Dental and oral radiography - a text book for students and practitioners of dentistry (1916) (14777123813)

Identifier: dentaloral00mcco (find matches)
Title: Dental and oral radiography : a text book for students and practitioners of dentistry
Year: 1916 (1910s)
Authors: McCoy, James David
Subjects: Radiography, Dental X-rays Teeth Mouth
Publisher: St. Louis : Mosby
Contributing Library: West Virginia University Libraries
Digitizing Sponsor: LYRASIS Members and Sloan Foundation



Text Appearing Before Image:
tube, throughthe compression diaphragm and cylinder can bemade to pass through the desired areas and casttheir shadows upon the small film within themouth (Fig. 34). In using this method upon the upper teeth, thegreatest care must be exercised if the shadowsproduced are free from distortion, for the filmmust be held within the upper arch against thelingual side of the teeth and the palate, and mustoccupy a position which is in a different planefrom that occupied by the roots of the teeth.Whenever it is necessary to direct the rays uponstructures which lie at an angle with the plateor film, correct shadows may be obtained by ad DENTAL AXD ORAL RADIOGRAPHY TECHXIC 85 hering to the following rule: Bisect the anglemade by the plane of the object, and the plane ofthe film, and direct the rays so that they willfall perpendicular to this bisected plane. Failure to adhere strictly to this rule is one ofthe most common causes of partial or completefailure in producing true shadowgraphic repre-
Text Appearing After Image:
Fig. 34. The patient can hold the film in position against the upper teeth by-exerting slight pressure with the thumb. sentatioiis of the dental structures. For instance,if the rays are directed from too low a source,the shadows will be lengthened, or if they be di-rected from too high a source, the shadows willbe fore-shortened, the amount of elongation or 86 DENTAL AND ORAL RADIOGRAPHY fore-shortening being in direct proportion to theamount of deviation from the proper focal point. The importance of adhering strictly to this ruleis graphically shown in Fig. 35, * where an uppercentral incisor and the adjacent teeth are radio-graphed. In the upper picture (A) the rays arepassing in from too low a source with the resultthat the image imposed upon the film is length-ened to the extent that the resulting radiograpliis useless. In the center picture (B) the rays arecoming from too high a source, the result beinga shortened image. Such a radiograph has butlittle value and in many instance