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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
The chemical activation of self curing acrylic being less efficient leads to more unreacted monomer Why is this a disadvantage?
- Acts as a plasticiser - Softens denture base - fracture risk - Reduces transverse strength - Potential tissue irritant if monomer leaches out
26
How does dimensional accuracy (size) affect self curing acrylic vs heat cured?
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
2 disadvantages of Heat Cure
1. Higher molecular weight | 2. Curing process may cause porosity
28
3 disadvantages of Self Cure
1. Higher monomer levels - irritant 2. Fits cast better but water absorption in mouth makes it oversized 3. Poorer colour stability
29
What are the advantages the new High Impact Heat Cure Acrylic Resin? (2)
- Greater degree of ductility - Helps to mitigate the effect of any micro-cracks that may be resent - Greater flexural strength - Will survive long
30
Whats a concern surrounding light cure?
Limited depth of cure | - Limits thickness of the denture
31
What is light activated resin mostly used for? (2)
1. Customised impression trays | 2. Reparing fractured dentures
32
Why should denture base materials ideally be radiopaque?
If any fragments break off and are swallowed they will show up on the radiograph
33
What is the most commonly used acrylic resin?
Heat cured

DMS (1 decks)

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