Stability

Question 1

Changes in the untreated dentition

Answer 1

crowding increases
lower arch shortens and narrows with age
lower incisors become more irregular
overbite increases

Question 2

Post Tx Change

Answer 2

1. physiological recovery –> return to original malocclusion (i.e., spaces or rotations)
2. unfavourable growth –> irrespective of orthodontic tx e.g., skeletal III discrepancy
3. True relapse –> changes occurring due to the placement of teeth in unstable positions

Question 3

How do we ensure maximum stability?

Answer 3

finish case correctly (achieve occlusal and soft tissue balance)
use appropriate retention protocol

Question 4

Correct finishing

Answer 4

expansion/contraction of arches
overjets/overbites
crossbites
interdigitation

Question 5

Expansion/contraction of arches

Answer 5

teeth exist in zone of balance
avoid expansion/contraction
use pts original arch form as a guide
maintain inter-canine and inter-molar widths

Question 6

Positive/increased overjet

Answer 6

low lip control is crucial
reduce overjet to 2-4mm
over tx to 0mm recommended

Question 7

Negative/reverse overjet

Answer 7

Must achieve positive incisal overbite at the end of tx
remember to allow for the reduction in overbite due to proclination of the upper incisors during tx

Question 8

Increased overbite

Answer 8

correct inter-incisal angle
correct lower incisal edge/cingulum plateau relationship
Over tx to 0mm is recommended

Question 9

Transverse stability

Answer 9

Over tx
Good buccal overlap

Question 10

Cases where stability will be an issue

Answer 10

Lower incisor crowding
Median diastema
Generalised spacing

Question 11

Lower incisor crowding

Answer 11

Recognise that lower incisor alignment is rarely maintained
Advise pts of the probability of post tx change
Some minor proclination of lower incisors is possible (1-2mm)
Permanent retention is the only way to guarantee stability