tooth coloured restorative materials 1: resin composite and bonding agents Flashcards
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what properties are we looking for in a material that can restore teeth
- rebuild teeth
-aesthetic teeth - not wear away
- universal composites
what is definition of composite
- 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
what are the advantages of composites
- aesthetics
- conservation of tooth structure
- adhesion to tooth structure( through a bonding system)
- Low thermal conductivity
alternative to amalgam
what are the disadvantages of composites
- technique sensitivity
- polymerisation shrinkage
- marginal leakage
- secondary caries
- postoperatie sensitivity
- decreased wear resistance
how does composite set?
- free radical addition polymerisation
- activation
- chemical - organic amine and organic peroxide
- light - camphorquinone + blue light (450-490nm)
- check light
- initation
- propagation
- termination
which type of polymerisation always result in shrinkage
addition polymerisation
- polymer occupy smaller volume than monomer
why is the bond to dentine poor
dentine is wet and acrylic is hydrophobic
what does poor bond to tooth lead to?
poor retention
staining
sensitivity
secondary cares
what do monomer provide
UDMA AND TEGMA
bis-GMA nad TEGMA
- binds filler particles together
- provides ‘workability’
describe the properties of Bis-GMA monomers
- extremely viscous
- large benzene rings
- lowered by adding TEGDMA
- freely movable
- increases polymer conversion
- increases crosslinking
- increases shrinkage
what happens during light curing
- 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
what are composite fillers used for
- 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
how are fillers classified?
- 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
what do inorganic fillers do
reduce
- polymerisation shrinkage
-water sorption
- thermal expansion
increase
- compressive/tensile strength
- modulus of elasticity
- abrasion resistance
what is the difference between macro fill,nanofill,nanohybrid?
- macro fill - larger filler particles
- nanofil- filler dispersed
- nandohybrid- combination
what does a coupling agent do
- chemical bond
filler particle - resin Matrix
transfers stresses - organosilane (bifunctional molecule)
-siloxane end bonds to hydroxyl groups on filler - methacrylate end polymerises with resin
what are functions of coupling agents
- improve adherence of resin to filler surfaces
- ## chemically coat filler surfaces and increase strength
what are the disadvantages of silanes?
- 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
what are common silane agents
vinyl triethoxysilane
methacryloxypropyltrimehtlyoxysilane
what is the compressive strength of coupling agents
170-260 MPa
(Enamel 100-360, dentine 250-350)
what is the tensile strength of coupling agents
30-55 MPa
(Enamel 10, Dentine 20-50)
what is the coefficndt thermal expansion of coupling agents
20-77 (Enamel 11.4, Dentine 8.3)
what percentage is the coupling agents prone to polymer shrinkage
3%
since 2007, how do companies advertise coupling agents
’ universal composite’
‘ flowable composite’
‘ packable composite’
the chemistry is basically identical, the only change is the viscosity or filler type
how much filler content is found in flowable composites
50 to 70 %
less than traditional hybrid composite resins which give them lower viscosity
what are the indications for flowable composites
- Class V restorations
- Micropreparations
- Extended fissure sealigns
- Adhesive cementation of ceramic restorations
- Blocking out cavity undercuts
- initial layer in any classification.
what is the disadvantage of flowable composites
the flowable composite resins have lower filler volumes and thus they exhibit increased shrinkage and wear with decreased strength
name some packable composites
- prodigy condensable
-Alert (Pentron) - Solitaire 2 (Kulzer)
- Surefill (Dentsply)|
- sdr (Dentsply)
- BULKFILL (3m)
what are the packable composites properties
- 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
what do composites contain and how do they polymerise
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
describe the way is enamel bonded
- predictable and relatively easy
what organic and inorganic substances doe enamel contain
95% Hydroxyapatite
4% water
1% Non- collagenous protein
After bonding , what is the next process when restoring a composite
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
what does the acid etch technique do to the microstructure of enamel
- 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
describe the organic components ned inorganic components of dentine
- 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
what is the ultimate aim for dentine bonding agents
- bond a hydrophobic , highly viscous composite to a hydrophilic adherent
- need something to change properties of dentine surface/smear layer form hydrophilic to hydrophobic.
what is a smear layer
- 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
what are the four strategies that have been used to achieve optimum bonding
- smear layer is left alone
- smear layer is removed
- smear layer is modified
= the smear layer is partially removed and partially modified
what is the basic mechanisms of bonding to enamel and dentine
- exchange process involving replacement of minerals by resin monomers which upon setting, become micro-mehcanically interlocked in the created porosities
what is hybridisation?
- 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
what are the full properties and how do we do acid etching
- 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
what are the properties of primer and how do we apply it
- resin - monomer
- improves wettability of prep
- penetrates etched dentin tubules
- applied in a thin layer; thinned with air; blot - May require light curing
what are the properties of bonding adhesive
- 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
what are the current types of approach of bonding in restorations
- 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
what step is followed after etching
priming step
what are the properties of a primer
- ampiphillic and low viscosity
- solvents are added to adjust primer viscosity and improve its wetting
- usually optimised for dentine surface characteristics rather than enamel
how are the etch and rinse primers classified
by primer solvent
- acetone based
- ethanol based
- water based
what options are there for the etch rinse methods
describe self - etch primer and adhesive
- 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
how must the performance be once upon application of the self etching primer
- 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
what is the pathway for successful bonding to dentine
- wetting
- inflation to produce a ‘hybrid zone’
- mechanical interlocking
- stress resistance
- ultimate goal is marginal integrity and sealing tubules to prevent ingress of bacteria
