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Dental Materials Y2 > Composite Bonding to Enamel and Dentine > Flashcards

Composite Bonding to Enamel and Dentine Flashcards

1
Q

Why are adhesives used in dentistry

A
  • Tooth tissue is hydrophilic
  • Most restorative materials are hydrophobic
  • So there is no chemical bonding between the two
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2
Q

What are the benefits of using adhesives

A
  • Better aesthetics
  • Conservation of tooth tissue
  • Reinforcement of weak tooth structure
  • Reduced marginal leakage
  • Reduced potential for pulp sensitivity
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3
Q

What are the ideal features of an adhesive

A
  • Provide high bond strength to enamel and dentin
  • Immediate and durable bond
  • Prevent ingress of bacteria
  • Safe to use
  • Simple to use
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4
Q

What is considered one of the best techniques for adhesives that there currently is

A

The acid-etch technique for bonding resin to enamel

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5
Q

What are some of the problems with bonding restoratives to enamel

A
  • Composites have no intrinsic adhesive qualities to tooth tissues
  • Composite resins are non-polar (hydrophobic)
  • Enamel is hydrophilic
  • Surface tension of enamel
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6
Q

How is the surface energy of enamel increased

A

The pellicle layer must be removed and the enamel surface has to be etched

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7
Q

Why do we want to increase enamel surface energy

A

So we can have better wetting and more SA between the composite and enamel

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8
Q

How is the pellicle removed and enamel etched

A
  • Pellicle layer and surface of the enamel structure are modified with the acid-etch technique using 30-50% phosphoric acid
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9
Q

What type of adhesive bonding does the acid-etch technique allow

A

Micromechanical

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10
Q

What effects does the acid-etch technique

A
  • Increased surface roughness of enamel hence increased bonding area
  • Surface energy is raised
  • Improved Wettability for resin to run into the enamel rods
  • Opens inner prism area for interlocking tag formation
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11
Q

How does the acid-etch technique

A
  • 30-50% phosphoric acid is applied to the enamel surface
  • Acid-base reaction is initiated, where the acid dissolves the enamel surface hydroxyapatite and this results in loss of enamel prism structure
  • When enamel has frosty appearance the etching is adequate
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12
Q

AY BAWS CAN I HABE DE NOTE PLZ

A

Over etching can breakdown enamel prisms for tag formation

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13
Q

What do you do after the acid etch technique when applying resins

A
  • Apply resin of low viscosity like unfilled BisGMA before placement of composite
  • Unfilled resin must be applied to dry/well etched enamel surface
  • Unfilled resin flows into etched enamel prisms and forms resin tags that penetrate to a depth of 30um.
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14
Q

AY BAWS CAN I HABE DE NOTE PLZ

A

Water - highly polar and resin is non polar so it will not adapt to the wet enamel surface

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15
Q

What can cause the adhesive bond to fail

A
  • Poor clinical technique

- Contamination of enamel surface before placement

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16
Q

What procedures can be done on Acid-Etched enamel

A
  • Fissure sealing
  • Direct composite restorations
  • Ceramic veneers
  • Resin bonded bridges
  • Orthodontic brackets
  • Periodontal splinting
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17
Q

Why does a restorative resin have to be adhesively bonded to dentin

A

To retain the restoration in the cavity and to eliminate marginal/internal gaps in order to prevent bacterial microleakage

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18
Q

How does the bonding agent affect the dentin

A

Provide strength

Seal the dentinal tubules to prevent dentin hypersensitivity

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19
Q

Describe the structure of dentin

A
  • Heterogenous structure, 70% inorganic hydroxyapatite, 20% organic material
  • Hydrophilic
  • Dentinal tubules communicate with the pulp and are permeable to drugs, chemicals that can damage the pulp
20
Q

What are the some of the difficulties involved in bonding to dentin

A
  • When the dentin is cut, fluid is pumped through the dentin tubules giving a wet surface
  • Inorganic hydroxyapatite crystals are broken up, the collagen is stretched, torn and smeared over the cut surface
21
Q

“Cut” dentin is covered by a smear layer, what is the smear layer composed of

A
  • A layer of denatured collagen and debris covering surface that is weakly bound to the dentin
  • It is contaminated with bacteria and cutting debris
22
Q

Why is cut dentin hard to bond to

A

Has a wet surface and the smear layer acts as a contaminant

23
Q

What must we be careful of when we try to remove the smear layer

A

The dentin tubules are open and exposed to bacteria and irritants so the adhesive resin must act as an effective seal that will seal the tubules

24
Q

What are the 3 essential components of using a dentin bonding agent and what order should they be used in

A
  1. Conditioner - acid modifies/clears smear layer
  2. Coupling (bonding) agent/primer - adhesive
  3. Sealer - bond/adhesive that seals the dentin tubules
25
Q

How is the dentin conditioner used and what does it do

A
  • Acid solution - stronger acid = more effect
  • Removes/modifies the smear layer via acid/base reaction with hydroxyapatite that dissolves
  • Rinsed with water
  • Demineralised dentin surface left
26
Q

What does the dentin bonding agent/primer do

A

Acts as an adhesive that bonds hydrophilic dentin to hydrophobic resin

27
Q

What is the dentin bonding agent/primer made up of

A

Bi-functional molecule e.g. hydroxyethyl methacrylate (HEMA), which contains a hydrophobic and hydrophilic end that is dissolved in a solvent

28
Q

What is the general basic structure of dentin bonding agents

A

Methacrylate molecule - R - X

29
Q

What does the methacrylate group in dentin bonding agents/primers bond to

A

The sealer/unfilled resin

30
Q

What does the R group in dentin bonding agents/primers allow

A

This is a spacer molecule that provides flexibility to the coupling agent

31
Q

What does the X group in dentin bonding agents/primers allow

A

Polar (hydrophilic end)

32
Q

Why is the polar end of the dentin bonding agent/primer very important

A

The polar end interacts with polar groups in the dentinal tubules e.g. hydroxyl groups on apatite and amino groups on collagen

33
Q

Why is the bonding agent/primer dissolved in a solvent

A

Needs to penetrate and saturate dentin tubules to a reasonable depth so that is seeks out and displaces water

34
Q

What solvents are dentin bonding agents/primers dissolved in

A

Ethanol/Acetone (water chasers)

35
Q

What is the role of HEMA in the bonding agent/primer

A

It penetrates the demineralised dentin and bonds to the collagen via hydroxyl group

36
Q

How do you apply the bonding agent/primer

A

Important to apply enough so might need a few coats.

Is applied to dentin surface and dried

37
Q

How is the dentin sealer cured

A

Light

38
Q

Give examples of dentin sealer

A

Unfilled BisGMA or UDMA

Recent sealers = Bis-GMA and HEMA mixture to improve adaptation of sealer to dentin surface

39
Q

What is the hybrid zone

A

This is the interpretation layer of dentin and resin

40
Q

What is the type of bonding between resins and dentin

A

Micromechanical/entanglement to inorganic salts (Ca2+)

Bonds to collagen via hydroxyl and amino groups

41
Q

What part of the Dentin primer (coupling agent) makes bonds to what

A

Methacrylate group of primer chemically bonds to methacrylate group of bond (sealer)

42
Q

What part of the Bond (sealer) makes bonds to what

A

Methacrylate group of bond chemically bonds to the methacrylate group on filled composite materials

43
Q

What are some of the biocompatibility disadvantages of dentin bonding agents and composite restorations

A
  • Excessive desiccation of dentin = Post operative pulpal sensitivity and a poor bond
  • Pulpal inflammation if bond failure occurs, leading to bacterial leakage
  • Avoid regular direct skin contact with primer/adhesive liquids - delayed allergic reaction of contact dermatitis
44
Q

Name some causes for the breakdown of an adhesive bond

A
  • Polymerisation shrinkage
  • Differential thermal expansion and contraction
  • Internal stresses from occlusal loading
  • Chemical attack (hydrolysis)
45
Q

What can a breakdown in the adhesive bond result in

A
  • Introduction of bacteria and debris into the cavity margins
  • Unsightly marginal staining
  • Pulpal sensitivity
  • Restoration may be lost
46
Q

How are etch and rinse systems used

A
  • 3 (acid etch, primer, bond) applied separately

- Acid applied separately followed by primer and adhesive in one bottle

47
Q

How are self etch systems used

A
  • Acid + primer in one bottle and adhesive in a separate bottle
  • Acid, primer and adhesive in one system (2 components, 4 steps)

Dental Materials Y2 (13 decks)

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