Dental Materials Intro Flashcards
what is a composite?
a composite is a combination of materials in which the individual components retain their identity and which posses diff. properties to the components acting alone
dental resin composites contain?
resin, filler, coupling agent
what are fibre reinforced materials?
a type of composite - fibres of high strength and modulus embedded/bonded to a matrix
maintain a distinct interface/boundary between the components
what are fibre reinforced materials used for?
construction/reinforcement of denture bases
inlays/onlays
crowns/bridges
posts to reinforce root treated teeth
legal requiremens of dental appliances?
medical devices directive changed march 2010
statement of manufacture to all pt’s
gdc encourages all pt’s to ask for one
oral environment subjects filling material to?
loading to 6kg on/off cyclical forces - fatigue chemicals temp fluctuations in microseconds teeth in shock absorbed force of 1N intrudes tooth force of 15N flexes bone/causes pain pH fluctuates 2-12
materials used by dental team?
gypsum, waxes, alloys, polymers, ceramics
tests of materials used to protect pt?
BSI - british standards institution
ISO - international standards organisation
tensile strength?
force applied to elongate rod
stress = 6 = force F (newtons)/area A mm2
strain has no units
change in length/original length
compressive strength?
not recommended for brittle materials
what is diametral tensile strength?
how force is distributed through an object
6 = 2F/pi x diameter x length
flexural strength?
6 = 3FL/(2 x breadth x diameter)squared L = support seperation, b&d define the specimen geometry
stress/strain definition?
modulus, measure of stiffness of material
ductility definition?
potential for material to be drawn into a wire
resilience definition?
energy absorbed by the material undergoing plastic deformation up to the elastic limit
toughness?
measure of total amount of energy a material can absorb up to the point of fracture
high value - tough
low value - brittle
fatigue?
application of cyclical loading for a defined number of cycles
material will eventually fail/survive
test of surface hardness?
indentor dimensions require expressed as a number large no. = low hardness small no. = high hardness
shear bond strength?
6= F/A
adhesive failure
cohesive failure
impact strength?
quoted in units of energy
pendulums swing and fractures specimen
this consumes energy
surface roughness?
profilometer. assesment of surface characterisitics
Ra = arithmetic mean deviation of surface profile
higher = rougher material
thermal properties?
K = thermal conductivity - rate of heart transfer through material
Cp = specific heat
energy required to heat up a material Q=mst
D - thermal diffusivity - rate/ temperature increase in material its applied to its surface
D = K/Cp*p
p = materials density
rheological properties?
materials flow properties composite in syringe luting cements veneer trial pastes viscosity = pressure P/speed S measure of how easy to extrude from a syringe
dilitant?
viscosity increased with applied pressure
