stability in orthodontics

Question 1

what changed happens in the untreated dentition?

Answer 1

> Crowding increases

> Lower arch shortens and narrows with age

> Lower incisors become more irregular

> Overbite increases

Question 2

what are the categories of relapse/ post treatment change?

Answer 2

1. Physiological recovery –return to original malocclusion (i.e. spaces or rotations)
2. Unfavourable growth – irrespective of orthodontic treatment
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

what is correct finishing?

Answer 4

> taking care of and acceptable management of =

• Expansion/contraction of arches
• Overjets/overbites
• Crossbites
• Interdigitation

> for long term stability

Question 5

what is the expansion and contraction of the arches caused by and how does this effect orthodontic treatment?

Answer 5

> Teeth exist in a zone of balance (tongue and cheeks)

> so Avoid expansion/contraction during orthodontic treatment

> Use patient’s original archform as a guide

> Maintain inter-canine and inter-molar widths = do not increase or reduce

Question 6

during orthodontic if you increase the lower arch size and the incisors move forward, what will happen?

Answer 6

> the lower lip will move the incisors back, but because the teeth have all moved forward there is no room and it will cause crowding

> long term - severe lower incisor crowding caused by ill judged over expansion of the arch

Question 7

when treating a positive/ increased overjet what is crucial for stability?

Answer 7

> lower lip control = this will keep the over jet reduced

> Reduce overjet to 2-4 mm

> Over-treatment to 0 mm recommended

Question 8

how much ideally should the lower lip cover of the upper incisor?

Answer 8

> 1/3 of the height

Question 9

what are you hope to achieve post orthodontic treatment for a patiet with a negative or reverse overjet?

Answer 9

> 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

> good long term stability

Question 10

at the end of orthodontic treatment when you are trying to fix an increased overbite, what must you pay attention to?

Answer 10

> Correct inter-incisal angle

> Correct lower incisal edge/cingulum plateau relationship

> Over-treatment to 0 mm is recommended for an increased overbite as some spring back may occur

Question 11

what should the inter incisal angle be for maximum stability of overbite reduction?

Answer 11

> 125-135 degrees

> you also want the lower incisor edge to rest on the upper part of the upper cingulum plateau

Question 12

what are the general principles for transverse (crossbite) stability?

Answer 12

> over treatment is key

> good buccal overlap of the molars and premolars to maintain cross bite reduction

Question 13

in what patients is it not likly to have a stable cross bite correction in the long term?

Answer 13

> patient with a narrow palate

Question 14

what is important to achieve at the end of orthodontic treatment?

Answer 14

> Ensure good buccal interdigitation of lower molars and premolars

Poor interdigitation can lead to post-treatment change

Question 15

If a patient has a poor interdigitiation at the end of treatment, what may it cause?

Answer 15

> cusps tend to want to find at more natural position so can lead to =

• increased overjet
• increased overbite
• increased crowding

Question 16

in what patients should you recognise that stability might be a problem?

Answer 16

patients with =

> Lower incisor crowding

> Median diastema

> Generalised spacing

(it is important to plan for these problems prior to treatment)

Question 17

what should you advise patients about lower incisor crowding prior to orthodontic treatment?

Answer 17

> Recognise that lower incisor alignment is rarely maintained

> Advise patients of the probability of post treatment change (70%)

> Some minor proclination of the lower incisors is possible (1-2mm), but any large expansion of lower incisors forwards is likely to lead to long term instability

> Permanent retention is the only way to guarantee stability

Question 18

what does the studies suggest about extractions to deal with Lower incisor crowding?

Answer 18

> not very successful

> however, those without extractions experienced a stronger spring back effect

Question 19

what should patient a patient be made aware of regarding stability prior to orthodontic treatment?

Answer 19

> Patients should be made aware of the potential for relapse and the need for retention at the outset of treatment

> Patient/parents should be made aware of the high potential for post treatment change if expansion is used

> Arch width and arch length constriction is a normal physiological process