Vertical Asymmetry Analysis
Vertical Asymmetry is a frontal (posteroanterior) cephalometric analysis that evaluates asymmetry in the up-and-down dimension rather than the side-to-side one. Two faces can have identical left and right widths and still look markedly unbalanced if one side of the mandible is vertically shorter than the other, or if the upper teeth are tilted so that one side of the smile sits lower than the other. This analysis is built specifically to detect and quantify that pattern.
It is the natural complement to the Grummons asymmetry analysis. Grummons is primarily transverse — how far each structure sits from the facial midline — while this analysis measures how far each structure sits below a stable horizontal reference, comparing right against left at each vertical level. Like Grummons, it is entirely self-referential: the norm is the patient's own symmetry, so no population data, age, or sex adjustment is involved.
What It Evaluates
The analysis uses the Z-plane — the line connecting the left and right zygomaticofrontal sutures (where the cheekbone joins the frontal bone) — as its horizontal reference. This plane is chosen because it is one of the most reproducible and growth-stable structures visible on a frontal radiograph, which makes it a trustworthy "true horizontal" for the skull even when the rest of the face is asymmetric.
From that reference, the vertical height of the mandible is measured on both sides at three levels — the condyle (the jaw joint), the gonial angle (the corner where the ramus meets the body of the jaw), and the antegonial notch (the concavity on the lower jaw border just in front of the jaw corner) — plus the midline height to menton (the lowest chin point). The upper first molars are then used to measure the cant of the occlusal plane: whether the biting surface of the upper teeth is level with the skull or tilted.
Learn more: Mandibular Asymmetry — Pocket Dentistry
Key Measurements
- Z-plane to condyle, left and right — the vertical distance from the horizontal reference down to the lateral pole of each condyle. A difference here means the jaw joints themselves sit at different heights, which usually reflects an asymmetry in the joint or in the cranial base rather than in the jaw itself. Norm: left equals right.
- Z-plane to gonion, left and right — the vertical distance to each jaw corner. Combined with the condylar height, this isolates the ramus (the vertical branch of the mandible): a short ramus on one side is the single most common cause of a canted, deviated mandible.
- Z-plane to antegonion, left and right — the vertical distance to the antegonial notch on each side, describing the vertical level of the body of the mandible.
- Z-plane to menton — the vertical height at the midline of the chin, used as the overall lower facial height reference.
- Left-to-right difference at each level — the difference between the paired heights at the condylar, gonial, and antegonial levels. Norm: 0 mm. The level at which the difference first appears is what localizes the asymmetry.
- Occlusal plane cant — the angle between the line joining the left and right upper first molar cusps and the Z-plane. Norm: 0° ± 2°. Values beyond this range indicate that the upper occlusion is tilted relative to the skull, with one side of the arch positioned lower than the other.
Learn more: Occlusal Cant and Its Challenges — A Review
Clinical Interpretation
The measurements are read top-down, and the level where the left-right difference appears tells the clinician where to intervene. If condylar heights match but gonial heights differ, the ramus is shorter on one side and the mandible is effectively rotated — a pattern typical of unilateral condylar hypoplasia (underdevelopment) or of joint degeneration that has reduced height on one side. If the difference is already present at the condyle, the asymmetry originates above the mandible, in the joint position or cranial base, and mandibular surgery alone would not fully resolve it. If all mandibular heights match but the occlusal plane is canted, the asymmetry is dentoalveolar rather than skeletal, and can usually be addressed with differential vertical tooth movement.
The occlusal cant deserves particular attention because it is the measurement patients notice. A canted occlusal plane is visible in the smile as an uneven gingival display and an uneven incisal edge line, and published work has shown that mandibular lateral displacement on the frontal film is significantly associated with the cant of the functional occlusal plane, together with reduced posterior vertical dimension and ramus height on the side the mandible is displaced toward. Two practical cautions apply to every reading: the head must be positioned reproducibly when the film is taken, because head tilt can create or mask an apparent cant; and small differences should be judged against the visual detectability threshold — asymmetries below roughly 3-4 mm or 3-4° are generally not noticeable to an observer and may not justify treatment on their own.
Learn more: Diagnosing Mandibular Asymmetry Using Posteroanterior Cephalograms