5 - Polymers And Composites In Dentistry Flashcards
What is a polymer?
A polymer is a large molecule (macromolecule) composed of repeating structural units typically connected by covalent chemical bonds
Made of monomer residues
Why do we need polymers in dentistry?
Polymers are used in dentistry in a wide range of applications:
Silicon impression material
Soft lining material ( in dentures )
Alginate impression material
Acrylic denture base
Composites ( dental resin composites - widely used restorative material )
Polymer synthesis
Why do dentists need to understand polymer synthesis ?
Dentists need to understand polymer synthesis because :
You conduct a polymerisation when you use a light to cure a dental composite
You prepare a denture base by polymerising a monomer
You repair a denture by polymerising at the chairside
Polymer synthesis
What are the methods of polymer synthesis / how do we make polymers?
What are the main methods of polymer synthesis ?
- ADDITION
- CONDENSATION
- CATIONIC
- ANIONIC
Main methods of polymer synthesis - ADDITION AND CONDENSATION
Addition polymerisation
Free radical addition polymerisation
What dental materials are cured using this?
Composites & denture bases are cured via a free radical addition polymerisation
Addition polymerisation - Free radical addition polymerisation
What is an addition reaction?
Addition reaction - joining of two molecules to form a third larger molecule
Addiction polymerisation involves addicting of reactive species with a monomer to form larger reactive species
This reactive species then adds onto another monomer unit continuing until get a long chain
Reactive species involved can be IONIC or FREE RADICAL
If reactive species is free radical reaction is - free radical addition polymeration
What are the 3 steps in free radical addition polymerisation
( Activation first )
What is the initiator in free radical addition polymerisation?
Initiator is Free radical
Free radical addition polymerisation
Initiation and activation?
What does step 2 in free radical addition polymerisation include?
What is step 3 of addition polymerisation and what happens?
What are the different activation methods (addition polymerisation) ?
Activation - chemical ?
What’s used?
Activation - thermal or heat initiation ?
Activation - photo initiation?
What is the activator?
What is it commonly used for?
Resin based composite restorations
Usually cured by?
Disadvantage?
Activation - combination of heat and light?
What are they used for ?
Why is combination of heat and light used?
Generally used for ‘composite inlays’ as very high degrees of curing are required.
Often used to improve degree of polymerisation
Higher the extent of polymerisation the better the mechanical properties
Composite inlays first cured using light and then subjected to heat cure cycle to improve degree of curing and thereby improving mechanical properties
Condensation polymerisation
What is condensation polymerisation?
It is also known as ‘Step Growth Polymerisation’ Condensation: Reaction between two molecules such as an organic alcohol or amine with an organic acid in which a small molecule is eliminated
When condense there two, water eliminated, but still have free hydroxyl and carboxyl group which can extend the chain - how chain forms in steps that’s why known as step growth polymerisation