Composite 2
No description yet. This curated deck is ready for daily study.
Card preview (24)
What are qualities of conventional, microfine and hybrid?
• Conventional: – strong but problems with finishing and staining • Microfine: – smaller particles - inferior mechanical properties but smooth • Hybrid: – originally compromise between conventional & microfine – most modern composites are hybrids • improved filler loading and coupling agents have led to improvement in mechanical properties
What is the compressive strenght and young’s modulus of composite?
compressive stress of around 350 MPa high Young’s modulus of around 15 GPa
What is hardness?
Resistance to scratching material surface (indentation existence)
What is abrasion?
Removal of surface layers when two surfaces make frictional contact
What does surface roughness affect?
Appearance Plaque retention Sensation when in contact with tongue
What component of composite is hard?
Filler particles
What are material factors affecting wear?
• filler material • particle size distribution • filler loading • resin formulation • coupling agent
What are clinical factors affecting wear?
• cavity size & design • tooth position • occlusion • placement technique • cure efficiency • finishing methods
What is a beneficial property of composite?
Bond to tooth/ compatible with bonding systems
How does composite bond to enamel and denting?
• enamel - acid etch technique • dentine - dentine / universal bonding systems
What is the acid etch technique?
30% phosphoric acid for 20 secs on original enamel surface
What is the typical bond strength in MPa dependent on surface preparation of tissue, composite brand and test method?
40 MPa
What does a good bond cause?
• reduce microleakage • counteract polymerisation shrinkage • good bond will reduce likelihood of gap between restoration and tooth
How should cavity design be for composite?
Minimise cavity design - no need for retention undercuts as the bond holds the restoration in place
What is good bonding in relation to stress?
Good bonding - stress spreads over contact areas restoration does not have to withstand full stress - stress transferred to tooth and bone However poor bond to tooth concentrates stress at the interface so failure more likely
What should the thermal conductivity of composite be?
of composite resin should be low to avoid pulpal damage from hot & cold foods/fluids - it is low
What is thermal diffusivity and how should it be for composite?
• How readily a material transmits heat when exposed to a short/transient stimulus • ideally it should be low – it’s similar to dentine
What should the thermal expansion of composite be?
of composite resin should be equal to tooth, to reduce microleakage- BUT it’s high-which is poor
What are properties of composite?
• Aesthetics - good, range of shades • Radiopaque - some radiopaque (diagnose secondary caries) • Handling / viscosity - variations in viscosity between products affects handling technique
What are components of aesthetics?
• shade range • translucency • maintenance of properties over lifetime • resistance to staining • surface finish
What are the handling/ viscosity components that should be considered?
• light curing • viscosity • should be “user friendly” – but not at expense of other properties
What is the shrinkage of composite?
• low setting shrinkage – polymerisation shrinkage still a problem as stresses develop at hard tissue surfaces (making de-bonding more likely) – bonding agents and clinical techniques help minimise impact of this
What is the biocompatibility of composite?
– generally thought to be OK – but increasing concern about resins in general (NB not all monomer is polymerised ! )
When is RMGI used, when is compomer used and when is composite resin used?
Resin Modified GI - high caries risk - frequent attenders Compomer - caries under control - regular attenders Composite resin - low caries risk patients