Midlines Analysis (Svanholt-Solow)
The Svanholt-Solow analysis was described by Svanholt and Solow in 1977 to study one specific aspect of transverse craniofacial development: the relationships between the midlines of the jaws and the midlines of the dental arches. It is the frontal cephalometric method that answers the question a deviated dental midline always raises — why is it off center?
An off-center dental midline is one of the most common and most persistent findings in orthodontics, and it has several possible causes that call for entirely different treatment: the upper jaw may be displaced sideways, the lower jaw may be displaced, the two jaws may be rotated relative to each other, or the teeth may simply have drifted or tipped sideways within jaws that are themselves correctly positioned. Correcting a dental midline that is compensating for a skeletal displacement produces a straight-looking arch on an asymmetric skeleton, which tends to relapse and can leave the face looking worse rather than better.
What It Evaluates
The analysis is built on a single principle that makes it unusually easy to read: every variable is constructed so that it equals zero in a perfectly symmetric subject. There is no population norm to consult and no age or sex adjustment — a value of zero means "centered", and the sign of the number tells the clinician which way the structure is displaced.
The reference is a mid-sagittal line built from the orbital region: a horizontal line is drawn between the left and right latero-orbitale points (the outer border of the orbit, where the eye socket meets the cheekbone), and the mid-sagittal reference is erected perpendicular to that line through its midpoint. Against that vertical reference, the analysis locates the midpoint of the maxillary base, the midpoint of the mandibular base, and the dental midline of each arch, then compares each one to its own skeletal base and to the opposing one.
Learn more: Posteroanterior Cephalometric Analysis — Pocket Dentistry
Key Measurements
The seven original variables fall into three groups: where each jaw sits, how the jaws relate to each other, and where the teeth sit relative to their own bone.
- Transverse maxillary position — the signed distance from the midpoint of the maxillary base (the midpoint between the left and right jugale points) to the mid-sagittal reference. Norm: 0 mm ± 2 mm. A non-zero value means the whole upper jaw is displaced to one side.
- Transverse mandibular position — the signed distance from the midpoint of the mandibular base (the midpoint between the left and right antegonial notches) to the mid-sagittal reference. Norm: 0 mm ± 2 mm.
- Transverse jaw relationship — the angle between the mandibular corpus line (antegonion to antegonion) and the maxillary plane (jugale to jugale). Norm: 0° ± 2°. This detects a transverse rotation of one jaw relative to the other, which is a different problem from a sideways displacement and requires different mechanics.
- Upper incisal position — the position of the upper dental midline relative to its own skeletal base, i.e. how far the upper teeth have drifted within the maxilla. Norm: 0 mm ± 2 mm.
- Lower incisal position — the same measurement for the lower dental midline relative to the mandible. Norm: 0 mm ± 2 mm.
- Upper incisal compensation — the position of the upper dental midline relative to the opposing base (the mandible). Norm: 0 mm ± 2 mm. This is the variable that reveals dentoalveolar compensation: teeth that have moved sideways to meet a displaced opposing jaw.
- Lower incisal compensation — the position of the lower dental midline relative to the maxillary base. Norm: 0 mm ± 2 mm.
Learn more: PA Cephalometric Analysis — Svanholt & Solow variables
Clinical Interpretation
The variables are designed to be read as a decision tree. If both jaw positions are near zero and the jaw relationship angle is normal, but an incisal position is displaced, the problem is purely dental — the teeth have drifted within a symmetric skeleton, and orthodontic midline correction will both look right and be stable. If a jaw position is displaced and the incisal position relative to that same jaw is near zero, the teeth are correctly centered on a displaced base: the dental midline deviation is skeletal in origin, and moving the teeth to the facial midline would decentre them on their own bone.
The compensation variables identify the intermediate and most clinically demanding case: a skeletal displacement that the dentition has already partially masked by drifting toward the opposing arch. Here the visible dental midline discrepancy understates the underlying skeletal one, and treatment must decide explicitly whether to reinforce the compensation (accepting the skeletal asymmetry, a reasonable choice for small discrepancies) or to decompensate the teeth first so the skeletal problem can be addressed orthopedically or surgically. A non-zero transverse jaw relationship angle adds a further constraint — with the two bases rotated relative to each other, no single sideways movement will coordinate the arches, and differential expansion or surgical repositioning becomes part of the discussion.
Learn more: Transverse Skeletal and Dental Asymmetry — Langberg, AJODO