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2c. BDS2 CDS DMS > 05. Bonding to Teeth > Flashcards

05. Bonding to Teeth Flashcards

1
Q

L5: What are the required properties of a dental bond?

A
  • Provide a high bond strength to tissues;
  • Immediate high strength bond;
  • Durable bond;
  • Impermeable bond;
  • Easy to use;
  • Safe.
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2
Q

L5: How easy is it to bond to enamel and why?

A

Easy, due to its structure

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3
Q

L5: What structural properties of enamel make it easy to bond to?

A
  • Heterogeneous, densely packed prisms;
  • Highly mineralised, 95% inorganic;
  • ‘Dry’.
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4
Q

L5: What is the purpose of applying acid etch?

A

To roughen the surface of enamel and produce a characteristic etched pattern

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5
Q

L5: Etching enamel provides a roughened surface to bond to, how do materials bond?

A
  • Microchemical interlocking of resin filling materials;
  • Increased surface energy of the enamel, due to removed surface contaminants i.e. better wettability;
  • Better wettability allows the resin to adapt better to the enamel surface;
  • Bonding is essentially mechanical.
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6
Q

L5: When bonding to enamel, what environmental factor is necessary?

A

Enamel should be dry

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7
Q

L5: In practice, what solution is usually used to etch?

A

A 30-50% aqueous solution of phosphoric acid

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8
Q

L5: What type of bond is typically applied to teeth, after etching?

A

A low viscosity Bis-GMA resin (plastic)

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9
Q

L5: When bond (low viscosity resin) is applied it flows into the roughness of enamel surface, then what happens?

A

It polymerises and forms a strong bond, >20 MPa

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10
Q

L5: What is the strength of a bond between enamel and dental bond?

A

> 20 MPa

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11
Q

L5: How easy is it to bond to dentine and why?

A
  • Difficult;
  • Presence of permeable tubules;
  • Fluid pumped from pulp to dentine floor making surface wet;
  • Inconsistent material depending on age and proximity to pulp;
  • Low surface energy;
  • Dentine is hydrophilic (most bonding agents are hydrophobic).
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12
Q

L5: What is the general composition of dentine and how does this change with age?

A
  • 20% organic (collagen), 70% inorganic (hydroxyapatite), 10% water;
  • Becomes more mineralised with age.
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13
Q

L5: What are the further requirements to bond to dentine?

A
  • Ability to flow;
  • Low viscosity;
  • Adhesion via mechanical, chemical and Van Der Waals forces.
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14
Q

L5: What is the primary form of bonding to dentine?

A

Mechanical (interlocking between resin and meshed surface)

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15
Q

L5: At a molecular level, how does DBA bond to mineralised dentine content?

A

Ionic bonding

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16
Q

L5: At a molecular level, how does DBA bond to organic dentine content?

A

Covalent bonding

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17
Q

L5: What is Van der Waals adhesion?

A
  • Based on electrostatic or dipole interaction between DBA and substrate;
  • Strength of interaction depends on bond angle (which indicates wettability of a solid, by a liquid).
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18
Q

L5: What contact angle, with VDW forces, means that a surface is hydrophilic?

A

<90 degrees

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19
Q

L5: For a liquid to stick to a surface it is placed on to, how must the surface energies differ?

A

Liquid must have a lower surface energy than the surface it is applied to

(remember PTFE has a very low surface energy, which is why nothing sticks to it)

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20
Q

L5: What should have a higher critical surface energy to form a bond, dentine or composite resins?

A

Dentine

if wet, it is lower than most resins and they therefore won’t stick!

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21
Q

L5: Some dental adhesive is absorbed into the dentine surface, where it can then… ?

A

Polymerise and entangle at a molecular level, leading to high bond strength

22
Q

L5: What is the smear layer?

A

An adherent layer of organic debris that remains on the dentine surface, after preparation of dentine during restoration of a tooth. This is generally contaminated with bacteria.

23
Q

L5: How thick is the smear layer?

A

0.5-5 microns thick

24
Q

L5: How does the smear layer affect adhesion to dentine?

A

It interferes with it as the smear layer is now firmly attached to the dentine

25
Q

L5: How can the smear layer be dealt with (2 options)?

A
  • Remove and bond to the ‘clean’ dentine beneath;

- Incorporate it into the DBA and stick it to the dentine below.

26
Q

L5: Previous etch generations were developed to bond to the smear layer however this proved ineffective, what two types of etch are now used?

A
  • Total etch;
  • Self etch.

(to remove and/ or modify the smear layer)

27
Q

L5: What are total etch bonding agents and how do they work?

A
  • 4th generation DBA;

- Involve complete removal of smear layer.

28
Q

L5: Give three examples of total etches:

A
  • Scotchbond multipurpose;
  • Clearfil photo bond;
  • Optibond FL.
29
Q

L5: What are the components of a total etch DBA and what do they do?

A
  • Dentine conditioner (an acid);
  • Primer (adhesive part, hydrophilic/ hydrophobic molecule);
  • Adhesive (a resin which penetrates into the surface).
30
Q

L5: What does the dentine conditioner (etch) component of a DBA do?

A

Usually phosphoric (35%) acid but can be EDTA/ nitric acid.

  • Removes smear layer;
  • Opens dentinal tubules by removing smear plugs;
  • Decalcifies uppermost layer of the dentine;
  • Collagen network exposed for penetration by next two components.
31
Q

L5: What does the primer component of a DBA contain and do?

A
  • Adhesive;
  • Coupling agent, bifunctional molecule;
  • One hydrophilic end (to bond to hydrophilic dentine surface) and;
  • One hydrophobic end (to bond to resin);
  • Spacer group to increase flexibility for bonds (therefore will be stronger, with more bonding sites);
  • These molecules are dissolved in a suitable solvent (ethanol/ acetone/ water).
32
Q

L5: Name a typical coupling agent in primers, of DBAs:

A

Hydroxy ethyl methacrylate (HEMA)

33
Q

L5: What does the adhesive component of a DBA contain and do?

A
  • Mixture of resins;
  • Usually Bis-GMA and HEMA;
  • Mainly hydrophobic;
  • May contain some filler particles to make it stronger;
  • Contains camphorquinone for light curing;
  • Penetrates the primed dentine surface (now hydrophobic);
  • Forms micro chemical bond within the tubules;
  • Molecular entanglement;
  • Forms the hybrid layer of collagen + resin.
34
Q

L5: Summarise bonding to dentine, by the three components of a total etch:

A

Etch:

  • Demineralisation of the outer layer;
  • Remaining collagen is hydrophilic and has low surface energy (resin will not bond).

Primer:

  • Penetrates the demineralised dentine, due to its bifunctional molecules;
  • Gives the surface high energy, making it hydrophobic.

Adhesive:

  • Can now penetrate;
  • Micro-mechanical retention.
35
Q

L5: What are the problems with overreaching when using a total etch?

A
  • Collapse of collagen fibres, so no resin can penetrate;

- Etching too deep so the primer cannot penetrate fully.

36
Q

L5: How do moisture parameters effect the performance of total etch?

A
  • Too dry: dentine surface collapses;
  • Too wet: primer dilutes and strength is reduced;
  • Not simple to get right.
37
Q

L5: When bonding to dentine, what environmental factor is necessary?

A

Dentine should be moist

38
Q

L5: How many clinical stages are there to total etches?

A

1 or 2, depending on whether the etch is separate or also combined into the primer/adhesive mix

39
Q

L5: How do the bond strengths of two-stage bonding agents compare to that of three part materials?

A

Comparable

40
Q

L5: What are self etch primers and how do they work?

A
  • 5th generation;

- Involve incorporation of smear layer into themselves.

41
Q

L5: How are self etching primers clinically less sensitive than other etches?

A
  • Do not require washing off;

- Removes the problem of how dry to make the dentine.

42
Q

L5: How does the bond strength of self etches compare to other etches?

A

Lower bond strength to tooth

43
Q

L5: What happens to the smear layer when using a set etch?

A

It is dissolved and incorporated into the hybrid layer, penetrating about 2um into the surface

44
Q

L5: How is the ‘no-drying’ stage of self etches beneficial to the patient?

A
  • Reduced chance of collapsed dentine architecture;
  • Prevents resin penetration;
  • Reduced sensitivity.
45
Q

L5: What is the difference in composition between a total etch and self etch?

A
  • Self etches contain an acidic monomer, that incorporate themselves into the surface;
  • Total etches (usually) contain phosphoric acid which removes the smear layer.
46
Q

L5: What is the fundamental mechanism of all dental bonding?

A
  • Mineral exchange;
  • Minerals removed from hard tissue;
  • Replaces by resin;
  • These mineralise and mechanically interlock in porosities;
  • i.e. molecular entanglement.
47
Q

L5: What is the most challenging aspect of developing a self etch?

A
  • Not removed by washing away;
  • Remaining etch can dissolve hydroxyapatite away;
  • This weakens the bond;
  • Must design an etch that penetrates the smear layer enough to get through it, but without decalcifying the tooth (too much) and removing the HA which is required for a strong bond;
  • HA also protects the dentine from hydrolytic breakdown.
48
Q

L5: What are the advantages of self etching bonding agents?

A
  • Less technique sensitive;
  • Simultaneous demineralisation and resin infiltration (less chance of post-op sensitivity);
  • Easier.
49
Q

L5: Why are self etching bonding agents less technique sensitive?

A
  • No rinsing (therefore less problems with moisture control);
  • No excessive drying (therefore prevents collapse of dentine architecture);
  • No dentine collapse (leading to low bond strength).
50
Q

L5: What are the disadvantages of self etching bond agents?

A
  • Great variability between products (initial pH);
  • Different pHs mean different etch penetration;
  • Lower pH materials may not etch efficiently;
  • Little evidence they form stronger bonds than total etches.

2c. BDS2 CDS DMS (12 decks)

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