Introduction into Dental Polymers

Question 1

What is a polymer?

Answer 1

Long, chain molecules consisting of many distinct repeating smaller units called monomers

Question 2

What reaction occurs to form polymers from monomers?

Answer 2

Polymerization

Question 3

In what 2 states do monomers exist?

Answer 3

1. Liquids

2. Gasses

Question 4

In what 3 states do polymers exist?

Answer 4

1. Crystalline solids
2. Amorphous solids
3. Fibres

Question 5

Name 2 types of polymers

Answer 5

1. Naturally occuring polymers

2. Synthetic polymers

Question 6

Name 4 examples of naturally occuring polymers

Answer 6

1 . Cellulose

2. DNA proteins
3. Latex
4. Sillk

Question 7

Name 3 examples of synthetic polymers

Answer 7

1. PVC
2. Nylon
3. Polystyrene

Question 8

What is plastic?

Answer 8

A material consisting of any of a wide range of synthetic or semi-synthetic organic compounds that are malleable and can be moulded into solid objects

Question 9

Name the 4 most produced plastics in the world

Answer 9

1. Polyeythlene (PE)
2. Polypropylene (PP)
3. Polyvinyl chloride (PVC)
4. Polyethylene terephthalate (PET)

Question 10

What are thermoplastics?

Answer 10

Plastics that do not undergo chemical change in their composition when heated and can be moulded again and again

Question 11

What are thermosets?

Answer 11

Thermosets can melt and take shape once; after they have solidified they stay solid as the thermosetting process is an irreversible chemical reaction

Question 12

Name 2 types of polymerization

Answer 12

1. Condensation

2. Addition

Question 13

What is the difference between condensation and addition polymerization?

Answer 13

A small molecule is produced as a by-product during condensation polymerization but no by-product is produced during addition polymerization

Question 14

When does addition polymerization occur?

Answer 14

Vinyl compounds as they are reactive organic compounds with carbon-carbon double bonds

Question 15

What are the 4 stages of addition polymerization?

Answer 15

1. Activation
2. Initiation
3. Propagation
4. Termination

Question 16

Name 3 ways activation is achieved during addition polymerization

Answer 16

1. Light
2. Heat
3. Chemicals

Question 17

What is the most common compound responsible for activation in dental applications?

Answer 17

Benzoyl peroxide

Question 18

What does the activation of benzoyl peroxide result in?

Answer 18

Production of free radicals - A very reactive chemical species with an unpaired electron

Question 19

Describe initiation during additional polymerization

Answer 19

Activated free radicals react with a monomer unit to initiate polymerization reaction

Question 20

Describe the propagation stage of addition polymerization

Answer 20

The reactive monomer-free radical complex produced in initiation react with each other to build a chain

FR-M* + M = FR-M-M* + M etc.

Question 21

What are 2 ways termination of an addition polymerization reaction can occur?

Answer 21

1. Monomers completely used up

2. Free radicals completely consumed

Question 22

Describe the physical changes on polymerization

Answer 22

• Liquid at first
• Molecular weight increases as reaction progresses
• Chain entanglement occurs and viscosity increases as becomes amorphous solid
• Cross linking between chains if cross-linking agent is present

Question 23

What is an example of a cross-linking agent?

Answer 23

Ethylene glycol dimethacrylate

Question 24

Name 3 properties of synthetic polymers

Answer 24

1. Glass Transition Temperature (Tg)
2. Plasticiser
3. Fillers

Question 25

What is glass transition temperature?

Answer 25

Temperature at which polymer softens which is specific to each polymer - Above Tg polymer acts as a rubber / Below Tg acts as a solid

Question 26

What is a plasticiser?

Answer 26

Reduces the force of attraction between polymer chains and they become more flexible

Question 27

What is the function of fillers?

Answer 27

Particles which give increased mechanical strength, colour or bulk

Question 28

Name 4 methods of shaping dental polymers

Answer 28

1. Compression moulding 2. Injection moulding 3. Pourable resin technique 4. Thermoforming

Question 29

Describe compression moulding

Answer 29

- Powder and liquid is mixed and begins to set - Product is placed into mould - Two halves of the mould reassembled and shape the polymer - Product allowed to set

Question 30

Describe injection moulding

Answer 30

- Mould is created from wax which is then boiled away - Sprue added to allow channel into mould - Polymer injected under pressure to take the shape of wax - Once taken shape polymerization must take place in hot water bath - Denture retrieved from mould, sprue cut off and processed

Question 31

Describe pourable resin technique

Answer 31

- Powder and liquid monomer mixed and poured into the mould

Question 32

Describe thermoforming in shaping dental polymers

Answer 32

- Model produced in gypsum and blank acetate placed on top of the model - Under pressure and heat, acetate sucked down through vacuum over the model to take its shape - Trimmed and fitted onto model

Question 33

Name 4 uses of dental polymers

Answer 33

1. Dentures 2. Glass ionomers 3. Composite 4. Impressions

Question 34

What is biocompatibility?

Answer 34

Safe in the mouth, for the dental team and the environment