L16 Adhesives And Adhesion To Tooth Tissue

Question 1

Why do we need adhesion?

Answer 1

Conservation of tooth structure (no undercuts needed for retention)
Reduce post-operative sensitivity
Reduce marginal leakage (marginal seal prevents bacterial invasion)
Many restorations are only possible with adhesion

Question 2

Which restorations are only possible with adhesion?

Answer 2

Orthodontic brackets, incisal tip restoration, veneers

Question 3

Pg93 image. What are the critical interfaces when adhering a composite to tooth structure?

Answer 3

Interface a - between adhesive and the enamel/dentine
Interface b - between the adhesive and resin composite

Question 4

Which interface presents more problems and why?

Answer 4

Interface a due to the dissimilarities in material chemistry’s that we are trying to stick together.
Not as much issue with interface b since bonding adhesive and resin composite are both resin based.

Question 5

What has a higher chance of achieving good bond strength at an interface?

Answer 5

Similar surface chemistries have a higher chance of achieving bond strength at the interface.

Question 6

What is the main problem with bonding resin to enamel and dentine?

Answer 6

Enamel and dentine are largely hydrophilic and the resin system is largely hydrophobic. And we don’t want resin-based composite to absorb water or it will break down.

Question 7

What is in the adhesive to try and resolve the problem?

Answer 7

There is a solvent within the adhesive to help penetrate into surface irregularities in enamel and dentine to help displace water. Try to make them more hydrophilic or less hydrophobic.

Question 8

What are the factors for ideal bonding?

Answer 8

Clean adherent
Enhanced wettability
Intimate adaptation
Bonding - specific to dental application
Good curing - specific to dental application

Question 9

Why is a clean adherent needed for ideal bonding?

Answer 9

Rinse mouth out before procedure to rid contaminants.
Etch cleans the surface.

Question 10

What is wettability?

Answer 10

How well the material adapts to the surface.

Question 11

What factors enhance wettability for ideal bonding?

Answer 11

Contact angle of adhesive on enamel/dentine
Viscosity contributing to it spreading
Making it more hydrophilic (by adding more water soluble resin), or try making the surface less moisture contaminated

Question 12

What is intimate adaptation?

Answer 12

Manipulating/modifying the surface you are trying to stick to

Question 13

How does intimate adaption affect ideal bonding?

Answer 13

E.g., etch roughens the surface and increases the surface area

Question 14

How can bonding factors be used to create ideal bonding?

Answer 14

Bonds with dental adhesives are primarily mechanical - retentive interlocking (like Velcro)
Physical bonds - electrostatic attraction
Chemical bonds - chelation to tooth surface

Question 15

How can good curing cause ideal bonding?

Answer 15

Light activated. Adhesives are infilled and thin so good curing is easy to optimise.

Question 16

Is the bonding predictable or unpredictable when bonding resin composites to enamel?

Answer 16

Predictable bonding due to homogenous structure of enamel with inorganic content and high surface energy.

Question 17

How is the surface of enamel modified and why is it predictable bonding?

Answer 17

Modified by etch to condition the surface, attacking different areas of the crystalline structure. Can attack periphery of prisms and within them, providing a surface amenable to high wetting of liquid being put on there. Thus more predictable than bonding to dentine.

Question 18

How long do you apply 37% phosphoric acid gel to enamel for and why?

Answer 18

15-20s to provide enough time to penetrate superficial layers of enamel. Should give a frosty appearance.

Question 19

Why is the etch a gel?

Answer 19

So it doesn’t run everywhere

Question 20

What is applied after etch?

Answer 20

Bonding agent when tooth is dry, which will flow in between the prisms and within the prisms.

Question 21

When bonding to enamel, what will moisture affect?

Answer 21

When bonding to enamel, moisture will affect the tag formation.

Question 22

What are the types of bonding between adhesive and enamel?

Answer 22

Physical - weak
Chemical - none
Mechanical - predominant
Macrotags - resin penetration between prisms
Micro tags - within prisms

Question 23

Why is the majority of bonding in enamel provided by microtags?

Answer 23

Microtags provide the majority of bond strength since there is more of them so a higher SA.

Question 24

Bonding properties of enamel, how is tag formation affected?

Answer 24

Tag length does not affect bond strength
Moisture affects tag formation
Curing affects tag formation

Question 25

Why is the bonding to dentine less predictable?

Answer 25

Because the microstructure changes throughout dentine e.g., concentration of tubules changes from coronal dentine to root dentine (increases in diameter and density as you go to root dentine). As you increase diameter of tubules, water content goes up.

Question 26

What is the bonding to dentine like?

Answer 26

Less predictable, higher variability, higher organic/moisture content

Question 27

What is the hybrid layer created when bonding to dentine?

Answer 27

Hybrid of the resin bond and the demineralised fibril network created through etching the dentine. Creates demineralised collagen matrix - gets rid of organics around collagen fibres to create a mesh to infiltrate the bonding resin.

Question 28

What does the etch do to dentine?

Answer 28

Acid etching demineralises the surface of intertubular dentine. Creates very small porosities (containing water)

Question 29

What is the relevance of the porosities created in dentine?

Answer 29

Bonding resin needs to penetrate porosities

Question 30

What happens to the porosities and thus bonding to dentine when they are dried?

Answer 30

Need to dry and evaporate the water, which collapses the porosities, so cannot infiltrate the bonding resin, so the hybrid layer cannot be created. This reduces bond strength. This bonding to dentine is very technique sensitive.

Question 31

In what ways is bonding to dentine technique sensitive.

Answer 31

Overwet: resin cannot penetrate porosities in the collagen fibrous matrix
Overdry: collagen fibrils collapse - no hybrid layer created
Not too dry, not too wet - very technique sensitive
Water-based primers can rehydrated collagen.

Question 32

What types of etch-and-rinse adhesives are there?

Answer 32

3-step: etch, prime, bond
2-step: etch, [prime+bond]

Question 33

What self-etch adhesives are there?

Answer 33

2 step: [etch+prime], bond
1 step: [etch+prime+bond]

Question 34

How do self-etch adhesives work?

Answer 34

Instead of separate etch, the primer is acidified - so will lower the pH and attack the surface of the enamel/dentine.

Question 35

Why are self-etch adhesives usually used?

Answer 35

Usually to save time but can get around potential problems or bonding to dentine.

Question 36

Advantages of etch/rinse technique

Answer 36

Good long term data
High/reliable bond strength to enamel

Question 37

Disadvantages of etch/rinse technique

Answer 37

Removal of smear layer might increase post-operative sensitivity
Wet bonding technique
Technique sensitive
Risk of fibril collapse

Question 38

Advantages of self-etch systems

Answer 38

Smear layer intact
Decreased post-operative sensitivity
Decrease risk of over drying
Less steps

Question 39

Disadvantages of self-etch

Answer 39

No long term data
Mild (less acidic) self etch systems have low bond strengths in enamel
More hydrophilic/acidic resins degrade faster
Decreased shelf life (store in fridge)

Question 40

What is the smear layer?

Answer 40

A layer created when cutting away the cavity

Question 41

Is removal of the smear layer good or bad?

Answer 41

In dentine, removal of the smear layer exposes the tubule. Can be good as then you can get resin penetration into the tubules, so a good chance of creating an effective hybrid layer. But increases post-op sensitivity and the potential to ovedry the dentine surface.

Question 42

Why might there be a reduction in bond strength to enamel in self-etch systems?

Answer 42

Potential reduction in bond strength to enamel because we are not using a high aggressiveness of acid, so not creating as much surface area than the total etch approach.

Question 43

Why might the stability of bond in self-etch systems be worse?

Answer 43

Due to a lower pH of the whole adhesive placed, H+ ions will attract water more readily than things that are not as acidic. So the stability of these bonds over time may be questionable.