L05: Types Of Dental Materials: Polymers, Polymerisation Flashcards
What is a polymer?
A long chain molecule with chains being held together by covalent bonds and bonds between chains being secondary bonds
Why are resin-based systems easy to use chairside?
Because it’s a light cured setting reaction. Very versatile and can make minor adjustments to change properties.
In what way are polymers versatile?
Less dense than metals/ceramics
Some compatibility with human tissue
Electrical insulation
Resists corrosion
What is PMMA?
Polymethyl methacrylate
What are the types of polymers?
Plastics
Elastomers
Long chain molecules
Hydrocarbons
Examples of commodity thermoplastics
Polyvinyl chloride (PVC)
Polypropylene
Polystyrene
Polyethylene
Examples of engineering thermoset polymers
Polyurethanes
Epoxies
Polyesters
More complex polymer chains (held together by cross-links or branching), cannot be softened with heat, will just breakdown
What polymers do we mainly deal with?
Silicones, polyesters, some epoxies
What is Bowen’s resin made of?
25% weight polymerisable resin
75% weight quarts or aluminosilicate glass filler
BisGMA or TEGDMA
Describe the properties of Bowen’s resin
Difunctional (methacrylate groups on either side).
High molecular weight monomer
Very viscous and bulky providing structural integrity to the resin matrix that’s used for resin-based composites
High weight of inorganic component (filler) needs to be added to strengthen it
Mix with lower viscosity resin to allow this
Define polymer, monomer, polymerisation and free radical.
Polymer: long chain molecules of repeating units
Monomer: units from which the chain is built
Polymerisation: the process of converting monomers to polymers
Free radical: chemical species with an unpaired electron
What is an addition reaction?
Reaction of 2 molecules to make a larger molecule
Same empirical formula as the monomer
Used more in dentistry
What is a condensation reaction?
Reaction of 2 molecules to make a larger molecule with the elimination of a smaller molecule
Different empirical formula
Briefly describe free radical addition polymerisation
Activation: provides a reactive species reacts with the monomers. Activation, usually by temperature.
Initiation: free radical reacts with monomer and polymerisation process is initiated.
Propagation: free radical reacts with more monomer, repeats and polymer chain grows. Self-limiting.
Termination: terminated either by lack of mobility, or mutual annihilation (2 radicals joining together).
How is propagation self limiting?
Because as the polymer chain grows, the mobility of the polymer chain reduces, so probability of radical going on to react with other chains reduces until the material freezes/vitrifies/forms a glass. Once there is no mobility left, reaction will terminate.