# Cephalometric Analysis and Orthognathic Treatment Planning

## Overview

Cephalometric analysis is the systematic measurement of craniofacial relationships using standardized radiographic or 3D imaging. It serves as the foundation of orthognathic surgical planning, identifying skeletal and dental discrepancies and quantifying the surgical correction needed. Modern planning integrates clinical examination, cephalometrics, dental models, facial photography, and 3D virtual surgical planning (VSP).

## Cephalometric Landmarks

### Skeletal Landmarks

The key skeletal landmarks include Sella (S), the center of the sella turcica; Nasion (N), the most anterior point of the frontonasal suture; Orbitale (Or), the lowest point on the infraorbital margin; Porion (Po), the uppermost point on the external auditory meatus; ANS and PNS, the tips of the anterior and posterior nasal spines respectively; Point A (Subspinale), the deepest concavity on the anterior maxilla between ANS and the alveolar crest; Point B (Supramentale), the deepest concavity on the anterior mandible between pogonion and the alveolar crest; Pogonion (Pg), the most anterior point of the bony chin; Menton (Me), the most inferior point of the mandibular symphysis; Gnathion (Gn), the most anteroinferior point of the chin; Gonion (Go), the most posteroinferior point of the mandibular angle; Articulare (Ar), the intersection of the posterior ramus border and the inferior cranial base surface; and Basion (Ba), the most anteroinferior point of the foramen magnum.

### Dental Landmarks

Dental landmarks include the upper and lower incisor tips and apices, the molar relationship (Class I, II, or III), and the occlusal plane (the line from incisor overlap to molar cusp tips).

### Soft Tissue Landmarks

Soft tissue landmarks include Glabella (the most prominent forehead point), Pronasale (nasal tip), Subnasale (Sn, the junction of columella and upper lip), Labrale superius and inferius (the most anterior points of upper and lower lip vermilion respectively), soft tissue Pogonion (Pg', the most anterior chin soft tissue point), and soft tissue Menton (Me', the lowest point on the soft tissue chin contour).

## Standard Cephalometric Analyses

### Steiner Analysis

| Measurement | Normal Value | Interpretation |
|---|---|---|
| SNA | 82 +/- 2° | Maxillary AP position (increased = prognathism) |
| SNB | 80 +/- 2° | Mandibular AP position (increased = prognathism) |
| ANB | 2 +/- 2° | Skeletal relationship (>4 = Class II; <0 = Class III) |
| Upper incisor to NA | 22° / 4 mm | Upper incisor inclination and position |
| Lower incisor to NB | 25° / 4 mm | Lower incisor inclination and position |
| Interincisal angle | 130 +/- 5° | Relationship of upper to lower incisors |

The SNA angle (normal 82 +/- 2 degrees) describes maxillary anteroposterior position relative to the cranial base; increased values indicate maxillary prognathism, decreased values indicate retrognathism. The SNB angle (normal 80 +/- 2 degrees) describes mandibular anteroposterior position; increased values indicate mandibular prognathism, decreased values indicate retrognathism. The ANB angle (normal 2 +/- 2 degrees) describes the skeletal relationship of maxilla to mandible: values greater than 4 indicate Class II skeletal pattern, negative values indicate Class III, and 0-4 indicates Class I. Additional measurements include upper incisor to NA (22 degrees angle, 4 mm distance), lower incisor to NB (25 degrees angle, 4 mm distance), and the interincisal angle (130 +/- 5 degrees).

### McNamara Analysis

The McNamara analysis measures maxillary position as the distance from Nasion perpendicular to Point A (normal 0 +/- 1 mm), mandibular position as the distance from Nasion perpendicular to Pogonion (normal -4 to 0 mm in females, -2 to +2 mm in males), upper pharyngeal airway width (normal 15-20 mm), lower pharyngeal airway width (normal 11-14 mm), effective maxillary length from Condylion to Point A (85-100 mm), effective mandibular length from Condylion to Gnathion (105-125 mm), and the maxillomandibular differential (20-23 mm in females, 23-28 mm in males).

### Arnett Soft Tissue Cephalometric Analysis

The Arnett analysis focuses on soft tissue aesthetics and proportions using the True Vertical Line (TVL), a vertical reference perpendicular to natural head position. Key measurements include upper lip to TVL (3-5 mm), lower lip to TVL (1-3 mm), soft tissue pogonion to TVL (-4 to 0 mm), nasolabial angle (85-105 degrees), interlabial gap at rest (0-3 mm), upper incisor show at rest (2-4 mm), facial thirds proportionality (upper, middle, and lower thirds ideally equal), and lower facial third proportions (upper lip composing one-third, lower lip and chin composing two-thirds). This analysis emphasizes the importance of soft tissue over skeletal measurements in planning.

### Wits Appraisal

The Wits appraisal uses perpendicular projections of Point A and Point B onto the occlusal plane to measure the AO-BO distance (normal 0 mm in females, +1 mm in males for Class I). It is useful when the SN plane is abnormal due to cranial base variation.

<image>Annotated lateral cephalometric radiograph demonstrating the major skeletal and dental landmarks used in Steiner, McNamara, and Arnett analyses, with key reference planes (SN, Frankfort horizontal, occlusal plane, mandibular plane) labeled</image>

## Clinical Examination for Orthognathic Surgery

### Facial Assessment (Systematic Approach)

The examination begins with establishing natural head position (NHP), with the patient looking at a distant point at eye level to define true horizontal. The frontal view assesses facial symmetry and midline, cant of the occlusal plane, facial thirds proportionality (trichion-glabella, glabella-subnasale, subnasale-menton), alar base width (ideally equal to intercanthal distance), lip competence at rest, and smile characteristics including gingival display (more than 3 mm constitutes a gummy smile), smile arc, and buccal corridors. The profile view evaluates facial convexity (convex for Class II, straight for Class I, concave for Class III), nasolabial angle, mentolabial fold depth, chin projection, lower facial height, and lip posture (strain on closure indicates mandibular deficiency or vertical maxillary excess). The submental view assesses mandibular symmetry and chin position.

### Dental Evaluation

The dental evaluation covers Angle classification (Class I, II, or III), overjet and overbite measurements, dental crowding, spacing, and missing teeth, curve of Spee, transverse discrepancy (crossbite), and dental compensation such as proclined lower incisors in Class III or proclined upper incisors in Class II, which must be decompensated orthodontically before surgery.

## Treatment Planning Workflow

### Conventional Planning

Conventional planning begins with diagnostic records: lateral and PA cephalograms, panoramic radiograph, facial photographs (8 standard views), and dental impressions or models. Cephalometric tracing and analysis follow. Model surgery is performed on an articulator after facebow transfer and model mounting. Prediction tracing simulates surgical movements on tracing paper. Intermediate and final splints are fabricated from the model surgery, and surgery is performed using these splints for positioning.

### 3D Virtual Surgical Planning (VSP)

VSP begins with full-skull CBCT acquisition and digital dental models (from intraoral scan or scanned impressions). Standardized facial photographs with optional 3D surface scanning are obtained. Data are uploaded to VSP software (ProPlan CMF, Dolphin 3D, or IPS CaseDesigner). 3D cephalometric analysis of skeletal and soft tissue is performed. Virtual osteotomies are performed on the 3D model, and movements (Le Fort I, BSSO, genioplasty) are simulated with real-time visualization. Soft tissue prediction modeling is generated. CAD/CAM surgical splints (intermediate and final) are designed and fabricated, along with optional cutting guides for precise osteotomies and optional patient-specific fixation plates.

### VSP Advantages

VSP provides 3D visualization that eliminates errors from 2D interpretation, accurate assessment of asymmetry (not possible with lateral cephalogram alone), precise roll, pitch, and yaw corrections, reduced operative time, more accurate positioning compared with conventional planning, and improved patient visualization and communication.

<image>Screen capture from a 3D virtual surgical planning session showing a simulated Le Fort I maxillary advancement and BSSO mandibular setback with the pre-surgical and planned post-surgical skeletal positions overlaid, along with the designed intermediate splint</image>

## Surgical Movements and Predictions

### Maxillary Movements (Le Fort I)

The maxilla can be advanced, set back, impacted (superiorly repositioned), inferiorly repositioned (downgrafted), differentially impacted (posterior impaction with anterior downgrafting for counterclockwise rotation of the occlusal plane), widened (segmental Le Fort I), or corrected for cant (differential vertical movement on each side).

### Mandibular Movements (BSSO)

The mandible can be advanced, set back, rotated (clockwise or counterclockwise), or corrected for asymmetry (differential advancement on each side).

### Genioplasty

The chin can be advanced, set back, vertically changed (lengthened or shortened), or laterally shifted.

### Soft Tissue Response Ratios (Approximate)

| Surgical Movement | Soft Tissue Follow (%) | Region Affected |
|---|---|---|
| Le Fort I advancement | 60-70% | Upper lip |
| Le Fort I impaction | ~40% | Upper lip |
| BSSO advancement | 90-100% | Lower lip |
| BSSO setback | 80-90% | Lower lip |
| Genioplasty advancement | 90-100% | Chin soft tissue |

Le Fort I advancement produces approximately 60-70% upper lip follow of bone movement. Le Fort I impaction produces approximately 40% upper lip follow. BSSO advancement produces 90-100% lower lip follow. BSSO setback produces 80-90% lower lip follow. Genioplasty advancement produces 90-100% chin soft tissue follow. The nasal tip elevates with maxillary advancement, but cinch sutures and V-Y closure mitigate this effect.

## Clinical Pearls

Planning should always begin from the maxillary incisors, establishing ideal upper incisor position relative to the upper lip first and building the plan around this. Cephalometric norms are guidelines rather than absolute targets, and individual facial aesthetics and patient desires matter more. Dental decompensation is essential before surgery, as proclined incisors mask the true skeletal discrepancy. The occlusal plane angle is one of the most important variables in treatment planning, and counterclockwise rotation (posterior impaction) improves both aesthetics and airway. The airway should always be evaluated using McNamara measurements and 3D airway volume on CBCT, as mandibular setback may compromise the airway in susceptible patients. The plan must be clearly documented and communicated with the orthodontist, since surgical-orthodontic coordination is critical for stable outcomes. VSP is becoming the standard of care for complex cases, with two-jaw surgery, asymmetry correction, and segmental procedures benefiting most.

## References
- Proffit WR, et al. Contemporary Treatment of Dentofacial Deformity. Mosby. 2003.
- Arnett GW, Gunson MJ. Facial planning for orthodontists and oral surgeons. Am J Orthod Dentofacial Orthop. 2004.
- Steiner CC. Cephalometrics for you and me. Am J Orthod. 1953.
- McNamara JA. A method of cephalometric evaluation. Am J Orthod. 1984.
- Swennen GR, et al. A cone-beam computed tomography triple scan procedure to obtain a three-dimensional augmented virtual skull model. Clin Oral Investig. 2009.
- Stokbro K, et al. Virtual planning in orthognathic surgery. Int J Oral Maxillofac Surg. 2014.