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Dental Materials > Bonding And Bonding Agents > Flashcards

Bonding And Bonding Agents Flashcards

1
Q

A dental bonding system provides which three essential functions

A
  1. Provides resistance to separation of an adherend substrate from a restorative/cementing material.
  2. Distributes stress along bonded interfaces
  3. Seals the interface via adhesive bonding between dentin and/or enamel and bonded material.
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2
Q

Which was the first bonding system based on

A

The first bonding agent was based on glycerophosphoric acid dimethacrylaye as a self-adhesive or self-ethching component for both enamel and dentin bonding

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3
Q

What are applications for bonding

A

Acid etching, effective ways to promote restoration and retention to ensure a sealed interfacial joint at restoration margins.

Provides strong,durable bond between resin and tooth structure.

Additional applications include pit and fissures sealants, amalgam bonding, enamel and dentin bonding,
Adhesive cements and endodontic sealers

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4
Q

True adhesion of restorative materials is to be achieved by

A
  1. Sound tooth structure must be conserved.
  2. Optimal retention must be achieved.
  3. Microleakage must be prevented
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5
Q

The fundamental mechanism of adhesion to tooth structure

A

Exchange by which the inorganic tooth material (hydroxyapatite) is replaced by synthetic resins

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6
Q

How is replacement of inorganic tooth material replaced by synthetic resins

A
  1. Removing hydroxyapatite to create microspores
  2. Infiltration of resin monomers into microspores and subsequent polymerization
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7
Q

Which factors can play roles in achieving adhesive bonds

A
  1. Surface energy and wetting
  2. Interpenetration (formation of hybrid zone)
  3. Micro mechanical interlocking
  4. Chemical bonding
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8
Q

Categories of wettability

A
  1. Mostly non wetting (>90°)
  2. Absolutely no wetting (180°)
  3. Mostly wetting (<90°)
  4. Absolutely wetting (0°)
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9
Q

Wettability can be enhanced by

A

Increasing the surface energy of substrates (enamel,dentin, synthetic materials)

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10
Q

What is important for achieving lasting intraoral bonds

A

For an adhesive monomer to wet hard tooth tissue as well as form a durable bond in the moist environment of the mouth, it must be:-
Hydrophilic for water compatibility and
Hydrolytically stable to ensure longetivity .

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11
Q

What is smear layer

A

When both enamel and dentin tissues are mechanically cut, a layer of adherent grinding debris and organic film known as smear layer is left on their surface and prevents strong bonding

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12
Q

What does the smear layer do in dentin

A

Becomes burnished into underlying dentinal tubules and lowers dentin permeability which is a protective effect .
But it is also a weak cohesive material and interferes with strong bonding.

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13
Q

Who gave first meaningful demo of acid etching

A

Michael Buonocore

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14
Q

What does phosphoric acid do to smear layer

A

It removes the smear layer and about 10 microns of enamel to expose prisms of enamel rods to create a honeycomb like high energy retentive surface.

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15
Q

Type 1 etching

A

The enamel rod centers

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16
Q

Type II etching

A

The peripheral areas

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17
Q

Higher surface energy ensures

A

That resin monomers will readily wet the surface, infiltrate into microspores and polymerize to form resin tags.

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18
Q

Who and when was the total etch concept introduced

A

Fusayama in 1979

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19
Q

Total etch used

A

Both dentin and enamel are etched simultaneously using 37% phosphoric acid.

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20
Q

What is hybrid layer

A

Hydrophilic resins can infiltrate the surface layer of acid-demineralized collagen fibres that is produced in etched dentin and can form a layer of resin infiltrated dentin with high cohesive strength

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21
Q

Hybrid layer forms

A

A very strong resin bonds through development of the interpenetrating network of polymer and dentinal collagen.

22
Q

Etch and rinse technique

A

Since total etch technique usually involves etching with an acid followed by rinsing to remove the acid.
It’s also known as etch and rinse.

23
Q

Why is denting etching more technique sensitive than enamel etching

A

Because of the complexity of the dentin structure.v
Dentin is a living tissue with 50 vol% of calcium phosphate mineral, 30 vol% organic material and 20 vol% fluid .

24
Q

Acid etching in dentin

A

Removes hydroxyapatite almost completely from several microns of sound dentin, exposing a microporous network of collagen suspended in water.

25
Q

Significance of water in dentin during etching

A

If insufficient water is present, the collagen network will collapse and produce a relatively impermeable layer that prevents resin infiltration and subsequent hybridization.

If too much water is present,resin infiltration cannot fully replace the water in the collagen network and sets the condition for later leakage in that locations.

26
Q

Process and procedural factors are:-

A

Etching time.
Rinsing and drying stage
Cleanness of bonding surfaces
Others

27
Q

Etching time

A

For most etching gels it’s 15 secs.

A permanent tooth surface with high fluoride content may require longer etching times as do primary teeth.

Advantages of short etching time:-
-Reduce treatment time
-yield acceptable bond strength
-conservation

28
Q

Rinsing and drying stage

A

Once the tooth is etched, it should be rinsed away in a stream of water for the 20s and the rinse water is removed.

Enamel is etched and is to be bonded with bis-GMA based resin. So it must be completely dry with warm air until it takes on white, frosted appearance.

Dentin cannot withstand such aggressive drying, which causes bond failure of the formation of impermeable collapsed collagen fibres, so in total etch for dentin both bonding agent and primer must be compatible for it moist dentin and enamel

29
Q

Cleanness of bonding surfaces

A

Although etching raises the surface energy, contamination can readily reduce the energy level of the etched surface.

Even momentary contact with saliva or blood can prevent effective resin tag formation and severely reduce bond strength.

Oil that is released from the air compressor and transported along the air lines to the air-water syringe.

If contamination occurs , the contaminant should be removed and the surface should be etched again for 10s.

30
Q

Denting bonding Agents

A

Are designed to provide sufficient strong interface between restorative composites and tooth structure. To withstand mechanical forces and shrinkage stress

31
Q

What types of bond formation result from use of dentin bonding agent

A

Micro mechanical, chemical bonding with enamel and dentin or both.

Copolymerization with the resin matrix of composite material

32
Q

A successful denting bonding system must meet the following requirements:-

A
  1. Adequate removal or dissolution of the smear layer from enamel and dentin
  2. Maintenance or reconstitution if dentin collagen matrix
  3. Good wetting
  4. Efficient monomer diffusion and penetration
  5. Polymerization within tooth structure
  6. Copolymerization with the resin composite Matrix.
33
Q

Composition of Etchant

A

-strong acids (ph 1-2)
-used to remove smear layers and to dissolve mineral phase to allow formation of micro mechanical interlocking in enamel and in dentin.
-phororic acid at 30% and 50%, typically 37% is preferred.
-Etchant is supplied as aqueous gels, made by adding colloidal silica or
Polymer beads to acid.

34
Q

What happens when the concentration of phosphoric acid is greater than 50% in Etchant.

A

Deposition of an adherent layer of mono calcium phosphate monohydrate in the etched surface which inhibits further dissolution.

35
Q

Composition of primer

A

Contains hydrophilic monomers dissolved in solvent as acetone, water or ethanol.
Monomers exhibit its hydrophilic property through carboxylic acid, alcohol, or ester functional groups.

36
Q

Why is priming necessary

A

To maintain an expanded collagen network while removing residual water to allow for infiltration of the hydrophobic adhesive monomer

37
Q

Most widely used primer monomer and why

A

HEMA (2-hydroxyethyl methacrylate) because of its high hydrophilicity and solvent-like nature.

38
Q

Rank of functional groups in their acidity is

A

Sulfonic acid> phosphonic> phosphoric> carboxylic>alcohol

39
Q

Solvents Used commonly and why

A

Water, acetone, ethanol.
Water- can ionize acidic monomers as well as expand the collapsed collagen network.
Ethanol and acetone have better miscibility with hydrophobic monomers and their “water chasing” ability facilitates water removal.

40
Q

Adhesives’ primary purpose

A

To fill the interfibrillar space of collagen network, creating a hybrid layer and resin tags to provide mircomechanical retention upon polymerization.

It should prevent fluid leakage along the restorative materials margin since they make up major part of intermediate layer between dentin and enamel and restorative composites.

41
Q

Why do adhesives needs to be hydrophobic

A

So that fluid will not be allowed to permeate through the intermediate layer.

42
Q

Adhesives are composed of

A

Hydrophobic dimethacrylates such as bis-GMA, TEGDMA and urethane dimethacrylates and small amount of hydrophilic monomer like HEMA

43
Q

Initiators

A

Photoinitiator system consisting of photosensitiser (camphorquinone)
And an initiator (tertiary amine)
And chemical initiator (benzoyl peroxide) .

44
Q

Filler particles

A

Nanometer sized silica particles added to some adhesive and thereby produce higher bond strengths.
But the strengthing effect is uncertain whether these fillers can penetrate into the demineralised collagen networks since the interfibrillar space of collagen network is withing the range of 20nm while the filler particles have size of 40nm.

45
Q

Other ingredients in Etchant

A

Glutaraldehyde - disensitizer
Monomer 12-methacryloydodecylpyridinium bromide, MDPB and paraben - antimicrobial
Fluoride- to prevent secondary caries.
Benzalkonium chloride and chlorhexidine - to prevent collagen degradation.

46
Q

Properties of bonding agents

A
  1. Measurement of bond strength
  2. Measurement of microleakage
  3. Aging effects and degradation of the hybrid layer.
47
Q

Why are dentin bond strength values so variable

A

The wide variance in data is described by the coefficient of variation , may be attributed to the variables inherent at the dentin surface such as water content, presence or absence of smear layer, dentin permeability, orientation of tubules relative to surface and difference in the invitro test design and stress distribution to the interface.

48
Q

How much should be the bond strength

A

20 MPa or higher

49
Q

How can the degree of microleakage be monitored

A

By the penetration of tracers and staining agents.

50
Q

What does the change of bond strength over time indicates

A

The bond strength of three step adhesive system show little or no decrease in contrast to 2-step adhesive system that decrease significantly over 4-5 year span.

The peripheral bonding to etched enamel which seals the resin bond from exposure to water can increase the bond durability.

Dental Materials (4 decks)

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