• This projection shows the facial skeleton and the maxillary antra, and avoids superimposition of the dense bones of the base of the skull. It is especially useful to detect middle third fractures (Le Fort I, II, III, zygomatic complex, nasoethmoidal complex, orbital blowout) and coronoid fractures.

• The cassette is placed perpendicular to the floor with its long-axis of cassette positioned vertically.

• The patient should be positioned such that the midsagittal plane should be vertical and perpendicular. Only the nose and chin should touch the cassette. The head is tipped back so that the radiographic baseline is at 45° to the film.

• The central ray is directed horizontally through the occiput.

• Exposure parameters are kVp—65, mA—10, seconds—2–3.

• This projection shows the facial skeleton, from a different angle enabling certain bony displacements to be detected. It is useful in detecting middle third fractures (Le Fort I, II III) and coronoid process fractures.

• The cassette is placed perpendicular to the floor in a cassette holding device. The long-axis of the cassette is positioned vertically.

• The patient is positioned such that the midsagittal plane is vertical and perpendicular to the cassette and the head is centred so that the nasion is in the centre of the cassette. Only the nose and chin touch the cassette; the head is tipped back so that the radiographic baseline is at 45° to the film.

• The central ray is directed 30° to the horizontal, centred through the lower border of the orbit.

• Exposure parameters are kVp—65, mA—10, seconds—2–3.

• This projection is primarily used to demonstrate the maxillary sinus, frontal, and ethmoidal sinuses. The sphenoidal sinuses can be seen if the patient is asked to open his mouth, where by the sphenoidal sinuses are projected on the palate.

• The orbit, frontozygomatic suture, nasal cavity, coronoid process of the mandible and the zygomatic arch are also seen.

• The cassette is placed perpendicular to the floor in a cassette holding device. The long-axis of the cassette is positioned vertically.

• The patient is positioned such that the midsagittal plane should be vertical and perpendicular to the plane of the film and the patient’s head is extended so that only the chin touches the cassette. The cassette is centred around the acanthion (anterior nasal spine).

• The canthomeatal line should be at 37° to the plane of the film and the line from the external auditory meatus to the mental protuberance should be perpendicular to the film.

• Waters (1915) specified that the tip of the nose should be 0.5 to 1.5 mm away from the cassette. Mahoney (1930) found that the petrosal shadows can be correctly placed by adjusting the orbitomeatal line at 37° to the horizontal.

• The patient’s head is extended as far as comfortable, to make the lower border of the mandible as parallel to the cassette as possible. Only the chin touches the cassette. The canthomeatal line should also be approximately parallel to the plane of the film.

• The central ray enters at the bregma and exits at the menton.

• Exposure parameters are kVp—65, mA—10, seconds—2–3

• This projection is primarily used to demonstrate the walls of the maxillary sinus (especially in the posterior areas), the orbits, the zygomatic arches and the nasal septum. It also demonstrates medial or lateral deviations of any of the mandible.

• The cassette is placed perpendicular to the floor in a cassette holding device. The long-axis of the cassette is positioned vertically.

• The patient is positioned such that the midsagittal plane should be vertical and perpendicular to the plane of the film.

i. Inflammatory changes thickened mucosal sinusitis

ii. Empyema–fluid levels

iii. Polyps, mucosal retention cysts, and mucocele

iv. Carcinoma

v. Postoperative maxillary cysts

vi. Foreign objects within maxillary sinus, and

vii. Soft tissue calcification like lymph nodes and sialoliths.

• Upper respiratory tract infection, e.g., common cold.

• Trauma, e.g., oroantral communication or a tooth fragment being pushed into the sinus.

• Periapical infection of posterior teeth. A single maxillary posterior tooth with chronic apical periodontitis may produce a localized inflammatory response. It is known as ‘periapical mucositis’.

• Periapical picture depicting antral halo because of resorption and remodelling of antral floor.

• A periapical lesion that has resulted in an inward bulging of the sinus floor is characterized by a periapical radiolucency surrounded by a thin opaque line of bone. The radiographic appearance has been called the ‘halo effect’.

• Opaque zone at the base of the sinus because of fluid collected in it.

• Total opacity of sinus is because of mucosal hypertrophy and fluid in sinus.

• Evidence of foreign body when applicable.

• Persistent infection of the sinus.

• Continued presence of a foreign body or communication.

• Irregular thickening of the radiopaque lining on the inner side of sinus because of mucosal hypertrophy.

• Shrinkage of the radiolucent cavity of the sinus.

• Radiopacity at the base of the sinus cavity due to collection of the fluid.

• Round dome-shaped radiopacity seen in the cavity may be because of a mucosal polyp.

• Increased thickness of the radiopaque lining of the sinus i.e., thickness of boundary walls.

• Fractures are commonly demonstrated by conventional radiographic techniques but CT is often necessary to show the fracture lines.

• Most injuries affect the paired nasal bones, which are best seen in the lateral skull view.

• In pure ‘blowout’ fractures, the orbital rim is intact with no injury to the globe.

• On plain films, the bone fragments are displaced into the superior aspect of the maxillary sinus and/or one end of the single fragment may be in contact with the remaining walls, the so-called ‘Trap door’ appearance, which is represented by a linear radiopacity that extends into the superior aspect of the maxillary sinus. This ‘trap door’ is a hallmark feature of the orbital blowout fracture.

• Waters’ view best demonstrates the intact orbital rim together with herniation of soft tissue contents into the maxillary sinus.

• Coronal CT scans are the most favoured imaging modality for identifying blowout fracture and evaluating involvement of adjacent tissues.

• The Waters’ or Caldwell’s views are usually adequate to demonstrate the integrity of the orbital rims.

• Coronal CT may also be used, though the former can also be used to see the frontal sinuses. Besides, an axial CT may be used to evaluate the integrity of the anterior cranial fossa.

• Zygomatic arch fractures may occur singly or may be associated with either a tripod fracture or a Le Fort III fracture.

• The plain film study of choice is the ‘soft tissue’ or low kVp submentovertex or ‘Jug handle’ view.

• Axial CT may be of use particularly in complex fractures.

• Three-dimensional CT scans have proved helpful in evaluating degrees of displacement.

• The fracture of suggestive bone usually results in radiopacity of maxillary antrum because of the presence of blood.

• Type I or nondisplaced or minimally displaced fractures can be visualized in plain films or in Waters’ view.

• Type II or segmented zygomatic arch or orbital rim fractures result in subtle rotation of the fragment. The coronal CT is the radiographic technique of choice.

• Type III or fractures with substantial rotation or displacement of the fracture fragment are best seen on a coronal CT scan.

• Type IV or comminuted fracture with gross rotation or displacement is best seen by coronal CT scan. Three-dimensional CT scans have proved helpful in evaluating degrees of displacement.

• Le Fort fractures are complex fractures, Le Fort I and Le Fort II involve the maxillary sinus and Le Fort III is a craniofacial disjunction. For such fractures, plain film radiograph is inadequate and scans are the modality of choice for evaluating all transfacial injuries.

• Cysts and tumours of the maxilla and maxillary antrum are space-occupying lesions which increase in size gradually to encroach on the contiguous structures such as walls of sinus or the ostium.

• The signs and symptoms then follow. Radiographic analysis provides an immense database to aid in the diagnosis of the sinus lesions.

• A panoramic radiograph is useful as a beginning investigation. Maxillary occlusal radiographs and periapical radiographs are also useful in addition to the more sophisticated modalities such as CT and MRI.

i. Radicular cysts

ii. Odontogenic keratocyst

iii. Dentigerous cysts

iv. Calcifying odontogenic cyst (Gorlin cyst)

i. Ameloblastoma

ii. Odontoma

iii. Squamous odontogenic tumour (benign epithelial odontogenic tumour)

iv. Cementoma or periapical cemental dysplasia

v. Benign cementoblastoma or true cementoma

vi. Odontogenic myxoma

• A sinus opacity and in most cases, antral wall destruction with adjacent bony involvement is pathognomic of maxillary sinus carcinoma.

• Besides the conventional views, 3–5 mm contiguous section of CT scan permits accurate evaluation of tumour extension.

• The primary pathologic and imaging feature of squamous cell carcinoma is the propensity to destroy bone even in the presence of a relatively small mass.

• An antrolith is a calcified mass in the maxillary sinus or antrum.

Radiographic features

• If the film moves at a speed that follows the moving projection of a certain point, this point will always be projected on the same spot on the film and will not appear unsharp.

• In the OPG, the film is attached to a rotating system and moves in the same direction as the beam. The film is given the correct speed by opposing this movement with a contrary movement relative to the beam.

• Explain the procedure to the patient.

• Make the patient wear a lead apron without a thyroid collar, and remove all objects from the head which will interfere with film exposure. Also have the patient remove jacket or bulky sweater; this allows more room between the bottom of the cassette holder and the patient’s shoulder.

• Load the panoramic film in the darkroom and cover the bite block with a disposable plastic cover slip.

• Set the exposure factors and adjust the height of the machine to accommodate the patient.

• Instruct the patient to sit or stand with the back straight and erect, and ask him to bite on the plastic bite block. The upper and the lower front teeth must be placed in an end-to-end position in the groove of the bite block.

• The midsagittal plane should be perpendicular to the floor and aligned with the vertical centre of the chin rest, and the Frankfort plane should be parallel to the floor, thus obtaining the correct position for the occlusal plane. The patient’s head is tilted downwards so that the tragus ala line is 5° down and forward.

• If the patient has a low palatal vault, increase the occlusal plane angulation slightly. If the patient has a high palatal vault, decrease the occlusal plane slightly. The indicator lights in the machine help as a guide and the patients head should be immobilized by the head band.

• Centre the lower border of the mandible on the chin rest and equidistant from each side.

• Instruct the patient to position the tongue on the palate and ask him to remain still while the machine is rotating during exposure. Also explain that the cassette holder will not strike him, although it may gently rub his ear and head at the limits as of the excursion.

• After the exposure is complete the film is subjected to routine processing.

• As a substitute for full mouth intraoral periapical radiographs.

• For evaluation of developmental anomalies and tooth development for children during the mixed dentition period as well as TMJ dysfunctions.

• To assess the patient for and during orthodontic treatment.

• To establish the site and size of lesions such as cysts and tumours in the body and ramus of the mandible.

• For progress of pathology and follow-up of treatment, or postoperative bony healing.

• Prior to any surgical procedures such as extraction of impacted teeth, enucleation of a cyst etc.

• For detection of fractures of the middle third and the mandible following trauma.

• In case of periodontal disease for an overall view of the alveolar bone levels.

• Assessment for underlying bone disease before constructing complete or partial dentures.

• Evaluation of the vertical height of the alveolar bone before inserting osseo-integrated implants.

• OPG is an extraoral procedure, which is convenient for the patient and requires a minimal amount of patient’s cooperation

• Useful in patients with trismus and gagging problems. Most units can be operated without radiation to demonstrate to the patient what the procedure will be like before the actual exposure will be made. It virtually eliminates problems with gaggers, patient with trismus, and fearful or uncooperative children.

• Time required is minimal compared to a full mouth intraoral periapical radiographs.

• Radiation dose to the patient is relatively low when compared with conventional full mouth intraoral radiography.

• Patient education: OPG films are a valuable aid in patient education and case presentation.

• Conditions such as impactions, eruption patterns of teeth, the need for replacement of missing teeth, and fractures are more easily illustrated on panoramic views.

• Size of the area radiographed: A broad anatomic region is imaged. The OPG covers an area that includes the entire mandible from condyle to condyle and maxillary region extending superiorly to the middle third of the orbits. Areas such as condyles, inferior border, angle and ascending ramus of the mandible, and entire maxillary sinus that are not visualized in intraoral surveys are seen routinely on OPG.

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