Dental Materials Intro

Question 1

what is a composite?

Answer 1

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

Question 2

dental resin composites contain?

Answer 2

resin, filler, coupling agent

Question 3

what are fibre reinforced materials?

Answer 3

a type of composite - fibres of high strength and modulus embedded/bonded to a matrix
maintain a distinct interface/boundary between the components

Question 4

what are fibre reinforced materials used for?

Answer 4

construction/reinforcement of denture bases
inlays/onlays
crowns/bridges
posts to reinforce root treated teeth

Question 5

legal requiremens of dental appliances?

Answer 5

medical devices directive changed march 2010
statement of manufacture to all pt’s
gdc encourages all pt’s to ask for one

Question 6

oral environment subjects filling material to?

Answer 6

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

Question 7

materials used by dental team?

Answer 7

gypsum, waxes, alloys, polymers, ceramics

Question 8

tests of materials used to protect pt?

Answer 8

BSI - british standards institution

ISO - international standards organisation

Question 9

tensile strength?

Answer 9

force applied to elongate rod
stress = 6 = force F (newtons)/area A mm2
strain has no units
change in length/original length

Question 10

compressive strength?

Answer 10

not recommended for brittle materials

Question 11

what is diametral tensile strength?

Answer 11

how force is distributed through an object

6 = 2F/pi x diameter x length

Question 12

flexural strength?

Answer 12

6 = 3FL/(2 x breadth x diameter)squared
L = support seperation, b&d define the specimen geometry

Question 13

stress/strain definition?

Answer 13

modulus, measure of stiffness of material

Question 14

ductility definition?

Answer 14

potential for material to be drawn into a wire

Question 15

resilience definition?

Answer 15

energy absorbed by the material undergoing plastic deformation up to the elastic limit

Question 16

toughness?

Answer 16

measure of total amount of energy a material can absorb up to the point of fracture
high value - tough
low value - brittle

Question 17

fatigue?

Answer 17

application of cyclical loading for a defined number of cycles
material will eventually fail/survive

Question 18

test of surface hardness?

Answer 18

indentor
dimensions require
expressed as a number
large no. = low hardness
small no. = high hardness

Question 19

shear bond strength?

Answer 19

6= F/A
adhesive failure
cohesive failure

Question 20

impact strength?

Answer 20

quoted in units of energy
pendulums swing and fractures specimen
this consumes energy

Question 21

surface roughness?

Answer 21

profilometer. assesment of surface characterisitics
Ra = arithmetic mean deviation of surface profile
higher = rougher material

Question 22

thermal properties?

Answer 22

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

Question 23

rheological properties?

Answer 23

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

Question 24

dilitant?

Answer 24

viscosity increased with applied pressure

Question 25

neutarian?

Answer 25

viscosity constant with pressure

Question 26

pseudoplastic?

Answer 26

viscosity decreases with pressure

Question 27

corrosion?

Answer 27

material needs good corrosion resistance

Question 28

solubility parameter?

Answer 28

square root of cohesive energy density

Question 29

biological properties?

Answer 29

lab screening
limited lab in vivo usage testing
human randomised controlled clinical trial