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BDS3 > Adhesion and Dental Materials > Flashcards

Adhesion and Dental Materials Flashcards

1
Q

How does adhesive dentistry conform to minimal intervention?

A
  • Retention of restorations
  • Repair of restorations
  • Conservation of tooth structure
  • Reinforcement of tooth structure
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2
Q

What are some of the clinical advantages brought about by adhesive dentistry?

A
  • Wider range of treatment options
  • Conforms with minimal intervention
  • Reduction in microleakage
  • Bonding of substrates of dissimilar composition
  • Reduced dentin hypersensitivity
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3
Q

What is adhesion, and what is the adhesive interface?

A

Adhesion: Bonding of two substrates

Adhesive interface: Junction between the two materials

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4
Q

What is an adhesive?

A

The material that joins the adherent and adherend

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5
Q

What is an adherent?

A

Exogenous material that is bonded to a foundation/adherend (examples of adherents are resin, acrylic, ceramic)

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6
Q

What is an adherend?

A

Material that acts as the foundation for the adherent to bond to (e.g. tooth structure, enamel, dentine, alloy, cermaic)

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7
Q

What are the types of adhesion in dentistry?

A
  • Macromechanical
  • Micromechanical
  • Chemical
  • Interfacial/chemical
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8
Q

What is interfacial/chemical adhesion? Give examples.

A

Broad term used to describe adhesion between two very dissimilar materials (usually combination of chemical and mechanical)

  • Ceramo-metal bridge
  • Ceramic crown bonded by resin cement
  • Metallic crown bonded by resin cement
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9
Q

What is macromechanical retention? Give some examples.

A

Retention created by visible mechanical interlocking between dissimilar materials, examples:

  • Restorations with pins, slots, undercuts,
  • Posts for endodontically treated teeth
  • Removable prostheses
  • Implant supported dentures
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10
Q

What is micromechanical retention? Give examples.

A

Retention created by microscopic mechanical interlocking between dissimilar materials, e.g.

  • Enamel resin bond
  • Dentine-resin bond
  • Bonded amalgam
  • Sandblasting
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11
Q

How is resin bonded to ceramic?

A

Silane:

  • Hydroxyl groups form oxygen bonds with silica in ceramic
  • Double carbon bond forms bond with resin
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12
Q

How is resin bonded to metal?

A

Metal primer:

  • Double carbon bond bonds to resin
  • Sulfur group forms bond with gold alloy
  • Other metal primers may bond to metal via an oxygen containing group (e.g. a C double bond O group/ketone group)
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13
Q

How would you repair exposed metal on a fractured porcelain fused to metal crown?

A
  • Sand blast
  • Metal primer
  • Resin
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14
Q

T/F Bis-GMA and UDMA bond to untreated metal surface

A

F

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15
Q

How can retention to metal primer be improved?

A

Sandblasting

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16
Q

What can cause adhesive failure?

A
  • Moisture control (lack of)
  • Insufficient strength
  • Improper use (e.g. not light curing if appropriate)
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17
Q

What is the difference between adhesive and cohesive failure?

A

Adhesive failure=failure in the bond keeping two materials together (e.g. in the micromechanical retention bonding resin to enamel)

Cohesive failure=failure in the materials involved in bonding (e.g. in the CR, tooth structure or luting cement material), usually caused by insufficient material strength

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18
Q

What are the conditions for optimal adhesion?

A
  • Clean bonding surface
  • Large bonding surface
  • Low wetting of adhesive (low viscosity)
  • Dimensionally stable adhesive
  • Close contact between two surfaces
  • Follow correct protocol
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19
Q

What factors can affect adhesion to tooth surfaces?

A

Type and quality of tooth structure:

  • Enamel (prismatic vs aprismatic, fluorosis, hypoplasia, AI)
  • Dentine: cavity depth/tubule density, tertiary dentine formation, presence of organic collagen
  • Cementum: high organic component

Cavity factors

  • Wetness of surface/moisture present
  • Resistance/retention
  • Smear layer, pellicle
  • Foundation of bonding substrate (e.g. infected dentine)

Material factors

  • Properties of material and type of bond formed (e.g. between resin and GIC, type of etch used)
  • Polymerisation shrinkage of resin based materials
  • Patient factors (e.g. tooth grinding, high erosion/caries risk, clenching, overbite, xerostomia)

Factors affecting performance of system

  • Concentration of etchant: determines length of resin tags
  • Phase separation (if water concentration too high can result in phase separation of hydrophilic and hydrophobic compounds)–>poorer bonding strength and adhesive failure
  • Permeability of hybrid layer (primer may not be able to penetrate to all the spaces, resulting in air bubbles that can act as stress points and increase permeability of hybrid layer); can also be caused by primer taking up water and creating water bubbles in simplified adhesive systems
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20
Q

What are the different types of enamel etch patterns?

A

Type I: preferential core
Type II: preferential periphery
Type III: mixed

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21
Q

What is the average tensile strength of the bond between resin/enamel?

A

20-25 MPa (Newtons/mm squared

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22
Q

What is the average tensile strength of the bond between GIC and enamel?

A

10-12 MPa

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23
Q

What is the average tensile bond strength between RMGIC and enamel?

A

15-20MPa

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24
Q

How do dentine tubules change towards the pulp?

A

Become larger in diameter and more densely concentrated

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25
Q

What are posssible sources of moisture on dentine?

A

Triple syringe
Humidity
Dentine tubules

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26
Q

What is the smear layer?

A

Layer created from debris from drilling (consists of enamel, dentine, bacteria, organic matter, blood, GCF, collapsed collagen)

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27
Q

T/F etching and conditioning opens tubules

A

True

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28
Q

What are some properties of GIC based adhesion?

A
  • Shallow layer for ion exchange
  • True chemical bond
  • Biocompatible and F release
  • Can trap air resulting in stress points
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29
Q

T/F intratubular dentine is the same as peritubular dentine?

A

True

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30
Q

Which erodes faster between intra and intertubular dentine?

A

Intratubular

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31
Q

How does primer affect collagen in dry bonding?

A

-Rehydrates and stiffens collagen

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32
Q

What is the difference in the primer type between wet bonding and dry bonding?

A

Wet: Acetone based primer
Dry: HEMA based primer

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33
Q

What are the pros and cons of dry bonding?

A

Pro:
-Moisture control

Con:

  • Moisture sorption in long term due to hydrophilic HEMA
  • Hybrid layer becomes semi-permeable
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34
Q

What are the pros and cons of wet bonding?

A

Pro:
Prevent collagen collapse

Con:
Acetone evaporates 
Overwet dentine
Traps water blisters in hybrid layer (at dentine primer interface)
Weaker bond strength
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35
Q

Why are water blisters an issue in wet bonding?

A
  • Water can separate from other components in what is known as phase separation, forming water blisters and monomer globules
  • Water blisters act as stress points where strength of material is reduced
  • Water blisters may result in an internal gap at the area of the dentine tubule, thus preventing formation of a resin tag and resulting in leakage/dentine sensitivity
  • If internal gap is open to the outside, can allow ingress of bacteria thus irritating pulp
  • Monomer globules may block up tubules preventing formation of tags
36
Q

What is nano-leakage?

A
  • When the resin tag does not block off the entire tubule, resulting in a small submicron channel around the tag that can allow for leakage of fluid (poor hybridisation)
  • Channels are too small for bacteria to enter
  • Clinical significance unclear: may increase risk of formation of larger channel
37
Q

What is 4th generation adhesive?

A

3 Step etch primer bond

38
Q

What is 5th generation adhesive?

A

2-Step but with total etch (etch as separate step, primer and adhesive combined)

39
Q

What is 6th generation adhesive?

A

2-step self etch (etch combined with primer and not rinsed off)
Tend to have shorter resin tags as lower acidity
Contain water to provide ionisation medium for monomers

40
Q

What is 7th generation adhesive?

A

Etch, primer, bond in one step

-Apply thin coating, dry into thin film x2, apply resin composite

41
Q

What are water trees?

A

Water filled channels caused by primer taking up excess water. Results in tree-shaped porosity that can be seen microscopically. Can increase permeability of hybrid layer

When left exposed for too long, primer can take up moisture resulting in water bubbles. This then results in the formation porosities filled with water in the hybrid layer, increasing it’s permeability. These porosities are tree-shaped, and thus known as water trees

42
Q

How does G-Bond work? What is it’s main advantage?

A

Contains no HEMA, uses 4-MET instead as the monomer

  • 4-MET contains a double bond carbon group at one end that bonds with resin
  • At the other end contains negatively charged carboxyl group that bonds with positively charged calcium in tooth enamel
  • Also contains negatively charged phosphate esters that bond with enamel calcium
  • Overall forms ionic chemical bond to tooth structure

-G-Bond is shown to form particularly good bonds with cervical restorations

43
Q

What is one usage of G-Premio other than as an adhesive?

A

Treatment of cervical dentinal hypersensitivity (apply + gently dry)

44
Q

What are the clinical steps for using G-Premio?

A

Self etch: no etch; Total etch: etch enamel + dentine
Apply G-Premio to all surfaces and leave for 10 seconds
Dry thoroughly for 5 seconds at max pressure
Light cure 10 seconds
Apply CR

45
Q

What is the difference in the hybrid layer between self and total etch?

A

Total etch: hybrid layer will be thicker

46
Q

What can happen when G-Bond is dried gently for 5 seconds rather than thoroughly as per manufacturer’s instructions when used as a primer?

A

-Hybrid layer trap water resulting in microscopic air bubbles that increase its permeability and reducing the seal integrity

47
Q

What are some issues that could be encountered with total etch systems?

A
  • Incomplete infiltration of primer/resin into demineralised collagen (formation of air bubbles as microporosity is deeper thus primer may not go all the way)
  • Long term water sorption into hybrid layer with HEMA based adhesives (as HEME is hydrophilic)
48
Q

What are some problems self-etch adhesives?

A
  • Formation of water blisters at resin/dentine interface
  • Results in semi-permeable membranes
  • Greater failure rates and poorer bonding strengths than total etch
49
Q

How does HEMA based primer work?

A

Hydrophilic end bonds to dentine
Hydrophobic end bonds to resin
Overall results in formation of hybrid layer that seals dentine preventing leakage of material through tubules

50
Q

What are the features of dentine tubules in hypersensitive individuals?

A
  • Denser

- Wider

51
Q

What is dentine hypersensitivity?

A

-Short sharp pain arising from exposed dentine in response to stimuli

(usually thermal, tactile, evaporative, chemical, tactile)

52
Q

What are the three theories of dentine hypersensitivity?

A

Receptor theory: Nerves directly detect stimulus (shortcoming=nerves located deep in dentine, application of pain inducing substances such acetylcholine fail to produce pain response)

Odontoblast transduction theory: Odontoblasts act as receptors and transmit signal to nerves (shortcoming=no neurotransmitters in dentine, odontoblast process do not extend to DEJ, odontoblast membrane potential too low to permit transduction)

Hydrodynamic: Movement of fluid is detected by nerves as pain/sensitivity (usually outward flow)

53
Q

What are some aetiological and predisposing factors of dentine hypersensitivity?

A
  • Erosive tooth wear (removes smear layer + expose dentine)
  • Abrasion
  • Recession
  • Periodontal disease
  • Periodontal therapy
54
Q

How should dentinal hypersensitivity be treated?

A

Prevention:
-Remove causative factors (e.g. abrasion, diet)

Treatment:

  • Tubule occlusion by adhesion of exogenous materials
  • Modification of nerve excitability
55
Q

What are the materials available to treat dentine hypersensitivity?

A
  • CPP-ACP (Tooth Mousse)/ CPP-ACFP (Tooth Mousse + )
  • Fluoride: hypermineralisation of tooth forms CaF2 on tooth surface which gets converted to hydroxyapatite at acidic pH

Potassium nitrate (sensodyne): high concentration of potassium outside nerve membrane prevents outflow of potassium and thus stops repolarisation

Sealant: e.g. Fuji Bond LC, G-Premio, RMGIC (bear in mind if apply restorative material need to scrape out after to prevent plaque adhesion)

Restoration: if wear is extensive enough

Bioglass:

  • On contact with saliva glass dissolves releasing calcium, phosphate, silicon
  • Precipitation of silicon gel then occurs
  • Silicon gel acts as a template for formation of calcium phosphate, which crystalises to hydroxycarbonate

Arginine (with calcium carbonate):

  • Bind to dentine surface
  • Attracts calcium ions into dentine tubules, sealing them
  • Increases resistance to low pH environments
56
Q

How to repair ceramic crown?

A
  • Roughen with hydrofluoric acid
  • Silane
  • Resin
57
Q

What does the inorganic phase of resin contain?

A

-Filler particles/glasses: strontium, quartz, barium, zirconia

58
Q

What does organic phase of resin contain?

A

-Bis-GMA, TEGDMA, UDMA

59
Q

What does the interfacial phase of resin contain? What does it do?

A

Silane

Joins organic and inorganic parts together + absorbs stress

60
Q

What do the miscellaneous phases of resin contain?

A

Accelerators and inhibitors

61
Q

What are possible uses of flowable resin?

A
  • Restoration of non-loaded areas
  • Repairing of old restorations
  • Fissure sealing
62
Q

What are packable amalgams, what are some of their properties, advantages, disadvantages?

A
  • Made to mimic packing feeling of amalgam
  • Contain macrofil particles (higher filler content)
  • Has better physical properties (wear resistance+compressive strength)
  • Can be packed into contact points

-However, rougher surface and lower polish retention

63
Q

How does CR set?

A

Initiation stage
-Initiator (light or chemical reaction) release free radical
Chemical cure radical: benzoyl peroxide
Light cure radical: camphorquinone
-Free radical has a free electron
-This causes the carbon double bond of the first monomer to open up and share one electron with the free radical, thus bonding the two together

Propagation Stage:

  • Due to sharing one electron with the free radical, the carbon from the monomer now has a free electron whereas the free radical becomes stable
  • This results in the next monomer opening up its own carbon double bonds and sharing an electron to bond with the first monomer, thus extending the length of the chain
  • This continues until a long chain polymer is formed
  • Transfer reactions may also occur in which a “free” monomer may transfer an electron to the last monomer at the end of a chain, thus completing said chain and creating another free radical to start another chain

Termination stage

  • End of polymer chain contains an unpaired electron
  • This gets paired with another unpaired electron from a second polymer chain
  • This results in two chains being bonded together and completion of reaction
64
Q

What is one issue with methacrylate monomers?

A

Monomers come together when polymerising thus causing shrinkage

65
Q

What is one advantage of oxirane monomers?

A

Rings open up instead of coming together during polymerisation, thus reducing shrinkage

66
Q

What are two advantages of bulk fill resin?

A

Can apply in a single increment due to transmission of light
Reduces voids and air bubbles

Larger monomers=less monomers per volume thus less shrinkage

67
Q

How does Sonic Fill work?

A
  • Apply to cavity
  • Handpiece makes material flowable allowing it to be adapted to cavity
  • Afterwards light cure
68
Q

What are the desirable properties of resin?

A
  • Aesthetic
  • Durable
  • Ease of handling
  • Low shrinkage
  • Wear resistant
  • Radiopacity
  • Anticariogenic (fluoride release)
  • Biocompatible

Clinical phase:
-Easy to handle

Curing phase:
-Low shrinkage

  • Finishing phase:
  • Aesthetics
  • Durability
  • Wear resistant
  • Biocompatible
  • Anticariogenic

Review phase:
-Radiopacity

69
Q

What is stress and strain and what is their application?

A
  • Stress is the force applied to a material per unit area
  • Strain is the change in length/distortion of the material in the direction of the force applied in relation to its original length

Slow of Stress vs. strain graph is the elastic modulus/rigidity of the material i.e. (stress/strain)=minimum force required to create the first bit of distortion of the material

70
Q

What is compressive strength?

A

-Ability of material to resist force attempting to compress it/shorten it

71
Q

What is tensile strength?

A

Ability of material to resist force that is trying to stretch it

72
Q

What is flexural strength?

A
  • Ability to resist bending forces

- Combination of tensile strength (on one side) and compressive strength (on the other side)

73
Q

What are properties to look for in dental materials?

A
  • Stress and strain
  • Polymerisation shrinkage
  • Compressive, tensile, flexural strength
  • Wear resistance
  • Surface roughness
74
Q

Explain the concept of diametral tensile strength

A
  • Most dental materials are brittle thus hard to grip ends to stretch to test tensile strength
  • Thus instead, cylindrical mass of material is compressed
  • This results in material stretching, thus allowing data collection on tensile strength
75
Q

What are the types of polymerisation shrinkage?

A
  • Volumetric (volume of shrinkage)
  • Linear (length of shrinkage)
  • Post-gel (shrinkage after curing)
76
Q

What is the difference between 2 and 3 body wear?

A

2 body involves two surfaces (e.g. opposing teeth)

3 body involves a third object in between (e.g. food, toothpaste)

77
Q

What are the survival rates of different materials?

A

GIC: 3 years
Resin: 7-10 years
Amalgam: 15 + years depending on patient factors

78
Q

What is the oxygen inhibition layer?

A
  • Thin microscopic layer at the surface of resin that can not be cured due to contact with oxygen
  • Usually not an issue, but can stain in some cases e.g. by spices
79
Q

What are some contra-indications to resin?

A
  • High load bearing areas
  • Insufficient peripheral enamel to bond to
  • Lack of moisture control
  • Deep gingival restorations (may require GIC base)
80
Q

What are the components of alginate?

A

Active ingredients (10-15%)

  • Potassium alginate
  • Calcium sulfate

Retarders: (2%)
-Sodium phosphate

Filler: (70%)
Diatomaceous earth

Other:

  • Zinc fluoride or potassium sulfate: improve surface
  • Flavouring and pigments
  • Glycol (prevent formation of silicon dust)
  • Quarternary ammonium compounds (disinfection)
81
Q

What is the setting reaction for alginate?

A
  • Calcium sulfate reacts with retarder first (this provides working time)
  • Calcium sulfate then reacts with potassium alginate to form insoluble potassium alginate
82
Q

What are the properties of alginate? How do chemical reactions influence this? What are some further advantages/ disadvantages?

A

Hydrophilic:
-Contents of powder contain salts that are designed to dissociate in water to release ions for reactions. These then react together to form insoluble gel, as such water is needed for reaction to occur hence hydrophilic

Dimensionally unstable

  • Syneresis: Movement of water onto surface
  • Evaporation: loss of water from surface
  • Imbibition: uptake of water

Setting speed changes with temperature:
-High temperature brings reactants closer to activation energy and increase frequency of collision of molecules

Elastic to limited degree (semi-rigid)

  • Depends on ratio of guluronan : mannuronan in alginate salt
  • Guluronan binds with calcium to form cross link between polymer chains
  • Higher guluronan= higher rigidity, strength, brittleness
  • Higher mannuronan=lower strength + rigidity, higher elasticity

Irreversible/single use:

  • Once potassium alginate precipitates it is no longer soluble
  • As such ions can no longer be dissolved and react with each other to reform the reactants

Low wetting/viscosity allowing recording of most detail

  • While not completely set, cross links are not yet formed
  • Thus molecules are not bound strongly to each other allowing for movement resulting in low viscosity

Further advantages:

  • Easy to manipulate
  • Does not require complex equipment
  • Relatively comfortable
  • Non-irritant/toxic
  • Acceptable taste/odour
  • Cost effective

Further disadvantages

  • Does not record all details
  • Pressure on gel can distort material
  • Can tear if severe undercuts or thin sections
  • Can not move tray during setting
  • Incompatible with epoxy resin dies
83
Q

Why does calcium sulphate react preferentially with sodium phosphate/retarder?

A

-Because the product calcium phosphate has lower solubility

84
Q

What features should you take note of prior to taking an alginate impression?

A

Tray selection
-Arch size

Stop you putting tray in

  • Unusual anatomy (e.g. tori)
  • Overerupted, tilted teeth
  • Retractability of lips

Alters your impression afterwards

  • Any food debris
  • Deep palatal vault
85
Q

What are the key features you should look for when evaluating alginates?

A
  • Tray is appropriate size
  • Mix is homogenous and smooth
  • Adequate time to be inserted, seated and set
  • Adequate amount of alginate + appropriate seating and muscle trimming
  • Tray removed correctly

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