Ortho Lab Techniques Flashcards
Stainless steel composition
72% Iron
18% Chromium
8% Nickel
1.7% Titanium
0.3% Carbon
Main component of stainless steel
Iron
What is the most widely used material for metal parts of ortho appliances?
Stainless steel
Two types of stainless steel, and which is used in ortho?
Hard and soft
Hard is used
How is hard stainless steel made?
Work hardening done in a cold state
4 reasons fractures of stainless steel wire can occur
Overworked
Mechanical abrasion crush or marked
Fatigue
Wed decay
What does it mean that stainless steel is AUSTENITIC?
Austenitic is the crystalline space lattice structure of the alloy. The alloy can not be heat hardened and remains in a soft condition unless it has been cold worked
What type of stainless steel is used in orthodontics?
18/8 austenitic stainless steel alloy
Why is chromium added to stainless steel?
Lowers the temperature at which martensite formed by quenching
Corrosion resistance due to chromium oxide film on surface
What is martensite?
The primary component of hard steel, formed by quenching from high temperatures. It consists of intergrown plate-like crystals with a distorted cubic structure arising from the presence of carbon atoms in the iron structure
Why is nickel added to stainless steel?
Helps achieve austenitic structure at room temperature by lowering the critical temp at which the austenitic structure breaks down on cooling
Improves strength and corrosion resistance
Why is titanium added to stainless steel?
To prevent precipitation of chromium carbides at the grain boundaries when the alloy is heated during welding or soldering
Carbon combines with titanium in preference to the chromium
What is the difference between austenite and martensite?
Is austenite the average unit cell is a perfect cube, the transformation to martensite sees it distorted by interstitial carbon atoms that do not have time to diffuse out during quenching.
These defects make the material harder as the layers of particles can no longer slide past one another in an organised fashion
What does ARAB stand for?
Active component
Retention
Anchorage
Baseplate
What must be included on a URA appliance design sheet?
Drawing
Description of what the appliance design is aiming to achieve
Active component
Retention
Anchorage
Baseplate
What is anchorage?
Resistance to unwanted tooth movement
What is the active component?
The name of the components that will be moving teeth with the application of force
What is retention?
Resistance to displacement forces
What is the job of the baseplate?
Connects all components together as a unit, provides anchorage and assists with retention
Advantages of URA orthodontics
Tipping action
Excellent anchorage
Generally cheaper than fixed
Shorter chairside time required
OH easier to maintain
Non-destructive to tooth surface
Less specialised training required for management
Can be easily adapted for overbite reduction
Can achieve block movements
Why are study casts useful?
Can look at dentition without patient present
Design purposes
Monitor progress
Try in appliances
Can build appliance without patient present
Disadvantages of URA orthodontics
Less precise control of tooth movement
Can be easily removed by patient
Only 1-2 teeth can be moved at a time
Specialist technical staff required to construct
Rotations very difficult to correct
What diameter of wire should be used for Adams clasps?
0.7mm
(0.6mm can be used for deciduous teeth or newly erupted premolars)
Describe placement of Adams clasps
Adams clasps are placed for retention. They used the mesial and distal undercuts of the buccal aspect of the teeth
Advantages of the Adams clasp
Small, neat, unobtrusive
Can be used on almost any tooth
A tooth that has not yet fully erupted can be clasped
Highly versatile and can be modified in a number of ways
Highly retentive
Its bridge provides a site to which the patient can apply pressure with the fingertips to remove appliance
Auxiliary springs can be soldered to the bridge of the clasp
Hooks can be soldered to the clasp or bent in during its construction to accept inter-maxillary traction
Tubes can be soldered to the bridge of the clasp to accommodate a facebow for extra-oral traction
Adams clasp checklist
Arrowheads must engage mesial and distal undercuts, except when tooth is rotated
The bridge of the clasp stands clear of the tooth at approx 45 degrees to the crown
Arrowheads are parallel
Arrowheads are at 45 degrees to tooth surface
Arrowheads must not touch adjacent teeth
Bridge should not protrude above the occlusal surface
The wire fits closely over the contact areas
There should be a clearance of 0.5-1mm between the wire and tissue in the palate
There must be tags present at the ends of the wire to supply addition mechanical retention within the baseplate
The gingival margin of any models should only be trimmed if the tooth present has not fully erupted
Basic principle of orthodontics
If prolonged force is applied to a tooth, tooth movement will occur
What effect does orthodontics have on bone?
Force exerted creates pressure which causes the bone around the tooth to remodel - a process where bone is selectively removed in some areas and added in others
Name 3 retentive components of URAs
Adams clasp
Southend clasp
Labial bow
ALL USE 0.7mm HSSW
Name potential active components for URAs
Finger springs + guard
Z-Spring
Flapper spring
T-Spring
Buccal canine retractors
Roberts retractors
ALL USE 0.5mm HSSW
Name two buccally placed active components
Buccal canine retractors
Roberts retractors
How to deliver a URA
Right appliance - right patient
Check the appliance matches the design
Inspect the appliance and run your finger over all surfaces looking for sharp areas
Check the wirework for damage or work hardening
Insert into patients mouth - check for blanching or soft tissue trauma
Check posterior retention
Check anterior retention
Activate the appliance
Demonstrate insertion and removal
Book 4-6 week review
What is the desired movement/time for ortho?
1mm/month
