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Clinical skills 2 > Tooth-coloured materials: resin composites and bonding agents > Flashcards

Tooth-coloured materials: resin composites and bonding agents Flashcards

1
Q

What is composite?

A

A product with at least 2 distinct phases. It has the purpose to combine 2+ materials to produce one
with superior properties

contains inorganic filler

and organic binder

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2
Q

What are the superior properties of composite?

A
  • Compressive strength 170-260 MPa
  • Tensile strength 30-55 MPa
  • High coefficient of thermal expansion at 20-77
  • Polymer shrinkage 3%
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3
Q

What are the advantages of composite?

A

Aesthetics

Conservation of tooth structure

Adhesion to tooth structure via bonding system

Low thermal conductivity

Alternative to amalgam

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4
Q

What are the disadvantages of composite?

A

Technique sensitivity

Polymerisation shrinkage

This can result in marginal leakage -> secondary caries ->postoperative sensitivity

Decreased wear resistance

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5
Q

What 3 things do companies advertise composite as?

A

universal, flowable, packable

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6
Q

What are the different classifications of resin composites?

A

restorative procedure

filler particle size

clinical applications

curing modes

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7
Q

What does the restorative procedure classification say?

A

direct / indirect

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8
Q

What does the filler particle size classification say?

A

macrofilled

microfilled

hybrid

modern hybrid

nano composites

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9
Q

What does the clinical applications classification say?

A

packable

flowable

poly acid modified

self-adhesive

osmotic

bulk fill

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10
Q

What does the curing modes classification say?

A

chemically activated

light activated

heat-cured

dual-cured

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11
Q

What are the 4 main steps in free radical addition polymerisation?

A

activation

initiation

propagation

termination

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12
Q

What are the 2 ways activation can occur in free radical addition polymerisation?

A

chemical - organic amine + organic peroxide

light - camphorquinone + blue light (450-490nm)

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13
Q

What amount of energy is required to break camphorquinone to form free radicals?

A

490nm

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14
Q

What amount of energy is required to break lucirin to form free radicals?

A

410nm

recent development

is a second photoinitiator used

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15
Q

What are polywave light curing units?

A

require more than one wavelength to activate composite

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16
Q

What happens up to the gel point?

A

as long as curing / setting material is regarded as liquid or gel

no stress is transferred onto tooth

stress is relieved up to this gel point

after which composite is unyielding

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17
Q

Other than proper light curing, why should we light cure in 2mm depths?

A

to minimise stress transfer

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18
Q

Why is there shrinkage after curing?

A

monomers join

volume is reduced

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19
Q

Is polymerisation exothermic or endothermic?

A

exothermic

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20
Q

Why is the composite bond to dentine poor?

A

dentine is wet

acrylic resin is hydrophobic

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21
Q

What happens due to poor composite bond to dentine?

A
  • Poor retention
  • Staining
  • Sensitivity
  • Secondary caries
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22
Q

What are the 2 primary monomers in composites?

A

Bis-GMA / UDMA

diluent monomer - TEGMA

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23
Q

What does a typical composite have?

A

BisGMA + TEGMA or UDMA + TEGMA

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24
Q

Why are monomers in composites dimethacrylates?

A

have C=C bonds at both ends

this can be broken to produce polymerisation.

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25
Describe Bis-GMA
extremely viscous due to large benzene rings
26
How does TEGMA affect Bis-GMA?
- Makes molecules freely movable - Increases polymer conversion - Increases crosslinking - Increases shrinkage
27
What effect do fillers have on dental composites?
reduce shrinkage
28
Name some composite fillers
Strontium glass Barium glass Quartz Borosilicate glass Ceramic Silica Prepolymerised resin
29
What are the 3 ways fillers are classified?
material, shape and size
30
What shapes can fillers have?
spherical irregular
31
What is an advantage of spherical shape fillers?
easier to incorporate into resin mix fill more space leaving less resin less shrinkage
32
What is the effect of smaller particles in the mixture?
fills the space between larger particles to take up more space - There is less resin remaining so less shrinkage on curing
33
What do inorganic fillers reduce?
Polymerisation shrinkage Water sorption Thermal expansion
34
What do inorganic fillers increase?
Compressive/tensile strength Modulus of elasticity Abrasion resistance
35
Why are coupling agents used?
to improve adherence of resin to filler surfaces by chemically coating filler surfaces and increase strength provide chemical bond between filler particles and resin matrix to facilitate stress transfer
36
What is a typical coupling agent?
organosilane Common silane agents are vinyl triethoxysilane and methacryloxypropyltrimethylsilane
37
Where does the siloxane end bond to?
hydroxyl groups on filler
38
Where does the methacrylate end bond to?
polymerises with resin
39
What are the disadvantages of silanes?
- They age quickly in a bottle and become ineffective - Sensitive to water so silane filler bond breaks down with moisture
40
What is the difference between flowable composites and traditional hybrids?
less % filler content by weight (50-70%) lower viscosity
41
What are the indications of flowable composites?
Class V restorations Micropreparation Extended fissure sealing Adhesive cementation of ceramic restorations Blocking out cavity undercuts Initial base layer in any classification
42
What is the issue with flowable composites?
These have lower filler volumes, so they exhibit increased shrinkage and wear with decreased strength
43
Describe packable composites (macrofilled hybrids)
firm and can be packed into preparation larger filler particles or even fibres to improve packing qualities high viscosity so they are difficult to sculpt and voids condensable composites even though they can’t be condensed
44
What are the several product types for packable composites
Prodigy condensable (Kerr) Alert (Pentron) Solitaire 2 (Kulzer) Surefill (Dentsply) SDR (Dentsply) BULKFILL (3m)
45
Why is bonding to enamel predictable and easy?
Enamel is 95% hydroxyapatite, 4% water and 1% collagenous protein there is barely any water content so is more likely to bond to hydrophobic dental composites
46
What is the pH of phosphoric acid?
0.2
47
What happens when etching?
Etching decalcifies portions of enamel rods Calcium salts are dissolved which exposes interprismatic and prism areas for interlocking tag formation with bonding resin
48
What is the smear layer?
created by any mechanical cutting of dentine due to dentine debris of variable thickness Smear plugs are also formed which block the dentinal tubules
49
What are the properties of the smear layer?
- Protects dentine and pulp from penetration of bacteria - Eliminates diffusion of dentinal fluid - Impairs bond of composite to dentine - Itself is only relatively loosely bound (not good to stick to) - Can harbour bacteria
50
How do we achieve optimum bonding with the smear layer?
1. Smear layer is left alone 2. Smear layer is removed 3. Smear layer is modified 4. Smear layer is partially removed and partially modified
51
What is hybridisation?
Infiltration of resin monomers into collagen fibrillar matrix of demineralised dentine, followed by polymerisation creates molecular-level mixture of adhesive polymers and dental hard tissues – the hybrid layer
52
What does primer do?
wet the collagen and provide hydrophobic surface for resin so has dual functionality, resin is applied on top and then you bond.
53
What does acid etching do in bonding to dentine?
Improves retention of restoration Increases dentine surface area Removes ‘smear layer’ from prep Allows penetration for bonding agent into dentine Pulps don’t like acid so protect against pulp exposure If desiccated, collagen fibres of dentine that have been exposed (hybrid layer) will collapse allowing for a weaker bond
54
What does primer do in bonding to dentine?
Improves wettability of prep Penetrates etched dentin tubules
55
What does bonding adhesive do in bonding to dentine?
Adhesive bonds to collagen fibres in dentine to mechanically lock-in and provide hybrid layer
56
Describe primer
ampiphillic and has low viscosity
57
Why are solvents added to primer?
adjust primer viscosity and improve its wetting
58
What are the 3 stages in bonding?
etch prime bond
59
What are the current approaches of bonding?
etch and rinse, prime and bond etch and rinse, one bottle primer resin self-etch primer and bond self-etch adhesives (all-in-one)
60
What are the 3 subclassifications of primers based on their solvent?
- Acetone based eg All-bond 2, One Step - Ethanol based eg Optibond Solo - Water based eg Scotchbond MP, Scotchbond 1
61
What do the 2-step etch and rinse adhesives combine?
combine the primer and adhesive resin into one application
62
What are self-etch adhesives?
combine all 3 steps into one bottle, this combines self-etch primer with adhesive resin to create all-in-one adhesive
63
What is the challenge with self-etch primers?
there is a shift away from phosphoric acid towards acidic organic monomers more challenging to etch and the pH range is only 1-3
64
What are the 4 components of self-etch adhesives?
monomers eg HEMA-phosphate cross-linking monomers eg TEGDMA monofunctional co-monomers eg HEMA additives - photoinitiators - solvents - stabilisers - fillers etc

Clinical skills 2 (13 decks)

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