🔍 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).

📈 Common Soft Tissue Changes

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.)

🔄 Soft Tissue:Hard Tissue (ST:HT) Ratios

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.)

Clinical Considerations

• 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.

🔵 MCQ 1: Predictive Analysis

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 mm
B. 3–4 mm
C. 4–6 mm
D. 5–7 mm

✅ Answer: C. 4–6 mm
Explanation: The upper lip typically retracts 33–67% of the hard tissue incisor movement. For a 6 mm setback, soft tissue movement would be approximately 2–4 mm (though some cases may show more).

🔵 MCQ 2: Clinical Decision-Making

A patient undergoing ASO shows an obtuse nasolabial angle preoperatively. What is the most appropriate surgical consideration to prevent worsening facial esthetics?

A. Proceed with ASO alone
B. Perform rhinoplasty simultaneously
C. Opt for mandibular setback only
D. Combine ASO with subnasal augmentation

✅ Answer: B. Perform rhinoplasty simultaneously
Explanation: ASO increases the nasolabial angle. In a patient with an already obtuse nasolabial angle, this can make the nose appear more prominent. Rhinoplasty may help balance facial esthetics.

🔵 MCQ 3: Application in Treatment Planning

Which of the following ST landmarks consistently showed minimal movement following ASO, making them less predictable targets for esthetic changes?

A. Labrale superius (Ls)
B. Subnasale (Sn)
C. Pronasale (Pn)
D. Labrale inferius (Li)

✅ Answer: C. Pronasale (Pn)
Explanation: Multiple studies showed minimal to no horizontal or vertical movement of the nasal tip (pronasale), suggesting limited nasal ST change from ASO alone.