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BDS 2: Dental Materials > Structure of Dental Composites > Flashcards

Structure of Dental Composites Flashcards

1
Q

Define Composite

A

Two or more materials put together, with each contributing to the overall properties

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2
Q

Why were silicate cements used as direct filling materials in the early 20th Century? (2)

A
  • Only tooth coloured material (aesthetics)

- Released fluoride

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3
Q

What are some disadvantages of silicate cements? (3)

A
  • Erodes within a few years
  • Soluble in oral fluids
  • Discoloured with time
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4
Q

What were direct filling acrylics based off?

A

Polymethyl methacrylate (PMMA)

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5
Q

What are some advantages of PMMA as a direct filling acrylics? (4)

A
  • Tooth like appearance
  • Low cost
  • Insoluble in oral fluids
  • Easy to manipulate
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6
Q

What are some disadvantages of PMMA as a direct filling acrylics? (3)

A
  • High setting shrinkage which leads to secondary caries
  • Poor wear resistance
  • Coefficient of thermal contraction different to tooth
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7
Q

How are some of the problems of PMMA as a direct filling acrylic resolved?

A

Resolved by adding quartz powder as a filler, which renders it to a composite

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8
Q

What do we use now as a composite filing material?

A

Bowen’s Resin

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9
Q

How do direct composite fillings work?

A

Placed in the unset state and then is cured (set) in the oral cavity

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10
Q

What are the 3 phases/components of a dental composite?

A
  • Organic Matrix
  • Inorganic filler
  • Coupling agent
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11
Q

What is the role of the organic matrix in a dental composite?

A

It is the plastic resin that polymerises to form a continuos phase

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12
Q

What is the role of the coupling agent in a dental composite?

A

To promote adhesion between filler and matrix resin

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13
Q

What monomer does the organic matrix of a composite consist of?

A

Bis-GMA

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14
Q

What is Bis-GMA prepared from? (2)

BA
GM

A
  • Bisphenol A

- Glycidyl methacrylate

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15
Q

What is the viscosity of Bis-GMA?

A

700,000 cps

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16
Q

Why is Bis-GMA used over MMA in composite fillings?

A

When MMA monomers polymerise there is a big volume shrinkage of the compound where it occur a lot less in Bis-GMA

17
Q

What is the role of hydroquinone in the organic matrix?

A

Acts as inhibitor to prevent setting of composite in the lab

18
Q

What minor substances could potentially be found in the organic matrix of a composite? (7)

A
  • Hydroquinone
  • Activator/Inhibitor for light curer
  • Activator/Inhibitor for room temp curer
  • Fillers
  • Pigments
  • UV stabilisers
  • Optical brighteners
19
Q

What are the advantages of incorporating fillers? (5)

A
  • Reduced setting shrinkage
  • Reduced coefficient of thermal expansion
  • Enhanced strength and compressive hardness
  • Provides radio-opacity
  • Control of aesthetics
20
Q

Why must the refractive index of both the filler and resin be the same?

A

To avoid the scattering of light otherwise full depth of light cure isn’t achieved

21
Q

Why are many fillers used in composites?

A

Single filler insufficient to attain most of the above goals

22
Q

What are the different types of fillers? (3)

A
  • Conventional (macro and micro)
  • Hybrid
  • Microfine
23
Q

What did the first composites use as macro fillers?

A

Used ground quartz

24
Q

What material is used as a micro filler?

A

Colloidal silica

25
Q

What does a micro filler do?

A

Increases viscosity of monomers so method of incorporation is further improved

26
Q

What are the advantages of hybrid fillers? (4)

A
  • Favourable physical, mechanical and optical properties
  • Improved wear resistance
  • Surface morphology superior to conventional but inferior to microfilled resins
  • Radiopacity possible.
27
Q

What is a disadvantage of hybrid fillers?

A

Increased surface roughness with time so resin wears away

28
Q

Typically how much inorganic filler is loaded into a composite?

A

30-70%

29
Q

Why are fillers hydrophilic?

A

Due to a surface layer of OH groups

30
Q

What coupling agent is used to bond the filler to the resin?

A

Silane coupling agent

31
Q

How does a silane coupling agent work?

A

The hydrophilic end of the coupling agent (OCH3) reacts with surface hydroxyl groups (OH) of the filler – via a condensation reaction

32
Q

How are room temperature composites dispensed?

A

Two paste containing;

  • Benzoyl peroxide
  • DHPT
33
Q

How are light cured composites dispensed?

A

One paste

BDS 2: Dental Materials (13 decks)

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