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BDS2 CDS DMS > 2. Bonding to Teeth > Flashcards

2. Bonding to Teeth Flashcards

1
Q

Properties of a dental adhesive (6)

A 
Provide a high bond strength to tooth tissues
Immediate high-strength bond
Durable bond
Impermeable bond
Easy to use
Safe
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2
Q

Features of bonding to enamel (4)

A

Relatively easy due to enamel structure
Essentially mechanical
Acid etch technique
Hydrophobic

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3
Q

Process of acid etch technique (6)

A

Long enamel prisms are filled with imperfectly packed hydroxyapatite crystals
This surface can be modified by the application of acid (the acid roughens the surface of the enamel producing a characteristic etched pattern)
This roughed surface allows micromechanical interlocking of resin filling materials
The etching also increases the surface energy of the enamel surface by removing surface contaminants leading to better wettability of the enamel
Better wettability allows the resin to adapt better to roughened enamel surface
For this to work, the enamel must be dry. Moisture contamination will prevent flow of the hydrophobic resin into the etched surface

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4
Q

Type of etch

A

30-50% orthophosphoric acid

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5
Q

Types of DBA (2)

A

Low viscosity Bis-GMA resin

Phosphorylated Bis-GMA resin

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6
Q

Features of bonding to difficult (5)

A 
Complicated
Full of permeable tubules, making it wet and difficult to bond to
Low surface energy
Hydrophilic
Inconsistent material
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7
Q

Are DBAs hydrophilic or hydrophobic

A

Hydrophobic

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8
Q

Requirements of DBA (4)

A

Ability to flow
Potential for intimate contact with dentine surface
Low viscosity
Adhesion to substrate (mechanical, chemical, van der Waals)

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9
Q

Features of DBA mechanical adhesion

A

Achieved by the DBA and dentine surface interlocking with minimum gaps

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10
Q

Features of DBA chemical adhesion

A

Bonding at molecular level

Mineralised = ionic; organic = covalent

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11
Q

Features of DBA van der Waals adhesion

A

Based on electrostatic/dipole interactions between bonding agent and substrate
Best adhesion/bonding is achieved when van der Waals forces are optimised

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12
Q

What does strength of interaction depend on

A

Contact angle

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13
Q

Contact angle <90 degrees

A

Means the solid surface is hydrophobic

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14
Q

Definition of critical surface energy

A

The surface tension of a liquid that will just spread on the surface of a solid

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15
Q

Features of critical surface energy (2)

A

A liquid must have a lower surface energy than the surface it is being placed on for it to flow onto it and stick
A low surface energy liquid will spread on a higher surface energy substrate because this leads to a lower surface energy of the material as a whole

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16
Q

Wet dentine surface energy (2)

A

Wet dentine has a low surface energy, lower than composite filling materials
For composite resin to stick to dentine, the dentine mist have a higher critical surface energy

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17
Q

What are DBAs

A

Surface wetting agents

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18
Q

Function of DBAs (2)

A

Increase the surface energy of dentine surface and allow composite to flow and stick to the surface
Allow composite resin to bond well to dentine

19
Q

How can adhesion to dentine occur

A

Through molecular entanglement

20
Q

Process of molecular entanglement (3)

A

Adhesive is absorbed onto the surface but can also penetrate into the surface of the dentine. This is due to good wetting of the dentine by the adhesive and appropriate surface energies of the two
The absorbed component can form a long chain polymer
This polymer meshes with the substrate (molecular entanglement) leading to a high bond strength

21
Q

Definition of smear layer

A

An adherent layer of organic debris that remains on the dentine surface after the preparation of the dentine during the restoration of a tooth

22
Q

Features of smear layer (4)

A

0.5-5um thick
Variably attached to dentine surface
Generally contaminated with bacteria and is considered to interfere with adhesion
Can be removed, allowing bond to clean dentine or incorporated, penetrated and infiltrated by the DBA allowing it to stick to the dentine below

23
Q

What is Bis-GMA

A

Bisphenol-A glyceryl methacrylate

24
Q

What is NPG-GMA

A

N-phenylglycidyl methacrylate

25
Q

Components of total etch (3)

A 
Dentine conditioner (acid)
Primer (adhesive hydrophilic  and hydrophobic molecule)
Adhesive (resin which penetrates into dentine surface)
26
Q

Types of dentine conditioners (3)

A

Phosphoric acid
EDTA
Nitric acid

27
Q

Function of dentine conditioners (3)

A

Removes the smear layer
Opens dentinal tubules (removes smear plugs)
Decalcifies uppermost layer of dentine

28
Q

Features of primer (4)

A

Coupling agent
Contains a bifunctional molecule with a hydrophilic end to bond to the hydrophilic dentine surface and a hydrophobic methacrylate end to bond to resin
Must also have a spacer group to make it long enough to be flexible when bonding (lack of flexibility reduces bonding sites and bond strength)
Dissolved in suitable solvent (water, ethanol, acetone)

29
Q

Primer bonding

A

C=C bond opens and forms a strong covalent bond with the next resin layer
Hydrophilic group can combine with similar polar groups on the HA and can react with amine groups on the collagen protein

30
Q

Types of primer chemicals (5)

A 
HEMA
NTG-GMA
4-META
MDP
GPDM
31
Q

Features of adhesive (4)

A

Mixture of resins (usually HEMA and Bis-GMA)
Mainly hydrophobic
May contain filler particles to make it stronger
Contains camphorquinone for light curing

32
Q

Adhesive bonding (3)

A

Penetrates primed dentine (which now has hydrophobic surface)
Forms micro mechanical bond within tubules and exposed dentinal collagen fibres (molecular entanglement)
Forms hybrid layer

33
Q

Problems with total etch (3)

A

Over etching leads to collapse of collagen fibres so no resin can penetrate
If etch is too deep, primer cannot penetrate to the full depth of the etch
Moisture dependent - too dry dentine surface collapses; too wet primer is diluted leading to reduced bond strength

34
Q

Features of self-etching primers (2)

A

Do not remove smear layer - infiltrate it and incorporate themselves into it
No as technique sensitive but weaker bond strength

35
Q

Key components of self-etching primers

A

Acid methacrylate monomers (methacryloylxyalkyl acid phosphate)

36
Q

Self-etching primer bonding

A

Acidic groups react with Ca in tooth, bonding to surface and creating amorphous Ca chelate on surface
Smear layer is dissolved then incorporated into hybrid layer - only penetrates 2um into surface
Evidence for reduced sensitivity

37
Q

Adhesion-decalcification (AD) concept (3)

A

Mineral exchange is the fundamental mechanism of all bonding
This is where minerals removed from the dental hard tissue are replaced by resin which, once mineralised, mechanically interlock in these porosities (molecular entanglement)
The interaction of these molecules with hydroxyapatite-based tissue is described as the adhesion-decalcification concept (AD concept)

38
Q

AD-concept bonding mechanism (4)

A

Initially all acid monomers bond to calcium in hydroxyapatite ionically
Whether they stay bonded depends on the stability of the hydroxyapatite-monomer bond
Monomers with a lower pKa do not form a stable bond (they continue to dissolve hydroxyapatite)
This leads to a hybrid layer with unstable calcium phosphates incorporate

39
Q

Problems with self-etch (3)

A

Etching by-products are not washed away – these are soluble and weaken the integrity of the bond
If too much hydroxyapatite is dissolved away, the exposed collagen is vulnerable to breakdown and the bond will fail
Strong self-etch bonds well to enamel but less well to dentine - mild self-etch only partially demineralises dentine (Hydroxyapatite crystals remain around the collagen to rpotect against hydrolytic breakdown and the remaining Ca ions allow ionic bonding)

40
Q

What agents are preferred in etches and what

A

MDP and 4-META agents are better than HEMA-containing materials
HEMA materials are more acidic and absorb more water, leading to a less durable bond

41
Q

Why is hydroxyapatite required (2)

A

For strong, durable bonding

Protects the dentine from hydrolytic breakdown

42
Q

Features of self-etching bonding agents (4)

A

Less technique sensitive (no rinsing/excessive drying/dentine collapse leading to low bond strength)
Simultaneous demineralisation and resin infiltration (less chance of post-op sensitivity)
Greater variability between products with regard to initial solution pH – this results in different etch and different penetration of resin
Little evidence of stronger bond to dentine than with total-etch

43
Q

Molecular entanglement is

A

The process by which resins bond to dentine

BDS2 CDS DMS (15 decks)

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