Composite Resin
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what is composite used for
restorative material for primary and secondary caries, trauma and abrasion
what are the ideal properties for composite
high mechanical strength, high YM, high hardness, abrasive resistant, low thermal expansion and thermal diffusivity, low polymerisation contraction shrinkage, good bond strength, good aesthetics, biocompatible
what are the constituents of composite resin
glass filler particles, resin, camphorquinone, low weight di-methacrylates, silane coupling agent
what is the importance of glass filler particles in composite
improve the mechanical properties, good mechanical strength
what is the size of glass filler particles
can vary, large and small - hybrid is a combination of sizes, large particles improve mechanical properties but small improve aesthetics
what is the importance of resin in composite
Bis-GMA is normally used, opposite to glass filler, improves viscosity, has little importance for mechanical properties, but contains bifunctional molecule with C=C bond, can be broken and undergo polymerisation - increases strength and viscosity of material
what is the role of camphorquinone
activated by blue light, produces free radicals which can then break the C=C in the resin and induce free radical addition polymerisation
what is the role of dimethacrylates
alter viscosity and reactivity
what is the role of silane coupling agent
allows a better bond between the glass filler particles and the resin material
how can composite be classified
filler particles - large, microfine, hybrid type of cure - light cure, self cure area of use - anterior, posterior
what is the effect of having more glass filler particles
improve mechanical properties, improved aesthetics, improve thermal properties, increased abrasion resistance, lower polymerisation shrinkage
what is meant by depth of cure
the most superficial surface of composite receives the most blue light therefore, is always cured. however, the depth at which the blue light can penetrate through the material to produce material with 50% of the hardness of the most superficial layer is the maximum depth of cure
what is an average value of depth of cure for composite
2mm
how do bulk fill composites work
they have lucirin in it as well as camphorquinone. this releases free radicals at a different wave length, therefore less light has to be received to induce it - at lower areas where less light is, still have polymerisation
what are some problems with curing
increases the temperature - can damage the pulp blue light might be dangerous for patient and operator polymerisation contraction shrinkage
how can polymerisation shrinkage be avoided
by lowering the configuration factor - small increments
give a value for compressive strength of composite and how does this compare with amalgam and enamel
300MPa, slightly lower than amalgams 400MPa, however, higher than enamel 250MPa
give a value for tensile strength of composite and how does this compare with amalgam and enamel
50MPa, slightly lower than amalgams 60MPa, but higher than enamel 35MPa
give a value for youngs modulus of composite and how does this compare with amalgam and enamel
14MPa, much lower than amalgam at 30MPa and enamel with 50MPa
give a value for hardness of composite and how does this compare with amalgam and enamel
90GPa, lower than amalgam with 100GPa but enamel is much better with 350GPa
what is an average value of bond strength for composite
40MPa
what should the polymerisation contraction shrinkage be below for a composite
less than 5%
compare the thermal expansion of enamel and dentine with amalgam, composite and glass ionomer
enamel - 8 dentine - 11 amalgam - 22-28 composite - 25-68 glass ionomer - 10
what is the importance of thermal expansion
ideally, a restorative material should expand and contract at the same rate as tooth tissue when exposed to hot and cold temperatures. If not, gaps will appear between the tooth and restoration, resulting in micro leakage of bacteria, water and food - resulting in secondary caries