Orthodontics

Question 1

what are 2 materials unique to orthodontics

Answer 1

NiTi Nickle TItanium
Stainless Steel

Question 2

give three materials to consider the safety of when in orthodontics

Answer 2

Nickel - 25% of women allergic
Latex - increasing allergies
Estrogenicity of resin - some materials leach out and act in the same way as oestrogen

Question 3

what is the most common material across all of dentistry and how is it formed

Answer 3

PMMA - poly methyl methacrylate
made by free radical vinyl polymerization from the monomer methyl methacrylate.

Question 4

what ways of curing are there for PMMA and compare

Answer 4

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)

Question 5

what percent range of residual monomer is left in set PMMA and why is this a problem

Answer 5

0.1-5% residual monomer
can leach out and cause allergies

Question 6

is PMMA itself allergenic

Answer 6

rarely
usually the components such as MMA cause the problems

Question 7

give three ways to avoid allergic reactions to PMMA products

Answer 7

Use heat cure PMMA - less residual monomer
Store appliance in water for several hours prior to fit
Use light cured ‘acrylic’

Question 8

what is the highest risk for allergy for the dentist whilst providing PMMA

Answer 8

EGDMA cross linking agent
more common for dentist to have allergies than patient

Question 9

give some ways of avoid dentist allergy to PMMA (EGDMA cross linking agent and MMA)

Answer 9

Wear gloves
Ventilation
Use down-draught extraction
send to lab to decrease personal exposure

Question 10

explain the difference between tensile, compressive and shear force

Answer 10

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).

Question 11

what are some ideal characteristics of orthodontic wire (7)

Answer 11

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

Question 12

what law refers to the directly proportional force needed to extend a spring by a certain distance

Answer 12

hookes law

Question 13

does stainless steel rust?

Answer 13

yes, it stains and rusts but LESS than other metals

Question 14

what are the pro’s of stainless steel

Answer 14

formability
biocompatibility and environmental stability
stiffness
resilience
low cost

Question 15

why must cobalt chrome be heated

Answer 15

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.

Question 16

give 2 pros and 2 cons of NiTi wire

Answer 16

Nitinol wires have a good spring back and low stiffness.

This alloy, however, has poor formability and ‘joinability

Question 17

how do we use NiTi’s properties to our advantage in orthodontics

Answer 17

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

Question 18

why might beta-titanium be better than NiTi

Answer 18

provide a combination of adequate springback, average stiffness, good formability, and CAN be welded to auxiliaries
NiTi has bad joinability

Question 19

explain the properties of multi-strand wire

Answer 19

have a high spring-back and low stiffness when compared with solid stainless steel wires
difficult to manipulate and hard to bend

Question 20

make an equation with strength, stiffness and range and explain each factor

Answer 20

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.

Question 21

compare the function of round and rectangular cross sectioned wire

Answer 21

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.

Question 22

how do we find resilience on a stress strain curve

Answer 22

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.

Question 23

how do we find formability on a stress-strain curve and what is it

Answer 23

Formability is the amount of permanent deformation that a material can withstand before breaking.

Question 24

which orthodontic have 1st 2nd and 3rd deflection for a set force and what is deflection

Answer 24

degree to which a part of a structural element is displaced under a load (because it deforms)

Niti, Beta-titanium , stainless steel

Question 25

what is NiTi made up of

Answer 25

almost equal amounts of nickel and titanium

Question 26

what are the two terms specific to NiTi qualaties

Answer 26

‘super elastic’ and ‘shape memory’

Question 27

what is shape memory

Answer 27

the process of restoring the original shape of a plastically deformed sample by heating it
this is repeatable

Question 28

why is constancy of stress important and how does this compare with stainless steel and NiTi

Answer 28

a constant, low stress back to an original shape is important so the teeth are put under constant, low stress.
NiTi have a very good slow constancy of stress, stainless steel is all pressure at once and can be less comfortable
This process is sped up by heat e.g. if drinking a hot drink, NiTi will move quicker

Question 29

what is adhesion

Answer 29

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

Question 30

what problems might bracket adhesives bring

Answer 30

cause white patches under bracket
plaque retentive factor

Question 31

which bracket adhesive is the best, give good qualities

Answer 31

no strong evidence proving any adhesive is better than another
good if it could be used on wet surfaces, if it released fluoride, if it didn’t leave white patches on teeth