Principles of Adhesion to Enamel and Dentine

Question 1

• What does adhesion depend on?

Answer 1

An adhesive making intimate physical contact with the substrate (wetting the surface)

Question 2

What are the substances adhesive holds together called?

Answer 2

Adherend

Question 3

What is meant by a wetting and non-wetting adhesive?

Answer 3

1. Wetting

An adhesive that adheres completely to a surface making it high energy

2. Nonwetting

An adhesive that adheres only partially to a surface, making it low energy:

Question 4

Give 4 types of adhesion.

Answer 4

1. Mechanical
2. Chemical bonding
3. Intermolecular bonding
4. Diffusion

Question 5

What surfaces are preferred for mechancial adhesion and why is this?

Answer 5

Rough or porous surfaces due to:

1. Large interfacial area
2. Micromechanical retention of the adhesive into the surface micro-voids

Question 6

Give 2 examples of mechanical adhesion.

Answer 6

1. Acid etching of enamel- creates a rough surface for adhesive.
2. Orthodontic brackets.

Question 7

How do some adhesives and adherends chemically bond?

Answer 7

Via Ionic and Covalent bonding:

1. Ionic

An ionic bond is formed when atoms donate electrons to another (dissimilar electronegativity)

1. Covalent

A covalent bond is a chemical bond in which 2 atoms share 1 or more pairs of electrons (similar electronegativity)

Question 8

Give 2 examples of chemical bonding adhesion.

Answer 8

1. Free radical reaction of vinyl groups (veneers)
2. Reaction of isocyanates to hydroxyl groups

Question 9

How do some adhesives and adherends bond via diffusion?

Answer 9

If the molecules of the adhesive and adherend are similar it may allow the molecules to move across the interface.

Question 10

Give 2 examples of diffusion adhesion.

Answer 10

1. Composite repairs
2. Dentine bonding agents.

Question 11

Give 4 ideal properties of an adhesive.

Answer 11

1. Low contact angle (under 90)

This allows the adhesive to wet fully wet the surface of the adherend.

2. The surface energy of the adhesive must be lower then the surface energy of the substrate.

A lower surface energy material will wet a higher energy surface.

3. Initial low viscosity.
4. Air must be displaced from the interface.

This needs to occur to avoid air pockets which would inhibit polymerisation.

Question 12

What are the 3 modes of failure between a material and adhesive?

Answer 12

1. Structural failure
   Failure within the material
2. Adhesive failure
   Failure at the adhesive interface
3. Cohesive failure
   Failure within the adhesive itself

Question 13

How does etching enamel lead to an irregular surface and what does it allow?

Answer 13

1. As acid etch selectively erodes certain hydroxyapatite formations.
2. This allows the penetration of adhesive forming resin tags- leading to micromechancial retention.
   Due to the exposure of the enamel prism/rod structure.

Question 14

What are the 3 types of pattern etched enamel can be?

Answer 14

1. Preferential dissolution of the prism core.
2. Preferential dissolution of the periphery of the prisms.
3. A mix of type 1 and 2.

Question 15

Why is it important to not agitate strongly acidic etchants placed on enamel?

Answer 15

When agitated, strongly acidic etchants placed on enamel can cause enamel to be removed more than intended, leading to a weakened bond.

Question 16

What does rinsing off the etch and drying enamel do to the surface?

Answer 16

Creates a high energy micro-rough surface.

Question 17

What etch and percentage is used to etch enamel?

Answer 17

37% phopshoric acid.

Question 18

How long is etch used on cut and on uncut enamel?

Answer 18

1. Cut - 15 seconds
2. Uncut - 30-60 seconds.

Question 19

How much does etch remove from the surface of enamel and what does this removed surface contain?

Answer 19

1. 5 microns
2. Adsorbed pellicle
3. Amorphous CaP layer (cut surfaces)

Question 20

What is the difference in bond strength when etching perpendicular to rod direction and parallel?

Answer 20

40% reduction in bond strength when parallel to rods:

Question 21

Is liquid or gel phosphoric acid better and why

Answer 21

Gel phosphoric acid is generally preferred because it is easier to control and less likely to run or pool, resulting in more precise etching and a more consistent surface. It is also homogenous

Question 22

What are the 2 different types of enamel bonding?

Answer 22

1. Single bond (etch and bond)

Uses phosphoric acid etching and rinsing before application of acidic monomers and resin in solvent.

1. Clearfil SE bond

Uses an acidic monomer primer to dissolve the surface HA followed by application of resin in solvent.

Question 23

Which out of bond and etch and self etch systems provide more uniform bonds?

Answer 23

Self etch when all cavity walls are considered.

Question 24

When are sealants used?

Answer 24

As a caries preventative measure on molars.

Question 25

Give 3 types of sealants.

Answer 25

1. Filled, unfilled 2. Self-cured 3. Light cured

Question 26

What etch is used with sealants and why?

Answer 26

Phosphoric acid- most effective based on studies.

Question 27

Why is bonding composite and dentine difficult?

Answer 27

1. Dentine is hydrophilic 2. Composites are hydrophobic

Question 28

What covers dentine that also affects its bonding capabilities?

Answer 28

A smear layer.

Question 29

What are 2 different compositions of a dentine bonding agent?

Answer 29

1. Etchant - this opens up dentinal tubules that causes the flow of dentinal fluid. 2. Primer 3. Sealant/Bonding agent. OR 1. Weak self etching primer/strong self etching primer. 2. Bond.

Question 30

What is the role of adhesive monomers in dentine bonding?

Answer 30

They enhance dentine bonding.

Question 31

How do adhesive monomers for dentine bond the dentine and composite together?

Answer 31

1. They are bifunctional monomers. 2. With a hydrophobic end that interacts with composite. 3. And a hydrophilic end that interacts with dentine. 4. They are separated by a hydrocarbon chain.

Question 32

How is a 4-META monomer formed, and what does it bond to?

Answer 32

1. n presence of moisture the anhydride reacts to form 2 carboxyl groups. 2. It requires a special cataylst for polymerisation. 3. It bonds to metal (base) and enamel/dentine.

Question 33

What is the most commonly used dentine bonding agent?

Answer 33

10-MDP

Question 34

What else in 10-MDP used in?

Answer 34

Cements adhesive to metal.

Question 35

What percentage by weight (concentration) does 10-MDP need to be sufficient for adhesion?

Answer 35

5-10%.

Question 36

In general percentage by weight (concentration) do adhesive monomers need to be sufficient for adhesion?

Answer 36

2-10%

Question 37

What’s another term for smear layer?

Answer 37

Acid labile layer.

Question 38

What causes a smear layer on dentine?

Answer 38

Any mechanical manipulation of dentine causes one: 1. Bur 2. Hand instrument 3. Wooden stick.

Question 39

What does a smear layer on dentine inhibit?

Answer 39

The flow of adhesive.

Question 40

- What is the role of acid etching on dentine?

Answer 40

1. Removes smear layer So dentinal tubules open so adhesive can flow.

Question 41

In terms of proximity to the pulp where are higher bond strengths found?

Answer 41

1. Tubules near DEJ - higher bond strengths. 2. Tubules near pulp - lower bond strengths. Overall bonding is increased superficially.

Question 42

What does etching and washing also do to the dentine that allows monomer infiltration?

Answer 42

Demineralises the dentine

Question 43

How is a hybrid layer formed after acid removes the smear layer?

Answer 43

Primer and resin can penetrate the collagen fibers in demineralised dentine to form a hybrid layer.

Question 44

Give the 4 types of dentine bonding agents.

Answer 44

1. 3 step - scotchbond MP+ 2. 2 step - optibond solo - total etch 3. 2 step - SE bond - self etch 4. 1 step - iBond

Question 45

What can be done to ceramics before cementing for better bonding?

Answer 45

Sandblasting.

Question 46

How does composite shrinkage in class I restorations come about?

Answer 46

When a dental composite is placed in a tooth cavity and exposed to a curing light, it undergoes a chemical reaction called polymerization. As the reaction progresses, the composite material undergoes a volumetric contraction or shrinkage. This shrinkage occurs because the monomers within the composite resin are converting into a more densely packed polymer network, resulting in a reduction in the overall volume of the material. In class I restorations, which involve filling small to moderate-sized cavities within the tooth, the composite material is typically placed in direct contact with the cavity walls. As the composite undergoes shrinkage during polymerization, it pulls away from the cavity walls, leading to several potential consequences: 1. Deformation of tooth places additional stress on the bonding and weakest bond (pulpal floor) fails. 2. This opens a fluid flow path to pulp leading to post op sensitivity:

Question 47

What is a common defect in adhesively bonded restorations which is commonly mistaken for caries?

Answer 47

Margin discolouration: