DMS summary - pros

Question 1

What types of PMMA are there

Answer 1

• heat cure
• self cure
• Light cure

Question 2

What is the difference between heat cure and self cure in terms of their compositions

Answer 2

Self cure is same as heat cure except benzoyl peroxide is activated by a promoter in the liquid

Question 3

What is in the heat cure powder

Answer 3

• Benzoyl peroxide (initiator)
• PMMA particles
• Plasticisers
• Pigments
• Co-polymers

Question 4

What are the constituents of liquid in PMMA

Answer 4

• Methacrylate monomer
• Inhibitor (hydroquinone)
• Co-polymers

Question 5

How does PMMA set

Answer 5

• Free radical addition polymerisation

Question 6

What are the 4 stages of free radical addition polymerisation

Answer 6

• Activation
• Initiation
• Propagation
• Termination

Question 7

What are the two mixing stages for PMMA

Answer 7

sandy

dough

Question 8

What happens if PMMA is not cooled down slowly

Answer 8

• will result in internal stresses which reduce the mechanical properties

Question 9

What happens if PMMA is undercured

Answer 9

• will have poor mechanical properties and irritate the patient’s mouth due to free monomer

Question 10

What is the cause of gaseous porosity

Answer 10

monomer boiling

Question 11

Where is gaseous porosity generally seen

Answer 11

• Will see this in bulkier parts e.g next to the teeth

Question 12

What is contraction porosity due to

Answer 12

polymerisation shrinkage

Question 13

What are causes of contraction porosity

Answer 13

• Too much monomer
• Insufficient excess material
• Insufficient clamp pressure

Question 14

What is the cause of granularity

Answer 14

too little monomer

Question 15

What is crazing (PMMA)

Answer 15

• when the material is not mixed properly and can happen when different manufacturers are mixed together

Question 16

What is the effect of porosity

Answer 16

• will affect strength, appearance, roughness and will absorb saliva

Question 17

What are useful properties of PMMA

Answer 17

• Non toxic
• Non irritant
• Generally insoluble
• Low density - overcome by the bulking however

Question 18

What are not so useful properties of PMMA

Answer 18

Poor mechanical properties - try to make up for it by bulking it up

Question 19

What are the 3 types of gypsum

Answer 19

plaster

dental stone

densite

Question 20

What is the composition of gypsum

Answer 20

calcium sulphate hemihydrate

potassium sulphate/borax

Question 21

What is the function of potassium sulphate

Answer 21

decreases setting time

Question 22

What is the function of borax

Answer 22

increases setting time

Question 23

What is the setting reaction for gypsum

Answer 23

mix with water to form calcium sulphate dihydrate