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BDS2: DM > Structure of Composites > Flashcards

Structure of 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

Disadvantages of Silicate Cements - 3

A
  • Cannot be used for permanent tooth erosion in a few years
  • Soluble in oral fluids
  • Discolouration
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3
Q

Advantages of PMMA - 4

A
  • Tooth like appearance
  • Insoluble in oral fluids
  • Easy to manipulate
  • Low Cost
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4
Q

Disadvantages of PMMA - 4

A
  • High setting shrinkage (causes secondary caries)
  • Poor wear resistance
  • Different coefficient of thermal expansion to tooth
  • Problems with reduced inclusion of quartz powder as filler
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5
Q

What type of composite is currently used?

A

Resin Based Direct Composite filling material

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6
Q

What are the 3 Phases of Dental Composites

A
  • Organic Matrix
  • Inorganic Filler
  • Bonding Agent
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7
Q

Why is Bis-GMA used instead of MMA in composite fillings?

A

MMA has a lower molecular weight -> more volume shrinkage of the material after polymerisation

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8
Q

Where does the Free Radical Substitution take place?

A

In the C=C double bond in the methacrylates.

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9
Q

What are the other additives in the Organic Matrix?

A
  • Hydroquinone
  • DHPT ( Activator for RTP Cure and LIGHT CURE)
  • Camphorquinone (LC)
  • Filler
  • Iron oxide (pigment)
  • UV stabilisers
  • Optical Brighteners
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10
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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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 continuous 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 consist of?

A

Bis-GMA

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14
Q

What is Bis-GMA prepared from?

A

Bisphenol A

Glycidyl Methacrylate

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15
Q

Viscosity of Bis-GMA

A

700,000cps

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16
Q

What is the role of hydroquinone in the organic matrix?

A

Acts as inhibitor to prevent the setting composite in the lab

17
Q

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
18
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 light cure is not achieved

19
Q

Why are many fillers used in composites?

A

1 filler is insufficient to attain most of the desired outcomes

20
Q

What are the 3 different types of fillers?

A
  • Conventional (micro and macro)
  • Hybrid
  • Microfine
21
Q

What did the first composites use as macro fillers?

A

Used ground quartz

22
Q

What material is used as a micro filler?

A

Collodial silica

23
Q

What does a macro filler do?

A

Increases viscosity of monomers so method of incorporation is further improved

24
Q

Advantages of Hybrid fillers? 4

A
  • Favourable physic, mechanical and optical properties
  • Improved wear resistance
  • Surface morphology superior to conventional but inferior to microfilmed resins
  • Radiopactiy possible
25
Q

Disadvantage of Hybrid Fillers

A

increased surface roughness with time

Resin wears away

26
Q

Usually how much inorganic filler is loaded into a composite?

A

30-70%

27
Q

Why are fillers hydrophobic?

A

Surface layer of OH groups

28
Q

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

A

Silane coupling agent

29
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 condensation reaction

30
Q

How are room temp. composites dispensed?

A

2 Paste containing:

  • Benzoyl peroxide
  • DHPT
31
Q

How are light cured composites dispensed?

A

1 paste

BDS2: DM (6 decks)

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