Polymers

Question 1

List examples of polymers in dentistry

Answer 1

• Denture bases and teeth
• Composite and RMGICs
• Impression materials
• Cements
• Temp crowns
• Sealants
• Mouthguards
• Retainers
• Splints

Question 2

Polymers are molecules made up of many , mainly joined bybonds.

Answer 2

• Monomers
• Covalent

Question 3

What is the process called by which monomer units become chemically linked togther to form a high molecular weight monomer

Answer 3

Polymerization

Question 4

What are the two types of polymerization and which one has a by-product

Answer 4

• Addition (no byproduct)
• Condensation (water or alcohol by product)

Question 5

Three stages of polymerization:

Answer 5

• Initiation
• Propagation
• Termintion

Question 6

2 methods of inhibiting polymerization

Answer 6

• Impurities which react with free-radicals and lower the number
• Presence of oxygen which reacts with free radicals

Question 7

Do polymers have an amorphous or crystalline structure?

Answer 7

Mostly amorphous, but some can be crystalline

Question 8

Biological considerations during curing of polymers:

Answer 8

Exothermic reaction so need to consider pulp/heat

Question 9

List 3 key physical changes which occur during polymerisation

Answer 9

1. Phase change- increase viscocity
2. Temperature change
3. Dimensional change (shrinkage)

Question 10

2 common methods to reduce shrinkage in polymers:

Answer 10

• Binding monomer with inert filler
• Use larger monomers

Question 11

List 3 benefits of binding monomers with an inert filler material for things such as composite resins

Answer 11

• Reduces shrinkage
• Reduces thermal expansion
• Increases mechanical properties

Question 12

What is the difference between thermoplastic and thermoset polymers?

Answer 12

Thermoplastic will soften on heating and solidify on cooling. They have a glass transition temperature. Thermoset very little or no softening on reheating - very strong.

Question 13

The temperature range at which a polymer ceases to be glasss like and becomes rubber like

Answer 13

Glass transition temperature

Question 14

5 factors which affect the properties of polymers

Answer 14

1. Chemical composition
2. Degree of polymerisation
3. Number of branches
4. Degree of cross-link
5. Presence of plasticizers or fillers

Question 15

What is the impact on Tg and E mod when you add fillers to polymers

Answer 15

Both increase

Question 16

4 key requirements of polymers in dental applications

Answer 16

• Mechanical properties
• Biological properties ( non toxic, allergenic, carcinogenic)
• Handling
• Aesthetic

Question 17

What are the polymer and monomer found in denture acrylic resin

Answer 17

Polymethylmethacrylate, methylmethacrylate

Question 18

What type of polymerisation reaction is involved in acrylic resin

Answer 18

Addition cured