List examples of polymers in dentistry
- Denture bases and teeth
- Composite and RMGICs
- Impression materials
- Cements
- Temp crowns
- Sealants
- Mouthguards
- Retainers
- Splints
Polymers are molecules made up of many , mainly joined bybonds.
- Monomers
- Covalent
What is the process called by which monomer units become chemically linked togther to form a high molecular weight monomer
Polymerization
What are the two types of polymerization and which one has a by-product
- Addition (no byproduct)
- Condensation (water or alcohol by product)
Three stages of polymerization:
- Initiation
- Propagation
- Termintion
2 methods of inhibiting polymerization
- Impurities which react with free-radicals and lower the number
- Presence of oxygen which reacts with free radicals
Do polymers have an amorphous or crystalline structure?
Mostly amorphous, but some can be crystalline
Biological considerations during curing of polymers:
Exothermic reaction so need to consider pulp/heat
List 3 key physical changes which occur during polymerisation
- Phase change- increase viscocity
- Temperature change
- Dimensional change (shrinkage)
2 common methods to reduce shrinkage in polymers:
- Binding monomer with inert filler
- Use larger monomers
List 3 benefits of binding monomers with an inert filler material for things such as composite resins
- Reduces shrinkage
- Reduces thermal expansion
- Increases mechanical properties
What is the difference between thermoplastic and thermoset polymers?
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.
The temperature range at which a polymer ceases to be glasss like and becomes rubber like
Glass transition temperature
5 factors which affect the properties of polymers
- Chemical composition
- Degree of polymerisation
- Number of branches
- Degree of cross-link
- Presence of plasticizers or fillers
What is the impact on Tg and E mod when you add fillers to polymers
Both increase
4 key requirements of polymers in dental applications
- Mechanical properties
- Biological properties ( non toxic, allergenic, carcinogenic)
- Handling
- Aesthetic
What are the polymer and monomer found in denture acrylic resin
Polymethylmethacrylate, methylmethacrylate
What type of polymerisation reaction is involved in acrylic resin
Addition cured
