Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Ortho DEN305 > Materials in orthodontics > Flashcards

Materials in orthodontics Flashcards

1
Q

List the common ortho materials

A 
PMMA
Stainless steel
Nickel titanium
Adhesives/cements
Plaster
Alginate
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is PMMA?

A

Vinyl polymer, made by free radical vinyl polymerisation from the monomer methyl methacrylate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Types of PMMA and their uses?

A

Heat cured - used for baseplates

Self cured - baseplates, contains activator (dimethyl-p-toluidine)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Negatives of PMMA?

A

Historical link between carcinogenic and embryotoxic potency

All components are allergenic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How to prevent allergy to PMMA?

A

Use heat cure PMMA
Store appliance in water for several hours prior to fit
Use light cured acrylic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the most common allergens of PMMA?

A

MMA, dibenzoyl peroxide and EGDMA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How to minimise PMMA exposure?

A

Gloves
Ventilation
Down-draught extraction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What do wires do?

A

Apply force = move teeth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

When are austenitic stainless steel wires used?

A

Removable and fixed appliances

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

When are elgiloy Co/Cr/Ni wires used?

A

Crozat appliances and fixed appliances - it has to be heat treated

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

When are β-titanium wires used?

A

Fixed appliances

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

When are NiTi wires used?

A

Fixed appliances

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q 
What does a:
Tensile force
Compressive force
Shear force
cause?
A 
Tensile = elongation in the direction of load applied
Compressive = contraction in the direction of the load applied
Shear = sliding displacement of 1 side of a specimen or twisting around its axis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What assesses the mechanical properties of a wire?

A

Tensile
Bending
Torsional tests

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Optimum characteristics of wire?

A

large springback,
• low stiffness,
• good formability,
• high stored energy,
• biocompatibility and environmental stability,
• low surface friction, and
• the capability to be welded or soldered to auxiliaries

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Why are stainless steel wires popular?

A 
formability,
• biocompatibility and environmental stability,
• stiffness,
• resilience, and
• low cost.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How to work out force and deflection of stainless steel springs?

A 
F = k d r4/l3
r = radius of the wire
d = deflection of the wire
l = length of the spring
k = stiffness of the wire (Young’s Modulus)
18
Q

How to work with Co-Cr wire?

A

Manipulate in softened state and subjected to heat treatment = properties similar to stainless steel

19
Q

Pros and cons of nitinol (NiTi)?

A 
Pros = good springback and low stiffness
Cons = poor formability and joinability
20
Q

Pros of beta-titanium?

A

Adequate springback
Good formability
Average stiffness
Can be welded to auxiliaries

21
Q

Pros of multi-strand wire? When are they used?

A

High spring back and low stiffness

Cheap substitute for NiTi and for bonded retainers

22
Q

How do orthodontists look at elastic properties of wires?

A 
Strength = stiffness x range
Strength = quality or state of being strong, relating to tensile strength
Stiffness = quality of being rigid, not easily bent
Range = distance a wire travels before permanent deformation
23
Q

List the orthodontic wires from highest to lowest in elasticity

A

Highest = austenitic stainless steel
Elgiloy Co/Cr/Ni
Beta-titanoim
NiTi

24
Q

What is stiffness equal to?

A

The product of the elastic modulus of the material times its area moment of inertia = change shape = change stiffness

25
Q

What is the inertia of a round cross section? In a rectangular cross section?

A 
Round:
I = [π X (diameter)4] /64
Fit loosely in brackets
Used for initial stages
Tilt teeth
Do not move root - root is dragged along passively through bone into an approximate position in arch

Rectangular:
I = [base X (height)3] /12
Used in 2nd stage of movement
Engage bracket more firmly = torque force on tooth
Torque acts on long axis of tooth = root moves into an angle parallel with masticatory forces

26
Q

Define strength

A

Measure of the force a material can withstand before

the material permanently deforms

27
Q

List the 3 ways strength may be viewed

A
  1. Proportional Limit =
    the point at which any permanent deformation first occurs.
  2. Yield Strength =
    the point at which 0.1% deformation is measured.
  3. Ultimate Tensile Strength = the maximum load that the wire can sustain.
28
Q

Define stiffness

A

Is the slope of the strength-range graph
and is equal to the product of the elastic
modulus of the material (E) times its area
moment of inertia (I).
Steeper slope means stiffer material.

29
Q

Define range

A

Deflection of material before permanent deformation occurs
From zero to proportional limit
Failure point - where it breaks

30
Q

Define resilience

A

Area under the curve out to the proportional limit

Represents the energy capacity of the material that is a combination of the strength and stiffness

31
Q

Define formability

A

Amount of permanent deformation that a material can withstand before breaking

32
Q

Features of nickel titanium wire?

A

= Family of inter-metallic materials = contains a
nearly equal mixture of nickel and titanium
Other elements added to adjust or “tune” the properties.
“Shape Memory” and “Superelasticity”.

33
Q

What is shape memory?

A

Restores original shapes by heating it

34
Q

What is superelasticity?

A

Martensite in Nitinol can be stress induced if stress is applied in the temperature
range above Aƒ(austenite finish temperature).
• Less energy is needed to stress-induce and deform martensite than to deform the austenite by conventional mechanisms.
Shows the type of deformational behaviour

35
Q

What do nitinol archwires do?

A

Move the teeth by applying a constant force for long treatment time and tooth position - apply a constant stress over a wide range

36
Q

What do the most successful bonding agents used in ortho rely on?

A

Mechanical retention to the enamel and bracket base

37
Q

Define adhesion

A

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

38
Q

Define mechanical adhesion

A

2 materials may be mechanically interlocked
Sewing forms a large scale mechanical bond
Velcro forms medium scale bond
Some textile adhesives form small scale bond

39
Q

Define chemical adhesion

A

2 materials may form a compound at the join

Strongest joins are where atoms of the two materials swap (ionic) or share (covalent) outer electrons

40
Q

Define disperse adhesion

A

Aka adsorption

2 materials may be held together by van der Waals forces

41
Q

Define electrostatic adhesion

A

Some conducting materials may pass electrons to form a difference in electrical charge at the join
Forms structure that has attractive electrostatic force between the materials
Electrons are passed if one conducting materials binds its electrons less strongly than the other does

42
Q

Define diffuse adhesion

A

Occurs when molecules of both materials are mobile and soluble in each other
Mechanism involved in sintering
Metal or ceramic powders are pressed together and heated, atoms diffuse from one particle to the next – joins the particles into one

Ortho DEN305 (16 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions