Materials Used in Ortho

Question 1

Commonly used materials in orthodontic?

Answer 1

PMMA
Stainless steel
Nickel titanium
Adhesive/ cement
Plasters
Alginate

Question 2

What materials may not be the most biocompatible?

Answer 2

Nickel/latex - allergy

Resin - estrogenicity of resin - mimic hormone

Question 3

What is PMMA?

Answer 3

Polymethylmethacrylate

Made by free radical vinyl polyermisation from monomer methyl methacrylate

Question 4

Difference between heat-cured and self-cured PMMA?

Answer 4

Self-cured similar to heat-cured but contains activator - dimethyl-p-toludine

Question 5

What can be released from baseplate if PMMA used?

Answer 5

0.1-5% residual monomer and additives can be leached

Question 6

Is PMMA allergenic?

Answer 6

Some components allergenic to some degree - cross-sensitisation within group of methacrylate compounds

Question 7

How to prevent allergy?

Answer 7

Use heat-cured PMMA - minimise amount free monomer
Store appliance water prior fit
Use light cured acrylic
Minimisation of exposure- gloves/ ventilation

Question 8

What are the properties of different wire?

Answer 8

See table in notes

Question 9

What is tensile force?

Answer 9

Tensile force = elongation in direction of load applied

Question 10

What is compressive force?

Answer 10

Contraction in direction of the load applied

Question 11

What is shear force?

Answer 11

Sliding displacement of one side or a twisting around its axis

Question 12

How are the mechanical properties of wire assessed?

Answer 12

Tensile/ bending/ torsional test

Test don’t necessarily reflect the behaviour of wire under clinical condition

Question 13

What are the optimum characteristics of wire?

Answer 13

Large spring back
Low stiffness
Good formability
High stored energy
Biocompatible
Low surface friction
Capability to be welded/ soldered to auxiliaries

Question 14

Characteristics of stainless steel?

Answer 14

Formability
Biocompatible
Stiff
Resilience
Lowe cost

Question 15

Properties of CoCr wire?

Answer 15

Can be manipulated into softened state then subject to heat tx
Heat tx result wire w/ properties similar SS

Question 16

Properties of NiTi wires?

Answer 16

Good spring back and low stiffness

Question 17

Properties of beta-titanium wire?

Answer 17

Combination adequate springback, average stiffness, good formability and can be welded to auxiliaries

Question 18

Properties of multi-stranded wire?

Answer 18

High spring back and low stiffness compared solid SS wires

Used as cheap substitute NiTi and for bonded retainers

Question 19

What is strength?

Answer 19

Strength = stiffness x range

Strength is the quality of state of being strong, relating to tensile strength

Question 20

What is stiffness?

Answer 20

The quality of being rigid, not easily bent

With change in shape - you will change stiffness

Question 21

What is equation for inertia?

Answer 21

I = [pie x (diameter/4)]/64

Question 22

What is the equation for a rectangular cross section

Answer 22

I = [base x (height/3)]/12

Question 23

What are round wires used for?

Answer 23

In cross-section fit loosely in bracket and are used for initial stages - don’t move root - dragged passively through bone into approximate position in arch

Question 24

What are rectangular wires used for?

Answer 24

Second stage of movement

Engage bracket firmly - allows torque to be placed on tooth

Question 25

How does torque move tooth?

Answer 25

Act on long-axis of tooth - root moves into an angle parallel with masticatory forces

Question 26

What are the 3 ways strength can be views?

Answer 26

1. Proportional limit - the point at which permanent deformation fist occurs 2. Yield strength - point at which 0.1% deformation is measured 3. Ultimate tensile strength - maximum load wire can sustain

Question 27

What are the 2 characteristics determined from stress-stain curve?

Answer 27

1. Resilience - Area under the curve out to proportional limit - Represent energy capacity of material that is combination of strength and stiffness 2. Formability - Amount of permanent deformation material can withstand before breaking

Question 28

NiTi wire composition?

Answer 28

Equal mixture nickel and titanium | Shape memory and super-elasticity

Question 29

What is shape memory?

Answer 29

Process of restoring the original shape of plastically deformed sample by heating it Crystalline phase change known as thermoelastic martensitic transformation

Question 30

Properties of adhesive for bonding brackets?

Answer 30

Successful agent that relies on mechanical retention to both enamel and bracket Chemical or light cured Some adhesive can prevent early decay due to F-