Neutral Symmetry
Neutral Symmetry evaluates how balanced the two sides of a patient's face are when the face is completely at rest — no smiling, no talking, no muscular tension. Using a single frontal-view photograph, the clinician compares the left and right halves of the face against a vertical facial midline, looking for shifts, tilts, or size differences between paired structures such as the eyes, cheeks, and sides of the jaw.
This assessment matters because facial symmetry is one of the strongest visual cues patients and clinicians use to judge attractiveness and treatment success, and because the position of the facial midline is a key diagnostic anchor. Deviations between the facial midline and the dental midlines (upper and lower) often signal an underlying skeletal, dental, or functional asymmetry that needs to be accounted for in treatment planning — not just corrected cosmetically at the level of the teeth.
What It Evaluates
On a frontal photograph taken with the patient's face relaxed and the head in natural head position, Neutral Symmetry looks at:
- The facial midline — a vertical reference line running down the center of the face, typically constructed by connecting the glabella (midpoint between the eyebrows) and the subnasale (base of the nose), and extended down toward the chin.
- Bilateral balance of paired landmarks — comparing the left and right eye position (canthi), cheekbone prominence, ear height, and gonial angle (jaw corner) for symmetry.
- Horizontal reference lines — the interpupillary (bipupillary) line, the canthal line (connecting the outer corners of the eyes), and the commissural line (connecting the corners of the mouth) are checked for being level and parallel to one another.
- Alignment of the chin and dental midlines to the facial midline — whether the soft-tissue pogonion (chin point) and the upper/lower dental midlines sit on, or deviate from, the facial midline.
Learn more: Clinical Dental Photography Standards: A Comprehensive Guide for Dentists and Orthodontists
Key References / Landmarks
- Facial midline (Glabella–Subnasale line) — The primary vertical reference for the whole analysis; ideally it passes through the tip of the nose, the philtrum, and the chin point with no lateral shift.
- Soft-tissue pogonion vs. facial midline — If the chin point falls off the midline, the mandible is considered deviated toward that side, which is a common sign of a skeletal or functional asymmetry rather than a purely dental issue.
- Bipupillary line — The horizontal line through the pupils; used as a level reference for the rest of the face and should be roughly parallel to the interpupillary and commissural lines.
- Canthal line (bi-exocanthion line) — Connects the outer corners of both eyes; should be level and parallel to the commissural and bipupillary lines. A tilt here can indicate orbital or maxillary asymmetry.
- Commissural line — Connects the corners of the mouth; compared against the canthal line to check for occlusal cant or lip asymmetry.
- Symmetry ratio of bilateral landmarks — For paired points (e.g., outer eye corners, mouth corners) equidistant from the midline, the ratio of the shorter to the longer distance is calculated; a ratio of 1.0 is perfect symmetry, and lower ratios indicate more pronounced asymmetry.
- Clinical detectability threshold — Published research indicates that asymmetries below roughly 3–4 mm (or 3–4° of canting) at prominent landmarks such as the oral commissure or brow line are generally not visually noticeable to an observer, which helps separate clinically significant asymmetry from normal facial variation.
Clinical Interpretation
Almost no face is perfectly symmetric, so the goal of this analysis is not to find "perfect" symmetry but to distinguish normal, non-noticeable variation from asymmetry that is large enough to be visible and clinically relevant. When the facial midline does not line up with the dental midlines, the orthodontist must decide whether to correct the dental midline to match the true facial midline (often the better esthetic choice) or to accept some dental midline discrepancy because the facial asymmetry itself is skeletal in origin and not correctable with aligners alone.
Findings from Neutral Symmetry feed directly into treatment planning decisions: a canted canthal or commissural line may point toward the need for differential vertical tooth movement or coordination with other specialists, a chin deviated from the facial midline may reshape expectations for how much the dental midline can realistically be improved, and a documented baseline lets the clinician track whether treatment is helping, worsening, or having no effect on the patient's facial balance over time. Because this analysis is done at rest, it also serves as the neutral baseline against which dynamic analyses (e.g., symmetry during smiling) are later compared.
Learn more: Facial Asymmetry | Orthodontics by Dr. Kieran Daly