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CDS- Dental Materials Science > Dental bonding > Flashcards

Dental bonding Flashcards

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1
Q

What are the properties of a dental adhesive?6

A

Provides a high bond strength to tooth tissues, immediate high strength bond, durable and impermeable bond, easy to use and safe

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2
Q

Is it hard to bond to enamel? Why?

A

Easy due to the structure of enamel

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3
Q

What is the structure of enamel?

A

Heterogenous structure: densely packed prismatic

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4
Q

Is enamel wet or dry?

A

Dry

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5
Q

What does acid etching do to enamel prisms?

A

Roughens the surface of the enamel producing a characteristic etched pattern (keyhole shape)

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6
Q

What does acid etching allow?

A

Micromechanical interlocking of resin filling materials

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7
Q

How does acid etching lead to better wettability of the enamel and WHY is this important?

A

Etching increases the surface energy of the enamel surface by removing surface contaminants- leads to better wettability of the enamel- allows resin to adapt better to roughened enamel surface.

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8
Q

Why must enamel be dry when bonding to resin?

A

Moisture contamination will prevent flow of the resin into the etched surface.

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9
Q

What is normally used for acid etching?

A

30-50% aqueous solution of phosphoric acid

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10
Q

Why is it bonding to dentine difficult?4

A

Dentine is constantly wet- fluid pumps up from pulp to dentine floor, inconsistent material ( aged dentine is more mineralised) and low surface energy, smear layer

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11
Q

What are the requirements for a dentine bonding agent?

A

Ability to flow into surface, potential for intimate contact with dentine surface, low viscosity, and adhesion to substrate MECHANICALLY, CHEMICALLY AND TO THE VAN DER WAALS FORCES

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12
Q

How to bond to dentine mechanically?

A

DBA and the dentine surface meshing and interlocking with minimum gaps.

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13
Q

In dentine, how is chemical adhesion achieved?

A

At a molecular level, mineralised constituent of dentine bonds ionically and the organic constituent of dentine bonds covalently

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14
Q

When is best adhesion to dentine achieved?

A

When van der waals forces are optimised

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15
Q

What is van der waals adhesion and what does the strength of interaction depend on?

A

Electrostatic or dipole interaction- depends on contact angle which is a good indication of wettability of a solid by a specific liquid.

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16
Q

What does a contact angle of less than 90 degrees mean?

A

Solid surface is hydrophilic- spreads out flat

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17
Q

What quality must a liquid have for it to flow and stick to a surface?

A

Lower surface energy than the surface

18
Q

Why will dentine not bond to composite directly?

A

Dentine has a low surface energy lower than composite

19
Q

How do we increase the surface energy of dentine to bond to composite?

A

Dentine bonding agents (surface wetting agents)

20
Q

How does the adhesive bond to dentine?

A

Adhesive absorbed onto the surface but can also penetrate into the surface of the dentine.

21
Q

What does the absorbed component on the dentine bonding agent form?

A

Long chain polymer

22
Q

What is the smear layer?

A

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

23
Q

Does the smear layer interfere with adhesion?

A

Yes

24
Q

How thick is the smear layer?

A

0.5-5 microns

25
Q

How do we remove the smear layer?

A

Total etch or self etch

26
Q

What used to be used to control the smear layer? Why is this not used anymore?

A

Phosphorylated esters of unfilled resins- ionic bond to the calcium in dentine by chlorophosphate or hydroxyl group- bond was only on to the top of the smear layer-inherently weak low bond strength and moisture caused hydrolysis of the bond resulting in leakage of the filling.

27
Q

What are the components of a total etch bonding agent?

A

Dentine conditioner : 35% phosphoric acid, primer: coupling agent with a hydrophilic end and hydrophobic end, adhesive: resin which penetrates into the surface of the dentine attaching to the primers hydrophobic surface.

28
Q

What does the dentine conditioner do? What is exposed to the next 2 components ready to be penetrated?

A

Removes smear layer, opens dentinal tubules by removing smear plugs and decalcifies the uppermost layer of the dentine. The collagen network in the top 10 micrometres of the dentine is exposed.

29
Q

In primer, which aspects bond to what?

A

C=C opens, forming a strong covalent bond on the hydrophobic side with the next resin layer. The hydroxyl group can combine with similar polar groups on the hydroxyapatite and can react with amine groups on the collagen protein. (Van der Waal not a intramolecular bond for the hydrophilic part)

30
Q

Why must primer have a spacer group?

A

Make it long enough to be flexible when bonding. Lack of flexibility reduces bonding sites and bond strength.

31
Q

Which coupling agent is found in many primers?

A

HEMA- hydroxy ethyl methacrylate

32
Q

What is the adhesive’s components and is it hydrophilic/hydrophobic?

A

Mixture of resins- Bis-GMA and HEMA, predominantly hydrophobic

33
Q

What does the adhesive contain to make it stronger and what does it contain to allow light curing?

A

Filler and camphorquinone

34
Q

What does the adhesive penetrate and form?

A

Penetrates the primed dentine which now has a hydrophobic surface- forms a micromechanical bond within the tubules and exposed dentinal collagen fibres (molecular entanglement), forming a hybrid layer of collagen plus resin.

35
Q

What are some problems with total etch?

A

Over etching- collapse of collagen fibres so no resin can penetrate, too deep an etch and primer cannot penetrate to the full depth leading to sensitivity.
If too dry- dentine surface collapses, decrease in porosity, poor penetration of dentine by primer, if too wet- primer dilutes and there is reduced strength

36
Q

Which texture is best for dentine to get a good bond? Why?

A

Moist dentine-expanded dentine surface is porous and will absorb primer hence giving a good bond

37
Q

What is in primer and sealer combined bottles?

A

HEMA/ GPDM/MDP/4-META combined with a resin Bis-GMA, a solvent and camphorquinone

38
Q

How do self etching primers work?

A

They don’t remove the smear layer- infiltrate it and incorporate themselves into it.

39
Q

Why does a strong self etch not bond well to dentine? 3

A

Etching by-products are not washed away- soluble and weaken the bond integrity, and if too much HA is dissolved the exposed collagen is vulnerable to breakdown and the bond will fail.

40
Q

How does mild self etch work? Disadadvantages?

A

Partially demineralises dentine, HA crystals remain around the collagen, protecting it against hydrolytic breakdown and the remaining Ca ions allow bonding.
If smear layer is thick then mild self etch won’t penetrate.

CDS- Dental Materials Science (2 decks)

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