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BDS2 Dental Materials Sciences > Bonding Systems > Flashcards

Bonding Systems Flashcards

1
Q

6 properties of dental adhesive

A
  • Provide a high bond strength to tooth tissues
  • Immediate high strength bond
  • Durable bond – lasts forever
  • Impermeable bond
  • Easy to use
  • Safe – no harm to patient
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2
Q

3 reasons why enamel bonding is easy

A
  • Heterogeneous structure: densely packed prismatic
  • Highly mineralised: 95% inorganic
  • ‘Dry’ no moisture
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3
Q

describe the mechanisms of ‘acid-etch’ technique

A
  • Long enamel prisms are filled with imperfectly packed hydroxyapatite crystals.
  • This surface can be modified by application of acid
  • The acid roughens the surface of the enamel producing a characteristic etched pattern.

Surface is broken down
Etching pattern like keyholes
Rough surface on microscopic level

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4
Q

what does the roughened surface of enamel allow?

A

the micromechanical interlocking of resin filling materials

and increases surface energy of enamel

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5
Q

what does higher surface energy of etched enamel allow?

A

better wettability

resin to adapt better to the enamel

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6
Q

what will prevent the flow of resin into etched enamel?

A

moisture contamination

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7
Q

what type of bonding is enamel bonding/

A

essentially mechanical

  • micromechanical adhesion
  • polymerises (goes hard)
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8
Q

what acid is commonly used in practice for enamel etching?

A

30-50% phosphoric acid

30-35% common

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9
Q

what is applied to etched and dried enamel?

A

dentine bonding agent

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10
Q

name a dentine bonding agent

A

low viscosity Bis-GMA resin

phosphorylated Bis-GMA

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11
Q

what does a dentine bonding agent do?

A

penetrates into the rough surface and is light cured

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12
Q

what is the breakdown of dentine composition?

A

20% organic (mostly collagen)
70% inorganic (most HA)
10% water

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13
Q

is dentine wetter than enamel?

A

yes

fluid pumps up from pulp to dentine floor of any cavity - surface wet

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14
Q

what is the surface energy of dentine?

A

low

due to wettness

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15
Q

is dentine hydrophillic or hydrophobic?

A

hydrophillic

whereas most simple bonding agents are hydrophobic

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16
Q

why is dentine hard to bond to?

A

its physical and chemical qualities

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17
Q

what are some of the qualities that make dentine hard to bond to?

A
  • full of permeable tubules
  • wetter/ lower surface energy than enamel
  • inconsistent material
  • smear layer
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18
Q

describe how dentine is inconsistent?

A
  • aged dentine is more mineralised
  • near the pulp has more tubules and increased moisture content.
  • Different sorts of dentine -Secondary and tertiary is harder to bond to
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19
Q

what are 4 qualities required of a dentine bonding agent?

A
  • ability to flow
  • potential for intimate contact with dentine surface
  • low viscosity
  • adhesion to substrate
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20
Q

how is dentine bonding achieved?

A

dentine bonding agent and the dentine surface meshing and interlocking with minimum gaps

  • easy to see microscopically and on SEM
  • stick to holes in the spaces around the lager holes
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21
Q

what type of bond does mineralised component of dentine form?

A

ionic

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22
Q

what type of bond does the organic component of dentine form?

A

covalent

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23
Q

what is Van der Waals adhesion based on/

A

electrostatic or dipole interaction between bonding agent and substrate

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24
Q

what do Van der Waal strength of interaction depend on?

A

contact angle

  • contact angle of less than 90 degree means the solid surface is hydrophilic - want lowest angle possible
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25
Q

when is the best dentine bonding/adhesion achieved?

A

when Van der Waal forces are optimised

Availability to flow onto surface is dependent on how polar material is compared to substrate

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26
Q

what is critical surface energy?

A

the surface tension of a liquid will just spread on the surface of a solid

  • A liquid must have a lower surface energy than the surface it is being placed on for it to flow onto it and stick.
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27
Q

what type of surface energy is required for something to spread?

A

lower

A low surface energy liquid will spread on a higher surface energy substrate because this leads to a lower surface energy of the material as a whole.
- Flows onto object, lowering surface energy as a whole

28
Q

what do dentine bonding agents do?

A

increase the surface energy of the dentine
allows composite to flow and stick to dentine

they are SURFACE WETTING AGENTS
o Wet end and oily end
o Wet end sticks to substrate oily end sticks out higher surface energy
o Intermediate chemical

29
Q

what is molecular entanglement adhesion?

A
  • The absorbed component can form a long chain polymer
  • This polymer meshes with the substrate - molecular entanglement
  • leading to high bond strength

This is due to good wetting of the dentine by the adhesive and appropriate surface energies of the two.

30
Q

what is the 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 a tooth.

  • Cut surface of dentine and what’s left over
    (Cut with high speed bur)
31
Q

qualities of the smear layer

A
  • It is 0.5 – 5 microns in thickness.
  • Variably attached to the dentine surface.
  • Generally contaminated with bacteria.
  • Originally it was thought of as a protective barrier reducing permeability of the dentine and protecting the pulp.Now it is considered to interfere with adhesion.
     Blockage to good adhesion
     Newer adhesion materials bond to it
  • Difficult to remove – need to use chemicals
32
Q

2 bonding solutions to the smear layer

A
  • Remove it and bond to the ‘clean’ dentine beneath

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

33
Q

what do modern dentine bonding agents rely on?

A

total etch
self etch

to remove and/or modify the smear layer

34
Q

examples of dentine bonding agents that use total/self etch

A
  • Scotchbond multipurpose (first one)
  • Clearfil photo bond
  • Optibond FL
35
Q

3 components of a total etch dentine bonding agent

A

Dentine conditioner:
- An acid, usually 35% phosphoric.

Primer:

  • Really the adhesive part of the agent with a hydrophilic/hydrophobic molecule
  • C=C end and hydrophilic end

Adhesive:

  • A resin which penetrates into the surface of the dentine attaching to the primers hydrophobic surface.
  • Mildly phosphorylated resin
36
Q

what does the dentine conditioner in a dentine bonding agent do?

A

Removes smear layer
- Opens dentinal tubules by removing smear plugs

Decalcifies the uppermost layer of the dentine

etchant is washed off with water.

The collagen network in this top 10um of the dentine is exposed and subsequently penetrated by the next two components.
- Extensive new surface area

37
Q

what does the primer component of dentine bonding agent do?

A

really the adhesive element in the process.

A coupling agent.
- Bifunctional molecule: a hydrophilic end to bond to the hydrophilic dentine surface and a hyrdophobic, methacrylate end to bond to the resin.

Molecule must also have a spacer group

  • Make it long enough to be flexible when bonding.
  • Lack of flexibility reduces bonding sites and bond strength.

Molecule or group of molecules is dissolved in a suitable solvent.
- Ethanol, acetone or water.

38
Q

what is a common coupling agent found in many primers of dentine bonding agents?

A

HEMA

- Hydroxy ethyl methacrylate

39
Q

name some chemicals used as dentinal primers in dentine bonding agents

A

HEMA
- Hydroxy ethyl methacrylate

NTG-GMA

4- META

MDP

GPDM

40
Q

what is the adhesive component of dentine bonding agents?

A

Mixture of resins.
- Usually Bis-GMA and HEMA.
Predominately hydrophobic.
- May contain some filler particles to make it stronger.

Will contain Camphorquinone to allow it to light cure.

41
Q

what does the adhesive component of dentine bonding agents do?

A

Penetrates the primed dentine which now has a hydrophobic surface.
- Forms a micromechanical bond within the tubules and exposed dentinal collagen fibres.

MOLECULAR ENTANGLEMENT
Forms the HYBRID LAYER of collagen plus resin.
- Collagen fibrils, hydroxyapatite and resin meshed in one layer

42
Q

what is the hybrid layer of collagen and resin?

A

Collagen fibrils, hydroxyapatite and resin meshed in one layer

formed by the micro-mechanical bond within dentinal tubules and exposed dentinal collagen fibres
- molecular entanglement due to adhesive

43
Q

3 main steps in bonding to dentine

A

Etching Dentine –> demineralisation of the outer layer.

  • The remaining collagen is hydrophilic and has low surface energy.
  • Normal resin will not bond to it.

Primer can penetrate the demineralised dentine due to its
bifunctional molecules. This gives the surface high energy,
making it hydrophobic
- Single molecule fit

Adhesive can now penetrate–> micro mechanical retention
- Resin tags into tubules
(impregnate)

44
Q

2 problems with total etch

A
  • over etching

- moisture dependent

45
Q

what will happen if you over etch dentine?

A

collapse of the collagen fibres so no resin can penetrate – can’t stick, decreased porosity (not loofa like)

  • too deep an etch and the primer cannot penetrate to the full depth of the etch. – primer doesn’t go deep enough – sensitivity
46
Q

what will happen if dentine is too wet?

A

primer is diluted so reduced bond strength

47
Q

what will happen if dentine is too dry?

A

dentine surface will collapse - nothing to stick to

dull, dry

48
Q

what are the 2 condensed versions of dentine bonding?

A
  • Separate etchant with primer and sealer combined. (2 separate)
  • Self-etching primer and sealer all combined and applied together as a single solution. (all combined)
49
Q

what is the separate etchant with primer and sealer combined dentine bonding technique?

A

Total Etchant is still Phosphoric Acid.

Primer and sealer are combined in a single bottle and applied to the etched, washed dentine and light cured.
- Should allow the wetting and sealing of the dentine to occur simultaneously.

The chemicals in the single bottle are the same as in the primer bottles (e.g. HEMA, GPDM, MDP, 4-META) but are combined with a resin Bis-GMA and a solvent such as alcohol or acetone
- and camphorquinone to allow light curing.

50
Q

what is the most commonly used dentine bonding technique?

A

separate etchant with primer and sealer combined

51
Q

how does self-etching dentine boning work?

A

Do not attempt to remove the smear layer. (no phosphoric acid)
- infiltrate it and incorporated themselves into it. (phosphoric monomers?)

They are not washed off.

  • This removes the problem of how dry to make the dentine.
  • No risk of over or under drying

Not as technique sensitive but bond doesn’t seem to be as strong to all tooth tissues.

52
Q

what are the molecules in self-etch like?

A

contain acidic methacrylate monomers such as Methacryloyloxyalkyl acid phosphatase.
- Acidic monomer

These very complex Bifunctional monomers etch and infiltrate the dentine surface with their hydrophilic end while polymerising like a simpler bis-GMA material at the hydrophobic end.
- Complicated long chain molecules, do everything at once

The acidic groups react with Ca2+ ions in the tooth bonding to the surface and also create an amorphous Calcium chelate on the surface.

53
Q

what happens to the smear layer in self-etching dentine bonding?

A

smear layer is dissolved but then incorporated into the hybrid layer
- only penetrates about 2 um into the surface but can give good bond strengths to dentine.

54
Q

what is an advantage of self-etching dentine bonding

A

evidence for reduced sensitivity.
- No drying stage so no chance of collapse of dentine architecture preventing resin penetration and hybrid layer formation

55
Q

what us the fundamental mechanism of all bonding?

A

mineral exchange

minerals removed from the dental hard tissue are replaced by resin which once mineralized mechanically interlock in these porosities.
- Molecular Entanglement

o Take mineral out of HA
o Matrix with them and resin

56
Q

what is the interaction if these molecules with HA based tissue described as?

A

Adhesion-Decalcification concept ‘AD-concept’

57
Q

what happens in the adhesion- decalcification concept?

A

Initially all acid monomers bond to the calcium in HA ionically.

Whether they stay bonded depends on the stability of the HA-monomer bond.
- Monomers with lower pKa (not necessarily pH) do not form a stable bond as they continue to dissolve HA

leads to a hybrid layer with unstable calcium phosphates incorporated

58
Q

what are the problems with strong self-etch to dentine?

A

Etching by-products are not washed away as in total etch
- These are soluble and weaken the integrity of the bond
- Acid stays there as is not washed away, causes weakening of bone – never want an extreme environment
stability

If too much HA is dissolved away the exposed collagen is vulnerable to breakdown and the bond will fail
- Hydrolytic enzymes in mouth dissolve bond between the dentine and resin

59
Q

what does strong self-etch bond better too?

A

bonds better to enamel than dentine

60
Q

what does mild self-etch do to dentine?

A

only partially demineralises the dentine (e.g. Scotchbond Universal)
- HA crystals remain around the collagen

  • Protective against hydrolytic breakdown
  • Remaining Ca ions allow more ionic bonding
61
Q

which chemicals are better for dentine bonds?

A

MDP
4-META

better than HEMA (more acidic and adsorb more water –> less durable bond)

62
Q

2 advantages of self-etching bonding agents

A

Less technique sensitive

  • No rinsing
  • No excessive drying
  • No dentine collapse leading to low bond strength

Simultaneous demineralisation and resin infiltration
- Less chance of post-op sensitivity

63
Q

what form of etching is best for self-etching DBAs?

A

selective etching of enamel

good bond to dentine already

64
Q

what is a problem with the smear layer?

A

If thick then ‘Mild’ self-etch adhesives may not penetrate through it.
- Not penetrated enough

3-4 microns into surface etching
5 microns smear layer

65
Q

what is HA role in bonding?

A
  • required for strong durable bonding

- protects the dentine from hydrolytic breakdown

BDS2 Dental Materials Sciences (13 decks)

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