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Dental Materials > Bonding Systems > Flashcards

Bonding Systems Flashcards

1
Q

What type of bonding is enamel bonding?

A

Mechanical

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2
Q

What acid etch is usually used for enamel bonding

A

30-50% phosphoric acid

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3
Q

What is the composition of dentine?

A

20% organic (mostly collagen)
70% inorganic (mostly hydroxyapatite)
10% water

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4
Q

How is dentine an inconsistent material?

A

Aged dentine more mineralised

Dentine near pulp has more tubules and increased water content

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5
Q

What is the surface energy of dentine like?

A

LOW surface energy

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6
Q

4 requirements of a dentine bonding agent

A

Ability to FLOW
potentional for INTIMATE CONTACT with dentine surface
LOW VISCOSITY
ADHESION to substrate

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7
Q

3 ways adhesion to substrate is achieved

A

Mechanical
Chemical
Van der Waals
(Or combination)

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8
Q

How is mechanical adhesion achieved?

A

Achieved by DBA and dentine surface MESHING and interlocking together with MINIMUM GAPS

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9
Q

How is chemical adhesion achieved?

A

Bonding at a MOLECULAR LEVEL

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10
Q

What type of bond would the mineralised and organic constituents of dentine have?

A

Mineralised- IONIC bond

Organic- COVALENT bond

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11
Q

How is Van der Vaals adhesion achieved?

A

Based on ELECTROSTATIC or DIPOLE INTERACTION

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12
Q

What does the strength of van der Waals adhesion depend on?

A

Depends on CONTACT ANGLE, which is a good indication of WETTABILITY of a solid by a specific liquid

A contact angle of

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13
Q

Define critical surface angle

A

The surface tension of a liquid that will JUST spread of the surface of a solid

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14
Q

Define contact angle

A

The angle between the liquid surface and the solid surface, when a solid and liquid make contact

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15
Q

What surface energy must a liquid have to flow and stick

A

A liquid must have a lower surface energy than the surface it is being placed on

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16
Q

What material is placed on frying pans because it has such a low surface energy?

A

PTFE

17
Q

What are surface wetting agents?

A

DBAs increase critical surface energy of dentine to allow composite to flow and stick to surface

18
Q

How are DBAa bonded to dentine

A

Adhesion through molecular entanglement

19
Q

Define smear layer

A

An adherent layer of ORGANIC DEBRIS that remains on the dentine surface after the preparation of the dentine during the restoration of the tooth

20
Q

2 ways to deal with smear layer

A

Remove it and bond to ‘clean’ dentine beneath

Incorporate it by penetrating it, infiltrating it with bonding agent and stick it to the dentine below

21
Q

4 problems with dentine bonding

A

Dentine is hydrophilic where as most adhesive are hydrophobic
Dentine is vital tissue
Dentine consists of both organic and inorganic material
Covered by smear layer

22
Q

What are the 3 components of total etch DBA

A
  1. Dentine conditioner: an acid- usually 35% phosphoric
  2. Primer: adhesive part- with hydrophilic/hydrophobic molecule
  3. Adhesive: a resin which penetrates into the surface of the dentine attaching to the primers hydrophobic substance
23
Q

What is the function of the dentine conditioner in total etch DBA.

A

Removes smear layer
Opens dentinal tubules (by removing smear layer)
Decalcifies uppermost layer of dentine

24
Q

Function of primer in total etch DBA

A

Adhesive element in process

A coupling agent (usually HEMA)
Bifunctional- hydrophilic end to bond to hydrophilic dentine surface
Hydrophobic, methacrylate end to bond to the resin

25
Q

Composition and function of adhesive in total etch DBA

A

A mixture of hydrophobic resins (usually Bis-GMA and HEMA)
May contain filler particles to make it stronger
Will contain CAMPHORQUINONE to allow it to LIGHT CURE

Penetrates primed dentine and forms micromechanical bond within tubules and exposed dentine collagen fibres

Forms HYBRID LAYER of collagen plus resin

26
Q

Summary of actions of total etch DBA

A

Etching dentine:

  • demineralisation of outer layer
  • remaining collagen in HYDROPHILIC and has LOW SURFACE ENERGY (normal resin will not bond to it)

Primer:

  • can penetrate dentine due to its BIFUNCTIONAL MOLECULES
  • gives the surface HIGH ENERGY, and making it HYDROPHOBIC

Adhesive:

  • can now penetrate
  • MICROMECHANICAL RETENTION
27
Q

2 problems with total etch

A

Overetching:

  • collapse of collagen fibres– resin can’t penetrate
  • too deep an etch, primer can’t penetrate full depth

Moisture dependant:

  • too dry and dentine surface collapses
  • too wet and primer is diluted- reduced strength
28
Q

Name 6 ideal dental adhesive properties

A 
Provide high BOND STRENGTH 
IMMEDIATE high bond strength 
DURABLE bond
IMPERMEABLE bond
EASY to use
SAFE

Dental Materials (1 decks)

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