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Dental Materials > Adhesion 2 > Flashcards

Adhesion 2 Flashcards

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
Q

Which primer is the most common?

A
  • HEMA
  • hydroxyethyl methacrylate
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26
Q

Features of HEMA

A
  • amphiphilic (hydrophobic and philic parts)
  • no chemical bond to dentine or enamel, mechanical bond only
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27
Q

New advancements on HEMA

A
  • newer monomers such as 10-MDP developed
  • chemical bonding possible
  • some evidence they have higher bond strength in vitro
28
Q

Conditioned dentine has either … or …

A
  • demineralised collagen layer on surface
  • demineralised collagen layer with modified smear layer on surface
29
Q

Primer must infiltrate what layer?
Partial infiltration means … and complete infiltration means …

A
  • hybrid
  • weak bond
  • strong bond
30
Q

The hybrid is a … structure
What’s involved?

A
  • composite
  • collagen, primer, smear layer
31
Q

In enamel, acid is washed away and enamel is dried. Do we do this with dentine?

A
  • 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
Q

What is the wet bonding approach?

A
  • 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
Q

Infiltration of demineralised layer depends on …

A
  • 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
Q

Cautions with the wet bonding approach

A
  • products differ wildly
  • very technique sensitive
35
Q

An alternative approach to wet bonding

A
  • self-etching primer
36
Q

Advantage of self-etching primer

A
  • weaker acids only modify smear layer
  • don’t need to be rinsed away
  • should remove the ‘too wet/too dry confusion’
37
Q

Early products of self etching primers

A
  • contained maleic acid diluted in HEMA
  • limited shelf life
  • poor bond strength durability
38
Q

Modern products of self etching primers

A
  • 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
Q

What pH is considered
- strong
- intermediary strong
- mild
- ultra-mild
in self-etching products?

A
  • less than 1
  • around 1.5
  • around 2
  • more than or equal to 2.5
40
Q

What’s good with leaving no open dentine tubule left on the surface?

A
  • leads to less sensitivity post-op
  • limited evidence
41
Q

Bonding agents have similar monomers to composites. Explain

A
  • methacrylate-based
  • bonds to primer and composite
  • seals dentine surface
42
Q

Explain filler level of bonding agents

A
  • 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
Q

Could the conditioning, priming, bonding be simplified?

A
  • using fewer steps could be more consistent
  • seems a logical assumption but not always true
44
Q

3 dentine bonding adhesive categories

A
  • 3 stage
  • 2 stage
  • 1 stage
45
Q

Explain the different categories of dentine bonding adhesive

A
  • 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
Q

Don’t confuse stages with steps. What’s the difference?

A
  • many steps are needed regardless of how many stages
  • mixing of material
  • air thinning
  • light curing
47
Q

Explain conditioning (priming and bonding)

A
  • 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
Q

Explain (conditioning and priming) , bonding

A
  • 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
Q

Explain (conditioning, priming and bonding)

A
  • single step adhesives
  • more than 1 step
  • typically 4 steps
  • dispense and mix components, apply to enamel and dentine, air dry, light cure
50
Q

Why is there variable results with (conditioning, priming and bonding)?

A
  • technique sensitivity
  • acid strong enough to etch enamel
  • air diffuses through thin layers quickly (potential for oxygen inhibition)
51
Q

How is enamel etched?

A
  • 10-60s
  • rinsed
  • air dried
  • chalky white appearance
52
Q

How is dentine etched?

A
  • 10-15s
  • rinsed
  • carefully dried
  • not clear appearance difference
53
Q

Can enamel etching and dentine etching be combined?

A
  • 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
Q

Does long exposure to acid irritate pulp?

A
  • 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
Q

Classifications of bonding agents

A
  • 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
Q

The smear layer must be effectively … and expose …

A

conditioned
demineralised dentine surface

57
Q

The hybrid layer is … and … establishes the bond

A
  • effective infiltration of demineralised layer with primer/resin
  • polymerisation
58
Q

Current issues in use of enamel and dentine adhesion

A
  • consequences for enamel bonding
  • differences in dentine
59
Q

Consequences of enamel bonding

A
  • 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
Q

Differences in dentine

A
  • sclerotic dentine (highly mineralised, acid well tolerated)
  • carious dentine (not highly mineralised, acid less well tolerated)
61
Q

Post operative problems

A
  • pulp inflammation
  • shrinkage of composite
62
Q

How is pulp inflammation a post-op problem?

A
  • acids no longer seen as a major issue
  • bond failure more important
  • leads to bacterial access to pulp
63
Q

Shrinkage of composite depends on…

A
  • filler content
  • monomer type
  • technique
  • cavity size
64
Q

Shrinkage of adhesives

A
  • bond strength takes 24hrs to develop
  • polymerisation of composites - 20s
  • marginal failure may occur before bond strength reaches maximum value
65
Q

Explain how shrinkage effects C-factor

A
  • more bonded surfaces more potential shrinkage effect - adhesive must compensate
  • more compensation for shrinkage by adhesive - more cuspal displacement of tooth to compensate
66
Q

Why is inconsistence of performance a current issue?

A
  • 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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