In our clinical practice, we occasionally perform the operation of unilateral removal of the submandibular gland in treating the submandibular diseases, malignant, benign tumors or chronic, specific inflammations. In such cases, it seems to be very interesting how the remaining major salivary glands behave histologically. Little work has been done, however, which observes the histological behavior of the remaining major salivary glands after unilateral removal of the submandibular gland. 33 adult mongrel dogs were used for the experiment and the patho-histological changes in the remaining major salivary glands, contralateral submandibular, bilateral sublingual and bilateral parotid glands, were studied during the period from the 1st to the 180th day after removal by trying the H-E, PAS, AB (pH 2.5) and AB (pH 1.0) staining. The results obtained are summarized as follows : 1. The change in the remaining submandibular gland was recognized 3-21 days after removal with a certain extent of increase in size in the serous cells of the demilunes. And the change reached its peak on the 5th day of removal. The nuclei showed tendency to increase in size 3-14 days after removal. In this period, PAS, AB (pH 2.5) and AB (pH 1.0) positive granules contained in the serous cells of the demilunes were found to be homogeneously distributed in the whole cell, which suggested the increase of PAS, AB (pH 2.5) and AB (pH 1.0) reactive substances, coincident with increase in size of cell. 2. In the period when the serous cells of the demilunes were found to be increasing in size, the mucous cells of the remaining submandibular gland maintained their normal states, except that the morphological irregularity was seen in the terminal portions. And they still proved to maintain the normality by the PAS, AB (pH 2.5) and AB (pH 1.0) staining. 3. As for the ductal system of the remaining submandibular gland, obvious changes were not observed. 4. There were 3 changes in the remaining sublingual glands ; the increase of mucous terminal portions which were observed continuously from the 3rd to 180th day of removal, the enlargement of the lumens in the mucous and the serous terminal portions which were observed 3-28 days after removal and finally the enlargement of the small ducts which were observed 1-21 days after removal. 5. In the remaining parotid glands, obvious systematic changes couldn't be observed at all. In many cases, they maintained their normality. It may be concluded from these observations that after unilateral removal of the submandibular gland, the changes appear on the gland cells which are in the deepest connection from the chemical quality with the removed salivary gland cells. And this would also suggest the compensatory activity of these gland cells.

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In oro-maxillo-facial region, trauma or surgical operation occasionally cause injuries or amputations of the nerve fibers which do damage to sensibility, gustation or motion. The physiological and pathohistological experiments were performed in order to investigate the process of functional recovery and healing of the nerve fiber damaged. The frog's glossopharyngeal nerve which was cut off at the root of the tongue, was used for the experiment. The results obtained are summarized as follows : A. Physiological findings 1. By the 12th day after operation of the unilateral cutting of the glossopharyngeal nerve, the afferent impulses were not generated from the cut nerve by applicating tactile or chemical stimuli to the tongue. 2. By the 13th day after operation, one of the 4 subjects, responding to each stimulus, showed discharge of afferent impulses in the glossopharyngeal nerve of cut side. The other 3 subjects didn't show any response. 3. Among 42 subjects which elapsed from the 14th to the 20th day after operation, 33 subjects showed responses to both tactile and chemical stimuli and 5 subjects only to tactile stimuli. 4. Both frequency and amplitude of the afferent impulses in the early stage of recovery, were low and small, they, however, increased as time passed. B. Pathohistological findings 1. The degeneration in the peripheral nerve started by 24 hours after operation. 2. The degeneration was in process from the 3rd to the 6th day after operation, that is rosary-degeneration, laceration or granular decomposition were observed in all the layers and nerve fibers had disappeared in the fungiform papillae. 3. Waller's degeneraton seemed to have been completed from the 7th to the 10th day after operation. 4. By the 10th day after operation, swelling and proliferating Schwann's cells were seen lined up in the muscular layers, and were also seen one or two fine regenerated nerve fibers along Schwann's cell. 5. After the 15th day of operation, one or two fine regenerated nerve fibers were seen also in the fungiform papillae proceeding toward the sensory cell. With lapse of time regenerated nerve fibers increased in diameter as well as in number. 6. Even in the period of degeneration or regeneration, the sensory cells lying along the free edge of the fungiform papillae didn't show any change, instead, they were observed located regularly. C. Relation between physiological and pathohistological findings 1. The regenerated nerve fibers were pathohistologically observed in some muscular layers after the 10th day of operation, while it was after the 13th day of operation that physiological responses to the stimuli of the tongue could be observed. 2. The regenerated nerve fibers were seen in the fungiform papillae after the 15th day of operation, while the afferent impulses were observed by the 13th day after operation. As the regenerative process of the nerve fibers advanced with lapse of time, the afferent impulses of regenerated nerve increased in frequency and amplitude. 3. Pathohistologically, by after the 35th day of operation, the amount of destribution of the regenerated nerve fibers were scanty than the normal nerve fibers and that the impulses from the regenerated nerve fibers were of lower frequency and amplitude as compared to the nerve fibers of the normal side.

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With the works in my mind of the senior students of the class who have taken up the appearance of atrophy in their studies of age change of the splitting lines, as well as Dr. Mori's records (1971) of the same laboratory on the change of splitting lines of mucous membrane of tongue in his research of the atrophy process of tongue, the author have examined the changing conditions of the respective splitting lines of articular surfaces on both medial and lateral condyles of femur and of tibia in the joint part of dog's knee, by the sciatic nerve amputation and observation of the splitting lines in the said portions at 8 different stages from one week to 6 months after the operation. The following are the conclusions thus obtained : The atrophy of articular cartilages in the knee joint caused by the sciatic nerve amputation, as viewed from the changing condition of the splitting lines, indicates slow atrophy process on account of being out of use. Conspicuous transverse and longitudinal atrophies are distinguishable only in the patellar articular surface of the knee joint, while the atrophy process of each of all articular surfaces of knee joint, or the patellar surface and both medial and lateral condyles of femur and of tibia, is learned to be the slow one for nonuse.

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Since when Prof. Nakayama emphasized the meaning of existence of the irregular splitting lines, publicizing his views that the line systems indicate the direction of growth, while the irregular splitting lines are the signs of disorder of the growing direction due to collision of internal growth strengths, or the physiological load or other external influences, in other words, the irregular splitting lines are the direct functional manifestation that may be interpreted as a sort of direct defence reaction of the tissue itself, his theory has been verified by the senior students of this laboratory on the various tissues, too. With the results of these research works in mind, the author have pursued the changes of the splitting lines of mandible after bite-hight was raised in the grown up dogs (1 to 2 years post natal) and observed the appearance or disappearance of the splitting line systems, especially of the irregular splitting lines, with the 19 specimens of 10 age stages ranging from 1 and 2 weeks, 1, 3, 5, 7, 9, 11, 13 and 15 months after mounting of the metal crown on the first molar. Following conclusions have been obtained by these experiments : 1) The overload to the tooth caused by the raised occlusion is prominently observed as the increase of the irregular splitting lines at the alveolar border, apex of the root, insertion parts of masticatory museles, pre-molar alveolar border and the transitional part between body and ramus of the mandible. 2) The splitting lines at the portion in contact with the apex of root of the experimented first mandibular molar is seen for a longer period of time in the lateral surface than in the medial surface. This is considered to be due to the occlusional condition whereby the first maxillar molar pressed the experimented first mandibular molar from lateral side to the medial side, resulting in that the portion in contact with the apex of root affects stronger external influence to the lateral side. 3) The fact that the insertion parts of muscles expanded the area of the irregular splitting lines earlier than the other parts is interpreted that it is the result of the raised occlusion directly influencing each insertion part externally as the excessive force of the masticator to lift the mandible, and the appearance or disappearance of the irregular splitting lines group thereafter is the state of the fluctuation of masticatory force to lift the mandible reflecting in the insertion parts of the masticator. 4) That the effect of the raised occlusion appeared in the alveolar border and transitional part between body and ramus of mandible seems to be that the former is the mandibular tissue's adaptation trying to let the engapped upper and lower anterior teeth parts between maxilla and mandible contact each other, and the latter is because the said transitional part is the center of distortion caused by the excessive occlusion force as it occupies the supporting position in the occlusion.

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Muhlreiter (1928) pointed out the curve symbol as one of the methods to identify the rightness or leftness of the tooth. This is an important element in the plaster sculpture, yet the matters relating to the curve symbol such as the angle to compose the curve symbol, its position or the relationship with the adjacent tooth have not been explained at all so far. In order to obtain effective guides for dental anatomy by the study of this subject, the author have investigated the extracted anterior right maxillary teeth, collecting 23 central incisors, 10 lateral incisors and 12 canines. Their crown lengths were transversally separated into 12 sections of even space, the contour line of each separated section recorded by the contracer, and the angles formed by the curvatures from the labial to the mesial direction and that from the labial to the distal direction were also recorded. The date thus obtained were examined from various view points, and the following conclusions have been reached in due consideration : 1. In the study of the contours by the incisal aspect, the average mesial curvature angle of the central incisor is 123.4°, 5.4° less than the distal curvature angle which averages 123.8°. A significant difference is observed between the mesial curvature angle and the distal one, and the latter is greater. In the case of lateral incisor, the average mesial curvature angle is 136.1°, 3.5° less than 139.6° average of the distal one. The difference is not significantly large enough. In the case of canine, the average mesial curvature angle is 128.2°, while the distal curvature angle averages 147.8°. The value of 19.6° between both shows a significant difference, that is, the distal curvature angle is apparently greater. In short, the curve symbol is most apparent in the canine, followed by the central then lateral incisors, but no apparent difference to mention is seen in the lateral incisor. 2. In the positional study of curve symbol of the central incisor, it is seen to be formed in the area between the 3rd and 9th separating lines, the central 2/3 of the crown length slightly closer toward the tooth cervical side. In the case of the lateral incisor, it is formed in the area between the 4th and 9th separating lines, central half of the crown length. In the case of the canine, it is in the area between the 2nd and 8th separating lines, the central area nearly 2/3 of the crown length in the labial surface slightly closer toward the cervical side. 3. We will be able to research detail subjects about the curve symbol of tooth without cutting off it. Because the contour of a incisal ridge-aspect obtained from composition of 12 separated contours, which written by contracer, of crown length of each tooth.

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In August of 1970 the author conducted somatometrical research of head and face of 195 adults (93 male and 102 female), the inhabitants of Katsumoto, and the results were discussed. Further-more, the correlations between the measurements of head and face, and those of dental arches and palate height were studied. The main results obtained are as follows : A) Somatometry 1) Head length : the mean value for the male is 186.9mm and for the female 177.9mm. Both belong to Short Type. 2) Head breadth : the mean value for the male is 155.5mm and for the female 148.4mm. Both belong to Broad Type. 3) Bizygomatic breadth : the mean value for the male is 144.0mm and for the female 136.8mm. Both belong to Broad Type. 4) Morphological face height : the mean value for the male is 131.9mm and for the female 122.8mm. Both belong to High Type. 5) The head-type of the inhabitants of Katsumoto belongs to Short Type and the face-type to High Broad Type. The brachcephalization and other generation-difference were noted apparently in the inhabitatants of Katsumoto. B) Correlation 6) No significant correlation is noted between the head length and the dental arch length. 7) Concerning the breadth, the significant positive correlations are noted only in the male between the breadths of head and dental arch, between bizygomatic breadth and inferior dental arch breadth and between bigonial breadth and inferior dental arch breadth, while the significant positive correlation is noted in both male and female between bizygomatic breadth and superior dental arch breadth. 8) Concerning the heiht, the significant positive correlation is noted between the head height and palate height only in the male, while that between morphological face height and palate height is noted in both male and female. 9) Concerning the length and breadth, the significant positive correlation is noted only in the female between the head length and superior dental arch breadth. 10) Concerning the length and hieght, no significant correlation is noted at all. 11) Concerning the breadth and height, the significant positive correlation is noted only in the male between head breadth and palate height. Whereas the male and female are studied respectively as above, when both sexes of Katsumoto inhabitants are observed as a whole, the significant positive correlation is apparently noted between the breadth in the various correlations between head and facial dimensions and dental arches and also palate height. Also, between the head and face, the face shows conparatively more significant positive correlation between both dental arches and palate height, and the head shows extremely frequent cases of positive correlations between superior dental arch and palate height than between the inferior dental arch and palate height.

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Based on Prof. Nakayama's view (1956) that the splitting line system, produced by penetration of needle with India ink along the main fiber fascicle of the tissue, is the manifestation of the growth direction of various tissues and the irregular splitting lines show the sign of disturbance thereto, and also on the presumption that the growth of nerve fibers plays the chief role in the determination of the central nervous system structure and their growth, and the trace of growth of the nerve fibers should be regarded as the line system of the splitting lines, the author presumed that the splitting lines of the white substance of brain indicates the direction of the nerve fibers in that area, and the line system exhibits the nervous tracts. Using an extracted brain without pathological portion of a grown-up human, and getting the specimens (4mm to 2.5mm thick) cut off from frontal, sagittal and horizontal directions with the frontooccipital-pol line and longitudinal fissure of cerebrum as the datum, the author applied the penetration of needle with India ink with the well studied pyramidal tract as the guide, and have obtained the following conclusions : 1. The lower part of the line systems from the precentral gyrus runs toward posterior mesial, turning its direction above the lentiform nucleus, and flows into the internal capsule knee or posterior crus. The upper part of them runs toward the mesial lower part and becomes the laterally convex arched line system group at the semioval center, and its lower end flows into the posterior crus of the internal capsule. The line system inside the internal capsule is seen as the arched line system group approximately aligned with the direction of the internal capsule, and passes through the central part of cerebral crus via the external area out of the hypothalamus. As it enters the bridge, it becomes the line system group scattering radially, and lowers down crossing with the transversal line system group in the bridge. The line systems staying in the bridge in the course of passage are seen at the abdominal inner part and dorsal outer part of the basal portion of bridge. The downward line systems get together again at the lower end of the bridge and lowers down through the pyramis of medulla oblongata, and those at the dorsal side of pyramis cross at the center from right and left directions, and those at the abdominal side are seen to go right down through the pyramis. 2. The splitting line systems from the precentral gyrus are observed to be uniformly parallel in their passage, and no sagittal nor transversal disorder is seen, indicating the nerve fibers are bundled together. They run in regular arrangement from lower to upper portion, from front to rear of the knee and posterior crus inside the internal capsule, and the frontal portion runs through the mesial side and the rear portion runs through the exteranl side in the central part of cerebral crus, taking the similar positions in the bridge, too. Above observations apparently show the passage of pyramidal tract and the notion of functional somatotopic localisation as stated in the text book, leading to the belief that the splitting line system method performs a great role in the research of the nerve tracts of the central nervous system.

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This experiment was made by the author in order to learn what kind of change may arise in the splitting lines' condition of the patellar articular surface and menisci, the articular fossa complemental to the knee joint, after sciatic nerve amputation. Adult dogs 2 years post natal were used for the experiment, and the sciatic nerve was cut off by about 1 centimeter long along the inferior border of the right gluteus maximus. Comparative observations of the said conditions of splitting lines were made on the 8 different stages ranging from 1 and 2 weeks, 1 to 6 months post operations pursuing the changes in the course of time. Following are the summaries of this study : 1. With regards to the splitting lines of the patellar articular surface, the whole surface of apical half was filled with irregular splitting lines in two weeks post operation, then the number of these irregular splitting lines increased toward the basal half with some fluctuation of the increasing rate depanding on the stage. However, distinct line systems were observed in the basal half closer to the basal edge until 6 months post operation. This changing condition is considered to be the increased irregular splitting lines appearing as the defence reaction due to the friction between the patellar surface of femur and patellar articular surface, in proportion with the atrophy of the patellar surface of femur. 2. In the case of splitting lines in the menisci, the changes are in short represented by the straightening of the arched splitting line systems attended with the appearance and disappearance of the irregular splitting lines, and no increase of the irregular splitting lines by the passage of time was observed. This is considered to be due to the loss of shock absorbing function of the menisci to weaken the pressure and friction existing between the medial and lateral condyles of the femur and tibia. In summary, the changing condition of the splitting lines in the patellar articular surface and menisci, the articular fossa complemental to the knee joint, after sciatic nerve amputation is considered to be illustrating the changing process of the fibre arrangement trying to adapt itself to suit the remaining function, responding to the atrophy process of the main articular surfaces.

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Muhlreiter (1928) pointed out the curve symbol, root symbol and angle symbol as the components to identify the rightness or leftness of the tooth. The curve symbol, one of these three symbols, is an importante element in the plaster sculpture, yet the matters relating to the curve symbol such as the angle to compose it, its position or the relationship with the adjacent tooth have not been explained. These have been reviewed in this laboratory to get effective guides for dental anatomy, and Mizuki (1977) has already made the matters clear concerning the right maxillary anterior teeth in this respect. The author followed the method employed by Mizuki and investigated the extracted maxillar right premolars. Their crown lengths were transversally separated into 12 sections of even space, the contour of each separating line recorded by the contracer, and the angles formed by the curvatures from the buccal to the mesial direction and that from the buccal to the distal direction were also measured. Detailed study of the data thus obtained was made from various view points, and the following conclusions have been reached in due consideration : 1. In the observation of the contours by the occulsal aspect of the maxillar right first premolar, the portion visible from the occulsal side is the area from the 5th separating line toward the occulsal surface. This is the area where the curve symbol is usually observed to identify the rightness or leftness of the tooth. The portion observed for such identification at this time is not the outermost contour, but where the difference between the mesial and distal curvature angles is most peculiar near the outermost contour, or the area around the 9th separating line. 2. Also in the maxillar right first premolar, it is learned that the mesial curvature angle is greater than the distal one at the two separating lines of the 8th and 9th, and an apparent curve symbol exists here contrary to the anterior teeth. Since the 9th separating line is where the curve symbol is most significatntly great, if the curve symbol is to be observed by the cut off surface of the tooth, it may be cut off at the 9th separating line after 12 separating lines were marked on. 3. In the case of the maxillar right second premolar, no curve symbol is observed at all as noted by the text book. If the comparison of the mesial and distal curvature angles is needed, it may be done by cutting off the tooth at the 7th separating line where the angle difference is greater by the same 12 separating lines method. As observed above the curve symbol may be studied by obtainining the 12 separating contours by the use of contracer.

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Abe (1959) of this laboratory stated that the direction of the splitting lines approximately coincide with that of the hair stream in his study of the relation between the splitting lines and hair stream of embryonic skin, and pointed out that the splitting lines are conditioned by the running direction of the fiber fascicle at the superficial layer of corium, and at the same time the hair stream is conditioned by the direction of fiber fascicle at the border between the corium and the subcutaneous tissue, where the hair bulbus are placed. However, no work has been reported on the relationship between the splitting lines of skin and the growth direction of the fat tissue layer. The author presumed, in view of the fact that the fat tissue is one of the components of the skin, though positioned at the deepest layer, that the growth direction of the fat tissue layer would coincide with the splitting lines direction, if the line system of the splitting lines is the manifestation of the growth direction. For this purpose, observations were made on the relations of the splitting lines and growth direction of the fat tissue layer in the trunk where the growth of fat tissue layer is notably seen in the human embryo, examining 15 samples altogether, or 3 samples each of the breast, upper and middle abdomen, lower abdomen, back and gluteus. Usual observation and experiment were made to the splitting lines of the skin, but special attention was paid to do not hurt the subcutaneous tissue in peeling off the skin to expose the fat tissue layer. In the observation of the fat tissue layer, the configurations, size and positional arrangements of the fat granules were observed in detail through the magnifier. Following conclusions have been obtained by these observations : 1. The conditions of splitting lines of skin and those of the fat tissue layer are, although slighty different in the umbilicus region, generally in well aligned mutual relationship. In the fat tissue layers of the areas, corresponding to the independent line systems of the splitting lines, fat granules of ellipsoidal shape and of respectively different sizes are arranged, and as their length diameter leads to an uniform direction, indicates the obvious growth direction of the fat tissue layer. This direction conforms well to the direction of the line systems of the splitting lines. 2. Some areas surrounded with 2-3 independent line system groups are filled with irregular splitting line groups. The fat tissue layer corresponding to such area is collecting small fat granules of cuboidal shape and does not indicate any direction. 3. Above observations evidently prove prof. Nakayama's view that "the line system is the manifestation of the growth direction and the irregular splitting lines show the disturbance of the growth direction", or in other words "the splitting lines are the growth architecture."

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By the observations of the enamel projection on the buccal, mesial and distal surfaces of the maxillary molars, using 197 samples of maxillary first molar and 110 samples of the maxillary second molar, classifying them into five types according to the projection lengths, the author observed the appearance frequency of each type and measured the length of enamel projection, and have obtained following conclusions : 1. The appearance frequencies of the enamel projection in the maxillary first molar are 77.7% on the buccal surface, 46.8% the mesial surface and 43.2% the distal surface. In the maxillary second molar, they are 93.3% on the buccal surface, 71.8% the mesial surface and 71.0% the distal surface. The frequency relating to each of the respective surface is significantly greater in the second molar than the first molar. 2. The frequency in the first molar is of such order as the Type 2 : 43.7%, Type 3 : 23.9%, Type 1 : 22.3% Type 4 : 9.6% and Type 5 : 0.5% on the buccal surface, indicating significant differences between the Type 2 and 3, Type 4 and 5. Only Type 1 : 53.2% and Type 2 : 46.8% appear on the mesial surface, and on the distal surface three types only, or Type 1 : 56.8%, Type 2 : 42.6% and Type 3 : 0.5%. In the maxillary second molar, such frequency order as Type 2 : 40.0%, Type 3 : 30.9%, Type 4 : 20.9%, Type 1 : 6.4% and Type 5 : 1.8% on the buccal surface is seen but the difference between the types is not significant. On the mesial surface, 71.8% of Type 2 is evidently greater than the only remaining Type 1 : 28.2%. Also on the distal surface is seen as same as on the mesial surface at all, Type 2 : 71.1% and Type 1 : 28.9%. 3. In the observation of the type combination of each surface, the combination of Type 2 of the buccal surface and Type 1 of both mesial and distal surfaces is the foremost with 22.9% in the first molar. In the second molar, the combination of type 2 in all of the buccal, mesial and distal surfaces is the foremost with 29.2%. 4. The lengths of the enamel projection on the buccal surface of the first molar are 0.97mm for Type 2, 2.79mm : Type 3 and 3.38mm : Type 4. In the second molar, Type 2 is 0.86mm long, Type 3 : 2.53mm, and Type 4 : 3.77mm. 5. Observing together with the appearance frequencies of the enamel projection in the mandibular molars reported by the author et al. in 1969, the appearance of enamel projection in the second molar, the closer one to the distal end of the dental arch, is more frequent than in the first, then this paper suggests to me, that may have some inter-relationship with the dental degeneration.

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This study was performed in order to observe the effect of ^<60>Co γ-ray irradiation on rabbits' mandible, for as long as possible, approximately 18 months. Materials used were 56 adult male rabbits, weighing approximately 2.5Kg. They were subdivided into four groups : Group 1 was irradiated 5, 000 R (9 cases), Group 2, 8, 000 R (12 cases) and group 3, 10, 000 R (12 cases) respectively. Group 4 was a control group and was given no irradiation (23 cases). Dosimetry was performed with a Victoreen R-meter, chamber 621 in air. Irradiation method was as follows : Prior to irradiation, the rabbits were anesthetized with subcutaneous injection of 25% Uretan solution. Radiation equipment used was ^<60>Co double rotation apparatus, RT 2000 made by Shimazu, Containing approximately 1300 curie of ^<60>Co, with Filter 0.5mm Cd., Field size 4×4 cm. Anesthetized rabbits were fixed, except the head, in a specially constructed metal box. Between the focus and the animals, a 10×10×15 cm Pb-schield block with a 15 mm perforation in the center was placed as close to the head as possible, and then, irradiation was performed through the hole towards the right side of the mandible as a single dose. Gross examination, radiographical and histopathological studies were done after irradiation. Results obtained can be summarized as follows : 1. Depilation was noticed on the irradiated field of the rabbits' skin in the three respective groups. The more dose of radiation given, the earlier the onset of depilation occured. 2. The upper anterior teeth of all experimental animals showed elongation, lateral flection and diasthema. 3. Gross examination and radiologic investigation of the lower anterior teeth showed shortening or disappearance of the crowns and resorption of the root apex in all experimental animals. These teeth were lost eventually. Molar teeth disclosed shortening of crowns and irregular and partial loss on the surface of the dentine. Pulp chambers were extremely narrowed. These changes were most conspicuous in the 10, 000 R irradiation group. 4. Mandibular fractures occured in 13 cases, which include 3 cases with 5, 000 R, 4 cases with 8, 000 R and 6 cases with 10, 000 R. 5. Histopathological examination revealed that the alveolar bones were resorped, as the result, and were replaced with mandibular bone trabeculae. Various types of ankylosis of root surface and mandibulars were seen. These changes were more frequently noted in the molar regions than the anterior regions and in the groups with higher doses and longer days after irradiation. 6. Bone trabeculae and cortex of the mandibles were resorped in the 3 irradiation groups in the early stage, but regeneration and thickening of the bones occured later. 7. The usual case was that the anterior bone marrow became more gelatinous and the molar marrow became more fibrous. Hyperemia and abscess formation were recognized in some cases. Although in the molar regions these pathological changes were conspicuous in proportion to the amount of dose, in the anterior regions, the same changes were more conspicuous in the 5, 000 R irradiation group than in the 8, 000 R group.

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It may appear that the absolute criteria for the evaluation of the image of radiograph do not exist, because the evaluation is greatly swayed by the final subjective judgement through the vision of the observer (the dentist). But as the formation of radiograph is based on physical reactions between the x-ray source, the objects, the x-ray film and so on, the physical factors on the radiograph image can be chosen as important objective criteria for the evaluation of the image quality. The major physical factors on the radiograph image are usually classified into three categories, namely, density, contrast and sharpness. The effects that the mutual relations between physical elements, such as x-ray source, objects and x-ray film, have to each of the major physical factors were examined experimentally, using dental x-ray source, several kinds of phantoms of oral tissues and dental films, The results obtained were summrized as follows : 1) The higher is the γ (density gradient) of dental x-ray film having the density (D=1.0&acd;1.2) optimum for the best diagnosis on the details of the object, the better becomes the image contrast. Nevertheless, as for the wider density range (D=0.3&acd;1.8) optimum for the universal diagnosis throughout the whole image, the higher the γ value the less the obtainable information. The optimum density range for dental radiograph image should be limited to about 0.45&acd;1.8, because the most radiopaque tissue like a tooth is contained in the object (the oral tissues). 2) The effective value of γ differs from one another even when the film density is identical. The thicker the layer and the higher the value μ (absorption coefficient) of the object, the lower the effective value of γ. 3) In general, the higher the value μ of the object the better the contrast of radiograph image, particularly where the object layer is thin. But when the value μ is quite high as a tooth, the contrast is extremely bad where the object layer is thick (more than ca. 8mm), and when the value μ is quite low as muscles the contrast is very bad where the object layer is thin (less than ca. 10mm). As for the object having a medium value of μ as bones the contrast is nearly proportional to the difference of the object thickness. 4) In general, the lower the value KVp (tube voltage) the better the contrast of radiograph image, particularly where the object layer is thin. But when the value μ is quite high as a tooth and that layer is thicker than ca. 8mm. the lower the value KVp the worse the contrast. 5) The contrast of radiograph image of decayed bones tissues in the soft tissue differs in accordance with the range and degree of decay. The larger the range and the harder the degree of decay, the better the contrast. 6) Density difference (contrast) is hardly obtained on the dental x-ray film image by the soft tissue of less than 10mm thickness. The thickness contrast (density difference obtained by every unit thickness) of the bone tissue is ca. (0.02&acd;0.05)/mm. and that of tooth tissue is ca. (0.04&acd;0.07)/mm. 7) The contrast of radiograph image is decreased by the effect of scattering x-ray, The value of decreasing rate was ca. 12% on the dental phantom image, but the value was augumented to ca. 15&acd;20% on the clinical dental radiograph image because of the additional scattering x-ray from the surrounding tissues. 8) The image unsharpness on dental radiograph film results mainly from two geometrical factors. One is the well known penumbra effect caused by the extension of tube focus, and the other is the geometrical absorption distance effect which has been hitherto payed no attention. For most of the dental image unsharpness the absorption distance effect (absorption unsharpness) is responsible. Only by the restricted cases where the object edge is located to the very proximity of the x-ray center axis, appears the penumbra effect. 9) The

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Vital pulp amputation was performed on the pulps of 9 root canals of human teeth, and the amputated pulp was covered with Calvital. The teeth were subjected to histopathologic analysis for the purpose of studying the blood vessels at the site of dentine barrier formation. Results were summarized as follows. 1) Remaining blood vessels are found at the site of dentine barrier formation of six root canals and two of them have very important blood vessels. These blood vessels exist between outside and pulp at the site of dentine barrier formation. 2) On the formation of dentine barrier in the human teeth, it often happens that remaining blood vessels at the dentine barrier become inhibitory factor of the formation. 3) The closeness is not always performed between outside and pulp by the formation of dentine barrier. From a clinical point of view, the above items 2) and 3) must be kept in mind for the performance of a vital pulp amputation.

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An observation on the transformation of screw-shaped blade of hand-reamer occurring with using for mechanical enlargement of root canal-wand were employed through measuring microscope (PRM-3XYZ). The materials available for this study consisted of a total of 561, 293 in Maillefer's reamers, 268 in Colorinox's reamers (table 1) which came into go out of use in endodontic practice of the hospital attached to this college. The deformation of blade form were observed as attrition or extension of each screw margin for the most part. The range of such changes (1_2 ; see Figure 1) within an effective blade was very variable according to each type of handreamer used. The measurement values obtained were as follows. 1. The range of deformation in Maillefer's No.1 reamers were 0.577 to 7.310mm distant out of the apex of reamers, in No.2, 3, 4, 5, 6 reamers of the same kind, 0.496 to 6.867mm, 0.493 to 6.697mm, 0.616 to 6.026mm, 0.591 to 6.936mm, 0.695 to 7.298mm, respectively. 2. Those in Colorinox's #15 reamers were 0.685 to 7.180mm distant out of the apex of reamers, in #20, 25, 30, 35, 40 reamers of the same kind, 0.426 to 6.375mm, 0.491 to 5.944mm, 0.804 to 5.996mm, 0.668 to 6.141mm, 1.119 to 6.842mm, respectively. 3. From the results mentioned above, it is considered that we should be careful fully in clinical common treatment of available reamers when the range of deformation came up to less than 8.0mm from the apex.

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We are investigating the disease prevention of the tooth, the gingiva and their oral environment. In our recent study, the new caries activity test "Cariostat Test" has been applied in addition to Snyder test. The subjects of the study consisted of 40 females aged from 19 to 20 years and the data obtained were compared with relations between the results of caries activity and the number of decayed teeth. The results were summarized as follows. 1. The Cariostat test was positive in 40.0%, and negative in 60.0%. The Snyder test was positive in 32.5%, questionable in 45.0%, and negative in 22.5%. 2. The Cariostat test was tested 3 times respectively among those 40 cases, and 70.0% of them were consistent with results through the 3 trials. 3. The Cariostat test and the Snyder test had significantly high degree of correlation with the number of D-T. 4. The result of the Cariostat test was equal to that of the Snyder test in 72.5%.

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In the radiographic image diagnosis of Regio viscerocranium, such problems have been noted as the difficulty in collecting accurate information from a single radiographic image because of the excessive object-contrast unavoidable due to the compilcated structure of the Regio viscerocranium, or the film economy as several radiographs need to be taken by different radiographic exposures for above reason, which further leads to the denger of dosing unnccessarily over exposure of radiation to the patient. The author reviewed what was developed and iotroduced by Edholm and Jacobson (1971), selecting from the several compensating filters devised to solve these problems, and have obtained radiograph of excellent image quality with which the film contrast was not hurt but the object-contrast was improved to deliver better image imformation. Besides, the dose to the patient may be reduced by about 30% less than the normal radiography. In order to comply with the recommendations of the ICRP Publication No.16 which demand reduction of the dose to the patient as well as the diagnosis by high image quality, it is considered that this kind of compensating filter should be used more extensively.

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