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BDS2 CDS Dental Materials Science > Bonding systems > Flashcards

Bonding systems Flashcards

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1
Q

what are the properties of a dental bond?

6

A

provide a high bond strength to tooth tissue
immediate high bond strength
durable bond
impermeable bond
easy to use
safe

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2
Q

why is bonding to enamel easier than bonding to dentine?

A

due to structure of enamel - densely packed prism, highly mineralised, dry

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3
Q

what acid is used for acid etch?

A

phosphoric acid 35%

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4
Q

how does acid etch change the surface of enamel?

A

roughens enamel surface
allows micromechanical interlocking of resins to enamel pits
increases surface energy by removing surface contaminants
leads to better wettability of enamel

enamel rods after etching
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5
Q

what is used after an etch?

A

dentine bonding agents - phosphorylated BIS-GMA
or low viscosity Bis-GMA

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6
Q

describe the properties and composition of dentine

5

A
  • 20% oroganic, 70% inorganic, 10% water
  • full of permeable tubules - fluid pumped from pulp to dentine, making dentine wet
  • secondary and tertiary dentine are irregular and more mineralised
  • low surface energy
  • hydrophilic
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7
Q

what are the requirements of a dentine bonding agent?

4

A

ability to flow
potential for intimate contact with dentine surface
low viscosity
adhesion to substrate

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8
Q

what is mechanical adhesion?

A

dentine bonding agent and the dentine surface meshing and interlocking with minimum gaps

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9
Q

what is chemical adhesion? how does mineralised and organic dentine adhere?

3

A

bonding at a molecular level
mineralised: ionic bonding
organic: covalent bonding

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10
Q

what is Van der Waals adhesion? and what does the strength of interaction depend on?

2

A

electrostatic or dipole interaction between bonding agent and substrate
strength depends on contact angle and is a good indication of wettability of a solid

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11
Q

what is the difference between high and low surface energy with a low surface energy liquid?

A

low surface energy substance with low surface energy liquid = does not spread
high surface energy substance with low surface energy liquid = will spread

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12
Q

does wet dentine have a high or low surface energy?

A

low surface energy so liquids/low viscosity resins do not spread

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13
Q

what do dentine bonding agents do to dentine?

A

increase the surface energy of dentine and allow the composite resin to flow and stick

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14
Q

what is molecular entanglement?

A

adhesive is absorbed onto the surface and penetrates dentine due to wetting by adhesive and surface energies
absorbed component forms long polymer that meshes with the substrate

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15
Q

what is the smear layer?

A

layer of organic debris that remains on the dentine surface after the preparation

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16
Q

what can you do with the smear layer in a restoration?

2

A
  • remove it and bond to “clean” dentine
  • incorporate it by penetrating it, infiltrating it with the bonding agent and stick it to the dentine below
17
Q

what are the components of total etch?

3

A

conditioner
primer
adhesive

18
Q

what does the conditioner in total etch do?

3

A

35% phosphoric acid
* removes smear layer and opens dentinal tubules
* decalcifies uppermost layer
* collagen network in top of dentine is exposed

19
Q

what does the primer in total etch do?

3

A
  • hydrophilic end bonds to hydrophilic dentine and hydrophobic end bonds to resin
  • has a spacer group to make it long enough to be flexible when bonding
  • gives dentine high surface energy, making it hydrophobic
20
Q

what does the adhesive in total etch do?

4

A

mixture of resins - Bis-GMA, HEMA
* contains camphorquinone to enable light cure
* penetrates the primed dentine which is now hydrophobic
* forms a micromechanical bond within the tubules and collagen fibres - molecular entanglement

21
Q

what are the problems with total etch?

3

A

over-etching collapses the collagen fibres so resin cannot penetrate
over-etching - too deep an etch and the primer cannot penetrate the full depth of the etch
moisture dependent - too dry and the surface of dentine collapses, too wet and the primer is diluted

22
Q

how does separate etch with primer and sealer work?

2

A

still a total etch techinque with same chemicals used
primer and sealant are combined and applied to the etched, washed dentine and light cured

23
Q

how do self-etching primers work?

A

they do not remove the smear layer, it infiltrates it and incorporates into it
it is not washed off and creates a hybrid layer

24
Q

what is shown in this picture?

A

hybrid layer and resin that has entered tubules

25
Q

what are the advantages to self-etching bonding agents?

2(3,1)

A

less sensitive technique
* no rinsing
* no excess drying
* no dentine collapse leading to low bond strength
simultaneous demineralisation and resin infiltration
* less chance of post-op sensitivity

26
Q

what is the disadvantage of self-etching bonding agents?

1(2)

A

variable initial pH between products
* different pH results in different etch and penetration of resin
* materials with lower pH may not etch enamel efficiently

27
Q

how do self-etching bond agents work?

3

A
  • contain bi-functional monomers that etch and infiltrate the dentine surface with the hydrophilic end
  • acidic groups react with Ca2+ ions in the tooth and create an amorphous calcium chelate
  • smear layer is dissolved and incorporated into the hybrid layer
28
Q

what is the adhesion-decalcification concept?

3

A
  • interaction between dentine bonding agent molecules and HA
  • all acid monomers bond to the calcium in HA ionically initially
  • monomers with a lower pK (acidic) do not form a stable bond as they continue to dissolve HA which leads to a hybrid layer with unstable calcium phosphates incorporated
29
Q

strong self-etch disadvantages

3

A
  • etching by-products are not washed away so tooth is continually etched
  • by-products are soluble and weaken the integrity of the bond
  • if too much HA is dissolved, the collagen is vulnerable to breakdown and the bond will fail
30
Q

what are problems with the smear layer?

A
  • if smear layer is thick then mild self etch adhesives may not penetrate
  • need to penetrate smear layer without decalcifying the tooth surface too much and removing HA

BDS2 CDS Dental Materials Science (5 decks)

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