What Is Downs Analysis?
Downs analysis was introduced by William B. Downs in 1948, making it the first standardised cephalometric analysis in the orthodontic literature. Downs developed his norms from lateral cephalograms of 20 white American adolescents (10 male, 10 female) with excellent dental occlusion, establishing a baseline for what balanced craniofacial relationships looked like.
The analysis comprises 10 measurements in total — five skeletal measurements that assess facial profile and jaw relationships, and five dental measurements that evaluate incisor position and angulation relative to facial planes. Because it was developed before modern imaging, all measurements are performed on 2D lateral cephalograms.
Despite being over 75 years old, the Downs analysis remains clinically relevant. Its skeletal measurements — particularly the facial angle, angle of convexity, and Y-axis — are still used in contemporary orthodontic diagnosis and are referenced by more recent analyses like Steiner and Tweed. Understanding Downs provides the conceptual foundation for most cephalometric analysis systems in use today.
For a broader introduction to how cephalometric analysis fits into the diagnostic workflow, see our guide on cephalometric analysis. To compare Downs against other analysis modules, see our cephalometric software comparison.
All 10 Downs Measurements — Norms and Interpretation
Downs analysis is divided into five skeletal and five dental measurements. Each measurement has an established mean value and clinical range. Values outside this range indicate skeletal or dental imbalance requiring clinical interpretation in context of the full diagnostic record.
| Measurement | Type | Mean Norm | Clinical Range | High Value | Low Value |
|---|---|---|---|---|---|
| Facial Angle | Skeletal | 87.8° | 82° – 95° | Prognathic mandible | Retrognathic mandible |
| Angle of Convexity | Skeletal | 0° | -8.5° to +10° | Class II convex profile | Class III concave profile |
| A-B Plane Angle | Skeletal | -4.8° | -9° to 0° | Class II denture bases | Class III denture relationship |
| Mandibular Plane Angle | Skeletal | 21.9° | 17° – 28° | Hyperdivergent / open bite | Hypodivergent / deep bite |
| Y-Axis (S-Gn to FH) | Skeletal | 59.4° | 53° – 66° | Downward-forward growth | Horizontal growth pattern |
| Occlusal Plane Angle | Dental | 9.3° | 1.5° – 14° | Steep occlusal plane | Flat occlusal plane |
| Interincisal Angle | Dental | 135.4° | 130° – 150.5° | Retroclined incisors | Proclined / bimaxillary protrusion |
| L1 to Occlusal Plane | Dental | 14.5° | 3.5° – 20° | Proclined lower incisor | Retroclined lower incisor |
| IMPA (L1 to MP) | Dental | 91.4° | 83° – 98° | Proclined / forward tipped | Upright / retroclined |
| U1 Protrusion (to APog) | Dental | +2.7 mm | 0 – 5 mm | Protruded upper incisors | Retruded upper incisors |
Norms derived from Downs (1948, 1956). Range values reflect ±2SD from the reported sample mean.
Clinical note on the skeletal measurements: The facial angle, angle of convexity, and A-B plane angle together describe the antero-posterior skeletal pattern. Interpret them as a set — a single discrepant value is less meaningful than a consistent pattern across all three measurements. The mandibular plane angle and Y-axis jointly describe the vertical dimension and growth direction.
Landmarks Required for Downs Analysis
Accurate landmark identification is the single largest source of error in cephalometric analysis. Downs analysis requires the following landmarks on a lateral cephalogram. In BCeph, landmarks are placed manually with magnification controls to ensure precision.
Clinical Interpretation of Downs Analysis
Reading the Skeletal Pattern
The five skeletal measurements should be interpreted together, not in isolation. The facial angle tells you where the chin sits relative to the upper face — a high value indicates mandibular prognathism, a low value indicates retrognathia. The angle of convexity and A-B plane angle refine this by describing the relationship between the maxillary and mandibular denture bases. In a Class II patient you typically see a low facial angle, positive convexity angle, and a less negative A-B plane angle.
The mandibular plane angle and Y-axis describe the vertical dimension. Both increasing together suggest a hyperdivergent (high angle) pattern with downward-backward mandibular growth. Both decreasing together suggest a hypodivergent (low angle) pattern. A discrepancy between the two warrants careful evaluation of landmark placement.
Reading the Dental Pattern
The dental measurements evaluate how the teeth have compensated for — or failed to compensate for — the underlying skeletal pattern. In a Class II skeletal case, the lower incisors may be proclined (low IMPA) as a dentoalveolar compensation. The interincisal angle captures the combined angulation of both incisor pairs; a low interincisal angle confirms significant proclination of one or both incisor groups.
The upper incisor protrusion measurement (U1 to A-Pog line) is comparable to the Ricketts and Steiner measurements for upper incisor position. A value above 5 mm indicates frankly protruded upper incisors regardless of the skeletal pattern. See also Ricketts analysis for the lower incisor protrusion to A-Pog norm of +1 mm.
The Downs Template
Downs developed a graphic template that visually plots each measurement as a deviation from the norm — a precursor to the polygon-style analysis summaries used in modern software. BCeph's report output displays each measurement with norm ranges and colour-coded deviation indicators, providing an equivalent visual summary without the manual template work.
Run Downs Analysis Free in BCeph
BCeph includes a complete Downs analysis module. Upload your lateral cephalogram, place the required landmarks, and all ten measurements are calculated and displayed automatically. No installation. No cloud upload. No subscription.
All patient data — including the cephalogram image and all landmark coordinates — remains on your device throughout the session. BCeph never uploads to any server, making it architecturally HIPAA-aligned without requiring a Business Associate Agreement.
BCeph also includes: Steiner analysis, Ricketts analysis, McNamara analysis, Wits appraisal, Tweed analysis, Björk-Jarabak analysis, Kim analysis, Holdaway analysis, and E-Line analysis. All modules are free with no feature gating.
Compared to paid alternatives like Dolphin Imaging ($1,000–2,000/year) or CephX ($79–199/month), BCeph delivers the core 2D lateral cephalometric workflow — including Downs — at zero cost. For residents tracing practice cases or solo practitioners running a lean diagnostic workflow, there is no cheaper option that matches this analytical depth.