Long Term Soft Lining Materials Flashcards

1
Q

How long are long term soft lining materials supposed to last

A

At least 4 weeks to several months/years

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2
Q

What patients do we tend to use long term soft lining materials for

A

Patients who can’t tolerate a rigid denture base material

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3
Q

Describe the function of long term soft lining materials

A
  • Distribute masticatory forces more evenly and absorb some of the energy
  • Lining deforms elastically, then the energy is released as it returns to pre-deformed shape
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4
Q

What are the 4 types of Long Term SLM

A
Heat Cured:
- Addition silicones
- Soft Acrylics
Room Temperature vulcanised cured:
- Condensation silicone
- Addition silicone
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5
Q

What are the uses for long term soft lining materials

A
  • Obturators (covers palatal defects) or other type of prostheses like maxillofacial ones
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6
Q

What are the disadvantages of Long term soft lining materials

A
  • Expensive
  • Difficult to modify and polish
  • More prone to fracture
  • Reduction in denture SLM thickness increases its hardness (minimum ~3mm)
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7
Q

What are the ideal properties of long term soft lining materials (just name as many as you can)

A
  • Non-toxic and non-irritant
  • Good adhesion to PMMA denture
  • Should not support the growth of candida
  • Permanently resilient
  • Permanently compliant
  • Low water absorption
  • Not adversely by denture cleansers
  • Easy to clean and not stained easily
  • Sufficient mechanical strength and abrasion resistance
  • wetted by saliva
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8
Q

What does it mean for a material to be resilient

A

This is the ability of a material to absorb energy when deformed elastically and to return it when unloaded

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9
Q

What is the setting reaction for heat cured silicones

A
  • Addition reaction involving free radicals
  • Peroxide initiator oxidises the CH3 on neighbouring siloxane chains to form cross links
  • Silane acts as a cross linker
  • the methacrylate groups react with the denture base to form a bond
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10
Q

How are heat cured addition silicones dispensed

A

One paste systems

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11
Q

How are room temperature vulcanised addition and condensation silicones dispensed

A

2 paste system - base paste and catalyst paste

RTV condensation silicones aren’t on the market anymore

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12
Q

Describe the composition of RTV addition silicone pastes

A
Paste 1:
- Vinyl terminated poly dimethylsiloxane
- Pt based catalyst e.g. chloroplatinic acid
- Filler
Paste 2:
- Vinyl terminated poly dimethylsiloxane
- Hydrogen terminated poly dimethyl siloxane
- Filler
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13
Q

What kinds of silicone SLM use glazes/polishes

A

RTV silicones

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14
Q

What do glazes/silicones do to silicone SLMs

A
  • Smooths and seals trimmed areas
  • Not used on tissue contact surface
  • Contain unfilled addition silicone, some with solvents
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15
Q

What are the advantages of using RTV addition silicones compared to Condensation silicones

A

Claim to have better mechanical and adhesion to PMMA

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16
Q

What are the advantages of using Heat-cured addition silicones compared to RTV silicones

A

These have the best adhesion to the denture and lower water uptake than RTVs

17
Q

What are the advantages of using Silicones (as opposed to acrylics) as SLMs

A
  • Silicones are resilient
  • Compliant
  • Theses properties are not adversely affected in the oral environment
18
Q

What are the disadvantages of using Silicones (as opposed to acrylics) as SLMs

A
  • Poor adhesion to PMMA
  • Poor tear strength
  • Not wetted by saliva (hydrophobic)
  • Some support the growth of candida
  • Single component hear cured materials require refrigeration (limited shelf life)
19
Q

How are soft acrylic SLMs usually dispensed

A

powder/liquid systems

20
Q

What is added to the acrylic SLMs to make them “soft”

A
  • Higher methacrylate e.g. EMA/BMA

- A plasticiser to reduce the Tg to below mouth temperature

21
Q

What is the Glass transition temperature (Tg)

A

This is the temperature range where a polymer substrate changes from a rigid glassy material to a soft (not melted) material

22
Q

What is the powder phase of soft acrylics usually made up of

A
  • PEMA

- OR BMA/EMA copolymer

23
Q

How does the Tg of PEMA compare to different BMA/EMA co polymers

A

PEMA’s Tg is higher than BMA/EMA copolymers

Higher BMA:EMA ratios = lower Tg

24
Q

Describe the composition of the liquid phase of soft acrylics and give examples where you can boi

A
  • Higher methacrylate monomer e.g. butyl, hexyl
  • Cross linking agent e.g. ethylene glycol dimethacrylate
  • Plasticiser, usually a phthalate e.g. butyl phthalyl butyl glycollate
    OR a citrate e.g. acetyl tribute citrate
25
Q

How do the monomers polymerise in the setting reaction of soft acrylics

A

Free radical addition polymerisation on heating

26
Q

What are the advantages of using soft acrylics as SLMs (as opposed to silicones)

A
  • Bond well to PMMA
  • Good tear resistance
  • Wetted by saliva
  • Initial compliance is good
  • Can be polished if chilled
27
Q

What are the disadvantages of using soft acrylics as SLMs (as opposed to silicones)

A
  • Hardening due to loss of plasticiser, potential toxicity concern
  • High water absorption
  • Less resilient than the silicones
  • Permanent deformation can occur
28
Q

What compound are light cured SLMs (these are usually acrylics) usually based on

A

Urethane dimethacrylate

29
Q

What do light cured SLMs require to take a mould with and name a disadvantage

A
  • Special moulds

- They do not bond well