Clinical aspects of resin composites Flashcards
what are factors of successful composite restoration
- case selection - is composite the correct choice
- material handling - moisture control, bonding, material handling, curing, polishing
- Maintenance - patient able to keep the restoration clean and have good oral health for the restoration to succeed
describe the chemistry of composite
have resin matrix with filler particles with silane coupling agents
when is methyl methacrylate - polymathy methacrylate developed
- developed in the 1930s
- mainly used for dentures today
- was used as a tooth coloured filling material in the 1950s
- chemically cured - mix two components together to start polymerisation reaction
what does free radical polymerisation do
- free radicals cause carbon bonds to break down
- as this happens the molecules get closer together
- volume shrinks
what was the issue with early acrylic restorations
- polymerisation is highly exothermic
- bond to dentine is poor as dentine is wet and acrylic is hydrophobic
- poor bond to tooth so easily pulled away from dentine which leads to :
poor retention, staining , sensitivity, secondary caries
what is the viscosity and hazards of Bis- GMA?
- viscosity 1200 Pa.s
Hazard: - causes skin irritation
- may cause an allergic skin reaction
- causes serious eye damage
- causes serious eye irritation
what is the viscosity of TEGDMA and what is it degraded by
viscosity 0.011Pa.s
degraded by cariogenic bacteria
promotes growth of S. Mutans and Lactobacilli
what do the filler particles play part in
- setting reaction
- take up space of the resin - less rein- less shrinkage
- advantageous properties to the material
- wear resistance
- strength
- radio opacity
- colour
what properties are good for fillers
in general
- the larger the particles, the high the strength at the expense of aesthetics
- small particles make for a weaker material, give better polish ability but hard to add a very large amount so more shrinkage
- most composites contain a mixture of different size filler- a ‘hybrid” - more space can be taken up if smaller particles are added with larger particle
what is the effect of fillers on properties
more filler and larger monomers
- improved mechanical properties
- reduced shrinkage
- reduced curing depth
- reduced flowability
name some class II problems regarding restorations
- secondary caries
(poor adaption, bond failure, shrinkage) - bulk fracture
- poor contact point formation
- is composite appropriate
- time consuming
what are solutions to the class II problems
- need a material that allows deeper curing than 2mm and adapt better to the cavity and reduce the adverse effects of shrinkage during curing
- materials have been developed that allow deeper curing by having less filler or using different activators that can allow deeper curing- can cure up to 4mm deep halving the time taken to cure
what are the 2 distinct direction that bulk fill materials are going
- flowable bulk fill
- sculptable bulk fill
what are flowable bulk fill
- lower filler to allow light penetration
- contain modulators to compensate for shrinkage reducing stress
- poor mechanical properties, need to be capped
- less filler- more flowable and better adaption, at expense of strength and increased shrinkage
strength problem overcome by placing 2mm of regular composite of the top - shrinkage problem overcome- having special functional polymer that breaks as shrinkage stress rises thus releasing stress
what are sculptable bulk fill materials found
- contain different activators to allow deeper light penetration
- normal amount of filler, so are less flowable, or used in combination with flowable bulk fill liner
