Grummons Analysis
The Grummons analysis is a frontal (posteroanterior) cephalometric method published by Dr. Duane Grummons and Dr. Margarite A. Martin in 1987, designed specifically to quantify facial asymmetry. Where a lateral cephalogram describes the face from front to back, the frontal film describes it from side to side — and Grummons' method turns that view into a structured, reproducible map of where a patient's asymmetry lives and how large it is.
Its defining feature is that it uses no normative database. Instead of comparing the patient to a population average, the analysis compares the patient's right side against their own left side. The reference is therefore perfect symmetry, and every asymmetry measurement has an ideal value of zero. This makes the analysis independent of the patient's age, sex, and ethnic background, and is the main reason it remains a standard tool for planning asymmetry correction and orthognathic (jaw) surgery.
What It Evaluates
Grummons answers two questions that a clinical photograph alone cannot: at which anatomical level does the asymmetry originate, and how much of it is there? The analysis works down the face level by level — cranial base, midface, maxilla (upper jaw), mandibular body, and chin — so a deviated chin can be traced back to its actual source rather than simply described as "the chin is off center".
It also checks whether the horizontal structures of the face are level with one another. A face can have perfectly matched left-right widths and still be asymmetric if the maxilla or the occlusion is tilted (canted) relative to the skull, so the parallelism of the horizontal planes is evaluated alongside the side-to-side distances.
Learn more: Posteroanterior Cephalometric Analysis — Pocket Dentistry
Key Measurements
The analysis is built on a single vertical reference: the Mid-Sagittal Reference line (MSR), constructed from crista galli (a bony ridge in the midline of the skull base) through ANS (anterior nasal spine, the forward tip of the upper jaw's nasal floor) and extended down to the chin. Every asymmetry measurement is taken against this line, and four horizontal planes are used to organize the face into levels: the Z-plane (through the zygomaticofrontal sutures, the most stable horizontal reference on a frontal film), the zygomatic arch plane, the jugal plane (through the maxillary base), and a plane through menton (the lowest point of the chin).
- Transverse distance to the MSR, per side — the perpendicular distance from each paired landmark to the mid-sagittal line, measured separately on the right and the left. Landmarks used include zygion (Zy, the widest point of the cheekbone), jugale (J, the junction where the upper jaw meets the cheekbone — the maxillary skeletal width), and the antegonial notch (Ag, the concavity on the lower border of the mandible — the mandibular skeletal width). Norm: right equals left.
- Left-to-right difference at each level — the numerical difference between the two sides at the midface, maxillary, and mandibular levels. Norm: 0 mm. This is the measurement that localizes the asymmetry: a difference confined to the mandibular level points to the lower jaw, while differences present at every level point to a whole-face asymmetry originating higher in the skull.
- Vertical distance to the Z-plane, per side — the perpendicular distance from each paired landmark down to the Z-plane, comparing right against left. Norm: right equals left. This separates vertical asymmetry (one side shorter than the other) from transverse asymmetry (one side wider than the other).
- Horizontal plane parallelism (cant) — the angle between each horizontal plane and the Z-plane. Norm: 0°. A canted jugal or occlusal plane means the structure is tilted rather than merely displaced.
- Midline deviation of the chin — the distance from menton to the MSR, which quantifies the chin deviation the patient and clinician actually see. Norm: 0 mm.
- Frontal vertical proportions — the ratio of the upper facial segment (crista galli to ANS) to the total facial height (crista galli to menton), used as a secondary check on vertical facial balance.
Learn more: Application of Grummons Analysis for Three-dimensional Facial Asymmetry Assessment
Clinical Interpretation
Because the norm is symmetry rather than a population average, the numbers are read as a gradient down the face. The clinician starts at the top: if the midface distances (zygion, jugale) are equal but the mandibular distances (antegonion, menton) are not, the asymmetry is mandibular in origin — typically a difference in ramus height or condylar growth on one side, which points toward a temporomandibular joint or growth cause and, in adults, often toward surgical rather than orthodontic correction. If the asymmetry is already present at the cranial base and midface levels, the mandible may simply be following an asymmetric foundation, and correcting the lower jaw alone would leave the face unbalanced.
The distinction between displacement and cant drives different treatment mechanics. A maxilla shifted sideways but level needs transverse repositioning; a maxilla that is level in position but canted needs differential vertical movement — one side moved down, the other up — which is a different plan with different anchorage requirements. Because some degree of asymmetry is present in virtually every face, the practical question is not whether asymmetry exists but whether it exceeds the threshold of visual detectability (generally around 3-4 mm or 3-4° at prominent landmarks), and whether the treatment plan can realistically address it. Grummons is normally read together with the lateral cephalometric analysis: the two films combined give the three-dimensional picture that neither provides alone.
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