Why can you add to PMMA dentures more easily/ why can they be easily adapted?
Polymeric matrix has free residual particles
What does PMMA stand for?
How do you classify PMMA?
Heat cure and self cure
In detail - the process of curing a PMMA
- Mix the powder and liquid to form a dough which is packed into a mould
- Apply heat
- Heat is generated once the process has started
- Large amounts of polymerised material in the powder
What reaction is involved in the process of curing?
Free radical addition polymerisation
What happens when there is porosity in a denture
There is premature failing and cracks forming
What is the activator of the process of curing and what does the activator do ?
Application of heat is the activator , by raising the heat greater than 60 degrees it will cause the breakdown of benzoyl peroxide to form free radicals
What type of reaction is does curing produce?
What is the purpose of a cross linking agent?
Cross linking agents will improve the mechanical properties of the cured material
Approximately, what is the powder to liquid ratio?
2.5 : 1
What happens when you cure both the liquid and the powder in comparison to just curing a monomer ?
It will reduce contraction shrinkage
What happens if we use too much powder in a PMMA heat curing reaction?
The particles will not be wetted sufficiently which may result in porosity
How long should you cure for and at what temperature ?
You should cure for 7 hours at 70degrees celsius and for 3 hours at 100degrees celsius
What is the significance of curing at 70degrees c for 7 hours
There is a lot of monomer but at hour 8 most of the monomer is gone, it means that there is no major issues with gaseous porosity
Why do you cure the PMMA for 3 hours at 100degrees celsius
This allows maximum cross linkage
What may be a reason for a denture not adhering properly?
Wasn’t boiled out properly so polymerisation wasn’t sufficient
What happens if a denture is too thick and what material can we use to avoid it?
Fatigue and it will fracture, CoCr avoid this issue because it is thinner