Acrylics 2 - Room temperature cured PMMA Flashcards
What are the uses of RT cured PMMA/MMA
- Repairing denture bases
- Re-lining denture bases at chair side
- Additions to denture
- Special trays
- Temporary crown and bridge material
What technique is used to mix the PMMA powder and MMA liquid in RT PMMA/MMA
the Dough technique as well bitch
What is PMMA/MMA also referred to as
RT PMMA
or
RT Acrylic
What are the constituents of the RT PMMA powder
- PMMA - the beads are a finer particle size than heat cured powder
- Benzoyl peroxide - initiator
- Colour pigments
- Opacifiers - Ti/Zn oxides
What are the constituents of the liquid MMA monomer in RT acrylics
- MMA monomer
- Hydroquinone inhibitor
- DMPT tertiary amine activator
Why is the tertiary amine added in the MMA monomer liquid of RT acrylics
As the benzoyl peroxide in the powder is activated by the tertiary amine (DMPT)
Why is the tertiary amine added in the MMA monomer liquid of RT acrylics
As the benzoyl peroxide in the powder is activated by the tertiary amine (DMPT)
What chemical processes happen when polymerisation of RT acrylics takes place
- The polymer beads dissolve in the monomer
- the DMPT reacts with the peroxide - BP providing the free radicals
How long does it take a RT Acrylic to polymerise
about 10 minutes depending on the coolness of the monomer and room temperature
Why do RT acrylics set quicker than HC acrylics
Has a finer polymer that allows much more rapid diffusion of the monomer into a hard mass at RT
Why do RT polymers have inferior physical properties compared with their corresponding HC versions
RT cured PMMA (polymers/acrylics) have lower molecular weights compared to HC PMMAs
What are the advantages of RT cured polymers compared to HC acrylics
- cheaper to produce (little/no technician time needed)
- Less technician time - with HC the technician has to prepare the denture from the impression taken by the dentist
- RT can be used chair side - dentures can be repaired chairside and patient doesn’t need to wait weeks
What are the disadvantages of RT cured polymers vs HC polymers
Physically weaker than HC due to:
- Cured material = lower molecular weight polymer chains
- Greater residual monomer content
- reaction is rapid so not all monomer can polymerise before material sets
- Residual monomer leaches into patients mouth causing hypersensitivity
What cause the poor colour stability in RT cured polymers
the tertiary amine causes yellowing
Why is porosity an issue in RT cured polymers
- More rapid gelation
- Hand mixing powder and liquid which results in incorporating of air
