Orthodontics Flashcards
(31 cards)
what are 2 materials unique to orthodontics
NiTi Nickle TItanium
Stainless Steel
give three materials to consider the safety of when in orthodontics
Nickel - 25% of women allergic
Latex - increasing allergies
Estrogenicity of resin - some materials leach out and act in the same way as oestrogen
what is the most common material across all of dentistry and how is it formed
PMMA - poly methyl methacrylate
made by free radical vinyl polymerization from the monomer methyl methacrylate.
what ways of curing are there for PMMA and compare
heat cure - supposedly stronger and last longer, less residual monomer
self cure - chemically very similar to heat cured PMMA but contains an activator (dimethyl-p-toluidine)
what percent range of residual monomer is left in set PMMA and why is this a problem
0.1-5% residual monomer
can leach out and cause allergies
is PMMA itself allergenic
rarely
usually the components such as MMA cause the problems
give three ways to avoid allergic reactions to PMMA products
Use heat cure PMMA - less residual monomer
Store appliance in water for several hours prior to fit
Use light cured ‘acrylic’
what is the highest risk for allergy for the dentist whilst providing PMMA
EGDMA cross linking agent
more common for dentist to have allergies than patient
give some ways of avoid dentist allergy to PMMA (EGDMA cross linking agent and MMA)
Wear gloves
Ventilation
Use down-draught extraction
send to lab to decrease personal exposure
explain the difference between tensile, compressive and shear force
A tensile force causes elongation in the direction of load applied.
A compressive force causes a contraction in the direction of the load applied.
A shear force causes either a sliding displacement of one side of a specimen or a twisting around its axis (torsion).
what are some ideal characteristics of orthodontic wire (7)
large springback
low stiffness
good formability
high stored energy
biocompatibility and environmental stability
low surface friction
the capability to be welded or soldered to auxiliaries
what law refers to the directly proportional force needed to extend a spring by a certain distance
hookes law
does stainless steel rust?
yes, it stains and rusts but LESS than other metals
what are the pro’s of stainless steel
formability
biocompatibility and environmental stability
stiffness
resilience
low cost
why must cobalt chrome be heated
Cobalt-chromium (Co-Cr) wires can be manipulated in a softened state and then subjected to heat treatment
Heat treatment of Co-Cr wires results in a wire with properties similar to those of stainless steel.
give 2 pros and 2 cons of NiTi wire
Nitinol wires have a good spring back and low stiffness.
This alloy, however, has poor formability and ‘joinability
how do we use NiTi’s properties to our advantage in orthodontics
NiTi has good springback so the wire are set in an arch shape (chosen based on the face, palm and mouth shape) and when we bend them to fit on the braces on the teeth, they slowly spring back to the original shape of the wire
why might beta-titanium be better than NiTi
provide a combination of adequate springback, average stiffness, good formability, and CAN be welded to auxiliaries
NiTi has bad joinability
explain the properties of multi-strand wire
have a high spring-back and low stiffness when compared with solid stainless steel wires
difficult to manipulate and hard to bend
make an equation with strength, stiffness and range and explain each factor
Strength = Stiffness X Range
Strength is the quality or state of being strong, relating to tensile strength.
Stiffness is the quality of being rigid; not easily bent.
Range is the distance a wire travels before permanent deformation.
compare the function of round and rectangular cross sectioned wire
Wires that are round in cross-section fit loosely in the brackets and are used for initial stages and only TILT teeth. They do not move the root, the root is dragged along passively through the bone into an approximate position in the arch.
Rectangular wires are used in the second stage of movement and engage the bracket much more firmly such that a torque force is placed on the tooth. This torque acts on the long-axis of the tooth such that the root moves into an angle parallel with masticatory forces.
how do we find resilience on a stress strain curve
Resilience is the area under the curve out to the proportional limit.
Resilience represents the energy capacity of the material that is a combination of the strength and stiffness.
how do we find formability on a stress-strain curve and what is it
Formability is the amount of permanent deformation that a material can withstand before breaking.
which orthodontic have 1st 2nd and 3rd deflection for a set force and what is deflection
degree to which a part of a structural element is displaced under a load (because it deforms)
Niti, Beta-titanium , stainless steel
