Stability and Retention in Orthodontics Flashcards
What is retention
Retention is the phase after active orthodontic treatment when teeth need to be maintained in their new positions
What is the objective of retention
Minimise relapse
What is defined as relapse? (BSI and Patient Perspective)
BSI: The return, following correction, of features of the original malocclusion
Patient: Any change from the final tooth position at the end of treatment (could be caused by age) - UNPREDICTABLE
What factors determine the stability post ortho treatment
- Periodontal and gingival tissues (soft tissue)
- Musculature (soft tissue)
- Apical base (Arch widths and mandibular incisors)
- Occlusion
- Growth
How does orthodontic tooth movement affect the periodontal and gingival tissues
Causes widening of PDL spaces and disruption of collagen fibre bundles
How long does reorganisation of periodontal and gingival tissues take (important for stability)
Alveolar bone remodelling: 1 month
PDL reorganisation: 3-4 months
Gingival tissues takes longer
Collagen fibres: 4-6 months
Elastic Supracrestal fibres: can displace a tooth up to >1year after debond
How does musculature of the lips, cheek and tongue affect the stability post ortho?
How can this be reduced?
Can aid or hinder stability depending on the direction of tooth movement
Avoiding encroachment beyond the neutral zone
How does occlusion affect the stability post ortho
- Well-interdigitated teeth are more stable (poor evi)
- Stability of deep overbite correction associated with positive occlusal stop
- Stability of single tooth crossbite correction associated with adequate overbite (at least 2mm)
How does growth affect the stability post ortho?
- Can cause recurrence of skeletal discrepancies –> deterioration of occlusal relationships
- Small age changes throughout life can lead to late lower incisor crowding - Mandibular rotation or forward growth –> Increases force of lower lip onto lower incisors –> crowding
What type of skeletal discrepancy worsens with age
Class III: Man prognathia
Is third molars a cause of relapse or late lower incisor crowding?
NO
What are the implications of stability in terms of planning treatment
- Timing (during or after growth)
- Correct diagnosis, treatment plan and mechanics
- Eliminate etiology of malocclusion (esp. habits)
- Minimise changes in arch form (esp lower)
- Consider magnitude of tooth movement
Prevention: Ensure adequate space for eruption
What are the implications of stability in terms of executing treatment
- Correct tooth position early (rotation, extrusion)
- Position teeth within basal bone (inclination. position)
- Achieve good intercuspation
- Overcorrect occlusal relationships and tooth position (rotation) - generally not done
How long should retention be put in place for?
- Adequate time for remodeling of periodontal and gingival tissues
- Until growth completion
How to improve retention?
- Permanent fixed/long-term retention
- Adjunctive techniques prn eg. circumferential supracrestal fiberotomy (CSF) - for severely corrected teeth, frenectomy
What is a case with limited need for retention?
Single tooth crossbite with sufficient (at least 2mm) of overbite
What are some cases which are prone to relapse
- Rotations
- Considerable spacing due to small/missing teeth, median diastemas
- Movements involving significant expansion (buccal movement)
- Periodontically involved teeth
Why do rotation cases relapse
Elastic supra-crestal gingival fibres remodel slowly (>1year) and hence there is residual tension and 20# relapse
Hence fixed retainers should be considered
Why do large diastemas relapse
Failure of gingival elastic fibres to cross the midline
Aggravated by large or inferiorly attached labial frenum (moves apically till 12)
What is the difference between orthopedic (young) vs surgical maxillary skeletal expansion
Orthopedic: gradual and stable
Surgical: drastic expansion hence less stable