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BDS3 - Orthodontics > ortho 2 zoom notes > Flashcards

ortho 2 zoom notes Flashcards

1
Q

what is the function of chromium in stainless steel

A

helps with corrosion

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2
Q

what does nickel help with in stainless steel

A

Nickel also helps with corrosion but some people have allergies

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3
Q

what type of stainless steel is easier to melt

A

Soft stainless steel is easier to melt

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4
Q

how does stainless steel change from soft state to hard state

A

Changes from soft state to hard state by cold working / work hardening
The more you bend the wire as it gets manipulated this starts to break up the stainless steel

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5
Q

what type of stainless steel is preferred in orthodontics

A

hard stainless steel

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6
Q

explain how a wire is manipulated

A
  • Hold adam’s no. 64 pliers in dominant hand
  • Bend wire with the other hand
  • Mark on wire where you want to grip the wire
  • Push the wire away from your face in case it slips
  • 90 degree = bending the wire

• Manipulating the wire = bending around a curvature
○ Do very small pushes
○ Keep pliers moving
○ Creates a curvature in the wire

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7
Q

what is URA

A

URA = Upper Removable Appliance

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8
Q

How do teeth move with a URA

A

teeth move on a fulcrum

They basically rotate on the midpoint

This is called tipping / tilting
= Tipping Movement

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9
Q

What are the advantages of URA

A
  • tipping of teeth
  • excellent anchorage
  • generally cheaper than fixed
  • shorter chair side time required
  • OH easier to maintain
  • non-destructive to tooth surfaces
  • less specialised training required to manage them
  • can be easily adapted for overbite reduction
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10
Q

what are the disadvantages of URA

A

• Less precise control of tooth movement
○ Just tipping and tilting

• Can be easily removed by the patient
○ Patient can remove and refuse to wear them

• Generally can only move 1-2 teeth at one time

• Specialist technical staff required to construct the appliances
○ Challenging to make these

  • Rotations very difficult to correct with removable appliances
  • Lots of limitations to removable appliances
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11
Q

What is needed if there is crowding

A

space to move teeth

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12
Q

how can we create space in an arch

A
  • removing teeth

- expanding / widening arch

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13
Q

when can patients get an URA

A

Normally wait for the permanent dentition to be through

Very rarely treat deciduous dentition with orthodontics because the teeth are going to fall out anyway
Only tend to intervene if there are potentially functional problems

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14
Q

what are the problems with an increased overjet

A
  • increased risk of trauma
  • Aesthetic issues
  • Significant functional problems (difficulty incising food)
  • Lip trap (lower lip trapped behind the upper lips)
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15
Q

what is the aim in the URA appliance design

A

good opening statement
what it is you are trying to achieve
what is the purpose of the appliance

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16
Q

what does procline mean

A

pushing forward

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17
Q

what does retrocline mean

A

pushing back

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18
Q

what does ARAB stand for in the URA appliance design

A

Active Component
Retentive
Anchorage
Baseplate

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19
Q

what is the active component

A

= the part that is actually moving the teeth through the application of force
= any component that move the teeth through the application of force

20
Q

why is it important to state the gauge of wire (this is the thickness)

A

○ The reason the thickness is important is because the thicker the greater the force
Using a thin wire means a gentler force

21
Q

give an example of what would be written for the active component in the URA appliance design

A

13 & 23 palatal finger spring & guards,

0.5mm hard stainless steel wire

22
Q

what is the retentive / retention

A

= the resistance to displacement forces

23
Q

what is a displacement force

A

= anything that can dislodge the appliance

24
Q

what are the 5 main displacement forces

A

○ Tongue
○ Gravity
○ Chewing / mastication / process of eating
○ Talking (creates vibration through the palate)
○ Active component (creates the largest force)

25
Q

what is the most commonly used clasp for retention

A

Adams clasp is the most commonly used

26
Q

give an example of what would be written for the retentive in the URA appliance design

A

16 & 26, Adams clasp, 0.7mm HSSW

11 & 21, Southend clasp, 0.7mm HSSW

27
Q

what is anchorage

A

= the resistance to unwanted tooth movement
Making sure that the teeth we want to move are the only teeth that move and the teeth we don’t want to move stay in the same position

28
Q

what are the functions of the baseplate

A 
○ Holds all the components together
○ Helps with retention 
	§ Cohesion
	§ Adhesion
○ Helps with anchorage 
	§ Helps with the resistance to unwanted tooth movement
29
Q

what material is the base plate made from

A

PMMA

Can make these appliances in heat cure but there are specific reasons we use self cure

30
Q

what are the advantages of heat cure PMMA

A

○ Can control the curing so can decide the working time
○ Better polymerisation as all the free monomer is used, little likelihood of an allergic reaction (although can still occur)
○ Considerably less shrinkage with heat cure than self cure
○ Fundamentally heat cure is stronger

31
Q

Why do we use self cure PMMA if heat cure PMMA has more advantages

A

Can have it made from start to finish in around an hour
And then curing takes just 20 minute
= it is faster to make

Self cure is satisfactory even though heat cured is better

32
Q

briefly explain the lost wax technique

A
  1. Wax up ~ 1 hour
  2. Use a mould (brass flask) and embed the partial denture (wax) into one side ~ 1 hour
  3. Something about plaster ~ 1 hour
  4. Put into a heating bath to melt the wax ~ 1 hour
  5. Heat cured acrylic then pack it into the area where the wax has been boiled from ~ 1 hour
  6. Heat the acrylic for 8 hours at 80˚ then to 100˚ for another few hours
  7. Break off plaster, then we have the right appliance

=15-20 hours = long time

33
Q

what is newton’s 3rd law

A

Newton’s 3rd law = every action / force there is an opposite and equal reaction

34
Q

what speed of tooth movement do we want with a URA

A

We want a mm of tooth movement per month ~ very slow

35
Q

How does the adams clasp achieve retention

A

by utilising mesial and distal undercuts

36
Q

what are the advantages of the adams clasps

A
  • small
  • unobtrusive
  • can be used on permanent, deciduous and partially erupted teeth
  • the bridge provides site of removal
37
Q

what material is most widely used for metallic parts of orthoodntic appliance construction

A

Material most widely used for the metallic parts of orthodontic appliance construction

38
Q

how is hard wire made

A

The hard wire is made by drawing the metal in a cold state through a series of dies in successively smaller diameter
This process also causes work hardening which gives the wire its spring properties

39
Q

how is stainless steel further work hardened

A

Stainless steel is further work-hardened during the bending process of constructing component parts for the appliances
This can be utilised to increase the spring properties of the wire

40
Q

when does fracture of stainless steel wire occurs

A
  1. Overworked
    ○ The wire has been excessively overworked by bending and then straightening the wire at the same point
    ○ This creates extreme stresses within the immediate area which can result in fracture
  2. Mechanical abrasion crushed or marked
    ○ This can occur if the wire has been damaged by burs or stones in the finishing process of removable appliances
    ○ Or if the wire has been marked or crushed during the fabrication of components
  3. Fatigue
    ○ This can be caused by repeated straining action
    ○ Eg continually strained to engage a deep undercut with an Adams clasp
  4. Weld Decay
    ○ Is an intergranular corrosion created by overheating the alloy
    ○ This causes the chromium carbides to precipitate at the grain boundaries
    ○ The oral fluid can now access the surface of other metals resulting in galvanic action which weakens the area sufficiently to result in fracture
41
Q

what type of stainless steel is commonly used in orthodontics

A

18/8 austenitic stainless steel alloy

This material is corrosion resistant when cold worked:

42
Q

what is austenitic

A

austenitic is a crystalline space lattice structure of the alloy
The alloy cannot be heat hardened and remains in a soft condition unless it has been cold worked

43
Q

what are the constituents of 18/8 austenitic stainless steel allloy

A

• 72% Iron
○ Main constituent
○ When combined with carbon it forms steel

• 18% Chromium
○ When added to steel lowers the content of carbon present and lowers the temperature at which martensite forms
○ Forms a passive oxide film over the surface of the metal that enables the stainless steel to be corrosion resistant

• 8% Nickel
○ Along with chromium assist in achieving the austenitic structure at room temperature by lowering the critical temperature at which the austenitic structures breaks down on cooling

• 1.7% Titanium
○ Added to the steel primarily to prevent the precipitation of chromium carbides at the grain boundaries when the alloy is heated during welding or soldering
○ Carbon combines with the titanium in preference to the chromium

• 0.3% Carbon

44
Q

what is martensite

A
  • The principal component of hard steel
  • Formed by quenching from high temperatures
  • Consists of intergrown plate-like crystals with a distorted cubic structure arising from the presence of carbon atoms in iron structure
45
Q

what is the difference between austenite and martensite

A
  • In austenite the average unit sell is a perfect little cube
  • The transformation to martensite sees this cube distorted by interstitial carbon atoms that do not have time to diffuse out during displacive transformation (quenching)
  • So that it is a tiny bit longer than before in one dimension and a little short in the other two
  • A microscopic crystallites of steel is millions of unit cells long
  • Since all these units face the same direction, distortions of even a fraction percent become magnified into a major mismatch between neighbouring materials

• This creates crystal defects within the material similar to work hardening
These defects prevent atoms from sliding past one another in an organised fashion, causing the material to become harder

BDS3 - Orthodontics (14 decks)

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