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Deposition of Radioactive Iodine in Teeth of Persons Treated for Disease of the Thyroid Gland
Deposition of radioactive iodine in teeth of persons treated for disease of the thyroid gland W . W . Wainwright* D.D.S., M .S .; Byron G. Butt,f D.D.S.; J. Donald Hauptfuehrer,% Chicago, and Harold L. Dute,§ D.D.S., Hines, III.
The early work of Bartelstone showed the interesting possibility of using human teeth from patients treated fo r thyroid disease with radioactive iodine for experimental pur poses. W h e n these patients require extractions, they can be scheduled at varying periods after the adm inistration of the radioactive iodine. The group working at the University of Illinois has extended Bartelstone's observations to periods as short as five hours and as long as 19 days. It is startling to learn that a substance can permeate com pletely the teeth of hum an beings within five hours, even though the patient only swallows a glass of w ater containing the radioactive iodine. The further fact that this iodine is retained for periods as long as two weeks, which is the limit possible for this particular radioisotope, is in itself o f startling significance since, under laboratory con ditions, the sam e iodine can be washed out of the teeth readily in changes of distilled water over the same period of time. The work of the gro u p at the University o f Illinois indicates vast possibilities for the extension of knowledge regarding the behavior of the tooth in its environment.
tact enamel, dentin and cementum, as well as enamel lamellas and damaged portions o f the tooth.1’ 2 Bartelstone3 has
Radioactive tracers have made possible entirely new types of laboratory and hu man studies of the changes which take place in teeth not only at the surface but also within the enamel and deeper in the dentin and pulp. In experiments with freshly extracted human teeth, it has been found that one type of salt shows sur face effects only and stays on the enamel surface even where there are grossly damaged portions underneath. A second group of compounds behaves in the classi cal manner as observed with silver nitrate and dyes; that is, these compounds do not penetrate intact enamel but readily penetrate enamel lamellas and damaged portions of the enamel and underlying dentin. Still a third type of penetration is exhibited by small organic molecules which rapidly and diffusely penetrate in
Study conducted in part under contract no. DA-49007-MD-I48 with the Medical Research and Develop ment Board, Office of the Surgeon General of the United States Army. The J 131 was obtained on alloca tion from the Isotope Division of the United States Atomic Energy Commission. ^Department of radiology, University of Illinois Col lege of Dentistry. Now at University of Southern C a li fornia School of Dentistry, Los Angeles. fUSPHS research fellow of the National Institute of Dental Research, University of Illinois College of Dentistry. Now first lieutenant, USAF, School of Avia tion Medicine, Randolph A ir Force Base, Texas. fSenior medical technologist, department of radi ology, University of Illinois College of Dentistry. §Veterans Administration Hospital, Hines, III. 1. Wainwright, W . W . Enamel penetration by radio active salts of zinc, calcium, silver, plutonium, palla dium and copper. J.A .D .A . 43:664 Dec. 1951. 2. Wainwright, W . W . Three levels of enamel per meability. New York J . Den. 21:308 Aug.-Sept. 1951. 3. Bartelstone, H. J . Survey of the use of radioactive isotopes in dentistry. New York J . Den. 20:320 Aug.Sept. 1950. 649
650 • THE JO U R N A L OF THE A M E R IC A N DENTAL A SSO C IA TIO N
Table 1 • List of patients
U P T A K E O F IO D IN E
Diagnosis of thyroid disease
Patient
Age of patient (years)
1
43
Papillary cystadenocarcinoma
2
57
Anaplastic carcinoma with métastasés
3
27
Papillary cystadenocarcinoma of left lobe with métastasés
4
63
Fetal adenoma of right lobe
5
32
Adenocarcinoma
demonstrated many of these same changes in living human teeth and has pointed out the ease with which in vivo studies may be accomplished. Further studies on the teeth of pa tients treated with radioactive iodine were made possible through the coopera tion o f A. Gordon Anderson and the staff of the dental clinic, isotope unit, and tumor clinic o f the Veterans Administra tion Hospital, Hines, 111. Twentyfive teeth were obtained from August 2 through October 18, 1951. The teeth were obtained from five men who had been treated for disease of the thyroid gland by the oral administration of I 131. The patients ranged in age from 27 to 63 years. The individual ages and diag noses are given in Table 1. The dosages of I 131, the reason for loss of the teeth, and the identity of the teeth are given in Table 2. The elapsed time from the ad ministration of the I131 until the extrac tion of the tooth is recorded as the ab sorption time. This varied from five hours to 19 days and the teeth fall into three groups according to the absorption time: the first from 5 to 6 hours, the second from 16 to 18 hours, the third from 15 to 19 days. The amounts of I 131 adminis tered were in most cases 25 millicuries although in two instances the dose was 50 millicuries.
The uptake of iodine in the five-hour specimens is illustrated in Figure 1. Fig ure 1, A shows a longitudinal section of a lower left second bicuspid. The radio autograph at the left shows a consider able uptake throughout the tooth, espe cially at the cervical margin and in certain portions of the cementum. The photograph of the ground section on the right o f Figure 1, A shows a carious class V cavity on the buccal aspect and slight surface caries on the lingual aspect. These areas correspond to the heavy exposures on the radioautograph. There is a heavy uptake o f iodine in the contents of the occlusal fissure. Along the lines of re cession of the pulpal horns there is a reduced uptake o f iodine, and in the speci mens these regions appear to be trans lucent. In Figure 1, B a series o f trans verse sections have been made through a lower left first bicuspid of the same patient. The first three sections are in the crown and the last three through the root at approximately even intervals through out the tooth. A general uptake of io dine through all of the dentin is seen, as well as heavy uptake in the carious occlu sal fissures and in the carious cavities on the distal and buccal aspects. In both Figures 1, A and B there is a very heavy uptake of iodine in areas far beneath the damaged surfaces. Examples of the second group, with an absorption time of 17 hours, are shown in Figures 2, A and 2, B, and of 18 hours in Figure 2, G. In general the appearance o f the radioautographs in the 17-hour specimens is much the same as that in the five-hour specimens. Direct comparison o f the radioautographs of the 17-hour and five-hour specimens is pos sible since the exposure times are re corded as equivalent exposure times;4
4. Wainwright, W . W . The permeability of human dental root structures to radioactive iodine. J . Periodont. 23:95 April 1952.
W A IN W R IG H T — BUTT— HAUPTFUEHRER— DUTE . . . VO LUM E 47, DECEMBER 1953 • 651
Table 2 • In vivo penetration of human teeth by radioactive iodine Absorption time
Patient number
Reason for loss
I131 Dosage Date 10-18-51
[ Millicuries 25
Periodontitis
5 hours
6 hours
Tooth Lower left second bicuspid (Fig. 1, A)
5
9-13-51
25
Preparation for denture
Lower left first bicuspid (Fig. 1, B) Upper left second bicuspid
2
10-18-51
25
Severe abrasion
Lower right cuspid
Preparation for denture 2
8-2-51
25
Severe abrasion
Lower left lateral incisor
Preparation for denture
Lower left central incisor
16 hours
Upper left lateral incisor (Fig. 2, A)
17 hours
1
8-30-51
25
Periodontitis
Upper left central incisor (Fig. 2, B)
Preparation for denture
Upper right central incisor Upper right lateral incisor Upper right cuspid
2
8-16-51
50
3
8-16-51
, 25
Severe abrasion Preparation for denture
Lower right lateral incisor Upper right third molar
Malposed
Lower right third molar
Caries
Upper left second molar
Periodontitis
Lower right second molar (Fig. 2, C)
18 hours
4
8-30-51
50
Lower left central incisor Lower right central incisor (Fig. 3, A) Lower right lateral incisor (Fig. 3, B) 15 days
1
10-18-51
25
Periodontitis Lower right cuspid Lower right first bicuspid Lower right second bicuspid Lower left cuspid
19 days
1
10-18-51
25
Periodontitis
lo w e r left lateral incisor (Fig. 3, D) Lower left central incisor (Fig. 3, C l
6S2 • THE JO U R N A L OF THE A M E R IC A N DENTAL A SSO C IA T IO N
Fig. 1 • Radioautographs and sections from teeth extracted five hours after administration o f 25 millicuries o f radioactive iodine to a 43 year old man. Equivalent exposure tim e, 3.3 days. A : L ow er left second bicuspid. ( Speci men 37, section 45, radioautograph 180, neg atives 245 and 2 8 0 ). B : L ow er left first bicus pid. ( Specim en 38, sections 47, 48, 50, 52, 54, and 61, radio-autographs 184, 186, 190, 194, 198, and 211, negatives 248, 250, 184, 188, 191, 205, 27, 68, 23, 76, 8, and 5 2 )
that is, the times have been corrected for radioactive decay and are expressed as though they were started at the time of iodine administration. In Figure 2, A it is notable that the two middle sections show heavy penetration of the normal dentin underneath the carious cavities; in fact, the dentin in this region is pene trated almost completely across the tooth. In Figures 2, B and 2, C several areas of diffuse penetration of intact enamel are to be seen. Examples of the teeth extracted more than two weeks after administration of I 131 are shown in Figure 3. Figures 3, A and 3, B show radioautographs and sec tions of lower right central and lateral in cisors of the same patient whose teeth
are illustrated in Figures 1 and 2, A and 2, B. Surprisingly the radioautographs show heavy uptake of iodine in several
W A IN W R IG H T — BUTT— HAUPTFUEHRER— DUTE . . . VO LU M E 47, DECEMBER 1953 • 653
Fig. 2 • A and B : Radioautographs and ground sections from teeth extracted 17 hours after administration of 25 millicuries of radio active iodine, to same patient as in Fig. 1, A. A : U pper left lateral incisor. Equivalent ex posure tim e 3.1 days ex cep t the sixth radio autograph which has an equivalent exposure tim e of 1.9 days. (S pecim en 16, sections 1, 2, 3, 5, 8, and 9, radioautographs 32, 34, 35, 36, 39, 15, and 47, negatives 237, 236, 238, 241, 151, 279, 278, 7, 4 , 5, 1, 33, 292, and 1 1 6 ). B : U pper left central incisor. Equivalent ex posure tim e 3.6 days. (S pecim en 15, section 4 0, radioautograph 132, negatives 166 and 5 3 ). C : Radioautographs and ground sections from tooth extracted 18 hours after adminis tration o f 50 millicuries of radioactive iodine to a 63 year old man. L ow er right second molar. Equivalent exposure times 4.0 and 3.1 days respectively. (S pecim en 10, sections 30 and 31, radioautographs 140 and 163, nega tives 299, 300, 21, and 2 8 )
654 • THE JO U R N A L OF THE A M E R IC A N DENTAL A SSO C IA T IO N
W A IN W R IG H T — BUTT— HAUPTFUEHRER— DUTE . . . VO LU M E 47, DECEMBER 1953 • 655
Fig. 3 • Radioautographs and ground sections from teeth. A and B extracted 15 days after, and C and D extracted 19 days after administration of 25 millicuries of radioactive iodine to same patient as in Fig. 1, A. A : Lower right central incisor. Equivalent exposure time 2.6 days. (Specimen 41, section 82, radioautograph 251, negatives 228 and 108). B: Lower right lateral incisor. Equivalent exposure time 2.6 days. (Specimen 42, section 88, radioautograph 263, nega tives 258 and 111). C : Lower left lateral incisor. Equivalent exposure time 3.6 days. (Specimen 46, sections 119, 120, 123, 124, and 126, radioautographs 325, 327, 337, 340, and 341, negatives 207, 210, 257, 220, 221, 56, 61, 65, 62, and 66). D : Lower left central incisor. Equivalent ex posure time 2.3 days. (Specimen 47, section 135, radioautograph 362, negatives 223 and 80)
significant regions of these teeth, espe cially in the dentin of the crown and in the cervical region. Again, there is com plete penetration o f the tooth at the neck. The fact that little exposure is seen over the root may be explained partially by the shorter equivalent exposure time, which is in this case 2.6 days instead of 3.3 days. Further information is given in Figure 3, C which is a lower left cen tral incisor extracted from the same pa tient (No. 1) 19 days after I 131 adminis tration. The equivalent exposure time on this tooth is 3.6 days. With this slightly longer exposure, iodine uptake is seen to occur throughout this tooth as in the case o f the 17-hour and five-hour speci mens. Figure 3, D shows a radioauto graph of the lower left central incisor from the same patient (No. 1) ; however, the equivalent exposure time is 2.3 days. Heavy uptake is seen here only in the exposed coronal dentin. It is possible that the absence of radioautographic expo sure in the rest of the dentin o f the tooth
is only due to the shorter equivalent ex posure time. SU M M A R Y AND CONCLUSION S
1. The in vitro observation of enamel surface uptake, penetration of enamel lamellas and damaged dental structures, and the diffuse penetration of intact enamel (by certain small organic mole cules) have all been duplicated in the living human subject in tracer studies with radioactive iodine. 2. No difference in amount of iodine localized in the teeth could be detected by radioautographic technics between teeth extracted at periods after radio active iodine administration varying from 5 hours to 19 days. 3. For unexplained reasons much of the experimental evidence obtained sug gests that the iodine is retained in approx imately the original amounts in human teeth under living and in vitro condi tions for at least two weeks.
The early work of Bartelstone showed the interesting possibility of using human teeth from patients treated fo r thyroid disease with radioactive iodine for experimental pur poses. W h e n these patients require extractions, they can be scheduled at varying periods after the adm inistration of the radioactive iodine. The group working at the University of Illinois has extended Bartelstone's observations to periods as short as five hours and as long as 19 days. It is startling to learn that a substance can permeate com pletely the teeth of hum an beings within five hours, even though the patient only swallows a glass of w ater containing the radioactive iodine. The further fact that this iodine is retained for periods as long as two weeks, which is the limit possible for this particular radioisotope, is in itself o f startling significance since, under laboratory con ditions, the sam e iodine can be washed out of the teeth readily in changes of distilled water over the same period of time. The work of the gro u p at the University o f Illinois indicates vast possibilities for the extension of knowledge regarding the behavior of the tooth in its environment.
tact enamel, dentin and cementum, as well as enamel lamellas and damaged portions o f the tooth.1’ 2 Bartelstone3 has
Radioactive tracers have made possible entirely new types of laboratory and hu man studies of the changes which take place in teeth not only at the surface but also within the enamel and deeper in the dentin and pulp. In experiments with freshly extracted human teeth, it has been found that one type of salt shows sur face effects only and stays on the enamel surface even where there are grossly damaged portions underneath. A second group of compounds behaves in the classi cal manner as observed with silver nitrate and dyes; that is, these compounds do not penetrate intact enamel but readily penetrate enamel lamellas and damaged portions of the enamel and underlying dentin. Still a third type of penetration is exhibited by small organic molecules which rapidly and diffusely penetrate in
Study conducted in part under contract no. DA-49007-MD-I48 with the Medical Research and Develop ment Board, Office of the Surgeon General of the United States Army. The J 131 was obtained on alloca tion from the Isotope Division of the United States Atomic Energy Commission. ^Department of radiology, University of Illinois Col lege of Dentistry. Now at University of Southern C a li fornia School of Dentistry, Los Angeles. fUSPHS research fellow of the National Institute of Dental Research, University of Illinois College of Dentistry. Now first lieutenant, USAF, School of Avia tion Medicine, Randolph A ir Force Base, Texas. fSenior medical technologist, department of radi ology, University of Illinois College of Dentistry. §Veterans Administration Hospital, Hines, III. 1. Wainwright, W . W . Enamel penetration by radio active salts of zinc, calcium, silver, plutonium, palla dium and copper. J.A .D .A . 43:664 Dec. 1951. 2. Wainwright, W . W . Three levels of enamel per meability. New York J . Den. 21:308 Aug.-Sept. 1951. 3. Bartelstone, H. J . Survey of the use of radioactive isotopes in dentistry. New York J . Den. 20:320 Aug.Sept. 1950. 649
650 • THE JO U R N A L OF THE A M E R IC A N DENTAL A SSO C IA TIO N
Table 1 • List of patients
U P T A K E O F IO D IN E
Diagnosis of thyroid disease
Patient
Age of patient (years)
1
43
Papillary cystadenocarcinoma
2
57
Anaplastic carcinoma with métastasés
3
27
Papillary cystadenocarcinoma of left lobe with métastasés
4
63
Fetal adenoma of right lobe
5
32
Adenocarcinoma
demonstrated many of these same changes in living human teeth and has pointed out the ease with which in vivo studies may be accomplished. Further studies on the teeth of pa tients treated with radioactive iodine were made possible through the coopera tion o f A. Gordon Anderson and the staff of the dental clinic, isotope unit, and tumor clinic o f the Veterans Administra tion Hospital, Hines, 111. Twentyfive teeth were obtained from August 2 through October 18, 1951. The teeth were obtained from five men who had been treated for disease of the thyroid gland by the oral administration of I 131. The patients ranged in age from 27 to 63 years. The individual ages and diag noses are given in Table 1. The dosages of I 131, the reason for loss of the teeth, and the identity of the teeth are given in Table 2. The elapsed time from the ad ministration of the I131 until the extrac tion of the tooth is recorded as the ab sorption time. This varied from five hours to 19 days and the teeth fall into three groups according to the absorption time: the first from 5 to 6 hours, the second from 16 to 18 hours, the third from 15 to 19 days. The amounts of I 131 adminis tered were in most cases 25 millicuries although in two instances the dose was 50 millicuries.
The uptake of iodine in the five-hour specimens is illustrated in Figure 1. Fig ure 1, A shows a longitudinal section of a lower left second bicuspid. The radio autograph at the left shows a consider able uptake throughout the tooth, espe cially at the cervical margin and in certain portions of the cementum. The photograph of the ground section on the right o f Figure 1, A shows a carious class V cavity on the buccal aspect and slight surface caries on the lingual aspect. These areas correspond to the heavy exposures on the radioautograph. There is a heavy uptake o f iodine in the contents of the occlusal fissure. Along the lines of re cession of the pulpal horns there is a reduced uptake o f iodine, and in the speci mens these regions appear to be trans lucent. In Figure 1, B a series o f trans verse sections have been made through a lower left first bicuspid of the same patient. The first three sections are in the crown and the last three through the root at approximately even intervals through out the tooth. A general uptake of io dine through all of the dentin is seen, as well as heavy uptake in the carious occlu sal fissures and in the carious cavities on the distal and buccal aspects. In both Figures 1, A and B there is a very heavy uptake of iodine in areas far beneath the damaged surfaces. Examples of the second group, with an absorption time of 17 hours, are shown in Figures 2, A and 2, B, and of 18 hours in Figure 2, G. In general the appearance o f the radioautographs in the 17-hour specimens is much the same as that in the five-hour specimens. Direct comparison o f the radioautographs of the 17-hour and five-hour specimens is pos sible since the exposure times are re corded as equivalent exposure times;4
4. Wainwright, W . W . The permeability of human dental root structures to radioactive iodine. J . Periodont. 23:95 April 1952.
W A IN W R IG H T — BUTT— HAUPTFUEHRER— DUTE . . . VO LUM E 47, DECEMBER 1953 • 651
Table 2 • In vivo penetration of human teeth by radioactive iodine Absorption time
Patient number
Reason for loss
I131 Dosage Date 10-18-51
[ Millicuries 25
Periodontitis
5 hours
6 hours
Tooth Lower left second bicuspid (Fig. 1, A)
5
9-13-51
25
Preparation for denture
Lower left first bicuspid (Fig. 1, B) Upper left second bicuspid
2
10-18-51
25
Severe abrasion
Lower right cuspid
Preparation for denture 2
8-2-51
25
Severe abrasion
Lower left lateral incisor
Preparation for denture
Lower left central incisor
16 hours
Upper left lateral incisor (Fig. 2, A)
17 hours
1
8-30-51
25
Periodontitis
Upper left central incisor (Fig. 2, B)
Preparation for denture
Upper right central incisor Upper right lateral incisor Upper right cuspid
2
8-16-51
50
3
8-16-51
, 25
Severe abrasion Preparation for denture
Lower right lateral incisor Upper right third molar
Malposed
Lower right third molar
Caries
Upper left second molar
Periodontitis
Lower right second molar (Fig. 2, C)
18 hours
4
8-30-51
50
Lower left central incisor Lower right central incisor (Fig. 3, A) Lower right lateral incisor (Fig. 3, B) 15 days
1
10-18-51
25
Periodontitis Lower right cuspid Lower right first bicuspid Lower right second bicuspid Lower left cuspid
19 days
1
10-18-51
25
Periodontitis
lo w e r left lateral incisor (Fig. 3, D) Lower left central incisor (Fig. 3, C l
6S2 • THE JO U R N A L OF THE A M E R IC A N DENTAL A SSO C IA T IO N
Fig. 1 • Radioautographs and sections from teeth extracted five hours after administration o f 25 millicuries o f radioactive iodine to a 43 year old man. Equivalent exposure tim e, 3.3 days. A : L ow er left second bicuspid. ( Speci men 37, section 45, radioautograph 180, neg atives 245 and 2 8 0 ). B : L ow er left first bicus pid. ( Specim en 38, sections 47, 48, 50, 52, 54, and 61, radio-autographs 184, 186, 190, 194, 198, and 211, negatives 248, 250, 184, 188, 191, 205, 27, 68, 23, 76, 8, and 5 2 )
that is, the times have been corrected for radioactive decay and are expressed as though they were started at the time of iodine administration. In Figure 2, A it is notable that the two middle sections show heavy penetration of the normal dentin underneath the carious cavities; in fact, the dentin in this region is pene trated almost completely across the tooth. In Figures 2, B and 2, C several areas of diffuse penetration of intact enamel are to be seen. Examples of the teeth extracted more than two weeks after administration of I 131 are shown in Figure 3. Figures 3, A and 3, B show radioautographs and sec tions of lower right central and lateral in cisors of the same patient whose teeth
are illustrated in Figures 1 and 2, A and 2, B. Surprisingly the radioautographs show heavy uptake of iodine in several
W A IN W R IG H T — BUTT— HAUPTFUEHRER— DUTE . . . VO LU M E 47, DECEMBER 1953 • 653
Fig. 2 • A and B : Radioautographs and ground sections from teeth extracted 17 hours after administration of 25 millicuries of radio active iodine, to same patient as in Fig. 1, A. A : U pper left lateral incisor. Equivalent ex posure tim e 3.1 days ex cep t the sixth radio autograph which has an equivalent exposure tim e of 1.9 days. (S pecim en 16, sections 1, 2, 3, 5, 8, and 9, radioautographs 32, 34, 35, 36, 39, 15, and 47, negatives 237, 236, 238, 241, 151, 279, 278, 7, 4 , 5, 1, 33, 292, and 1 1 6 ). B : U pper left central incisor. Equivalent ex posure tim e 3.6 days. (S pecim en 15, section 4 0, radioautograph 132, negatives 166 and 5 3 ). C : Radioautographs and ground sections from tooth extracted 18 hours after adminis tration o f 50 millicuries of radioactive iodine to a 63 year old man. L ow er right second molar. Equivalent exposure times 4.0 and 3.1 days respectively. (S pecim en 10, sections 30 and 31, radioautographs 140 and 163, nega tives 299, 300, 21, and 2 8 )
654 • THE JO U R N A L OF THE A M E R IC A N DENTAL A SSO C IA T IO N
W A IN W R IG H T — BUTT— HAUPTFUEHRER— DUTE . . . VO LU M E 47, DECEMBER 1953 • 655
Fig. 3 • Radioautographs and ground sections from teeth. A and B extracted 15 days after, and C and D extracted 19 days after administration of 25 millicuries of radioactive iodine to same patient as in Fig. 1, A. A : Lower right central incisor. Equivalent exposure time 2.6 days. (Specimen 41, section 82, radioautograph 251, negatives 228 and 108). B: Lower right lateral incisor. Equivalent exposure time 2.6 days. (Specimen 42, section 88, radioautograph 263, nega tives 258 and 111). C : Lower left lateral incisor. Equivalent exposure time 3.6 days. (Specimen 46, sections 119, 120, 123, 124, and 126, radioautographs 325, 327, 337, 340, and 341, negatives 207, 210, 257, 220, 221, 56, 61, 65, 62, and 66). D : Lower left central incisor. Equivalent ex posure time 2.3 days. (Specimen 47, section 135, radioautograph 362, negatives 223 and 80)
significant regions of these teeth, espe cially in the dentin of the crown and in the cervical region. Again, there is com plete penetration o f the tooth at the neck. The fact that little exposure is seen over the root may be explained partially by the shorter equivalent exposure time, which is in this case 2.6 days instead of 3.3 days. Further information is given in Figure 3, C which is a lower left cen tral incisor extracted from the same pa tient (No. 1) 19 days after I 131 adminis tration. The equivalent exposure time on this tooth is 3.6 days. With this slightly longer exposure, iodine uptake is seen to occur throughout this tooth as in the case o f the 17-hour and five-hour speci mens. Figure 3, D shows a radioauto graph of the lower left central incisor from the same patient (No. 1) ; however, the equivalent exposure time is 2.3 days. Heavy uptake is seen here only in the exposed coronal dentin. It is possible that the absence of radioautographic expo sure in the rest of the dentin o f the tooth
is only due to the shorter equivalent ex posure time. SU M M A R Y AND CONCLUSION S
1. The in vitro observation of enamel surface uptake, penetration of enamel lamellas and damaged dental structures, and the diffuse penetration of intact enamel (by certain small organic mole cules) have all been duplicated in the living human subject in tracer studies with radioactive iodine. 2. No difference in amount of iodine localized in the teeth could be detected by radioautographic technics between teeth extracted at periods after radio active iodine administration varying from 5 hours to 19 days. 3. For unexplained reasons much of the experimental evidence obtained sug gests that the iodine is retained in approx imately the original amounts in human teeth under living and in vitro condi tions for at least two weeks.