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Semester II - Dental Materials > Dental Bonding > Flashcards

Dental Bonding Flashcards

1
Q

What does Adhesion mean?

A

Force which binds 2 differing materials together when they are in intimate contact with one another

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2
Q

What does Dental bonding mean?

A

Process of attaching a resin composite based material to the underlying tooth tissue using some form of intermediate material

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3
Q

What does Sealing mean?

A

Achievement of an impermeable barrier between the cavity wall and the restorative material to prevent the passage of bacteria

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4
Q

Give 6 advantages of bonding?

A
  • No preparation of any mechanical retentive features necessary so tooth tissue is preserved
  • Enhanced retention of the restoration to tooth tissue
  • Seals the margins of the restoration with the tooth so reducing or eliminating microleakage
  • Polymerisation shrinkage may be reduced
  • Bonding to the tooth tissue may have a reinforcing effect on the weakened tooth structure
  • Permits tooth coloured restorative materials to be used
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5
Q

What are the characteristics of Bonding?

A
  • Solid-liquid interface is commonly encountered i.e intervening layer (adhesive) is generally applied as a liquid
  • More readily wets the surface to be bonded
  • Easier with a liquid and solid surfaces rather than solid-solid
  • Needs good wetting for good bonding
  • Viscosity of the liquid will limit the degree to which it wets the surface - less viscous the better
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6
Q

What is wetting?

A

Ability of a material to achieve an intimate microscopic contact with another

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7
Q

What’s surface Tension?

A

The elastic tendency of the a fluid surface which makes it acquire the least surface area possible

AKA

Ability of the surface of a liquid to resist an external force

  • Higher the surface tension, the lower is the ability of bonding to it

(Oil doesn’t bond to/stays on top of water due to having a greater surface tension)

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8
Q

How many types of adhesion are possible at the interface?

A

3

Mechanical
Physical
Chemical

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9
Q

What’s Mechanical Adhesion?

A
  • Utilises the rough aspect of all surfaces at a microscopic level

If both surfaces are uncontaminated, the irregularities in surface can connect and an attempt to slide one against the other is resisted by friction

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10
Q

What’s Physical Adhesion?

A
  • Due to molecular charges
  • Dipolar molecule is attracted to an opposing charge on the other substrate
  • Substrates orientate themselves so that the oppositely charged ends of the molecules are adjacent to eachother - relatively weak
  • Increasing the surface area increases the forces to attract
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11
Q

What’s Chemical Adhesion?

A
  • Dissociation of a substrate structure after the application onto the surface of other
  • Bonding process enhanced when the fluid contains a chemical which interacts with the substrate surface
  • Failure is due to substrates rather than interface
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12
Q

What’s the aim of Dental Bonding?

A

Use a combination of adhesion methods to bind the restoration to the tooth

  1. Tooth surface is usually rough and intervening layer of resin fills these micro/macroscopic irregularities
  2. Restorative surface has a relatively rough surface due to the filler causing irregularities
    - Liquid resin (bonding agent) flows into the irregularities produced by the surface modification of the enamel (created by etching)

Resin solidifcation on polymerisation and the 2 materials become mechanically and chemically bound together

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13
Q

What are the essential prerequisities of a substrate (tooth) surface?

A
  1. Rough
  2. Large surface area
  3. Good wetting properties
  4. High surface energy
  5. Free from debris and organic material
  6. Dry
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14
Q

How do you ensure the tooth surface is free from debris and organic material?

A

Prophylaxis

  • Surface should be cleaned thoroughly to remove AEP and plaque
  • Use a pumice slurry and make sure a rubber dam is used
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15
Q

Why do we need to acid etch enamel?

A
  • Outer layer is amorphous and has very little means of retention
  • Very smooth and poor for micro-mechanical bonding
  • > To enhance irregularities
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16
Q

What is Acid Etch?

A

Partially demineralise the crystalline structure of enamel to create a pitted surface for resin infiltration

  • Critical requirement or any bonding process - substrate (tooth) prep
  • Removes interprismatic enamel creating pits/clefts
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17
Q

What will etching of the enamel do?

A
  1. Increase surface area for bonding
  2. increase surface roughness
  3. Decrease surface tension
  4. Increase wettability
  5. Increase the surface energy
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18
Q

What’s the appearance of enamel after etching?

A

Frosted

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19
Q

Why does bevelling enamel improving the quality of etching?

A
  • Removes the outer amorphous enamel exposing fresh enamel for bonding and roughening its surface
  • Alters the angulation of the enamel prisms and ensures that no unsupported prisms remain
  • Higher bond strength may be achieved
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20
Q

What should you take into consideration when etching?

A
  • Etching time should be extended for unprepared enamel to achieve a successful etch
  • Same with older enamel due to increased fluoride content
  • Primary enamel contains more prismless enamel surface so etching time needs to be increased to penetrate deep into the underlying prismatic enamel
  • Bond strength is generally low though
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21
Q

What’s over-etching?

A
  • Leaving the etch on for too long

Causing decalicifation of the substrate to too great a depth so losing the etch pattern and decreased ability of the resin to form tags to penetrate into the etched pattern

  • LOWER BOND STRENGTH AND INCREASED SENSITIVITY
22
Q

What acid is typically used to etch enamel?

A

Ortho-phosphoric acid

  • 35-37% conc applied for 15-30 secs (30-50% optimum range)
  • Most be strong enough to etch but not too concentrated so that the small amount of water present doesn’t get saturated as this would slow dissolution rate
  • Read manufacturers instructions
23
Q

What forms can etching agents be found in?

A

Liquid and gel

24
Q

What’s liquid etching agent?

A

Typically a low viscousity liquid; flows easily - aids localisation of the acid solution = more precision

  • But difficult to control
  • Viscosity can be increased via the addition of fine particles
    of collodial silica
25
Q

What’s gel etching agent?

A
  • More viscous than liquid and stays in place
  • A balance is needed in terms of viscosity - should be viscous enough to be placed precisely + remain there

BUT

  • Not too viscous where it doesn’t penetrate into the smallest fissures

WE USE: SCOTCHBOND ETCHANT (3M) (35% PHOSPHORIC ACID GEL)

26
Q

What should you do after apply etch (either liquid or gel)?

A
  • Newly etched surface and exposed crystallites are friable and may breakdown
  • Acid should be gently agitated during application - removes etch solution at the surface of the tooth which has been contaminated with products of dissolution
  • Movement introduces fresh acid to the surface so enhancing the efficacy and effectiveness of the etch process
27
Q

What do you do to the enamel after applying and washing off the etch?

A
  • Apply Bonding material
  • Low viscosity dilute dimethacrylate resin (bis-GMA + TEGDMA)
  • Add after etching - flows into the crevices formed - monomer is then polymerised to form a solid polymer

up to 30μm deep into enamel surface

  • The resin composite is then added to this
28
Q

Should you treat Dentine differently?

A

YES

  • It’s a living tissue and heterogeneous
  • More problematic for bonding:
    + always wet
    + surface is difficult to clean
    + frequently contaminated with smear (debris from cutting process)
29
Q

What considerations should be applied to dentine?

A
  • Smear layer must be removed or else the restoration won’t be viable
  • Dentinal fluids flow out of the tubules which can contaminate the surface
30
Q

What 3 chemical processes must occur to bond to dentine?

A
  1. (Priming) Removal of the smear layer and the etching of the dentine
  2. (Coupling agent) impregnation of the dentine by a water miscible fluid or one which will substitute for the water
  3. (Sealer) Application of a fluid which will bond to both the impregnated material and the overlying restorative or cast restoration
31
Q

What is used to remove the smear layer and dentine etching?

A 
- Phosphoric acid
OR
- Nitric acid
OR
Ethylene diamine tetra-acetic acid (EDTA)
32
Q

What happens during Dentine Etching (priming)?

A

Modifies/removes the smear layer

Followed by partly demineralisation of the intertubular dentine and the periphery of the dentinal tubules

  • Extends to depths of 10μm
33
Q

What’s the end result of dentine etching (priming)

A

Collagen matrix is left and uncollapsed (like dried spaghetti sticking up)

  • Acts as a scaffolding which may be impregnated with the primer

(TOO MUCH ETCHING OR DRYING MAY COLLAPSE THE COLLAGEN MATRIX SCAFFOLDING)

34
Q

What’s the coupling and sealing process?

A
  • Bifunctional monomer has the role of ionically linking to the hydrophobic methacrylate groups in the sealer to the collagen and hydroxyapatite in the hydrophilic dentine
  • Called AMPHIPHILIC (has a polar, water-soluble group attached to a non-polar, water-insoluble hydrocarbon chain)
  • Has a inert backbone
35
Q

How is the bonding agent carried?

A
  • Chemicals for bonding are dissolved in some form of solvent (hydrophilic chemicals which rapidly pass through the conditioned dentine carrying the coupling agent with them)
  • Infiltrates the partly demineralised layers as well as passing into the dentinal tubules

ALCOHOL/ACETONE/WATER USED

36
Q

What are the benefits of using a solvent as a carrier?

A

It displaces water in the dentine and are removed after they have served their function

37
Q

What are the features of alcohol-based carriers?

A
  • Evaporates less quickly
  • Less sensitive to dentinal moisture
  • Not as good at water chasing as acetone
  • Decreased postoperative sensitivity
  • May increase shelf-life of product containing acetone
38
Q

What are the features of acetone-based carriers?

A
  • Evaporation may be too fast; limiting penetration of the solute into the dentine
  • More sensitive to dentinal moisture so more technique sensitive if the tooth is overdried
  • Aggressive water chasing (removal of water of dentinal tubules)
  • Bad odour
  • Multiple coats may be require
39
Q

What are the features of water-based carriers?

A
  • Hydrophilic so better for substrate (dentine)
  • Does not need to evaporate but has a long drying time
  • Rehydrates demineralised collagen after drying of the primer
  • Water may interfere with adhesion
  • Difficult to remove
40
Q

Why should you keep the caps of carrier bottles on?

A
  • Solvent will evaporate without it

- Thickens the carrier solution

41
Q

What’s hybridisation and why is it important?

A
  • The infiltration of partly demineralised dentine with the conditioning agent

Forms the hybrid layer

  • Failure to achieve hybridisation results in voids leading to microleakage in the long term
42
Q

What’s wet bonding and why is it important?

A

Dentine the must be kept moist

  • Over-drying the dentine or the collagen causes it to collapse which will decrease compromise bond strength
  • CAN BE SAVED
  • Remoistening with water will rehydrate the collagen and the fibrils stiffen slightly but not to their normal amount
  • After air-drying the dentine should be left moist with glassy appearance
43
Q

Why should you air-thin the bonding agent?

A
  • Increase evaporation of residual solvent
- Strong blast will blow bond off the surface =
\+ incomplete covering of the cavity
\+ Formation of voids
\+ Bond failure
\+ Postoperative sensitivity
44
Q

What’s the Total Etch technique?

A
  • Etches both enamel and dentine in one application
  • Controlled acid penetration (less than 15μm) - minimal pulp risk
  • Less time consuming
  • Higher bond strengths gained
45
Q

What should you do after using total etch?

A
  • Wash and Dry BUT not over dry
  • Apply bond and lightly dry
  • Light cure and apply resin composite
46
Q

What’s a Selective Etch technique?

A
  • Selectively etching just Enamel (or a substrate) at a different time to Dentine
  • Etch the Enamel for an appropriate amount of time then etch the dentine
  • Less potential to over etch the dentine
47
Q

What are Self-Etching Systems?

A
  • Self-conditioning etch adhesive system attempting to combine conditioning, priming and bonding in a single step
  • Reduces working time
  • No-post-conditioning rinsing = less technique sensitive
  • Less sensitive to the degree of wetness/dryness of the dentine surface
48
Q

What are some of the features of the Self-etch systems?

A
  • Smear-layer adhering to dentine is dissolved then incorporated into the hybrid layer
  • Simultaneous demineralisation and resin-infiltration means it’s impossible to over-etch dentine so reduced post-operative sensitivity
  • Reduced leakage due to better sealing ability
49
Q

How does Self-etch Systems work?

A

Passenger Train & Tunnel:

  • Train locomotive (etch part of the molecule) enters the tunnel (dentine tubule) pulling its carriages behind it (primer/bonding component)
  • When the train (etch) gets some way into the tunnel it may stop (etching depth) but the carriages are still attached
  • Penetration depth of the acid and the bonding agent are the same = no void where leakage or incomplete curing may result
50
Q

What does a Self-Etch System compose?

A

Mixture of:

  • Acidic etchant to demineralise the tooth
  • Linking molecule or primer and the bonding agent
  • Solvent to carry the mixture to the sites of action (acetone or alcohol)
51
Q

What’s the drawback of using a self-etch system?

A
  • Reduced bond strength compared to etch and bond system

- Can only use a light cure resin composite

Semester II - Dental Materials (8 decks)

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