The advent of radiology enabled us to photograph the unseen human skeleton on a unique radiographic film. The discovery of X-ray is one of the most valuable applications of physics in medicine.

August J. Pacini, an anthropologist, laid the foundation of cephalometry by demonstrating lateral skull radiographs in his anthropologic craniometric studies as early as 1922. Pacini was the first to use a standardised radiopaque reference object to calculate the magnification of the skull X-ray. Pacini advanced the acquisition of radiographs of dried skulls in a standardised manner, a prototype which led to the development of the cephalostat. A practical method still needed to be perfected for obtaining standard radiographs of living humans.

A standardised ‘head position’ was desired, which could be used as a reference to reorient the head in the previous position. It implied that the ‘head holder’ could be used to orient the subject’s head in the same predetermined orientation to take radiographs at different intervals. The repeated radiographs in the same head orientation will not be less distorted; hence, measurement errors are expected to be minimal.

In 1931, Hofrath, a prosthodontist based in Germany, and Broadbent, an orthodontist hailing from the United States, independently developed a specialised apparatus known as a ‘head holder’. This device was designed to facilitate the consistent positioning of the head and face in a standardised manner to enable the acquisition of a standardised skull radiograph. This device allowed for establishing a predetermined standard of head and face orientation, resulting in a more consistent and reproducible radiographic image.

Dr. Bolton added a ruler scale to the head holder, converting it into the Broadbent–Bolton cephalometer.

The radiographic film cassette was always held on the left side of the face closest to the head. The distance between the subject’s mid-sagittal plane (MSP) of the head and the source of X-rays was constant at 5 ft. The peak kilovoltage (kVp) and milliampere (mA) influencing image quality were also standardised to 15 kVp and 5 mA for adults.

The Broadbent cephalometer soon became popular and was extensively used to study infinite variations of the human face. Cephalograms were initially used as a research tool to study the growth of the face and jaws. The research findings had significant clinical implications in the diagnosis and treatment planning of growing and non-growing children with deviations of teeth, face and jaws. Cephalometrics quickly became the primary means to assist orthodontic practitioners in diagnosing and planning treatment. ‘Cephalometrics became the language for the poetry of orthodontics’.

• 1.

  A serial cephalogram is taken at a 1-year interval to determine the growth pattern in a growing child with malocclusion keep radiation hazards in mind and follow principles of As Low As Reasonably Achievable (ALARA).

• 2.

  A pre-treatment/diagnostic cephalogram is indicated to evaluate the location and severity of skeletal and dental dysplasia and its relations with craniofacial structures, face and airway. A pre-treatment cephalogram in a case of malocclusion helps to establish the following:

  • a.

    The severity of dental malocclusion.

  • b.

    The severity of skeletal malocclusion.

  • c.

    Identify the location of dysplasia.

  • d.

    Evaluate the soft tissue integument of the face and its relationship to the dental hard tissues and skeleton of the face.

  • e.

    Evaluate the nasopharyngeal airway, soft palate and position of the tongue.

  • f.

    Aids in treatment planning, decision-making on extraction versus non-extraction treatment/growth modification/surgical orthodontics, and the type of mechanotherapy to be employed.

  • g.

    In addition, cephalometrics aids in designing and planning retention strategies.

• 3.

  Stage and post-treatment cephalograms are taken to monitor the progress of treatment and treatment outcome.

• 4.

  Post-treatment and long follow-up cephalograms helped to evaluate immediate treatment outcomes and long-term stability.

• 5.

  The case study records with follow-up constitute useful data for the purpose of research in evaluating outcome of various treatment modalities, pattern of relapse and derive useful considerations in future treatment planning.

• 6.

  Cephalograms were used to measure the lengths, heights and proportions of the craniofacial and dentoalveolar structures. Numerous angles were drawn from the stable (which do not significantly change with growth) bony landmarks in the skull, which were used for analyses of the orientation of jawbones to their respective bases and the cranium. These parameters helped to assess the direction and amount of growth.

A posteroanterior cephalogram (PA Ceph) is used to evaluate the cranium, face, jaws and dentition in transverse and vertical dimensions.

PA cephalogram: It is used to assess facial asymmetry or symmetry in children with developmental deformities such as:

• 1.

  Arrested growth of the mandible due to injury to the TM joint.

• 2.

  Excessive growth of the mandible as in unilateral condylar hyperplasia.

• 3.

  Facial asymmetry due to hemifacial hypertrophy/atrophy.

• 4.

  Facial asymmetry due to trauma.

• 5.

  Developmental or congenital face asymmetry.

• 6.

  To evaluate transverse maxillary deficiency or excessive width of the mandible.

• 7.

  Transverse changes of maxillary expansion differentiate dental versus skeletal expansion.

• 8.

  Facial heights.

Before taking a cephalogram, it is essential to familiarise the patient with the environment of the cephalometric room and explain the steps involved in the procedure. This helps to alleviate any concerns the patient may have and makes them feel more relaxed. It is also essential to demonstrate to the patient how to maintain a relaxed lip posture while keeping the buccal teeth in occlusion.

A radiation protection cervical collar should be used during the procedure to ensure patient safety. A lead apron is also used for additional radiation protection for younger patients. It is important to note that pregnant women should avoid any routine radiation exposure.

The cephalostat should be raised beyond the subject’s height, with ear rods at a maximum opening and orbital pointer/nose support turned upwards to avoid injury to the patient. To begin, the subject is asked to stand relaxed under the cephalostat head holder. Next, the cephalostat (head holder) should be brought down gently, with the ear rods placed in the external auditory meatus. At this stage, look for any neck strain and resolve it through adjustments in posture or cephalometer. The cephalostat height should be adjusted for an unstrained neck position, not vice versa, where the head holder may be slightly high or low with the subject trying to either extend their neck or flex down. Once ear rods are in place and the patient is comfortable, the FH position is gently manoeuvred by tilting the chin/forehead up and down, rotating supero-inferiorly around the transmeatal axis.

The FH plane is a line connecting the superior border of the external auditory meatus with the infraorbital rim. This plane is usually 10 degrees inferior to the canthomeatal line, which runs from the outer canthus of the eye to the tragus of the ear, connecting the ‘orbital pointer’ to the ‘ear rod’. Head holders used in the old version had an orbital pointer to align the face in the FH plane. This pointer was placed near the orbital foramen, the thickest part of the inferior orbital rim that can be gently felt. The head was secured in this position with nasal support. Before taking the X-ray, the patient was asked to relax, and their teeth were checked to ensure they were in a centric occlusion position. It was essential to keep the patient’s lips relaxed during this process to avoid incorrect information on soft tissue parameters.

Cephalograms are sometimes taken with the mandible in the rest position or on first tooth contact when there is a functional shift of the mandible. In such cases, the cephalogram is taken in a forced centric relation, which is possible when supported with a wax bite.

It is important to document the patient’s information on the film, including the name, hospital registration number or unique health identification number (UHID) and the date of the cephalogram.

The film is exposed to radiation once the machine and patient are adjusted. Most cephalometric machines were tuned to 65 kVp and 10–15 mA. The exposure time varied with the patient’s age, the standard being 0.5–0.6 s.

The correct head orientation is the basis of accurate measurements in PA cephalometry. The head orientation can be achieved using the Frankfort horizontal plane (FHP) as a reference or in a NHP. The method of correct head orientation is given in the following:

• 1.

  Conventionally, the head can be positioned with the tip of the nose and forehead in light contact with the film cassette holder sensor. This position is suitable for evaluating craniofacial anomalies that require special attention to the upper face.

• 2.

  The standard method is to keep the FHP parallel to the floor while the patient faces the X-ray film cassette as close as possible within the limits of nose prominence.

• 3.

  To ensure the correct orientation of the head in the FHP, patient positioning should be guided by scribing a line on the ear rod assembly at a point 15 mm above the ear rod. The height of the orbit is about 3 cm, and the lateral canthus is at the centre of the orbit or 15 mm. The patient should be oriented such that his ear canals tuck snugly against the top of the ear rods with the head positioned so that the lateral canthus of the eye is located at the same level as the line described above.

• 4.

  Cephalograms should be taken with the mouth of the patient slightly open in cases of significant mandibular displacement.

• 5.

  PA cephalogram can also be obtained by orienting the head in the NHP.

• 6.

  It is essential to mark the (L) or (R) side of the head while taking a PA view radiograph. A cephalogram in a correct position in the head holder should exhibit external auditory meatus (EAM) shadows (either rings or around a radiopaque marker) in a horizontal plane. However, these anatomical features may have to be ignored in children with gross craniofacial deformities.

• 7.

  PA cephalogram would exhibit temporal bones, orbits, frontal and ethmoid sinuses, maxilla and its antrum, nasal cavity, palatal floor and the mandible from the condyle to the symphysis.

• 8.

  A PA cephalogram is indicated to evaluate the symmetry of the right and left sides, and efforts should be made to distinguish any apparent difference from actual deformity from the left to right side. The rotation of the head around a transverse axis may exhibit facial asymmetry in an otherwise symmetrical face.

Besides a blend of sharpness, contrast and density, which constitute an excellent radiographic film, the other essential features of a cephalogram are those related to head positioning ( Fig. 21.3 ).

(A) A lateral cephalogram showing good contrast and sharpness of skeletal, dental and soft tissue structures. Note a near-perfect overlap of right and left structures, teeth in centric occlusion and unstrained lip posture. The neck is unstrained, and the ear rods are nearly concentric. (B) Soft tissue profile contrast has been enhanced with the application of radio-opaque barium gel along the mid-line of the face.

A cephalogram is taken with the objective in mind that there should be a minimum amount of magnification of the cranium and dentofacial structures, with the left and right sides showing a perfect overlap exhibiting a single shadow.

A cephalogram should be grossly evaluated for normal anatomy and any possible pathology that may be an unexpected or incidental finding. Some of these are listed in Table 21.1 .

• 1.

  Clean the tracing table and make it dust-free using a soft cloth and switch on the illumination.

• 2.

  Tracing paper should be mounted on the radiographic film in such a way that its lower border extends about 1 in. below the chin point. An orientation cross is marked on the cephalogram film at the top left corner of the film with the help of a sharp pointed tool. This orientation cross is transferred to the tracing paper, which serves as an orientation guide. The transfer guide helps reorient the tracing paper onto a cephalogram correctly. The tracing paper is held with transparent tape on the left side. Using opaque matte blotting paper to mask portions of the film except the immediate areas being traced reduces eye strain. It allows for more accurate tracings in ‘faded’ areas. Excess light can be reduced in delicate, darker facial structures by looking through a black paper cone. Fine detail may be revealed by lifting the tracing paper from the film for an unobstructed view of the section to be studied.

All tracings should be done with a pencil with a chisel point.

The distinction between the left and right sides in bilateral structures is complicated and is a common source of error, particularly in tracing dental morphology. Hence, tracing the average of the right side and left configurations is acceptable when skeletal or significant dental asymmetry is not involved. Most anatomical structures of the facial skeleton are bilateral. If symmetrical, they offer double the resistance to X-ray penetration when they appear as single shadows seen with high contrast. Practically, even if the face is perfectly oriented, and the bilateral structures are symmetrical, they are not necessarily superimposed because the X-rays are divergent from the source of origin at the X-ray tube head. Therefore, if a double image is seen in the film, it does not mean asymmetry. Tracing the anatomical structures of the left side is recommended since it is less magnified and more accurate.

Accurate and sharp cephalogram tracing is an art and requires considerable experience in identifying skeletal and dental structures. The author prefers to start tracing with the soft tissue profile of the patient, which begins at the forehead going down to the contour of the neck. Soft tissue filters have dramatically enhanced the visualisation of soft tissue contours. Follow smooth visible contours to trace the forehead, face, nose, lips, chin and neck.

The structures that need to be carefully traced are the outer cortex of the frontal bone, extending down to the nasal process and marking bony nasion. Tracing follows the nasal process anteriorly and completes it by returning to the internal cortex of the frontal bone. The frontonasal suture is often visible, which should be traced for a better anatomical presentation of the tracing.

The Sella (S) appears as a sharp radiolucent shadow, except at the anterior clinoid process. However, it is possible to demarcate the boundary of Sella by its sharp outline overshadowed by a less dense anterior clinoid process. Trace the anterior cranial base starting from the cranial side of the frontal bone, going backwards to the anterior clinoid process, Sella, and posterior clinoid process and follow the sphenoid bone up to the spheno-occipital suture, appearing as a faint outline.

Porion (Po) is identified on the outer border of the metal rings seen in ear rods. Anatomical Porion is recognised as an elliptical shadow seen superoposterior to the condylar fossa in the body of the sphenoid bone. The sphenoid is a complex bone, and considerable experience is needed to locate the anatomical Porion accurately.

The orbital rims which appear as condensed arc-like shadows below the anterior cranial base, descending downwards and anteriorly, where they often get more radiopaque. Orbitale is located here as the inferior point on the orbital rim.

The maxillary sinus is seen as a radiolucent shadow below the orbital rims. The superior boundary of the palatal shadow is traced anteriorly to form ANS, merging anteriorly into the anterior alveolar process, the deepest point here being point ‘A’. The oral side of the palate can be traced starting at the cingulum of the maxillary incisor and backwards, smudging onto the soft palate. The posterior nasal spine (PNS) is often not clearly demarcated due to the overlying shadow of the developing third molar.

The pterygopalatine fissure is an inverse teardrop-shaped structure marked by a sharp, dense radio-opaque line surrounding a greyish radiolucent shadow. The thin hair-like shadow often merges down into the superior border of the palate.

The thick triangular shadows below the orbital arches are the zygoma’s maxillary process, making a radiopaque buttress descending back towards the maxillary first molar. The triangular density in this area signifies the key ridge.

Further, the superior border of the condyle is traced, continuing in an anterior direction extending into the pterygoid fossa, which needs to be clearly demarcated. Further, mesially, the coronoid process is outlined. It is impossible to see and trace the anterior border of the ramus. The condyle is traced posteriorly and inferiorly, completing the mandible ramus’s posterior outline. The inferior border of the body of the mandible is traced next. In case two borders are seen, both edges are outlined, and a dotted line is used to draw a border, which is the average of both.

The mandibular symphysis is traced from the junction of the alveolus with the mandibular incisor, going down into a more profound point (B), following the contour of the chin (Pogonion), turning around (gnathion), and completing the lingual boundary of the mandible.

The first molars and most prominent incisors are traced in both jaws. Care should be taken to discarnate the overlapping cusps of the molars.