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BDS3 Dental Materials > Acrylic > Flashcards

Acrylic Flashcards

1
Q

What type of material is acrylic?

A

polymer

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2
Q

requirements for a denture base?

  • dentist and lab point of view
A

adequate strength to withstand occlusal loading

easy to manipulate and process

not produce toxic fumes or dust during processing

remain unstained and unaffected by fluids and temperature changes in oral cavity

simple to repair when necessary

maintain its shape, form and aesthetics in normal function

biocompatible

radiopaque

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3
Q

requirements for the denture - from a pt point of view?

A

fit well and b compatible in use

not traumatise the tissues

easy to clean

aesthetically pleasing both immediately on placement and in the linger term

allow good heat diffusion to retain normal perception

permits food to be tasted normally so that food can remain appealing

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4
Q

PPMA?

A

poly methylmethacrylayte

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5
Q

what forms is PMMA available in?

A

gel

sheet

blank

powder/liquid

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6
Q

powder?

A

polymer

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7
Q

liquid?

A

methylmecarylate

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8
Q

initiator in PMMA?

A

benzoyl peroxide

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9
Q

what is the carcinogenic component?

A

phthalates as the plasticiser can be hazardous at high concentrations

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10
Q

MMA monomer boiling point?

A

100 dc

can boil out

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11
Q

MMA toxic?

A

yes, toxic if inhaled for prolonger period

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12
Q

what is in inhibitor of MMA?

A

HYDROQUINONE

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13
Q

role of hydroquinone?

A

inhibitor - prevents monomer polymerizing during storage

preferentially react with any random free radicals to prevent premature reaction

stop polymerisation procoess

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14
Q

What needs to happen before polymerisation can occur?

A

all the hydroquinone must be use up before the polymerisation reaction may take place

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15
Q

the role of plasticisers in acrylics?

A

prevent interaction between polymer molecules

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16
Q

what cold affect the biocompatbility of PMMA?

A

phthalates and carcinogenic

methacrylate will polymerise - less likely to leach out over time

failure of methacrylate to polymerise could lead to subsequent hardening of the denture base over time

17
Q

setting reaction of PMMA?

A

Initiated by an organic peroxide such as benzoyl peroxide

free radicals produced wither by heating (heat cured) or by reacting with chemical accelerator such as an organic amine

highly exothermic reaction

heat is slow to displace as processing is carried out on a plaster mould

18
Q

why does polymerisartion shrinkage occur?

A

shrinkage of the material occurs on setting reaction is a plymerisation reaction

processing regime look t reduce the heat production

19
Q

mechanical propertis of PMMA?

A

low tensile strength and low elastic modulus

flexes in use

will result in fracture of the denture base over time

due to cyclical loading aka fatigue fracture

midline fracture

20
Q

what does fracture toughness mean?

A

behaves as a brittle material on impact

21
Q

advise to pt when cleaning denture to prevent fracture?

A

clean over sink half full with water

22
Q

properties of PMMA?

A
  • Brittle (EASILY BREAK)
  • low tensile strength (fracture)
  • high coefficient on thermal expansion (may lose ceramic teeth due to contraction of material)
  • low thermal conductivity
  • high dimensional stability
  • polymerisation shrinkage (dont let it dry out - shrinkage and crazing)
  • low density
  • relatively lightweight
  • easy to wear
  • no taste
  • relatively cheap
  • easy to process
23
Q

problems of low thermal conductivity of PMMA?

A
  • pt sensation of hot and cold food is reduced
  • oral mucosa may become less keratinised … if denture lost or replaced by fixed restoration, oral mucosa is sensitive to hot temps

lab
- during processing the het produced form the exothermic reaction cannot escape - gaseous porosity

24
Q

how to prevent polymerisation shrinkage of denture?

A

keep wet, overnight etc

PMMA absorbs fluid - water sorption

drying out cause shrinkage and crazing

25
Q

what does long-term water sorption cause?

A

discolour and stain - aesthetics

26
Q

Problems of residual monomer?

A

denture base weaker and more flexible

fracture may result

polymer may creep under load over the long term and deform the denture base

more marked with cold-cure acrylic and can create problems

crosslinking agents may b added in an attempt to minimize this effete

loss of material due to water solubility low

presence of organic solvents such as alcohols and chloroform has an adverse effect on methacrylates

27
Q

crazing?

A

fine cracks in surface of acrylic

can no longer support stress

lead to fracture

28
Q

what can minimise crazing?

A

Keeping denture moist

29
Q

what can cause crazing?

A

not kept moist

heat

30
Q

problems of PMMA being radiolucent?

A

not ideal if swallowed, cant find n xray

BDS3 Dental Materials (13 decks)

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