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Flashcards in dental materials Deck (89)
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function of dental composites (2)

-restorative (filling) materials
-special tray construction


wide scope of dental materials/ how their use can differ from engineering applications

-light curing technology used in car repair fillers/paints as well as dental occlusins (ICI dental occlusion)
-fibre reinforced materials/kevlar (v strong) used in bullet proof vests/fluoroelastomer rubber, may be incorporated into dental treatments
->unlike civil engineering, restoration must function within minutes of placement


what triggers the polymerisation of light curing materials

camphorquinone (photo-initiator)


dental composite definition

combination of materials in which indiv. components retain their identity and posses diff properties to the components acting alone


components of dental resin composite (3)

-most importantly, a coupling agent


what are fibre reinforced materials

type of composite consisting of:
-fibres of high strength
-a modulus
->embedded/bonded to matrix
->distinct interface/boundary between components


legal requirements relating to the prescription of laboratory made dental appliances (5)

-patients name/confirmation made for them
-prescribers name/registered address
-technicians name/registered address
-description of appliance
-confirmation meets legal standards


what are dental materials susceptible to within oral environment (5)

-loading up to 6kg
-cyclical forces causing fatigue
-temp fluctuations (-14 to 60 degrees)
-pH fluctuations (2-12)


what is the shock absorber teeth are suspended within

periodontal ligament


eg's of dental materials (5)

-gypsum materials (plaster and stone)


what standards do dental materials have to make

-standards to protect the user and patient
-met by BSI (british standards institution) and ISO (international standards organisation)
->lab tests are used to ensure materials meet these standards, inappropriate selection/application compromises durability/ risks safety of both patients/members of dental team


strain calculation

=change in length divided by original length (has no units)


stress equation

=force (newtons) divided by area (mm squared)
-units of stress = MPa


mechanical properties of materials that are determined by lab tests (and how they are calculated) (7)

-tensile strength (elongation, force over area)
-compressive strength (not for brittle objects, force over area)
-diametral tensile strength (looks like compressive, to elongate spheres etc/brittle objects, placed between two supporting blocks, stress equation = 2F/3.14DL)
-flexural strength (3 point, stress=3FL/2b(d squared), where L is support separation)
-surface hardness (indented, dimensions measured and expressed as a number, high no's = low hardness)
-shear bond strength (strength to separate bond between two structures, force div. by area)
-impact strength (in units of energy)


how to measure stiffness on stress/strain curve

linear region of curve


how to measure ductility on stress/strain curve

straight line from end point to...?
->potential for material to be drawn out into a wire


what is given by measuring the area under stress/strain curve of the linear elastic region

resilience (energy absorbed by material in undergoing plastic deformation up to elastic limit)


what is given by measuring the area under the entire stress/strain curve

-toughness (total amount of energy a material can absorb up until the point of fracture)
->high value = tough
->low value = brittle


physical properties of materials determined by lab tests (4)

1-surface roughness (the higher the Ra the rougher the material)
2-thermal properties (conductivity/K - rate of heat transfer through material, energy required two heat up material/Q=mst, thermal diffusivity/D - rate temp will rise within material when heat is applied to its surface = K/Cp*p, -> Cp = spec. heat and p = material density)
3-rheological properties (material flow properties through syringe etc, viscosity is proportional to pressure/speed -> viscosity can increase (dilatant), decrease (pseudoplastic) or stay the same (newtonian) due to applied pressure)
4-thermal expansion and contraction (match as closely to tooth surf. being replaced)


properties of materials that can be determined by lab tests (4)



chemical properties of materials that can be defined by lab tests

-corrosion (defines chemical reactivity of metals/alloys, should display good corrosion resistance)


ideal biological properties of materials used in dentistry (5)

-non toxic
-non irritant
-harmless to dental pulp
-no carcinogenic potential
-no irritancy


ideal properties of model/die materials (5)

-dimensional accuracy
-fluid when poured
-good wetting
-once set, hard and also fracture resistant
-compatible with all materials it contacts


classify gypsum products according to ISO standards (5)

1-impression plaster
2-dental plaster for models
3-dental stone for die/model
4-dental stone, die high strength, low expansion
5-dental stone, die high strength, high expansion


gypsum products used for models/dies (3)

-dental plaster (plaster of paris)
-dental stone


gypsum equation (manufacturing of gypsum products)

-gypsum -> gypsum product + water
-2CaSO4*2H2O -> (CaSO4)2*H20 + 3H20
-calcium sulphate dihydrate -> calcium sulphate hemihydrate (alpha/beta)


chemical name of gypsum

calcium sulphate dihydrate


chemical name of gypsum products (2)

-beta calcium sulphate hemihydrate (dental plaster)
-alpha calcium sulphate hemihydrate (dental stone)


conditions which favour formation of dental plaster from gypsum

120 degrees


conditions which favour formation of dental stone from gypsum

steam pressure in autoclave to 125 degrees