from the ascending ramus of the jaw at a point near the third molar, to where it enters the mental foramin.

The mental foramin is in itself a well known landmark. Into this area the Hyoid bone is also projected, and both are often mistaken for abnormal manifestations. With these two factors well established in attaining this position, abnormal conditions can be easily recognized. The Hyoid bone may be projected in such a way that it appears almost like a tooth root, but, when recognized and eliminated as a factor, it will cease to be an element of doubt.

Many radiographs show a close relationship of teeth to the inferior dental canal. When, may I ask, would its actual contact be demonstrated?

Your essayist has often surmised a close relationship, but a point I would like to have cleared up is "What constitutes radiographic proof of contact otherwise than that demonstrated stereoscopically?

The picture now on the screen (Fig. 6) is one taken to determine nerve irritation in a case of epilepsy.

You will note an area of decreased density immediately below the second right molar. The question is asked, "Does this area include, or in any way give evidence of having reached a point which would indicate contact with this nerve?"

The case was referred to me by the attending physician with instructions to eliminate all peripheral irritations. Extraction of this tooth gave no apparent results. However, while treating the case for a rather advanced stage of pyorrhea of his lower anterior teeth, he had an attack immediately when instrumentation progressed to a point near the apex of his lower right lateral incisor.

Fair progress, that is, a lessening in the number and severity of the attacks has been accomplished, but no cure.

The question remains unanswered in my mind, as to whether the destruction

First molar has partial root filling, but with no abnormal radiographic manifestations at the apices. The entire lower mandible assumed to be normal. Extrac

tion and treatment of the teeth mentioned, was not followed by any appreciable improvement of arthritic conditions. All other possible foci of infection eliminated, the attending physician insisted upon further examination of the mouth to discover any other focus. A careful re-study of the plates and films failed to show any further evidence of pathological conditions. However, yielding to the physician's judgment, I commenced to drill into each tooth in the mouth, to determine whether any other teeth contained dead pulps. This resulted in roy discovering that the upper right central, upper right cuspid and lower left central contained putrescent canals. These three teeth last mentioned, gave no evidence as regards color or radiographically of being in a diseased condition. Treatment of these canals has not resulted in any betterment of the patient's condition. There may have been evidence of changes in tissue density here, but with my present experience I failed to distinguish them.

ACUTE OR CHRONIC CASES.

Faulty phraseology is often used in trying to express whether a lesion is acute or chronic, recent or old, there being no characteristic roentgenological points of differenciation to warrant any such

term.

The accompanying radiograph (Fig. 9) was taken to determine the cause of irritation following the filling of a root canal. It shows clearly an area of lessened density around the apex, of the lower second bicuspid, with a line of increased density in continuity with the root canal. In other words, the root-filling was forced out thru the apical foramin, causing local irritation, visible in the area of decalcified cancellous tissue. Here an acute stage without infection is under

tistry the word, "abscess" is employed, when the only conclusion that can be drawn from a radiograph is that of an area, or in a stereo-radiogram of a cavity of lesser density of tissue. The nature of the contents must find clinical explation. The word syphilitic, tuberculous, etc., should not be heard in making a Roentgen diagnosis.

The film (Fig. 10) shows how a radiogram may nevertheless help clear up the obscure etiology of a cavity filled with pus. In this case, pus was exuding at a point above the first bicuspid. The radio

graph shows the location, extension, and relation of the cavity to the adjacent teeth, but not, of course, the source of infection.

Removal of the crown, also root-filling of the first bicuspid, and drainage thru this root giving no relief, the tooth was extracted under the belief that necrosis at the apex was the cause. The extraction also having no effect, the second bicuspid was drilled into and found to contain a dead pulp. Suitable treatment now cleared up the diseased area and established the etiology.

RELATION TO SURROUNDING
TISSUE.

It is important to ascertain the relation of a lesion to the surrounding tissue. This can only be shown with a plate, if possible stereoscopically. The relation of cavities, containing pus, to the teeth, as well as to the superficial tissues, the relation of growths, benign or malignant, to the adjacent tissues, and the involvement of surrounding tissues, must be looked for. Visible changes shown up by the X-Rays, are destruction of cancellous bone tissue, especially noticeable around the roots of teeth, irritative opposition of calcifying pericementitis and calcifying periositis.

The accompanying radiograph (Fig. 11) is that of a patient referred by Dr. G. V. I. Brown, with a tumor of the lower jaw, being external, but not movable upon

Fig. 11.

and causing a zone of reactive calcification around the border, not involving the molar, however, or originating from any subinvolved tooth root, as at first surmised.

These characteristics justify one in assuming a malignant growth of a bony nature, involving a large area of the lower jaw. The operative removal disclosed an osteo-sarcoma of unknown origin.

Until the last few years, we have only been called upon to look for the abnormal, as regards developmental pathological manifestations. The location of un

plate has a value in giving a gross view of the dental organs in their entirety and precludes the danger of the diagnostician losing sight of some particular pathologic point. Its value as compared to the film appears, however, to end there as far as it relates to a diagnostic study of any local abnormality. There is nothing that the essayist has said about the advantage of an exact technique that does not apply to the film as well as to the plate. When the dentist finally has found the exact spot in the jaw upon which he must base his judgment and plan of operation, the method by which the minute detail of this small area is best portrayed becomes the most valuable. It appears impossible to correctly focus the ray at one tooth on a film without getting better detail of tissue than can be obtained with the same technique when the focal ray must be directed against practically most of the jaws.

As the author has said, immobility of the patient is the first essential desideratum. If this immobility can be maintained, as it most frequently can for twenty seconds, much sharper detail, and con

sequently finer diagnostic discrimination of tissue can be secured, than if the power and penetration of the ray is doubled so as to obtain a good picture in one-half the time. A satisfactory picture with a given tube requires a ray with a given amount of power and penetration. This resulting total of energy can be obtained almost instantaneously, as in the flash picture or prolonged by time exposure. Numerous experiments appear to make a twenty second exposure far more valuable for diagnostic purpose than exposures of lesser time. Thruout this valuable essay is heard the cry for aid in being able to make the fine discriminations that are necessary in order to substantiate a positive diagnosis. Frequently the stereoscopic picture be comes invaluable, but this often fails to meet the requirement.

The essayist has very tritely drawn attention to the fact that location of the dental organs and the nature of the involved tissues make it possible for the dental Roentgenogram to surpass in accuracy of the detail, the Roentgenograms of other human tissues. It is our belief that this discriminating detail can be still greatly increased, and experiments with this object in view have been under way for some time.

There is a close bearing on this important point, and the implied criticism of the essayist against the general radiographer taking dental Roentgenograms.

His criticism of dentists having the pictures for their patients taken by men who have not been thoroly educated as dentists, is most timely, but altogether too mild. I have yet to see one of these radiographers who have only a medical education, display any accurate knowledge of dental tissues even after years of work in this field. Their interpretation of the Roentgenogram would often appear ludicrous, if it were not for the fact that the following of so many incorrect interpretations was productive of evil instead of good. Incorrect interpre