RADIOGRAPHY

from the library of Robert L. Talley, DDS.

The x-ray technology used in our office is the Quint Sectograph head and neck tomographic unit, which delivers a distortion and smear-free tomographic image. In addition to providing temporomandibular joint tomographic sagittal and cross-sectional slices, we can provide an entire range of static skull and cervical views. These include anteroposterior, posteroanterior, lateral and submentovertex skull images as well as Waters and Towns views. Standard cervical images include not only the static c-spine views of lateral, frontal and oblique, but also dynamic views with the head in flexion, extension, left side bending and right side bending to demonstrate normal or pathobiological vertebral movement under function. Our equipment has less than 1/150th of the radiation used by the standard CAT scan technology. Each 8" x 10" film uses less x-radiation than two single dental x-ray films.

The tomograph creates a true radiograph, whereas the CT scan is a computerized reconfiguration of digital data. The main advantages of tomography are in comfort of image production, drastically reduced cost, and, of paramount importance, significantly less radiation dosage.

Tomography unlike a CAT scan is done in the sitting position in an open machine. The amount of x-radiation used for a typical study is 240 mrad. The CT scan, on the other hand, uses approximately 36,900 mrad. (As means of comparison, the average single dental x-ray uses 140 mrad.) To accomplish similar imaging the CAT exposure uses 154 times more radiation than the typical tomographic study of the head and TMJ's.

We are also equipped with the latest in medical processing and image duplicating equipment.
It is our goal to consistently provide "textbook" archival quality radiographs for diagnostic use.

MORE ON TOMOGRAPHY:

Tomography is a technique of taking radiographs from any part of the body in layers. Working on the principal of a moving x-ray source, a moving x-ray film, and a stationary focal plane, tomography takes advantage of the fact that any movement causes structures, other than those precisely at the level of the focal plane, to be "blurred out" and not recorded on the film. This method of taking radiographs can be applied to the temporomandibular joint and allows us to create a focal plane that can be narrow, medium or wide, depending on the amount of the structures to be radiographed. Also, the location of depth of the focal plane can be changed from radiograph to radiograph, to afford images of the same anatomical structure, at several levels. This is especially beneficial for lateral views of the condyle to exam the lateral pole, middle and medial pole of the condylar head. Typically, a tomogram of the temporomandibular joint is taken in a parasagittal plane. This plane is determined either by the accurate calculation of the angle from the long axis or the condyle to the mid-sagittal plane. These are techniques used by which that angle is estimated, rather than precisely determined; however, accuracy is lost by doing so. Tomographic views of the various anatomical structures of the head, neck and mandible can be taken with machines currently available to dentistry. Each of the machines has individual characteristics that must be carefully weighed as to its benefit to the clinician.

Techniques and types of films taken still vary greatly, but standardization is not too far away.

General observations: The glenoid fossa should be evaluated to determine if its outline demonstrates a smooth unbroken layer of lamina dura extending anteroposteriorly and mediolaterally. The eminence should be evaluated to determine erosion or pitting and the presence of any sclerosis. The early stages of sclerosis will appear as thickening of the lamina dura. The eminence can also be evaluated for pneumatization.

Insults to the temporomandibular joint, involving microtrauma, will frequently lead to sclerosis, rather than degenerative changes. The adaptive capacity of the individual may cause calcium to be precipitated into the area, rather than a complete breakdown of the joint tissues. However, as the insult persists or increases, we may see osseous breakdown in the form of osteoarthritic (degenerative) changes.

The condylar head should be examined to note that it has a consistent layer of lamina dura that is unbroken and that it has a rounded form. Erosion, pitting, osteophytic formation, exostosis, hyperplasia and other anomalies should be checked carefully.

The angle of the head of the condyle to the condylar neck should be evaluated and determined. It can be divided into three order of bends. The first order bend shows a relatively straight condylar head on top of the neck. A second order bend shows a forward angulation of the condylar head on the neck of the condyle. A third order bend shows a severe angle bend of the head on the condylar neck. The forward bending of the condyle represents an adaptive, compensatory change to a chronically posteriorized condyle.

The anterior, superior, posterior, medial and lateral joint space can be evaluated by reviewing the composite of all the tomograms. On the parasagittal film, the anterior joint space should be the narrowest of all, but never thinner than 1.5 mm. The superior joint space generally should be the medium thickness and the posterior joint space should be the greatest. Concentricity or slight anterior position of the condyle in the centric occlusion position is a must of normal joint and neuromuscular function.

SUBMENTAL VERTEX RADIOGRAPH:

The submental vertex radiograph is usually considered to be a step in achieving the actual imaging desired. However, if time is taken to review the submental vertex, it can provide a great deal of diagnostic information, beyond just simple condylar width and condylar angle to the sagittal plane. It is a virtual study of the anatomy of the cranial base. Obvious landmarks include the extended cervical spine, the foramina magnum, the odontoid process position, the foramin ovale, the posterior nasal appature (or choana), the sphenoid sinuses, and border landmarks such as the zygomatic process and the temporal and occipital bones.

LATERAL SKULL RADIOGRAPH:

The lateral skull radiograph is taken by using a cephalometric headholder a standard 60 inch distance between the x-ray source and the film. The patient stands or sits upright with his teeth closed in centric occlusion. The film cassette is positioned as low as possible on the patient's shoulder. If necessary, the patient holds a 5 lb. weight in each hand to further lower his shoulders.

The lateral skull radiograph is an important diagnostic tool for evaluating orofacial growth, form and function. When its orthopedic considerations are added, it becomes one of the best medical/dental diagnostic radiographs.

PANORAMIC RADIOGRAPH:

The panoramic x-ray is the "work horse" of dentistry. Since the first panoramic films were introduced, the ability to scan the region of the oral pharynx and surrounding tissues has provided a great increase in the dentist's diagnostic capabilities. With the advent of the uninterrupted panoramic film, that is most commonly used today, we have an even more clearly portrayed image of the orofacial structures.

This two-dimensional representation of the three-dimensional orofacial area allows us to graphically visualize the anatomy of both dental and skeletal components. Soft tissues may also be visualized, when the interpreter understands all seen. From the simple outline of the ear lobe to the airway opening, we can visualize tissues that are encompassed by, or surround, the skeletal and dental structures.