Common occurrence:
- Posterior / anterior crossbite
- Tooth-size discrepancy
Correction devices
- Expansion maxilla: RME – bonded appliance – skeletal change
- Expansion mandible: Schwarz appliance in 40% of cases – dentoalveolar change
Decision making for expansion
- Transpalatal arch-width – measured from narrowest point
- Average dimensions: Howe 1983 & Riolo 1974
- Adult 35-39mm
- Child 32-35mm
- If -31mm require expansion
- Average dimensions: Howe 1983 & Riolo 1974
- Mesial-distal width of the central incisor
- Average dimensions: Riolo 1974
- Male 8.9mm +/- 0.6
- Female 8.7mm +/- 0.6
- If 2 SD greater than average = 10mm – consider delay treatment as likely require extraction therapy as tooth size discrepancy significant.
- Average dimensions: Riolo 1974
- Arch-length discrepancy:
- +6mm delay as likely extractions
- 3-6mm borderline – ideal for expansion
Timing of treatment
- Eruption of all 1st molars, lower 2-2 and upper centrals
Treatment protocol
- Maxillary expansion
- 1 x activation per day
- 28 days of activation
- Over-expansion
- Mandibular expansion
- Activated 1 x week Schwarz appliance
- 4mm of expansion
- Wear: full time, including meals
- Dento-alveolar = upright posterior teeth and expansion of arch
- Active expansion 5 months
- No retention – as intercuspation retainers – require only upper retainer
Long term effects?
- RME Vs no MRE 8 year follow up 12-20 years of age MnNamara 2003
- Control = Reduction of maxillary arch perimeter 6mm
- RME = Reduction of maxillary arch perimeter 1.5mm
- = overall RME 4.5mm longer arch perimeter
- Passive expansion of mandibular arch 2.5mm Geran 2006
Class 2 correction with RME?
- Bite plane effect from bonded RME
- Following removal patient postures forward = growth at condyle
- Guest 2010 = 90% improved, of which 50% 2mm molar correction
