Composites: Bonding to Dentine Flashcards

1
Q

Is tooth tissue hydrophobic or hydrophilic?

A

Hydrophilic

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2
Q

Are most restorative materials hydrophobic or hydrophilic?

A

Hydrophobic

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3
Q

What adhesive bonds can occur between tooth tissue and restorative material? (3)

A
  • Micromechanical
  • Molecular entanglement
  • Chemical
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4
Q

Which bond needs to be achieved for longevity between tooth tissue and restorative material?

A

Chemical bond

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5
Q

What are some advantages of adhesives? (6)

A
  • Better aesthetics
  • Conservation of tooth tissue
  • Reinforcement of weak tooth structure
  • Reduced marginal leakage
  • Reduced potential for pulp sensitivity
  • Range of techniques
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6
Q

What are the ideal requirements for adhesives? (5)

A
  • Provide high bond strength to enamel and dentine
  • Immediate and durable bond
  • Prevent ingress of bacteria
  • Safe to use
  • Simple to use
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7
Q

Composition of enamel structure by weight;

Mineral?
Organic material?
Water?

A
  • 96% Mineral
  • 1% Organic material
  • 3% Water
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8
Q

When would you need to bond a restoration to enamel? (2)

A
  • Orthodontic appliances

- Bridges

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9
Q

Comment on the surface tension of enamel compared to the adhesive resin

A

Surface tension of enamel is lower than that of the adhesive resin so perfect wetting cannot take place, (The resin will not flow/cover the enamel surface appropriately)

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10
Q

What layer covers enamel?

A

Pellicle layer

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11
Q

How can adhesion onto an enamel surface be achieved?

A
  • Pellicle layer of enamel must be removed

- Enamel surface must be etched to raise surface tension

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12
Q

How is the pellicle layer removed and enamel
etched?

What chemical is used for this?

A
  • Using the acid-etch technique

- Using 30-50% phosphoric acid on the enamel surface

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13
Q

What are the main effects of the acid etch technique? (4)

A
  • Increased surface roughness
  • Surface energy is raised
  • Improved wettability
  • Opens inner prism area for interlocking tag formation
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14
Q

What visible appearance is present when adequate etching has been achieved?

A

When the enamel has a ‘frosty appearance’

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15
Q

What is recommenced to apply after an acid-etch before you place a composite?

A

Recommended to apply a resin of low viscosity (eg. unfilled Bis GMA, or dentine adhesive resin)

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16
Q

Name some dental procedures where the acid-etched enamel is used for (6)

A
  • Fissure sealing
  • Direct composite
  • Ceramic veneers
  • Resin bonded bridges
  • Orthodontic brackets
  • Periodontal splinting
17
Q

Why does a restorative resin have to be adhesively bonded to dentine?

A

To retain the restoration in the cavity and to
eliminate marginal gaps in order to prevent
bacterial microleakage

18
Q

Composition of dentine structure by weight;

Inorganic hydroxyapatite?
Organic material?
Water?

A
  • 70% Inorganic HA
  • 20% Organic material (Hydrated Collagen)
  • 10% Water
19
Q

What happens when dentine is cut? (2)

A
  • Fluid is pumped through the dentine tubules giving a wet surface
  • Inorganic HA crystals are broken up, the collagen is stretched, torn, and smeared over the cut surface
20
Q

What is the organic material of dentine mostly composed of?

A

Hydrated collagen

21
Q

What are the 3 essential components of a dentine bonding agent?

A
  • Conditioner
  • Coupling agent
  • Sealer
22
Q

What is the role of the conditioner in a dentine bonding agent?

What property of the conditioner allows it to do that?

A

Acidic so clears smear layer

23
Q

What is the role of the Coupling agent in a dentine bonding agent?

What molecule does it contain?

A

Used as the adhesive

Hydroxyethyl methacrylate (HEMA)

24
Q

What is the role of the Sealer in a dentine bonding agent?

What agents can be used as sealers?

A

Seals the dentine tubules

Unfilled Bis GMA or UDMA

25
Q

The interpenetrating layer of dentine and resin is referred to as?

A

The hybrid zone

26
Q

What are the bonds found in dentine adhesion? (2)

A
  • Micromechanical

- Entanglement

27
Q

Explain the bonding between the dentine tubules and coupling agent

A

Molecular entanglement with OH groups of primer

28
Q

Explain the bonding between the coupling agent and the sealer

A

Methacrylate group of coupling agent chemically bonds to Methacrylate group of sealer

29
Q

Explain the bonding between the sealer and filled-composite material

A

Methacrylate group of sealer chemically bonds

to Methacrylate group on filled composite materials

30
Q

What will happen if there is excessive desiccation of dentine?

A

Post operative pulpal sensitivity and a poor bond

31
Q

If there is bond failure amongst dentine adhesion what may occur?

A

Pulpal inflammation leading to bacterial leakage

32
Q

What are some potential causes for adhesive bond breakdown? (4)

A
  • Polymerisation shrinkage
  • Differential thermal expansion and contraction
  • Internal stresses from occlusal loading
  • Chemical attack (hydrolysis)