composite resins 2 and 3 Flashcards
what are dental composites composed of
methacrylate resin
silica powder i.e. filler
photoinitiator
stabliser
composites are hydrophilic or phobic
hydrophobic therefore need bonding agent
what is the main resin monomer in all composites
bisGMA
what can the addition of other monomers lead to
altered viscosity
improved mixing
how can composites set
via free radical polymersation
what does vinyl refer to
presence of C=C bond
- electrons have potential to polymerise other methacrylate groups
- photo initiators seek out c+cbond
what do free radical polymerisation lead to
polymerisation shrinkage
examples of photoinitiators
camphorquene
PPD Lucirin
what do coupling agents do
improve adhesion of resin to filler surfaces to increase strength and toughness
- they chemically coat the filler particle surfaces
- prevent brittleness of mateirals
disadvantages of silanes
- age during storing
- lose potency
- sensitive to water
what can water being absorbed into composite preparationslead to
hydrolysis of the saline bond and gradual loss of properties
what are the phases of copsoites
1) organic phase
2) disperse phase
3) interfacial phase
what is the organic phase
resin martix - monomer - photoinitiator - pigments - filler forms the polymer backbone to provide tensile strength
dispersed phase and benefit/use
inorganic filler - glass - quartz - colloidal silica Improves mechanical properties(i.e. wear and compressive strength) and decreases shrinkage
interfacial phase
provides adhesive bond between organic and dispersed organic phases
what does the polymerisation reaction result in
set matrix containing dispersed filler particles (typically silica)
what can composites be used along side
bases and liners where the pulp needs additional protection
what cannot be used underneath composites and why
zinc eugenol
- inhibits polymerisation by mopping up the free radicals
claimed advantages of nano filled over conventional compsosites
- potentially superior fracture toughness, high strength and wear resistance
- high polihsiabilotu and low PS
- high surface to vol ratio, allowing high filler loading
- nano sized fillers uneatable to scatter light so increase translucency
no clinical improvement however, only in lab
advantages of smaller filler sizes
increased resistance to wear and greater straight
increased ability to polish
improved translucent
combined with increased filled vol, potential to decrease PS
what is inevitable with methacyrlates
PShrinkage
risks of bulk placement of comppsie
- inadequate cure at depth
- shrinkage may cause weak or incomplete interface with tooth tissue
(risk of micro leakage, discolouration of margins, secondary caries in long term)
