stability and retention Flashcards
Why are retainers needed
- Prevent relapse
- Allow for reorganisation of gingival and periodontal tissues
- Permit neuromusuclar adaptation to corrected tooth position
- Minimise changes due to growth or normal age changes
- Maintain teeth in unstable position necessary due to compromise for aesthetics
What are the 5 factors determining stability
- Periodontal and gingival tissues
- Occlusion
- Growth
- Musculature
- Apical base
How do periodontal and gingival tissues impact stability after ortho treatment
Alveolar bone remodel within a month. PDL 3-4 months. Collagen fibres 4-6 months. Elastic supracrestal fibres may take more than a year to remodel
What are the features associated with stability of deep bite and of single tooth cross bite
- Stability of deep bite: positive occlusal stop, ideal interincisal angle 135º
- Single tooth crossbite stability associated with adequate overbite (at least 2mm)
How does musculature affect stability of ortho treatment outcome
Neutral zone, tongue movement
What about the apical base affects stability of ortho treatment outcome
Within alveolar bone — more support, greater stability
Adjunctive technique that can be used for retention
Supracrestal fiberotomy, indicated for patients with very severe rotations
In what situations would you consider permanent or semi permanent retention
- Severe rotation (residual tension in supracrestal gingival elastic fibres)
- Labiolingual malposition
- Considerable or generalised spacing
- Anterior dental expansion — there is now pressure from soft tissue or move beyond alveolar bone where there is less periodontal support
- Periodontically involved
- Surgical skeletal expansion (less stable than orthopedic expansion)
- Impacted incisors and canines which have tendency for reintrusion or BL displacement. consider severity of impaction and speed of correction
Compare Hawley and vacuum formed retainer
- vacuum formed retainer more aesthetic
- Hawley retainer does not cover occlusal surfaces so allow for settling in of occlusion
- Hawley more expensive and more time consuming to fabricate than vacuum formed retainer
- Vacuum formed retainer less effect on speech as does not cover anterior part of the palate
- Hawley can have components incorporated to maintain growth correction eg functional appliance while vacuum formed retainer cannot
- Vacuum formed retainer likely to have a tighter fit
- Vacuum formed retainer covers occlusal surfaces hence can protect teeth in grinders and clencher
Disadvantages of fixed retainer
- Localised retention hence if used alone may have movement in other areas of arch
- Wire distortion, fracture, debonding may lead to unwanted dental movement
- Complicates interproximal hygiene
- Challenging to adjust/repair chair side
Advantages of fixed retainer
- Usually invisible from the front, more aesthetic
- Reduced need for patient compliance
- Good for potentially unstable outcomes
