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BDS2 CLINICAL Dental Materials > PMMA > Flashcards

Flashcards in PMMA Deck (65)
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1

what are the denture errors often based on

production
usage

2

how does production result in an unfitting denture

o The initial impression is flawed as there is no material nor method that is 100% accurate
o The curing process has severe potential error sources
o You may not achieve the perfect fit at first attempt and sometimes refinements may be required at chairside

3

how does usage result in an unfitting denture

o Fits the patient only for a short period and they may feel overtime that it doesn’t fit them
o Fractures during use or by accident
o Uncomfortable
o Becomes warped
o Surface suffers wear, roughens and becomes uncomfortable

4

what are the ideal properties of a denture base material

dimensionally accurate and stable in use
high softening temperature
unaffected by oral fluids overtime
high young modulus
high proportional limit/elastic limit
thermal expansion = artificial teeth
high thermal conductivity
low density
natural colour
non toxic/irrititant

5

why is it important that the material is dimensionally accurate and stable in use

o Must fit patients mouth AND be retained

6

why is it important that the material has a high softening temperature

so it does not distort during ingestion of hot fluids or during cleansing

7

why is it important that there is a high young modulus

o Want it to be rigid so that large stresses produce small strain so that it doesn’t change shape

8

why is it important that there is a high proportional limit/elastic limit

o Only large stresses will cause permanent deformation

9

why do we want thermal expansion = artificial teeth

we want to avoid internal stresses on cooling during manufacture

10

why do we want high thermal conductivity

o We want transmission of thermal stimuli to mucosa to avoid scalding of back of the throat or oesophagus

11

why do we want a low density

o To aid retention of upper denture as the heavier the material the greater the gravity pull

12

how is an acrylic resin denture made

made by the process of free radical addition polymerization to form poly methyl methacrylate.

13

what is the monomer

methyl methacrylate.

14

what is free radical addition poylermisation

the chemical union of two molecules either the same or different to form a larger molecule without the elimination of a smaller molecule. It involves molecules with C=C bonds.

15

what bond are we looking to break

the double bond

16

what are the stages of acrylic polymerization

- Activation of the initiator to provide free radicals
- Initiation of the free radicals to break the C=C bond in the monomer and transfer free radical
- Propagation of the growing polymer chain
- Termination of polymerization

17

what is the initiator

is benzoyl peroxide – C6H5COO-OOCH5C6

18

how can activation occur

can be through heat (>72 degrees celcius) or through self cure.

19

what is the difference between self cure and heat cure

The chemistry of the self cure resin is identical to that of the heat cured resins except that the cure is initiated by a tertiary amine rather than heat.

20

what does activation provide

C6H5COO*

21

what are the 2 components of PMMA

powder
liquid
brought together in deep curing process

22

what does the powder consist of

initiator
PMMA particles
plasticizer
pigments
co-polymers

23

what are the PMMA particles

pre-poylmerised beads
o PMMA that has been produced before, ground into beads that is put into the powder itself which will react with the liquid

24

what is the plasticizer

o Will allow for quicker dissolving in monomer liquid e.g dibutyl phthalate
o The improved dissolution of the monomer liquid speeds up the process

25

what do the pigments do

give natural color

26

what are the co-poylmers

improve mechanical properties e,g ethylene glycol dimethacrylate

27

what does the liquid consist of

methacrylate monomer
inhibitor
copolymer

28

what does methacrylate monomer do

dissolves PMMA particles (polymerises)

29

what is the inhibitor

(hydroquinone, 0.006%)

30

what does the inhibitor do

o Prolongs shelf life – reacts with any free radicals produced by heat, UV light. this prevents any free radicals that are produced inadvertently