Transverse Analysis (Betts)

The Transverse analysis is a frontal (posteroanterior) cephalometric method introduced by Dr. Norman J. Betts and colleagues, building on Ricketts' earlier frontal measurements. Its purpose is narrow and highly practical: to determine whether a patient's upper jaw is genuinely too narrow relative to the lower jaw at the skeletal level, and therefore whether widening it requires surgical assistance or can be achieved with orthopedic and dentoalveolar expansion alone.

This matters because a posterior crossbite — upper back teeth biting inside the lower ones — can arise from two very different causes. The teeth may be tipped inward over a normally sized jaw (a dental problem, correctable by uprighting them), or the maxillary bone itself may be narrow (a skeletal problem, where tipping the teeth outward only camouflages the discrepancy and tends to relapse). The frontal cephalogram is the conventional plain radiograph of choice for making that distinction, because it shows the skeletal bases of both jaws in the same transverse dimension.

What It Evaluates

The analysis is deliberately built around relative width rather than absolute width. Instead of measuring the maxilla and comparing it to a population table, it measures how far the maxillary base sits from a line drawn along the lateral facial contour of the same patient — from zygion (Zy, the widest point of the cheekbone) down to the antegonial notch (Ag, the concavity on the lower border of the mandible). The point measured against that line is jugale (J, the junction where the maxilla meets the cheekbone, representing the skeletal width of the upper jaw).

Because both jaws contribute to the reference on each side, the resulting value expresses the maxillomandibular width relationship for that side of the face, and it is measured independently on the right and the left. A crossbite present on only one side produces a normal value on the unaffected side and a deficient value on the affected one, which immediately separates unilateral from bilateral transverse deficiency.

Learn more: Diagnostic Methods for Assessing Maxillary Skeletal and Dental Transverse Deficiencies — A Systematic Review

Key Measurements

  • Maxillomandibular width, right side — the perpendicular distance from jugale (right) to the lateral facial line running from zygion (right) to the antegonial notch (right). Normal value: 10 mm ± 1.5 mm.
  • Maxillomandibular width, left side — the same measurement taken on the left. Normal value: 10 mm ± 1.5 mm.

A value below the normal range on one side indicates that the maxillary base is positioned too far inward relative to the facial and mandibular contour on that side: a skeletal transverse deficiency, as opposed to a dental one. A value above the range indicates the opposite — a relatively wide maxilla or a narrow mandible on that side.

The literature also describes a Maxillomandibular Transverse Differential Index (MMTDI), which combines the maxillary width (jugale to jugale) and mandibular width (antegonion to antegonion) into a single differential and applies the well-known rule that a discrepancy beyond roughly 5 mm calls for surgically assisted expansion rather than orthodontic camouflage. That index depends on age-matched expected widths, and is therefore reported separately from the per-side measurement above.

Learn more: Transverse Development of the Jaws — Norms for the Posteroanterior Cephalometric Analysis

Clinical Interpretation

This is the analysis that informs the expansion decision. In a growing patient with a skeletal transverse deficiency, the mid-palatal suture is still open and conventional rapid maxillary expansion can widen the bone itself. In a skeletally mature patient the suture has fused, so the same appliance mostly tips teeth and bends alveolar bone rather than separating the maxilla; when the deficiency is genuinely skeletal and substantial, the options become surgically assisted rapid palatal expansion (SARPE), miniscrew-assisted expansion (MARPE), or segmental surgery. Reading the two sides separately is what tells the clinician whether the expansion needs to be symmetric or differential.

Two caveats belong in any diagnostic report built on this analysis. Reliability: the frontal cephalogram superimposes many structures in a single image, which makes some landmarks harder to identify precisely; a systematic review comparing transverse analysis on frontal films against cone-beam CT found the frontal film misdiagnoses roughly 18% of transverse cases, against roughly 8% for CBCT. Magnification distortion and head rotation during exposure contribute to that error, so a borderline value should prompt a CBCT assessment rather than a treatment decision. Population: the Ricketts and Betts reference values were derived from Caucasian samples and should not be extrapolated to other ethnic groups without caution, since normal transverse proportions vary meaningfully between populations.

Learn more: Comparison of Transverse Analysis Between Posteroanterior Cephalogram and Cone-Beam Computed Tomography — The Angle Orthodontist

References