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CSA > tooth coloured restorative materials 1: resin composite and bonding agents > Flashcards

tooth coloured restorative materials 1: resin composite and bonding agents Flashcards

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1
Q

what properties are we looking for in a material that can restore teeth

A
  • rebuild teeth
    -aesthetic teeth
  • not wear away
  • universal composites
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2
Q

what is definition of composite

A
  • composite is a product with at least 2 distinct phases (matrix and strengthening phase)
  • purpose is to combine 2 or more materials to produce one with superior properties
  • dental composites contain inorganic filler and an organic binder
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3
Q

what are the advantages of composites

A
  • aesthetics
  • conservation of tooth structure
  • adhesion to tooth structure( through a bonding system)
  • Low thermal conductivity
    alternative to amalgam
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4
Q

what are the disadvantages of composites

A
  • technique sensitivity
  • polymerisation shrinkage
  • marginal leakage
  • secondary caries
  • postoperatie sensitivity
  • decreased wear resistance
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5
Q

how does composite set?

A
  • free radical addition polymerisation
  • activation
  • chemical - organic amine and organic peroxide
  • light - camphorquinone + blue light (450-490nm)
  • check light
  • initation
  • propagation
  • termination
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6
Q

which type of polymerisation always result in shrinkage

A

addition polymerisation
- polymer occupy smaller volume than monomer

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7
Q

why is the bond to dentine poor

A

dentine is wet and acrylic is hydrophobic

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8
Q

what does poor bond to tooth lead to?

A

poor retention
staining
sensitivity
secondary cares

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9
Q

what do monomer provide

A

UDMA AND TEGMA
bis-GMA nad TEGMA
- binds filler particles together
- provides ‘workability’

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10
Q

describe the properties of Bis-GMA monomers

A
  • extremely viscous
  • large benzene rings
  • lowered by adding TEGDMA
  • freely movable
  • increases polymer conversion
  • increases crosslinking
  • increases shrinkage
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11
Q

what happens during light curing

A
  • stresses set up at bonding interface
  • stress relieved up to ‘ gel point’
  • after gel point composite= unyielding
  • stress transferred to tooth
  • 2mm depth of cure recommended to minimise stress transfer
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12
Q

what are composite fillers used for

A
  • fillers are placed in dental composites to reduce shrinkage upon curing
  • materials such as strontium glass, barium glass, quartz, borosilicate glass, ceramic, silica prepolymerized resin or the like are used
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13
Q

how are fillers classified?

A
  • fillers are classified by material, shape and size
  • fillers are irregular or spherical in shape depending on the mode of manufacture
  • spherical particles are easier to incorporate into a resin mix and to fill more space leaving less resin
  • one size spherical particle occupies a certain space
  • adding smaller particles fills the space between the larger particles to take up more space
  • less resin remaining and therefore, less shrinkage on curing
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14
Q

what do inorganic fillers do

A

reduce
- polymerisation shrinkage
-water sorption
- thermal expansion
increase
- compressive/tensile strength
- modulus of elasticity
- abrasion resistance

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15
Q

what is the difference between macro fill,nanofill,nanohybrid?

A
  • macro fill - larger filler particles
  • nanofil- filler dispersed
  • nandohybrid- combination
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16
Q

what does a coupling agent do

A
  • chemical bond
    filler particle - resin Matrix
    transfers stresses
  • organosilane (bifunctional molecule)
    -siloxane end bonds to hydroxyl groups on filler
  • methacrylate end polymerises with resin
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17
Q

what are functions of coupling agents

A
  • improve adherence of resin to filler surfaces
  • ## chemically coat filler surfaces and increase strength
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18
Q

what are the disadvantages of silanes?

A
  • quickly age in a bottle and become ineffective
  • sensitive to water so the silane filler bond breaks down with moisture
  • water absorbed into composites results in hydrolysis of the silence bond and eventual filler loss
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19
Q

what are common silane agents

A

vinyl triethoxysilane
methacryloxypropyltrimehtlyoxysilane

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20
Q

what is the compressive strength of coupling agents

A

170-260 MPa
(Enamel 100-360, dentine 250-350)

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21
Q

what is the tensile strength of coupling agents

A

30-55 MPa
(Enamel 10, Dentine 20-50)

22
Q

what is the coefficndt thermal expansion of coupling agents

A

20-77 (Enamel 11.4, Dentine 8.3)

23
Q

what percentage is the coupling agents prone to polymer shrinkage

A

3%

24
Q

since 2007, how do companies advertise coupling agents

A

’ universal composite’
‘ flowable composite’
‘ packable composite’
the chemistry is basically identical, the only change is the viscosity or filler type

25
Q

how much filler content is found in flowable composites

A

50 to 70 %
less than traditional hybrid composite resins which give them lower viscosity

26
Q

what are the indications for flowable composites

A
  • Class V restorations
  • Micropreparations
  • Extended fissure sealigns
  • Adhesive cementation of ceramic restorations
  • Blocking out cavity undercuts
  • initial layer in any classification.
27
Q

what is the disadvantage of flowable composites

A

the flowable composite resins have lower filler volumes and thus they exhibit increased shrinkage and wear with decreased strength

28
Q

name some packable composites

A
  • prodigy condensable
    -Alert (Pentron)
  • Solitaire 2 (Kulzer)
  • Surefill (Dentsply)|
  • sdr (Dentsply)
  • BULKFILL (3m)
29
Q

what are the packable composites properties

A
  • composites are firm and can be packed into a preparation
  • contain larger filler particles or even fibres to improve packing qualities
  • Because of their high viscosity they are more difficult to sculpt and voids are more common
30
Q

what do composites contain and how do they polymerise

A

Bis- GMA resin. and other methacrylate
- polymerise through photoiniated mechanisms
- Available in various shades and opacities
- Does not adhere to tooth tissue unless are specifically self etching

31
Q

describe the way is enamel bonded

A
  • predictable and relatively easy
32
Q

what organic and inorganic substances doe enamel contain

A

95% Hydroxyapatite
4% water
1% Non- collagenous protein

33
Q

After bonding , what is the next process when restoring a composite

A

an acid (mosrtly 30-40% phosphoric acid) is applied and rinsed off
- pH is 0.2 (very strong acid) and decalcification occurs in 5-8 seconds
- Etching decalcifies portions of enamel rods

34
Q

what does the acid etch technique do to the microstructure of enamel

A
  • calcium salts are dissolved which exposes interprismatic and prism areas for interlocking tag formation with the bonding resin
  • roughens surface of enamel
  • mechanical bonding, not true adhesion
  • bond strength 20 MPs
35
Q

describe the organic components ned inorganic components of dentine

A
  • dentine contains
  • 33% by volume of organic component
    (mainly type 1 collagen)
  • 45% by volume of inorganic component (HAP)
  • 23% by volume of water
  • moist, living tissue
36
Q

what is the ultimate aim for dentine bonding agents

A
  • bond a hydrophobic , highly viscous composite to a hydrophilic adherent
  • need something to change properties of dentine surface/smear layer form hydrophilic to hydrophobic.
37
Q

what is a smear layer

A
  • created by any mechanical cutting of dentine
  • essentially dentine debris of variable thickness
  • smear plugs are formed which block dentinal tubules
  • ca protect dentine through prenetraiton of bacteria
  • can harbour bacteria
38
Q

what are the four strategies that have been used to achieve optimum bonding

A
  • smear layer is left alone
  • smear layer is removed
  • smear layer is modified
    = the smear layer is partially removed and partially modified
39
Q

what is the basic mechanisms of bonding to enamel and dentine

A
  • exchange process involving replacement of minerals by resin monomers which upon setting, become micro-mehcanically interlocked in the created porosities
40
Q

what is hybridisation?

A
  • the infiltration of resin monomers into the collagen fibrillar matrix of demineralisation dentine followed by polymerisation.
  • process that creates a molecular- level mixture of adhesive polymers and dental hard tissues - the hybrid layer
41
Q

what are the full properties and how do we do acid etching

A
  • improves retention of the restoration
  • increases surface area of the dentine
  • removes ‘ smear layer’ from prep
  • allows for penetration of bonding agent into dentin
  • protect pulp exposures before using
  • Phosphoric acid (35-37%) gel or liquid
  • Isolate teeth, apply ethcnant, wait (5-15 seconds)
  • rinse - don’t desiccate! blot prep to remove water
42
Q

what are the properties of primer and how do we apply it

A
  • resin - monomer
  • improves wettability of prep
  • penetrates etched dentin tubules
  • applied in a thin layer; thinned with air; blot - May require light curing
43
Q

what are the properties of bonding adhesive

A
  • un-filled or lightly filled resin
    -adhesive bonds to collagen fibres in dentin mechanicially ‘ locks-in’ - hybrid layer’
  • applied in a thin, uniform layer
  • light cured 10-20 seconds
  • new generation being developed
  • dental composite then applied
44
Q

what are the current types of approach of bonding in restorations

A
  • apply these 3 steps separately or together
  • etch and rinse, prime and bond
  • self-etch primer and bond
  • performance assessed in the lab
  • performance assessed in Class V clinical studies
45
Q

what step is followed after etching

A

priming step

46
Q

what are the properties of a primer

A
  • ampiphillic and low viscosity
  • solvents are added to adjust primer viscosity and improve its wetting
  • usually optimised for dentine surface characteristics rather than enamel
47
Q

how are the etch and rinse primers classified

A

by primer solvent
- acetone based
- ethanol based
- water based

48
Q

what options are there for the etch rinse methods

A
49
Q

describe self - etch primer and adhesive

A
  • application of the self etch primer is followed by the application of a hydrophobic bonding resin
  • without the need for rinsing, application time of self etc adhesives is shorter and the technique sensitivity is lower
50
Q

how must the performance be once upon application of the self etching primer

A
  • dissolve the smear layer
  • decalcify interlobular dentine
    whilst
  • penetrating to embed superficial collagen and produce an effective hybrid layer
  • many complicated competitive events
  • consequently, systems relativity unstable
51
Q

what is the pathway for successful bonding to dentine

A
  • wetting
  • inflation to produce a ‘hybrid zone’
  • mechanical interlocking
  • stress resistance
  • ultimate goal is marginal integrity and sealing tubules to prevent ingress of bacteria

CSA (32 decks)

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