Lateral Cephalometric Projection
Dental Radiology · Orthodontic & Craniofacial Imaging
TL;DR
The lateral cephalometric projection is the standardised lateral skull radiograph that underpins orthodontic diagnosis, treatment planning, and growth monitoring.
- The lateral cephalometric projection (lateral ceph) is a standardised lateral skull radiograph taken with the patient in a cephalostat — a head-positioning frame that maintains a fixed, reproducible source-to-patient-to-receptor geometry
- It is the cornerstone of orthodontic diagnosis and treatment planning, enabling measurement of angular and linear relationships between the skull, jaws, teeth, and soft tissue profile
- Key angular measurements include SNA (~82°, maxillary position), SNB (~80°, mandibular position), and ANB (~2°, maxilla-to-mandible relationship) — deviations indicate skeletal Classes I, II, or III
- The cephalostat ensures reproducible geometry between serial radiographs, allowing growth monitoring and treatment outcome comparison over time
- Additional uses include orthognathic surgery planning, sleep apnoea (airway) analysis, and assessment of craniofacial anomalies
Key Facts
What Is It?
The lateral cephalometric projection — commonly called the “lateral ceph” or “lat ceph” — is a standardised lateral radiograph of the skull taken with the patient positioned in a cephalostat (a head-positioning device, also called a cephalometer or cephalostatic device). The cephalostat holds the patient’s head in a fixed, reproducible orientation relative to the X-ray source and image receptor, allowing accurate measurement of craniofacial structures and enabling reliable comparison of serial radiographs taken months or years apart.
The technique was introduced by Broadbent (US) and Hofrath (Germany) independently in 1931 and has since become the single most important radiographic tool in orthodontic practice. Unlike a routine lateral skull radiograph — which is taken without positional standardisation — a true lateral cephalometric projection requires the cephalostat to be valid for cephalometric analysis.
Cephalometric analysis is the process of identifying specific anatomical points (landmarks), drawing lines and planes through them, and measuring the angles and distances between these planes to describe the skeletal, dental, and soft tissue relationships of the patient’s craniofacial complex.
Why It Matters
The lateral ceph translates a complex three-dimensional craniofacial structure into a quantifiable, reproducible two-dimensional image that can be compared against population norms and monitored over time. No other single radiograph provides this breadth of diagnostic information in orthodontics.
Clinical Relevance
- Orthodontic diagnosis: The lateral ceph allows the clinician to determine whether a malocclusion has a skeletal or dental basis — critical for treatment planning. A Class II malocclusion, for example, may be due to maxillary prognathism (increased SNA), mandibular retrognathism (decreased SNB), dental procumbency, or a combination — each with different treatment implications.
- Growth assessment: Serial lateral cephs taken over years allow monitoring of jaw growth patterns, enabling timely orthodontic intervention (e.g., functional appliances during growth spurts).
- Treatment planning: Determines whether extraction vs non-extraction treatment, whether growth modification (orthopaedics) vs camouflage vs surgery is appropriate.
- Surgical planning: For orthognathic surgery, the lateral ceph is used to plan osteotomy movements (e.g., Le Fort I, BSSO) and predict soft tissue changes.
- Airway analysis: The lateral ceph allows measurement of pharyngeal airway dimensions — used in assessment and monitoring of obstructive sleep apnoea (OSA).
- INBDE relevance: Cephalometric landmarks, planes, angles, and their normal values are high-yield INBDE topics.
Technique & Equipment
The Cephalostat
The cephalostat is the defining feature of a true lateral cephalometric projection. Without it, the image cannot be used for cephalometric analysis.
- Positions the patient’s head with ear rods placed in both external auditory meatuses (EAMs), stabilising the head in a fixed lateral orientation
- A nasion rest may also be used to prevent rotation
- The Frankfort horizontal plane (from porion to orbitale) is positioned parallel to the floor
- The patient stands or sits with the teeth in centric occlusion (or natural rest position)
- The midsagittal plane is positioned at a fixed distance from the receptor (typically 15 cm / 6 inches in most cephalostat designs)
- The X-ray source is positioned at a standardised source-to-midsagittal distance (typically 60 inches / 152 cm or 5 feet)
Why Standardisation Matters
- Fixed geometry ensures that any magnification is consistent and predictable (same across all patients and serial radiographs on the same machine)
- True magnification factor: The lateral ceph slightly magnifies structures. Because the left side of the skull is closer to the receptor, left-sided structures are slightly less magnified than right-sided structures. Most modern digital cephalometric software corrects for this.
- Without a cephalostat, measurements are not valid for cephalometric analysis — a “lateral skull” taken in A&E or on a panoramic unit cannot be used for cephalometric measurement.
Receptor and Exposure
- Traditional: 8×10 inch or 10×12 inch film with a rare-earth intensifying screen cassette
- Modern: Digital flat-panel detector or PSP plate sized for the skull
- kVp: Typically 80–90 kVp (higher penetration needed for skull)
- Exposure time: Short to minimise motion blur
- A metal wedge filter (aluminium step wedge) is often placed between the tube and the soft tissue profile region to balance the density difference between the soft tissue and the dense bony cranium — allowing both to be seen on the same image
Cephalometric Landmarks
Landmark identification is the foundation of all cephalometric analysis. Landmarks are grouped into categories based on the structures they describe: cranial base (stable reference points), skeletal (jaw position and morphology), dental (incisor position), and soft tissue (lip and chin prominence).
Cranial base landmarks (Sella, Nasion) are used as reference points because they are stable after age 7–8 and do not change with orthodontic treatment or jaw growth. Skeletal, dental, and soft tissue landmarks describe the structures that change with growth and treatment, and are therefore measured relative to the stable cranial base.
| Landmark | Abbreviation | Definition | Plane or Use |
|---|---|---|---|
| Sella | S | Centre of the sella turcica (pituitary fossa) — round radiolucency at base of skull | SN plane (cranial base reference) |
| Nasion | N | Most anterior point of the frontonasal suture on the midsagittal plane | SN plane; reference for facial profile |
| Orbitale | Or | Most inferior point of the bony orbital rim | Frankfort plane |
| Porion | Po | Most superior point of the external auditory meatus (bony EAM) | Frankfort plane |
| A-point (Subspinale) | A | Most posterior point (deepest concavity) of the anterior maxilla, between ANS and the alveolar crest | Maxillary position — SNA angle |
| B-point (Supramentale) | B | Most posterior point (deepest concavity) of the anterior mandible, between pogonion and the alveolar crest | Mandibular position — SNB angle |
| Anterior Nasal Spine | ANS | Tip of the anterior nasal spine | Palatal plane |
| Posterior Nasal Spine | PNS | Most posterior tip of the hard palate | Palatal plane |
| Menton | Me | Most inferior point of the mandibular symphysis | Facial height; Y-axis |
| Gnathion | Gn | Most inferior and anterior point of the mandibular symphysis | Y-axis; facial type |
| Pogonion | Pog | Most anterior point of the mandibular symphysis | Chin prominence; Holdaway line |
| Gonion | Go | Most posterior-inferior point of the mandibular angle | Mandibular morphology; ramus angle |
| Articulare | Ar | Point at intersection of the posterior border of the mandibular ramus and the inferior border of the cranial base | Condylar position |
| Upper Incisor Apex | UIA | Root apex of the most prominent maxillary central incisor | Upper incisor angle to SN or maxillary plane |
| Upper Incisor Edge | UIE | Incisal edge of most prominent maxillary central incisor | Incisor relationship |
| Lower Incisor Apex | LIA | Root apex of most prominent mandibular central incisor | IMPA and other dental angles |
| Lower Incisor Edge | LIE | Incisal edge of most prominent mandibular central incisor | Interincisal angle |
| Soft Tissue Nasion | N′ | Most concave point of the soft tissue nose bridge | Soft tissue profile |
| Soft Tissue Pogonion | Pog′ | Most anterior point of soft tissue chin | Lip-chin relationship; E-plane |
| Upper Lip | UL | Most anterior point of upper lip | E-plane (esthetic line) |
| Lower Lip | LL | Most anterior point of lower lip | E-plane |
Cephalometric Planes & Angles
Reference Planes
- Frankfort Horizontal (FH): From Porion to Orbitale. Approximates the natural horizontal head position. Reference for many vertical and anteroposterior measurements.
- Sella-Nasion (SN) plane: From Sella to Nasion. Represents the anterior cranial base. Most commonly used reference in angular analysis.
- Palatal plane: From ANS to PNS. Represents the maxillary occlusal base.
- Mandibular plane (GoMe or GoGn): From Gonion to Menton (or Gnathion). Represents the lower border of the mandible. Steep mandibular plane = high angle (vertical growth pattern); flat = low angle (horizontal growth pattern).
- Occlusal plane: Bisects the interdigitation of the posterior teeth.
- Y-axis (facial axis): From Sella to Gnathion. Represents the direction of facial growth.
Key Cephalometric Angles
| Measurement | Definition | Normal Value | Interpretation |
|---|---|---|---|
| SNA | Angle at Nasion between Sella–Nasion and Nasion–A-point | 82° ± 2° | >84° = maxillary prognathism; <80° = maxillary retrognathism |
| SNB | Angle at Nasion between Sella–Nasion and Nasion–B-point | 80° ± 2° | >82° = mandibular prognathism; <78° = mandibular retrognathism |
| ANB | SNA minus SNB (angle at Nasion between A-point and B-point) | 2° ± 2° | >4° = Class II skeletal; <0° = Class III skeletal |
| SN–Mandibular Plane | Angle between SN plane and mandibular plane (GoMe) | 32° ± 5° | High (>37°) = vertical/hyperdivergent; Low (<27°) = horizontal/hypodivergent |
| FMA (Frankfort-Mandibular Angle) | Angle between Frankfort horizontal and mandibular plane | 25° ± 5° | High FMA = vertical growth pattern; Low FMA = horizontal growth pattern |
| UI to SN | Angle of upper incisor long axis to SN plane | 102° ± 5° | >107° = proclined upper incisors; <97° = retroclined |
| IMPA | Angle of lower incisor long axis to mandibular plane | 92° ± 5° | >97° = proclined lower incisors; <87° = retroclined |
| Interincisal Angle | Angle between long axes of upper and lower central incisors | 130° ± 10° | <120° = both incisors proclined; >140° = one or both retroclined |
| Nasolabial Angle | Angle between columella of nose and upper lip | 90–110° (varies) | >110° = lip retrusion or nose prominence; <90° = lip protrusion |
| E-plane (Ricketts) | Distance of upper and lower lips to line from nasal tip to soft tissue pogonion | UL: −4 mm; LL: −2 mm behind E-plane | Lips ahead of E-plane = protrusion; behind = retrusion |
Clinical Considerations
- Serial cephalometric analysis: To assess growth or treatment change, serial lateral cephs must be taken on the same machine with the same cephalostat settings. Superimposition on stable cranial base structures (SN plane, registered at Sella) allows accurate before-and-after comparison.
- Cephalometric superimposition: Serial films are overlaid on a stable reference structure to distinguish skeletal change from dental change. Common registration points: SN plane at Sella (cranial base), maxillary structures (palatal plane at ANS — to show upper arch changes), mandibular internal structures (to show lower arch changes).
- Soft tissue cephalometrics: Modern cephalometric analysis increasingly incorporates soft tissue profile because treatment outcomes are judged by facial appearance as well as occlusion. Ricketts’ E-plane, Holdaway’s H-line, and Steiner’s S-line are common soft tissue references.
- Digital cephalometry: In modern practice, digital lateral cephs are analysed using software (e.g., Dolphin, OrthoAnalyzer, Nemoceph) that auto-traces landmarks or allows manual placement, then calculates all measurements automatically. Students must still understand the underlying landmarks and planes to verify software accuracy.
- Limitations: The lateral ceph is a 2D projection of a 3D structure — bilateral structures (condyles, gonial angles, orbital rims) are superimposed. CBCT with 3D cephalometric reconstruction is increasingly used for complex cases but at significantly higher dose.
- Frankfort horizontal plane reliability: The ear rods position the head so the Frankfort plane (Po to Or) is horizontal. However, orbitale is notoriously difficult to identify on the lateral ceph, and slight head tilt introduces error. Some analyses use the SN plane as the primary horizontal reference instead.
Common Mistakes & Misconceptions
Understanding these common errors is essential for both clinical practice and examination success.
-
Misconception: “A lateral skull radiograph taken without a cephalostat can be used for cephalometric analysis.”
Correction: Cephalometric analysis is only valid when taken with a cephalostat that standardises the source-to-patient-to-receptor geometry. An unstandardised lateral skull may look similar but cannot be used for landmark measurement or serial comparison. -
Misconception: “ANB angle of 0° is normal.”
Correction: Normal ANB is approximately 2° (±2°). An ANB of 0° is at the borderline of Class III skeletal tendency. Class I = ~0–4°; Class II = >4°; Class III = <0°. -
Misconception: “A high SNA angle always means the patient needs maxillary retraction.”
Correction: SNA only describes the maxillary position relative to the cranial base. A high SNA combined with a proportionally high SNB (normal ANB) represents maxillary and mandibular prognathism together — not necessarily a Class II relationship requiring maxillary retraction. -
Misconception: “The E-plane is used to assess skeletal jaw position.”
Correction: Ricketts’ E-plane (from nasal tip to soft tissue pogonion) is a soft tissue measurement used to assess lip prominence relative to the facial profile. Skeletal relationships are assessed using SNA, SNB, and ANB. -
Misconception: “Cephalometric norms are universal across all ethnic groups.”
Correction: Cephalometric norms were originally derived from Caucasian populations (Broadbent, Steiner, Ricketts, Tweed). Different ethnic groups have different normative values — for example, average ANB and incisor inclinations differ between Caucasian, African, and East Asian populations. Applying Caucasian norms to all patients is inappropriate.
Related Topics
The lateral cephalometric projection is embedded within the broader context of dental radiology and orthodontic science.
References & Sources
The following foundational texts and peer-reviewed sources inform this article.
- Jacobson A & Jacobson RL (eds), 2006. Radiographic Cephalometry: From Basics to 3-D Imaging. 2nd ed. Quintessence Publishing.
- White SC & Pharoah MJ, 2014. Oral Radiology: Principles and Interpretation. 7th ed. Elsevier Mosby.
- Proffit WR, Fields HW & Sarver DM, 2013. Contemporary Orthodontics. 5th ed. Elsevier Mosby.
- Steiner CC, 1953. Cephalometrics for you and me. American Journal of Orthodontics, 39(10):729–755.
- Broadbent BH, 1931. A new X-ray technique and its application to orthodontia. Angle Orthodontist, 1(2):45–66.
- Ricketts RM, 1972. The biologic significance of the divine proportion and Fibonacci series. American Journal of Orthodontics, 82(5):351–370.
Summary
The lateral cephalometric projection is the foundation of orthodontic diagnosis — a standardised radiograph that transforms the craniofacial complex into a set of measurable landmarks, planes, and angles that can be compared to population norms and monitored across time. The cephalostat is not an optional accessory but a prerequisite: without standardised geometry, the image is simply a lateral skull radiograph, not a cephalometric one.
Understanding the landmarks (especially S, N, A, B, ANS, PNS, Po, Or, Go, Me), the reference planes (SN, Frankfort, palatal, mandibular), and the key angles (SNA, SNB, ANB, SN–MP, UI to SN, IMPA) is not merely an examination requirement. It is a core clinical competency for any dentist who plans, monitors, or communicates about orthodontic treatment — and it directly informs decisions about growth modification, extraction versus non-extraction, and the boundary between orthodontic camouflage and orthognathic surgery.
Key Takeaways
- Cephalostat is mandatory: The lateral ceph requires a cephalostat — standardised geometry is what makes serial comparison and cephalometric analysis valid. A plain lateral skull X-ray cannot be used for cephalometric measurements.
- Three core angles for INBDE: SNA (~82°) = maxillary position; SNB (~80°) = mandibular position; ANB (~2°) = jaw relationship. ANB >4° = Class II skeletal; ANB <0° = Class III skeletal.
- Mandibular plane angle: SN–MP or FMA describes vertical facial growth pattern: high angle = vertical/hyperdivergent (long face); low angle = horizontal/hypodivergent (short face).
- Dental angles: Upper incisor to SN (~102°) and IMPA (~92°) describe incisor inclination — critical for determining whether malocclusion has a dental compensation component and whether extraction is required.
- Ethnic norms matter: Cephalometric norms are population-specific. Caucasian norms (Steiner, Ricketts, Tweed) should not be uncritically applied to patients of other ethnic backgrounds.
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