Orthopantomography (OPT) is the most widespread radiographic investigation carried out today. It represents an extraoral study technique in which both revelation system and radiogenic source are external to the oral cavity.

OPT is a radiologic examination which allows to accurately plan odontoiatric treatment in a remarkable number of cases. Indeed, the methodology is able to provide complex data on the masticatory apparatus and the surrounding structures allowing the evaluation of normal anatomy and the majority of pathological conditions. Orthopantomography is also called panoramic radiography of dental arches. The term orthopantomography comes from the Greek words: ορθος (“ortós”: orthogonal) = radiant beam perpendicular to the teeth major axis, παν (“pán”: all) = global vision of both arches and τομος (“tómos”: cut, section) = radiological technique able to generate section images (tomography), a methodology known in traditional radiology also as stratigraphy. It exploits the cancellation principle through the kinetic blur of the structures beyond the interest area.

Consequently, panoramic radiography’s hardest challenge is to transfer the aforementioned anatomical structures into a bidimensional radiological image. Those images are characterised by correct parameters of exposition and by the minor rate of structure superimposition and geometrical distortion. There is no doubt that this goal is not easy to achieve when considering the extreme variability of patient’s morphology and structure thickness taken into examination. Moreover, innumerable individual differences among the whole population have to be considered. OPT is based on the simultaneous employment and integration of two basic principles which derive from traditional radiology: tomography and fissure radiography.

Tomography is a technique which consists in a synchronous and integral movement, occurring in opposed directions, of radiogenic source (radiogenic tube) and revelation system (radiographic film or digital detector), around a mechanically fixed point, called rotation fulcrum, which identifies the interest area (tomographic plane).

The tube detection system movement gives rise to structures’ cancellation beyond the interest area (both in front and behind). This is the result of kinetic blur or movement blur optical phenomenon. In OPT, such movement is realised with arch trajectories at about 200–240° (Fig. 1.1).

As a consequence of what was aforementioned, a clear representation of all anatomical structures included in the tomographic plane is realised. The representation is radiographically optimal, as it is ‘in focus’. This is possible as the system rotation fulcrum corresponds to the structure of interest, which, during the tube detector translation movement, appears optically still. Thereby, they are better radiologically representable than what is situated beyond the tomographic plane, which will be blurred and therefore deleted. The cancellation phenomenon turns out to be only partial. Indeed some structures, even if out of the interest plane, can interfere with the final image, generating the so-called parasite images or images of transport. This is due to their high density or radiolucency and/or their close anatomical contiguity to the area of interest.

It is more to say that, in linear tomography, the thickness layer varies depending on the ‘oscillation angle’ (major angles generate thinner layers whereas minor angles determine thicker layers).

The principle of tomography applied in OPT is obviously adapted to the need of representing curvilinear morphology structures, such as dental arcades. Indeed, OPT mainly exploits, not only one rotation fulcrum (as it happens in normal linear tomography) but three rotation fulcrums (one for each lateral arcade and one for the central elements’ representation). Angular movement of the tomographic system creates a minor angle to represent lateral arcades (characterised by major thickness), while it performs a major angle to represent frontal elements (which present minor thickness).

Thereby, this technical peculiarity allows to adapt the thickness of the tomographic plane to different thicknesses which characterise maxillaries’ various portions.

Therefore, the tomographic movement articulated in three fulcrums generates a section plane with variable thickness which can be quantified in about 15–16 mm for lateral sectors analysis and about 8–9 mm for the study of thinner structures characterising the frontal part of the dental arcades (Fig. 1.2).

Tomographic systems with variable geometry rotation fulcrum are the most technologically advanced pieces of equipment, performing well in image quality. They do not employ fixed rotation fulcrums, but realise a unique fulcrum continuous variation along a prefixed elliptical trajectory.

Those tools allow to operate, according to the case, using different elliptical trajectories which are adaptable in different needs (paediatric age, jaws’ malformations, etc.)

OPT system rotation time, and therefore image acquisition time (independently on the type of technology used), varies from about 15 to 20 s.

Fissure radiography or scanography represents the other OPT technical peculiarity.

It entails the use of a fissure collimator (from which fissure radiography takes its name) aiming at eliminating the radiation beam oblique component.

This artifice reduces the photon beam into a thin sheet, hitting selectively the single dental alveolus elements. The relative image is gradually impressed on a thin layer of the film. Such image is deprived of any deformations and has a minor diffuse radiation.

This procedure is possible thanks to the tube and the collimator synchronical movement. As a consequence, the revelation system (radiographic film or digital plate) is progressively impressed.

The digital revelation system or radiographic cassette, beyond the already translation movement described above, will obviously have a running capacity articulated in autonomous micromovements. As a consequence, always different points of the revelation system detection plane will be exposed to the photon layer.