstructure that is not yet fully understood
Such a structure, if damaged cannot be properly be repaired with today’s technologies

Question 2

What is a compound system?

Answer 2

Number of different materials coming together synergistic effect - when combine, greater than individual materials

Question 3

What is the compound system that makes up a tooth?

Answer 3

Enamel - hard and translucent, can be brittle
Dentine - softer, porous, tough not brittle, supports enamel
PDL - bounces back to shape, active suspension system, responds to loading, active proprioceptive mechnism - this fails in bruxism and epilepsy
Alveolar bone
Pulp - moisture and innervation
Stomatognathic musculature

Question 4

What is the elastic modulus of enamel compared to dentine?

Answer 4

E - 85 Gpa - more brittle

D - 15 Gpa - more resillient

Question 5

What is the fracture strength of enamel compared to dentine?

Answer 5

Enamel - 10Mpa

Dentine - 50 Mpa

Question 6

What is the compressive strength of enamel compared to dentine?

Answer 6

E - 4000 Mpa

D - 300 Mpa

Question 7

What needs to be done when restoring compound systems?

Answer 7

restore Structure
Restore Form and colour/shade
Resist functional/ parafunctional forces 
Resist ware and degradation 
Resist static and dynamic fatigue

Question 8

How do we aim to restore the compound structure of teeth by? (3 ways)

Answer 8

Using compound systems made up of components with desireable properties
By careful bio-mechanical design considerations
By using an effective and reliable adhesive interface assembly

Question 9

What are the relavent properties of restorative materials?

Answer 9

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

Question 10

The tooth has a coefficient of thermal expansion of 10ppm degrees C, Composite has a coefficient of thermal expansion of 50ppm degrees C. What can this cause to happen?

Answer 10

This can cause the composite to expand more and fracture the tooth

Question 11

What is the strength of the bone of the composite to the tooth?

Answer 11

26mpa

Question 12

What is a composite material

Answer 12

A single entity containing 2 or more constituent phases e.g. dental composites

Question 13

What do composite fillers do?

Answer 13

Alters the propertied and behaviour of the material
Reduced polymerisation shrinkage
Limits fracture propagation 
Increases wear resistance 
Improves optical properties

Question 14

What is the need for compound structures

Answer 14

To restore compound structure
To compensate for inadequate properties in otherwise useful materials
To utilise materials with different properties
To create a system which utilises the most desirable property of each desirable material

Question 15

What are examples of compound systems?

Answer 15

Enamel bonded to dentine 
Composites bonded to ionomers
Beta quartz inserts in composites
Porcelain bonded to metal 
Porcelain bonded to alumina 
Glas infiltrated ceramic crowns 
Porcelain-acrylic metal dentures

Question 16

How can you join materials in a compound system?

Answer 16

Specific adhesion 
Micromechanical adhesion 
Mechanical interlocking 
Moulding around base material 
Casting against second material
Welding 
Soldering 
Adhesives

Question 17

What are the desirable benefits of the compound structure?

Answer 17

Complementary properties e.g aesthetics vs strength
Mechanical protection
Adhesion

Question 18

What are the unavoidable drawbacks of material interactions?

Answer 18

Electromechanical corrosion
Mismatched thermal expansion coefficiet - interface damage
Unstable dimensional form

Question 19

What properties are needed for a dentine replacement?

Answer 19

Low elastic modulus 
Adhesive 
Resilient to absorb shocks
Fluoride-releasing 
resistant to degradation

Question 20

What propertied are needed for an enamel replacement?

Answer 20

High elastic modulus 
Tooth-coloured 
Reliable bonding mechanism
High strength 
Abrasion matched to enamel 
Resistance to mechanical fatigue 
Resistance to static fatigue

Question 21

What are the bio-mechanical design considerations for restoring teeth?

Answer 21

Block form e.g. plastic restoration - doesn’t withstand load very well
Shell form e.g. crown
Laminate form e.g. porcelain veneer/dentine bonded crown - alone weak, need to be bonded for strength

Question 22

What is the key to success when restoring a compound system?`

Answer 22

Match the restorative system to the remaining substrate by the appropriate choice of compound system and appropriate design construct
Compensate for inadequacies of materials properties by design construct and vice versa
Effective and reliable adhesive assembly

Question 23

Materials vs design

Gold shell crown vs adhesive porcelain crown

Answer 23

Gold shell crown - ductile and easily deformed, 360 degree wrap prevents deformation
Adhesive porcelain crown - brittle and easily fractured if deformed, adequate bulk prevents deformation

Question 24

How can you get effective and predictable adhesive assembly? What needs to be considered?

Answer 24

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