stability in orthodontics Flashcards
what changed happens in the untreated dentition?
> Crowding increases
> Lower arch shortens and narrows with age
> Lower incisors become more irregular
> Overbite increases
what are the categories of relapse/ post treatment change?
- 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
how do we ensure maximum stability?
> Finish case correctly (achieve occlusal and soft tissue balance)
> Use appropriate retention protocol
what is correct finishing?
> taking care of and acceptable management of =
- Expansion/contraction of arches
- Overjets/overbites
- Crossbites
- Interdigitation
> for long term stability
what is the expansion and contraction of the arches caused by and how does this effect orthodontic treatment?
> 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
during orthodontic if you increase the lower arch size and the incisors move forward, what will happen?
> 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
when treating a positive/ increased overjet what is crucial for stability?
> lower lip control = this will keep the over jet reduced
> Reduce overjet to 2-4 mm
> Over-treatment to 0 mm recommended
how much ideally should the lower lip cover of the upper incisor?
> 1/3 of the height
what are you hope to achieve post orthodontic treatment for a patiet with a negative or reverse overjet?
> 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
at the end of orthodontic treatment when you are trying to fix an increased overbite, what must you pay attention to?
> 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
what should the inter incisal angle be for maximum stability of overbite reduction?
> 125-135 degrees
> you also want the lower incisor edge to rest on the upper part of the upper cingulum plateau
what are the general principles for transverse (crossbite) stability?
> over treatment is key
> good buccal overlap of the molars and premolars to maintain cross bite reduction
in what patients is it not likly to have a stable cross bite correction in the long term?
> patient with a narrow palate
what is important to achieve at the end of orthodontic treatment?
> Ensure good buccal interdigitation of lower molars and premolars
Poor interdigitation can lead to post-treatment change
If a patient has a poor interdigitiation at the end of treatment, what may it cause?
> cusps tend to want to find at more natural position so can lead to =
- increased overjet
- increased overbite
- increased crowding
in what patients should you recognise that stability might be a problem?
patients with =
> Lower incisor crowding
> Median diastema
> Generalised spacing
(it is important to plan for these problems prior to treatment)
what should you advise patients about lower incisor crowding prior to orthodontic treatment?
> 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
what does the studies suggest about extractions to deal with Lower incisor crowding?
> not very successful
> however, those without extractions experienced a stronger spring back effect
what should patient a patient be made aware of regarding stability prior to orthodontic treatment?
> 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
