CSA tooth coloured materials 1 resin compo Flashcards
What are composites?
material with 2 phases:
o Inorganic glass filler (glass)
o Organic binder (polymer matrix)
How do we bond composite?
silane coupling agent
What does composite contain
- camphorquinone- allows for lighting
- chemicals to stabilise and increase shelf life
What are the advantages of composites?
- Good aesthetics
- Conserves tooth structure & minimally invasive
- Adhesion to tooth surface occurs via bonding system
- Low thermal conductivity
- Good alternative to amalgam now that minimata convention phasing it out
What are disadvantages of composite?
- good moisture control is required
- Polymerisation shrinkage
- Lower wear resistance than amalgam
- No chemical adhesion to tooth like GIC
What does polymerisation shrinkage lead to?
leads to marginal leakage, secondary caries, staining
What chemicals involved in placing composite?
- Acid etch – opens prisms, exposes collagen & dentinal tubules
- Bond – Forms hybrid layer between hydrophilic dentine & hydrophobic composite
What is chemical activation of composite?
- Chemical Organic amine + Organic peroxide
* Light Camphorquinone + blue light (450-490nm) – more common method of setting
What is part 1 of the initiation stage?
camphorquinone splits under presence of blue light (photo initiator) & forms a free radical
What is part 2 of initiation stage ?
Free radical attacks weak pi bond in monomer of double bond and causes it to split open, this activated monomer
What is propagation ?
• activated monomer acts as radical and joins other monomers, breaking open their double bonds and forming a string of reactions to form very long chain of monomers (polymers)
What is termination ?
• 2 radicals (can be very long chain of monomers) collide and reaction ceases
What is shrinking?
distance between monomers decreases during polymerisation
What is polywave for setting?
more than 1 wavelength (450-490 nm) to set composite to ensure max. amount of monomer is polymerised
What happens when composite pulled away from enamel/dentine?
o Poor retention
o Staining
o Sensitivity
o Secondary caries
What types of monomers are there?
- Bisphenol A glycidyl methacrylate (Bis-GMA) –
- Urethane dimethylacrylate (UDMA)
- Triethylene glycol dimethacrylate (TEGMA) –
- All are dimethylacrylates
Why is Bis GMA?
Viscous due to benzene ring
What does TEGMA act as ?
diluent for Bis-GMA and makes composite easier to work with, increases polymer conversion more cross linking but more shrinkage
How are they all dimethylacrylates?
C=C on each end of molecule that makes polymerisation possible
What happens during light curing?
o Stresses form at bonding interface due to shrinking, as monomers cross link
When are stresses relieved during curing?
“gel point” > composite is no longer a liquid and loses ability to flow
What happens after gel point?
composite becomes unyielding/stiff and stresses is transferred to tooth
What is recommended to decrease stress transfer?
2mm curing depth
What does composite filler do ?
decrease strength & wear resistance of material
• Materials include: strontium glass, barium glass, quartz, borosilicate glass, ceramic, silica or prepolymerised resin
What is filler classified by?
material ,shape and size
What shape is filler?
regular or spherical
What are spherical shapes easier to do?
add to resin matrix & fill more space (less matrix/resin)
What does adding smaller filler particles do?
particles fills space between larger particles & take up more space Less resin remaining so less shrinkage on curing
What do inorganic fillers reduce?
o Polymerisation shrinkage
o Thermal expansion
o Water sorption
What do inorganic fillers increase?
o Compression/Tensile strength
o Modulus of elasticity (Inc. stiffness)
o Abrasion resistance
What are different types of composites ?
- Traditional
- Microfill
- Hybrid
- Microhybrid
- Nanohybrid
- Nanofilled
what leads to loss of polish with composite?
• Matrix wears away faster than filler
What can toothbrushing do to composite?
• Leads to poor light refraction of material Decreases aesthetics
Microfilled composite benefit ?
- Filler is smaller
* Matrix & filler wear at same time so reasonable aesthetics is achieved
Nanofilled/hybrid composites ?
filler size was smaller than microfilled
• Most composites nanofilled or nanohybrid (including universal composites)
What do coupling agents do?
bonds filler particles to the resin matrix (allows for transfer of stress)
What is coupling agent in the form of?
organosilane
o siloxane end bonds to OH group in filler
o methacrylate end polymerises within resin
What are advantages to coupling agent?
- Inc. resin to filler surfaces
- Chemically coat filler surfaces & increase strength
What are disadvantages to coupling agent?
- Ages quickly & becomes useless
- Sensitive to water – water absorbed into material hydrolyses silane bond leading to filler attachment loss
What are common coupling agents?
o Vinyl triethoxysilane
Methacryloxypropyltrimethyloxysilane
What are general properties of composites?
- Compressive strength
- Tensile strength
- Co-efficient of thermal expansion
- Polymer shrinkage 3%
What are the different types of composite used?
- Universal
- Flowable composites
- Packable composites
What is packable composite ?
SDR and Bulkfil
What is packable composite like?
o More firm/ viscous than flowable composite
o Large filler particles
o Very viscous so difficult to sculpt material
- voids commonly seen
o Less shrinkage
How to use packable ?
don’t require placement of 2mm increments, light cure whole thing & place aesthetic composite on top
What is flowable composute?
50-70% filler content by weight - have less viscosity
What does Bis GMA monomer contain?
BPA
What is shrinkage dependant on ?
cement type and thickness
What does etching do?
decalcifies portions of enamel rods
o Calcium salts dissolved and interprismatic areas exposed for interlocking tag formation with bonding resin
What do bonding agent form?
pure mechanical bond with tooth surface’s enamel
What is benefit of etching?
- Removes debris + surface enamel (5 micrometres)
- SA increased by 10-20 folds
- Increase free surface energy of enamel so exceeds surface tension of resin
- Increases wetting
What is volume of dentine?
- 33% vol. of organic component (mainly type 1 collagen
- 45% vol. of inorganic component (Mainly HAP)
- 23% volume of water
Why is hard for composite to bond to dentine?
high moist area
What is aim of dentine bonding agents?
- bond hydrophobic highly viscous material (composite) to hydrophilic surface
- change surface properties of dentine to hydrophilic to hydrophobic
How is smear layer formed?
cutting of dentine, it blocks the dentinal tubules
What does smear layer do ?
o protect dentine/pulp from bacterial penetration – tubules blocked
o Prevents diffusion of dentinal fluid
o Impairs bond of composite to dentine
o Can harbour bacteria
What is mechanism of bonding ?
- replacement of minerals removed from hard tissues (by etch) by resin monomers
o Bond mechanically interlocked with porosities created upon setting
What is dentine hybrid layer formed at dentinal surface ?
due to hybridisation
What is hybridisation ?
Infiltration of resin monomers (within bond) into collagen fibrillar matrix at superficial layer of demineralised dentine
what causes mechanical bond?
resin tags
Why must we gently dry after etch ?
over dry causes collagen meshwork to collapse – primer cannot penetrate onto collagen & bonding fails
What are advantages of etching ?
- Increased retention
- Increases SA of dentine (more collagen is exposed)
- Removes smear layer
- Allows for penetration of bonding agent onto dentine (resin tags)
What is priming with HEMA resin monomer ?
o solvent helps HEMA penetrate denial tubules easily & removes residual moisture
What does priming help create?
penetrates tubules, helps create resin tags
What does bonding do ?
- Adheres to hydrophobic ends of HEMA & forms a hybrid layer/resin tags
- Composite adheres to bonding surface
What etch systems are there?
etch and rinse
self etch system
all in one system
What etch and rinse primers are used?
oAcetone based (e.g. All-bond 2, one step) oEthanol based (e.g. optibond solo) oWater based (scotchbond MP, Scotchbond 1)
What is self etch system?
- 2 step system
- Acidic monomers simultaneously etch & prime dentine THEN BOND
- No rinsing/ drying as no chance of scaffolding collapsing
advantage of Self etch SE system?
takes less time & is less technique sensitive
What is problem with acid organic monomers in SE?
Phosphoric acid better in opening enamel prisms & better at exposing collagen & dentinal tubules
What does SE primer need to do ?
o Dissolve smear layer & decalcify intertubular dentine
o Whilst exposing superficial collagen & produce an effective hybrid layer
Why isn’t SE system used much ?
unstable
What is the all in one system?
• SE primer combined with bonding resin so 1 application
problem with all in one system?
same problems as with SE system & must now also create a hydrophobic surface for composite to bond to
• acidity of bonding resin may interfere with setting of self-cure composite
What components used in all in one system?
HEMA Phosphate
TEGDMA
HEMA
Additives- solvents, filler
