Composite revision cards Flashcards
What does the organic matrix consist of in composite?
Bis-GMA which has outstanding ability to cross-link, resist compressive forces, and good water sorption response. Very viscous due to aromatic rings and hydroxyl groups.
teg-GMA reduces the viscosity of the matrix and allows for more filler loading and increases cross-linking density and flexibility.
UDMA is highly viscous and functions to increase filler loading.
What do fillers do to the composite?
Functions to reinforce the composite by increasing the hardness and strength and decreasing the wear.
What do fillers do to the composite?
Decrease the wear
Increase elastic modulus
Reduce shrinkage
Reduce thermal coefficient
Reduce water absorption
What are the types of fillers used?
Quartz and glass: has the best properties but radiolucent and difficult to finish.
Silica: Very small particles and microfilled. Has decreased properties from quartz.
Heavy metal glass: Radiopaque, fine particles, polishability is good for aesthetics, wear resistant, low cost but is soluble and difficult to attach to matrix
Zirconium: Harder than heavy metal glass. However, it should be coated with silica and attached to the matrix but isn’t as hard as quartz.
What are the types of shapes that fillers can take?
Irregular with rounded edges
Spherical
Porous
Irregular with sharp edges
What are the types of classification of composites?
Particle size classification: Megafilled, macrofilled, midifilled, minifilled, microfilled, and nanofilled. Hybrids consist of 2 particle sizes.
Method of filler loading: Homogenous, or heterogenous (Mixture of pre-cured composite with resin and filler)
Handling properties or texture: All purpose, flowable, packable
Mode of cure: Light cured, chemically cured, dual cured
What is composite composed of?
Resin matrix: Copolymers in here such as bis-GMA, teg-DMA, and UDMA.
Fillers: Glass+quartz, Silica, heavy metal glass, and zirconium
Coupling agent: Silane acts as a coupling agent. Methoxy group binds to humidity on fillers and surfactant. C=C group bonds to the oligomers
Activator-initiator system: Camphorquinone and accelerator as well as co-inhintiators can be used to create more free radical polymerization.
Inhibitors: Prevent spontaneous polymerization.
Optical modifiers/colouring agents: Pigments that make composite tooth coloured.
What are the properties and limitations of composite?
Composite has lower susceptibility to dessication than GIC
Thermal expansion is larger in composite than GIC
Working and setting time is very good in composite with 75% of polymerization occuring in the first 10 minutes after curing.
Colour and aesthetic appearance is most important feature of composite.
bis-GMA, teg-DMA, and UDMA are cytotoxic meaning that composite isn’t very biocompatible. Can cause post-operative hypersensitivity and contact allergy for practitioners.
Polymerization shrinkage is the most notable limitation of composite. Microfilled composite shrinks more than the larger filled composites.
Hardly any fluoride release in composites.
Strength of composite is much higher than GIC (more usable in high occlusal loading areas)
