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PMMA Flashcards

1
Q

List ideal properties of a PMMA denture (7)

A
  1. Dimensionally accurate + stable
  2. High softening temp
  3. Unaffected by oral fluids
  4. Thermal expansion
  5. Low density
  6. Radiopaque
    - Ideally show up on a radiograph
  7. High thermal conductivity
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2
Q

List ideal properties of a PMMA denture in terms of how it looks (4)

A
  1. Non toxic/non irritant
  2. Colour/translucency
  3. Easy + inexpensive to manufacture
  4. Easy to repair
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3
Q

List mechanical properties a PMMA denture should display (4)

A
  1. High young elastic modulus
  2. High fatigue strength
  3. High impact strength
  4. High hardness/abrasion resistance
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4
Q

What kind of reaction does Acrylic resin undergo?

A

Free radical addition polymerisation

Involves C=C double bonds

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5
Q

What are the 4 steps of acrylic polymerisation?

A
  1. Activation
  2. Initiation
  3. Propagation
  4. Termination
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6
Q

What happens at the activation stage?

A

Activation of initiator to provide free radicals

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7
Q

What happens at the initiation stage?

A

Free radicals break the C=C bond and transfer the free radical

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8
Q

What happens at the propagation stage?

A

Propagation of the growing polymer chain

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9
Q

What happens at the termination stage?

A

Termination of polymerisation

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10
Q

What are the components of acrylic resin powder? (5)

A
  1. Initiator
  2. PMMA particles
  3. Plasticiser
  4. Pigments
  5. Co-polymers
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11
Q

What is the function of the plasticiser in acrylic resin powder?

A

Allows quicker dissolving in monomer liquid

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12
Q

What is the function of pigments in acrylic resin powder?

A

To give a natural colour

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13
Q

What is the initiator in acrylic resin powder?

A

Benzoyl peroxide

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14
Q

What is the function of co-polymers in acrylic resin powder+liquid?

A

To improve mechanical properties

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15
Q

What are the components of acrylic resin liquid? (3)

A
  1. Methacrylate Monomer
  2. Inhibitor (Hydroquinone)
  3. Co-polymers
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16
Q

Function of methacrylate monomer in acrylic resin liquid

A

Dissolves PMMA particles

17
Q

Function of inhibitor in acrylic resin liquid

A

Prolongs shelf life

18
Q

List acrylic properties (4)

A
  1. Fatigue strength
  2. High hardness/abrasion resistance
  3. Thermal expansion = same as artificial tooth
  4. High thermal conductivity
  5. High softening temp
19
Q

Define fatigue strength

A

The ability to resist repeated application of low level stress (during mastication)

20
Q

Why is using porcelain teeth in an acrylic resin denture base worse than acrylic?

A

Porcelain teeth will expand less than the acrylic resin denture base

21
Q

Since acrylic resin has a high softening temp, what advice would you give a patient about this?

A

Don’t use boiling water to clean it

22
Q

Whats a key difference between self curing acrylic and heat cured?

A

Benzoyl peroxide activated by tertiary amine NOT heat

Chemical cure vs heat cure

23
Q

State a benefit of self curing acrylic > heat cured

A
  • Less thermal contraction
    As its polymerisation requires no heating stage
  • Better dimensional accuracy (better fitting more accurate denture)
24
Q

State a disadvantage of Self Curing Acrylic

A
  • Chemical activation less efficient
  • Lower molecular weight
  • Poorer mechanical properties
25
Q

The chemical activation of self curing acrylic being less efficient leads to more unreacted monomer
Why is this a disadvantage?

A
  • Acts as a plasticiser
  • Softens denture base - fracture risk
  • Reduces transverse strength
  • Potential tissue irritant if monomer leaches out
26
Q

How does dimensional accuracy (size) affect self curing acrylic vs heat cured?

A

SELF CURED

  • Less thermal contraction during polymerisation so it fits original cast better
  • BUT water absorption gives expansion
  • Oversized

HEAT CURED
- Undersized (better tolerated)

27
Q

2 disadvantages of Heat Cure

A
  1. Higher molecular weight

2. Curing process may cause porosity

28
Q

3 disadvantages of Self Cure

A
  1. Higher monomer levels - irritant
  2. Fits cast better but water absorption in mouth makes it oversized
  3. Poorer colour stability
29
Q

What are the advantages the new High Impact Heat Cure Acrylic Resin? (2)

A
  • Greater degree of ductility
  • Helps to mitigate the effect of any micro-cracks that may be resent
  • Greater flexural strength
  • Will survive long
30
Q

Whats a concern surrounding light cure?

A

Limited depth of cure

- Limits thickness of the denture

31
Q

What is light activated resin mostly used for? (2)

A
  1. Customised impression trays

2. Reparing fractured dentures

32
Q

Why should denture base materials ideally be radiopaque?

A

If any fragments break off and are swallowed they will show up on the radiograph

33
Q

What is the most commonly used acrylic resin?

A

Heat cured

DMS (1 decks)

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