Introduction into Dental Polymers Flashcards
What is a polymer?
Long, chain molecules consisting of many distinct repeating smaller units called monomers
What reaction occurs to form polymers from monomers?
Polymerization
In what 2 states do monomers exist?
- Liquids
2. Gasses
In what 3 states do polymers exist?
- Crystalline solids
- Amorphous solids
- Fibres
Name 2 types of polymers
- Naturally occuring polymers
2. Synthetic polymers
Name 4 examples of naturally occuring polymers
1 . Cellulose
- DNA proteins
- Latex
- Sillk
Name 3 examples of synthetic polymers
- PVC
- Nylon
- Polystyrene
What is plastic?
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
Name the 4 most produced plastics in the world
- Polyeythlene (PE)
- Polypropylene (PP)
- Polyvinyl chloride (PVC)
- Polyethylene terephthalate (PET)
What are thermoplastics?
Plastics that do not undergo chemical change in their composition when heated and can be moulded again and again
What are thermosets?
Thermosets can melt and take shape once; after they have solidified they stay solid as the thermosetting process is an irreversible chemical reaction
Name 2 types of polymerization
- Condensation
2. Addition
What is the difference between condensation and addition polymerization?
A small molecule is produced as a by-product during condensation polymerization but no by-product is produced during addition polymerization
When does addition polymerization occur?
Vinyl compounds as they are reactive organic compounds with carbon-carbon double bonds
What are the 4 stages of addition polymerization?
- Activation
- Initiation
- Propagation
- Termination
Name 3 ways activation is achieved during addition polymerization
- Light
- Heat
- Chemicals
What is the most common compound responsible for activation in dental applications?
Benzoyl peroxide
What does the activation of benzoyl peroxide result in?
Production of free radicals - A very reactive chemical species with an unpaired electron
Describe initiation during additional polymerization
Activated free radicals react with a monomer unit to initiate polymerization reaction
Describe the propagation stage of addition polymerization
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.
What are 2 ways termination of an addition polymerization reaction can occur?
- Monomers completely used up
2. Free radicals completely consumed
Describe the physical changes on polymerization
- 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
What is an example of a cross-linking agent?
Ethylene glycol dimethacrylate
Name 3 properties of synthetic polymers
- Glass Transition Temperature (Tg)
- Plasticiser
- Fillers
What is glass transition temperature?
Temperature at which polymer softens which is specific to each polymer - Above Tg polymer acts as a rubber / Below Tg acts as a solid
What is a plasticiser?
Reduces the force of attraction between polymer chains and they become more flexible
What is the function of fillers?
Particles which give increased mechanical strength, colour or bulk
Name 4 methods of shaping dental polymers
- Compression moulding
- Injection moulding
- Pourable resin technique
- Thermoforming
Describe compression moulding
- 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
Describe injection moulding
- 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
Describe pourable resin technique
- Powder and liquid monomer mixed and poured into the mould
Describe thermoforming in shaping dental polymers
- 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
Name 4 uses of dental polymers
- Dentures
- Glass ionomers
- Composite
- Impressions
What is biocompatibility?
Safe in the mouth, for the dental team and the environment
