🔍 Overview
- Procedure: ASO corrects bimaxillary dentoalveolar protrusion, primarily in Asian populations.
- Goal: Predict soft tissue (ST) changes from hard tissue (HT) movements.
- Method: Systematic review of 11 studies (199 patients; lateral cephalometry used in all).
| Region | Change |
|---|---|
| Upper lip (Ls) | Retrusion: −0.9 to −7.25 mm Vertical change: −2.4 mm to +1.2 mm |
| Lower lip (Li) | Retrusion: −1.1 to −8.36 mm Vertical change: +0.92 to +2.6 mm |
| Nasolabial angle | Increased by +8.9° to +18.8° (except mandibular-only ASO = slight decrease) |
| Interlabial gap | Reduced (improved lip competence) |
| Nasal tip (Pn) | Minimal or variable changes (−0.5 mm to +0.4 mm) |
| Philtrum length | Increased by ~3% (PARK et al.) |
| Lip width | Decreased by ~6% (PARK et al.) |
| Landmark | Ratio |
|---|---|
| Upper lip retraction | 33–67% of maxillary incisor setback |
| Lower lip retraction | 67–89% of mandibular incisor setback |
| A’ to A (soft vs hard tissue A point) | ~63% |
| B’ to B | ~81% (LEW et al.) |
- Greater effect on labial prominence than nasal or chin structures.
- Nasolabial angle mostly affected by upper lip retraction—not nasal tip.
- Genial and nasal landmarks remain relatively stable.
- Lip competence improves (reduced interlabial gap).
- Be cautious with patients with obtuse nasolabial angle—ASO may exaggerate nasal tip prominence.
A 24-year-old female patient with bimaxillary dentoalveolar protrusion is scheduled for bimaxillary anterior segmental osteotomy (ASO). If the maxillary incisor segment is planned for a 6 mm posterior movement, what is the most likely range of upper lip retraction based on systematic review evidence?
A. 1–2 mmB. 3–4 mmC. 4–6 mm
D. 5–7 mm