Orthodontics, Cephalometric Analysis

Anatomy and Physiology

Cephalometric analysis assesses the anteroposterior and vertical relationships of the mandible and maxilla in relation to the cranial base and each other, as well as the upper and lower teeth in relation to the mandibular and maxillary bones (see Image. Common Cephalometric Points). The analysis involves comparing patient-specific proportions and angle measurements with population averages, which can be obtained through manual tracing or digital methods. The results of the cephalometric analysis are subject to projection errors and measurement variability and are dependent on the operator. Therefore, the cephalometric values for an individual patient must be interpreted in the clinical context, as deviations from average values may be compensated by other features in the face or skull. The tables below describe commonly used cephalometric points (see Table 1) and planes (see Table 2).[2][3]

Table 1. Cephalometric Points

 Table 2. Cephalometric Planes

Indications

Cephalometric analysis helps diagnose dental and skeletal malocclusions, plan corrective treatments, and evaluate treatment outcomes and growth changes.

Technique or Treatment

Standardized Lateral Cephalometric Radiographs

Lateral skull radiographs provide a 2-dimensional representation of the head and neck and measure the sagittal and vertical dimensions of the skull. Sagittal measurements assess the position and inclination of the maxilla and mandible, while vertical measurements evaluate the height of the facial structures and the relationship between the jaw.[4] In contrast, posteroanterior radiographs, taken from the front of the head, measure transverse and vertical dimensions, offering insights into the width of the face and the relationship between the jaws in the transverse plane.[5] However, in clinical practice, cephalometric analysis primarily relies on lateral radiographs, as posteroanterior projections are more challenging to interpret.

A standardized technique is essential for obtaining radiographs to ensure accurate comparisons over time and between patients. Image quality depends heavily on the proper positioning of the patient. The patient should be positioned with the Frankfort plane horizontal, ear rests placed in the external auditory meatuses, the nasion aligned on the bridge of the nose, and teeth in centric occlusion.[6] The radiographic source is fixed at a distance of 5 feet (150–180 cm) from the patient's mid-sagittal plane, with a film-to-mid-sagittal plane distance of 30 cm.[6] A calibrated steel ruler is included in each image, ensuring precise measurements are documented.

Cephalometric Tracing

Lateral cephalometric radiographs are traditionally traced manually. First, a tracing acetate is placed over the film. Anatomical landmarks are identified and marked on the acetate using a sharp 4H pencil. These points are then connected to form lines and angles, and the resulting measurements are recorded and interpreted.

Digital tracing using specialized software streamlines the cephalometric analysis process. The software automatically identifies anatomical landmarks on radiographs and calculates measurements. This also provides standards for comparison based on ethnicity, sex, and age while enabling predictions for soft tissue alterations, growth, and surgical outcomes.[7] Both manual and digital tracing techniques are appropriate for cephalometric analysis.

Clinical Significance

Interpretation of Cephalometric Analysis Results

Average angular measurements and proportions are established for the general population, but these values serve as general guidelines. Standard measures may vary based on age, sex, and ethnicity.[8] A comprehensive orthodontic assessment must incorporate the patient’s unique skeletal and dental characteristics alongside cephalometric findings.

Anteroposterior Evaluation

SNA angle: The SNA angle assesses the anteroposterior position of the maxilla relative to the anterior cranial base.[9] The SNA angle is formed by connecting the sella, nasion, and A-point. The average SNA angle is 81 ± 3 degrees. For example, a patient with an SNA angle of 82 degrees demonstrates a well-positioned maxilla relative to the cranial base.[10]

An increased SNA angle indicates that the maxilla is positioned protrusively relative to the cranial base compared to the average.[3] Conversely, a decreased SNA angle suggests that the maxilla is retruded relative to the cranial base compared to the norm.[3]

SNB angle: The SNB angle evaluates the anteroposterior position of the mandible to the anterior cranial base.[9] The SNB angle is formed by connecting the sella, nasion, and B-point. The average SNB angle is 78 ± 3 degrees.[10] An increased SNB angle indicates that the mandible is positioned anteriorly relative to the cranial base compared to the average.[11] Conversely, a decreased SNB angle suggests that the mandible is retruded relative to the cranial base compared to the norm.[11]

ANB angle: The ANB angle evaluates the anteroposterior relationship between the maxilla and mandible.[12] The ANB angle is calculated as the difference between the SNA (sella-nasion to A-point) and SNB (sella-nasion to B-point) angles, using the formula: ANB = SNA - SNB.[10]

The average ANB angle for a class I skeletal pattern is 2 degrees. An ANB angle greater than 4 degrees suggests a class II skeletal pattern, while an angle less than 2 degrees indicates a class III skeletal pattern.[13] However, the ANB angle can vary based on the position of the nasion and the prominence of the lower face. When the ANB angle is abnormally increased or decreased, alternative methods such as the Wits analysis should be considered.

Wits Analysis

The Wits analysis provides an alternative approach to evaluating the anteroposterior skeletal pattern without relying on the cranial base. This method involves drawing perpendicular lines from points A and B to the occlusal plane, defined as the line joining the cusps of the posterior teeth.[14] The intersections of the perpendiculars from points A and B with the occlusal plane define points AO and BO, respectively.[14] The distance between AO and BO is then measured. For a class I skeletal pattern, BO is typically 1 mm (±1.9 mm) anterior to AO in males, while in females, BO and AO are generally equal (±1.77 mm).[14]

Vertical Evaluation

The maxillary-mandibular plane angle (MMPA) assesses the vertical relationship between the maxilla and mandible. The MMPA is formed by projecting lines from the mandibular and maxillary planes until they meet posteriorly. The average MMPA value is 27 ± 4 degrees. A normal MMPA indicates a well-proportioned lower face and a normal overbite. An increased MMPA value suggests a long lower face and an open bite, while a decreased MMPA value indicates a shorter lower face and a closed bite.[15] 

Incisor Position: Angular Evaluation

The angular measurement of the maxilla is determined by measuring the angle from the incisor to nasion-A, while the angular measurement of the mandible is calculated from the incisor to nasion-B. These values indicate the inclination of teeth—proclined teeth are angled forward, retroclined teeth are tilted backward, and normally inclined teeth are in a neutral position.[8] The normal incisor to nasion-A angle is 22 degrees, and the normal incisor to nasion-B angle is 25 degrees. An increased incisor to nasion-A or nasion-B angle indicates proclination of the incisor, while a decreased angle suggests retroclination.[3]

The position of mandibular incisors is further evaluated by the angle formed between the long axis of the tooth and the mandibular plane, which extends from gonion to gnathion.[10] The normal mandibular incisor to mandibular plane angle (Go-Gn) is 87 degrees. An increased mandibular incisor to mandibular plane angle indicates that the incisors are proclined, whereas a decreased value indicates the incisors are retroclined.[8]

Incisor Position: Linear Evaluation

The linear measurement of the maxilla is taken from the maxillary incisor to nasion-A, while the linear measurement of the mandible is taken from the mandibular incisor to nasion-B. These measurements describe the relationship between the tooth and its supporting basal bone, indicating whether the tooth is in a normal, procumbent (ahead of the supporting bone), or recumbent (behind the supporting bone) position.[10]

The average value for both incisor to nasion-A and incisor to nasion-B is 4 mm. An increased incisor to nasion-A or -B value indicates that the incisor is procumbent, whereas a decreased value suggests that the incisor is recumbent.[16]

Enhancing Healthcare Team Outcomes

Cephalometric analysis is crucial in diagnosing and treating malocclusions, requiring an interprofessional healthcare team of dental health professionals, including general dentists, orthodontists, and oral surgeons. This technique provides valuable insights into the extent of skeletal and dental misalignments, as well as potential causative factors. If a malocclusion is too severe to be treated by an orthodontist alone, a referral to an oral surgeon may be necessary. The oral surgeon can collaborate with the orthodontist to correct the misaligned jaw through orthognathic surgery, thereby highlighting the importance of an interprofessional approach to diagnosing and managing complex orthodontic malocclusions. Meticulous planning and collaboration with other healthcare professionals involved in orthodontic treatment are essential for ensuring successful patient outcomes.