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Adhesion 2 Flashcards

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1
Q

For effective bonding, the bond should …

A
  • form rapidly
  • withstand polymerisation shrinkage forces
  • overcome hydrophilic/phobic barrier
  • withstand oral environment
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2
Q

Important factors in enamel bonding

A
  • effective etching, rinsing and drying
  • avoid contamination
  • applying low viscosity resin
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3
Q

Composition of enamel

A
  • densely calcified
  • 96% mineral/apatite
  • 1% organic
  • 3% water
  • apatite crystals tightly packed into prisms
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4
Q

Composition of dentine

A
  • permeable tubular structure
  • 70% mineral (apatite)
  • 20% organic (collagen)
  • 10% water
  • heterogenous (philic and phobic components)
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5
Q

There are pressure difference between the … and the dentine floor. Why?

A
  • pulp
  • fluid pumps through tubules - dry field impossible
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6
Q

Is it safe to acid etch dentine?

A
  • may cause post-op pain
  • what if there’s pulp exposure
  • need an appropriate acid
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7
Q

Is it possible to etch enamel but not dentine?

A
  • difficult/impossible in practice
  • results show it leads to low bond strength, leakage, loss of restoration (class V)
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8
Q

Do you rinse and dry dentine?

A
  • see effect of the dentine water concentration
  • excessive drying can lead to irreversible damage to vital pulp
  • can contamination be avoided?
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9
Q

Dentine is hydrophilic/phobic

A

philic

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10
Q

2 reasons for failure of early bonding agents

A
  • no acid used on dentine
  • smear layer has weak adhesion to dentine
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11
Q

What happens if no acid is used on dentine?

A
  • debris layer forms on surface
  • debris from cavity prep
  • contaminated with bacteria
  • gelatinous layer called the smear layer
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12
Q

Smear layer has strong/weak adhesion to dentine
Explain

A
  • weak
  • no mechanical bonding
  • chemical attachment is weak
  • easily disturbed by composite shrinkage
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13
Q

3 possibilities for dealing with the smear layer

A
  • bond directly to the smear layer
  • remove smear layer
  • modify smear layer
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14
Q

Why would you usually choose not to bond to smear layer?

A
  • weak bond
  • bad idea
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15
Q

How is removing the smear layer a way to deal with it?

A
  • a total etch approach
  • requires a strong acid - often phosphoric acid
  • rinse acid after use
  • bond to bulk dentine
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16
Q

How is modifying the smear layer a way of dealing with it?

A
  • a self-etch approach
  • requires weaker acid than if you were removing the layer
  • a range of acids are common, with self-etching primers
  • don’t rinse acid after use
  • bond to mixture of modified smear layer and bulk dentine
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17
Q

Stages of bonding to dentine

A
  • conditioning/acid etching
  • priming
  • bonding
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18
Q

Define conditioning/acid etching stage

A
  • treatment to remove, disturb or penetrate the smear layer
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19
Q

Explain priming

A
  • dentine is hydrophilic and the monomers in composite are hydrophobic
  • drying dentine can damage it
  • treatment needed on conditioned dentine to prepare it for bonding
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20
Q

Bonding resin is similar to what concept?

A
  • enamel acid-etch procedure
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21
Q

Structure of primer

A
  • general structure of M-S-R
  • M is the methacrylate group
  • S - spacer
  • R - reactive group
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22
Q

In primer, what does the methacrylate group do?

A
  • bonds to composite
  • can polymerise
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23
Q

In primer, what does the spacer do?

A
  • allows primer to be flexible
  • low viscosity to enable flow
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24
Q

In primer, what does the reactivegroup do?

A

affinity for moist dentine

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25
Which primer is the most common?
- HEMA - hydroxyethyl methacrylate
26
Features of HEMA
- amphiphilic (hydrophobic and philic parts) - no chemical bond to dentine or enamel, mechanical bond only
27
New advancements on HEMA
- newer monomers such as 10-MDP developed - chemical bonding possible - some evidence they have higher bond strength in vitro
28
Conditioned dentine has either ... or ...
- demineralised collagen layer on surface - demineralised collagen layer with modified smear layer on surface
29
Primer must infiltrate what layer? Partial infiltration means ... and complete infiltration means ...
- hybrid - weak bond - strong bond
30
The hybrid is a ... structure What's involved?
- composite - collagen, primer, smear layer
31
In enamel, acid is washed away and enamel is dried. Do we do this with dentine?
- no - drying of dentine can lead to collagen network collapse - poor bond formation due to difficulty in primer penetrating - may be able to rehydrate - may lead to pulp damage - led to 'wet bonding approach'
32
What is the wet bonding approach?
- must rinse strong acid of dentine - to prevent over etching but leaves the cavity too wet - bond strength is low as hydrophobic monomers don't infiltrate - need to dry dentine but leads to collagen dentine
33
Infiltration of demineralised layer depends on ...
- ability to displace water with primer - many primers contain water to help with infiltration - solvents such as ethanol and acetone claimed to displace water for better adhesion possibly?
34
Cautions with the wet bonding approach
- products differ wildly - very technique sensitive
35
An alternative approach to wet bonding
- self-etching primer
36
Advantage of self-etching primer
- weaker acids only modify smear layer - don't need to be rinsed away - should remove the 'too wet/too dry confusion'
37
Early products of self etching primers
- contained maleic acid diluted in HEMA - limited shelf life - poor bond strength durability
38
Modern products of self etching primers
- range of pHs - strong, intermediary strong, mild, ultra-mild - lower pH more disruption of smear layer - lower pH more calcium phosphate remains in hybrid layer, leach out over time (soluble), compromise bond durability? - no open dentine tubule left on surface
39
What pH is considered - strong - intermediary strong - mild - ultra-mild in self-etching products?
- less than 1 - around 1.5 - around 2 - more than or equal to 2.5
40
What's good with leaving no open dentine tubule left on the surface?
- leads to less sensitivity post-op - limited evidence
41
Bonding agents have similar monomers to composites. Explain
- methacrylate-based - bonds to primer and composite - seals dentine surface
42
Explain filler level of bonding agents
- traditionally unfilled - filler particle size to big - stopped penetration of demineralised dentine - filled sealers nano-size fillers - potentially improve compressive strength - no clinical evidence of advantage
43
Could the conditioning, priming, bonding be simplified?
- using fewer steps could be more consistent - seems a logical assumption but not always true
44
3 dentine bonding adhesive categories
- 3 stage - 2 stage - 1 stage
45
Explain the different categories of dentine bonding adhesive
- 3 stage is conditioning, priming, bonding - 2 stage is conditioning (priming and bonding), self-etching primer, bonding - 1 stage is all in one - conditioner, primer, bond
46
Don't confuse stages with steps. What's the difference?
- many steps are needed regardless of how many stages - mixing of material - air thinning - light curing
47
Explain conditioning (priming and bonding)
- one bottle systems (confusing as actually 2 bottles) - separate acid step (similar acid to enamel etchants - 30-40% phosphoric acid) - combined primer and bonding agent (similar monomers to composite with HEMA) - repeat applications needed (saturate demineralised dentine, optimise hybrid layer) - reduce steps but not necessarily time
48
Explain (conditioning and priming) , bonding
- two bottle systems - etching and priming step combined - demineralise and infiltrate dentine simultaneously, no rinsing step, modifies smear layer and pH of acid varies between products, typically requires repeated applications - bonding resin has similar monomers to composites, some resins contain HEMA
49
Explain (conditioning, priming and bonding)
- single step adhesives - more than 1 step - typically 4 steps - dispense and mix components, apply to enamel and dentine, air dry, light cure
50
Why is there variable results with (conditioning, priming and bonding)?
- technique sensitivity - acid strong enough to etch enamel - air diffuses through thin layers quickly (potential for oxygen inhibition)
51
How is enamel etched?
- 10-60s - rinsed - air dried - chalky white appearance
52
How is dentine etched?
- 10-15s - rinsed - carefully dried - not clear appearance difference
53
Can enamel etching and dentine etching be combined?
- total-etch approach acid is the same as acid-etch approach - are self-etching primers strong enough? - evidence suggests you need a full acid-etch procedure of unprepared enamel or bonding will fail
54
Does long exposure to acid irritate pulp?
- acid penetration typically 4-5 micrometres dentine - evidence shows normally no pulp irritation - proper seal of cavity more important - prevents access to dentine tubules
55
Classifications of bonding agents
- generations (1st or 2nd etc) but clincially unhelpful - one bottle/two bottles - but number of bottles not the same as stages so no indication of how to use - total etch/self etching primer - some indication of clinical procedures
56
The smear layer must be effectively ... and expose ...
conditioned demineralised dentine surface
57
The hybrid layer is ... and ... establishes the bond
- effective infiltration of demineralised layer with primer/resin - polymerisation
58
Current issues in use of enamel and dentine adhesion
- consequences for enamel bonding - differences in dentine
59
Consequences of enamel bonding
- simultaneous bonding preferred by dentists (total etch is okay, self-etching primers may not be sufficient) - wet or dry conditions needed? (enamel needs drying before bonding, dentine damaged by excessive drying) - enamel condition important factor (is enamel freshly cut?)
60
Differences in dentine
- sclerotic dentine (highly mineralised, acid well tolerated) - carious dentine (not highly mineralised, acid less well tolerated)
61
Post operative problems
- pulp inflammation - shrinkage of composite
62
How is pulp inflammation a post-op problem?
- acids no longer seen as a major issue - bond failure more important - leads to bacterial access to pulp
63
Shrinkage of composite depends on...
- filler content - monomer type - technique - cavity size
64
Shrinkage of adhesives
- bond strength takes 24hrs to develop - polymerisation of composites - 20s - marginal failure may occur before bond strength reaches maximum value
65
Explain how shrinkage effects C-factor
- more bonded surfaces more potential shrinkage effect - adhesive must compensate - more compensation for shrinkage by adhesive - more cuspal displacement of tooth to compensate
66
Why is inconsistence of performance a current issue?
- wide range of products (lots of steps and technique sensitvitity) - bond strength durability (hydrophilic components, may lead to plasticisation of bond, hydrolysis of components, enzymatic degradation of collagen) - questionable shelf-life (bond strength decrease over time, only in vitro but worrying)

Dental Materials (17 decks)

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