Cephalometric Analyses Compared: Downs, McNamara, Sassouni
There is no single cephalometric analysis. Each author chose landmarks, planes and norms to answer a different question: where the jaws sit, where the incisors should go, which way the face grows. This guide compares seven analyses met in courses and in the literature (Downs, Steiner, Tweed-Merrifield, Ricketts, McNamara, Sassouni and Björk-Jarabak) with the idea, key measurements, contribution and limits of each. It ends with a frequent question, which analysis to use for a skeletal open bite, answered with criteria rather than one name.
The seven analyses at a glance
| Analysis | Main reference | Core idea | Key measurements | What it brings | Main limit |
|---|---|---|---|---|---|
| Downs | Frankfort horizontal | Compare the face with population norms | Angle of convexity (NA/APog), facial angle | A Frankfort-based reading of the profile, published in 1948 | Our course base gives few of its norms |
| Steiner | S-N line | A short sheet, from diagnosis to incisor targets | SNA, SNB, ANB, SN-GoGn, U1-NA, L1-NB | Chevrons and Steiner box for planning | Depends on Nasion and S-N inclination |
| Tweed-Merrifield | Frankfort and mandibular plane | Position the lower incisor according to divergence | FMA, IMPA, FMIA, Z angle, facial height index | Turns the vertical into an incisor target and arch space | Mandibular plane and target cut-offs vary between courses |
| Ricketts | Several, incl. facial axis and A-Pog | Norms that change with age | Facial axis, facial angle, convexity, L1-APog | Age-corrected norms, growth prediction | Many landmarks; norms tied to an age |
| McNamara | Nasion perpendicular | Jaws related to the cranium and to each other, in mm | A to N-perpendicular, Co-A, Co-Gn, maxillomandibular differential | Linear values readable for surgery and airway | Needs calibration; agrees less with other analyses |
| Sassouni | The patient’s own planes | Architectural: the face compared with its own proportions | Relationships between horizontal planes | Does not depend on one population’s norms | No verified numeric norms in our sources |
| Björk-Jarabak | S-N, facial heights, gonial region | Typology and growth rotation | Polygon sum, posterior/anterior facial height ratio, structural signs | Growth direction in the growing patient | Weak link with profile esthetics |
Boileau, as cited in our D.U. knowledge base, sorts them into three families: typological analyses (Björk), dimensional analyses that compare the patient with population norms (Downs, Tweed, Steiner, Ricketts) and architectural analyses in which the patient is his or her own reference (Sassouni, Delaire).
Downs: the Frankfort-based pioneer
W. B. Downs published "Variations in facial relationships; their significance in treatment and prognosis" in 1948 (Am J Orthod, PubMed). PubMed holds no abstract for it, so we do not reproduce its sample or its original values here.
The idea. A dimensional analysis, built on the Frankfort horizontal, that compares the patient with average values from a reference group.
Key measurements. Our course base credits Downs with the angle of convexity (NA to APog), the convexity of the skeletal profile, and lists it next to the facial angle (N-Pog to Frankfort).
What it brings. A reading of the profile that does not rely on S-N; Downs remains a common entry in comparison studies.
Limits. Frankfort depends on Porion and Orbitale, two fragile landmarks, and the norms come from one historical sample.
Steiner: the cranial base as reference
Steiner, in the early 1950s, fit the measurements he found most useful on one sheet, all related to S-N: SNA, SNB and ANB, SN-GoGn, U1-NA and L1-NB in degrees and millimeters, and the S line.
What it brings. A path from diagnosis to treatment goal: the chevrons set the acceptable incisor compromise for the expected ANB, and the Steiner box converts it into arch space.
Limits. ANB depends on Nasion, the inclination of S-N and jaw rotation, hence the Wits check; the landmarks remodel; and the effect of the vertical on the lower incisor is ignored. Our guides to the Steiner analysis, the ANB angle and the Holdaway ratio cover it in detail.
Tweed-Merrifield: the lower incisor and the vertical
The D.U. course dates Tweed’s analysis to 1940; Merrifield later added the Z angle, the total space analysis and a difficulty index. It rests on the Tweed triangle: FMA (Frankfort to mandibular plane), IMPA (lower incisor to mandibular plane) and FMIA (lower incisor to Frankfort), which add up to 180°.
What it brings. It ties the lower incisor target to the vertical: the higher the FMA, the more upright the incisor, with the gap converted into arch length at 0.8 mm per degree. The facial height index and the Z angle complete the reading.
Limits. The mandibular plane differs between analyses, the cut-offs of Tweed’s rule vary between courses, and a target can be out of reach on a thin symphysis. See our mandibular plane angle guide and, in French, the Tweed analysis and the Tweed-Merrifield total space analysis.
Ricketts: norms that change with age
Ricketts’ analysis is dimensional, with one distinctive feature in our sources: several norms are corrected for age. The EMC resident’s manual, cited in our base, gives a simplified version at 9 years in which the facial axis is stable while the facial angle, the mandibular plane and the convexity change by a set amount over time.
Key measurements. Facial axis, facial angle, mandibular plane angle, lower facial height, mandibular arc, convexity (A to N-Pog), lower incisor to A-Pog in millimeters and degrees, and the lower lip to the E-line. The Ricketts and Grummons frontal analyses extend the approach to the face seen from the front, for asymmetry in particular (Grummons and Ricketts, 2004, World J Orthod, PubMed).
What it brings. Age-aware norms, a dental reference for the lower incisor (A-Pog), growth prediction and a visual treatment objective (VTO). Dolichofacial and brachyfacial are Ricketts’ terms.
Limits. More landmarks, more error, and norms that only make sense at a known age. Boileau reminds that no growth prediction is 100% reliable. Our Ricketts E-line guide covers the soft-tissue part.
McNamara: linear values from Nasion perpendicular
J. A. McNamara published "A method of cephalometric evaluation" in 1984. According to its abstract, the analysis relates the maxilla and the mandible to cranial structures and to each other, gives criteria for the anteroposterior and vertical position of the upper and lower incisors with documented standards, and covers the analysis of serial films (McNamara, 1984, Am J Orthod, PubMed).
Key measurements. Point A relative to the Nasion perpendicular (the "McNamara line" in several studies, for example Matsumura et al., 2022); maxillary length (Co-A), mandibular length (Co-Gn) and the maxillomandibular differential between them (Alam and Alfawzan, 2025, Maedica); the facial axis for the vertical; and the airway. In a meta-analysis of 16 studies on pediatric sleep apnea, McNamara’s and Linder-Aronson’s airway parameters were among those significantly associated with the condition (Shreya et al., 2024).
What it brings. Millimeter values that speak to surgical planning, and a reading of the airway.
Limits. Every linear value needs a calibrated radiograph, and lengths depend on the patient’s size. In a comparison of 125 cephalograms, McNamara’s analysis showed less agreement with the other analyses for the sagittal jaw relationship (Monisha et al., 2025). In 94 cephalograms, the facial axis performed less well than SN-GoGn and FMA for classifying the vertical pattern (Azeez, 2023, Indian J Dent Res). We do not give McNamara’s numeric standards here: we found none in an abstract we could verify.
Sassouni: the face compared with itself
V. Sassouni’s papers indexed in PubMed include "Planes of reference in roentgenographic cephalometry" with S. K. Nanda (1965, Angle Orthod, PubMed) and "A classification of skeletal facial types" (1969, Am J Orthod, PubMed). Neither has an abstract in PubMed.
The idea. An architectural analysis: instead of measuring the patient against a population average, it looks at how the patient’s own horizontal planes and structures relate to each other. Our D.U. vertical course lists Sassouni’s terms, open bite and deep bite types, among the equivalent vocabularies for vertical patterns, next to Schudy (hyper- and hypodivergent), Ricketts (dolicho- and brachyfacial) and Björk (posterior and anterior rotation). The same course reads, in hyperdivergent faces, a posterior convergence of the palatal, occlusal and mandibular planes.
What it brings. A typology that does not depend on one population’s norms, which matters: Argyropoulos and Sassouni recalled that Sassouni, Ricketts and others had found norms to differ between Caucasians and other ethnic groups (Argyropoulos and Sassouni, 1989, AJODO), and a Rabat study of 102 Moroccan adults concluded that Caucasian norms cannot be applied to Moroccan faces (Lahlou et al., 2010, Eur J Orthod).
Limits. Our sources give no numeric thresholds for Sassouni’s typology, and the original description is not available as a verifiable abstract. Use it as a way of reasoning about proportions, not as a scorecard.
Björk and Jarabak: typology and growth rotation
Björk described the structural signs of mandibular growth rotation ("Prediction of mandibular growth rotation", 1969, Am J Orthod, PubMed). The D.U. course teaches them as a qualitative reading (condylar neck, mandibular canal, antegonial notch, gonial angle, symphysis), and Boileau adds that they are only reliable when the rotation is marked and the patient is well into growth. In an implant sample of 21 subjects followed for 6 years around puberty, four variables combined gave the best estimate (86%) of total mandibular rotation: mandibular inclination (posterior/anterior facial height index, lower gonial angle or NSL-ML), the intermolar angle, the shape of the lower border and the inclination of the symphysis; the authors stress that the sample was made of extreme cases (Skieller et al., 1984, Am J Orthod).
The Björk-Jarabak analysis, as used in current studies, relies on the Björk polygon sum and the Jarabak ratio (posterior to anterior facial height) to classify patients as hypo-, normo- or hyperdivergent: a smaller polygon sum describes a hypodivergent pattern (Sambale et al., 2025, J Orofac Orthop), and the ratio serves to form vertical groups in CBCT studies (Rajesh et al., 2025, Cureus).
What it brings. A typology of growth direction, useful when the question is "which way will this mandible rotate?" rather than "how far is this value from the mean?".
Limits. Prediction is a probability, not a forecast. And this family says little about the profile: among nine analyses tested against the attractiveness ratings of 210 untreated Chinese adults, Jarabak’s explained the least variation (6.1%), Holdaway’s the most (41.5%) (Ren et al., 2025, Am J Transl Res). We do not give the polygon or ratio norms here: none was available in an abstract we could verify.
Do the analyses agree?
Less than one might hope. On 125 lateral cephalograms analyzed with Downs, Steiner, Wits, Tweed, Björk, Ricketts and McNamara, overall agreement was moderate for the sagittal jaw relationship (kappa 0.41), fair for the growth pattern (0.24), mandibular position (0.25) and incisor positions (0.38 upper, 0.21 lower), and only slight for maxillary position (0.18). Normal relationships were diagnosed less consistently than clearly deviant ones (Monisha et al., 2025, J Oral Biol Craniofac Res).
So name the analysis behind every value, never mix norms (Steiner’s Go-Gn and Tweed’s mandibular plane give different numbers), and expect borderline cases to disagree: there, the clinical examination decides.
Which analysis for a skeletal open bite?
The analyses most often associated with the question are Sassouni, whose typology names open-bite and deep-bite faces, and Björk-Jarabak, which describes the direction of growth. But no single analysis diagnoses a skeletal open bite. These criteria help choose what to measure:
- Dental or skeletal first. Extent of the open bite (incisors only, or reaching premolars), habits, tongue, lower face height. Our open bite guide details the clinical signs.
- Measure the vertical with more than one indicator. In 1,056 patients of the Arab population in Israel (621 open bites), the mandibular plane angle to the cranial base best separated open bite from controls, followed by the facial axis and the posterior/anterior facial height ratio; the design was exploratory (Abu Shahin et al., 2026, J Clin Med). In Tweed terms: FMA, SN-GoGn and the facial height index together.
- In a growing patient, add the growth direction. Björk’s structural signs and the Jarabak ratio tell you whether the mandible tends to rotate backward, with the reliability limits above.
- When population norms fit poorly, reason in proportions. That is Sassouni’s architectural logic: is this patient’s anterior face long relative to his or her posterior face?
- Do not expect a predictor of stability. In 41 treated open-bite patients followed at least 9.5 years out of retention, more than 35% had an open bite of 3 mm or more, and neither the initial open bite, the mandibular plane angle nor any single parameter reliably predicted stability (Lopez-Gavito et al., 1985, Am J Orthod).
The D.U. approach already covers most of this with Tweed’s vertical indicators and Björk’s signs; Sassouni and Jarabak add a vocabulary and a second reading of the same face.
In practice: a checklist
- Choose a base analysis and write its name on the tracing.
- Use only the norms of that analysis, with their source and, for Ricketts, the age.
- Calibrate the radiograph before reading any millimeter value (McNamara, Wits, facial heights).
- Cross-check each key reading: ANB with the Wits or the beta angle, FMA with SN-GoGn and the height index.
- Place the landmarks carefully: our cephalometric landmarks guide and tracing guide cover the technique common to all analyses.
- In a growing patient, read Björk’s structural signs before predicting anything.
- When two analyses disagree, report the disagreement and go back to the face.
Frequently asked questions
Which cephalometric analysis is used for skeletal open bite?
Sassouni’s analysis, which classifies faces into open-bite and deep-bite types, and the Björk-Jarabak analysis, which describes growth direction, are the ones classically associated with the vertical. In practice, a skeletal open bite is read with several indicators: mandibular plane angle (FMA, SN-GoGn), posterior/anterior facial height ratio, facial axis and Björk’s structural signs, always together with the clinical examination.
Who developed the Sassouni analysis?
V. Sassouni. His papers indexed in PubMed include a classification of skeletal facial types (1969) and a study of reference planes in cephalometry with S. K. Nanda (1965). His approach is architectural: the patient’s face is compared with its own proportions rather than with a population average.
What is the Downs analysis?
The analysis published by W. B. Downs in 1948. It is a dimensional analysis based on the Frankfort horizontal that compares the patient with average values; the angle of convexity (NA/APog) is the measurement our course base attributes to it.
What does the McNamara analysis measure?
The position of point A relative to the Nasion perpendicular, maxillary and mandibular lengths (Co-A, Co-Gn) and their difference, the vertical (facial axis), the incisors and the airway. Its values are mostly linear, so the radiograph must be calibrated.
With GS Ortho
In GS Ortho, AI places 29 landmarks on the lateral cephalogram and the Steiner and Tweed analyses are calculated straight away; you check each landmark, correct it if needed, then validate. The measurements feed the 12-panel guided diagnostic studio, alongside the clinical examination, the photographs and the treatment plan of the same patient. The platform also includes pedagogical guides and fictitious training cases. From any panel, "Request an opinion" sends your question, with the panel attached, to a colleague or supervisor you choose; the answer stays in the record. Our free cephalometric analysis tool calculates the Steiner and Tweed measurements from the landmarks you place, without sign-up. The GS Ortho interface is currently available in French.