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BDS3 CDS Ortho > Laboratory Techniques > Flashcards

Laboratory Techniques Flashcards

1
Q

Soft or hard SSW is used in orthodontic appliances ?

A

Hard - HSSW.

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2
Q

Explain two ways which HSSW undergoes work hardening in orthodontic appliances.

A

During manufacture - drawing metal in cold state through series of dies of successively smaller diameter.
Bending.

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3
Q

Explain Bauschinger effect.

A

If coil activated in same direction as previous bending, elastic recovery is greater than if it deflected in opposite direction.

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4
Q

What are the four reasons for SS fracture ?

A

Overworked.
Mechanical abrasion crushed or marker.
Fatigue.
Weld decay.

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5
Q

What is the specific type of stainless steel wire used in orthodontics ?

A

18/8 austenitic stainless steel alloy.

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6
Q

What does austenitic mean ?

A

Crystalline space lattice structure alloy - cannot be heat hardened and remains in soft condition unless it has been cold worked.

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7
Q

What are the 5 constituents of HSSW ?

A

72% Iron.
18% Chromium.
8% Nickel.
1.7% Titanium.
0.3% Carbon.

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8
Q

What two constituents form steel ?

A

Iron combined with Carbon.

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9
Q

What is martensite ? And what is its structure ?

A

Principle component in hard steel, formed by quenching from high temperatures - intergrown plate-like crystals with distorted cubic structure arising from presence of carbon atoms in iron structure.

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10
Q

What is the function of chromium in HSSW ? How ?

A

Corrosion resistance - by forming passive oxide film on surface.
Aids in achieving austenitic structure.

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11
Q

How does nickel and chromium assist in achieving austenitic structure at room temperature ?

A

Lowers critical temperature at which austenitic structure breaks down on cooling.

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12
Q

What is the function of nickel in HSSW ?

A

Corrosion resistance and increasing strength.

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13
Q

What is the function of titanium in HSSW ? How ?

A

Prevent precipitation of chromium carbides at grain boundaries when alloy is heated during welding or soldering as carbon combines best with titanium.

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14
Q

What is the difference between austenite and martensite ?

And which one is harder ?

A

Austenite - average unit cell - perfect cube.
Transformation to martensite - cube distorted by interstitial carbon atoms that do not have time to diffuse out during quenching.

Martensite has structural defects preventing atoms from sliding past one another in organised fashion - means material is harder.

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15
Q

What diameter of HSSW is an Adams clasp made from in permanent and deciduous dentition ?

A

0.7mm round HSSW for permanent teeth.
0.6mm round HSSW for deciduous teeth.

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16
Q

What undercuts of teeth do Adams clasps utilise ?

A

Mesial and distal undercuts on buccal aspect of teeth.

17
Q

What are the advantages of an Adams clasp ?

A

Small and unobtrusive.
Any tooth - deciduous or permanent or not fully erupted teeth.
Highly retentive.

18
Q

What are the key functions of an Adams clasp ?

A

Retentive feature.
Provide resistance to displacing forces.

19
Q

What are the 10 points on the checklist for the Adams clasp ?

A
20
Q

What is the key principle of orthodontic treatment ?

A

If prolonged force is applied to a tooth, tooth movement will occur due to pressure causing bone remodelling controlled by PDL.

21
Q

What is the meaning of bone remodelling ?

A

Bone is selectively removed in some areas and added in others.

22
Q

What are the advantages of removable orthodontics ?

A

Tipping of teeth.
Anchorage.
Cheaper.
Shorter chair side time.
OH easier to maintain.
Non-destructive to tooth surface.
Less specialised training required.
Easily adapted for overbite reduction.

23
Q

What are the disadvantages of removable orthodontics ?

A

Less precise control of tooth movement.
Easily removed by patient so patient compliance.
Generally only 1-2 teeth moved at one time.
Specialist technical staff required in construction.
Rotations difficult to correct.

24
Q

What are the four components to URA appliance design ?

A

Active components.
Retentive.
Anchorage.
Baseplate.

25
Q

What is Index of Orthodontic Treatment Need (IOTN) ? What does it aim to do ?

A

Ranking system which attempts to rank malocclusion in terms of significance to various occlusal traits for an individual’s health and perceived aesthetic impairment.

Aims to identify those who would benefit most from orthodontic treatment.

26
Q

What are the two components of Index of Orthodontic Treatment Need (IOTN) ?

A

Aesthetic component.
Dental health component.

27
Q

What diameter of HSSW should a Southend clasp be made from ?

A

0.7mm HSSW.

28
Q

What diameter of HSSW should a labial bow be made from ?

A

0.7mm HSSW.

29
Q

What are three types of retentive components in a URA ?

A

Adams clasp.
Southend clasp.
Labial bow.

30
Q

What are six types of active components in a URA ?

A

Finger springs and guards.
Z-spring (double cantilever).
Flapper spring.
T-spring.
Buccal canine retractor.
Roberts retractor.

31
Q

What is the name of the passive component in URA ?

A

Stops.

32
Q

What diameter of HSSW should all active components in URA be made from ?

A

0.5mm HSSW.

33
Q

What are the two active components in a URA which are buccally placed ?

A

Buccal canine retractor.
Roberts retractor.

Should be sheathed with 0.5mm internal diameter tubing.

34
Q

What are the 10 stages to fitting a URA ?

A
  1. Ensure patient details are correct.
  2. Check appliance matches design specifications.
  3. Inspect appliance looking for traumatic areas.
  4. Check integrity of framework.
  5. Insert appliance into patients mouth looking for blanching.
  6. Check posterior retention.
  7. Apply same principles to anterior retention.
  8. Activate appliance - 1mm movement approx. per month.
  9. Demonstrate to patient and get them to show you.
  10. Book review in 4-6 weeks.
35
Q

How many mm of tooth movement should you aim for in one month ?

A

1mm.

36
Q

What are 10 things the patient should be informed of as part of patient information and instruction for URA ?

A
  1. Will feel bulky.
  2. Excessive saliva - 24hrs.
  3. Impinge speech.
  4. Discomfort and ache.
  5. Worn 24/7 - meal and sleep.
  6. Remove at meals and clean.
  7. Remove and store in protective container during sports.
  8. Avoid hard or stick foods.
  9. Missing appointments and non-compliance will lengthen treatment,
  10. Emergency contact details.
37
Q

What is the function of a Roberts retractor ?

A

To reduce overbite.

BDS3 CDS Ortho (8 decks)

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