Stability Flashcards
What are the changes in the untreated dentition?
*Crowding increases
*Lower arch shortens and narrows with age
*Lower incisors become more irregular
*Overbite increases
What is the post treatment change?
- Physiological recovery
- Unfavourable growth
- True relapse
Physiological recovery
return to original malocclusion (i.e. spaces or rotations)
Unfavourable growth
irrespective of
orthodontic treatment
True relapse
changes occurring due
to the placement of teeth in unstable positions
Key issues with stability?
How do we ensure maximum stability?
*Recognising where stability will be a problem
How do we ensure maximum stability?
Finish case correctly (achieve occlusal and soft tissue balance)
*Use appropriate retention protocol
Correct finishing- how?
*Expansion/contraction of arches
*Overjets/overbites
*Crossbites
*Interdigitation
Expansion/contraction of arches- why does it work?
*Teeth exist in a zone of balance
How does it work?
Avoid expansion/contraction
*Use patient’s original archform as a guide
*Maintain inter-canine and inter-molar widths
Positive/increased overjet (3)
*Lower lip control is crucial
*Reduce overjet to 2-4 mm
*Over-treatment to 0 mm recommended
What to note about the lower lip
Lower lip often trapped behind upper incisors in Class II/1
Ideally lower lip should cover 1/3 of u
Negative or reverse overjet
Aim of treatment and important considerations?
Must achieve positive incisal overbite at the end of treatment
*Remember to allow for the reduction in overbite due to proclination of the upper incisors during treatment
What could be used to create a positive overbite?
Surgery
Increased overbite- aims of treatment?
*Correct inter-incisal angle
*Correct lower incisal edge/cingulum plateau relationship
*Over-treatment to 0 mm is recommended
Interincisal angle?
125-135 degrees
Transverse (crossbite) stability (2)
Overtreatment
Good buccal overlap
Proportional change in transverse (crossbite) from pre to post treatment
AB shoud reduce significantly CD should remain the same
What’s important about buccal interdigitation?
*Ensure good buccal interdigitation
*Poor interdigitation can lead to post-treatment change
Poor interdigitation?…
Increases
Overbite
Overjet
Crowding
Where would stability be a problem?
*Lower incisor crowding
*Median diastema
*Generalised spacing
Lower incisor crowding- recognise that…
lower incisor alignment is rarely maintained
With lower incisor crowding tell patient…
*Advise patients of the probability of post treatment change (70%)
*Some minor proclination of the lower incisors is possible (1-2mm)
*Permanent retention is the only way to guarantee stability
University of Washington study showed that in 600 patients 5 years out of retention
In premolar extraction cases
Majority (half) the patients had moderate crowding and 30 percent had satisfactory and 20 percent severe crowding
