What Is Ricketts Analysis?
Robert M. Ricketts developed his cephalometric analysis through the Rocky Mountain Data Systems (RMDS) project, which processed thousands of cephalograms to identify reliable predictors of growth and treatment outcomes. The resulting analysis is one of the most comprehensive in orthodontics — it includes over 30 measurements in its full form, covering skeletal pattern, dental relationships, soft tissue profile, and even aesthetic balance.
The analysis is anchored by two unique features. First, the facial axis — the line from the PT point (at the pterygomaxillary fissure) to Gnathion — replaces the Y-axis as the primary descriptor of mandibular position and growth direction. The facial axis angle formed with the Ba-N line (cranial base) is remarkably stable across growth, making it one of the most reliable cephalometric measurements for long-term prediction. Second, Ricketts was among the first to adjust norms for age, recognising that skeletal and dental measurements change predictably during growth.
BCeph implements the core Ricketts measurements — the skeletal set and primary dental measurements — sufficient for a complete orthodontic diagnosis. For an overview of how Ricketts fits into the full diagnostic toolkit, see the cephalometric analysis guide. For comparison with the Steiner analysis approach, the key distinction is Ricketts' use of the Ba-N cranial base plane versus Steiner's SN plane.
Ricketts Measurements — Norms and Interpretation
| Measurement | Category | Mean Norm | SD | High Value | Low Value |
|---|---|---|---|---|---|
| Facial Axis (PT-Gn to Ba-N) | Skeletal | 90° | ± 3.5° | >90° = Anterior rotation | <90° = Posterior rotation |
| Facial Depth (FH to N-Pog) | Skeletal | 87° at age 9 | ± 3° | Prognathic mandible | Retrognathic mandible |
| Mandibular Plane Angle (FH–Go-Gn) | Skeletal | 26° at age 9 | ± 4° | Hyperdivergent | Hypodivergent |
| Lower Facial Height (ANS-Xi-Pm) | Skeletal | 47° | ± 4° | Increased lower face height | Decreased lower face height |
| Mandibular Arc (Dr-Xi to Xi-Pm) | Skeletal | 26° | ± 4° | Increased arc = anterior rotation | Decreased arc = posterior rotation |
| Convexity (A to N-Pog) | Skeletal | +2 mm at age 9 | ± 2 mm | Convex / Class II profile | Flat/concave / Class III |
| Lower Incisor Protrusion (L1 to APog) | Dental | +1 mm | ± 2 mm | Proclined / protruded L1 | Retruded / upright L1 |
| Lower Incisor Inclination (L1 to APog) | Dental | 22° | ± 4° | Proclined lower incisor | Retroclined lower incisor |
| Upper Incisor to FH (U1-FH) | Dental | 111° | ± 6° | Proclined upper incisor | Retroclined upper incisor |
| Molar Relation (U6 to PTV) | Dental | (Age ÷ 2) + 3 mm | ± 3 mm | Distal molar position | Mesial molar position |
| Interincisal Angle (U1-L1) | Dental | 130° | ± 10° | Retroclined incisors | Proclined / bimaxillary protrusion |
Norms from Ricketts (1960–1972). Age-adjusted norms apply to facial depth (grows ~0.33°/yr) and mandibular plane angle (decreases with growth). Convexity norm decreases ~0.2 mm/yr. Molar relation norm increases with age.
U1 to FH angle: The norm of 111° exceeds 90°, which means measurements using the acute angle between lines would give incorrect results. BCeph uses the full angle between line directions (not the acute-capped version) to compute U1 to FH correctly — a common source of error in manual implementations and some digital tools.
Landmarks Required for Ricketts Analysis
Ricketts analysis requires several unique landmarks not used in other analyses — particularly the PT point and Xi point. These require careful radiographic interpretation but are critical for the facial axis and lower facial height measurements respectively.
Clinical Interpretation of Ricketts Analysis
The Facial Axis as a Growth Predictor
The facial axis angle (PT-Gn to Ba-N) is stable at approximately 90° across growth — deviations from 90° reflect a structural feature of the craniofacial complex, not a transient developmental state. An angle above 90° means Gnathion lies forward of the perpendicular to Ba-N, indicating an anteriorly-rotated mandible — characteristic of a short-face, deep bite pattern. An angle below 90° indicates a posteriorly-rotated, long-face, open bite tendency.
Because the facial axis is stable with growth, a patient with a 93° facial axis at age 10 is expected to maintain that anterior rotation tendency into adulthood. This makes the facial axis highly valuable for long-term treatment planning — it informs the clinician about what the patient's face is structurally predisposed to do, not just its current state.
Convexity and Skeletal Pattern
Ricketts convexity measures the perpendicular distance from A point to the N-Pog facial plane. Unlike the Downs angle of convexity (which measures the angle at A point), Ricketts convexity is a linear measurement in millimetres. Positive values (A anterior to N-Pog) indicate a convex, Class II skeletal profile. Values at or below 0 mm indicate a Class I or Class III flat/concave profile. The age adjustment (−0.2 mm per year from age 9 onwards) reflects normal forward growth of the chin relative to A point during adolescence.
Lower Incisor Position: Protrusion vs Inclination
Ricketts' separate measurement of lower incisor protrusion (distance) and inclination (angle) relative to the A-Pog line allows clinicians to distinguish between a lower incisor that is tilted forward (high inclination, normal protrusion) versus one that has bodily moved forward (high protrusion, possibly normal inclination). This distinction matters clinically: bodily protrusion has different soft tissue implications and stability characteristics than axial inclination change. Cross-reference with the Tweed IMPA and Downs IMPA measurements for a complete lower incisor diagnostic picture.
Run Ricketts Analysis Free in BCeph
BCeph implements the full core Ricketts measurement set including the facial axis angle (using the full angle between line directions, not the acute-capped version), convexity, mandibular plane, lower facial height, and all dental measurements. The U1-FH angle is computed correctly at approximately 111° — a value that requires the full angle calculation rather than the acute-angle clipping used in some implementations.
The PT point, Xi point, and PTV are supported in BCeph's landmark set. Landmark placement assistance is provided in the tool's interface for the more complex constructed landmarks. All data stays on your device throughout the session.