Acrylics 3 - Other RT Cured Acrylics Flashcards
By what reaction do the monomers in HC and RT cured polymers polymerise
Free radical, addition polymerisation
What is the difference found in the composition of other RT cured acrylics
These materials use other polymer powders instead of PMMA and a higher methacrylate monomer (Ethyl, n-butyl etc)
What is PEMA
Poly ethyl methacrylate
What does PEMA do in “Other” RT Cured acrylics
Reduces the shrinkage and exotherm - acts as a virtual filler and doesn’t take part in the free radical addition polymerisation
Why can PMMA only be mixed with MMA monomer
Otherwise it would form an incoherent gel
Why can’t PEMA be mixed with MMA monomer
Forms an incoherently mixed product
What monomers can PEMA be mixed with
Several higher molecular weight monomers (in place e of MMA)
- Can also be used without a monomer
What are some examples of using PEMA
- Soft lining materials
- Tissue conditioners
- Temporary crown and bridge materials
- Extension of impression trays and dentures
- Hard reline material
- Functional impression material
- Maxillofacial prosthesis (e.g. obturators)
- Denture lining
What is a soft lining material used for
Used to make the denture more comfortable for the patient
Why might the lower denture cause more pain than the top one
Less surface area to distribute the load
What are the constituents of the powder phase of RT cured soft lining materials based on PEMA as an example
- PEMA powder or BMA/EMA copolymer powder
- Benzoyl peroxide (BP) - initiator
- Colour pigments
- Opacifiers
What are the constituents of the liquid phase of RT cured soft lining materials based on PEMA as an example
- Higher methacrylate monomers e.g. ethyl, butyl, hexyl methacrylates
- Di-n-butyl phthalate or citrate plasticiser
- Hydroquinone - inhibitor
- DMPT - activator
- Cross linking agent
Why do RT cured soft lining materials adhere well to the acrylic denture base
- RT cured soft lining materials contain acrylic groups
What does the addition of a plasticiser do to a RT cured soft lining materials
This lowers the glass transition temperature
What kind of chemical is a plasticiser normally
An Aromatic ester or a di-n-butyl-phthalate
What is a plasticiser
This is an organic liquid that acts as a lubricant that seeps between polymer chains and lowers the intermolecular forces between them
Why should RT cured soft lining materials contain little plasticisers
The plasticiser tends to leach out into the oral fluids with time; consequently the material hardens - obvs limiting the life of the soft lining material
What is the biocompatibility problem with some RT cured soft lining materials
some plasticisers are phthalate based which is fooked
What is being used to replace phthalate based plasticisers
Citrate based plasticisers
What are temporary crowns
they’re used to protect the tooth after being prepared for a permanent crown
How long can you leave temp crowns in for
Can take several weeks before a permanent crown is put in place
What are the constituents of the powder of RT cured temp crowns and bridges/extension materials
- PEMA powder
- benzoyl peroxide - initiator
- colour pigments
- Opacifiers
What are the constituents of the liquid of RT cured temp crowns and bridges/ extension materials
- Butyl methacrylate monomer
- Hydroquinone - inhibitor
- DMPT - activator
Why is the dough technique used when making PEMA RT cured temp crowns and bridges
The dough technique is used to reduce the overall shrinkage and exotherm of the material
