Ortho materials Flashcards
commonly used materials
1) polymethylmethacrylate (PMMA)
2) stainless steel
3) nickel titanium (NiTi)
4) adhesives/cements
5) plaster
6) alginate
ways of curing PMMA
heat - thought to be stronger and last longer,
self - contains activator
both used for baseplates
how is PMMA made
free radical vinyl polymerisation
issues with PMMA
residual monomer and additives that are released from base plate
can lead to allergies
how to prevent allergies to PMMA
use heat cured PMMA
store appliance in water several hrs prior to fit
use light cured acrylic
what is the cross linking agent for PMMA
EDGMA
types of wires used in ortho and uses of them
stainless steel - removable and fixed appliances
NiTi - fixed appliances
B- titanium - fixed appliances
Co/Cr/Ni - fixed appliances
types of fore
tensile
compresive
shear
tensile force
causes elongattion in the direction of load applied
compressive force
causes a contraction in the direction of the load applied
shear
causes either a sliding displacement of one side od a specimen or twisting round its axis (torsion)
how are mechanical properties assessed
tensile
bending
torsional tests
optimum characteristics of a wire
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
hookes law - law of elasticity
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
why is SS good in ortho
formability BC and ES stiffness resilience low cost
cobalt chrome wire
can be manipulated in a softened state then subjected to heat treatment
NiTi wires ad and dis
good spring back low stiffness dis difficult to hsape difficult to add onto
comes in preformed shape, wire returns to org shape overtimr
beta titanium
adequate springback
avg stiffness
good formability
can be welded to auxilaries
elastic propertjes of wire formula
strength (force)= stiffness x range (length)
strength
quality or state or being strong
relating to tensile strength
stiffness
quality of being rigid not early bent
range
distance a wire travels before permanent deformation ie deflection of the material
rectangular vs circular wires
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
how can internal stresses and external strains be calculayed
force deflection curve
- slope is the elastic modulus
proportional to stiffness
resilience
area under the curve out to the proportional limit
formability
amount of permanent decoration that a material can withstand before breaking
terms to describe NiTi
shape memory
super elasticity
shape memory
process of restoring the org shape of a plastically deformed small by heating it
- repeatable, not permanently deformed
constancy of stress
amount of load on the material, it will unload similarly
will return to its org position evenly and slowly
bonding brackets
base often has wire mesh
tooth surface smooth therefore need etch with acid
adhesion
force of attraction between the molecules or atoms on two different surfaces as they are brought into contact
