29.1 Extraoral Orthodontic Assessment

1. Comprehensive Extraoral Orthodontic Assessment

The extraoral examination establishes the soft tissue envelope, underlying skeletal framework, and facial aesthetic balance before intraoral occlusal features are evaluated.

Extraoral Orthodontic Examination Framework
  │
  ├── Frontal View
  │     ├── Facial Symmetry (Interpupillary line, midline, chin deviation)
  │     └── Vertical Facial Thirds (Upper, middle, and lower anterior face height [LAFH])
  │
  ├── Profile View (Sagittal & Vertical)
  │     ├── Sagittal Profile Convexity (Convex [Class II], Straight [Class I], Concave [Class III])
  │     ├── Nasolabial Angle (Normal 90°–110°; obtuse vs acute)
  │     └── Mandibular Plane Angle (Clinical assessment of high vs low angle)
  │
  └── Dynamic Soft Tissue & Smile Aesthetics
        ├── Lip Competence (Competent, Incompetent, Potentially Competent)
        ├── Lip Line & Incisor Display at Rest (Normal: 2–4 mm display in young females, 1–3 mm in males)
        └── Smile Arc (Consonant vs Non-consonant/Flat) and Buccal Corridors

Facial Symmetry and Frontal Proportions

• Transverse Symmetry: Assessed with the patient seated upright looking straight ahead in the natural head position (NHP). The facial midline is established through the midline of the forehead, nasal bridge, philtrum of the upper lip, and the center of the chin symphysis. Minor subclinical asymmetries are physiological, but chin deviations exceeding 2 mm or canted occlusal planes (assessed using a wooden tongue spatula resting across the premolars relative to the interpupillary line) represent significant skeletal or dental discrepancies.
• Vertical Facial Thirds: Measured in the frontal plane:
  • Upper Third: Trichion (hairline) to Glabella.
  • Middle Third: Glabella to Subnasale.
  • Lower Third (Lower Anterior Face Height - LAFH): Subnasale to Menton.
  • In a balanced facial profile, these three vertical segments are approximately equal in height.
• Subdivision of the Lower Facial Third:
  • Subnasale to Stomion superius (upper lip length): accounts for the upper one-third (approximately 33%).
  • Stomion inferius to Menton (lower lip and chin): accounts for the lower two-thirds (approximately 67%).
  • Increased LAFH: Associated with vertical maxillary excess, backward mandibular rotation, steep mandibular plane angles, and anterior open bites.
  • Reduced LAFH: Associated with vertical maxillary deficiency, forward mandibular rotation, flat mandibular plane angles, and deep overbites.

Facial Profile Analysis

With the patient seated in the natural head position and the Frankfort horizontal plane (porion to orbitale) parallel to the floor, the profile is assessed:

• Convex Profile: The mandible is retrognathic relative to the maxilla and forehead; characteristic of Skeletal Class II malocclusions.
• Straight (Orthognathic) Profile: Maxilla and mandible are in balanced sagittal harmony; characteristic of Skeletal Class I.
• Concave Profile: The mandible is prominent (prognathic) or the maxilla is retrognathic; characteristic of Skeletal Class III.
• Nasolabial Angle: Formed by the intersection of the columella of the nose and the philtrum of the upper lip. The normal range is 90° to 110°. An acute angle (< 90°) indicates maxillary dentoalveolar proclination or maxillary prominence. An obtuse angle (> 110°) indicates retroclined upper incisors (as in Class II div 2) or maxillary skeletal retrusion.

Lip Competence and Perioral Muscle Activity

Evaluating resting lip posture is essential for determining soft tissue stability following orthodontic tooth movement:

1. Competent Lips: The lips produce an airtight oral seal at rest without any conscious contraction of the orbicularis oris or mentalis muscles.
2. Incompetent Lips: The lips are separated by more than 3 to 4 mm at rest. Achieving a lip seal requires active, strained contraction of the circumoral musculature and the mentalis muscle (visible clinically as "mentalis puckering" or chin strain).
3. Potentially Competent Lips: The lips are morphologically of normal length and would easily seal at rest, but are physically held apart by severely proclined upper central incisors (e.g. Class II div 1 with an overjet of 10 mm). Once the incisors are retracted orthodontically, the lips become completely competent.
4. Lip Trap: A clinical scenario in Class II division 1 where the lower lip habitually rests entirely behind the proclined upper central incisors. The continuous resting posture and swallowing thrust of the lower lip against the palatal surfaces of the upper incisors actively exacerbates and maintains the increased overjet.

Smile Aesthetics and Incisor Show

• Incisor Display at Rest: With lips relaxed, 2 to 4 mm of the maxillary central incisor edge should be visible in young adults. This display naturally decreases with advancing age due to soft tissue laxity.
• Incisor Display on Full Smile: Ideally, 75% to 100% of the clinical crown of the maxillary central incisors is displayed, with up to 1 to 2 mm of continuous gingival margin show. Excessive gingival display (> 3–4 mm) is termed a "gummy smile" (vertical maxillary excess, hypermobile upper lip, or altered passive eruption).
• Smile Arc: The contour of the maxillary incisal edges relative to the curvature of the lower lip during a social smile:
  • Consonant Smile Arc (Aesthetic): The incisal edge curve follows and parallels the gentle upward concavity of the lower lip.
  • Flat or Reverse Smile Arc (Unaesthetic): The incisal edges are straight or curve downward contrary to the lower lip; often an iatrogenic complication of improper bracket placement or excessive orthodontic intrusion of maxillary anterior teeth.
• Buccal Corridors: The negative dark space between the buccal surfaces of the posterior teeth and the corners of the mouth during smiling. Normal buccal corridors are aesthetic; excessively wide corridors suggest transverse maxillary arch collapse, whereas completely eliminated corridors produce an artificial, "denture-like" broad appearance.

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