Ortho materials

Question 1

commonly used materials

Answer 1

1) polymethylmethacrylate (PMMA)
2) stainless steel
3) nickel titanium (NiTi)
4) adhesives/cements
5) plaster
6) alginate

Question 2

ways of curing PMMA

Answer 2

heat - thought to be stronger and last longer,
self - contains activator
both used for baseplates

Question 3

how is PMMA made

Answer 3

free radical vinyl polymerisation

Question 4

issues with PMMA

Answer 4

residual monomer and additives that are released from base plate
can lead to allergies

Question 5

how to prevent allergies to PMMA

Answer 5

use heat cured PMMA
store appliance in water several hrs prior to fit
use light cured acrylic

Question 6

what is the cross linking agent for PMMA

Answer 6

EDGMA

Question 7

types of wires used in ortho and uses of them

Answer 7

stainless steel - removable and fixed appliances
NiTi - fixed appliances
B- titanium - fixed appliances
Co/Cr/Ni - fixed appliances

Question 8

types of fore

Answer 8

tensile
compresive
shear

Question 9

tensile force

Answer 9

causes elongattion in the direction of load applied

Question 10

compressive force

Answer 10

causes a contraction in the direction of the load applied

Question 11

shear

Answer 11

causes either a sliding displacement of one side od a specimen or twisting round its axis (torsion)

Question 12

how are mechanical properties assessed

Answer 12

tensile
bending
torsional tests

Question 13

optimum characteristics of a wire

Answer 13

1) large spring back
2) low stiffness
3) good formability
4) high stored energy
5) biocompatibility and environmental stability
6) low surface friction
7) the capability to be welded or soldered to auxiliaries

Question 14

hookes law - law of elasticity

Answer 14

for small deformations of an object the displacement or size of deformation is directly proportional to the deforming force or load
- ie will return to its org shape and size once load remvoed

F=Kx

Question 15

why is SS good in ortho

Answer 15

formability 
BC and ES
stiffness
resilience
low cost

Question 16

cobalt chrome wire

Answer 16

can be manipulated in a softened state then subjected to heat treatment

Question 17

NiTi wires ad and dis

Answer 17

good spring back 
low stiffness
dis
difficult to hsape
difficult to add onto

comes in preformed shape, wire returns to org shape overtimr

Question 18

beta titanium

Answer 18

adequate springback
avg stiffness
good formability
can be welded to auxilaries

Question 19

elastic propertjes of wire formula

Answer 19

strength (force)= stiffness x range (length)

Question 20

strength

Answer 20

quality or state or being strong

relating to tensile strength

Question 21

stiffness

Answer 21

quality of being rigid not early bent

Question 22

range

Answer 22

distance a wire travels before permanent deformation ie deflection of the material

Question 23

rectangular vs circular wires

Answer 23

round
- fit loosely in brackets
used for initial stages
only tilt teeth 
do not move root, root dragged along passively through bone

rectangular
- 2nd stage
engage bracket more firmly
torque forced placed on tooth 
acts on long axis of tooth so root moves into angle parallel with masticatory forces

Question 24

how can internal stresses and external strains be calculayed

Answer 24

force deflection curve
- slope is the elastic modulus
proportional to stiffness

Question 25

resilience

Answer 25

area under the curve out to the proportional limit

Question 26

formability

Answer 26

amount of permanent decoration that a material can withstand before breaking

Question 27

terms to describe NiTi

Answer 27

shape memory

super elasticity

Question 28

shape memory

Answer 28

process of restoring the org shape of a plastically deformed small by heating it
- repeatable, not permanently deformed

Question 29

constancy of stress

Answer 29

amount of load on the material, it will unload similarly

will return to its org position evenly and slowly

Question 30

bonding brackets

Answer 30

base often has wire mesh

tooth surface smooth therefore need etch with acid

Question 31

adhesion

Answer 31

force of attraction between the molecules or atoms on two different surfaces as they are brought into contact