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DENTAL AND ORAL RADIOGRAPHY 
 
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DENTAL AND ORAL 
 
 EADIOGRAPHY 
 
 A TEXTBOOK FOR STUDENTS AND PRACTITIONERS 
 OF DENTISTRY 
 
 BY 
 
 JAMES DAVID McCOY, D.D.S. 
 
 PROFESSOR OF ORTHODONTIA AND RADIOGRAPHY, COLLEGE OF DENTISTRY, 
 UNIVERSITY OP SOUTHERN CALIFORNIA, LOS ANGELES, CALIFORNIA 
 
 WITH 123 ILLUSTRATIONS 
 
 SECOND EDITION 
 
 ST. LOUIS 
 
 C. V. MOSBY COMPANY 
 
 1919 
 

 n 
 
 Copyright, 1916, 1918, bv C. V. Mosby Company 
 
 Press of 
 
 C. V. Mosby Comf^any 
 
 St. Louis, Mo. 
 
PREFACE TO SECOND EDITION 
 
 During the preparation of the second edition of this book the 
 author has endeavored at all times to keep in mind the needs of 
 the beginner in radiography rather than consider matters of in- 
 terest to those who have progressed beyond this stage. 
 
 That radiography is essential in the practice of dentistry is 
 no longer a debatable question. The wide interest being mani- 
 fested in it by our profession and the numerous instances where 
 dentists are installing their own x-ray laboratories bear elo- 
 quent testimony of this fact. While the author is willing to plead 
 "guilty to a great degree of enthu.siasm" regarding the value 
 of the x-ray in dentistry, he feels that he is within reasonable 
 bounds in asserting that the x-ray has done more to improve 
 dentistry than any other agent that has come into it during the 
 past ten years. If it were of value ''in root canal operations 
 only" the benefits to this field alone would justify the foregoing 
 statement, for we must all acknowledge that as commonly prac- 
 ticed in the past this branch represented the greatest short- 
 coming of our profession. 
 
 Fortunately root canal work does not represent the only field 
 in dentistry where the radiogram is a benefit, for it has been 
 demonstrated that it is of equal value and in fact is often abso- 
 lutely essential in the other branches of practice. These facts 
 are not only now fairly well appreciated by dentists, but the 
 laity have been quick to grasp them with the result that den- 
 tists who attempt certain operations witiiout radiographic guid- 
 ance are open to censure from their patients. 
 
 The awakening of the rank and file of the profession to the 
 necessity of a more universal adoption of the x-ray has been 
 slow, and it is doubtful if some will ever become fully conscious, 
 as they continue to exhibit a lethargy toward this field which 
 is either indicative of lack of foresight or sheer laziness. 
 
 In contrast to such, it is refreshing to recall that some mem- 
 bers of our profession were quick to see the possibilities to den- 
 
 5 
 
6 PREFACE 
 
 tistry offered through the adoption of the x-ray. Conspicuous 
 among these was Dr. C. Edmond Kells, of New Orleans, who in 
 1896 (within the year following the discovery of the x-ray) 
 installed x-ray equipment in his office and applied it to his 
 dental practice. So great were his convictions and so genuine 
 was his enthusiasm that in July, 1906, he took his x-ray equip- 
 ment to Ashville, N. C, and there gave a clinic before the South- 
 ern Dental Association. Dr. Kells w#s the first dentist to make 
 radiograms by placing small films in the mouth, and he also 
 originated the plan of placing diagnostic wires in the roots of 
 teeth. 
 
 Among those who shared Dr. Kells' foresight during those 
 pioneer days and adopted the x-ray as part of dental practice 
 are numbered such men as Drs. Van Wort, M. L. Rhein, E. W. 
 Caldwell, T. P. Hinman, and "Weston A. Price. 
 
 Within the last few years a large number of our dental schools 
 have included radiography in their teaching eurriculums and 
 some have even shown the foresight of establishing it as a dis- 
 tinct department with equal rank and consideration with the 
 other important branches. This will in time bear fruit which 
 will result in a more adequate appreciation of the merits and 
 possibilities of the x-ray and its inseparable relationship to 
 dentistry. 
 
 The author wishes to gratefully acknowledge the assistance 
 given him in the preparation of this edition by Dr. Julio Endel- 
 man, whose friendly criticism and interest have been a constant 
 source of help. Grateful acknowledgment is also made to Dr. 
 Richmond C. Lane, who was kind enough to contribute several 
 radiograms from practical cases illustrating root canal opera- 
 tions, root resections, and cysts. The author has also been aided 
 by various manufacturers of x-ray equipment who have fur- 
 nished many cuts of value to the text, and last, but not least, 
 the publishers have by their cooperation and patience through 
 many delays rendered less irksome the task of the w^riter. 
 
 James D. McCoy. 
 
 Los Angeles, Cal. 
 
PREFACE TO FIRST EDITION 
 
 This book has been written primarily as a textbook for stu- 
 dents of dentistry. It is essentially a book for beginners, and 
 as the majority of the dental profession are at present to be 
 regarded as beginners in this comparatively new branch of den- 
 tistry, the author entertains the hope that it will prove of inter- 
 est to practicing dentists who appreciate the value of the x-ray, 
 and are desirous of adding radiography to their accomplish- 
 ments. 
 
 A few years ago the x-ray was considered in the light of a 
 cultural asset to dentistry, but today the far-seeing members 
 of our profession have awakened to the fact that it is a real 
 necessity. 
 
 The x-ray will give the maximum amount of service in dental 
 practice only to such of our profession who master the technic 
 of radiography, and in addition are possessed of an accurate 
 knowledge of the anatomy and pathology of the dental and oral 
 structures. 
 
 The author is indebted to the pioneers in dental radiography 
 who have so generously contributed to its literature. Of these, 
 much of value has been derived from the writings of such men as 
 Drs. A. H. Ketcham, Weston Price, Sidney Lange, Howard R. 
 Paper, F. L. P. Satterlee and Edward H. Skinner. 
 
 During the preparation of this work, the author has been 
 aided by various manufacturers of x-ray equipment who have 
 generously furnished cuts whenever requested. G-rateful ac- 
 knowledgment is also made to Dr. J. P. McCoy and to Laura 
 Spruill who have made the drawings used as illustrations, and 
 last and by no means least, to the publishers who have, through 
 their forbearance and many courtesies, lessened the burdens of 
 the writer. 
 
 James D. McCoy. 
 
 Los Angeles, Cal. 
 
CONTENTS 
 
 PAGE 
 CHAPTER I 
 
 Introduction 17 
 
 CHAPTER II 
 
 The Nature of the X-ray and Its Discovery 22 
 
 CHAPTER III 
 
 High Tension Electric Currents — Magnetism — Electromagnetic 
 
 Induction 31 
 
 CHxVPTER IV 
 
 RlIUMKORFF OR INDUCTION COIL — TESLA OR HiGII FREQUENCY COIL — 
 
 Interrupterless Transformer 43 
 
 CHAPTER V 
 
 Requisites op the Dental X-ray Laboratory 62 
 
 CHAPTER VI 
 
 Teciinic of Dental and Oral Radiography 88 
 
 CHAPTER VII 
 
 Teciinic of Dental ant) Oral Radiography (Continued) . . . 107 
 
 CHAPTER VIII 
 
 Correct Exposure and Development of X-ray Plates and Films 115 
 
 CHAPTER IX 
 The Interpretation op Dental and Oral Radiograi.es .... 122 
 
 CHAPTER X 
 
 Indications for. the Use of the X-ray in the Practice op 
 
 Dentistry 135 
 
 CHAPTER XI 
 
 Dangers of the X-ray and Methods of Protection 167 
 
 9 
 
ILLUSTRATIONS 
 
 FIG. PAGE 
 
 1. William Conrad Roentgen 24 
 
 2. Michael Faraday 25 
 
 3. Sir William Crookos 26 
 
 4. Ilcinrich Hertz 27 
 
 5. The action of iron filings in forming definite curved lines about 
 
 an ordinary bar magnet 35 
 
 6. Diagrammatic illustration of the magnetic lines of force . . . 3G 
 
 7. Diagrammatic illustration of the magnetic field surrounding a 
 
 coil of wire through which an electric current is passing . . 37 
 
 8. An iron bar placed within the windings of a solenoid is subject 
 
 to its magnetic field and becomes a magnet 38 
 
 9. Magnet with diagrammatic illustration of ''magnetic lines of 
 
 force" surrounding it 39 
 
 10. Battery from which an electric current is passing through the 
 
 solenoid 40 
 
 11. Diagrammatic illustration of the essential parts of an induction 
 
 coil 44 
 
 12. Diagram of the electrolytic interrupter 46 
 
 13. Diagram of the induction coil 47 
 
 14. Induction coil adapted for use in the dental x-ray laboratory . . 49 
 
 15. Induction coil adapted for use in the dental x-ray laboratory . 50 
 
 16. Induction coil adapted for use in the dental x-ray laboratory . 51 
 3 7. Diagram of the high frequency coil 54 
 
 18. Small type high frequency coil 55 
 
 19. Medium-sized high frequency coil 55 
 
 20. Large type high frequency coil 56 
 
 21. The working principles of the interrupterless transformer ... 57 
 
 22. Interrupterless traiif-former adapted for use in the dental x-ray 
 
 laboratory 58 
 
 23. Interrupterless transformer adapted for use in the dental x-ray 
 
 laboratory 59 
 
 24. Interrupterless transformer adapted for use in the dental x-ray 
 
 laboratory 60 
 
 25. Diagram of an x-ray tulje 65 
 
 26. The coil or transformer tube 66 
 
 27. The high frequency tube 67 
 
 28. Connecting tube to x-ray machine 68 
 
 29. The hydrogen tube 68 
 
 30. The Coolidge x-ray tube 69 
 
 31. The tube stand 71 
 
 11 
 
12 ILLUSTRATIONS 
 
 FIG. PAGE 
 
 32. Illustrating liow the tube may be placed at any desired angle . 72 
 
 33. Illustrating reasons for using the tube shield, compression dia- 
 
 phragm, and compression cylinder 78 
 
 34. Leadipd glass tube shield 74 
 
 35. A convenient manner of arranging the necessary ajiparatus when 
 
 not in use 75 
 
 36. The portable darkroom 77 
 
 37. The patient holding the film in position against the upj)er teeth 82 
 
 38. Correct and incorrect technic 83 
 
 39. Technic for the upper molar teeth 85 
 
 40. Special compression cylinder made of leaded glass 86 
 
 41. The patient holding the film in position against the lower teeth 87 
 
 42. The Ketcham film holder 89 
 
 43. The Leach film holder 90 
 
 44. The Dorr film holder with detachable handle 91 
 
 45. Procedure for making complete radiographic examination of den- 
 
 tal arches 91 
 
 46. Arrangement of dental chair allowing patient's head to rest 
 
 easily and firmly upon it 93 
 
 47-^. Tube stand with platerest and head support 94 
 
 47-i?. Position of head and angle for left side of jaws 94 
 
 48. The arrangement of the apparatus prei^aratory to seating the 
 
 patient 95 
 
 49. The patient seated and the apparatus arranged for making a 
 
 radiogram of the left side 95 
 
 50. Technic for left side 98 
 
 51. Technic for right side 99 
 
 52. The result of correct technic 100 
 
 53. Incorrect technic 101 
 
 54. The result of incorrect technic 102 
 
 55. Technic for radiographing areas in the upper and lower jaws 
 
 extending from the median line to the first premolar . . . 103 
 
 56. Technic for radiographing structures at the median line includ- 
 
 ing the incisors, both above and below 104 
 
 57. Supporting the patient's head by a bandage of gauze to insure 
 
 perfect immobility 105 
 
 58. Connecting the tube to the x-ray machine 109 
 
 59. Diagram of an x-ray tube 112 
 
 60. X-rayproof film and plate chest 116 
 
 61. Eadiographic appearance of the teeth and their surrounding 
 
 structures under normal conditions 124 
 
 62. A cuspid tooth lying against the anterior wall of the antrum . 127 
 
 63. A radiogram to determine the state of dentition of the right 
 
 side in the mouth of a child eleven years old- 127 
 
ILLUSTRATIONS 16 
 
 FIG. PAGE 
 
 64. An alveolar abscess involving the roots of an upper central in- 
 
 cisor and latei'al incisor 128 
 
 65. Eadiogram showing evidence of an alveolar abscess 128 
 
 66. Large alveolar abscess about the root of a lower first bicijspid 128 
 
 67. An upper bicuspid tooth with an alveolar abscess at its root apex 129 
 
 68. Small abscesses at the apices of two upper bicuspid teeth , . 130 
 
 69. A necrotic area about the roots of an upper central and lateral 1.30 
 
 70. A necrotic area lying below a lower cuspid 131 
 
 71. Eoot canal fillings in a lower first molar 132 
 
 72. Eoot canal filling material forced beyond the root apex of an 
 
 upper second bicuspid 132 
 
 73. A steel wire introduced into the root canal to determine its length 132 
 
 74. A destructive process involving the pericemental and alveolar 
 
 tissues about an upper first bicuspid 132 
 
 75. Characteristic aj^pearance of the enveloping tissues about the 
 
 upper bicuspids and molars in a well-developed case of 
 
 pyorrhea alveolaris 132 
 
 76. An osteosarcoma of the mandible 133 
 
 77. Well-developed cyst over an upper lateral incisor 133 
 
 78. Well-developed cyst lying below the lower incisors .... 133 
 
 79. Extra-oral radiogram of the right side made for purposes of 
 
 general examination 137 
 
 SO. Intra-oral radiogram used as a means of confirmation of the 
 
 findings of the extra-oral radiogram 138 
 
 81. Alveolar abscesses at the apex of each bicuspid root .... 138 
 
 82. Upper bicuspid teeth with abscesses 138 
 
 83. Severe inflammatory process in progress about upper lateral 
 
 incisor 138 
 
 84. Extra-oral radiogram of the lower molars showing the j^i'esence 
 
 of a large alveolar abscess 139 
 
 85. Eadiograms showing imperfectly filled canals, diagnostic wires 
 
 in place, and same teeth after being filled 140 
 
 86. Eadiograms showing imperfectly filled canals, diagnostic wires 
 
 in place, and same teeth after being filled 141 
 
 87. Eadiograms showing imperfectly filled canals, diagnostic wires 
 
 in place, and same teeth after being filled 141 
 
 88. Eadiograms showing condition present, diagnostic wires inserted, 
 
 root canals filled, and resection of roots 142 
 
 89. Eadiograms showing central incisor before resection, after re- 
 
 section, and several months later, showing regeneration of 
 osseous tissue 143 
 
 90. Upper central root before resection, and after resection, showing 
 
 partial regeneration 144 
 
 91. A well-developed case of pyorrhea alveolaris involving the mo- 
 
 lars and incisors 145 
 
14 ILLUSTRATIONS 
 
 FIG. PAGE 
 
 92. Au unerupted cuspid tooth making an attempt to erupt un- 
 
 der a bridge 147 
 
 93. Eadiogram made to be sure no root fragments were present in 
 
 the tissues under the bridge 147 
 
 94. Inflammatory process under a small bridge 147 
 
 95. Extra-oral radiograms of impacted and unerupted third molars 149 
 
 96. Intra-oral radiograms of impacted lower third molars . . . 150 
 97-^. Large cyst in the mandible lying below a molar tooth . . 151 
 97--B. Same case as shown in Fig. 97-^, six months after curette- 
 
 ment, showing partial regeneration of the osseous structure 151 
 
 98. Large abscess with cyst formation, involving the upper, central, 
 
 lateral, and cuspid roots 152 
 
 99. Eadiogram revealing the fact that there is a congenital absence 
 
 of permanent molars on the left side 153 
 
 100. Radiogram revealing the fact that all but one of the permanent 
 
 molars are congenitally absent on the right side .... 153 
 
 101. Unerupted lower second bicuspid for which space must be made 
 
 to permit its eruption 155 
 
 102. Unerupted cuspid for which space must be made if it is to 
 
 erupt in its normal position 155 
 
 103. Unerupted lower lateral incisor for which space must be made 156 
 
 104. Unerupted lower second molar prevented from erupting through 
 
 impaction against the lower first molar 156 
 
 105. Unerupted upper bicuspid teeth which are being deflected to 
 
 the lingual 157 
 
 106. Unerupted biscup)id teeth which are rotated and erupting to 
 
 the lingual 157 
 
 107. Eadiograms showing unerupted cusj^id, same tooth after re- 
 
 moval of lateral incisor and deciduous cuspid, showing at- 
 tachment for moving the unerupted tooth; cuspid tooth 
 moved down to the point of eruption 158 
 
 108. Supernumerary teeth. Case after extraction 158 
 
 109. An unerupted lower second bicuspid in a patient twelve years 
 
 old 160 
 
 110. Unerupted upjjcr and lower bicuspids in a patient eleven years 
 
 of age 160 
 
 111. Unerupted cuspid teeth whose relationship to the roots of the 
 
 incisors must be taken into consideration during tooth 
 movement 161 
 
 112. An unerupted lower third molar which is crowding the incisors 162 
 
 113. An erupting lower third molar which has been responsible for 
 
 the crowding of the lower incisors and cuspids .... 162 
 
 114. Nonvital tooth being used as' an' anchor tooth and nonvital tooth 
 
 which was not considered safe for anchorage . . . . . 164 
 
 115. Supernumerary upper second bicuspid 164 
 
ILLUSTRATIONS 15 
 
 FIG. PAGE 
 
 116. Lower deciduous central incisors having the appearance of 
 
 sui^ernumerary teeth 164 
 
 117. Radiogram showing either an anomalous central incisor or a 
 
 central incisor lying in a horizontal position to the other 
 
 teeth 164 
 
 lis. Patient seated and tlie apparatus aiiangcd to make a radio- 
 gram of the left side 165 
 
 119. Patient seated and the apparatus airnngod to make a radio- 
 
 gram of the right side 165 
 
 120. An x-ray tube inclosed within a leaded glass tube sliicld . . 172 
 
 121. Types of lead-lined protection screens 17.3 
 
 122. Lead-impregnated glove 174 
 
 123. X-ray protection apron 175 
 
DENTAL AND ORAL RADIOGRAPHY 
 
 CHAPTER I 
 
 INTRODUCTION 
 
 When William Conrad Roentgen announced his dis- 
 covery to the world, he called it the "x-ray," but the civ- 
 ilized world has for the most part seen fit to designate it 
 the ''roentgen ray" in honor of the discoverer. Roent- 
 genology is, therefore, defined as "the study and prac- 
 tice of the roentgen ray as it applies to medicine and 
 surgery. ' ' 
 
 For purposes of study, roentgenology may be divided 
 into two distinct fields, depending upon the purpose for 
 which the roentgen ray is to be utilized. In the first, 
 which is the one enlisting the interest of dentists, it is 
 used for the production of shadow pictures or radio- 
 grams. In other words, it embraces what is commonly 
 called the "field of radiography," or "roentgenog- 
 raphy. ' ' 
 
 The other branch mentioned includes the use of the 
 roentgen ray for therapeutic purposes, and is known 
 as "radiotherapy," or "roentgenotherapy." With this 
 field, the dentist is happily not directly concerned, and, 
 therefore, his responsibilities are not so great as the 
 medical roentgenologist. 
 
 Of the various collateral sciences of medicine, there is 
 no other which has developed more rapidly, or which has 
 assumed a more important bearing in many branches of 
 practice than has the science of roentgenology. With the 
 increased appreciation of its value, and its wide adop- 
 
 17 
 
18 DENTAL AND ORAL RADIOGRAPHY 
 
 tion, it has been developed through a comparatively 
 short period of evolution, until now it can be regarded, 
 broadly S]3eaking, in the light of an exact science. 
 
 In spite of this fact, there is still apparent a great de- 
 gree of misconception as to the responsibilities of one 
 who is to actively engage in this work. 
 
 To the uninitiated, this field of labor often presents 
 alluring possibilities, and they are all too apt to rush 
 in without adequate preparation. To such, the reward 
 of bitter disappointment must eventually come, when they 
 become mired in the mud of their own poor judgment and 
 lack of technical knowledge. 
 
 To avoid such an end, or perhaps what is almost as 
 ignominious, — the acquiring of "a partial knowledge" 
 of the subject, which at best can only carry one half- 
 way upon the journey of success — the student should 
 first come to a realization that the practice of roentgen- 
 ology or any of its branches, requires more than a mere 
 training in the mechanics of the x-ray laboratory. 
 
 Undoubtedly, many a man has, in the contemplation of 
 x-ray apparatus for his office, given serious thought to 
 the type of equipment ivhich he ivished to install, and has 
 assumed that with a modern laboratory, he would be in 
 a position to render the best of service. Such a mis- 
 guided individual all too soon learns that a very large 
 part of the battle lies ivithin himself, and if his own 
 knowledge is deficient, the finest equipment in the world 
 will not make him a roentgenologist. 
 
 It is important, therefore, that those who contemplate 
 any indulgence in the field of radiography should not 
 underestimate the task that confronts them. 
 
 In addition to becoming familiar with the electro- 
 physics of x-ray laboratory equipment, its practical ap- 
 plication in his chosen field, the dangers which surround 
 it if improperly used, one should realize that the real 
 
INTRODUCTIOiSr 19 
 
 practice of roentgenology begins when the x-ray picture, 
 or radiogram, has been produced. It is quite impos- 
 sible for such an image to be of value unless the roent- 
 genologist is thoroughly familiar with the anatomy, phys- 
 iology, and pathology of the field under examination; 
 and even these qualifications are not adequate unless 
 backed up by practical clinical experience. 
 
 For those who can qualify, there is a real field and a 
 rare opportunity, and it will be found that every man 
 who engages in this work will receive just that amount 
 of recognition and respect from his colleagues to which 
 his abilities entitle him. 
 
 One of the first things which the beginner should do 
 is to become familiar with the terminology of this sub- 
 ject, and cultivate the habit of using terms correctly. 
 Instead of using the term ''x-ray picture," such an image 
 should always be spoken of as a "radiogram," or as a 
 ' ' roentgenogram. ' ' 
 
 The physician or the dentist maintaining an x-ray lab- 
 oratory should not be called ''an x-ray specialist," but 
 should be spoken of as "a medical or a dental roent- 
 genologist." 
 
 Not infrequently, we hear physicians or dentists speak- 
 ing of a dental radiogram as a "dental x-ray." Such an 
 expression only exposes their crudity of thought, and 
 certainly expresses nothing else. 
 
 It is thought by some terminologists that in addition to 
 always speaking of the x-ray as the roentgen ray, in honor 
 of the man who discovered it, we should include the name 
 roentgen in every descriptive word connected with the 
 work. To such, the term "radiograph" (verb) and 
 "radiogram" (noun) will doubtless appear improper, 
 but the author feels justified in continuing their use, as 
 these words are thoroughly descriptive and less cum- 
 bersome than "roentgenograph" and "roentgenogram." 
 
20 
 
 DENTAL AlsTD ORAL RADIOGRAPHY 
 
 For the same reason, the term ''radiography" is pre- 
 ferred rather than "roentgenography" to designate the 
 art of making radiograms. 
 
 Briefly summarized, the following roentgen terminol- 
 ogy will be found to be quite adequate : 
 
 Roentgen ray, or 
 X-ray : 
 
 Roentgenology, or 
 Radiology:^ 
 
 Roentgenologist, or 
 Radiologist : * 
 
 A phenomenon in physics discovered by 
 William Conrad Roentgen. 
 
 The study and practice of the roentgen 
 ray as applied to medicine and surgery. 
 
 One skilled in roentgenology, or radi- 
 ology. 
 
 The shadow picture produced by the x- 
 ray upon the photographic emulsion. 
 
 (Verb.) To make a roentgenogram, or 
 radiogram. 
 
 The art of making roentgenograms, or 
 radiograms. 
 
 Treatment by the application of the 
 roentgen ray. 
 
 Skin reaction due to too strong or too 
 often repeated application of the roent- 
 gen ray. 
 
 Roentgenographic examination, or The examination and study of the shadow 
 
 Roentgenogram, or 
 Radiogram : 
 
 RoentgenograjDh, or 
 Radiograph : 
 
 Roentgenography, or 
 Radiography : 
 
 Roentgenotherapy, or 
 Radiotherapy : " 
 
 Roentgen dermititis, or 
 X-ray dermatitis : 
 
 Radiographic examination : 
 
 Roentgen diagnosis, or 
 X-ray diagnosis: 
 Pathoroentgenography, or 
 Pathoradiography : t 
 
 pictures produced by the x-ray upon 
 the photographic emulsion. 
 
 Diagnosis by aid of the roentgen ray. 
 
 Tlie study of pathologic lesions as re- 
 vealed by the radiogram, or roentgeno- 
 gram; it implies and renders impera- 
 tive a knowledge of the pathology and 
 of the interpretation of normal and 
 abnormal tissue densities as recorded 
 in the radiogram. 
 
 To apply the roentgen ray. 
 
 The application of the roentgen ray. 
 
 The untoward effect of the roentgen ray. 
 
 *The term is rather confusing, as it could also refer to the practice and therapy 
 of radium or other radiotherapeutic agents. 
 tTerms suggested by Dr. Julio Endelman. 
 
 Roentgenize : 
 Roentgenization : 
 Roentgenism : 
 
INTRODUCTIOIT 21 
 
 Some writers add other descriptive terms to the fore- 
 going list, but the author feels that a terminology should 
 be just as brief as is consistent with adequate descrip- 
 tion ; hence, several terms appearing in current literature 
 on different phases of roentgenology have been omitted. 
 
CHAPTER II 
 
 THE NATURE OF THE X-RAY AND ITS 
 DISCOVERY 
 
 In order to gain an intelligent conception of the x- 
 ray, it is quite necessary tliat the student start mth 
 a consideration of certain phases of electrophysics, and 
 radiant energy, or in fact the very foundation of matter 
 itself. 
 
 According to the most plausible theories and beliefs, 
 all matter is suspended or contained in the medium 
 knoA\Ti as ether, which is an elastic medium filling all 
 space, interatomic and interelectronic, as well as all 
 other space of which we have any knowledge. 
 
 Furthermore, many facts brought out by the close 
 study of chemistry and physics seem to justify the be- 
 lief that all substances of matter are composed of mi- 
 nute particles called "molecules," and that each mole- 
 cule is made up of two or more elements called "atoms," 
 while these atoms are also further divided in particles 
 knoAvn as electrons. 
 
 These electrons, or units of matter, are never still, but 
 are in a constant state of motion or vibration, each sub- 
 stance having its OA\m specific atom and the electrons of 
 such atoms having their own rate of vibration. 
 
 The vibration of these electrons produces disturbances 
 in the ether kno^^t as ' ' ether waves ' ' which var}^ in length 
 according to the rate at which electrons are vibrating. 
 If the rate of vibration of the electrons be changed or 
 disturbed, there is a change in the ether waves, resulting 
 in a corresponding change in the phenomenon produced. 
 
 If this theory of matter is correct, as the evidence of 
 
 22 
 
NATURE OF X-RAY AND ITS DISCOVERY 23 
 
 modern science would lead ns to believe, all matter then 
 is made up of the same constituents, and its various forms 
 are determined, not by any essential difference of com- 
 position, but by the number, arrangement and amount 
 of motion of the ultimate particles making up the atom. 
 
 All this has a practical significance to us in under- 
 standing the phenomenon which we call the x-ray. As 
 stated before, it is known that a certain rate of vibra- 
 tion of electrons will produce other waves resulting in a 
 definite phenomenon, while a change in this rate will 
 produce an entirely different phenomenon. For instance, 
 a slow rate of vibration (75,000,000 per second) produces 
 what are known as electromagnetic waves. A little 
 higher up the scale where the electrons are made to vi- 
 brate faster, heat waves appear. Another increase, and 
 light waves appear. If we continue to accelerate the 
 rate of vibrations of the electrons, there will be pro- 
 duced successively ultra-violet, or Finsen rays ; then cath- 
 ode, or radium, rays, and finally the x-ray. 
 
 It will then be seen that the x-rays are produced as the 
 result of the most rapid rate of vibration of which we 
 have any knowledge. In the laboratory this phenomenon 
 is produced by the sudden stopping of a stream of rapidly 
 moving free electrons in a vacuum tube which has been 
 exhausted to one millionth of an atmosphere. 
 
 The x-ray, therefore, may he defined as that form of 
 radiation ivhich emanates from a highly exhausted tube 
 ivhen an electric current of high tension is passed through 
 the tube. The object of the vacuum tube is to establish 
 a medium in which all source of resistance is removed, 
 so that the electric current may excite the exquisitely 
 rapid vibrations necessary to produce the phenomenon 
 desired, the electric current being the source of excita- 
 tion. 
 
 The radiation thus produced gives neither heat nor 
 
24 
 
 DEXTAL AND ORAL RADIOGIIAPHY 
 
 liglit, nor can it be deflected, reflected, or polarized. In 
 fact, it can only be recognized by its effect npon the 
 photographic plate and npon such chemicals as willem- 
 ite, calcinm, and tnngstate, which fluoresce or glow un- 
 der its influence. 
 
 The Discovery of the X-ray 
 
 The x-ray was discovered in 1895 by William Conrad 
 Roentgen, Professor of Physics, at the Eoyal University 
 
 Fig. 1. — William Conrad Roentgen. 
 
 of AViirzbnrg, in Germany. This discovery, marking as 
 it did, a distinct epoch in the science of medicine, was re- 
 ceived by the world with incredulity and amazement, for 
 
NATURE or X-RAY AND ITS DISCOVERY 
 
 25 
 
 its reported possibilities savored almost of the occult. 
 "A new ray had been discovered by means of which it 
 was possible to look through opaque substances." 
 
 While it fell to the lot of Professor Eoentgen to make 
 this discovery, there is no doubt but that other experi- 
 menters in the field of physics, unconsciously produced 
 this same ray. In fact, its discovery was made possible 
 by the work of other scientists who preceded Roentgen 
 and laid the foundation for its advent. 
 
 Fig. 2. — Michael Faraday. 
 
 Of these, Michael Faraday was the pioneer. In 1831 
 he discovered electric magnetic induction, which made 
 possible the induction coil and the other electric machines 
 
26 
 
 DENTAL AND ORAL RADIOGRAPHY 
 
 utilized to generate currents of great potential. As early 
 as 1838 he conducted a series of experiments to deter- 
 mine the effect of electric discharges upon rarified gases, 
 and invented the terms "anode" and "cathode" for 
 positive and negative electrodes. 
 
 In 1857 Geisgler constructed Jhe Jir st vacuum tubes 
 and it was noted at this time that an electric discharge 
 passed through these tubes would produce a peculiar 
 
 ■iS^APiiSBT-'^'^ =';''.=''.' 
 
 Fig. 3. — Sir William Crookes. 
 
 gloAv or phosphorescence, the coloring of which depended 
 upon the character of the rarefied gas contained in the 
 tube. This phenomenon became known as "fluores- 
 cence. ' ' 
 
 A few years later (1860) Professor Hittorf, a cele- 
 brated physicist of Miinster, conceived the idea of ex- 
 hausting the Geissler tube to a higher degree of vacuum 
 and found as a result an increased resistance to the pass- 
 
NATURE OF X-RAY AND ITS DISCOVERY 
 
 27 
 
 ing of the electric discharge, and that the color of the 
 rarefied gases under fluorescence, varied with the degree 
 of rarefication. He also discovered another fact which 
 was to have an important bearing upon the work of later 
 experimenters, and that was that the luminous discharge 
 in a Geissler tube could he deflected by a magnet. 
 
 The important work of these early experimenters was 
 followed later (1878) by Sir William Crookes, who suc- 
 
 Fig. 4. — Heinrich Hertz. 
 
 ceeded in constructing a more perfect vacuum tube, that 
 is, one that could be exhausted to a much higher degree 
 of vacuum. With these improved tubes, Crookes discov- 
 ered that with a sufficiently high vacuum the luminous 
 glow within the tube disappeared, and demonstrated that 
 within it there was a rectilinear radiation from the 
 cathode, which he conceived as being a projection of par- 
 ticles of highly attenuated gas at exceedingly high veloc- 
 
Z8 DEN^TAL AND ORAL EADIOGEAPHY 
 
 ity. To this radiation lie gave the name ' ' cathode rays, ' ' 
 and because of the peculiar behavior of gas in this ex- 
 ceedingly rarefied state, he concluded that it was as dif- 
 ferent from gas in its properties as ordinary air or gas 
 is different from a liquid. He found that the impact of 
 the cathode rays against the wall of the tube would pro- 
 duce within it a greenish "phosphorescence" or "fluores- 
 cence" and an increase in temperature; also that these 
 rays could be intercepted by metallic plates within the 
 tube. By concentrating the rays at the focus of a con- 
 cave cathode, he was able to produce a brilliant fluores- 
 cence and a very high temperature, both at the walls of 
 the tube and in various substances within it. Without 
 doubt, Sir William Crookes unconsciously produced the 
 x-ray in the course of these experiments. 
 
 In 1892 Professor Heinrich Hertz discovered that 
 cathode rays would penetrate gold leaf and other thin 
 sheets of metal placed within the tube. Soon after this 
 discovery, Hertz died, and his experiments were con- 
 tinued by his assistant, Lenard, who was able to demon- 
 strate that many of the phenomena of the cathode rays 
 could be observed outside of the Crookes tube. By clos- 
 ing a vacuum tube at the end opposite the cathode with 
 a thin sheet of aluminum, he demonstrated that a radia- 
 tion proceeded through or from the aluminum walls of 
 the tube which would pass through many substances 
 opaque to ordinary light, and after passing through such 
 substances, it would excite fluorescence in crystals of ba- 
 rium platino-cyanide, and would affect sensitive photo- 
 graphic plates in much the same manner as ordinary 
 light. Lenard considered that all these phenomena were 
 due to the cathode rays alone, although in the light of 
 our present knowledge, there is no doubt that, not only 
 in his experiments, but in those of Crookes, Hertz, and 
 other investigators, x-rays were produced. However, 
 
NATURE OF X-RAY AND ITS DISCOVERY 29 
 
 they were not recognized as such until 1895, when Pro- 
 fessor Roentgen startled the world hj the announcement 
 of his discovery. 
 
 Upon the memorable day of his discovery, Professor 
 Roentgen was duplicating one of Lenard's experiments 
 in the laboratory of the Wiirzburg University. The ex- 
 periment consisted of passing an electric current through 
 a Crookes tube covered with black cardboard, to test its 
 fluorescence upon a piece of cardboard coated A\dth ba- 
 rium platino-cyanide. A fresh specimen of this chemical 
 had been prepared and spread upon the cardboard which 
 was placed against the wall on the opposite side of the 
 room to dry. The room was darkened and the current 
 was passing through the tube, when to his amazement. 
 Roentgen noticed that the chemically covered cardboard 
 on the other side of the room was glowing with a wierd 
 fl.uorescence. He approached the cardboard, and in doing 
 so, passed between it and the Crookes tube, and beheld 
 his shadow upon the cardboard. Picking up a book, he 
 held it in front of the screen and noticed that it also cast 
 a shadow. He then discovered that the luminous glow or 
 fluorescence on the cardboard appeared and disappeared 
 with the turning on and off of the current. With the 
 tube operating, he picked up the cardboard, and while 
 examining it, noticed the shadow of his hand on its 
 surface, the bones appearing much darker than the soft 
 parts of the hand. He also found that the fluorescence 
 was produced in the cardboard regardless of whether the 
 chemically coated side was turned toward or away from 
 the Crookes tube, showing that the rays had the power 
 to penetrate substances at a distance from the tube. 
 
 Further investigation proved that the radiation pro- 
 ducing these phenomena emanated from the point of im- 
 pact of the cathode rays against the glass wall of the 
 Crookes tube; that nearly all substances were trans- 
 
30 DENTAL AjSTD OKAL RADIOGRAPHY 
 
 parent to it, although in widely different degrees, varying 
 roughly with their density ; that the radiation was recti- 
 linear; that it could not be refracted, reflected, or de- 
 flected by a magnet. Hence it was plain to Roentgen that 
 these rays were quite different from the cathode rays of 
 Crookes, Hertz, or Lenard. 
 
 Using photograiDhic plates wrapped in black paper to 
 protect them from ordinary light, he obtained with these 
 new rays shadow pictures of metallic objects in a wooden 
 box, and of the bones of the hand. 
 
 He continued his experiments both with the fluorescent 
 screen and the photographic plate, and in December, 
 1895, communicated his discovery to the Physico-Medical 
 Society of Wiirzburg. Being unable to determine the 
 exact nature of this new ray other than classing the 
 phenomenon as longitudinal vibrations of ether. Roent- 
 gen called it the x-ray, the letter "x" representing the 
 unknown in the mathematical formula. Even today the 
 exact nature of the rays has not been determined, al- 
 though the concensus of opinion seems to be that they 
 are violent ether pulses set up by the sudden stoppage 
 of the cathode rays as they strike upon the walls of the 
 tube or upon any intervening obstruction. If this theory 
 be correct, x-ra^^s are of the same general nature as light 
 waves, but of such short wave length that they lie out- 
 side the visible spectrum. 
 
CHAPTER III 
 
 HIGH TENSION ELECTRIC CURRENTS- 
 MAGNETISM— ELECTROMAGNETIC 
 INDUCTION 
 
 High Tension Electric Currents 
 
 As stated previously, the x-ray is produced Avhen an 
 electric current of high tension is passed through a vac- 
 uum tube. Therefore, let us consider the character of 
 this current and the means employed to produce it. 
 
 There are several kinds of electric currents, but of 
 these we need concern ourselves only with two — the 
 direct current, commonly designated by the abbreviation 
 D.C. ; and the alternating current, designated as A.C. 
 
 The direct current is one in which the electricity flows 
 along a conductor in one direction at a uniform rate of 
 pressure, while the alternating current flows along a con- 
 ductor first in one direction, then reverses and flows in 
 the opposite direction, these changes taking place with 
 great rapidity (50 to 120 per second). Such a current in 
 making these changes is said to have completed a cycle, 
 and its frequency is designated by the number of alter- 
 nations which occur each second. 
 
 A high tension current is one which has high voltage, 
 or, as it is expressed in electrical terms, has great elec- 
 tromotive force, or pressure. 
 
 The Volt is defined as the unit of electromotive force, 
 and is analogous to the pressure caused by a difference 
 in level of two bodies of water connected by a pipe — the 
 pressure tends to force the water through the pipe and 
 
32 DENTAL AED ORAL RADIOGRAPHY 
 
 the electromotive force or voltage tends to cause the elec- 
 tric current to flow along a conductor. 
 
 The Ampere is the unit of current strength, or in other 
 words, the amount of current passing a given point on a 
 conductor in a given time. If Ave again use the analogy 
 of the two bodies of water at different levels connected 
 by a pipe, it would be the amount of water which could 
 pass through the pipe in a given time. 
 
 The 0]i7n is the unit of resistance. Just as the water 
 in flowing through a pipe is resisted somewhat in its pas- 
 sage by the friction offered by the surface of the pipe, 
 or by the limited capacity of the pipe, so, likewise, the 
 electric current is resisted in varying degrees in its pas- 
 sage along a conductor, the degree of resistance depend- 
 ing upon the degree of conductivity of the material used 
 as the conductor, its length, cross section, etc. 
 
 The Watt is the unit of electromotive powder or the 
 ability of a current to do work. The wattage of a cur- 
 rent is determined by the voltage, or pressure, and the 
 amperage or quantity, the wattage of a given current be- 
 ing determined by multiplying the voltage by the am- 
 perage. 
 
 From the foregoing, then, we see that the character of 
 an electric current is determined by several factors, all 
 of which must be taken into consideration. 
 
 If we wish to know the strength of a given current, we 
 have but to remember this strength will depend upon the 
 pressure or electromotive force and the resistance of- 
 fered by the conductor through which the current is pas- 
 sing, just as the strength of a stream of water flowing 
 from a tank would depend upon the pressure and the size 
 *>jOf the pipe carrying the water. In other words, the 
 strength of the electric current equals the pressure di- 
 vided by the resistance. Reducing this to an equation 
 we have — 
 
HIGH TENSION ELECTRIC CURRENTS 33 
 
 voUs E.M.F. 
 Amperes = ^^^^^ or C equals —^ 
 
 This is known as "Olim's Law" and is one of the fun- 
 damental laws upon which electrical science is based. 
 This important law has two other forms which make it 
 possible to learn the relationship and amount of any of 
 these three units, provided two are knoAvn. For instance, 
 by transposing the formula of Ohm's law, we have — 
 
 Volts = amperes x ohms, or E.M.F. := C x R. 
 
 If we wish to determine the resistance offered b)^ a 
 given conductor, we apply the formula as follows : 
 
 E.M.F. E.M.F. 
 
 Resistance = or R = z^ 
 
 amperage U 
 
 As stated before, the current which is passed through 
 the vacuum tube to generate the x-rays must be a cur- 
 rent of high tension, or great pressure ; or, expressed in 
 the terms of the units just described, it must have very 
 high voltage. The ordinary lighting current of 110 volts 
 is inadequate, as this current is of far too low potential 
 to pass through the tube, as the vacuum offers great re- 
 sistance, a resistance which to the ordinary current 
 amounts to an absolute nonconductor. AVe are obliged, 
 therefore, to make use of some means which mil pro- 
 duce a current of great voltage, a current, we will say, 
 of at least 75,000 to 150,000 volts. 
 
 To do this, we must make use of one of the electric 
 machines which can generate such a current by utilizing 
 the principle of electromagnetic induction. Lest the stu- 
 dent become confused, we will first review very briefly 
 some of the elementary principles of electromagnetism 
 and its relation to the production of the high tension cur- 
 rent necessary in x-ray production. 
 
34 DENTAL AND ORAL RADIOGRAPHY 
 
 Magnetism 
 
 Magnetism is the term applied to substances which 
 have the property of attracting small pieces of iron. A 
 material possessing this property was first foimd by the 
 ancients at Magnesia, in Asia Minor, from which fact 
 arose the name magnet. 
 
 The natural magnet is an oxide of iron and is also 
 called the lodestone. Artificial magnets can be made by 
 rubbing a bar of hard steel with a lodestone, or with an- 
 other artificial magnet, or by means of an electric cur- 
 rent. Artificial magnets acquire the same magnetic 
 properties Avhich the lodestone or natural magnet pos- 
 sesses except that they acquire them to a much greater 
 extent, and are, therefore, always used in preference to 
 natural magnets. 
 
 In addition to the property of attracting small pieces 
 of iron, magnets have other characteristics worthy of 
 mention, such as polarity, or the property of assuming, 
 when suspended and perfectly free to move, a north and 
 south position. The compass is quoted as a familiar 
 example. 
 
 At the ends of a magnet, or in other words at its poles, 
 the greatest power or attraction exists. This is easily 
 illustrated by placing one end of an ordinary magnet in 
 some iron filings and withdramng it. The filings will 
 cling to it in great numbers, as they will likewise do to 
 the other end of the same magnet if it too be placed in 
 the filings. The middle of the magnet (or that portion 
 midway between the two poles), however, does not pos- 
 sess this property; but as the ends are approached, the 
 attraction increases until the poles are reached, where it 
 reaches the maximum. 
 
 In observing the action of the two poles of a magnet 
 in attracting the iron filings, no particular difference is 
 
HIGH TEXSTON ELECTRIC CURREXTS 
 
 6.} 
 
 observed. They both attract the iron filings. There is a 
 difference, however, which may he shown l)}^ experiment- 
 ing with two magnets, one of which should be suspended 
 at its center like an ordinary compass, while the other is 
 held in the hand. If the north pole of the magnet held 
 in the hand is moved near the north pole of the sus- 
 pended magnet, they ivill repel each other. Likewise if 
 their south poles are approached, they will repel each 
 other. But if the north pole of one be placed near the 
 south pole of the other, they will attract each other. 
 
 Fig. 5. — The action of iron filings in forming definite curved lines about an or- 
 dinary bar magnet indicates that the magnetic field exerts its influence in certain 
 definite directions which are called "the magnetic lines of force.'"' 
 
 This shows that like poles repel each other, ivhile unlike 
 poles attract each other. 
 
 The space surrounding a magnet which is subject to 
 its influence is known as its magnetic field. The presence 
 of this magnetic field is easily demonstrated by placing a 
 magnet under a sheet of paper upon which iron filings 
 have been evenly spread. By tapping the paper lightly, 
 the filings will form into a series of curved lines extend- 
 ing from one pole of the magnet to the other pole, as il- 
 lustrated in Fig. 5. The formation of these definite 
 
36 DENTAL AND ORAL RADIOGRAPHY 
 
 curves indicates that the magnetic field exerts its influ- 
 ence in certain definite directions which are called the 
 lines of magnetic force. These lines of force start at one 
 IDole of the magnet, pass in curved lines around to the 
 opposite pole, where they re-enter and pass on through 
 the magnet again, so that if any line is followed through 
 its entire length, one will eventually come back to the 
 starting point, as shown in Fig. 6. 
 
 It is by virtue of its magnetic field, that a magnet has 
 the power of attracting pieces of iron. A¥hen a piece of 
 
 '11/^' ^^ \ \ \ \ 
 
 > \ \\\ ' ' ,,////// 
 
 \ ^ \\s \ M / / / //^^/ 
 
 \ \ \ \ "-^ ^^ / I \ ^ 
 
 Fig. 6. — Diagrammaiic illustration of the magnetic lines of force. 
 
 iron is brought under its influence, it becomes a tem- 
 porary magnet, and for the time being has its two poles. 
 If the north pole of a magnet is brought close to a piece 
 of iron, a south pole will be induced in the iron next to 
 this north pole, and a north pole in the portion farthest 
 from it. The attraction is then exactly similar to the at- 
 traction between two permanent magnets when two un- 
 like poles are brought together. This action of a mag- 
 net in developing magnetism in iron placed in its mag- 
 netic field is called magnetic induction. 
 
 When a piece of iron is in contact with a magnet, the 
 attraction is greatest; but actual contact is unnecessary 
 
HIGH TENSION ELECTRIC CURRENTS 6( 
 
 to magnetize the iron, as it need only be placed within 
 the magnetic field, or, in other Avords, within the mag- 
 netic lines of force of the magnet. 
 
 Magnetism may be induced in iron in another way not 
 yet described, and to us this is of great importance. If 
 an ordinary electric current is passed through a coil of 
 wire, the coil becomes equivalent to a magnet and is sur- 
 rounded by a magnetic field similar to that of a bar mag- 
 net. Such a coil of Avire is called a helix, and if its 
 length is many times its diameter, it is called a solenoid. 
 
 / ^ .^ ^^ \ \ 
 
 Fig. 7. — Diagrammatic illustration of the magnetic field surrounding a coil of wire 
 through which an electric current is passing. 
 
 Since a solenoid is surrounded by a magnetic field sim- 
 ilar to that of a magnet (see Fig. 7) it follows that a 
 solenoid is capable of magnetizing pieces of soft iron 
 and attracting them in the same Avay as does an ordinary 
 steel magnet. The magnetic field of a solenoid is 
 strongest Avithin its Avindings and therefore if a bar of 
 soft iron is placed Avithin the coil, the bar ayIII be much 
 more strongly magnetized than if placed in any other 
 position about the coil. Such a coil adapted to carry a 
 current and provided Avith a soft iron bar or core is 
 called an electromagnet (Fig. 8). 
 
do DENTAL AND ORAL EADIOGRAPHY 
 
 In order to permit the wire to be closely wound and 
 at the same time to allow the current to pass through 
 each turn, the wire must be covered with insulation 
 throughout its length. It should also be remembered 
 that the iron core witliin the solenoid remains a magnet 
 only ivMle the current is passing through the coil, as 
 "only electric charges in motion produce magnetic 
 effects." 
 
 Electromagnets are much more powerful than ordinary 
 magnets; that is, their fields have much greater strength, 
 
 Fig. 8. — An iron bar placed within the windings of a solenoid is subject to its mag- 
 netic field and becomes a magnet. 
 
 for the field of the electromagnet is equal to the sum of 
 the field due to the core, plus the field due to the current 
 passing through the coil. 
 
 Thus far we have discussed the fact that a magnetic 
 substance in the field of an ordinary magnet, or a con- 
 ductor carrying an electric current, is magnetized. This 
 phenomenon, we know, is due to magnetic induction. It 
 is also a fact that an electric current may he induced in 
 a conductor hy causing the latter to move through a mag- 
 netic field. It makes no difference whether this field 
 comes from an ordinary magnet or from an electric 
 charge passing through a conductor. This action of a 
 
HIGH TENSION ELECTRIC CURRENTS 6.) 
 
 magnet or of a current on a conductor moved in its field 
 is called electromagnetic induction. 
 
 Principles of ElectromagTietic Induction 
 
 If the ends of a coil of wire are connected with a gal- 
 vanometer (Fig. 9) and the coil is moved down over an 
 ordinary magnet, the galvanometer will show that a mo- 
 mentary electric current has passed through the coil. 
 The current continues as long as the coil is in motion, 
 
 Fig. 
 
 9. — A, magnet with diagrammatic illustration of "magnetic lines of force" sur- 
 rounding it. B shows a coil of wire connected to a galvanometer, C. 
 
 and ceases as soon as the coil is brought to rest. If the 
 coil is withdrawn from the magnet, a current is also in- 
 duced which flows in an opposite direction to the current 
 which was induced when the coil was carried down over 
 the magnet. 
 
 These induced currents are produced hy the field sur- 
 rounding the magnet moving or cutting across the ivires 
 composing the coil. If a current is passed through the 
 coil, it creates a magnetic field, and, on the other hand. 
 
40 
 
 DENTAL AND OEAL EADIOGRAPHY 
 
 the movement of a magnetic field within the coil produces 
 a current. 
 
 As a solenoid is surrounded by a magnetic field similar 
 to an ordinary bar magnet, it follows that if a solenoid 
 carrying a current were thrust within (Fig. 10) another 
 coil, induced currents will be produced in the latter. 
 These induced currents, as in the case where the magnet 
 is used, only flow while there is a relative movement be- 
 tween the magnetic field and the conductor. When the 
 
 Fig. 10. — A, battery from which an electric current is passing through the solenoid, 
 B; C, large coil into which the smaller coil B is passed; D, galvanometer. 
 
 solenoid is passed into the other coil, the induced cur- 
 rent will flow in an opposite direction to the current 
 fjOiuing in the solenoid, and upon tvithdrawing the sole- 
 noid, the induced current ivill floiu in the same direction 
 as the current in the solenoid. 
 
 Suppose the two coils just described are jolaced one 
 mthin the other (there being no current passing) and 
 while in this position a current is started in the inner 
 coil. Upon the passage of the current in the inner coil, 
 a momentary current is induced in the outer coil, just the 
 
HIGH TENSION ELECTRIC CURRENTS 41 
 
 same as if a magnet had been moved within it, as sho-wn 
 in Fig. 9. This induced current remains only while the 
 current in the inner coil is increasing in value from zero 
 to its normal strength. As soon as this normal strength 
 is reached, the induced current ceases to flow. Now if 
 the circuit of the inner coil is broken and its current 
 ceases to flow, at this instant another momentary cur- 
 rent is induced in the outer coil, which flows in a direc- 
 tion opposite to the current Avhich Avas induced by start- 
 ing the current. These two induced currents created by 
 starting and stopping the primary current, or in other 
 words, by ''making" and ''breaking" the current, are 
 not of equal strength, the one produced by the "hreah" 
 of the current being much the stronger. 
 
 Such an instrument arranged with one coil within the 
 other, but without any connection between the two coils, 
 is known as an "induction coil." The inner coil which 
 is usually supplied with an iron core, is kno^vn as the 
 "primary coil;" and the outer coil, in Avhich the current 
 is induced, is known as the "secondary coil." 
 
 Induced currents are greatly intensified when soft iron 
 cores are placed within the primary coils, as the cores 
 become magnets and increase the strength of the field 
 by adding largely to the lines of force therein. 
 
 If an induction coil is constructed mth the same num- 
 ber of turns of wire in the "secondary" as are present 
 in the "primary," the current induced in the secondary 
 will be exactly equal to the current passed through the 
 primary. The voltage ivill not he increased. On the 
 other hand, if the secondary contains twice as many 
 turns as the primary, the induced current will be double 
 the voltage of the primary, as each turn of the secondary 
 induces a current in the turns directly adjacent to it, 
 which must be added to the current induced in the first 
 layer by the action of the primary current. Therefore, 
 
42 DENTAL AND ORAL RADIOGRAPHY 
 
 it should be apparent that as we increase the number of 
 turns in the secondary, we increase the E.M.F., or volt- 
 age. This increase of E.M.F. , or voltage, is due to the 
 phenomena of "self-induction" which is the principle 
 utilized in all x-ray machines or other electrical appara- 
 tus used to ''step up" the E.M.F., or voltage. 
 
CHAPTER IV 
 
 X-EAY MACHINES 
 
 RHUMKORFF OR INDUCTION COIL— TESLA 
 
 OR HIGH FREQUENCY COIL-INTERRUP- 
 
 TERLESS TRANSFORMER 
 
 The Rhumkorff or Induction Coil 
 
 The Rhumkorff, or ''induction coil," which is the most 
 common type of x-ray machine in use today, consists of 
 two principal parts, each of which is a coil of mre, one 
 being contained within the other, although they have no 
 electrical connection (see Fig. 11). 
 
 The inner coil, or "primary," as it is called, consists 
 of a few turns of very coarse insulated ^^ire Avrapped 
 about a bundle of soft iron which is knomi as "the mag- 
 netic core." 
 
 The outer coil, or "secondary" is made up of a great 
 many turns of fine insulated wire. It has been estimated 
 that in a 12-inch induction coil the secondary coil is 
 wound with between twenty and thirty miles of wire. 
 This, of course, makes possible an enormous number of 
 ' ' turns of wire ' ' so that when we consider that each turn 
 of the secondary induces a current in the turn directly 
 adjacent to it, which must be added to the current in- 
 duced in the first layer by the action of the primary cur- 
 rent, the sum total of the current coming from the sec- 
 ondary amounts to something tremendous. 
 
 To. compute the E.M.F., of the induced current (or 
 that coming from the secondary), we have but to remem- 
 ber that "the E.M.F., of the induced current is to that 
 of the primary current, as the number of turns in the 
 
44 
 
 DENTAL AND OKAL RADIOGEAPHY 
 
 Fig 11.— Diagrammatic illustration of the essential parts of an induction coil. 
 A' and A are the terminals of the "primary coil." D represents the windings ot^the 
 "primary" about the magnetic core C. The insulating medium between ^^the pri- 
 mary" and "secondary" is shown at E. The windings of the "secondary coil are 
 designated by F, and the "secondary" terminals by B and B' . 
 
X-RAY MACHTI^TES 45 
 
 secondary coil is to the number of turns in tlie primary." 
 For instance, suppose we have an induction coil with 10 
 turns of wire in the primary, and 100 turns of wire in 
 the secondary. If we pass a current of 110 volts through 
 the "primary," the voltage of the "secondary" current 
 will be — 
 
 110 
 -Yq-xIOO^hIIOO volts. 
 
 Notwithstanding the great change in voltage, the wat- 
 tage of the secondary current is the same as it was in 
 the primary (except for a small loss due to internal re- 
 sistance). This is not true, however, of the amperage. 
 For example, if the primary current of 110 volts carries 
 5 amperes, its wattage would be 550. The wattage of the 
 secondary current would also be 550, and since wattage 
 equals amperes multiplied by volts, the amperage of the 
 secondary current would be. 
 
 550 
 jj^ = y-2 ampere. 
 
 Thus it will be seen that as the voltage, or E.M.F., is 
 increased in the before described manner, the amperage 
 or current strength is decreased in equal ratio. It should 
 be plain, therefore, that the original current running to 
 the primary is not changed in actual value, but is sim- 
 ply transformed to a state or condition where it will do 
 the special work required of it. 
 
 In our consideration thus far we have considered the 
 manner in which an electric current may be transformed 
 from a low to the high voltage necessary to energize an 
 x-ray tube. We have not, however, named one important 
 requisite of a current to be used for this purpose, namely, 
 that the current must flow continuously and in the same 
 direction. 
 
 In considering the manner of obtaining a current in 
 
46 
 
 dejsttal and oral radiography 
 
 the secondary, we learned that such a current is produced 
 by "making" and ' ' brealdng " the primary current. If 
 a continuous current is to be kept flowing, we must utilize 
 some instrument which will rapidly ' ' make ' ' and ' ' break ' ' 
 the current in the primary circuit. Such an instrument 
 is knoA^m as an " interrupter ' ' and is essential to any in- 
 duction coil. 
 
 + ,.'P - ,'N 
 
 T 
 
 V 
 
 ^^ 
 
 Fig. 12. — Diagram of the electrolytic interrupter. P, terminal of the positive 
 electrode; A', terminal of the negative electrode; T, procelain sheath or tube cov- 
 ering the positive electrode; /, platinum point of the positive electrode; L, negative 
 electrode constructed of lead. 
 
 There are two classes of these instruments, both of 
 which utilize some automatic principle, and are known 
 as "mechanical" and "electrolytic." 
 
 Mechanical interrupters, a simple illustration of which 
 is the ordinary vibrator used on small coils, electric bells, 
 etc., will rapidly make or break the primary current and 
 thereby induce a fairly constant current in the secondary ; 
 but this form of interrupter has not been found to be so 
 satisfactory for x-ray work as the electrolytic type. 
 
X-RAY MACHIXES 
 
 CJ 
 
 <r "th:. .iiT?''^'''f1 °^ the induction coil. C, induction coil; P, "the primary" 
 s^'at InH fndn^f ^= ^' f'^'^t'-olytic interrupter in circuit with the ^rin^ary coil; /"rheo- 
 stat and inductance control; X, x-ray tube connected to the terminals of the secondary 
 
4s DENTAL AND ORAL RADIOGEAPHY 
 
 Of the various forms of electrolytic interrupters, the 
 Wehnelt type is the one most miiversally used. It con- 
 sists of a large battery jar which is nearly filled with a 
 solution composed of sulphuric acid one part and water 
 six parts. Into this solution are introduced two elec- 
 trodes. The negative electrode is constructed of lead and 
 has a large surface exposed, while the positive electrode 
 is contained within a porcelain or hard rubher tube ex- 
 tending down into the solution with only the tip or end of 
 the electrode exposed. The tip of this electrode is usually 
 made of platinum. (See Figs. 12 and 13.) 
 
 The electrolytic interrupter is connected in the primary 
 circuit and operates briefly as follows: As the current 
 passes from the platinum point (the positive electrode) 
 through the solution to the negative electrode, by virtue 
 of its chemical action upon the solution bubbles of gas 
 are formed around the exposed platinum point. These 
 bubbles act as a source of insulation and the current 
 ceases to flow — "It is interrupted." At the instant it is 
 interrupted, the bubbles are dispersed, the solution again 
 comes in contact with the electrode, and the current is re- 
 established only to be broken again and so on, these 
 changes taking place with tremendous frequency. With 
 such an instrument the primary current may be inter- 
 rupted from 60 to 30,000 times a minute. These inter- 
 rupters are sometimes constructed with several platinum 
 points which makes possible a greater amperage in the 
 current without decreasing the rate of interruptions. For 
 dental radiography, however, a single point interrupter 
 will usually suffice, and at most, not more than a two 
 point interrupter need be used. 
 
 The interrupter, then, serves the purpose of creating 
 the magnetic impulses which keep a constant current flow- 
 ing from the secondary. We should bear in mind, how- 
 ever, that the current produced by the "make" and 
 
X-RAY MACHIXES 
 
 49 
 
 "break" are not currents of equal strength, the current 
 produced at tlie ''break" liaving much the liig'hest value. 
 The fact that this current is the strongest, and that the 
 magnetic impulses come from the same direction (as the 
 
 Fig. 14. — Induction coil adapted for use in the dental x-ray laboratory. 
 
 induction coil is used on the direct current) it prevails 
 over the weaker. Therefore the induced or secondary 
 current which Ave use to energize the x-ray tube is the 
 current which is created at the instant of the break. 
 
50 
 
 DENTAL Als^D OEAL RADIOGRAPHY 
 
 Fig. 15.— Induction coil adapted for use in the dental x-ray laboratory. 
 
X-RAY MACHINES 
 
 51 
 
 Fig. 16.-I„ductio„ coil adapted for use in the dental x-ray laboratory. 
 
52 DENTAL AND OKAL RADIOGRAPHY 
 
 The other wave, or that created by the "make," is 
 current in the wrong direction, and is called "inverse 
 current." In some induction coils this inverse current 
 is the source of much trouble, and where it is present 
 to any appreciable extent, will result in blurred radio- 
 grams. It can be controlled, however, by the use of 
 "valve tubes," or a "spark gap," arranged in series with 
 the x-ray tube, the valve tube or spark gap serving the 
 function of cutting out the weaker or inverse current, 
 without interfering to any appreciable extent with the 
 stronger current which is delivered to the terminals of 
 the x-ray tube. 
 
 The induction coil is used on the direct current of 110 
 or 220 volts. Where only the alternating current is avail- 
 able, some means must be used to change the current from 
 alternating to direct before it enters the primary circuit 
 of the coil. 
 
 This change in the current can be accomplished by 
 the use of " a rotary converter, ' ' of which several makes 
 are available, or by a " chemical rectifier. ' ' These recti- 
 fiers generally consist of two electrodes immersed in a 
 solution of the phosphate salts of potassium, sodium, or 
 ammonium, one electrode being made of aluminum, and 
 the other of lead„ iron, or carbon. When working prop- 
 erly, the current will flow to the aluminum through the 
 solution, but not away from it, thus cutting out one wave 
 of the alternating current; or it is possible, by properly 
 connecting up three or four jars containing the electrodes, 
 to utilize both waves of the current. 
 
 Induction coils are usually rated as to power by the 
 maximum width of the secondary spark gap ; that is, the 
 amount of distance the spark will jump between the sec- 
 ondary terminals. For example, a 12-inch induction coil 
 is capable of producing a spark that will jump twelve 
 inches of atmosphere. While these coils are made in va- 
 
X-RAY MACHIlSrES 53 
 
 rious sizes, capable of producing a spark from six inches 
 to forty inches in lengtli, there is no particular advantage 
 in using more than a 12-inch coil for dental radiography. 
 (See Figs. 14, 15, and 16.) 
 
 Tesla, or High Frequency, Coil 
 
 The Tesla, or high frequency, coil differs considerably 
 in construction from the induction coil, although many 
 of its principles are the same (Fig. 17). In a way it is 
 a double induction coil with the secondary of one coil 
 acting as the primary of the other coil. An alternating 
 current is utilized in the i^rimary of the first coil and by 
 means of the secondary of this same coil is stepped up 
 to a high voltage. This ''stepped-up" current is then 
 carried to a condenser. As the current leaves the con- 
 denser, it is oscillating at a great rate of frequency and 
 passes into the primary of the Tesla, or second, coil 
 where it induces a current in the secondary of this coil. 
 From the terminals of the last secondary, it is carried to 
 the x-ray tube. The principles involved in this type of 
 apparatus are sho^^ai in Fig. 17. 
 
 Like the current of the induction coil, the current from 
 the Tesla coil is high in voltage and low in amperage, but 
 unlike the current from the induction coil it is not uni- 
 directional, but is alternating in character. For this rea- 
 son, it is considered by some as being less desirable for 
 radiographic purposes. However, this apparently ob- 
 jectionable feature is overcome by using an x-ray tube 
 constructed in such a way as to cut out one wave of the 
 current and thereby produce practically the same result 
 as where a unidirectional current is used. 
 
 These coils have the advantage of being less cumber- 
 some, require less space and are less expensive than the 
 other form of apparatus, but they can not be depended 
 upon to do the character of work that the powerful "in- 
 
54 
 
 DENTAL AND ORAL EADIOGRAPHY 
 
 ■O- 
 
 VVW\A 
 
 AAA 
 
 ci 
 
 ^ 
 
 VwvwwwwW 
 
 AAAAAAAM 
 
 Fig. 17. — Diagram of the high frequency coil. T, alternating current transformer; 
 C, condenser; G, spark gap; R, oscillation transformer; D, high tension discharge gap.; 
 X, high frequency 5c-ray tube. 
 
X-RAY MACHINES 
 
 55 
 
 duction coil" or "interrupterless transformer" will do. 
 Notwithstanding this fact, this type of apparatus un- 
 doubtedly has a place in the x-ray laboratory of the den- 
 tist, and if constructed along proper lines can render 
 splendid service. Three sizes of these coils are sho^^^l in 
 Figs. 18, 19, and 20. 
 
 Fig. 18. — Small type high frequency coil. 
 
 Fig. 19. — Medium-sized high frequency coil. 
 
 Interrupterless Transformer 
 
 The interrupterless transformer is the newest and by 
 all means the most powerful x-ray machine made. Aside 
 from controlling and measuring apparatus, it consists 
 of three principal parts, a rotary converter, if direct cur- 
 rent is the source of supply, or a synchronous motor if 
 
56 
 
 DENTAL AND ORAL EADIOGRAPHY 
 
 the alternating current is the source of supply, a step-up 
 transformer, and a rectifying smtch. 
 
 Two types of these machines are made; viz., a direct 
 
 Fig. 20. — Large type high frequency coil. 
 
 current machine, and an alternating current machine, the 
 underlying principles of which are shown in Fig. 21. . 
 When used on the direct current, the rotary converter 
 
X-EAY MACHIlSrES 
 
 57 
 
 is set in motion and generates an alternating current 
 which is sent through the primary of the step-np trans- 
 former. This induces a current in the secondary of the 
 proper voltage, but alternating in character. The rectify- 
 ing switch then changes this current from an alternating 
 
 sr^CHffo^Ol/S mrofi 
 
 t^ 
 
 Fig. 21. — The working principles of the interrupterless transfornTer are here 
 shown. The synchronous motor used to operate the rectifying switch of the alter- 
 nating current machine may also be used as a rotary converter where the direct cur- 
 rent is desired for other purposes in the laboratory. 
 
 to a direct current and as such it is delivered to the ter- 
 minals of the tube. 
 
 The alternating current machine differs only from the 
 direct current machine in that the alternating current is 
 run directly into the primary of the step-up transformer. 
 This induces a current in the secondary of proper voltage 
 
05 DENTAL AND ORAL RADIOGRAPHY 
 
 but alternating in character. The rectifying switch then 
 changes this high voltage alternating current to a direct 
 current, and as such it is carried to the terminals of the 
 tube. 
 
 The interrupterless transformer is, as stated before, 
 the most iDowerful and efficient type of apparatus avail- 
 able for x-ray work. It is likewise the most expensive, — 
 too expensive in fact to be considered for the x-ray lab- 
 
 Fig. 22. — Interrupterless transformer adapted for use in the dental x-ray laboratory. 
 
 oratory of the average practitioner of dentistry, in view 
 of the fact that with the induction coil and other less ex- 
 pensive apparatus such excellent results can be obtained. 
 The preceding remark, however, should not be con- 
 strued as an argument against the interrupterless trans- 
 former. To the prospective purchaser who desires the 
 very best, regardless of expense, or who expects to do a 
 great deal of radiography, the initial expense should not 
 
X-RAY MACHIj^ES 
 
 59 
 
 be the prime consideration, as oftentimes the most ex- 
 pensive things in the long run prove a matter of economy. 
 In conclusion, I would emphasize the fact that the char- 
 
 Fig. 23. — Interrupterlcss transformer adapled for use in the dental x-ray laboratory. 
 
 acter of the radiography which any physician or dentist 
 is able to do, does not depend entirely upon the excellence 
 of his laboratory equipment. Instances could easily be 
 
60 
 
 DENTAL AND ORAL EADIOGRAPHY 
 
 Fig. 24. — Iiiterrupterless transformer adapted for use in tlie dental x-ray laboratory. 
 
X-RAY MACHINES 61 
 
 cited where the best of equipment fails to produce the 
 highest type of results, and vice versa, where unpreten- 
 tious equipment in some hands has proved more than 
 satisfactory. After all, the comparative degree of effi- 
 ciency of the various type of x-ray machines must depend 
 largely upon the judgment and skill of those who operate 
 them. 
 
 In Figs. 22, 23, and 24 several interrupterless trans- 
 formers adapted for use in the dental x-ray laboratory 
 are shown. 
 
CHAPTER V 
 
 REQUISITES OF THE DENTAL X-RAY 
 LABORATORY 
 
 The requisites of a dental x-ray laboratory are not 
 numerous but consist of — 
 
 1st — A so-called x-ray machine. 
 
 2nd — An x-ray tube. 
 
 3rd — An adjustable "tube stand" for holding the tube, 
 which should include a ''tube shield" made of leaded 
 glass, serving as a means of confining the rays and as a 
 source of protection to the operator, and a lead ''com- 
 pression diaphragm" and lead-lined "compression 
 c^dinder. ' ' 
 
 4th — A photographic darkroom. 
 
 As x-ray machines have already been discussed, let us 
 now take up the others, in the order in which they have 
 been 2:iven. 
 
 b' 
 
 X-ray Tube 
 
 The x-ray tube is a thin glass bulb six or eight inches 
 in diameter, having two elongations or stems projecting 
 from the bulb opposite and in line with each other (see 
 Fig. 25). One of these elongations has within it a sheet 
 iron tube at one end of which is a block of copper, faced 
 with platinum or tungsten, and set at an angle of 45 de- 
 grees. The other end of this sheet iron tube carries a 
 platinum wire which is sealed into the glass at the end of 
 the elongation and connected to a cap on the outside 
 which serves as an electrical connection. 
 
 The other elongation carries a rod at one end of which 
 is a concave aluminum reflector, the other end being con- 
 
 62 
 
KEQUrSITES OF DENTAL X-HAY LABORATOIIY ()o 
 
 nected by means of a platinum wire sealed in the glass to 
 a cap on the outside of the elongation, and also serves 
 as an electrical connection. 
 
 The cancave reflector is knoAvn as ''the cathode" and 
 the metallic block opposite it and located upon the end 
 of the sheet iron tnbe is knoA\ai as the "target" or 
 "anode." Above the anode and at an angle there is an- 
 other stem projecting which carries a metallic terminal 
 known as the "assistant anode." 
 
 This assistant anode has a platinum wire extending 
 from it which is sealed into the glass and connected to a 
 metallic cap on the outside of the tube. The outer ter- 
 minals of the assistant anode and the anode are connected 
 by means of a spiral spring. 
 
 Directly above the anode on the top of the tube there 
 is a small chamber with an arm extending from it at right 
 angles. This is known as "the regulating chamber." 
 The arm extension of this chamber is filled mth asbestos 
 impregnated with chemicals, and arranged about or AAith- 
 in a small metal tul)e from which a platinum wire ex- 
 tends, is sealed into the glass and connected to a metallic 
 cap on the outside end of the chamber arm. 
 
 Before being finally sealed, the tube is pumped to a 
 high degree of vacuum (about 1/100,000 part of an atmos- 
 phere), only enough air being left in it to afford a path 
 for the passage of the electric current. 
 
 Three general types of tubes are made for radiographic 
 work, all of which embody the same general principles 
 but vary according to the type of the machine upon which 
 they are to be used. 
 
 They are designated as follows : 
 
 1. The coil tube. 
 
 2. The transformer tube. 
 
 3. The high frequency tube. 
 
 Coil tubes and transformer tubes are similar in con- 
 
64 DENTAL AISTD ORAL RADIOGRAPHY 
 
 struetion but not in vacuiim (see Fig. 26). Coil tubes 
 are exhausted to a much higher degree of vacuum in or- 
 der to lessen the tendency for inverse current, and give a 
 high degree of penetration. The transformer tube is 
 made comparatively low in vacuum as the current from 
 the transformer is entirely free from inverse, and of such 
 high voltage that the high vacuum is neither necessary 
 nor advisable. 
 
 The high frequency tube differs slightly in construc- 
 tion from the coil and transformer tubes owing to the 
 fact that the high frequency current is not unidirectional. 
 Therefore, a means must be resorted to for cutting out 
 or disposing of one wave of the alternating current. This 
 is accomplished, as shown in Fig. 27, by placing the anode 
 or target in the position occupied in the coil tube by the 
 assistant anode except that it extends down to the center 
 of the tube. Then by having what really amounts to two 
 cathode terminals, only one of which is focused against 
 the face of the anode, and the other into a funnel in the 
 back of the target, almost the same effect is produced as 
 results from a unidirectional current. 
 
 Connecting the Tube to the X-ray Machine 
 
 In connecting up the tube to a coil or transformer 
 (Fig. 28), the anode terminal (A) is connected by means 
 of a wire cord coming from a reel attached to the posi- 
 tive terminal of the machine {A'), and the cathode ter- 
 minal (C) is connected in a similar manner to the nega- 
 tive terminal of the machine C")- 
 
 A third wire cord is usually run from a reel {R') sit- 
 uated on the coil near the negative terminal to the cap on 
 the regulating chamber (R). This third terminal on the 
 coil has a spark gap between it and the negative terminal 
 the length of which is adjustable (designated by S' and 
 S). 
 
KEQUISITES OF DENTAL X-IIAY LABOEATOKV 
 
 Of) 
 
 Operating the X-ray Tube 
 
 When the current is started in the machine, it enters 
 tlie tube at the anode and passes across the gap to the 
 cathode, from which it is reflected back as the invisible 
 cathode stream to strike a focal point on the target where 
 the x-rays are produced and pass out tlirough the walls 
 of the tube (see Fig. 25). 
 
 With the passing of the current througli the tube, it 
 should light up in a characteristic manner, forming two 
 hemispheres which have a definite line of demarcation. 
 
 A — Anode. 
 i-B- -Assislam Anode 
 C— Cathode 
 D— Regulating 
 
 Chamber 
 F— Regulating Ad 
 
 juster 
 G— Hcinispheie 
 H-Conned.on 
 
 Wire 
 I— Assistant Anode 
 
 Cap 
 K— Anode Cap 
 L— Cathode Cap 
 M— Cathode Stream 
 N— Focal Point 
 
 Fig. 25. — Diagram of an x-ray tube. 
 
 The hemisphere in front of the target which is the active 
 hemisphere, is evidenced by a green fluorescence, the 
 shade of coloring depending upon the degree of vacuum 
 of the tube. The fluorescence of a highly exhausted tube 
 will be a light yellowish green, a tube low in vacuum will 
 show a bluish green, while a medium tube will be an inter- 
 mediate green. 
 
 For dental radiography, a fairly high tube is indicated 
 and its vacuum should be kept as nearly uniform as pos- 
 sible. This is made possible by utilizing the third ter- 
 minal from the x-ray machine. By placing the spark gap 
 of tliis terminal about three or four inches from the nega- 
 
66 
 
 DEN'TAL AND ORAL RADIOGEAPHY 
 
 tive terminal of the machine, the current will, when the 
 vacuum of the tube gets high enough to resist its pas- 
 sage, pass over the gap, down the third terminal wire 
 
 Fig. 26. — The coil or transformer tube. 
 
 into the regulating chamber where by heating the as- 
 bestos it will liberate gas and thereby reduce the vacuum 
 of the tube. 
 
REQUISITES OF DENTAL X-IIAY LABORATORY 
 
 67 
 
 In addition to tlie general types of tubes already de- 
 scribed, there are certain specialized forms of tubes which 
 
 Fig. 27. — The high frequency tube. 
 
 are highly useful, and fast becoming popular. Of these, 
 the ''hydrogen tube" and the ^Coolidge tube" are, by 
 far, the most important. 
 
DENTAL AND ORAL EADIOGRAPHY 
 
 Fig. 28. 
 
 Fig. 29. — The hydrogen tube. 
 
IlIi(iLJlSlTl-:S OF DENTAL X-1L\V LABOIIATOUY (J!J 
 
 Hydrogen Tube 
 
 The hydrogen tube, shown in Fig. 29, differs from the 
 ordinary gas tube in that in addition to having the reduc- 
 ing feature, in common with other tubes, it has the added 
 advantage of having a raising device. This means that 
 the hydrogen tube may be raised or lowered, at will. As 
 the name implies, this tube contains hydrogen, Avhich is 
 greatly responsible for its unusual flexibility. 
 
 It is claimed for this tube that it has a slightly greater 
 penetration than other tubes for a given parallel spark 
 
 Fig. 30. — The Coolidge x-ray tube. 
 
 length. The target is made of tungsten, and the cathode 
 is protected in the same manner as the tubes already 
 mentioned. 
 
 Coolidge Tube 
 
 The Coolidge tube, shown in Fig. 30, is radically dif- 
 ferent in design from the other tubes already described, 
 and is ditferent in operation, in that it is energized by 
 two independent currents, one of high voltage, and the 
 other of low voltage. For this reason, certain auxiliary 
 apparatus must be used with it, in addition to the x-ray 
 generator. This auxiliary apparatus consists of a low 
 voltage transformer and regulator, and an insulated 
 stand or shelf for holding the transformer, and an am- 
 meter. The low voltage current serves the purpose of 
 
70 DENTAL AND OEAL EADIOGKAPHY 
 
 heating electrically a spiral filament of flat, closely wound 
 tungsten wire located within a cylinder on the cathode. 
 This electrically heated filament serves the important 
 function of controlling the milliamperage of the current 
 passing through the tube. The higher the filament tem- 
 perature, the larger the number of milliamperes will flow 
 through the tube and hence the shorter will be the ex- 
 posure required. 
 
 This tube is fast becoming popular, due to the fact that 
 it is rugged of construction, will stand hard and continu- 
 ous service, and because of its ease of control, will give 
 uniform results. 
 
 Tube Stand 
 
 The tube stand, Avhich serves the purpose of holding 
 the tube, should be sufficiently heavy to support it against 
 motion and vibration, and should be sufficiently adjust- 
 able so that the tube can be raised or lowered, or placed 
 at any desired angle. Its base should be mounted upon 
 casters so that it may be moved with ease. Such a tube 
 stand is shown in Figs. 31 and 32. 
 
 Tube Shield, Compression Diaphragm, and Compression 
 
 Cylinder 
 
 The tube, tube stand, tube shield, compression dia- 
 phragm and compression cylinder, when adjusted for 
 work, as shown in Figs. 31 and 32, really comprise a 
 single piece of apparatus. Bearing in mind the fact that 
 the x-rays pass out in every direction from the face of 
 the anode, or target, (see Fig. 33-^) which is situated in 
 the center of the tube, it is necessary, if the clearest pos- 
 sible shadows are to be produced, to use only those rays 
 that have the same general direction and that have an 
 equal amount of penetration. Now it is known that the 
 most rapid and effective rays are those that pass out at 
 
REQUISITES OF DENTAL X-RAY LABORATORY 71 
 
 Fig. 31. — The tube stand. 
 
72 
 
 DENTAL AND ORAL RADIOGEAPHY 
 
 Fig. 32.— Illustrating how tlie tube may be placed at any desired angle. 
 
REQUISITES OF DENTAL X-1!AY i.AllOKATOItV 
 
 (6 
 
 Fig. 33-A. 
 
 Fig. 33-C. 
 
74 
 
 DENTAL AND OKAL KADIOGRAPHY 
 
 right angles from the cathode stream designated by PR. 
 Inasmuch as we desire to nse these rays, and these rays 
 only, in casting our shadows, we must establish some 
 means of preventing the other rays {S,S,S,S) from es- 
 caping from the immediate area surrounding the tube, 
 and this is accomplished by means of the tube shield, 
 compression diaphragm, and compression cylinder. 
 
 The tube shield (Fig. 34), a sectional diagram of which 
 is shoA^m in Fig. 33-Z? by TS is made of leaded glass, 
 there being a sufficient amount of lead in the glass to 
 
 Fig. 34. — Leaded glass tube shield. 
 
 prevent ordinary rays from passing through it. The 
 compression diaphragm makes up the floor of the tube 
 shield (D), and is constructed of sheet lead with an open- 
 ing of the proper size to allow the desired rays to pass 
 through. The compression c^dinder (CC) (Fig. 33-C) is 
 made of aluminum with a lead lining that absorbs any 
 secondary rays that have succeeded in passing through 
 the diaphragm. It should be apparent to anyone that 
 with this apparatus, the only x-rays that succeed in leav- 
 ing the immediate area of the tube are those that are 
 used to cast the shadows of the parts desired, which is 
 
EEQUISITES OF DENTAL X-KAY LABORATORY 
 
 75 
 
 of great importaneo, not only in obtaining radiograms 
 that are sharp and clear and uniform, hut also to the 
 health of the operator and others associated with him in 
 the office. 
 
 Arrangement of the Apparatus in the Office 
 
 If dental x-ray equipment is desired, the question nat- 
 urally arises, "Where can the necessary apparatus be 
 
 Fig. 35. — A convenient manner of arranging the necessary apparatus when not in use. 
 
 placed?" While a separate room is desirable, it is by 
 no means necessary, as the ordinary operating room of 
 "healthy size" can be made to accommodate it. 
 
 The coil or transformer, and the tube stand can be 
 placed against the v/all at the left of the room, while the 
 tubes can be hung in a suitable rack upon the wall where 
 they will be out of harm's way (Fig. 35). Arranged in 
 this manner, x-ray apparatus is not in the way, and is 
 accessible for use at any time. 
 
76 DENTAL AND ORAL EADIOGRAPHY 
 
 The dental chair with its multitude of adjustments 
 serves an important purpose in the dental x-ray labora- 
 tory, for the patient must be supported in such a manner 
 as to be able to hold perfectly quiet during the time the 
 exposures are made. Owing to the stability of the chair 
 and its many adjustments, it mil not only serve this pur- 
 pose, but is preferable to having the patient lie upon a 
 table which has been the method employed by many radi- 
 ographers in the past. 
 
 Photographic Darkroom 
 
 Thus far we have discussed all but one of the requisites 
 of the dental x-ray laboratory; viz., the photographic 
 darkroom. This is a very important requisite, and any- 
 one attempting to do radiography without it is greatly 
 handicapped. It need not be large or elaborate, and run- 
 ning water is not absolutely essential, although it is an 
 advantage. A closet 3^x5 feet will suffice if nothing bet- 
 ter is available. A broad shelf should be placed at one 
 end to hold the developing trays and other photographic 
 accessories. 
 
 With a darkroom always available, the dental radiog- 
 rapher is able to develop his plates or films immediately, 
 profit by their findings, or, in case they do not come out 
 satisfactorily, make others without subjecting the patient 
 to the inconvenience of another appointment. 
 
 Where limited space precludes the possibility of a reg- 
 ular darkroom, a developing cabinet, or so-called "port- 
 able darkroom" may be utilized. (See Fig. 36.) Such 
 a cabinet may be placed upon a small table or attached to 
 the wall at the proper height from the floor. It should be 
 large enough to contain the necessary developing trays 
 and other photographic necessities. The front panel 
 should be hinged so as to permit easy access to the in- 
 terior for the arrangement of the trays, solutions and 
 
REQUISITES OF DENTAL X-IIAY LABOItATORY 
 
 it 
 
 for their removal after development. The riihy lamp for 
 lighting the interior slionld l)e an integi-al part of tlie 
 cabinet and the "observation windoAv" at the top shonld 
 be so placed that the operator can have an nnobstructed 
 view of the interior. This window must be covered with 
 ruby glass, and around it should be constructed a shield 
 
 Fig. 36. — The portable darkroom. 
 
 which will shut out all outside light while the operator 
 is looking into the cabinet. 
 
 , With the portable darkroom, plates and films may be 
 satisfactorily developed, but the process can not be car- 
 ried with the same degree of comfort as where "a reg- 
 ular darkroom" is available. Therefore, any dentist in- 
 tending to do any considerable amount of radiography 
 can well afford to go to the trouble and expense of con- 
 structing a darkroom which will be comfortable, and con- 
 lain all the conveniences. 
 
CHAPTER VI 
 TECHNIC OF DENTAL AND ORAL RADIOGRAPHY 
 
 Having discussed the requisites of the dental x-ray 
 laboratory, let us now proceed to a consideration of their 
 application in the actual work of radiography. 
 
 The very nature of the structures with which Ave con- 
 cern ourselves, their gross as well as minute anatomy, 
 renders them somewhat difficult to radiograph, and neces- 
 sitates a refinement of technic greater than that de- 
 manded for most of the other portions of the human an- 
 atomy. It would, therefore, seem obvious that an ac- 
 curate knowledge and anatomic appreciation of the 
 structures of the oral cavity and associated organs and 
 structures is the first requisite for successful dental and 
 oral radiography. 
 
 We should keep in mind the fact that radiograms are 
 shadow pictures, and that the effect produced by the x- 
 ray upon the photographic plate is but a shadowgraphic 
 representation of the tissues through which the rays have 
 passed. We know that this ray penetrates all matter in 
 inverse ratio to its mass or density, and therefore the 
 shadow picture which is left upon the photographic plate 
 is simply a record of the varying density of the tissues 
 through which the rays have penetrated. 
 
 The x-rays are particularly applicable to the dental and 
 oral structures, owing to the fact that these structures 
 differ enough individually in degree of density to permit 
 of their appearing in a characteristic manner upon the 
 photographic plate. For instance, it will be noted upon 
 the examination of a dental radiogram, that metallic fill- 
 ings appear as white masses, and root fillings as some- 
 
 78 
 
DENTAL AND ORAL RADIOGRAPHY TECIINIC 79 
 
 what less dense lines. The enamel and dentin are next 
 in density, and root canals show plainly as dark channels 
 in the dentin, while the alveolar process and maxillae show 
 their fine uniform cancellous structure in various degrees 
 of density depending upon their thickness. 
 
 As a tooth is much more dense than the bony structures 
 of the jaw, any anomaly of form, size or position in the 
 jaws is easily discernible even though it occupy a posi- 
 tion far from what might be expected; as for instance, 
 impacted molars, teeth in the antrum, etc. 
 
 Due to the fact that the structures within the field of 
 our specialty have a characteristic appearance under nor- 
 mal conditions, any alterations or change in these struc- 
 tures is at once evident upon the plate. We thus are af- 
 forded a means of studying intra vitam the gross pa- 
 thology of the structures of the oral cavity. 
 
 I would again emphasize a point pre^dously made ; viz., 
 that a radiogram is not a x)hotograph, but a shadow pic- 
 ture which is produced by using the x-ray as the source 
 of illumination and the photographic plate as a screen 
 for recording permanently the shadows cast. 
 
 Therefore, in maldng radiograms, we must adhere to 
 the same rules which apply in making correct shadows 
 with ordinary light. If correct shadows are cast, a cer- 
 tain definite relationship must exist between the source 
 of illumination, the object, and the screen. Any change 
 or variance in this relationship will result in a changed 
 image. A simple experiment will suffice to illustrate to 
 a beginner the truth of this statement. 
 
 Use a piece of ordinary white writing paper as a screen 
 and hold it about two feet away from a lamp, and place 
 your hand or any other small object, midway between the 
 lamp and the improvised screen, and observe the shadow 
 cast. You will note, first, that it is very much enlarged ; 
 and, second, that it is very faint and indistinct. Now, 
 
80 DENTAL AND OEAL RADIOGRAPHY 
 
 slowly move the object toward the screen. As it ap- 
 proaches, the shadow becomes more distinct and smaller 
 mitil at length when the object is 'almost touching the 
 screen, the shadow will be good, black and distinct, and 
 of practically the exact size of the actual object. It will 
 also be found that the shadow can be altered by chang- 
 ing the position of the light, that is, moving it toward the 
 object or away from it, by lowering it below the level of 
 the object or raising it higher than the object ; or by mov- 
 ing it to the right or to the left. Eventually, however, 
 a point can be found which will cause the shadow to as- 
 sume its most correct proportions as well as its sharp- 
 est outline. When this point is established, the light rays 
 will be traveling in a perpendicular direction to a plane 
 which lies midway between the plane of the object and 
 the plane of the screen, and the light will be placed at 
 w^hat we call the proper focal distance. 
 
 Applying the laws deduced from this simple illustra- 
 tion of shadow making to radiography, we learn, first, 
 that the closer we can bring the photographic plate to 
 the tissues we wish to show, the clearer and sharper will 
 be the resulting radiogram; second, that the x-rays in 
 passing through the tissues, must travel perpendicularly 
 to a line which lies midway between the plane of the tis- 
 sues desired and the XDlane occupied by the photographic 
 plate; and third, that the source of the x-ray production 
 (the target of the tube) must be placed at a proper focal 
 distance. 
 
 In order to obtain a radiogram of any portion of the 
 body, it is necessary to have a photographic or x-ray 
 plate, or film (properly prepared so as to exclude all light 
 and moisture), placed in such a position that the rays 
 passing through the structures desired, will register their 
 shadows with the least amount of distortion possible upon 
 the plate. 
 
DEIN'TAL AND ORAL EADIOGRAPHY TECHXIC 81 
 
 In securing shadowgrapliie ropTosontations of the den- 
 tal and oral strnctnres, two general nietliods of procedure 
 are open to us, each of which has its values and special 
 indications. These are known as the "inta-oral" and 
 "extra-oral" methods. 
 
 With the first, only small films are used which are 
 placed within the month opposite the area to be radio- 
 graphed, and held in position either by means of a tray 
 or film holder, or by the assistant, or better still, by the 
 patient exerting slight pressure with the finger. This 
 method is indicated where radiograms of small areas only 
 are desired, as, for instance, two or three of the teeth, 
 with the adjacent alveolar process. 
 
 With the other method of procedure mentioned; viz., 
 the "extra-oral" method, large plates or films are used 
 and the areas desired are brought in as close contact as 
 possible with the plate by pressing or resting the face 
 against it. The x-rays are then passed through the struc- 
 tures from the other side of the skull, and oftentimes 
 must pass through the entire face or skull, in transit. 
 
 When using this method, large areas may be radio- 
 graphed, which in some instances will embrace the lateral 
 lialves of both the upper and lower jaws from the cusx)id 
 region anteriorly to the angle of the jaw posteriorly, and 
 from the floor of the orbit above to the inferior margin 
 of the mandible below. In fact, it is possible by making 
 several exposures to obtain in detail a shadowgraphic 
 representation of the dental apparatus in toto, as well 
 as its associated organs and structures, the nasal cavity 
 and pneumatic sinuses, the maxilla and the mandible. 
 
 It should be apparent to anyone that the first method 
 greatly reduces the possibilities of the x-ray. Both meth- 
 ods have their advantages and neither should be dis- 
 carded in favor of the other. 
 
82 DENTAL AND ORAL RADIOGRAPHY 
 
 Intra-oral Method 
 
 "We shall first discnss the intra-oral method by which 
 small areas are radiographed. First of all, the patient 
 should be placed in a comfortable position, and the head 
 supported so that it may he held perfectly still. After 
 the tube has been tested out and the proper degree of 
 vacuum established, the tube stand (complete with the 
 
 Fig. 37. — The patient can hold the film in position against the upper teeth by exerting 
 slight pressure with the thumb. 
 
 other apparatus before described) is moved to a position 
 where the rays coming from the tube, through the com- 
 pression diaphragm and cylinder can be made to pass 
 through the desired areas and cast their shadows upon 
 the small film within the mouth (Fig. 37). 
 
 In using this method upon the upper teeth, the great- 
 est care must be exercised if the shadows produced are 
 free from distortion, for the film must be held within the 
 upper arch against the lingual side of the teeth and the 
 palate, and must occupy a position which is in a different 
 
DENTAL AND ORAL RADIOGRAPHY TECHNIC 
 
 plane from that occupied by the roots of the teeth. When- 
 ever it is necessary to direct the raj's upon structures tliat 
 lie at an angle with the plate or film, correct shadows 
 may be obtained by adhering to the following rule : "Bi- 
 
 Fig. 38. — Correct and incorrect technic. 
 
 sect the angle made by the plane of the object, and the 
 plane of the film, and direct the rays so that they ivill 
 fall perpendicidar to this bisected plane." 
 
 Failure to adhere strictly to this rule is one of the 
 
84 DENTAL AND ORAL RADIOGRAPHY 
 
 most common causes of partial or comxDlete failure in 
 producing true shadowgraphic representations 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 directed from too high a source, the shad- 
 ows will be foreshortened, the amount of elongation or 
 foreshortening being in direct proportion to the amount 
 of deviation from the proper focal point. 
 
 The importance of adhering strictly to this rule is 
 graphically shown in Fig. 38,* where an upper central 
 incisor and the adjacent teeth are radiographed. In the 
 upper picture {A) the rays are passing in from too low 
 a source with the result that the image imposed upon the 
 film is lengthened to the extent that the resulting radio- 
 gram is useless. In the center picture (B) the rays are 
 coming from too high a source, the result being a short- 
 ened image. Such a radiogram has but little value and 
 in many instances Avould prove very misleading. In the 
 lower picture (C) the rays are passing in at the cor- 
 rect angle; viz., they are directed perpendicularly to a 
 plane which lies midway between the plane of the teeth 
 desired and the plane of the film. The result is a radio- 
 gram in which the images of the teeth desired are im- 
 posed upon the film in their correct proportions. 
 
 It will be noted upon a close examination of this last 
 radiogram (C) that an abscess is present upon the root 
 of the right central incisor. By examining the other 
 radiograms {A and B) it will be seen that this condition 
 is not apparent in them, which lends emphasis to the 
 importance of an exact technic. 
 
 The technic illustrated (by C of Fig. 38) is indicated 
 for all of the upper teeth. Occasions may arise, however, 
 where it will not suffice for the upper molar teeth owing 
 to the fact that the buccal roots and the lingual roots may 
 
 *Technic of Dr Weston Price, 
 
])ENTAL AND OJIAI. JtADJOGKAL'Jl Y TECJIXIC 
 
 s.-) 
 
 diverge to the extent of assuming different planes. In 
 this event, it may be necessary to make more than one 
 radiogram, if information of an exacting character is de- 
 
 Fig. 39. — Technic for the upper molar teeth. 
 
 sired concerning an upper molar. The plan of procedure 
 is shown in Fig. 39, A, B, and C. 
 If a general picture of the molar is desired (shown by 
 
8b DENTAL AND ORAL RADIOGRAPHY 
 
 A), the plane of the tooth is assumed as lying midway 
 between buccal roots and lingual root, and the rays are 
 passed in perpendicularly to the plane lying midway be- 
 tween this assumed plane and the film. In the resulting 
 radiogram none of the roots will appear in their exact 
 proportions, but the buccal roots will be slightly short- 
 ened, while the lingual root will be slightly lengthened. 
 
 When it is desirable to obtain a radiogram of the buc- 
 cal roots in their exact length, they must be assumed as 
 being the plane of the tooth (B) and the rays must pass 
 in perpendicularly to a plane lying midway between them 
 
 Fig. 40. — Special compression cylinder made of leaded glass. 
 
 and the film. In this event, the image of the lingual root 
 is elongated. 
 
 If the lingual roots are under scrutiny (C), they must 
 be considered the plane of the teeth, and the rays passed 
 in perpendicularly to a plane lying midway between the 
 lingual root and the film. In this event, the image of 
 the lingual root will have its correct proportions, but the 
 image of the buccal roots will be slightly shortened. 
 
 The upper molars are by all means the most difficult 
 teeth to radiograph; that is, to obtain radiograms that 
 are as comprehensive as those made of the other teeth. 
 
DENTAL AND ORAL RADIOGRAPHY TECHNIC 87 
 
 However, by going to the extra work entailed by the 
 foregoing procedure, valuable radiographic information 
 can oftentimes be gained. 
 
 The task of radiographing the upper molars and pre- 
 molars can be rendered less difficult by using a special 
 compression cylinder made of leaded glass, as sho^\ni in 
 Fig. 40.* The end of the glass cone or cylinder is beveled 
 at the end so that it can be placed close to the face and 
 still remain at the desired angle, its glass construction 
 
 Fig. 41. — The patient can hold the film in position against the lower teeth by exert- 
 ing slight pressure with the finger. 
 
 enabling the operator to view the area under exposure 
 at all times, and thereby lessen the liability of inaccurate 
 work. 
 
 With the lower teeth (Fig. 41) we do not have this diffi- 
 culty to contend with to so great a degree, as the films 
 can be placed for the most part in such a position that 
 they lie parallel to the long axis of the teeth, and the rays 
 can be directed in a perpendicular direction both to the 
 plane of the teeth and the plane of the film. 
 
 In placing the films in the mouth preparatory to mak- 
 
 * Suggested by Dr. F. K. Ream. 
 
88 dejsttal a:n^d oral eadiogeaphy 
 
 ing radiograms of the lower teeth, difficulty is sometimes 
 encomitered, owing to the fact that the tissues are usually 
 quite sensitive. Inasmuch as the film must he pressed 
 well cloivn between the tongue and the teeth, it is advis- 
 able to first see that no sharp corners exist on the film 
 covering, or better still, provide a rubber envelope or 
 film holder ivhich has no sharp corners. Such an en- 
 velope is easih^ improvised by the use of ordinary black 
 vulcanite rubber. A loieceof this rubber which should be 
 a little more than double the size of the film, is wrapped 
 about it and the free edges pressed together. These edges 
 are then trimmed with a pair of scissors so that the cor- 
 ners are rounded. Such an envelope containing the film 
 can be introduced into the mouth and placed well dovm 
 on the lingual side of the teeth Avitli a minimum amount 
 of discomfort to the patient. 
 
 Film Holders. — Some operators prefer to use a film 
 holder to support the film during exposure. Of these, 
 there are several varieties upon the market, all of which 
 will accomplish the work for which they are intended. 
 
 The Ketcham Film Holder.* — The Ketcham film 
 holder consists of a metal block with a rubber band 
 around it, Avhich can be cjuickly changed, a bolt secured 
 by a wing nut to pass through a slot in the block, and five 
 ]3airs of film holders. These film holders are rights and 
 lefts, and graded in size, and shape, so as to fit different 
 mouths. (See Figs. 4:2-A, B, and C.) A "stereoscopic 
 finder" is also a part of this set, which allows the oper- 
 ator to make a second radiogram of a given area, by re- 
 moving the exi^osed film and placing another in its place 
 in exactly the same ijosition. 
 
 The Leach Film Holder.! — The Leach film holder is 
 very sim]Dle in design, and two film holders constitute a 
 set. (See Fig. 43.) 
 
 *Des!gned by Dr. A. H. Ketcham. 
 tDesigned b}' Dr. F. D. Leach. 
 
DENTAL AND ORAL RADIOGRAPHY TECIINIC 
 
 89 
 
 B. 
 
 C. 
 
 Fig. 42. — The Kctcham film holder. A, right and left film holders in graded sizes; 
 B, metal block with film holder attached to it and film in position ready to be placed 
 in the mouth. By closing the teeth upon the metal block, the film holder is held in 
 the position desired; C, stereoscopic finder attached to the film holder. 
 
90 
 
 DENTAL AND ORAL EADIOGRAPHY 
 
 With these, the patient holds the film in position by 
 grasping the handle part of the holder, and the operator 
 can by noting the angle of the handle, determine the di- 
 rection in which the rays mnst be directed. 
 
 The smaller holder is designed for the upper six and 
 lower eight anterior teeth, and the larger holder is de- 
 signed for the posterior areas of the month. 
 
 The Dorr Film Holder.* — The Dorr film holder is de- 
 signed so that the film is lield in position for exposure 
 
 Fig. 43.— The Leach film holder. 
 
 by closing the teeth upon a flange which is part of the 
 holder. (See Fig. 44.) A removable handle is attached 
 to the edge of the flange and assists in placing the film 
 holder (carrying the film) in the desired position in the 
 mouth, after which the handle can be removed. 
 
 Two film holders constitute a set of which one has an 
 obtuse angle and is designed for the upper teeth, while 
 the other is placed at right angles to the flange and is 
 intended for use upon the lower teeth. 
 
 *Designed by Dr. P. P. Dorr. 
 
DENTAL AND ORAL RADIOGllAPIIY TECIINIC 
 
 91 
 
 Where it is necessary to make a complete radiographic 
 examination of the dental arches, it can be accomplished 
 in the average case, by making six exposures of each 
 arch. The procedure to be followed is diagrammatically 
 shoA\ai in Fig. 45. The numbers 1, 2, 3, 4, 5, 6 indicate the 
 position of the x-ray tube in its relation to the dental 
 
 Fig. 44. — The Dorr film holder with detachable handle. 
 
 Fig. 45. 
 
 arch, and the ends of the lines coming from the numbers 
 show the position of the mesial and distal edges of the 
 film used for each exposure. It mil be noted that each 
 adjacent film position overlaps its neighbor which is ad- 
 visable so that no area is left out. 
 
 In making radiograms of the anterior part of the arch, 
 it is a mistake to attempt to radiograph more than two 
 
92 DENTAL AND ORAL EADIOGRAPHY 
 
 or three teeth at a tmie, as the curvature of the arch 
 usually renders it impossible to get more than that num- 
 ber free from distortion. 
 
 Another point in technic which should not be over- 
 looked if sharp outlines are to be obtained, is the one in 
 regard to having the tube placed at the proper distance 
 from the structures to be radiogaphed. To establish the 
 best focal distance for work about the teeth or jaws, the 
 target of the tube should be about twenty inches from the 
 plate or film. 
 
 With a good x-ray machine, and a properly regulated 
 tube, good radiograms can be obtained by very short ex- 
 posures, particularly by using the intra-oral method, as 
 the rays need only penetrate a comparatively short dis- 
 tance before reaching the film. With the apparatus now 
 available good radiograms can often be obtained by in- 
 stantaneous exposures. However, instantaneous expo- 
 sures are not necessary for good dental radiography. X- 
 ray apparatus which is capable of producing sharp, 
 clear "intra-oral" radiograms in from two to five sec- 
 onds, is efficient enough for use in the x-ray laboratory 
 of the dentist. 
 
 Extra-oral Method 
 
 The extra-oral method is, in the author's opinion, the 
 one offering the widest range of usefulness in our work. 
 As stated previously, this is the method used to obtain 
 radiograms of large areas. Not only can larger areas be 
 obtained by this method, but locations and structures in- 
 accessible to the small films are reached and their images 
 accurately and clearly recorded upon the larger plates. 
 Therefore, the advantage of this method is well founded. 
 
 The technic is simple when once mastered, but must be 
 adhered to accurately if the results are to be depended 
 upon for diagnosis. In using the extra-oral method, large 
 
DENTAL AND OltAL llADIOGRAPIIY TECHNIG 93 
 
 plates or films are used and the areas desired are brought 
 in as close contact as possible with the plate, hy pressing 
 or resting the side or portion of the face upon tvhich 
 the structures desired are located, against the plate. 
 
 First of all, the patient must be placed in a position so 
 that the head can he held perfectly still. The dental chair 
 with a few adjustments offers an excellent means for 
 accomplishing this. One of the chair arms is lowered 
 down against the side of the chair or removed, and the 
 
 Fig. 46. — The headrest of the dental chair with its many adjustments can easily be 
 arranged so that the patient's head may rest easily and firmly upon it. 
 
 patient placed sideways in the chair. The chair back is 
 adjusted so that the patient lies against it in an easy 
 position, and the headrest wings are adjusted so as to 
 lie flat and thereby form an excellent resting x)lace for the 
 plate. The headrest with its many possible adjustments 
 can easily be placed so that the patient's head rests easily 
 and firmly upon the plate, rendering it an easy matter to 
 remain perfectly quiet. This position is shown in Fig. 
 46. 
 
94 
 
 DENTAL AND OKAL EADIOGRAPHY 
 
 Fig. Al-A. — Tube stand with platerest and head support. (Eisen and Ivy.) 
 
 Fig. 47-B. — Position of head and angle for left side of jaws. (Eisen and Ivy.) 
 
DENTAL AND ORAL IIADIOGRAPIIY TECHNIC 95 
 
 Fig. 48. — The arrangement of the apparatus preparatory to seating the patient. 
 
 Fig. 49. — The patient seated and the apparatus arranged for making a radiogram 
 of the left side. The comfortable position of the patient renders it an easy matter 
 to remain perfectly quiet. 
 
96 DENTAL AND ORAL RADIOGRAPHY 
 
 For this character of work some operators prefer to 
 use a platerest and head supporting device attached to 
 the tube stand as shoA^ni in Fig. 4:7 -A. Where such a 
 method is followed, the head is supported in its proper 
 relationship to the plate as shown in Fig. 47-5.* 
 
 Author's Method of Seating the Patient 
 
 In the author's opinion, there is another method of 
 seating the patient for this character of work which 
 will be found to be advantageous where such special ap- 
 paratus is not available. It is accomplished by using an 
 ordinary chair Avith a straight back and small arms, 
 placed against the back of the dental chair. The head- 
 rest of the chair is turned over and adjusted to the 
 proper height, position and angle, so that the patient's 
 head can rest against it in any desired position. In this 
 way the patient is afforded the firm support of the heavy 
 dental chair, and, therefore, has little difficulty in re- 
 maining perfectly quiet, and the ojjerator can by making 
 a few changes in the position of the small chair, by mov- 
 ing and readjusting the tube stand and the headrest, 
 have radiographic access to any part of the oral cavity 
 or associated structures. The arrangement of the appa- 
 ratus preparatory to seating the patient is shown in 
 Fig. 48. 
 
 The fact that this requires but a few moments, does 
 not disarrange the office, or put the patient to discom- 
 fort, justifies the author in feeling that it is by all means 
 the preferable method for use in the average dental office. 
 
 With the head thus supported, as shown in Fig. 49, the 
 rays are directed from the opposite side of the head, 
 and, therefore, must pass through the entire face or 
 skull in transit. The question naturally arises, how is 
 this to be accomplished without superimposing the shad- 
 
 *Eisen, 15. J., and Ivy, Robert H. : American Journal of Roentgenology, May, 1916. 
 
DENTAL AND ORAL RADIOGRAPHY TECHNIC 97 
 
 ows of one side upon the shadows of the other side, and 
 thereby producing a chaotic result. 
 
 For instance, let us suppose that we wish to obtain 
 a radiogram of the left side of the upper and lower jaws 
 extending from the cuspid region in front to the angle 
 of the jaw behind, and from the floor of the orbit above 
 to the inferior margin of the mandible below. If we are 
 to get a correct shadowgraphic representation of this 
 area, it should be free from the shadows of the opjDosite 
 side, and this can only he accompUshed hy directing the 
 rays in such a manner that they tvill miss the areas not 
 desired and will pass through those we wish to record. 
 
 In accomplishing this, we must take into consideration 
 two structures; viz., the spine and the ascending ramus 
 of the mandible (on the right side in this instance as 
 the left side is to be radiographed) and cause the rays 
 to pass in through this opening and thereby reach the 
 desired area. The way in which this is accomplished is 
 shown in Fig. 50, A and B, and Fig. 51, A and B. 
 
 An important factor in accomplishing this is the posi- 
 tion in which the patient's head is held as it is pressed 
 against the plate. Held in the manner shoAvn, the rays 
 can be made to pass in between the ascending ramus of 
 the mandible and the spine, and can pass in at approxi- 
 mately a perpendicular direction to the long axis of the 
 teeth and the plate, giving correct shadow lengths upon 
 the plate. Fig. 52 shows a radiogram made by using this 
 technic. 
 
 If this rule is disregarded and the rays passed through 
 the structures, as shown in Fig. 53, A and B, the shadows 
 of the opposite side will be superimposed upon the shad- 
 ows of the structures desired, and a chaotic result pro- 
 duced. The result of such technic is shown in Fig. 54. 
 
 In a similar manner as shown in Figs. 50 and 51, with 
 slight adjustments in the position of the plate, the head, 
 
DENTAL AND ORAL RADIOGRAPHY 
 
 Fig. 50-^. 
 
 Fig. 50-B. 
 
 Fig. 50. — Technic for left side. M-L, median line; S, the spine; A, ascending ramus 
 and angle of lower jaw; P-F, plate or film. 
 
DENTAT. AND OTlATv RADTOGTIAPTTY TECIFNIC 91) 
 
 Fig. 51-/1. 
 
 Fig. Sl-B. 
 
 Fig. SI. — Technic for right side. M-L, median line; S, the spine; A, ascending ramus 
 and angle of lower jaw; P-F, plate or film. 
 
100 
 
 DENTAL AND ORAL RADIOGRAPHY 
 
 and the tube, the areas in the upper and lower jaws ex- 
 tending from the median line to the first premolars, and 
 from the nose above to the inferior margin of the man- 
 dible below, can be radiographed (Fig. 55, A and B). 
 
 Fig. 52. 
 
 Likewise the structures at the median line including the 
 incisors, both above and below, the anterior portions of 
 the mandible and maxilla, the nasal cavity and its ac- 
 cessory sinuses, may be radiographed by passing the 
 
DENTAL AND ORAL RADIOGRAPHY TECHNIC 101 
 
 Fig. S3-A. 
 
 Fig. 53-B. 
 
 Fig. S3.— Incorrect technic. The shadows of both sides will be imposed upon 
 
 the plate. 
 
102 DENTAL AjSTD OEAL RADIOGRAPHY 
 
 rays directly through the skull, as sho^^m in Figs. 56 and 
 57. In this instance, the shadow of the spine will be 
 superimposed upon the dental structures, but owing to 
 
 Fig. 54. — The result of incorrect technic. This is a radiogram of the same subject as 
 
 shown in Fig. 52. 
 
 the fact that it is so far removed from the plate, its 
 shadow does not interfere seriously. It is important, in 
 making these pictures, to have the patient's head sup- 
 ported in such a manner that it can be held still for a 
 
DENTAL AND OIIAL KADIOGIlArilY TECirXIC 103 
 
 Fig. 55 -.4. 
 
 Fig. SS-B. 
 
 I'"ig. 55. — The ai-eas in the upper and lower jaws extending from tlie median lin< 
 lo Ihc lirst premolar can Ije radiographed by utilizing tliis teehnic. A, techiiie Im 
 left sirle; B, teehnic for right side. 
 
104 
 
 DENTAL AND ORAL RADIOGRAPHY 
 
 longer period than is required in making the exposures 
 of the other areas mentioned. 
 
 When ready to make the exposure for extra-oral radio- 
 grams, the apparatus is arranged with the anode of the 
 tube about twenty inches from the plate. The patient 
 is instructed to heep the mouth closed tvith the teeth 
 together in their natural occlusion. They should also be 
 warned as to the approximate length of time the ex- 
 posure will require, and that they must remain perfectly 
 quiet. 
 
 Fig. 56. — The structures at the median line including the incisors, both above and 
 below, may be secured in this way. 
 
 With the more powerful types of apparatus, extra-oral 
 radiograms require but short exposures, but if an oper- 
 ator does not possess high power apparatus, he should 
 not hesitate to use this method, as a patient properly 
 seated and supported, as shown in Fig. 49, can easily re- 
 main quiet for five or ten seconds, or perhaps even longer, 
 should it be necessary. 
 
 In making a complete radiographic examination of the 
 teeth, the maxilla and mandible, the author suggests the 
 following procedure. Extra-oral radiograms should be 
 
DENTAL AND ORAL RADIOGRAPHY TECIIISriC 105 
 
 made of each side, using the technic ilhistrated in Figs. 
 50, 51, and 55. This would mean two plates for each 
 side. Then by the use of intra-oral films, the region ly- 
 ing between the cuspids both above and below, should be 
 radiographed. These plates and films should then be 
 developed and examined. If the procedure has been car- 
 ried out with due regard for all the elements involved, 
 the result should constitute a general radiographic sur- 
 
 Fig. 57. — In following the technic illustrated in Fig. 56 the patient's head should be 
 supported by a bandage of gauze to insure perfect immobility. 
 
 vey of the teeth, the maxilla and the mandible. Should 
 any of the plates or films exposed fail to result in good 
 radiograms, additional exposures should be made, as 
 nothing but good radiograms should be depended upon 
 for diagnosis. 
 
 It is sometimes advisable after making a complete radi- 
 ographic examination by the method just advocated, "to 
 check up" the findings of extra-oral radiograms by the 
 use of the intra-oral films. For instance, suppose a large 
 
106 DEISTTAL AND ORAL RADIOGRAPHY 
 
 plate shows what appears to be an abscess upon the root 
 of an upper bicuspid or molar tooth. An intra-oral radio- 
 gram of this particular area will often settle any doubts, 
 as a higher degree of detail can often be obtained by con- 
 centrating upon the small area in question. 
 
 The author would not wish to impl}^ by the preced- 
 ing remarks upon technic, that the few rules enumerated 
 constitute a safe and never failing means of producing 
 good radiograms. There are many points to be consid- 
 ered which can not be included in so limited a text, but 
 which must be learned in the school of experience, such 
 as the necessary variations from the given rules of tech- 
 nic because of anatomic variations in the dental and oral 
 structures of patients. Therefore, the rules of technic 
 which have been presented must be accepted only in the 
 light of principles. 
 
CHAPTER VII 
 
 TECHNIC OF DENTAL AND ORAL RADIOGRAPHY 
 
 (Continued) 
 
 Successful radiography depends upon a sequence of 
 operations, each of which must be carried out with scien- 
 tific accuracy. These steps, upon which the finished prod- 
 uct depends, may be enumerated as f oIIoavs : 
 
 1st — Correct technic of position. 
 
 2nd — Proper tube and current conditions. 
 
 3rd — Correct exposure and development of plates and 
 films. 
 
 It would be difficult to determine which of these steps 
 is the most important; in fact, they are all so important 
 that a radiogram is a success or failure in accordance Avith 
 the degree of accuracy with which each is carried out. 
 In the preceding chapter, the actual technic of radiog- 
 raphy, so far as the arrangement of apparatus is con- 
 cerned and its relative position to the patient and the 
 plate (or film), has been discussed. We Avill, therefore, 
 proceed to the next factor for consideration. 
 
 Proper Tube and Current Conditions 
 
 The character of the x-rays produced in a tube de- 
 pends upon the degree of its vacuum and the current 
 which passes through it. We know that the x-rays are 
 produced by the cathode stream striking the anode or 
 target, and that this cathode stream (Fig. 59-M) is gen- 
 erated by the flow of the current in the tube. The veloc- 
 ity of the cathode stream depends upon the voltage of 
 the current entering the tube, therefore, the higher the 
 
 107 
 
108 DENTAL AND ORAL RADIOGRAPHY 
 
 voltage, the faster the cathode stream travels, and the 
 more intense or penetrating are the x-rays produced. 
 The quantity of x-rays produced depends upon the mil- 
 liamperage of the current. 
 
 In considering the role enacted by the voltage and mil- 
 liamperage in the x-ray production, we have assumed 
 that the tube is exhausted to a high degree of vacuum, 
 for the degree of vacuum determines to a large extent, 
 the value of the other two factors. The degree of vac- 
 uum of a tube is designated as high, medium, or low, 
 a "high tube" being one in which the vacuum is well 
 nigh complete; in a ''medium tube" the vacuum is less 
 complete, while a "low tube" is one in which the vacuum 
 is far from complete. 
 
 For dental radiography a fairly high tuhe is indicated, 
 as with such a tube x-rays may be produced having a de- 
 gree of penetration sufficient to pass thsough the oral 
 structures and produce the desired effect upon the emul- 
 sion of the plate or film. 
 
 When a current of high voltage is passed through 
 such a tube, it should light up in a characteristic man- 
 ner forming two hemispheres which have a definite line 
 of demarcation. The hemisphere in front of the target 
 which is the active hemisphere, is evident by a fluores- 
 cence deep apple green in color, while the other hemi- 
 sphere should be evident by a lack of greenish light. 
 
 To Determine the Vacuum of a Tube 
 
 The comparative degree of vacuum of a tube can be 
 determined in the following manner : Connect the tube 
 to the x-ray machine as shown in Fig. 58. See that the 
 third terminal {S') is moved well away from the nega- 
 tive terminal {S), or better still, disconnect the wire run- 
 ning to the regulation chamber {R). Now, move the 
 sliding rods {B and D) of the secondary spark gap, to- 
 
DENTAL AND ORAL RADIOGRAPIIY TECTINIC 
 
 109 
 
 ward each other until they are ahout three inches apart, 
 and start the current. Unless the tube is loiu, the cur- 
 rent will jump the spark gap instead of passing through 
 the tube. If the tube resists the current and causes it 
 to jump the spark gap, it is said to have "backed up" 
 three inches of spark. Thus a "low tube" will back up 
 
 two or three inches of spark, a "medium tube" five or 
 six inches, while a high tube will back up six or eight 
 inches. In fact, the vacuum of a tube may be so great 
 that only the most powerful x-ray machines will operate 
 it. Such a tube, however, is not useful for dental radiog- 
 raphy. 
 
 The vacuum of a tube may also be determined by the 
 use of an instrument known as a milliampereineter. 
 This instrument which is usually an accessory of either 
 the induction coil or transformer, is connected in circuit 
 with the tube, and measures the current passing through 
 the tube. With a "low tube" the milliamperemeter will 
 
110 DENTAL AND ORAL RADIOGRAPHY 
 
 show a reading of 15 to 18, while with a "medium tube" 
 the reading will be from 10 to 12, and with a ' ' high tube ' ' 
 the milliamperemeter will register 5 or less. 
 
 Relative Merits of Low, Medium, and High Tubes 
 
 A low tube under average current conditions gives a 
 clear sharp hemisphere of pale greenish light in front of 
 the target, with usually a trace of bluish light in the re- 
 gion of the assistant anode. If the tube is very low, the 
 cathode stream shows blue, and there is a bluish light 
 back of the active hemisphere. Such a tube will not do 
 good radiographic work, as the x-rays produced by it 
 are lacking in penetration. 
 
 A "medium tube" gives a clear, sharp hemisphere of 
 light greenish color, and there is an absence of bluish 
 light back of the target. The rays emanating from such 
 a tube are more penetrating than those from the "low 
 tube," but are not so well suited for "bone radiography" 
 as those which come from a tube fairly high in vacuum. 
 When such a tube is operating, it gives a clear sharp 
 hemisphere deep apple green in color, with a lack of 
 greenish light back of the target. The x-rays emanat- 
 ing from such a tube are of degree of penetration ivliich 
 is best suited for hone radiography, for they penetrate 
 and pass through the soft tissues and to a sufficient de- 
 gree through the bone structure to give good contrast. 
 
 It is ver}^ important that the vacuum of such a tube be 
 kept uniform, for if it gets low, the power of penetration 
 of the rays is decreased, and, on the other hand, if the 
 vacuum gets too high, the penetrating power of the rays 
 will be increased, with the result that they will penetrate 
 through the bone structure as easily as the soft tissues. 
 Consequently, unless very short exposures are given, 
 there will be little if any contrast and the plate will be 
 dark and hazy. 
 
DENTAL AND ORAL RADIOGllArj H' TEC II NIC 111 
 
 Reg-ulating" the Tube 
 
 Prior to seating and arranging the i:)atient, the tube 
 should be tested out and any needed change in its vac- 
 uum effected. This is easily accomplished by utilizing 
 the third terminal of the x-ray machine. The tube should 
 be connected to the machine as sho^vn in Fig. 58. The 
 terminals of the regulating spark gap (S'S) should be 
 placed about four inches apart, and the current (of cor- 
 rect working strength) turned on for an instant. If a 
 line of sparks jum^D between S' and S, it shows the vac- 
 uum of the tube is too high. In this event the regulating 
 spark gap (S'S) should be reduced to about two inches, 
 and a small amount of current turned on. This weaker 
 current will jjass across the spark gap (S'S), travel down 
 the wire connected to the regulating chamber, and by 
 heating the asbestos (impregnated with chemicals), will 
 liberate enough gas to reduce the vacuum. Unless the 
 tube is very high, a few seconds will suffice to reduce it 
 to the vacuum desired. To be sure the vacuum is right, 
 the regulating spark gap (S'S) should be widened to 
 about four inches, and the desired working current again 
 passed through the tube for an instant. If the tube lights 
 up with a clear sharp active hemisphere deep apple 
 green in color with a lack of greenish light back of the 
 target, you then know it is ready for work. 
 
 If an x-ray machine is not equipped with a third termi- 
 nal, the same results in regulating the tube may be ef- 
 fected by using the regulating adjuster (Fig. 59), the end 
 of which can be placed at the desired distances from 
 negative wire near its point of attachment to the tube. 
 The tube may also be lowered by attaching the negative 
 wire directly to the regulating chamber and passing a 
 small amount of current through the circuit. 
 
 These manipulations should be carried out with the 
 
112 DENTAL AND ORAL RADIOGRAPHY 
 
 greatest caution, for a tube is an extremely delicate and 
 sensitive piece of apparatus and ivill not stand abuse. 
 A careless operator can quite easily reduce the vac- 
 uum to such a degree that the tube is useless. Such a 
 tube has a purple appearance when the current is passed 
 through it. If such a tube has not been too greatly 
 abused, it will often regain its vacuum if given a rest. If 
 this does not bring the vacuum up, it can often be brought 
 back in the following way: The spiral spring (Fig. 59) 
 connecting the anode and assistant anode should be re- 
 moved and the positive wire from the machine attached 
 
 A— Anode. 
 
 U- -Assistant Anode 
 
 C— Cathode 
 
 D-RcRulat.ng 
 ChamlKT 
 
 r-RegulaiinB Ad- 
 juster 
 
 G— Hemispluie 
 
 H-Conneclion 
 
 Wire 
 I-Assistani Anode 
 Cap 
 
 K-Anode fa|. 
 
 l^Cathode Call 
 
 M— Cathode Stream 
 
 N-Focal I'oint 
 
 Fig. 59. 
 
 to the assistant anode (/). The negative wire is at- 
 tached as usual (at L) and a light current is run through 
 the tube for a minute or two at a time. If this is done 
 once or twice a day for several days, the vacuum will 
 usually come up. Any increase in vacuum will be indi- 
 cated by the milliampere readings dropping off, or by 
 the increased length of spark gap the tube will ''back 
 
 up." 
 
 If a tube does not respond to this treatment but con- 
 tinues to be purple while operating, it indicates that it 
 is practically non vacuous or "punctured." It is then 
 useless and should be sent back to the manufacturer for 
 
DENTAL AND ORAL RADIOGRAPHY TECHNIC 113 
 
 repairs. In the event a tnhe is "completely punctured," 
 the current in passing through it simply jumps the gap 
 ])etween the anode and cathode, and is evident as a line 
 of white sparks. 
 
 One tube complication not yet mentioned is sometimes 
 encountered in the use of induction coils. This is knoA\Ti 
 as ''inverse in the tube," and is the result of the pres- 
 ence of inverse current (current in the wrong direction) 
 in the secondary circuit of the coil. "Inverse" is evi- 
 dent in the tube by the appearance of rings of light back 
 of, and usually running at an angle to, the active hemi- 
 sphere, or by a fullness of greenish light back of the ac- 
 tive hemisphere, with rings about the assistant anode. 
 
 Inverse current in a tube will generate secondary rays 
 which have the tendency to make the outline of the image 
 on the plate hazy or "less sharp," as these rays are pro- 
 duced in the tube elsewhere than at a focal point on the 
 target. It also produces heat in the tube which lowers 
 the vacuum and hence lessens the penetration of the rays 
 coming from it. 
 
 "Inverse" in the tube can usually be controlled or pre- 
 vented by the use of " a multiple spark gap " or " a valve 
 tube" arranged in series with the x-ray tube, and by 
 using a tube which is fairly high in vacuum. If it still 
 persists after these precautions are taken, it indicates 
 an imperfect adjustment of the induction coil or some of 
 its accessories. 
 
 All manufacturers of x-ray tubes furnish full instruc- 
 tions as to the care of and manner of using x-ray tubes. 
 These instructions should be carefully read and explic- 
 itly foUoived. 
 
 In order that uniform results may be obtained, it is 
 advisable to always use the tube at the same vacuum, 
 with the same amount of current. The proper "working 
 current" may be determined in the following way: 
 
114 DENTAL AND ORAL RADIOGRAPHY 
 
 With the tube disconnected, set the sliding rods {B and 
 D of Fig. 58) of the machine about six inches apart. 
 Then start the current in the machine, and beginning 
 with a low current increase it until a fat fuzzy "cater- 
 pillar spark" is produced across the spark gap. As 
 soon as this spark or discharge appears, the switch 
 should be pulled out, but the rheostat or other control- 
 ling apparatus left as it was when the spark appeared, 
 so that Avhen the tube is connected, the proper working 
 current will come from the machine. 
 
 The tube should then be connected up and given a trial. 
 If it is not too high in vacuum, it should take the cur- 
 rent, or in the event it is too high, it Avill "back up" the 
 spark, and the discharge instead of passing through the 
 tube will jump the gap. If the tube requires regulating, 
 it can be done by the methods before described. 
 
 With the working current and vacuum established, it 
 is a good idea to separate the sliding rods on the ma- 
 chine to at least eight inches, to insure against the tube 
 backing up the current, for in the event the tube should 
 start going up during the time the exposure is being 
 made, the startling noise made by the discharge jumping 
 the gap, may cause the patient to move and thereby blur 
 the radiogram. If several exposures of five or ten sec- 
 onds each are made, the tube should be given sufficient 
 rest between exposures so that it will not heat up. This 
 is important. 
 
 With proper tube and current conditions, the length of 
 time required for the exposure will depend upon the t^^pe 
 of x-ray machine used, and the thickness and density of 
 the parts to be radiographed, varying with different pa- 
 tients according to age and structural make up. 
 
CHAPTER ^^III 
 
 CORRECT p]XPOSURE AND DEVELOP:\rENT OF 
 X-RAY PLATES AND FILMS 
 
 X-ray plates and films differ from those used in or- 
 dinary photography in that their emulsion is more sen- 
 sitive and better adapted to record the shadows jorodueed 
 b}^ the x-ray. Therefore, they should ahva3's be used in 
 preference to ordinary plates and films. 
 
 The same general photographic rules apply to x-ray 
 plates and films as apply to the ordinary kind, except 
 perhaps that they demand a greater degree of accuracy 
 and care throughout the process of exx)osure and devel- 
 opment, if the very best results are to be obtained. 
 
 X-ray Plates 
 
 X-ray plates are supplied by the manufacturers, packed 
 in lightproof boxes containing one dozen plates. They 
 are obtainable in any desired size, but for dental and 
 oral radiograph}^, a 5x7 plate is large enough. If stored 
 in the laboratory, they should be kept in a lead-lined box 
 prior to their preparation for exposure, or they will be- 
 come ''fogged," as lightproof boxes offer no protection 
 whatever from the x-ray. 
 
 A suitable plate and film storage box is shown in Fig. 
 60. Such a box should be about twelve inches square 
 and five inches deep. This will enable the storage of 
 several boxes of 5x7 plates, and in addition, three or four 
 dozen dental films. 
 
 In their preparation for exposure, each plate is placed 
 in two lightproof envelopes, one of which is black and 
 
 115 
 
116 
 
 DENTAL AND ORAL, EADIOGRAPHY 
 
 the other red or orange in color. Such envelopes are 
 furnished by plate manufacturers and are obtainable in 
 the desired size. The transference of the plate from its 
 original box to the envelopes must, of course, only he done 
 in the photographic darkroom. The plate is first slipped 
 into the smaller envelope which is usually the black one, 
 with the emulsion side of the plate facing the smooth 
 side of the envelope (the side free from seams or over- 
 lapping edges). The envelope containing the plate is 
 then placed in the larger or yellow envelope, flap-end 
 first, with the smooth side of the inner envelope facing 
 the smooth side of the outer one. Plates prepared in 
 
 X-rayproof film and plate chest. 
 
 this way are then ready for exposure and can be placed 
 back in the lead-lined box until needed. 
 
 In "loading these envelopes," care should be taken 
 lest the emulsion of the plate become scratched, as 
 scratches even though they be very slight will often cur- 
 tail the value of the finished radiogram. 
 
 It is not advisable to keep large quantities of plates 
 loaded in envelopes, unless they are to be used within a 
 few days, as the contact of the paper with the emulsion 
 will in time affect it adversely. 
 
 All "brands" of x-ray plates are not the same, there- 
 fore, if the best results are obtained in using any par- 
 
DEVELOPMENT OF PLATES AND FILMS 117 
 
 ticular kind, they must be handled in strict accordance 
 with the manufacturers' instructions. For dental and 
 oral radiography, a plate should be fairly rapid (that is, 
 it should not require a long exposure), give a high de- 
 gree of detail and good contrast, and should be uniform 
 in its reaction to the x-ray. 
 
 X-ray Films 
 
 In making intra-oral radiograms, a film is preferable 
 to a plate as it is flexible and, therefore, can be more 
 easily adapted to the inside of the mouth. These films 
 are obtainable in several convenient sizes, wrapped in 
 lightproof and dampproof coverings ready for expos- 
 ure. Like plates they should be kept in a lead-lined box 
 for protection. 
 
 With these "dental films" as they are called, you have 
 the choice of two different emulsions, one of which is 
 much more ' ' rapid ' ' than the other. 
 
 The "rapid" or "fast film" requires only about one- 
 fourth or one-third as long an exposure as the "regular" 
 or "slow film," and therefore is an advantage to the 
 radiographer who uses one of the less powerful types 
 of x-ray machines. However, such a film does not have 
 as much latitude as the slow film, and is therefore more 
 apt to be overexposed. If properly exposed, either one 
 will give satisfactory results. 
 
 When arranging a plate or film for exposure, the emul- 
 sion side should lie next to the structures being radio- 
 graphed. If this rule is systematically followed, it is an 
 easy matter to identify radiograms, i. e., whether they 
 represent structures on the right or left side of the me- 
 dian line. 
 
 Development of Plates and Films 
 
 The process of "development" of either plates or 
 films may be briefly described as follows: At a con- 
 
118 DENTAL AND ORAL RADIOGEAPHY 
 
 venient time following the "exposure," the plate or 
 plates (or films) are taken into the ''darkroom." Such 
 a room has all white light excluded from it, and is illu- 
 minated only by a so-called "ruby light" or darkroom 
 lantern. The darkroom should be supplied with a shelf 
 or table about two and a half feet wide and three feet 
 long placed at ordinary table height from the floor, so 
 that the operator may sit ujoon a stool while at work. 
 Upon this shelf there should be four trays, one for the 
 "developing solution," one for the "fixing bath," and 
 the other two for water. Where a darkroom is supplied 
 with running water and a sink, only three trays are nec- 
 essary. 
 
 With all light excluded from the room except the ruby 
 light coming from the darkroom lantern, the plate (or 
 film) is taken out of its envelope and immersed emulsion 
 side up in the developing solution. In order to insure a 
 uniform action by the developer, the tray should be fre- 
 quently rocked Avith a gentle motion. If the plate (or 
 film) has been properly exposed, development should be 
 complete in about five minutes (although the time varies 
 with different formulae). 
 
 The plate or film is then removed from the developer 
 and placed in a tray of water to thoroughly wash the 
 developing solution from it. This, of course, requires 
 but a moment, and it is then immersed in the "fixing 
 bath," keeping the emulsion side up. As soon as the 
 plate has been in the fixing bath a few seconds, the dark- 
 room door may be opened and light admitted without in- 
 jurious effects. However, the plate (or film) must still 
 remain in the fixing bath until it has "cleared" (until 
 all milkiness is gone from the back of the plate), which 
 will usually require from five to ten minutes. In fact, 
 it is better to let it "fix" for at least five minutes longer 
 than is required for it to become clear. 
 
DEVELOPMENT OF PLATES AND FILMS 119 
 
 When the fixing process is complete, the plate must be 
 placed in water and thoroughly washed to remove all the 
 fixing solution from it. This can he accomplished hy 
 washing it in several changes of water, or better still, 
 place it in a basin or tray of cold "running water" for 
 ten or fifteen minutes. 
 
 When the washing process is complete, the emulsion 
 side of the plate or film should be gently rubbed with a 
 clean piece of wet cotton, holding the plate (or film) 
 under a cold water faucet during the act. The developed 
 radiogram is then ready to dry. Plates should be stood 
 on edge or placed in a suitable rack so that nothing Avill 
 come in contact with the emulsion side, and left until 
 perfectly dry. Films may be pinned to the edge of a 
 shelf, or secured to a line with suitable clips. The drying 
 process should take place in a room free from dust or 
 soot, for these will prove injurious to the drying emulsion. 
 
 The size of the trays used in the darkroom will depend 
 upon the number of plates or films which are to be 
 carried through the developing process at a time. For 
 plates, the author uses trays 8x10 inches in size. With 
 such trays two 5x7 plates can be carried through at a 
 time. Where a large number of plates are being devel- 
 oped, additional trays can be used and if necessary 
 "tanks" capable of holding a dozen plates, utilized in 
 the fixing or washing process. In developing "dental 
 films, ' ' small trays Avill be found convenient, and unless a 
 large number are to be developed at a time, a 4x5 or 5x7 
 tray will be large enough. 
 
 Trays should be labeled according to the purpose for 
 which they are to be used, and used for that purpose 
 only. That is, developing trays should be used for the de- 
 veloper only, and fixing trays, only for the fixing bath, 
 if troublesome chemical reactions are to be avoided. 
 Any one of several good formulae may be used in the 
 
120 DENTAL AND OKAL EADIOGKAPHY 
 
 developing and fixing process. The following has given 
 satisfactory results in the hands of the author, and is 
 easily prepared: 
 
 Developer 
 
 Water (distilled) 20 oz. 
 
 Metol 20 gr. 
 
 Hydroquinone 80 gr. 
 
 Sodium sulphite (dry) 1 oz. 
 
 Sodium carbonate (dry) 1 oz. 
 
 Potassium bromide 10 gr. 
 
 Fixing Bath 
 Solution A: 
 
 Water (distilled) 30 oz. 
 
 Hyposulphite of soda 1 lb. 
 
 Solution B: 
 
 Water (distilled) 15 oz. 
 
 Chrome alum 1 oz. 
 
 Sodium sulphite (dry) 2 oz. 
 
 Solution C: 
 
 Water (distilled) 5 oz. 
 
 Sulphuric acid (C.P.) % oz. 
 
 Add C to B (when cold) and the mixed solutions to A. 
 
 If the best results are to be obtained in developing, 
 the temperature of the solution should be kept between 
 65° and 75° F. If the temperature gets much over 75°, 
 the plate will develop too fast, while if the temperature 
 goes much below 65°, development mil be retarded. 
 
 It is a mistake to try to develop a large number of 
 plates with the same mixture of developer, for after it 
 has developed a half dozen plates, it will become weak 
 and not give the best results. Therefore, do not hesitate 
 to use plenty of fresh developer if you expect to get satis- 
 factory results. 
 
DEVELOPMENT OF PLATES AND FILMS 121 
 
 The same rule applies to the fixing solution. It must 
 be fresh and clean to give good results. 
 
 Under proper tube and current conditions, and with 
 correct length of exposure, a plate should require about 
 five minutes for its development. An overexposed plate 
 will not require so long, while an underexposed plate mil 
 require a longer time. 
 
 To get the most out of a plate, it should be developed 
 until fairly dense, that is, until it is about the same color 
 on each side. If, after it has cleared in the fixing bath, 
 it appears too dark or dense, you know that it has been 
 overexposed. Therefore, in making subsequent expo- 
 sures decrease the length of exposure. If, upon clear- 
 ing, the image on the plate is faint and indistinct, you 
 have reason to think it has been underexposed. There- 
 fore, increase the length of exposure. 
 
 By keeping the tube and current conditions right, the 
 approximate length of exposure for any given case is 
 easily determined by the operator, after a little experi- 
 ence. As stated before, this mil depend upon the t3rpe 
 of x-ray machine used, the thickness and density of the 
 parts to be radiographed, and the age and structural 
 make up of the patient. 
 
CHAPTER IX 
 
 THE INTERPRETATION OF DENTAL AND 
 ORAL RADIOGRAMS 
 
 The ability to correctly interpret dental and oral ra- 
 diograms is an accomplishment which every dentist 
 should possess. In fact, it should be viewed, not only in 
 the light of an accomplishment, but as a requisite of 
 modern dentistry. 
 
 Unfortunately, the assertion is not infrequently made 
 by certain ill-informed members of the dental profession 
 that only minor importance should be attached to the 
 findings of the radiogram, their claim being that such 
 images can be construed as showing conditions which do 
 not actually exist. 
 
 Such an attitude can be explained as being the out- 
 growth of several things, among which a lack of knowl- 
 edge of the fundamental principles of radiography and 
 its various branches, and especially of the science of in- 
 terpretation, stands as an important factor. Therefore, 
 opinions of the x-ray and its application in dentistry ex- 
 pressed by those unqualified, should not be regarded 
 seriously. 
 
 The idea also seems to prevail in the dental profes- 
 sion that the interpretation of radiograms is an ex- 
 tremely simple matter, requiring little if any prepara- 
 tion on the part of the one who is to make the interpre- 
 tation. This erroneous idea is doubtless responsible, 
 not only for many errors being committed, but also for 
 a lack of greater appreciation b}^ the profession of the 
 value of the radiogram. 
 
 122 
 
INTERPJlETATIOISr Oi-' HA1JI0(JIIAMS 123 
 
 The first requisite of interpretation is an accurate 
 hnoivledge of the anatomy and physiology of the struc- 
 tures involved, for a radiogram is a shadoiv picture, and 
 a shadoiv picture is meaningless unless one is thoroughly 
 familiar ivith the main characteristics of the original. 
 
 The radiogram may be said to vary from an ordinary 
 shadow picture, as, in addition to mere outlines, varying 
 densities are shown due to the fact that the x-ray pene- 
 trates all matter in inverse ratio to its mass or density. 
 
 If one is possessed of an accurate knowledge of the 
 anatomy and physiology of the dental and oral struc- 
 tures, the next step toward acquiring the ability to cor- 
 rectly interpret radiograms of these structures, would 
 be to become familiar ivith their radiographic appear- 
 ance under normal conditions, for unless one be familiar 
 with the appearance in the radiogram of the structures 
 under normal conditions, it is obviously impossible to in- 
 telligently recognize pathologic or anomalous conditions 
 unless they were of a glaring nature. 
 
 When we speak of the radiographic appearance of the 
 structures under normal conditions, we refer, not only 
 to a freedom from pathologic or anomalous involvement, 
 but also to the character of the radiogram itself, which 
 must be normal in that it must he made in accordance 
 ivith a technic which results in the shadows of the struc- 
 tures under scrutiny being imposed upon the plate or 
 film in their correct proportions. 
 
 Therefore, it is essential that in addition to the before 
 mentioned requisites, one who would intelligently inter- 
 pret radiograms must understand enough of the funda- 
 mental rules of radiographic technic to know when ex- 
 amining a radiogram, ivhether or not the technic in- 
 volved in its making ivas correct or fcmlty, and if fcmlty, 
 whether or not the degree of faidt is sufficient to render 
 it so inaccurate as to be useless. 
 
124 
 
 DENTAL AND OEAL RADIOGRAPHY 
 
 In correctly made radiograms, the dental and oral 
 structures under normal conditions have a characteristic 
 appearance, for, owing to the var^dng densities of the 
 contained structures in our field, they appear upon the 
 plate or film in a manner most advantageous for obser- 
 vation. For instance, it will be noted upon the examina- 
 tion of such a radiogram, that metallic fillings, if they 
 are present, appear as white masses, and root fillings as 
 somewhat less dense lines. The enamel and dentin are 
 next in density, while root canals show plainly as dark 
 channels in the dentin, and the alveolar process and max- 
 illse show their fine uniform cancellous structures in vari- 
 
 # r ^ 
 
 A. B. 
 
 Fig. 61. — The radiographic appearance of the teeth and their surrounding struc- 
 tures under normal conditions are here shown. A, upper bicuspids and molars; B, 
 lower molars. 
 
 ous degrees of density, depending upon their thickness. 
 (See Fig. 61.) 
 
 In examining a radiogram, it is essential that the 
 original plate or film only be used, and this should be 
 examined carefully and in a proper light, if the maximum 
 amount of information is to be obtained from it. 
 
 This is best accomplished by utilizing some sort of 
 illuminating box or cabinet from which varied degrees 
 of light are obtainable. The face of such a cabinet 
 should be covered with ground glass, so that the light 
 transmitted will be equally distributed and free from 
 shadows. As a radiogram is a transparency, a dim light 
 
INTERPRETATIOiSr OF RADIOGRAMS 125 
 
 behind it will bring out one set of shadows to their 
 greatest clearness. An increase in the light will show 
 forth still other effects ; while a high degree of illumina- 
 tion will bring out the more dense portions. 
 
 In this manner each portion of the radiogram may be 
 studied under a degree of light destined to bring out the 
 maximum amount of detail. 
 
 Now with a ''print" or "lantern slide" one can study 
 the field only from a one light aspect and oftentimes in 
 order to secure any detail in the higher or less dense 
 areas, it will be found that the dense areas must be 
 printed almost to an inky blackness. This fact accounts 
 for the unsatisfactory appearance of many radiograms 
 used as illustrations in our journals, for when reduced 
 to halftone engravings, much of their valuable detail is 
 lost. 
 
 In examining intra-oral radiograms, it is an advan- 
 tage to place them in a film mount which will hold them 
 securely and render it unnecessary to view them while 
 being held between the fingers. Such a "mount" should 
 preferably be made of celluloid Avith one side clear and 
 the other side dull, which allows the light transmitted 
 to be of the same character as that coming through 
 ground glass. 
 
 If one be unfamiliar with the fundamental rules of ra- 
 diographic technic, he can not know, when examining a 
 radiogram, just what portions of it are to be relied upon 
 to give dependable information, for as a rule, owing to 
 anatomic arrangement of the structures in our field, only 
 limited areas can be relied upon to be "in focus" in each 
 radiogram. But if one is possessed of an accurate 
 knowledge of the anatomy and physiology of the parts 
 involved, understands the fundamental rules of radio- 
 graphic technic, and is familiar with the appearance in 
 the radiogram of the dental and oral structures under 
 
126 DENTAL AND ORAL RADIOGRAPHY 
 
 normal conditions, it should hy no means he difficult to 
 see any alterations or changes ivhich occur in these struc- 
 tures as a residt of anomalous or pathologic conditions. 
 
 The mere ability to note an alteration, or change, in 
 the structures does not fulfill the requirements of intelli- 
 gent interpretation, for these alterations, or changes, 
 can have their full significance only to one ivho under- 
 stands the pathologic conditions which may develop in 
 these structures, and the character of the anatomic 
 changes ivhich they bring about. Therefore, it should 
 be apparent that the ability to intelligently interpret ra- 
 diograms is not a thing to be acquired overnight, but 
 must come as the result of study in several important 
 branches, and anyone who attempts it otherwise as- 
 sumes responsibilities unworthily. 
 
 Assuming that you are familiar with the appearance 
 in the radiogram of the dental structure under normal 
 conditions, let us consider some of the changes to be 
 found in the presence of anomalous and pathologic con- 
 ditions. 
 
 As a tooth is much more dense than the boiry struc- 
 tures of the jaw or adjacent parts, any anomaly of form, 
 size, or position, is easily discernible even though it oc- 
 cupy a position far from what might be expected; as, 
 for instance, in the case of impacted molars, teeth in the 
 antrum, etc. (See Fig. 62.) 
 
 Likewise, and for the same reason, the presence in, 
 or absence from, the jaws of successors of the deciduous 
 teeth can easil}^ be determined, as Avell as the state of 
 development of any unerupted tooth (Fig, 63). 
 
 Fractured roots or fractures of the bone even with- 
 out displacement, are often discernible at the line of 
 fracture, owing to the fact that the line of fracture of- 
 fers less resistance to the penetration of the ra^^^s, and, 
 therefore, is apparent upon the plate as a dark line. 
 
INTERPRETATION OF RADIOGRAMS 
 
 12' 
 
 Fig. 62. — A cuspid tooth lying against the anterior wall of the antrum, 
 noted that the cuspid is inverted in its position. 
 
 It will be 
 
 . iMg. 63. — A radiogram to determine the state of dentition of the right side in 
 the mouth of a child eleven years old. The developing second molars are shown, 
 likewise the upper second bicuspid and the lower first bicu.^iiid about to erupt. It 
 will be noted that the lower second deciduous molar has no successor, nor is 
 there an upper first bicuspid present in the jaw. 
 
128 
 
 DENTAL AND ORAL RADIOGRAPHY 
 
 In examining radiograms, we should bear in mind the 
 fact that very dense tissues are characterized by white 
 areas, while less dense tissues appear darker, and the 
 absence of tissue is indicated by blackness. To avoid 
 confusion, we should remember that in ordinary negative 
 photographic prints, this color spectacle is reversed.* 
 
 Fig. 64. 
 
 Fig. 65. 
 
 Fig. 64. — An alveolar abscess involving the roots of an tipper central incisor and 
 lateral incisor. No root canal fillings are present in either tooth. 
 
 Fig. 65. — There is evidence of a small alveolar abscess about the apex of the 
 root of the first bicuspid, while, a larger one is shown to exist about the apex of 
 the second bicuspid. 
 
 Fig. 66. 
 Fig. 66. — Ivarge alveolar abscess about the root of a lower first bicuspid. 
 
 One of the most characteristic alterations or changes 
 in the tissues to be noted in the radiogram, is that to be 
 found where an alveolar abscess is present. We know 
 that when such an abscess takes place there is always 
 an accompanying destruction of the cancellous bone tissue 
 
 *In this text positive prints have been used so as to reproduce as nearly as pos- 
 sible the color spectacle of radiograms. 
 
INTERPIlKTATrON OF RADIOGRAMS 
 
 129 
 
 at the immedito seat of tlie innammatory process. Know- 
 ing that the absence of tissue is indicated in the radio- 
 gram by a dark or black area, such an area if located 
 at the apex of a devitalized tooth, or about a root or frag- 
 ment of a root, would indicate the presence of an alve- 
 olar abscess. In fact, where these dark areas are found 
 in the alveolar process, and are not natural cavities, such 
 as the antrii, or nasal cavities, or such well-defined nerve 
 
 B. 
 
 C. 
 
 Fig. 67. — A shows an upper bicuspid tooth with an alveolar abscess at its root 
 apex. It will be noted that the root canal is improperly filled. B shows the same 
 tooth about two months after it was treated and the root canal properly filled. The 
 rarefied area about the apex has greatly decreased in size. C shows the same tooth 
 about six weeks later. The abscess area has entirely disappeared and the bone 
 structure about the apex appears to be normal. 
 
 openings as the mental foramina, and where they are 
 markedly circumscribed, that is having a distinct and 
 abrupt line of demarcation between the dark area and its 
 surrounding tissue, we can in nearly every case, even if 
 a clinical history be lacking, make the positive diagnosis 
 of alveolar abscess. (See Figs. 64, 65 and 66.) 
 
130 
 
 DENTAL AlStD ORAL RADIOGRAPHY 
 
 Not infrequently, dentists are prone to disregard such 
 evidence, as these areas are often to be fomid about the 
 apices of teeth giving no inflammatory symptoms. How- 
 ever, in the light of our present knowledge of these 
 conditions, we know that this fact no longer carries 
 weight, nor is it worthy of special consideration. The 
 fact remains, as indicated in the radiogram, that a 
 change has taken place in the structures, and such 
 changes occur only as a result of the presence of an in- 
 flammatory process. Furthermore, it has been demon- 
 strated that when such inflammatory processes are really 
 
 rig. 6S. 
 
 Fi.s 
 
 Fi- 68— 'Small abscesses are shown at the apices of two upper bicuspid teelh. 
 If in°making the radiogram the images of the teeth had been lengthened as the re- 
 sult of incorrect technic, these areas would not be discernible. 
 
 Fig. 69. — A necrotic area about the roots of an upper central and lateral. 
 
 eliminated, the cancellous tissues involved will again re- 
 gain their normal character. (See Fig. 67.) 
 
 Alveolar abscesses do not by any means present a 
 "stereotyped" appearance in the radiogram, but vary 
 greatly in size. For this reason, the smaller ones may 
 sometimes be overlooked, or not be regarded seriously 
 by those lacking the requisites of intelligent interpreta- 
 tion. Likewise, these small abscesses may sometimes not 
 be apparent in the radiogram as a result of the employ- 
 
INTEEPRETATIOiN" OF r.ADIOGRAMS 
 
 131 
 
 nient of incorrect teclmic in the exposure of the plate 
 or film. (Fig. 68.) 
 
 Necrosis likewise appears upon the plate as a dark 
 area, but differs in a characteristic way from the or- 
 dinary alveolar abscess in that it is not circumscribed; 
 
 Fig. 70. — A necrotic area lying below a lower cuspid. It will be noted that there 
 is not a distinct and abrupt line of demarcation between the light area and its sur- 
 rounding tissue as is the case with alveolar abscesses, but the area gradually shades 
 off from light into dark. 
 
 namely, that there is not a distinct and abrupt line of 
 demarcation hetiveen the dark area and its surrounding 
 tissue, as is the case with the circumscribed infections, 
 but the area gradually shades off from dark into light, 
 portraying the progessive characteristics of this disease. 
 (See Figs. 69 and 70.) 
 
132 
 
 DENTAL AND ORAL EADIOGRAPHY 
 
 The different filling materials vary but little in rela- 
 tive graduation of density, and when used as root filling 
 materials, are plainly visible as light lines. Because 
 they differ in density from cementum and dentin, the 
 
 rig. 71. Fig. 72. 
 
 Fig. 71. — Root canal fillings in a lower first molar. 
 
 Fig. 72. — Root canal filling material forced beyond the root apex of an upper 
 second bicuspid. 
 
 Fig. 73. 
 
 Fig. 74. 
 
 Fig. 73. — A steel wire introduced into the root canal to determine its length. It 
 has passed through the apex and entered the antrum. 
 
 Fig. 74. — A destructive process involving the pericemental and alveolar tissues 
 about an upper first bicuspid. 
 
 Fig. 73. — Characteristic appearance of the enveloping tissues about the upper bi- 
 cuspids and molars in a well-developed case of pyorrhea alveolaris. Compare the 
 condition shown here with that shown in Fig. 61-A and B. 
 
INTERPRETATION OF RADIOGRAMS 133 
 
 extent to which they have been introduced into the root 
 canals is easily discernible. (See Figs. 71 and 72.) 
 
 Broken-off broaches and other instruments, or small 
 wires introduced into root canals to determine their 
 length or the extent to which they have been opened, be- 
 
 Fig. 76. — An osteosarcoma of the mandible. 
 
 Fig. 77. 
 
 Fig. 78. 
 
 • i^l-^' 77.— -Well-developed cyst over an upper lateral incisor. Root filling mate- 
 rial forced through the ape.x of the lateral incisor is plainly visible. 
 Fig. 78. — Well-developed cyst lying below the lower incisors. 
 
134 DENTAL, AND ORAL KADIOGEAPHY 
 
 cause of their great density, appear very white and are 
 easily differentiated from root canal fillings or tooth 
 structure. (See Fig. 73.) 
 
 Where a destructive process has ensued in the peri- 
 dental membrane, or in the bony wall of the alveolus 
 (pyorrhea pockets) and is present on the mesial or distal 
 side of a tooth, these conditions appear upon the plate 
 as dark areas owing to the fact that the rays pass 
 through them more easily, and effect the emulsion of the 
 plate to a greater degree than if normal bone structure 
 is present. The approximate extent of the destructive 
 process is, therefore, easily determined. (Figs. 74 and 
 75.) 
 
 Cyst and tumors of the maxilla or mandible, owing to 
 the fact that the character of the changes they bring 
 about renders the areas involved less dense, are visible 
 upon the plate as a dark area. (Figs. 76, 77 and 78.) 
 
 In seeking out the various anomalies and pathologic 
 conditions to which the teeth and oral structures are 
 subject, ive should not he misled hy indefinite shadoivs 
 upon the x-ray plates. The very nature of these struc- 
 tures, their gross, as well as minute, anatomy, renders 
 them somewhat difficult to radiograph, and necessitates 
 a refinement of technic greater than that demanded with 
 most of the other portions of the human anatomy. 
 Therefore, only radiograms made in accordance ivith a 
 definite and exacting technic should he relied upon for 
 diagnosis. If a douht exists in any given instance, an ad- 
 ditional or even several more exposures should he made, 
 so that any conclusions reached will he founded upon 
 definite evidence. 
 
CHAPTER X 
 
 INDICATIONS FOR THE USE OF THE X-RAY 
 IN THE PRACTICE OF DENTISTRY 
 
 Prior to the discovery of the x-ray and its adoption in 
 dental practice, the diagnosis of many abnormal condi- 
 tions in the alveolar process and in the maxilla or mandi- 
 ble proper had to be accomplished, or at least attempted 
 by the dentist largely by relying upon his "judgment" 
 and "experience." As these excellent attributes are not 
 infallible, the progessive members of the profession were 
 quick to recognize in the x-ra}^ a veritable godsend, be- 
 cause it rendered more positive and accurate than here- 
 tofore, the diagnosis of many pathologic conditions. It 
 has also aided just as materiall}^ in prognosis and treat- 
 ment. In fact, so indispensable has it become that if 
 the dentist attempts certain operations without its aid, 
 he assumes unworthily his professional responsibilities. 
 
 In enumerating the many instances where this agent 
 should be used, the author will not attempt to give 
 preference or importance to any particular field, or to 
 classify the indications in the order of their frequency 
 of occurrence, for this will depend largely upon the 
 character of practice enlisting the efforts of different 
 men. When the need arises for its use, it should he 
 used whether the need arises in the practice of the or- 
 thodontist, prosthedontist, oral surgeon, or general 
 practitioner, etc., for the obligation is the same if the 
 dentist expects to do his full duty b}^ his patients. 
 
 For Purposes of General Oral Examination 
 
 Not infrequently the dentist is consulted by patients 
 who are undergoing no discomfort or pain from their 
 
 135 
 
136 DENTAL AND ORAL RADIOGRAPHY 
 
 teeth, but realizing their importance as etiologic factors 
 of systemic disease, wish to midergo a thorough exami- 
 nation. In many instances, such an examination will not 
 be complete without a radiographic survey of the mouth. 
 Especially is this true where such patients have pulpless 
 teeth, or where large fillings, bridge work or crowns 
 are present. Notwithstanding the fact that often the 
 clinical history of such cases reveals nothing that will 
 lead the dentist to believe that active septic foci have 
 existed in such mouths, the radiographic examination 
 should, nevertheless, be made, for in the light of our 
 present knowledge, it must be concluded that these con- 
 ditions frequently exist without subjective or objective 
 symptoms. 
 
 Such examinations are particularly important in the 
 case of patients suffering from some systemic conditions, 
 who are referred by a physician to determine whether or 
 not the teeth are an etiologic factor. 
 
 Where such an examination reveals no active septic 
 foci, but shows the presence of one or several pulpless 
 teeth with root canal fillings which do not measure up 
 to the full requirements of such fillings, it is important 
 that such teeth be resubjected to radiographic examina- 
 tion at regular intervals to see whether or not they re- 
 main in a healthy state. 
 
 Radiographic Requirements. — In order to do justice 
 to such cases, extra-oral radiograms should be made of 
 each side. These should show the upper and lower teeth 
 and adjacent structures posterior to the cuspids. Intra- 
 oral radiograms of the upper and lower incisors and 
 cuspids should also be secured, and the whole series de- 
 veloped and examined. (See Fig. 79.) 
 
 Where the extra-oral radiograms show suspicious 
 areas about the teeth which do not show with sufficient 
 clearness to meet the demands of diagnosis, intra-oral 
 
INDICATIONS FOR X-RAY IN DENTISTRY 137 
 
 radiograms may then ho made of these areas, as a means 
 of confirmation. (See Fig. 80.) Some operators prefer 
 to use the intra-oral method entirely, in making a general 
 examination, hut this, in the author's opinion, is a mis- 
 take, for the reason that all areas of pathologic impor- 
 tance are not accessible to these small films. 
 
 Fig. 79. — Extra-oral radiogram of the right side made for piirposes of general ex- 
 amination. Suspicious areas are to be seen above the upper first bicuspid and about 
 roots of the lower second molar. An unerupted upper third molar is also visible. 
 
 To Determine the Seat of Pericemental Infections 
 
 Not infrequently it is a difficult matter to determine 
 the tooth responsible for a pericemental infection or an 
 alveolar abscess, as the inflammatory process may be in 
 progress in the region of several teeth, each of Avhich 
 may be under suspicion, or the infected area may be at 
 a point remote from the suspected tooth. A radio- 
 grapliic examination will quickly settle all doubts, for the 
 radiogram will reveal the source and determine whether 
 
138 
 
 DENTAL AND ORAL RADIOGRAPHY 
 
 or not one or more teeth are involved. •> It will likewise 
 show the extent to which the periapical tissnes have be- 
 come involved and will often shed valuable information 
 on the prognosis of the case. (See Figs. 81, 82 and 83.) 
 
 Fig. 80. 
 
 Fig. 81. 
 
 Fig. SO. — Intra-oral radiogram used as a means of confirmation of the findings of 
 the extra-oral radiogram. 
 
 Fig. 81. — Alveolar abscesses are shown to be present at "the apex of each bicuspid 
 root. 
 
 Fig. 82. 
 
 Fig. 83. 
 
 Fig. 82. — Upper bicuspid teeth with abscesses. 
 
 Fig. 83. — Severe inflammatory process in progress about an upper lateral incisor. 
 The root end shows a mariced hypercementcsis. 
 
 Radiographic Requirements. — Intra-oral radiograms 
 will usually suffice. Where the lower molars and bicus- 
 pids are under examination, and the tissues under the 
 tongue are very tender, the extra-oral method can be used 
 to advantage, if the patient's comfort is a consideration. 
 (See Fig. 84.) 
 
INDICATIONS rOR X-RAY IN DENTISTRY 139 
 
 Root Canal Treatment 
 
 Of the various dental operations, there is none that is 
 more nniversally in need of further elucidation than the 
 treatment and filling of root canals. As generally prac- 
 ticed at the present time, this work can easily be termed 
 the "greatest shortcoming of dentistry." To those who 
 recognize the uncertainty of results in this field, and the 
 serious results which accompaii}^ failure to render sterile 
 
 Fig. 84. — E.xtra-oral radiogram of the lower molars showing the presence of a large 
 
 alveolar abscess. 
 
 and to com^Dletely fill root canals, the x-raA^ offers indis- 
 pensable aid. 
 
 Before considering the treatment of a tooth (or teeth), 
 a radiogram should be made to show the topography of 
 the roots to be treated. If these are proved to be ana- 
 tomically within the range of treatment, an attempt may 
 then be made to remove all organic material from the 
 canals and to open them up to the very apical foramen. 
 Fine diagnostic wires should then be inserted and car- 
 ried to the end of the canal, or as far as the operator has 
 
140 
 
 DE^TTAL AZCD OEAL EADIOGBAPHY 
 
 been able to iDtroduce the broaches. After- sealing them 
 in with gutta percha, a second radiogram shonld be 
 made. Becanse of their greater density, the Tores will 
 show distinctly in the radiogram and will enable the 
 operator to determine to what extent the canal or canals 
 have been opened. It will likewise determine whether 
 any opening leading from the pnlp chamber is a canal or 
 a perforation. 
 
 Vig. 85. — A^ two c;;tr 
 teeth with the ramal'i cl££^ 
 after tlie root ranala hare 
 
 :tly Slled canals; B, the same 
 s in place; C, the same teeth 
 
 liVhen the canals are open to the end (as shown by 
 the inserted wires) and the necessary treatment and 
 sterilization has been completed, the root canal fillings 
 can then be inserted. Another radiogram should tlien 
 be made to determine whether or not the root fillings ex- 
 tend to the apical foramina and seal the canals. If they 
 do not. thev shonld be removed and the before-men- 
 
INDICATIONS FOR X-RAY IN DENTISTRY 
 
 141 
 
 c. 
 
 Fig. 86. — A, lower second bicuspid needing root canal treatment and filling; B, 
 same tooth with canal cleaned out and diagnostic wire in place; C, same tooth with 
 
 the root canal filled. 
 
 B. 
 
 C. 
 
 Fig. 87. — A, an upper first bicuspid needing root canal treatment and filling; B, canals 
 
 have been cleaned out and diagnostic wires put in place; C, canals filled. 
 
142 
 
 DEISTTAL AiSTD OEAL RADIOGRAPHY 
 
 tionecl operative and .roentgenographic process repeated 
 until success is obtained. 
 
 Even when all precautions are taken and results seem 
 eminently satisfactory, several radiograms should be 
 made at regular intervals of from three to six months 
 following the filling of .the roots, to determine whether 
 or not the operation has been successful, so far as the 
 periapical tissues are concerned. This is especially im- 
 
 C. D. 
 
 -A, showing condition present; B, diagnostic wires inserted; C, root canals 
 filled; D, resection of roots. 
 
 portant where roots have been the seat of periapical in- 
 fections prior to the time when treatment was inaugu- 
 rated. (See Figs. 85, 86 and 87.) 
 
 Radiographic Requirements. — Intra-oral radiograms 
 exclusively should be used for this work. An excep- 
 tion might be made in the case of the lower molars and 
 bicuspids, if the tissues under the tongue are sufficiently 
 
INDICATIONS FOR X-RAY IX DENTISTRY 14d 
 
 tender to make the placing of the fihiis for exposure a 
 hardship to the patient. Excellent extra-oral radio- 
 grams of tliis area may be obtained, providing the opera- 
 tor has the ability and constancy to master the neces- 
 sary technic. 
 
 Root Resection 
 
 Where root resection is contemplated, the intelligent 
 dentist should first obtain accurate radiograms of the 
 
 t' t 
 
 A. 
 
 C. 
 
 I'ig. 89.— -^4, upper central incisor before resection; B, radiogram made immedi- 
 a.ely following resection; C, radiogram made after several months, showing regen- 
 eration of osseous tissue. 
 
 roots under consideration. These aid him greatly, pri- 
 marily in determining whether or not a resection is in- 
 dicated, and if it is, it will give him a fairly concrete idea 
 of the field of operation as well as the extent of the root 
 to be resected; secondarily, in determining whether or 
 
144 
 
 DENTAL AjS^D OEAL RADIOGEAPHY 
 
 not the root canal has been sufficiently well filled so that 
 the filling extends past the point where resection is to 
 take place. 
 
 Following root resection, a radiogram should he made 
 as a matter of record and be used for purposes of com- 
 parison as the process of healing progresses. Subse- 
 quently, additional radiograms should be made every 
 three months to determine whether or not the process 
 of bone-regeneration is progressing in a satisfactory 
 manner. (See Figs. 88, 89 and 90.) 
 
 A. B. 
 
 Fig. 90. — A, an upper central root before resection; B, the same root six weeks after 
 resection, showing partial regeneration. 
 
 Radiographic Requirements. — Intra-oral radiograms 
 should be used exclusively. In fact, the necessity for 
 anything else could hardly arise, as root resection is 
 usually confined to the anterior teeth. 
 
 For Purposes of Examination and Diagnosis in 
 Pyorrhea Alveolaris and Allied Diseases 
 
 A radiographic examination of the teeth and their in- 
 vesting structures is of great advantage in diagnosis and 
 treatment. In the first place, accurately made radio- 
 grams will often show the extent to which the destruc- 
 
INDICATIONS FOR X-RAY IN DENTISTRY 
 
 145 
 
 tive process lias progressed, especially if areas of ab- 
 sorption and ''pockets" exist npon the mesial or distal 
 aspects of teeth. Even where such areas are visible 
 to the eye, the radiogram serves an important function 
 in acquainting the patient with the true state of affairs, 
 thereby securing the patient's cooperation in the treat- 
 ment. (See Fig. 91.) 
 
 Fig. 91. — A well-developed case of pyorrhea alveolaris involving the molars and in- 
 cisors. (After Arthur H. Merritt.) 
 
 When the destructive process is sho^\T.i to be exten- 
 sive about certain teeth, the operator can more safely 
 judge whether or not the treatment of such teeth should 
 be attempted or whether they should be extracted. 
 
 Where suppuration is occurring at the gingival margin, 
 the radiogram is often indispensable in helping to deter- 
 mine (by showing the contents of the root canals) 
 whether the adjacent teeth are vital, and if nonvital 
 
146 DENTAL AK^D ORAL RADIOGRAPHY 
 
 whether or not the suppuration is clue to a chronic alveo- 
 lar abscess. 
 
 In cases of gingival irritation about crowned teeth or 
 teeth carrying large fillings or inlays, a radiogram will 
 reveal jagged or overhanging edges, the removal of which 
 is so essential if the tissues are to be restored to health. 
 
 Finally, the radiogram or a series of radiograms will 
 be of value after active treatment has been completed, 
 to determine whether or not the destructive process has 
 been successfully checked. 
 
 Radiographic Requirements. — Intra-oral radiograms 
 will suffice for such cases, as pockets seldom extend be- 
 low the apical area of the roots. Such radiograms should 
 be made in series, so that no area about the teeth is left 
 unsurveyed. 
 
 In Crown and Bridgework 
 
 Where teeth are to be crowned individually, or as 
 bridge abutments, the radiogram will give valuable in- 
 formation, not only as to the length and shape of the 
 roots, and the condition of the investing structures, but 
 also as to that of the periapical tissues. Where the neces- 
 sity for the devitalization of such teeth occurs, the op- 
 erator can also judge by the shape and condition of the 
 roots whether or not the prognosis for successful root 
 treatment and filling is favorable. 
 
 Where ^'posts'' are to be placed in the roots, their 
 extent and direction can be noted, and Avhere the ana- 
 tomic peculiarities of such roots make them liable to 
 perforation, precautions for avoiding such calamities 
 may be taken. 
 
 Where spaces are to be bridged, and the exact status 
 of the area which is to lie beneath the bridge is not 
 known, a radiogram should be made to be sure that un- 
 erupted teeth or root fragments are not present. (See 
 Figs. 92, 93 and 94.) 
 
INDICATIOlSrS FOR X-RAY IN DENTISTRY 
 
 147 
 
 Radiographic Requirements. — Intra-oral radiograms 
 are indicated for this character of work. 
 
 Reflexes of Obscure Origin 
 
 Where painful reflexes occur about the face or head, 
 and a clinical examination does not immediately deter- 
 mine their possible origin, a radiographic examination 
 of the teeth and their adjacent structures is indicated. 
 Where such reflexes are the result of unerupted, im- 
 
 Fig. 92. Fig. 93. 
 
 Fig. 92. — An unerupted cuspid tooth making an attempt to erupt under a bridge. 
 The patient was twenty-eight years of age. 
 
 Fig. 93. — Radiogram made to be sure no root fragments were present in the tis- 
 sues under the bridge. 
 
 Fig. 94. — Inflammatory process under a small bridge. An extensive pocket is shown 
 upon the mesial aspect of the root of the bridge abutment. 
 
 l^acted, or anomalous teeth, the presence of an^^ of these 
 is quickly demonstrated. Likewise, if the reflexes are 
 caused by an alveolar abscess, its presence can be 
 thereby determined. 
 
 Where pulp stones are producing the trouble, they can 
 often be detected, if intense care is exercised in making 
 
148 DENTAL AND ORAL RADIOGRAPHY 
 
 the radiograms. If these reflexes are the result of "hid- 
 den caries," the radiogram will frequently suggest the 
 presence of such a condition, providing the cavities occur 
 upon the mesio-or disto-approximal surfaces of the teeth, 
 and are sufficiently extensive so that the density of the 
 tooth structure in the region of the cavity is decreased, 
 or the contour of the tooth is altered. 
 
 Radiographic Requirements. — Approximately the 
 same plan of examination should be used as where a 
 general radiographic examination of the mouth is made ; 
 viz., extra-oral radiograms of each side with intra-oral 
 radiograms of the anterior teeth. These can be further 
 augmented with confirmatory intra-oral radiograms, if 
 necessary. (See Figs. 79 and 80.) 
 
 In Oral Surgery 
 
 Perhaps the most frequent indication for the use of 
 the x-ray in oral surgery occurs in cases in which the 
 extraction of certain teeth is necessary. For instance, 
 if one or more third molars are to be removed, a radio- 
 gram of these teeth and their surrounding structures 
 will acquaint the operator with any abnormalities of po- 
 sition or formation, and will make it possible to proceed 
 with the operation without unknown handicaps. 
 
 Following the removal of teeth, a radiogram of the 
 field of operation is often of value as a matter of record, 
 to make sure that no root fragments or bone fragments 
 are left remaining. 
 
 Where necrotic areas are to be curetted, a radiogram 
 not only aids greatly in confirming the diagnosis, but 
 gives the operator a more comprehensive idea of the 
 extent to which the curettement must be carried out. As 
 a postoperative precaution, the radiogram is also fre- 
 quently of value, especially where the process of healing 
 does not progress in a manner satisfactory to the pa- 
 
INDICATIONS ron X-EAY IN DENTISTRY 149 
 
 Fig. 95-A. 
 
 Fig. 95-B. 
 Fig. 95. — Extra-oral radiograms of impacted and unerupted tliird molars. 
 
150 
 
 DENTAL AND OKAL RADIOGRAPHY 
 
 tient or operator. Such postoperative radiograms are 
 particularly advantageous where patients move from one 
 locality to another, and, therefore, must change surgeons. 
 
 In handling fractures of the mandible, the x-ray is 
 seldom necessary for purposes of diagnosis, but it can 
 often be used to advantage, and in some instances, is quite 
 indispensable. As a postoperative precaution it should 
 be used so that no doubt may arise as to the proper 
 placement of the fractured parts. 
 
 Where fractures of the maxilla occur, a radiogram may 
 be of value as a means of confirming the clinical diag- 
 nosis. 
 
 A. B. 
 
 Fig. 96. — Intra-oral radiograms of impacted lower third molars. Such radiograms 
 are not as satisfactory as those made by the method shown in Fig. 95. 
 
 Where C3^sts or tumors are suspected, the radiogram 
 will confirm the clinical findings, and comprehensively 
 outline the field of operation. Following operations for 
 the relief of those conditions, radiograms should be made 
 at frequent intervals to determine whether or not the 
 process of healing is progressing satisfactorily. 
 
 In gunshot wounds about the face or mouth, properly 
 made radiograms will localize the bullets or shot, and 
 thereby aid in their removal, as well as in determining 
 the extent of injury to the osseous structures. 
 
 AVhere drills, hypodermic needles or other instruments 
 are broken off and left remaining in the tissues, they may 
 
INDICATIONS FOR X-llAY IN DENTISTRY 
 
 101 
 
 Fig. 97-A. Ivarge cyst in the mandible lying below a molar tooth. 
 
 Fig. 97-B.— Same case six months after curettement, showing partial regeneration 
 of the osseous structure. 
 
152 
 
 DENTAL AND ORAL RADIOGRAPHY 
 
 be easily located by correctly made radiograms, and their 
 removal rendered more certain. 
 
 Radiographic Requirements. — Both the extra-oral and 
 intra-oral radiograms are indicated in this field. For 
 impacted third molars, the extra-oral method is best, as 
 it will clearly show not only the third molar, but its re- 
 lationship to all other adjacent structures. In the case 
 of single-rooted teeth, snch as incisors, cuspids, etc., 
 where hypercementosis is suspected, the intra-oral 
 method will prove adequate. (See Figs. 95, 96 and 97.) 
 
 Fig. 98. — Large abscess with cyst formation involving the upper central, lateral and 
 
 cuspid roots. 
 
 Where a curettement is to be carried out, intra-oral 
 radiograms will prove sufficient, provided the field is not 
 large (Fig. 98.) 
 
 In fractures of the mandible, the extra-oral method 
 should always be used, so that the entire field in the re- 
 gion of the fracture can be visualized. 
 
 For fractures of the maxilla, intra-oral radiograms 
 will usually suffice. 
 
 In the Practice of Orthodontia 
 
 The necessity for using the x-ray in orthodontic prac- 
 tice varies with different patients, bat, generally speak- 
 
INDICATIO]\TS FOIl X-P.AY IX DENTISTRY 
 
 153 
 
 Fig. 99. — This radiogram reveals the fact tliat there is a congenital aljsence of per- 
 manent molars on the left side. 
 
 Fig. 100. — This radiogram reveals the fact that all but one of the permanent molars 
 are congenitally absent on the right side. 
 
154 DENTAL AND ORAL RADIOGRAPHY 
 
 ing, may be summarized under ten different headings as 
 follows : 
 
 1. As a means of determining the presence or ab- 
 sence of ufierupted permanent teeth before treatment is 
 undertaken. 
 
 The majority of patients requiring orthodontic treat- 
 ment usually have a mixed dentition ; viz., the deciduous 
 molars and cuspids are usually present. It is essential, 
 therefore, to determine whether or not these deciduous 
 teeth have their permanent successors. If the upper and 
 lower incisors have erupted, information concerning the 
 other permanent teeth is easily obtained by making a 
 radiogram of each side by the extra-oral method. Such 
 radiograms are shown in Figs. 99 and 100. 
 
 Such radiograms give the operator a very adequate 
 survey of these unerupted teeth, and leave no doubt as to 
 their presence or absence. 
 
 2. As a means of determining the approximate size 
 of unerupted teeth, for luhich space must be made in the 
 arches. 
 
 Where the deciduous molars or cuspids have been shed 
 prematurely, with the usual resultant loss of space in the 
 arch, the radiogram can be made to show quite accurately 
 the amount of space which it will be necessary to pre- 
 pare for the unerupted teeth. (See Figs. 101, 102, and 
 103.) 
 
 3. To determine the state of development of unerupted 
 teeth ivhich are tardy in their eruption. 
 
 Not infrequently permanent teeth fail to erupt when 
 expected. By utilizing the radiogram, their state of de- 
 velopment is easily determined, and often the cause for 
 their noneruption is determined. Steps can then be taken 
 to open up spaces and to hold them until such a time as 
 the teeth involved progress in their development to the 
 point of eruption. (See Fig. 104.) 
 
INDICATIONS FOR X-IIAY IN DENTISTIIY 
 
 155 
 
 Fig. 101. — Unerupted lower second bicuspid for which space must be made to permit 
 
 its eruption. 
 
 ig. 102. — Unerupted cuspid for which space must be made if it is to erupt in its 
 
 normal position. 
 
156 
 
 DENTAL AND OEAL EADIOGEAPHY 
 
 Fig. 103. — Unerupted lower lateral incisor for which space must be made. 
 
 Tig. 104. — Unerupted lower second molar prevented from erupting through impaction 
 against the lower first molar. 
 
INDICATrOXS FOR X-RAY IN DENTISTRY 
 
 157 
 
 4. To determine the approximate direction in ivhich 
 teeth are erupting and the relationship ivhich they ivill 
 hear to the line of occlusion ivhen erupted. 
 
 Where the deciduous teeth have been retained in the 
 mouth longer than the normal time and Avhere the roots 
 of these teeth have not been entirely absorbed, the erupt- 
 ing permanent teeth will sometimes be deflected from 
 
 Fig. 105. — Unerupted upper bicuspid teeth which are being deflected to the lingual. 
 
 A. B. 
 
 Fig. 106. — Unerupted bicuspid teeth which are rotated and erupting to the lingual. 
 
 their normal course. It is an advantage to know the di- 
 rection in which they are deflected, so that if retaining 
 appliances are to be placed, they may be arranged in 
 such a way and in such a relationship to the erupting 
 teeth that they will not interfere with them. In fact, 
 it is sometimes possible to construct the retainer in such 
 a way that the tooth which is deflected from its course 
 may be guided towards its normal position or moved 
 
158 
 
 DENTAL AND ORAL RADIOGRAPHY 
 
 A. 
 
 B. 
 
 C. 
 
 Fig. 107. — A, unerupted cuspid; B, same tooth after the removal of the lateral 
 incisor and the deciduous cuspid showing the attachment for moving the unerupted 
 tooth; C, cuspid tooth moved down to the point of eruption. 
 
 A. 
 
 B. 
 
 Fig. 108. — A, two supernumerary incisors are present with the normal central 
 
 lying above them; B, the same case after the extraction of the supernumerary teeth. 
 
 An attachment has been made to the central preparatory to moving it down into 
 place. The patient was fourteen years of age. 
 
INDICATIONS FOR X-RAY IN DENTISTRY 159 
 
 there before the inclined planes of the opposing teeth he- 
 come a factor in estahlishing it entirely out of its normal 
 position. (See Figs. 105 and 106.) 
 
 5. As a guide ivhere it is necessary to make attach- 
 ments to unerupted teeth, to aid in their eruption. 
 
 While it is not often necessary to secure attachments 
 to teeth lying beneath the gingival tissues, the occasion 
 for this sometimes arises, as shoAvn in Figs. 107 and 108. 
 In such cases, radiograms should be made as a guide in 
 securing the attachment. After the attachment is se- 
 cured, others should be made to determine the direction 
 in which force should be applied to accomplish the desired 
 tooth movement. 
 
 6. To determine the most opportune time for the ex- 
 traction of the deciduous teeth. 
 
 Where the deciduous tooth persists in the mouth, and 
 shows no sign of being shed, it is an advantage to deter- 
 mine the extent of absorption of the roots, as well as the 
 development of its successor, so that if extraction is re- 
 sorted to, it can be done with the knowledge that the de- 
 veloping tooth will not be disturbed or injured, and that 
 the successor has reached a degree of development Avhich 
 will insure its eruption within a reasonable time. (See 
 Figs. 109 and 110.) 
 
 7. To observe the movement of the roots of teeth and 
 their relationship to other roots and structures. 
 
 In the bodily movement of teeth, and particularly of 
 th€ incisors, it is important in young subjects that these 
 roots do not encroach upon each other or upon other 
 teeth; for instance, an unerupted cuspid. It is there- 
 fore, advisable, where any doubt exists, to determine the 
 exact status of this relationship. (See Fig. Ill, A, B, C.) 
 
 8. To determine the relationship of developing third 
 molars to certain recurrent malocclusions, and also as a 
 precaution so that steps mag he taken to prevent these 
 
160 
 
 DENTAL AND ORAL RADIOGRAPHY 
 
 Fig. 109. — An unerupted lower second bicuspid in a patient twelve years old. 
 
 Fig. 110. — -Unerupted upper and lower bicuspids in a patient eleven years of age. 
 
INDICATIONS FOR X-RAY IN DENTISTRY 
 
 IGl 
 
 teeth from becoming a cause of malocclusion dnrmr/ their 
 eruption. 
 
 The pressure exerted by developing lower third molars 
 is often sufificiently great to cause a crowding of the lower 
 incisors and cuspids. (See Figs. 112 and 113.) This 
 can be true, even though malocclusion has not existed 
 in this region previous to the development of the third 
 
 %jj^ 
 
 B. 
 
 C. 
 
 Fig. 111. — Unerupted cuspid teeth whose relationship to the roots of the incisors 
 must be taken into consideration during tooth movement. 
 
 molars. By making radiograms from time to time of 
 patients at the age of the eruption of these teeth, the 
 status of the developing teeth can be determined and the 
 necessary precautions taken to prevent the crowding of 
 the incisors and cuspids. 
 
 9. To observe nonvital teeth prior to tooth movement, 
 
162 
 
 DEISTTAL AND ORAL EADIOGRAPHY 
 
 Fig. 112. — An unerupted lower third molar which is crowding the incisors. 
 
 Fig. 113. — An erupting lower third molar which has been responsible for the crowding 
 of the lower incisors and cuspids. 
 
INDICATIONS FOR X-RAY IN DENTISTRY 163 
 
 to determine their fitness for movement or anchorage, 
 and their state of health during the process of ortho- 
 dontic treatment. 
 
 Where it is necessary to either move nonvital teeth, or 
 utilize them as anchorage, it is essential to the patient's 
 welfare and comfort to know that such teeth and their 
 investing tissues are in a healthy condition. By determin- 
 ing this prior to instituting orthodontic treatment, much 
 trouble, both to the patient and operator, can often be 
 avoided. (See Fig. 114.) 
 
 10. In cases ivhere anomalous teeth are present, to dif- 
 ferentiate hetiveen anomalous and normal teeth. 
 
 In a majority of instances, this can be done without the 
 aid of the radiogram, unless the teeth in question have 
 failed to erupt. Under such conditions, by utilizing ac- 
 curacy in the technic of making the radiograms, little dif- 
 ficulty is encountered in determining the difference be- 
 tween normal and anomalous teeth. Examples are shoAvn 
 in Figs. 115, 116, and 117. 
 
 Radiographic Requirements. — Owing to the fact that 
 patients undergoing orthodontic treatment are usually 
 children whose ages necessitate their being handled with 
 tact and gentleness, if confidence is to be maintained, 
 precaution should be taken to rid every operation of 
 fear or discomfort. Especially is this essential in mak- 
 ing radiograms, for any considerable degree of move- 
 ment on the part of a patient will either curtail the value 
 of the finished radiogram, or render it useless. 
 
 In selecting a method of procedure for making radio- 
 grams of children, the child's comfort must be taken 
 into consideration, and with this idea in mind, the 
 author has found it an advantage to use the extra-oral 
 method quite universally. In fact, he has used it in 
 nearly all cases except where the region embracing the 
 upper anterior teeth is under scrutiny. The wisdom of 
 
164 
 
 DEN^TAL Al^D ORAL RADIOGRAPHY 
 
 Fig. 114. — A, nonvital tooth being used as an anchor tooth; B, nonvital tooth which 
 was not considered safe for anchorage. 
 
 rwy 
 
 Fig. 115. 
 
 Fig. 116. 
 
 Fig. 115. — Supernumerary upper second bicuspid. Upon the extraction of the 
 supernumerary, the normal tooth erupted. 
 
 Fig. 116.- — Lower deciduous central incisors having the appearance of supernu- 
 merary teeth. The radiogram leaves no doubt as to their identity, and also shows 
 that these teeth have no permanent successors. 
 
 I '^' 
 
 Fig. 117. 
 
 Fig. 117. — Radiogram showing: either an anomalous central incisor or a central 
 incisor lying in a horizontal position to the other teeth. The patient was sixteen 
 years of age. 
 
loSTDICATIONS FOR X-RAY IN DENTISTRY 
 
 165 
 
 Fig. lis. — The patient is seated and the apparatus arranged to make a radiogram 
 of the left side. Fig. 99 shows the extent of radiograms made by using this technic. 
 
 Fig. 119. — The patient is seated and the apparatus is arranged to make a radiogram 
 of the right side. Fig. 100 shows the extent of radiograms made by using this technic. 
 
166 DEXTAL AXD OEAL RADIOGRAPHY 
 
 this course will be apparent to anyone who has experi- 
 enced the discomfort of having intra-oral films placed 
 lingnally to the lower teeth, where the tissues are very 
 sensitive, or has had them placed posteriorly in the 
 molar region, against the palate, where they so fre- 
 quently induce gagging. These unpleasant features are 
 all eliminated by using the extra-oral method, and good 
 radiograms of the structures can be secured on the 
 larger plates. (See Figs. 118 and 119.) This statement 
 should not be construed as a protest against the use of 
 intra-oral films in dental radiography, for it is very 
 often necessary to use such films with adult patients 
 where a high degree of detail is essential, in determin- 
 ing the condition about nonvital teeth, root canal fillings, 
 etc. In orthodontic practice, however, where we are 
 dealing with young subjects entirely, a sufficient degree 
 of detail can be obtained in the majority of instances to 
 satisfy the needs of the operator, by using the extra-oral 
 method. 
 
CHAPTER XI 
 
 DANGERS OF THE X-RAY AND METHODS OF 
 PROTECTION 
 
 Almost invariably when any phase of x-ray work is 
 discussed, some one raises the query as to the dangers 
 connected with it and the injuries resulting from its use. 
 In fact, the impression is quite broadcast among the 
 laity, and to a degree among the profession, that the 
 x-ray is a dangerous agent and as such should only be 
 employed in cases of dire emergency. 
 
 This impression, erroneous as we know it to be for 
 the most part, gained credence as a result of the first 
 few years' use of the x-ra}^, during Avhich period its 
 dangers were not suspected nor the laAvs governing its 
 use well understood. During this period a sufficient 
 number of patients and operators were injured so that„ 
 notwithstanding the fact that mth our present knowU 
 edge of the subject and with the marked improvement 
 in x-ray apparatus these accidents are no longer neces- 
 sary, the early impression still prevails to a certain 
 extent. 
 
 In order that we may not underestimate the dangers 
 of this valuable agent and consider lightly our responsi- 
 bility in using it, we will now consider the character of 
 injuries possible through its misuse. 
 
 We should bear in mind the fact that the x-ray in 
 medicine serves a double purpose. It is used as a diag- 
 nostic agent; that is, in making radiograms and fluoro- 
 scopic examinations, and as a therapeutic agent. In the 
 latter capacity patients are subjected to repeated ex- 
 posures, the length of which are very far in excess of 
 
 167 
 
168 de:n^tal aistd oral eadiogeaphy 
 
 that required in making radiograms. In fact the length 
 of exposure in one average x-ray therai3y treatment will 
 more than out-total the necessary exposures to radio- 
 graph a half dozen patients for diagnostic purposes. 
 Therefore, the responsibilit}^ of the x-ray therapist, and 
 the danger connected with his work are far in excess of 
 the man who limits his activities with x-ray to radiog- 
 raphy alone. 
 
 Of the various ill effects attributed to the x-ray, the 
 so-called ''x-ray burn" or dermatitis is the most com- 
 mon. This injur}'' occurs in various degrees of severity, 
 depending upon the amount of overexposure to which 
 the one afflicted has been subjected, and is designated as 
 "acute" and "chronic." 
 
 Acute X-ray Dermatitis 
 
 Acute x-ray dermatitis in its simplest form manifests 
 itself in somewhat the same way as ordinary sunburn. 
 There is a slight pinkish erythema, dry in character, 
 accompanied oftentimes by the sensation of tingling or 
 burning. If x-ray exposures are continued, this condi- 
 tion is augmented b}'' the appearance of vesicles and the 
 affected surface becomes moist or "weeping," and the 
 patient has similar sensations as those produced by any 
 blistering burn. If exposures to the ray be discontinued 
 at this stage, the affected area will slowly clear up with 
 no permanent ill effect except perhaps a slight pig- 
 mentation. 
 
 If the exposures be continued, the next degree of der- 
 matitis will ensue. The affected area becomes an angry 
 red in appearance, congestion is intense, and the surface 
 is covered with a yellowish white necrotic membrane, 
 which is epithelial in character. In fact, up to this point 
 the connective tissue is not affected except for more or 
 less swelling. This degree of dermatitis is exceedingly 
 
X-EAY DANGERS METPIODS OF PROTECTIOX 100 
 
 slow in healing, months being required for the necrotic 
 membrane to disappear, and when this has occurred it is 
 followed by a horny epidermis which appears in spots 
 over the area affected, eventually covering it. This new 
 skin while smooth and natural looking is usually char- 
 acterized by the absence of all hairs and follicles. 
 
 The most severe form of acute x-ra}^ dermatitis is char- 
 acterized by somewhat the same symptoms as those just 
 described, except that they are greatly exaggerated. 
 The degree of congestion is very great, the necrotic 
 membrane extends deeper into the tissue, necessitating 
 the surgical removal of masses of dead tissue to prevent 
 gangrene. This sloughing or necrotic area shows a 
 strong tendency to spread and according to some 
 authors, is apt to become malignant. With such a der- 
 matitis patients often suffer very intense pain. Inju- 
 ries of this degree of intensity are exceedingl}^ slow in 
 healing, a number of years sometimes being necessary 
 for the process of reconstruction. Even after it occurs, 
 the skin is not natural in appearance, but hard and 
 horny and covered in places with scar tissue. 
 
 Chronic X-ray Dermatitis 
 
 After a person has been exposed to the x-ray a great 
 many times covering a period of perhaps months or 
 years, and has had one or more "burns" which Avere 
 not allowed to heal before new effects Avere added by 
 additional exposures, the dermatitis which results be- 
 comes "chronic." This chronic x-ray dermatitis is con- 
 fined almost entirely to x-ray operators and others con- 
 stantly associated with the x-ray. The hands because of 
 their exposed position are most often the seat of this 
 affection. The skin becomes thin and atrophic with red 
 patches of a vascular nature, and there is usually an 
 entire absence of all follicles and hair. Codman describes 
 
170 dejsttal and oeal radiography 
 
 this condition as follows: ''In tlie less pronounced 
 forms the skin appears chapped and roughened, and the 
 normal markings are destroyed ; at the knuckles the folds 
 of skin are swollen and stiff, while between there is a 
 peculiar dotting resembling small capillary hemorrhages. 
 The nutrition of the nails is affected so that the longi- 
 tudinal striations become marked and the substance be- 
 comes brittle. If the process is more severe, there is a 
 formation of blebs, exfoliation of epidermis, and loss of 
 nails. In the worst form the skin is entirely destroyed 
 in places, the nails do not reappear and the tendons 
 and joints are damaged," 
 
 Another author states that "while the condition in 
 chronic forms of x-ray irritation is as a whole atrophic, 
 there is usually a peculiar tendency to hyperkeratosis, 
 which shows itself in increased horniness of the epi- 
 dermis about the knuckles and in the formation of kera- 
 totic patches. In some cases this is very marked, so that 
 the affected parts, usually the backs of the hands, have 
 scattered over them many keratoses with or without in- 
 flamed bases. The appearance is very similar to that 
 seen in senile keratosis where the patches are inflamed 
 and have a tendency to epitheliomatous degeneration. 
 The development of epitheliomas in these patches of x- 
 ray keratosis has within the last feAv 3^ears been well 
 established." Carcinoma may also have its origin from 
 the same source, in fact many x-ray operators who have 
 failed to take the proper precautions have been subject 
 to this dreaded malady, the hands being the parts most 
 often affected. 
 
 Other 111 Effects 
 
 In addition to the before described injuries, there are 
 still other ill effects attributed to the x-ray, such as loss 
 of hair, sterility, and certain systemic effects. The loss 
 of hair due to x-ray exposure is not to be regarded seri- 
 
X-RAY DANGERS — METHODS OF PROTECTIOX 171 
 
 onsly, unless it is associated with a dermatitis of suffi- 
 cient severity to destroy the hair follicles, for unless this 
 complication is present, the hair comes back within five 
 or six weeks. 
 
 The x-ray has a deleterious effect upon developing em- 
 bryonic cells and can therefore be the cause of sterility 
 in the male by destroying the spermatozoa, and in the 
 female by the destruction of the primordial o\ailes. This 
 condition is brought about by continued exposures, and 
 x-ray operators are the ones usually affected. It is not 
 accompanied by impotence, is temporary in duration, 
 and can be avoided entirely by adopting protective 
 measures. 
 
 Eegarding the so-called injurious systemic effects pro- 
 duced by the x-ray, too little evidence of a convincing 
 character has ^-et been presented to really fasten the 
 blame upon the x-ray for conditions other than those 
 before enumerated. Therefore, until its guilt is scien- 
 tifically substantiated, we must not indict it for condi- 
 tions which may be but coincident with its use. 
 
 Methods of Protection 
 
 The evil effects of the x-ray can be entirely avoided by 
 utilizing the protective measures afforded in modern x- 
 ray apparatus. Inasmuch as lead is impervious to the 
 rays, it can be used in different forms and in various 
 pieces of apparatus in such a way as to control or con- 
 fine the rays according to the will of the operator. 
 
 Tube Shield 
 
 The most essential piece of protective apparatus is 
 the tube shield (Fig. 120). This is constructed of leaded 
 glass, there being a sufficient amount of lead salts incor- 
 porated in the glass to prevent ordinary rays from pass- 
 ing through it. The sides extend up over the highest 
 
172 
 
 DENTAL AND ORAL RADIOGRAPHY 
 
 part of the tube and the opening at the top is often cov- 
 ered Avith a rubber cap, in which lead is also incorporated. 
 At the bottom directly opposite the target of the tube an 
 opening of the proper size is left to allow the desired 
 rays to pass out. The size of this opening may be con- 
 trolled by interchangeable diaphragms of various sizes, 
 which are constructed of sheet lead about one-sixteenth 
 of an inch in thickness. 
 
 This apparatus is usually augmented by a compres- 
 
 ^- 
 
 Fig. 120. — An x-ray tube inclosed within a leaded glass tube shield. 
 
 sion cylinder, which is attached to the base of the tube 
 shield, against or in contact with the lead diaphragm. 
 Such a cylinder is usually constructed of aluminum with 
 a lead lining, is made in various lengths and diameters 
 according to the character of the work for which it is to 
 be used, and serves the purpose of confining the rays 
 coming through the diaphragm from the target of the 
 tube. 
 
 These pieces of apparatus are usually integral parts 
 
X-RAY DANGERS METHODS OF PROTECTIOX 
 
 of the modern tube stand, sold by all reliable manufac- 
 turers of x-ray apparatus. It should be apparent to 
 anyone that with such apparatus, the only rays which 
 leave the area of the tube are those which pass through 
 the diaphragm and cylinder and are used upon the pa- 
 
 ^ 
 
 Fig. 121. — Types of lead-lined protection screens. 
 
 tient. In radiographic work these do not injure the 
 patient, as the exposures are too short to produce ill 
 effects, even if numerous exposures are necessar^^ 
 
 On the other hand the radiographer who fails to use 
 these protective measures, or who carelessly places him- 
 
174 DEI^TAL AI^D ORAL EADIOGRAPHY 
 
 self in the direct path of the rays will in time through 
 the accnninlative effect of the x-ray be very apt to reap 
 as a resnlt of his foU}^ some of the dread injuries before 
 described. 
 
 Other Means of Protection 
 
 In addition to the protective measures thus far de- 
 scribed, there are other means that afford additional pro- 
 tection, and if a person is working constantly with the 
 x-ray these should be used. Among these is the leaded 
 screen behind which the operator stands during the time 
 exposures are made (Fig. 121). Such a screen is usually 
 placed in front of the controlling apparatus and has a 
 leaded glass window, so that the operator can watch the 
 
 Fig. 122. — Lead-impregnated glove. 
 
 patient during the exposure. Lead-impregnated gloves 
 (Fig. 122) and aprons (Fig. 123) are also used by some 
 as a precaution, but such extreme measures are not nec- 
 essary for the dentist doing his own radiography. 
 
 With a properly constructed leaded glass tube shield, 
 lead diaphragm, and lead-lined cylinder the operator is 
 safe, provided he takes the precaution of avoiding the 
 direct rays. 
 
 We all realize that many very useful agents in medi- 
 cine and surgery are dangerous when used carelessly, in- 
 discriminately, or may we say ignorantly. The old say- 
 ing that "fools rush in where angels fear to tread," per- 
 haps applies with greater significance in many branches 
 of medicine than we would care to admit. But the fact 
 
X-RAY DAls^GERS METHODS OF PROTECTION 175 
 
 that through the misuse of dangerous agents, many 
 patients have met death, or have been subjected to need- 
 less suffering, is no argument against their use when 
 placed in competent hands. In such hands the x-ray 
 
 Fig. 123. — X-ray protection apron. 
 
 stands today as one of the greatest adjuncts to the mod 
 ern art of healing, a blessing to humanity, even if in its 
 early history it left its martyrs here and there ; its bene- 
 fits and triumphs far out-balance any evils connected with 
 its use. 
 
INDEX 
 
 Alternating current, 31 
 
 Alveolar abscesses, 12S, 137 
 
 Ampere, 32 
 
 Anode, 26 
 
 Anomalous teeth, 158, 164 
 
 Arrangement of apparatus, 75, 95 
 
 B 
 Broken-off broaches, 133 
 
 C 
 Cathode, 26 
 Cathode rays, 28, 29 
 Coil, 37, 39 
 
 primary, 41, 43 
 
 secondary, 41, 43 
 Compression cylinder, 70 
 Compression cylinder, special, 86 
 Compression diapihragm, 70 
 Coolidge tube, 69 
 Crookes, Sir William, 27 
 Crookes tubes, 27 
 Crown and bridgework, 146 
 Current conditions for radiography, 
 
 107 
 Cj'sts and tumors, 134-150 
 
 D 
 
 Dangers of the x-ray, 167 
 Darkroom, 76 
 portable, 77 
 Developer for plates and films, 120 
 Development of plates and films, 117 
 Drying plates and films, 119 
 
 E 
 
 Electric currents, 31 
 alternating, 31 
 
 Electric currents — Cont 'd. 
 
 amperage, 32 
 
 direct, 31 
 
 high tension, 31 
 
 voltage, 31 
 
 wattage, 32 
 Electrolytic interrupter, 46 
 Electromagnetic induction, 39 
 Electromagnets, 38 
 Electromotive force, 31 
 Electrons, 22 
 Extra-oral radiograms, 81-92 
 
 Faraday, Michael, 25 
 
 Filling materials, appearance of, 
 
 132 
 Film holders, 88 
 Films, x-ray, 117 
 
 film chest, 116 
 
 preparation for exposure, 117 
 Fluorescence, 26 
 Fractures, 126, 150 
 
 Geissler, 26 
 
 G 
 
 H 
 
 Hertz, Heinrich, 28 
 High frequency coils, 53 
 
 diagrams of, 54 
 Hittorf, 26 
 Hydrogen tube, 69 
 
 Illuminating cabinets, 124 
 Impacted teeth, 126-149 
 Induced currents, 38-39 
 Induction coils, 43 
 diagram of, 44, 47 
 
 177 
 
178 
 
 INDEX 
 
 Induction coils — Cont'd. 
 
 essential parts of, 43 
 
 illustrations of, 49, 50, 51 
 Interpretation of radiograms, 122 
 Interrupterless transformer, 55 
 
 illustrated, 57 
 Interrupters, 46 
 
 electrolytic, 46 
 
 mechanical, 46 
 Intra-oral radiograms, 81, 82 
 
 L 
 Lead apron, 174 
 
 Lead compression diaphragm, 70, 73 
 Lead gloves, 174 
 Lead screen, 174 
 Leaded glass tube shield, 70, 171 
 Lead-lined compression cylinder, 74 
 Lines of force, magnetic, 36 
 Low vacuum tubes, 110 
 
 M 
 
 Magnet, electro, 38 
 
 poles of, 35 
 Magnetic effect of electric current, 
 
 37 
 Magnetic field, 35 
 Magnetic force, lines of, 36 
 Magnetic induction, 36 
 Magnetism, 34 
 Milliamperemeter, 109 
 Missing teeth, 127-164 
 
 N 
 Nature of the x-ray, 23-30 
 Necrosis, 131 
 
 O 
 Ohm, defined, 32 
 Ohm's law, 33 
 Oral examination, 135 
 Oral surgery, 148 
 Orthodontia, 152 
 
 radiographic requirements in, 163 
 
 Pathoradiograpliy, 20 
 Penetration of x-rays, 110 
 
 Pericemental infection, 137 
 Photographic darkroom, 76 
 Plate chest, 115 
 Plates, x-ray, 115 
 
 care of, 115 
 
 development of, 117 
 
 drying, 119 
 
 preparation of, 115 
 Portable darkroom, 77 
 Power rating of coils, 52 
 Primary coil, 43 
 Protection from x-rays, 171 
 Pyorrhea pockets, 134-144 
 
 E 
 
 Radiogram, 20, 78 
 
 examination of, 124 
 
 extra-oral, 81-92 
 
 interpretation of, 122 
 
 intra-oral, 81, 82 
 
 proper tube and current condi- 
 tions for, 110, 111 
 
 rules for making, 80 
 Radiographic examination, complete, 
 
 91 
 Rectifier, chemical, 59 ' 
 Rhumkorff coil, 43 
 Roentgen, William Conrad, 17-24 
 Roentgenogram, 20 
 Roentgenograph, 20 
 Roentgenolog}', 20 
 Root canal treatment, 139 
 Root resection, 143 
 Rotary converter, 59 
 
 S 
 
 Secondary coil, 43 
 Self-induction, 42 
 Solenoid, 37 
 Spark gap, 52 
 
 Technic of radiography, 78, 82-92. 
 correct and incorrect, diagram of, 
 83 
 
INDEX 
 
 179 
 
 Terminology, 20 
 Tesla coils, 53 
 
 Transformers, interrupterless, 55 
 Tube, connection to x-ray mechinc, 
 64 
 
 inverse in, 113 
 
 regulation of, 04-107 
 Tube conditions for radiograms, 108 
 Tube shield, 74 
 Tube stand, 70 
 
 with platerest, 94 
 Tubes, low, medium, and high, 110 
 
 IT 
 
 Unerupted teeth, 126 
 
 Unit of electromotive force, 31 
 
 current strength, 32 
 
 resistance, 32 
 
 V 
 
 Vacuum of tube, how to determine, 
 108 
 relative merits of low, medium, 
 and high, 110 
 
 Vacuum tubes, 62, 108 
 Volt, 31 
 Voltage, 31 
 
 W 
 
 Watt, 32 
 Wattage, 32 
 
 X 
 
 X-ray, dangers of, 167 
 defined, 23 
 dermatitis, acute, 168 
 
 chronic, 169 
 discovery of, 24 
 effect upon photographic plates, 
 
 30 
 machines, 43 
 nature of, 30 
 penetration of, 30 
 production of, 23 
 protection from, 171 
 tube, 62 
 
 connected to the coil of trans- 
 former, 64 
 
 essential parts, 62 
 
 tyi^es of, 63, 69 
 
 A'acuum of, 63-108 
 
Date Due 
 
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RK270 
 
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