DMS summary - pros Flashcards
What types of PMMA are there
- heat cure
- self cure
- Light cure
What is the difference between heat cure and self cure in terms of their compositions
Self cure is same as heat cure except benzoyl peroxide is activated by a promoter in the liquid
What is in the heat cure powder
- Benzoyl peroxide (initiator)
- PMMA particles
- Plasticisers
- Pigments
- Co-polymers
What are the constituents of liquid in PMMA
- Methacrylate monomer
- Inhibitor (hydroquinone)
- Co-polymers
How does PMMA set
- Free radical addition polymerisation
What are the 4 stages of free radical addition polymerisation
- Activation
- Initiation
- Propagation
- Termination
What are the two mixing stages for PMMA
sandy
dough
What happens if PMMA is not cooled down slowly
- will result in internal stresses which reduce the mechanical properties
What happens if PMMA is undercured
- will have poor mechanical properties and irritate the patient’s mouth due to free monomer
What is the cause of gaseous porosity
monomer boiling
Where is gaseous porosity generally seen
- Will see this in bulkier parts e.g next to the teeth
What is contraction porosity due to
polymerisation shrinkage
What are causes of contraction porosity
- Too much monomer
- Insufficient excess material
- Insufficient clamp pressure
What is the cause of granularity
too little monomer
What is crazing (PMMA)
- when the material is not mixed properly and can happen when different manufacturers are mixed together
What is the effect of porosity
- will affect strength, appearance, roughness and will absorb saliva
What are useful properties of PMMA
- Non toxic
- Non irritant
- Generally insoluble
- Low density - overcome by the bulking however
What are not so useful properties of PMMA
Poor mechanical properties - try to make up for it by bulking it up
What are the 3 types of gypsum
plaster
dental stone
densite
What is the composition of gypsum
calcium sulphate hemihydrate
potassium sulphate/borax
What is the function of potassium sulphate
decreases setting time
What is the function of borax
increases setting time
What is the setting reaction for gypsum
mix with water to form calcium sulphate dihydrate
