acrylic resin PMMA

Question 1

what properties are ideal for a denture base material? - 4

Answer 1

dimensionally accurate and stable

high thermal conductivity

low density

non-toxic

Question 2

what mechanical properties are required for a denture base material?

Answer 2

high elastic modulus
high proportional limit
high fatigue, impact and transverse strength
high hardness

Question 3

define free radical addition polymerisation

Answer 3

chemical union of two molecules to form a larger molecule without the elimination of smaller molecules

Question 4

molecules with which bonds are involved in free radical addition polymerisation?

Answer 4

C=C double bonds

Question 5

what are the stages of acrylic polymerisation?

Answer 5

activation
initiation
propagation
termination

Question 6

in what stage of acrylic polymerisation do free radicals break C=C bonds in monomer and transfer free radicals?

Answer 6

initiation

Question 7

what happens in the propagation stage of acrylic polymerisation?

Answer 7

growth of polymer chain

Question 8

what is the initiator in heat cured acrylic powder?

Answer 8

benzoyl peroxide

Question 9

what is the purpose of co-polymers in in heat cured acrylic?

Answer 9

improve mechanical properties - cross-linking of polymers

Question 10

what will efficient polymerisation of acrylic result in?

Answer 10

high molecular weight and good mechanical properties

Question 11

how might acrylic irritate patient?

Answer 11

if not fully polymerised - monomer release

Question 12

describe the thermal conductivity of acrylic resin

Answer 12

low - disadvantage

Question 13

describe the hardness of acrylic resin

Answer 13

high - good

Question 14

describe the density of acrylic

Answer 14

low which is good
advantage if offset by the need to increase bulk to overcome poor mechanical properties

Question 15

describe the softening temperature of acrylic

Answer 15

unaffected by ingested fluids but don’t clean in boiling water

Question 16

what counteracts the 0.5% contraction of heat cured PMMA during manufacture

Answer 16

0.4% expansion due to water absorption

Question 17

what is a benefit of self curing acrylic?

Answer 17

lower temperature so less thermal contraction leading to better dimensional accuracy

Question 18

what are the disadvantages of self curing acrylic?

Answer 18

• lower molecular weight and poorer mechanical properties
• unreacted monomer causing irritation

Question 19

between heat cure and self cure, which is more effective in polymerisation/produces least unreacted monomer?

Answer 19

heat curing

Question 20

what impact will water absorption of self cure acrylic have on the finished denture?

Answer 20

over sized

Question 21

what is the effect of water absorption on the finished denture made of heat cured acrylic?

Answer 21

undersized - thermal contraction is 0.5% and expansion is 0.4 %

better tolerated than over sized

Question 22

give a disadvantage of heat curing acrylic

Answer 22

curing process may cause porosity

Question 23

what is the most commonly used denture base material?

Answer 23

heat cured PMMA

Question 24

what is a disadvantage of nylon?

Answer 24

water absorption leading to swelling

Question 25

constituents of acrylic powder and liquid

Answer 25

powder
initiator - benzyl peroxide
PMMA particles - pre polymerised beads
plasticiser - allows quicker dissolving in monomer liquid
pigments - give natural colour
co-polymers - improve mechanical properties

liquid
methacrylate monomer - dissolves PMMA particles - polymerises
inhibitor - reacts with free radicals (hydroquinone)
co-polymer - improves mechanical properties - cross linking of polymers