Removable appliances in orthodontics Flashcards
42% of removable appliance cases in GP
Showed “no improvement” (as measured by the PAR index)
Advantage
Removable
Distadvantage
• It’s removable! – not in the mouth – not
working, can be lost/ damaged…
• Can only tip teeth
• Affects speech
• Poorly tolerated in lower arch
• Intermaxillary traction not possible
• Inefficient for multiple tooth movements
One-point contact at tooth crown
Can only tip teeth
Fully controlled movement
Need attachment to tooth
-full 3D control
Designing a removable appliance
Keep
It
Simple
Stupid
Components (ARAB)/ Design
- Active components - how to move teeth
- Retention – stop it falling out
- Anchorage – stop the wrong teeth moving
- Baseplate and Biteplanes
Active components: moving teeth with removable appliances
Springs -palatal springs -(buccal springs) Screws Elastics *decreasing order of preference*
Properties of springs
Force of spring depends on
- thickness of wire
- length of wire
- amount of deflection
Length of wire
Force is proportional to (1/length^3)
Coil near acrylic increases length
Thickness of wire
Force is propertional to diameter ^4
Use 0.5-0.6mm diameter wire for active components
Z-spring
Incisor spring
T-spring
Longer so exerts less force and given space for expansion
Palatal finger spring
0.5-0.6mm sire Coil near acrylic (increases length) Coil on side away from direction of movement Can use any teeth -not good on buccally placed teeth
Screws
Closed or open
Adjustment of screws
Quarter turn = 0.2mm
1 turn per week = just <1mm per month
2 turn per week = just <2mm per month
Indications for screws
Moving blocks of teeth
Can move tooth and use for retention
Screws
Moving upper labial segment
Orthodontic elastics
Poor control
Rarely used
Posterior retention - Adams cribs
MB and DB undercuts
Only need undercut of 0.25mm
Anterior retention
Due to inclination there will be a downward vector
C-clasp
Southend clasp
Anchorage
The control of unwanted tooth movement
Newton’s 3rd law of motion
-to every action is an equal and opposite reaction
25g-30g on canines ideal force
How not to lose anchorage
- Light forces
- Only move one tooth per side
- Large anchor unit
- more teeth included in appliance design
- Headgear?
Problems with headgear
Co-operation
Safety
-pts were actually wearing 6.5 hours instead of 12 hours
Headgear safety
Catapulting accident
Night-time dismantling
Problems of eye injury
Hihg risk of infection Excellent culture medium Difficult to control with antibiotics Sympathetic ophthalmitis -safety mechanisms essential
Baseplate
- Connects components
- Carries passive wirework
- Additional anchorage
- Carries biteplanes
Biteplanes
Anterior biteplane
• Flat
• Inclined
Posterior biteplane
Flat anterior bite plane
Reduces overbite
Inclined bite plane
Post functional appliances
Anterior: to retain functional appliance treatment, proclines lower incisors (unfortunately)
Posterior biteplane
Free occlusion
Cases to treat with removable appliances
• Disimpaction of first molars • Class III - Anterior crossbite • Posterior crossbite (with associated mandibular displacement) in mixed dentition or expansion prior to functional appliances • Space maintenance • (Overbite correction)
Adjusting Adams Cribs
Gently roll arrowhead in or out with pliers
Z-spring adjustment
Pull forwards and upwards, away from baseplate
Fitting of a URA
- Check lab ticket
- Explain how the appliance works
- Try-in
- Adjust retentive components if required
- Activate
- Adjust bulky biteplanes if appropriate
- Demonstrate then check pt can fit and remove
- Instructions when to wear, how to clean etc
- Document everything you have done
Visit by visit assessment
- Talk to patient (and parent)
- Assess for signs of wear
- Assess progress, measure changes
- Assess OH
- Assess retention
- Check if active component is active
- Reassess anchorage
- Document findings and plan
Which spring is the preferred method of reducing overjet?
Robert’s retractor
