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IODC - Orthodontics > Materials Used in Ortho > Flashcards

Materials Used in Ortho Flashcards

1
Q

Commonly used materials in orthodontic?

A 
PMMA
Stainless steel
Nickel titanium
Adhesive/ cement
Plasters
Alginate
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2
Q

What materials may not be the most biocompatible?

A

Nickel/latex - allergy

Resin - estrogenicity of resin - mimic hormone

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3
Q

What is PMMA?

A

Polymethylmethacrylate

Made by free radical vinyl polyermisation from monomer methyl methacrylate

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4
Q

Difference between heat-cured and self-cured PMMA?

A

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

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5
Q

What can be released from baseplate if PMMA used?

A

0.1-5% residual monomer and additives can be leached

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6
Q

Is PMMA allergenic?

A

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

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7
Q

How to prevent allergy?

A

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

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8
Q

What are the properties of different wire?

A

See table in notes

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9
Q

What is tensile force?

A

Tensile force = elongation in direction of load applied

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10
Q

What is compressive force?

A

Contraction in direction of the load applied

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11
Q

What is shear force?

A

Sliding displacement of one side or a twisting around its axis

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12
Q

How are the mechanical properties of wire assessed?

A

Tensile/ bending/ torsional test

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

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13
Q

What are the optimum characteristics of wire?

A 
Large spring back
Low stiffness
Good formability
High stored energy
Biocompatible
Low surface friction
Capability to be welded/ soldered to auxiliaries
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14
Q

Characteristics of stainless steel?

A 
Formability
Biocompatible
Stiff
Resilience
Lowe cost
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15
Q

Properties of CoCr wire?

A

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

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16
Q

Properties of NiTi wires?

A

Good spring back and low stiffness

17
Q

Properties of beta-titanium wire?

A

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

18
Q

Properties of multi-stranded wire?

A

High spring back and low stiffness compared solid SS wires

Used as cheap substitute NiTi and for bonded retainers

19
Q

What is strength?

A

Strength = stiffness x range

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

20
Q

What is stiffness?

A

The quality of being rigid, not easily bent

With change in shape - you will change stiffness

21
Q

What is equation for inertia?

A

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

22
Q

What is the equation for a rectangular cross section

A

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

23
Q

What are round wires used for?

A

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

24
Q

What are rectangular wires used for?

A

Second stage of movement

Engage bracket firmly - allows torque to be placed on tooth

25
Q

How does torque move tooth?

A

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

26
Q

What are the 3 ways strength can be views?

A
  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
27
Q

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

A
  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
28
Q

NiTi wire composition?

A

Equal mixture nickel and titanium

Shape memory and super-elasticity

29
Q

What is shape memory?

A

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

30
Q

Properties of adhesive for bonding brackets?

A

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-

IODC - Orthodontics (18 decks)

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