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Prosthetics > Polymeric Denture Base Materials > Flashcards

Polymeric Denture Base Materials Flashcards

1
Q

What is a denture base?

A

The component of a removable denture which is contact with the denture bearing mucosa and which carries the teeth and replaces lost oral tissues

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2
Q

Name 4 ideal properties of a denture base material

A
  1. Biological / Chemical properties
  2. Physical properties
  3. Mechanical properties
  4. Other properties
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3
Q

Describe 3 ideal biological / chemical properties of a denture base material

A
  1. Biocompatible (non-toxic, non-irritant)
  2. Chemically inert (impermeable to oral fluids, tasteless and odourless)
  3. Chemical bond to prosthetic teeth
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4
Q

Describe 6 ideal physical properties of a denture base material

A
  1. Aesthetic
  2. Glass transition value which is high enough to prevent distortion
  3. Minimal thermal expansion if alloy
  4. Dimensionally stable
  5. Light in weight
  6. Radio-opaque
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5
Q

Describe 4 mechanical properties of a denture base material

A
  1. Good rigidity - High MoE and proportional limit
  2. High fatigue strength
  3. High impact strength
  4. Hard surface and resistant to abrasion
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6
Q

What is the difference between fatigue and impact strength?

A

High fatigue strength is resistance to fracture on function but high impact strength is resistance to fracture on impact

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7
Q

Name 4 other properties which are ideal for denture base materials

A
  1. Easy to process and accurate manipulation
  2. Relatively inexpensive
  3. Easy to repair
  4. Easy to clean
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8
Q

Name 4 common denture base materials in current use

A
  1. Polymethylmethacrylate (acrylic resin)
  2. Cobalt-chrome alloy
  3. Thermoplastic polyamides (nylon)
  4. Titanium alloy
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9
Q

Name 4 historically used denture base materials

A
  1. Wood, ivory or porcelain
  2. Celluloid, rubber
  3. Gold and stainless steel
  4. Polycarbonate
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10
Q

Describe 4 possible “upgrades” to PMMA as a denture base material

A
  1. Flexible
  2. Injection moulded
  3. High impact
  4. Fibre reinforced
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11
Q

Describe PMMA resin as a material

A
  • Glassy, colourless, hard, brittle acrylic
  • Developed as a glass reinforcement
  • Easy to colour
  • Adequate strength
  • Low water sorption, low solubility and non-toxic
  • Categorized by its method of curing / activation
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12
Q

Describe 3 applications of heat-cured acrylic

A
  1. Denture bases
  2. Gum-work on metallic denture bases
  3. Artificial teeth
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13
Q

What is the composition of PMMA?

A

Liquid monomer and preformed polymer powder

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14
Q

What is the monomer found in the liquid which makes up PMMA?

A

Methylmethacrylate monomer

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15
Q

What is the stabiliser found in the liquid which makes up PMMA?

A

Hydroquinone

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16
Q

What is the cross linking agent found in the liquid which makes up PMMA?

A

Ethylene glycol dimethacrylate

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17
Q

What is the initiator found in the powder which makes up PMMA?

A

Benzoyl peroxide initiator

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18
Q

What is the pigments are found in the powder which makes up PMMA?

A

Cadmium (red) and Fe salts / titanium dioxide (white)

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19
Q

What is the plasticiser found in the powder which makes up PMMA?

A

Dibutylphthalate

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20
Q

Name 3 parts of the liquid part of PMMA

A
  1. Monomer
  2. Stabiliser
  3. Cross-linking agent
21
Q

Name 5 parts of the powder part of PMMA

A
  1. Preformed PMMA beads
  2. Initiator
  3. Pigments
  4. Nylon
  5. Plasticiser
22
Q

What is the most common manipulation technique of PMMA?

A

Dough moulding technique

23
Q

What occurs if the polymer : monomer ratio is too high in manipulation of PMMA?

A

Granular acrylic forms which is weak and opaque

24
Q

What occurs if the polymer : monomer ratio is too low in manipulation of PMMA?

A

Polymerization shrinkage occurs to a higher extent

25
Q

Describe 7 steps to dough moulding method

A
  1. Mixing
  2. Mould lining
  3. Packing
  4. Curing
  5. Cooling
  6. Deflasking
  7. Finish and polishing
26
Q

Describe what physical changes occur when mixing polymer and monomer in the manipulation of PMMA

A
  • Wet sand
  • Tacky
  • Doughy (snappy)
27
Q

What is the function of mould-lining in dough moulding technique?

A

Prevents monomer entering plaster and mould prevents water entering the resin

28
Q

What is the function of packing in the dough moulding method?

A

Fill to excess to avoid contraction porosity

29
Q

Name 3 methods of curing when using heat-cured PMMA and the dough moulding method

A
  1. Water bath
  2. Air oven
  3. Microwave oven
30
Q

What occurs if PMMA is under cured?

A

High residual monomer content leading to weakened acrylic

31
Q

What occurs if a temperature is raised too fast during the curing of PMMA?

A

Gaseous porosity

32
Q

What is the function of cooling in the dough moulding technique?

A

Allow stress relief

33
Q

Name 6 critiques of injection moulding

A
  1. Denser base material - reduced risk of porosity
  2. Reduced dimensional change
  3. No risk of increase in OVD
  4. Finer reproduction of gingival wax work
  5. No monomer exposure
  6. Expensive equipment
34
Q

Describe 6 properties of heat cured PMMA

A
  1. Residual monomer of around 0.2-0.5%
  2. Water content of 2%
  3. Susceptible to crazing
  4. Low impact and fatigue strength
  5. Tg of heat cured PMMA of 120 degrees
  6. Allergy to PMMA possible
35
Q

Name 3 reasons for crazing of heat cured PMMA

A
  1. Stress on repeating drying and wetting
  2. Stress concentration around inserts
  3. Monomer from repairs
36
Q

Name 5 properties of chemically cured PMMA

A
  1. Content same as heat cured but liquid contains chemical activator dimethyl-p-toluidine
  2. Greater porosity
  3. Reduced strength
  4. Residual monomer content of 2%
  5. Poor colour stability
37
Q

Name 3 components of chemically cured PMMA powder

A
  1. Pre-polymerized PMMA spheres
  2. Benzoyl peroxide (initiator)
  3. Pigment
38
Q

Name 4 contents of chemically cured PMMA liquid

A
  1. Methylmethacrylate monomer
  2. Hydroquinone (inhibitor)
  3. Ethylene glycol dimethacrylate (cross linking agent)
  4. Dimethyl-p-toluidine (activator)
39
Q

Name 5 uses of chemically cured PPMMA

A
  1. Denture repairs and additions
  2. Denture copy technique
  3. Impression trays
  4. Relines
  5. Orthodontic appliances
40
Q

What are 2 main reasons for modifying PMMA

A
  1. Improve low impact strength (brittle with low ductility)

2. Improve fatigue strength (susceptible to crack propagation)

41
Q

Name 2 high impact acrylics

A
  1. Trevalon Hi

2. Acron Hi

42
Q

Describe how PMMA is modified to improve fatigue and impact strength

A
  • Polymer bead are made by co-polymerizing PMMA and butadiene styrene rubber in an emulsion
  • Coat resultant beads in PMMA producing micro-dispersed rubber phase polymers
  • Absorb energy and reduce crack propagation
43
Q

Name 3 types of reinforcing fibres found in modified PMMA

A
  1. Carbon fibre inserts
  2. Glass fibres
  3. Polyethylene fibres
44
Q

What is a drawback of PMMA during major trauma?

A

It is radio-lucent so will not show up on x-rays

45
Q

Describe 3 ways PMMA may be modified to become radio-opaque

A
  1. Metal inserts (poor appearance and weakens base)
  2. Barium salts (considerable weakens base)
  3. Bromine-containing additives (expensive and not used commerically)
45
Q

What is the most commonly used flexible denture base material?

A

Nylon

46
Q

Name 2 major issues with flexible dentures

A
  1. Design

2. Health

47
Q

Describe 2 reasons health is compromised in flexible dentures

A
  1. Pressure is exerted on soft tissues

2. Coverage of gingival margins

Prosthetics (16 decks)

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