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Semester II - Dental Materials > Resin Based Composite Materials > Flashcards

Resin Based Composite Materials Flashcards

1
Q

What is a Composite Material?

A
  • Material made from 2 or ore constituent materials with significantly different physical or chemical properties that, when combined, produce a material with characteristics different from the individual components
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2
Q

What is Resin based Composite?

A
  • Composed of a chemically active resin and an inorganic filler bound together by a silane coupling agent
  • Other chemicals are also present
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3
Q

Resin based Composites: What’s the resin components principle monomer?

A
  • Traditionally. main resin component is based on:

Bisphenol A
Glycidyl methacrylate

= bis-GMA

” Bowen’s resin”

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4
Q

What’s the viscosity of bis-GMA?

A
  • Long chain monomer with methacrylate group at either end of an aromatic spine
  • Highly viscous
  • Cannot be manipulated clinically
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5
Q

Resin Component: What’s a Diluent monomer?

A
  • Viscosity controllers
  • Lower molecular weight monomers which are required to permit clinical handling and proper mixing with the inorganic components
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6
Q

Examples of Diluent monomers are?

A
  • Methylmethacrylate (MMA)

- Ethylene glycol dimethacrylate (EGDM)

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7
Q

If resin as used alone, what would the material exhibit?

A
  • High strinkage
  • Inadequate wear
  • Increased exothermic reaction
  • Poor mechanical properties
  • No radiopacity
  • Inorganic filer is incorporated into the system to compensate
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8
Q

What are the benefits of adding a filler component?

A
  • Increases strength
  • Increased wear resistance
  • Reduced polymerisation shrinkage (decreases micro-leakage)
  • Radiopacity via the addition of heavy metals
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9
Q

What are the classifications of resin composites?

A

Filer type:

  • Gasses
  • Ceramics
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10
Q

What are Glass fillers?

A
  • Amorphous solid material

Quartz:

  • Silicon dioxide
  • Fine particle
  • Neither opaque or radioopaque

Silica-based glasses:

  • Barium-aluminium silicate glass
  • Fine particle
  • Radiopque
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11
Q

What are the features of glass fillers?

A
  • Quartz is the hardest
  • Silicate glasses contain barium but are slightly softer and degrade very slowly when exposed to water
  • Barium, Strontium and lithium are easy to finish
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12
Q

What are Macrofilled Composites?

A
  • Large filler particle size
  • Range from 15-35μm
  • Large particles can support higher loads due to lower surface area to volume ratio - however you can’t pack as much in
  • Difficult to finish and polish to an acceptable level - becomes rough quickly - plaque retention site and poor wear resistance
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13
Q

What are Fine particle Composites?

A
  • Small particle size leading to better packing of filler and the reductin in the inter-particular distance filled with resin
  • Reduction to wear
  • More spherical particles means better finish and smoother surface
  • Enhanced mechanical properties
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14
Q

What are Hybrid Composites?

A
  • Contains particles of various sizes
  • Theoretically has the benefits of both micro and macrofilled resin composites
  • High filler density as the particles fit like a mosaic
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15
Q

What are Nanofilled Composites?

A
  • Discrete non-agglomerated and non-aggregated particles between 20-70 nanometers
  • Nanoparticles coalesce into Nanocluster fillers
  • These Nanoclusters act as a single unit enabling high filler loading and strength
  • Strength of a hybrid material but easier to polish
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16
Q

What happens to the composite when you add filler/when the filler load increases?

A
  • Increasing the filler load is to make the mechanical properties of the resin composite closer to the filler
  • Increasing the compression strength BUT increases brittleness
  • Wear resistance increases but surface breakdown can occur if too much filler is added as there will be less resin to hold it together
  • Too much filler increases stiffness - poor manipulation
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17
Q

What is a Silane Coupler used for?

A
  • To bond the resin and filler (i.e. glass/ceramic) together
  • Surface of the filler particles must be chemically coated to facilitate their bonding with the chemically active resin
  • y-MPTS is a VINYL SILANE COMPOUND
18
Q

Is the Silane molecule biofunctional?

A

YES

  • Has a group which reacts with the inorganic filler (hydrophilic groups)
  • Another group reacts with the organic resin (hydrophobic groups)
19
Q

What are the repercussions of adding a Silane Coupler?

A
  • Stress concentrations occur at the interface between the filler and resin forming crack initiation sites
  • Stress transferred from the strong filler particles to the next though the low strength resin… can give in
20
Q

How do you cure a Resin Composite?

A
  • Light
  • Chemical
  • Dual (light and chemical)
21
Q

How does the Chemical cure process work?

A
  • Typically a two-paste system

- Settings reaction commences when the 2 pastes are blended (but you’ll never get 100% mix/reaction)

22
Q

How does the Light curing process work?

A
  • Use of a photo-initiator and a accelerator
  • Peroxidase
  • Diketone
  • Lucirin TPO
  • Accelerator is a tertiary amine
23
Q

Why is an ultraviolet stabiliser needed?

A
  • The material colour will change when exposed to natural light due to OXIDATION
  • Prevented by the addition of an ultrviolet absorber such as
    2-hydroxy-4-methoxybenzophenone
24
Q

How does the ultraviolet stabiliser work?

A

Absorbs electromagnetic radiation

25
Q

What polymerisation/curing inhibitors used for?

A
  • Polymerisation is the conversion of monomers to polymers (curing)
  • Monomethyl ether of hydroquinone is added to the resin composite to:
    + Prevent premature setting
    + Increase the matieral’s shelf-life
26
Q

Why do we add a radiopaque material to the composite?

A
  • Restorative materials need to be radiopaque in order to see them on an X-ray and identify secondary caries
  • Add heavy metals like barium
  • Radiodensity will vary depending on volume of radiopaque filler used
27
Q

What’s the significance of adding pigment to the resin composite mixture?

A
  • The materials optic properties should exactly match the tooth being restored
  • Inorganic oxide compounds are added to the resin in small quantities
28
Q

What’s Polymerisation shrinkage?

A
  • Most important shortcoming on the curing process
  • If a lot of shrinkage occurs there will be a gap left at the tooth/restoration interface leading to microleakage
  • Microleakage of debris and microorganisms though the space will undermine the restoration and tooth leading to secondary caries
29
Q

What are the effects of Polymerisation shrinkage stress?

A
  • High levels of stress can be built up within the tooth causing bulk or microfracture of the tooth tissue
  • Debonding of the restoration
  • Bulk or microfracture of the restorative material
30
Q

How can the placement of composite minimise polymerisation shrinkage stress?

A
  • Configuration factor (C factor) ratio of bonded to unbonded surfaces

Higher the ratio the more stress is potentially incorporated into the situation

31
Q

How should you place a composite filling to minimise Poly.shrinkage stress?

A
  • Layer it up/incremental build-up

- With each cured increment shrinkage is minimised and compensated for to some extend

32
Q

Why is the compliance of the tooth important for placing a restoration?

A
  • ability of the tooth to withstand flexure
  • Dependent on:
    + Amount of remaining tooth tissue
    + Quality of remaining tooth tissue
    + Position of remaining tooth tissue
33
Q

Why should you be aware of ambient light?

A
  • Resin composite is photophilic and ambient light can set it
  • Strength and amount of ambient light in the clinical can prematurely set the material which is clinically detrimental
  • Angle operating light away
34
Q

What is the oxygen inhibition layer in reference to resin composites?

A
  • Composite won’t fully cure in air; surface remains tacky with inferior mechanical properties
  • Partly cured layer should be removed and the restoration trimmed back to remove this layer (i.e. polish the composite with composite finishing burs) OR
  • Create an anaerobic environment covering with glycerine or dentine bonding agent
35
Q

Why should you make sure the working environment is devoid of water?

A
  • All resin-based composites are inherently hydrophobic

- Water can be taken up by the dental materials causing irreversible degradation of properties of the resin composite

36
Q

What’s Hygroscopic expansion?

A
  • Material swelling with water sorption

- Starts 15 minutes after initial polymerisation and continues for up to 10 weeks

37
Q

What’s coefficient of thermal expansion?

A
  • Resin composites have a coefficient of thermal expansion similar to tooth tissue
  • Expansion is greatest with those resin composites that have a large volume fraction of resin
  • Tooth/restoration interface is stressed during thermal cycling as restoration shrinks or expands more than the tooth - can cause microleakage - and compresses the tooth tissue which it is in contact with
38
Q

What are the advantages of resin composites?

A
  • Superior aesthetics
  • More conservative cavities
  • Command set
  • Can be repaired adequately
  • Lower microleakage compared to amalgam
39
Q

What are the disadvantages of resin composites?

A
  • Time consuming to place
  • Expensive
  • Hydrophobic
  • Photophilic
  • Polymerisation shrinkage
  • Technique sensitive
  • Difficult to finish adequately
40
Q

What are the 3 groups of Resin Composites based on their handling characteristics?

A
  1. Universal: Can be used for all applications but there may be some compromise in specific uses
  2. Flowable: More fluid composites used especially for the ultraconservative restoration of teeth
  3. Packable: More viscous materials generally only used in posterior situations
41
Q

If a material has a high filler content, how does it effect its stiffness?

A
  • Stiff materials is related to a higher filler loading

- Low filler amount lower viscosity

42
Q

What’s Universal Resin composite?

A
  • Performs satisfactorily in many situations and often provides a clinically acceptable look
  • Optic properties limit their application in specialist practice where more complex and challenging aesthetic treatments are being carried out

Semester II - Dental Materials (8 decks)

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