Introduction1

The use of radiograph as a diagnostic tool has become an indispensable routine in dentistry. The presence and extension of many pathologic or abnormal conditions can be traced only by radiograph. In numerous situations, the use of radiographs is also essential during therapy and to follow the progress of treatment effects.

For a long time, radiographic film was the most important medium to achieve the diagnostic image. But with the electronic era, however, more specialized equipments are introduced into different phases of the imaging procedure.

A conventional radiographic image consists of all the arrangement of silver grains in the photographic emulsion. The density of silver grains depends on the intensity of the X-ray beam. When a radiograph is viewed on a light box using transmitted light, the pattern of different densities of the silver grains is transferred to the eyes and perceived as different shades of gray. A structure that lacks sufficient density to attenuate the beam does not appear on the radiograph. If the density of a structure of interest is too low to meet sufficient diagnostic need, the contrast and density can be improved artificially.

With the help of artificial contrast most of the salivary gland lesion and internal derangement of temporomandibular joint (TMJ) can be diagnosed. 2The changes first happened in 1980 in dental radiography. Although film based imaging is not yet abandoned completely, digital imaging is now a well-accepted modality.

In digital imaging, instead of silver halide grains, a large number of small light sensitive elements are used to record the image data from the X-ray shadow. To display the image, different shades of gray are produced by the amount of light emitted from the monitor screen. The fundamental difference between conventional radiographic image and digital image is that in radiographic image, the silver grain is randomly dispersed in the emulsion, whereas the electronic elements of a digital sensor are arranged in a regular grid of rows and columns. The quantitative characteristics of the light sensitive elements of the electronic sensor results in gray shades having a discrete value for proper diagnosis.

In maxillofacial region, dental point of view the most commonly affected organs and structures are temporomandibular joint, base of skull, paranasal sinus and salivary glands. Conventional radiographs are routinely used for the examination of this site. However, the overlaps of structures may impair a proper interpretation, because of this 3-dimentional imaging techniques have become increasingly important in diagnostic imaging in the oral and maxillofacial region.

Internal derangement of TMJ may be an important factor in pathogenesis of chronic facial pain and facial dysfunction. For proper evaluation of external and internal changes in TMJ apart from the some conventional radiograph, nowadays many new imaging modalities are used in maxillofacial radiography. Computed tomography (CT), magnetic resonance imaging (MRI), ultrasonography (USG) and computed radiography (CR) are all used. All of them have been developed for making diagnosis, but today they are highly appreciated in the dentistry. As a consequence of this, alternative modalities of investigation like xeroradiography, scintigraphy, etc. were invented and utilized for oral and maxillofacial radiodiagnosis.

Xeroradiography is an electrostatic imaging process in which the image produced by an X-ray beam is recorded on a special plate instead of radiographic film. It is most widespread use is in xeromammography, an accepted diagnostic method in the examination of larynx, tracheo-bronchial tree, lymph nodes, salivary glands, brain, long bone and joints.

Radionuclide salivary imaging (scintigraphy), involves the intravenous injection of radioactive compounds with special affinity for particular tissue and later detection of them by means of external detector and imaging systems. Salivary scintigraphy measures the uptake; concentration and 3secretion by the salivary glands. Radionuclide imaging, or functional imaging technique are the only means by which physiologic changes that are direct result of biochemical alteration may be assessed.

Angiography, a radiographic procedure carried out by injecting radiopaque dye into vessels and making radiograph. Angiography demonstrates the nature of the vascular derangements, its relationship to the bone defect and associated abnormal arterial and venous vasculature.

Ultrasound is noninvasive, nonionizing imaging technique. Ultrasonography or ultrasound uses sound as sonar does to image structures deep within soft tissue. Ultrasonic scanner uses a transducer to convert electrical energy into high frequency sound waves that pass into the tissue. As the waves strikes, tissues of different densities, some of the vibrational energy is reflected back to the scanning transducer, where the sound waves are converted back to electrical energy. This electrical energy is amplified, enhanced, and displayed on video monitor. It is also good at determining the outlines of structures but not necessarily their contents. Ultrasound is inexpensive, and produces no side effects. Doppler ultrasound is particularly useful in identifying soft tissue vascular lesions.

MRI is the latest noninvasive imaging modality that uses electrical signals generated from the response of hydrogen nuclei (proton) to strong magnetic field and radio waves/radiofrequency pulses to produce an image to allow specialist to explore the inner working of human body, to detect and define the differences between healthy and diseased tissue without the use of X-ray. It enables the radiologist to view, slices of the body cut in different planes increasing the diagnostic ability. MRI can aid in diagnosing TMJ internal derangement.

Conventional radiographic techniques—the advanced radiographic modalities alongwith their indication, contraindications, advantages and disadvantages are discussed in detail.

The various imaging techniques for maxillofacial region can be grouped as under: