Ricketts analysis explained: the lateral measurements in Simplified Ceph
Key points
- Simplified Ceph computes 30 Ricketts readings on the lateral cephalogram, in five groups: chin in space, convexity and maxilla, teeth, profile, and cranial structure and ramus.
- The frame is Frankfort horizontal (FH) and the pterygoid vertical (PtV), a line through point Pt at a right angle to FH.
- Several readings use constructed points: CF where PtV crosses FH, CC where the facial axis crosses Ba-N, and Xi at the centre of the ramus.
- For some readings, the reference value Simplified Ceph shows changes with the age and sex entered for the patient. The readings themselves do not.
- Simplified Ceph shows the published reference value next to each reading. This article explains what each reading measures and gives no reference values.
What the Ricketts analysis is
The Ricketts analysis is named after its author, R. M. Ricketts [1]. In Simplified Ceph it covers his lateral summary and comprehensive analysis, measured on FH and the pterygoid vertical. It is the largest analysis in the tool, so this article goes group by group and gives each reading as the tool defines it, with its value on the Simplified Ceph sample tracing.
Every reading is measured from landmarks, points placed on the radiograph at defined sites [2]. Other sources may define a point or a line slightly differently, which is worth knowing before comparing numbers from two programs. Simplified Ceph also has a separate Ricketts frontal analysis, on the frontal (PA) cephalogram, in the Plus and Pro plans. This article covers the lateral analysis only.
The frame and the constructed points
- FH: from porion (Po), the highest point on the upper margin of the external auditory meatus, to orbitale (Or), the lowest point on the lower margin of the orbit.
- Pt point: the junction of the lower border of the foramen rotundum with the back wall of the pterygomaxillary fissure.
- PtV, pterygoid vertical: a line through Pt at a right angle to FH. Distances “to PtV” are measured parallel to FH, positive in front of the line.
- CF, centre of the face: where PtV crosses FH.
- Ba-N: from basion (Ba), the lowest and most posterior point on the front margin of the foramen magnum, to nasion (N).
- Facial axis: from Pt to gnathion (Gn). CC is where it crosses Ba-N.
- Xi point: the centre of the ramus. Simplified Ceph builds it from four ramus points: R1, the deepest point on the front border of the ramus; R2, the point on the back border opposite R1; R3, the lowest point of the sigmoid notch; and R4, the point on the lower border of the mandible below R3. Measured in the FH frame, Xi lies midway between R1 and R2 from front to back and midway between R3 and R4 from top to bottom.
- DC: the centre of the neck of the condyle, where the Ba-N line crosses it.
- PM, protuberance menti: the point above pogonion where the outline of the symphysis changes from concave to convex.
- Functional occlusal plane: from the midpoint of the cusp overlap of the first molars to that of the first premolars.
Chin in space
| Reading | How Simplified Ceph measures it | Sample tracing |
|---|---|---|
| Facial axis | Angle between Ba-N and the facial axis Pt-Gn | 93.3° |
| Facial depth | Inner angle where the facial plane N-Pog meets FH | 88.4° |
| Mandibular plane to FH | Angle between FH and Go-Me | 24.5° |
| Lower facial height | Angle ANS-Xi-PM, at Xi | 44.9° |
| Mandibular arc | 180° minus the angle DC-Xi-PM: the angle between the line DC-Xi, continued forward past Xi, and Xi-PM | 25.8° |
Simplified Ceph also combines these five readings into a short summary of the facial pattern, from how far each lies from its reference value. This article does not cover that summary.
Convexity and maxilla
| Reading | How Simplified Ceph measures it | Sample tracing |
|---|---|---|
| Convexity | Distance from point A to the facial plane N-Pog, at a right angle to it; positive when A lies in front | 1.6 mm |
| Maxillary depth | Inner angle where N-A meets FH, measured the same way as facial depth | 90.0° |
| Maxillary height | Angle N-CF-A, at CF | 59.2° |
| Palatal plane to FH | Angle between the palatal plane (PNS-ANS) and FH; positive when the front of the palatal plane is tipped up | 2.2° |
| Landes angle | Angle Ba-N-A, at nasion | 64.6° |
Teeth
| Reading | How Simplified Ceph measures it | Sample tracing |
|---|---|---|
| Lower incisor to A-Pog | Distance from the lower incisal edge to the A-Pog line; positive in front | 2.1 mm |
| Lower incisor inclination | Angle between the lower incisor long axis and the A-Pog line | 23.2° |
| Upper incisor to A-Pog | Distance from the upper incisal edge to the A-Pog line; positive in front | 5.3 mm |
| Upper incisor inclination | Angle between the upper incisor long axis and the A-Pog line | 25.4° |
| Upper molar to PtV | Distance from PtV to the distal surface of the upper first molar crown (A6), parallel to FH | 19.0 mm |
| Interincisal angle | Angle between the upper and lower incisor long axes | 131.5° |
| Overjet | Distance from the lower to the upper incisal edge along the functional occlusal plane | 3.3 mm |
| Overbite | Distance from the upper to the lower incisal edge at a right angle to the functional occlusal plane; positive when they overlap | 1.7 mm |
| Lower incisor extrusion | Height of the lower incisal edge above the functional occlusal plane; negative below it | −0.4 mm |
| Molar relation | Distance from the distal surface of the lower first molar (B6) to that of the upper (A6), along the functional occlusal plane; negative when A6 lies behind B6 | −3.3 mm |
Profile
| Reading | How Simplified Ceph measures it | Sample tracing |
|---|---|---|
| Lower lip to E-line | Distance from the lower lip (Li) to the E-line, from the nose tip (Pn) to the soft tissue chin (Pog′); positive in front | −2.3 mm |
| Upper lip length | Distance from ANS to the lowest point of the upper lip vermilion (stomion superius) | 25.1 mm |
| Lip embrasure to occlusal plane | Height of the lip embrasure (midway between the two stomion points) relative to the functional occlusal plane; negative when the embrasure lies above the plane | −3.0 mm |
Ricketts introduced the E-line in 1968 [3]. The soft tissue profile lines article explains it next to two other lip lines.
Cranial structure and ramus
| Reading | How Simplified Ceph measures it | Sample tracing |
|---|---|---|
| Cranial base angle | Angle N-S-Ba, at sella | 132.0° |
| Ba-S-PNS | Angle Ba-S-PNS, at sella | 60.7° |
| Cranial deflection | Angle between Ba-N and FH | 25.4° |
| Anterior cranial length | Distance from CC to nasion | 59.0 mm |
| Ramus height | Distance from CF to gonion | 63.1 mm |
| Ramus position | Angle between FH and the line CF-Xi, on the back side | 72.9° |
| Porion location | Distance from PtV to porion, parallel to FH; negative behind PtV | −39.0 mm |
Worked example: the sample tracing
The values in the tables above come from the Simplified Ceph sample tracing (Load a sample tracing), a drawn example, not a patient. We computed them with the tool’s own code, as the tool shows them when the sample is loaded: calibrated, profile facing right, entered as a 25-year-old female. Four things stand out.
- Shared readings. Facial depth (88.4°) uses the same lines as the Downs facial angle. The mandibular plane to FH (24.5°) is the same angle in Downs and McNamara. The facial axis (93.3°) minus 90° is McNamara’s facial axis angle (3.3°). The lower incisor to A-Pog (2.1 mm) appears in McNamara, and the upper incisor to A-Pog (5.3 mm) in Downs. Each analysis compares these with its own reference value.
- Constructed points follow FH. CF and Xi are built in the FH frame. Raising orbitale by 1 mm, with every other point left in place, changed facial depth from 88.4° to 87.7°, the palatal plane to FH from 2.2° to 1.5° and the upper molar to PtV from 19.0 to 18.5 mm. Lower facial height (44.9° to 45.0°) and the mandibular arc (25.8° to 25.6°) changed too, although neither angle uses FH directly: Xi moved with the frame.
- Porion moves CF. Raising porion by 1 mm instead changed the ramus height from 63.1 to 63.5 mm and the maxillary height from 59.2° to 59.3°, through CF.
- Age and sex change the reference values only. Loading the same tracing with another age or sex gives the same 30 readings. Only the reference values shown next to some of them change, because Simplified Ceph adjusts those for growth where an adjustment is defined.
Limits
- Landmarks are placed by eye. Pt, basion, the ramus points and DC lie where several outlines overlap. Two careful people can place a point on a curve in different spots [4]. The cephalometric landmarks article covers identification error.
- Constructed points inherit errors. Xi depends on four ramus points and on FH, CC on two lines, and CF on Pt and FH. An error in any of them moves every reading built on the point, as the worked example shows.
- Millimetres need calibration. Distances are only as accurate as the calibration on the film ruler. Simplified Ceph shows a millimetre reading only after the radiograph is calibrated.
- Reference values come from particular samples. Most reference values come from specific study groups, so read them with the patient’s age, sex and ethnic background in mind.
- Check your own error. Tracing a few films again after a while shows how far your own points move [5].
- Description, not decision. This article describes the measurements. It does not cover diagnosis or treatment planning.
Do this in Simplified Ceph
Simplified Ceph includes the Ricketts analysis: the lateral summary and comprehensive analysis on Frankfort and the pterygoid vertical, with norms adjusted for age where they are defined. You place the landmarks on a lateral cephalogram, and the readings update as you go. Simplified Ceph shows the published reference value next to each reading. There is a Free plan for lateral cephalometric analysis; the Ricketts frontal analysis is in Plus and Pro.
Educational content for clinicians and students. Reference values vary between populations. This page does not replace clinical judgement.
References
- Ricketts RM. A foundation for cephalometric communication. Am J Orthod. 1960;46(5):330-357. doi:10.1016/0002-9416(60)90047-6.
- Jacobson A, Jacobson RL, eds. Radiographic Cephalometry: From Basics to 3-D Imaging. 2nd ed. Chicago: Quintessence; 2006. ISBN 978-0-86715-461-0.
- Ricketts RM. Esthetics, environment, and the law of lip relation. Am J Orthod. 1968;54:272-289. doi: 10.1016/S0002-9416(68)90278-9
- Baumrind S, Frantz RC. The reliability of head film measurements. 1. Landmark identification. Am J Orthod. 1971;60(2):111-127. PMID: 5283996.
- Houston WJB. The analysis of errors in orthodontic measurements. Am J Orthod. 1983;83(5):382-390. doi:10.1016/0002-9416(83)90322-6.
More to read
- Cephalometric analysis in Simplified CephRicketts and the other analyses in the tool
- Cephalometric landmarks explainedThe main points and reference lines, and sources of identification error
- Downs analysis explainedThe Frankfort-based skeletal and dental readings
- McNamara analysis explainedThe nasion perpendicular, jaw lengths and airway
- Steiner analysis explainedSNA, SNB, ANB and the other Steiner readings
- Soft tissue profile lines explainedThe E-line next to the S-line and Burstone’s line
- All articlesOrthodontic analyses, explained