1. Core Clinical Facts

• Prevalence of AOB in mixed dentition: 17.7% (~1 in 5 orthodontic patients)
• Major independent risk factors:
  1. Prolonged sucking habits (thumb/finger or dummy) beyond age 3
  2. Facial hyperdivergency (skeletal vertical excess)
• Highest risk group: Patients with both prolonged sucking habits + hyperdivergent face
  • AOB prevalence 36.3% → ~4× higher than those without risk factors (9.1%)

2. Diagnostic Criteria

AOB Diagnosis: Overbite ≤ 0 mm, with all permanent incisors fully erupted.

Facial Hyperdivergency:

• FMA ≥ 25°
• S-Go / N-Me ≤ 0.62 (posterior:anterior facial height ratio)
• ANS-Me / N-Me ≥ 0.55 (increased lower anterior facial height)

3. Clinical Takeaways

• Mechanical factor (habit) + skeletal factor (hyperdivergency) = high AOB risk
• Early habit cessation (before age 3) dramatically lowers risk
• Skeletal vertical excess can worsen severity of AOB and affect treatment stability
• Interceptive protocols:
  • Habit-breaking appliances (removable/fixed grids)
  • Growth modification to control vertical dimension (eg, high-pull headgear, bite blocks)