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Dental Materials > Composite Resin > Flashcards

Composite Resin Flashcards

1
Q

What are the different phases in CR?

A
  1. Organic phase
  2. Dispersed phase
  3. Interfacial phase
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2
Q

What does the organic phase consist of?

A
  1. Monomers, mainly BisGMA
  2. Viscosity controllers
  3. Inhibitors
  4. Thermochemical and photochemical initiators
  5. Accelerators
  6. Additional components
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3
Q

What are the properties of BisGMA?

A
  1. High viscosity
  2. Colourless liquid
  3. Undergoes extensive cross-linkage, making it harder than acrylic resin
  4. High molecular weight (hence, low volatility)
  5. Relatively low polymerisation shrinkage (5-6%)
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4
Q

What are the disadvantages of BisGMA?

A
  1. Radiolucent
  2. Polymerisation is inhibited by air
  3. Absorbs water and takes in stains
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5
Q

What is the purpose of viscosity controllers?

A

To improve the handling properties (by decreasing viscosity) of CR during mixing and insertion as BisGMA, the main monomer, is highly viscous

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6
Q

What is the inhibitor used in CR? What is its purpose?

A

Hydroquinone. To prevent premature polymerisation and ensure long shelf life.

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7
Q

What are the initiators in CR?

A

Photochemical: Camphorquinone
Thermochemical: Benzoyl peroxide

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8
Q

What is the accelerator used in CR?

A

Tertiary aromatic amine

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9
Q

What type of bipolar coupling agent is most commonly used in CR?

A

Silane coupling agent

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10
Q

What is the purpose of coupling agent?

A
  1. Serves as a stress absorber at the filler-matrix interface
  2. Allows adhesion of 2 dissimilar materials, filler and matrix
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11
Q

What are the factors that affect the physical and mechanical properties of CR?

A
  1. Filler fraction
  2. Degree of polymeristion
  3. Water sorption
  4. Coupling efficacy
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12
Q

What are the effects of underpolymerisation of CR?

A
  1. Excessive wear and softness
  2. Loss of retention, leading to breakage
  3. Decreased mechanical properties
  4. Increased solubility
  5. Increased susceptibility to stains
  6. Poor colour stability
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13
Q

What are the 2 principles of polymerisation shrinkage?`

A

Principle 1: CR pulls away from least retentive surface, leading to gap formation and cuspal deformation

Principle 2: Direction of shrinkage is towards light source for light-cured resins, towards centre of mass for auto-cured/chemical-cured resins

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14
Q

What is C factor and the significance of it?

A

C factor is the ratio of bonded surfaces to unbonded surfaces

Significance: The lower the c factor, the lesser the number of bonded surfaces, the lesser the contraction stress on adhesive bond

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15
Q

How does polymerisation shrinkage lead to post-op sensitivity?

A

Polymerisation shrinkage results in gap formation and cuspal deformation.

Gap formation allows for bacteria and fluid to penetrate into tooth, in the long run, possibly leading to pulpal inflammation and thus pain and sensitivity.

Cuspal deformation: Flexure of CR under occlusal load causes hydraulic pressure in tubular fluid to be transmitted to odontoblastic processes

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16
Q

How to reduce risk of post-op sensitivity?

A

Line with dycal for pulpal protection

17
Q

How to compensate for polymerisation shrinkage stress?

A

Incremental placement of CR to reduce C factor and overall setting contraction/polymerisation shrinkage stress

18
Q

Which CR properties does filler fraction affect?

A
  1. MOE
  2. Fracture strength
  3. Fracture resistance
  4. Wear resistance
19
Q

What are the advantages of CR over other restorative materials?

A
  1. Good aesthetics
  2. Good polishability
  3. Availability of different shades to suit patient
  4. Good wear resistance (can withstand abrasive forces of brushing of buccal surfaces of teeth)
  5. Good longevity
  6. No galvanic currents
  7. Micromechanical adhesion to tooth structure
  8. Low thermal conductivity
  9. Biocompatible
  10. Radiopaque - can distinguish between restoration, tooth structure and caries
  11. Mercury-free option of restoration
20
Q

What are the disadvantages of CR over other restorative materials?

A
  1. Technique sensitive
  2. Tooth surface must be cleaned and dry before etching
  3. Polymerisation shrinkage: Incremental placing of CR to reduce polymerisation shrinkage
  4. Problems in bonding to dentin:
    (due to complex histologic structure and variable composition of dentine - constant outward flow of dentinal fluid from pulp reduces adhesion to dentin + presence of odontoblastic processes from pulp into inner portion of dentin; if chemicals used for bonding gets too close to pulp, may cause sensitivity + tooth surface must be dried sufficiently before etching )
  5. Microleakages can lead to post-op sensitivity
  6. Water sorption, takes in stains

Dental Materials (10 decks)

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