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Dental Materials > Adhesion 1 > Flashcards

Adhesion 1 Flashcards

1
Q

Issues with fillings without adhesion

A
  • restorations need to be mechanically retained (need undercut design, leads to cutting of larger cavities - removing healthy tooth tissue)
  • restricted ability to restore some teeth (incisors may lack sufficient bulk to have an undercut)
  • marginal gaps may form (can cause staining and secondary caries, or thermal and electrical stimuli reaching the pulp)
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2
Q

Enamel and dentine do not adhere to what materials?

A
  • amalgam
  • composite
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3
Q

Enamel and dentine not bonding to composite/amalgam led to what?

A
  • conservative dentistry
  • resin-bonded bridges
  • orthodontic bonding
  • fissure sealants
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4
Q

Why is time an issue with adhesion?

A
  • need effective bond within minutes
  • most ‘glues’ take longer
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5
Q

Problem with cavity size effect in adhesion

A
  • bigger cavities have more surface area
  • more potential for the bond to fail
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6
Q

Problem with lack of natural affinity in adhesion

A
  • tooth surface moist/hydrophilic
  • resins hydrophobic
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7
Q

Problem with mouth being warm/moist in adhesion

A
  • bonding may be destroyed
  • adhesive needs to be stable in an aq environment
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8
Q

Problem with thermal fluctuations in adhesion

A
  • thermal expansion/contraction
  • put adhesive bond under repeated stress
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9
Q

3 requirements for adhesion

A
  • need intimate contact
  • need an adhesive
  • the ability of a liquid to flow over a surface
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10
Q

Explain the need for intimate contact in adhesion

A
  • the more contact between surfaces, the stronger the bond
  • hard to achieve with two solids
  • roughness can get in the way
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11
Q

An adhesive is …
The surfaces are called … so adhesives bonds …

A
  • material that joins two surfaces together
  • adherends
  • adherends together
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12
Q

Most adhesives are what state?
Why?

A
  • liquids
  • can flow over surfaces
  • need to make sure no droplets form and ensure the liquid won’t flow over surfaces
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13
Q

What is the term for the ability of a liquid to flow over a surface?

A

wetting

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14
Q

Wetting depends on what 2 factors?

A
  • surface tension of the liquid
  • surface energy of substrate
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15
Q

Liquids tend to form …

A

spherical droplets

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16
Q

Solid surfaces have … bonds

A

free

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17
Q

Wetting needs…

A
  • surface energy to be higher than surface tension
  • droplets start to flatten
  • contact angle between droplet and surface
  • primers
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18
Q

What is a primer?
Why do you need them?

A
  • chemicals that modify the nature of the surface
  • improves the wetting of the liquid
19
Q

Mechanical bonding mechanisms

A
  • macro-mechanical is the idea of the enamel undercut
  • rough surface may have micro-undercuts
  • liquid can flow into these and form tags when low viscosity
  • liquid needs to flow well/wet
20
Q

Chemical bonding mechanism

A
  • ionic or covalent bonds possible
  • bonds can be reversible or irreversible
  • can be subject to hydrolysis
20
Q

Complex bonding mechanism

A
  • various contributory factors
  • combination of mechanical and chemical
21
Q

… is the pre-requisite for strong adhesion

A

intimate contact

22
Q

What’s was the first approach to adhesive dentistry?

A
  • enamel bonding
23
Q

What’s the effect of pellicle in enamel bonding?

A
  • pellicle is weakly adhered to enamel
  • must be removed prior to adhesion
24
Q

Effect of amorphous enamel outer layer on enamel bonding

A
  • formed during normal remineralisation
  • non-normal hydroxyapatite (HaP) structure
  • not ideal for adhesion
25
Q

Acid-etch technique was successful?

A
  • yes - first successful procedure
  • still commonly used for enamel bonding
26
Q

Technique of acid-etch technique

A
  • clean enamel
  • apply acid
  • apply resin-based material to enamel
27
Q

How to clean enamel?

A
  • pumice and water
  • ensure water supply is oil-free
28
Q

What does applying acid in acid etch do?

A
  • acid dissolves enamel surface
  • partially demineralises enamel
  • makes it rough
29
Q

What happens when resin-based material is added to enamel?
Important factors

A
  • material flows under undercuts
  • viscosity of material, surface wetting, setting time for materials is all important
30
Q

Enamel is made of …
The main component is … which is susceptible to …

A
  • biological apatite
  • calcium hydroxyapatite
  • acid dissolution
31
Q

What is used for etching?
How is it given to dentist?

A
  • phosphoric acid (around 37%)
  • as a liquid or a gel
32
Q

Different viscosities of etch effects what?

A

spread to the acid

33
Q

Acid etch is usually used for … to … seconds

A

10-60

34
Q

If etch is used for too short a time, what happens?

A
  • insufficient etching
  • leads to poor bonding
35
Q

If etch is used for too long a time, what happens?

A
  • apatite precipitation onto surface
  • poor bonding
36
Q

After you’ve finished etching, what do you do?

A
  • rinse enamel with oil free water supply
  • blow air over surface
  • give a chalky white appearance, microscopically visible enamel prisms, etched prisms used as microscale undercuts
37
Q

Things to beware of in acid etching

A
  • avoid salivary contamination (reduces bond strength and re-etch if it has)
  • differences in enamel (variation in teeth, in patients which leads to unpredictable results)
38
Q

2 reasons you can’t apply composite straight onto enamel

A
  • monomer viscosity (too viscous to flow into undercuts)
  • filler particles (big particles occlude undercuts)
39
Q

What is added for composite to bond to enamel?

A

bonding resins

40
Q

Why do bonding resins help composite bond to enamel?

A
  • monomer composition - similar to composite
  • filler concentration - originally unfilled, modern materials can be filled with smaller particles
41
Q

Setting mechanism of bonding resin

A
  • originally chemically activated
  • viscosity increases quickly with setting
  • may not penetrate undercuts
  • modern light activated
  • command set - in theory better penetration
42
Q

Applications of acid etch

A
  • class IV restorations
  • class V restorations
  • resin bonding bridges
  • bonding of orthodontic brackets
  • fissure sealants
43
Q

Is acid etch used for dentine bonding?

A

possibly

Dental Materials (17 decks)

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