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Dental Material Science > Bonding to Teeth > Flashcards

Bonding to Teeth Flashcards

1
Q

Properties of a dental adhesive (3)

A
  1. Provides a high bond strength to tooth tissues
  2. Immediate high strength bond
  3. Durable + impermeable bond
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2
Q

Describe why bonding to enamel is easy

A
  1. Heterogenonus structure (densely packed prismatic)
  2. Highly mineralised: 95%
  3. Dry
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3
Q

What technique is used to bond to enamel?

A

Acid etch technique

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4
Q

Describe the process of the acid etch technique for enamel bonding (4)

A
  1. Long enamel prisms are filled with imperfectly paced hydroxyapatite crystals
  2. This surface can be modified by the application of acid
  3. The acid roughens the surface of enamel producing an etched pattern
  4. The roughened surface allow micro mechanical interlocking of resin filling materials
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5
Q

How is a better wettability of enamel achieved?

A

The etching increases the surface energy of the enamel surface by removing surface contaminants and leading to better WETTABILITY

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6
Q

What is the advantage of better wettability?

A

Allows the resin to adapt better to roughened enamel surface
It then polymerises leading to a strong bond >20 MPa

For this to work the enamel must be dry

Moisture contamination will prevent the flow of resin into the etched surface

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7
Q

What inorganic acid is used for enamel etching?

A

30-50% aqueous solution of phosphoric acid

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8
Q

What is applied to the etched, dried enamel surface?

A

A low viscosity Bis-GMA resin or dentine bonding agents

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9
Q

What makes up dentine composition? (3)

A
  1. 20% organic (mostly collagen)
  2. 70% inorganic (mostly hydroxyapatite)
  3. 10% water
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10
Q

Why is bonding to dentine not as simple as enamel? (7)

A

> Dentine is inconsistent

> Smear layer

> Dentine contains more water, full of permeable tubules

> Hydroxyapatite crystals are arranged randomly in the organic matrix

> Fluid present in dentinal tubules constantly flows dentine pulp to dentine floor of any cavity, which makes the surface wet and educes the adhesion of the composite resin to dentin bond

> Dentine near the pulp has more tubules (containing vital process of the pulp, odontoblasts) and increased moisture content - this makes the dentine a sensitive structure

> Dentine is hydrophilic whereas most simple bonding agents are hydrophobic

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11
Q

What is the smear layer?

A

An adherent layer of organic debris that remains on the dentine surface during the restoration of a tooth

Interferes with adhesion

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12
Q

State the requirements of a DBA (4)

A
  1. Ability to flow
  2. Potential for intimate
    contact with dentine surface
  3. Low viscosity
  4. Adhesion to substrate
    - Mechanical
    - Chemical
    - VW forces
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13
Q

How is MECHANICAL bonding to dentine achieved?

A

SAME AS ENAMEL

> Achieved by DBA and dentine surface interlocking with minimum gaps

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14
Q

In CHEMICAL bonding to dentine whats the bond type for mineralised dentine?

A

Ionic

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15
Q

In CHEMICAL bonding to dentine whats the bond type for organic dentine?

A

Covalent

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16
Q

How does VAN DER WAALS adhesion for dentine occur?

A
  • Based on electrostatic or dipole interaction between bonding agent and substrate
  • Best adhesion/bonding is achieved when VW forces are optimised
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17
Q

What does the strength of VW interaction depend on?

A

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

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18
Q

What does a contact angle of <90 reflect?

A

Means the solid surface is hydrophilic

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19
Q

Define critical surface energy

A

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

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20
Q

What properties of a liquid allows it to flow

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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21
Q

How is a lower surface energy of the material as a whole achieved

A

A low surface energy liquid will speed on a higher surface energy substrate because this leads to a lower surface energy of the material as a whole

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22
Q

Surface energy of wet dentine

A

Wet dentine has a low surface energy, lower than composite filling materials

For composite resin to stick to dentine the surface of the dentine must have a higher critical energy than the composite

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23
Q

How do DBA’s allow composite to stick to the surface?

A

DBA’s increase the surface energy of the dentine surface and allow comp to flow and stick to the surface

(SURFACE WETTING AGENTS)

24
Q

Name an example of a surface wetting agent

25
Q

What makes up the composition of a surface wetting agent? (2)

A
  1. Wet end (lower surface energy than substrate, so will stick to the dentine)
  2. Oily end sticks to double bonds
26
Q

How does molecular entanglement lead to HIGH bond strength? (4)

A

> Adhesive is absorbed onto the surface but can also penetrate into the surface of the dentine

> This is due to good wetting of the dentine by the adhesive and appropriate surface energies of the 2

> The absorbed component can form a long chain polymer

> This polymer meshes with the substrate (MOLECULAR ENTANGLEMENT) leading to a HIGH BOND STRENGTH

27
Q

How thick is the smear layer?

A

It is 0.5-5 microns in thickness

Generally contaminated with bacteria

28
Q

What should be done with a 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

29
Q

DBA’s rely on either ___ or ____

A
  1. Total etch
  2. Self etch

To remove and/or modify the smear layer

30
Q

Examples of total etch 2 stage bonding agents

A
  1. Scotchbond one
  2. Prime and bond
  3. Optibond
31
Q

What make up the components of a total etch DBA?

A
  1. Dentine conditioner
    - Usually 35% phosphoric acid
  2. Primer
    - Really the adhesive part of the agent with a hydrophilic / hydrophobic molecule
  3. Adhesive
    - A resin which penetrates into the surface of the dentine attaching to the primers hydrophobic surface
32
Q

Whats the function of the primer?

A
  1. It is the adhesive element in the process (coupling agent)
  2. Penetrates the demineralised dentine due to its bifunctional molecules
    - This gives the surface high energy, making it hydrophobic
    - Adhesive can now penetrate
    - —> leasing to micro mechanical retention
33
Q

Whats the function of the dentine conditioner?

A
  1. Removes smear layer
  2. Opens dentinal tubules by removing smear plugs
  3. Decalcifies the uppermost layer of dentine
  4. Etchant is washed off with water, the collagen network in this top 10um is exposed and subsequently penetrated by the next 2 components
34
Q

Why does a DBA primer require a spacer group?

A

To make it long enough to be flexible when bonding

Lack of flexibility reduces bonding sites and bond strength

35
Q

Name examples of a coupling agent found in many primers (3)

A

HEMA
4-META
MDP

36
Q

How does the HEMA coupling agent work?

A
  1. The C=C bond opens and forms a strong covalent bond with the next resin layer
  2. The hydroxyl group can combine with similar polar groups on the hydroxyapatite and can react with amine groups on the collagen protein
37
Q

State properties of adhesive (3)

A

> Predominantly hydrophobic
May contain some filler particles to make it stronger
Will contain camphorquinone to allow it to light cure

38
Q

What 2 ends make up a DBA primer?

A

Bifunctional molecule with 2 ends:

Hydrophilic end (bonds to hydrophilic dentine surface)

Hydrophobic end (methacrylate end to bond to the resin)

39
Q

Name some disadvantages of total etch

A
  1. OVER ETCHING
    - leads to to collapse of the collage fibres so no resin can penetrate or stick to it
    - too deep an etch and the primer can’t penetrate to the full depth of the etch
  2. MOISTURE DEPENDENT
    - too dry and dentine surface collapses
    - too wet and the primer is diluted, leading to reduced strength
  3. Can lead to sensitivity for patient
40
Q

What happens if the tooth is over dried during bonding?

A

Dull dry dentine surface leads to:

> Collapsed dentine
Decrease in porosity
Poor penetration of dentine by primer
Leading to POOR bond

41
Q

Explain why moist dentine gives a good bond

A

Moist shiny surface achieved by:

> Expanded dentine surface is porous and will absorb primer
Leading to a GOOD bond

42
Q

What are the 2 components of the bonding system that have been combined?

A
  1. Separate etchant with primer and sealer combined

2. Self etching primer and sealer all combined and applied together as a single solution

43
Q

Advantage of:

Separating etchant with primer and sealer combined

A

> The primer and sealer are combined in a single bottle and applied to the etched, washed dentine and light cured (camphorquinone)

> Allows wetting + sealing of the dentine to occur simultaneously

44
Q

What solvents allow light curing along with camphorquinone?

A
  • Alcohol

- Acetone

45
Q

Function of the self etching primers

A

They work in a different way than other materials

> They do not attempt to remove the smear layer, they infiltrate it and incorporate themselves into it

> They are not washed off

> This removes the problem of how dry to make the dentine

46
Q

Disadvantage of self etching primers

A

Not as technique sensitive but bond does not seem to be as strong to all tooth tissues

47
Q

Function of acidic methacrylate monomers in DBA’s

A

The complex bifunctional monomers etch and infiltrate the dentine surface with their hydrophilic end, while polymerising like a simpler bis-GMA material at the hyodrophic end

48
Q

Disadvantage of monomers with lower pKa

A

Do not form a stable bond as they continue to dissolve HA

This leads to a hybrid layer with unstable calcium phosphates incorporated

49
Q

Disadvantage if too much HA is dissolved away

A

The exposed collagen is vulnerable to breakdown and the bond will fail

50
Q

What does strong self etch work better on?

51
Q

Function of mild self etch

A

> Only partially demineralises the dentine

> HA crystals remain around the collagen

  • Protective against hydrolytic breakdown
  • Remaining Ca ions allow ionic bonding
52
Q

Name an example of a mild etching material

A

Scotchbond universal

53
Q

Disadvantage of HEMA materials

A

HEMA materials are more acidic and absorb more water, leading to a less durable bond

54
Q

Disadvantages of the smear layer

A
  1. If its too thick the mild self etch adhesives won’t be able to penetrate through it
  2. Challenge = penetrating the smear layer without decalcifying tooth surface too much and removing the HA
55
Q

Why does HA need to be preserved in a tooth?

A
  1. Required for a strong durable bonding

2. The HA protects the dentine from hydrolytic breakdown

56
Q

Advantages of self etching bonding agents (6)

A
  1. Less technique sensitive
  2. No rinsing
  3. No excessive drying
  4. No dentine collapse leading to low bond strength
  5. Less chance of post-op sensitivity
  6. Simultaneous demineralisation and resin infiltration
57
Q

Disadvantages of self etching bonding agents (3)

A
  1. There is greater variability between products, with regard to initial pH of the solution
  2. The difference in pH results different etch and different penetration of resin
  3. Materials with lower initial pH may not etch enamel efficiently

Dental Material Science (7 decks)

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