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Dental Materials > Composite 1 > Flashcards

Composite 1 Flashcards

1
Q

Historical development of tooth coloured filling materials

A
  • silicate cements and acrylic resins
  • silicate developed to glass ionomer cements and acrylic to composites
  • 3 types used today - resin-modified glass ionomer cements, giomers and compomers
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2
Q

Silicate cements are developed from …

A

construction material

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3
Q

Composition of silicate cements

A
  • white-ish powder hand mixed with liquid
  • powder is fluoroaluminosilicate glass
  • liquid is 50% phosphoric acid
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4
Q

Setting reaction of silicate cements

A
  • acid and base = salt and water
  • fluoride released
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5
Q

How does set silicate cement resemble amalgam?

A
  • composite structure
  • original powder surrounded by reaction products
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6
Q

Advantages of silicate cement

A
  • good initial appearance - shade and translucency similar to enamel
  • coefficient of thermal expansion - same as tooth
  • low thermal diffusivity - protects pulp but never used for deep cavities
  • fluoride release - unexpected, wasn’t understood
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7
Q

Disadvantages of silicate cements

A
  • sensitive to moisture
  • acidic due to phosphoric acid
  • post-op sensitivity - acid may have irritated pulp
  • no adhesion - needed undercut, marginal gaps formed
  • very brittle
  • solubility
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8
Q

Silicate cement was brittle. How was this controlled?

A
  • only used in small anterior cavities
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9
Q

Why is solubility of silicate cement a disadvantage?

A
  • poor stability and durability
  • due to acids and dietary factors
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10
Q

How were acrylic resins developed?

A
  • polymers based on acrylic monomers
  • 1930s-50s
  • polymethyl methacrylate - maybe useful
  • had very large shrinkage on polymerisation
  • so used mix pre-polymerised PMMA into monomer (21 to 6% shrinkage)
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11
Q

Acrylic resins contained what powders?
Role of them

A
  • polymethylmethacrylate beads
  • benzoyl peroxide to initiate
  • pigments - tooth like appearance
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12
Q

Liquids in acrylic resins
Roles

A
  • methylmethacrylate monomer
  • NN’ dimethyl-p-toluidine - activator (at low temps)
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13
Q

Setting reaction of acrylic resins

A

free-radical addition polymerisation

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14
Q

Stages of acrylic resin reactions

A
  • activation
  • initiation
  • propagation
  • termination
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15
Q

Advantages of acrylic resins

A
  • good initial appearance from pigments
  • low solubility - more stable than silicates
  • low acidity - less post-op irritation
  • good insulator - protect pulp
  • less brittle than silicates
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16
Q

Disadvantages of acrylic resins

A
  • exothermic reaction
  • residual monomer
  • flexible
  • soft and easily damaged
  • marginal leakages and staining
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17
Q

Why is acrylic resin having an exothermic reaction a disadvantage?

A
  • temp rise
  • can cause pain and pulp damage
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18
Q

Why is acrylic resin having residual monomer a disadvantage?

A
  • low degree of polymerisation
  • irritant to tissues
  • plasticiser
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19
Q

Why is acrylic resin being flexible a disadvantage?

A
  • easily deformed in mastication
  • plasticiser makes it worse
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20
Q

Why is acrylic resin having marginal leakage and staining a disadvantage?

A
  • high shrinkage (incremental technique to build up layers didnt help)
  • high coefficient of thermal expansion - higher than enamel and dentine
  • no adhesion
  • water absorption
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21
Q

What did we learn from silicate cement and acrylic resin to take into modern day materials?

A
  • addition of pre-polymerised PMMA
  • reduced polymerisation shrinkage, reduces setting temp rise
  • since it’s already polymerised and takes up space in cavity
  • but doesn’t improve water absorption, thermal expansion or mechanical proporties significantly
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22
Q

Define ‘composite materials’

A
  • blend of 2 or more materials
  • distinct phases relating to original components
  • has all properties of composite not achieved by using them independently
23
Q

Uses of composite

A
  • automobile and aviation
  • sports
  • medicine
24
Q

Filler makes the … phase of composite and matrix has the …

A
  • discrete
  • continuous
25
Q

Components of dental composites

A
  • glass component or filler (simple quartz or more complex)
  • resin component or matrix (one or many monomers)
  • coupling agent
  • initiator activator system
  • pigments
  • radio-opacifiers
  • stabilisers
26
Q

What does the coupling agent do?

A
  • bonds the matrix to filler
  • improves properties
27
Q

What is the initiator-activator system?

A
  • relates to how the composite polymerises
28
Q

Why is glass filler added?

A
  • glass is strong and stiff
  • has low coefficient of thermal expansion
  • insulating
29
Q

First composites were called … composites
Features

A
  • conventional
  • had quartz/silicon dioxide particles
  • 1-50 micrometres in size
30
Q

The first fillers needed a … adding but this could … the composite

A
  • radio-opacifier
  • weaken
30
Q

As filler concentration increases, what properties reduce?

A
  • polymerisation shrinkage
  • coefficient of thermal expansion
  • setting temp rise
30
Q

As filler concentration increases, what properties increase too?

A
  • hardness
  • stiffness
  • strength
  • fracture toughness
31
Q

Whats the maximum filler possible?

A
  • up to 75% weight (50% by volume)
32
Q

What was the first effort to increase filler concentration?
Problem

A
  • reduce size of particles
  • decrease in size leads to increase in energy so particles stuck together and couldn’t be mixed
33
Q

2 new product classes of filler

A
  • microfilled - one size of small particle
  • hybrid - two or more blends of particle size
  • can have nanocomposites but not new
34
Q

How to add more filler to microfilled composites?

A
  • high temp to reduce monomer viscosity
  • high pressure
35
Q

Explain microfilled composites

A
  • manufacturer mixes particles and monomer
  • polymerise composite in factory
  • break it up into particles
  • add composite particles to monomer
  • inorganic glass in polymer matrix
36
Q

Clinical uses of microfilled composites

A
  • anteriorly mainly
37
Q

Advantages of microfilled composites

A
  • good aesthetics
  • small particles give smooth surface for better gloss
38
Q

Disads of microfilled composites

A
  • poor mechanical properties
  • pre-polymerised polymer-glass components weakly bonded to matrix
  • care needed in polishing
39
Q

Explain structure of hybrid materials

A
  • 2 or more filler particle sizes
  • smaller ones can fit between bigger particles
  • combine them to optimise content
  • get increased mechanical properties
40
Q

Ads of hybrid material

A
  • better mechanical properties
  • more suitable for posterior use and larger cavities
  • higher filler conc and lower shrinkage
41
Q

Nanozised particles have been used in dentistry for … years. They’re cheaper/dearer

A
  • 40 +
  • dearer
42
Q

Advantages of nanoparticles

A
  • wear resistance possibly
  • not lab data to prove
43
Q

Nanoparticles are made via different techniques termed …

A

bottom up

44
Q

Disads of nanoparticles

A
  • more expensive but not much different
  • small particles clump together and act like big particles so no advantage
  • clumps are also weakly bound together so even worse
45
Q

What form do current nanocomposites take?

A
  • combination of larger particles and nanoparticles
  • called nanohybrids
46
Q

Which is the strongest of these materials?

A
  • hybrid
  • for compressive, yield, tensile and flexural strength
47
Q

Alternatives to conventional composite filler

A
  • amorphous silica
  • silica-based glasses
  • colloidal silica
  • cermaics
48
Q

Why is amorphous silica an alternative to conventional composite filler?

A
  • same composition as quartz
  • not as hard
49
Q

Why is silica-based glasses an alternative to conventional composite filler?

A
  • contain metals so radio-opaque
  • softer than SiO2 - easier to polish
  • not inert - degrades in water and acid (bad)
50
Q

Why is colloidal silica an alternative to conventional composite filler?

A
  • small particle size
  • but hydrophilic/hydrolytic degradation and not radio-opaque
51
Q

2 ceramics used as filler

A
  • zirconia-silica
  • zirconium oxide

Dental Materials (17 decks)

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