The structures and developmental process of guinea pig's lower molar teeth were studied histologically using varying developmental stages from 30 fetal days to postnatal 7 days, new-born and adulthood. The results obtained were summarized as follows. 1. The cheek teeth, which were rootless and continued to grow as their occlusal surfaces were worn down, were compound teeth composing of three plates, mesial, distal and central plates. Each plate were covered with the enamel circumference of the dentin from occlusal to basal side, except only the lingual of them which was covered with the primary cement. There were stood between each plate the cartilage cement with which they were fixed strongly. 2. The periodontal membrane between the lingual cement and the alveolar bone showed structure similar to those of the rooted teeth. However, those between neighboring teeth showed characteristic construction to the present animals ; on the surfaces of the enamel there were distributed at almost regular intervals the cement pearls, from which the bundles of Sharpey's fibers were radiated and intersected with those of the opposite side from the lamina propria mucosae of the gingiva to the tip of the alveolar septum. On the surfaces of the enamel among the cement pearls there were arranged distinct layers of epithelial cells from the enamel organ of the basal portion to the oral mucosae, but their appearance varied depending on their location. 3. The Sharpey fiber bundles disappeared after the lapse of sudden loosing and resolving below the lamina propria mucosae of the gingiva. 4. The majority of germinal tissues in the basal end composed of large enamel organ occupied buccal and bilateral side, the dental papilla and dental sac surrounding them. As following toward the upper end, however, another small enamel organ was occurred within the lingual side of the distal dental papilla. Thereby, the distal dental papilla was divided into two parts. Large and small enamel organ were connected with only outer and inner enamel epithelium at the lingual side of the dental papilla. This connection portion were disappeared presently, and then replaced with dental sac, instead of them. 5. The mesial plate was made of the mesial portion of large enamel organ and the mesial dental papilla, the central and distal plates were made of the distal portion of large enamel organ, small enamel organ and two divided distal dental papilla, respectively. As following toward the upper end, the central portion of large enamel organ and small enamel organ were replaced with the dental sac from which the cartilage cement were formed. 6. The cartilage cement was derived from the growth of the cartilage cement pearls, and the cartilage cement pearls were based on the cement pearls. The cell nucleus of the cartilage cement showed almost necrotic degeneration. 7. Each molar teeth were developed with conical two cusps, but at the tip of the cones enamel formation did not take place. By reason of occlusion movement based on some physiological irritation, the conical cusps flattend at birth. Through thus attrition, the central plate became to appeared gradually between the mesial and distal plates. 8. The deciduous premolar showed crown shaped appearance with three cusps. There were seen at the tips of the cusps as free enamel area as the cusps of the molars. Conspicuous absorpting phenomenon was observed in the cervical dentin after 45 fetal days, without nearly forming their roots. 9. Order of these rooted and rootless teeth to erupt was as follows ; pm and M_1 (fetal 50 days), PM and M_2 (fetal 55 days) and M_3 (within a week after birth). By fetal 55 days, deciduous premolar came into shedding.

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Tooth eruption has been clinically considered to cover a definite time interval from the moment of the first appearance of a section of tooth crown on the top of alveolar ridge until full exposure and attainment of the crown to the occlusal position. In the present study, the whole process of permanent tooth eruption was divided into 4 consecutive stages or degrees according to sizes of tooth crown as it appeared into the mouth, and the 1st to 4th degrees of eruption respectively refered to 1/3, 1/2, 3/4 and 1/1 the full size of crown appearance in the mouth. By means of alotting the coefficients, 0.3, 0.5, 0.75 and 1.0 to each of the above 4 degrees of eruption, frequency of each degree for individual teeth was converted so as to obtain eruption rate and time, M^^-_2, F^^-_2 for the male and female subject groups respectively. Studies on the incidence of dental caries among primary and secondary school children have so far relied on DMFT as an important indicator under a general notion that individual permanent teeth has the same degree of eruption. The present study undertook to investigate the rate of DMFT of individual teeth with reference to different degrees of eruption shown by each tooth, and following results were obtained. 1. Frequency of Eruption of Individual Permanent Teeth Hardly any difference was noted in the frequency of eruption among pairs of the same named teeth on both sides of upper and lower jaws. The frequency of eruption, however, was higher in the teeth of lower jaw than in those of upper jaw, and was lower in teeth of the male subjects than in those of the female subjects. When individual teeth were compared, the first molar showed the shortest period of time for completion of eruption through both sexes of subjects, followed by central incisors, lateral incisors, 1st premolars and 2nd premolars in order. The canine and the 2nd premolar were the latest in the completion of eruption. The frequency of eruption as examined within limit of one year period was slightly smaller when the degree of eruption was taken into account. 2. Eruption Time of Individual Permanent Teeth Symbols M^^-_1 and F^^-_1 were arbitrarily given the conventional eruption time for male and female groups of subjects, and symbols M^^-_2 and F^^-_2 were respectively given to the eruption time adjusted by the degree of eruption in both sexes groups. Results showed that the female had earlier eruption time than the male in both cases as illustrated by the formulae, M^^-_1>F^^-_1, M^^-_2>F^^-_2 and M^^-_1>M^^-_2, F^^-_1>F^^-_2. 3. Rate of DMFT Comparison in the rate of DMFT between antagonizing teeth of four quadrants did not yield any noticeable difference of statistical significance within the same sex group. The rate for the male being ranged from 14.3% to 32.4% and the one for the female from 11.8% to 28.5% and the rates for both sexes being increased during the interval from 72-84 months to 180-192 months of age. Generally, every teeth in the female suffered dental caries after eruption earlier than in the male, so that the teeth except the cuspids in the female showed signs of incipient caries as early as one to two years after eruption. When the degree of eruption was taken into consideration, caries lesion was first seen almost during the period of 4 degree of eruption and in fewer cases at 3 degree of eruption. The relation between the degree of eruption and the time of caries incipience may be understood more fully, if teeth were observed in detail by classifying them into groups divided at every 4 months of age after completion of eruption. 4. F-T Rate There was no appreciable difference in F-T rate between the teeth on both sides of the same dental arch nor between those of upper and lower jaws. The rate for the male was 20.0% and for the female 22.7% at 72 to 84 months of age, both of which increasing with progressive age and reaching respectively 55.0% in

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A study was undertaken to look into the general pattern of nerve distribution in the growing molar teeth of rats from birth to 50 days of age, and results obtained were summarized as follows. 1) Directly after birth of the animal, presence of tooth germs of both 1st and 2nd molars could be seen in both upper and lower quadrants of jaw, of which the former was in an early form of the bell stage and the latter appeared far less developed than the former. In the loose connective tissues filling between basal portion and bony sac of the 1st molar tooth germ, there was observed a small bundle of nerve running collaterally with tiny blood vessels. The nerve bundle was consisted of a few nonmedulated nerve fibers, and stopped there without entering into the dental papilla. 2) By 3 days after birth of animal the whole body of the casps of 1st molar germ except occlusal tip was deposited with enamel substance. Many tiny blood vessels were seen entering into the dental papilla. In the tooth germ of 2nd molar, on the other hand, formation of thin layer of enamel substance was seen only along the oblique surface of the casp. At this stage of growth, a single nerve fiber of finest size in company with tiny blood vessels could be seen entering into the lower part of dental papilla, frequency of which being one in five cases. In the 2nd molar tooth germ, one could see small nerve bundles running through its basal dental sac, but they were never seen to enter the dental papilla. 3) By 10 days after birth of animal, there was already seen formation of tooth roots starting in the 1st molar, and appearance of 3rd molar tooth germ of upper jaw in early shape of bell stage. At this time, some of the nerve fibers were seen to ascend through the tooth pulp, branching on the way to become non-medulated, and reaching as far as to odontoblast layer with their terminal branches. In the 2nd molar tooth germ at this stage, number of the nerve fibers to be noticed to enter into the tooth pulp was yet very limited. 4) By 15 days after birth of animal, enamel substance of the 1st molar showed increased calcification and, with accerelated growth of the root, the whole length of tooth became extended. Growth of tooth roots had also begun in the 2nd molar, and in the 3rd molar germ there was now appearance of small blood vessels within the enamel pulp. There could be seen in the 1st molar the nerve fibers reaching at this time as far as to the odontoblast layer near the pulpal horns, whereas in the 2nd molar no such nerve fiber was seen reaching there, and in the tooth germ of 3rd molar not a single nerve could be seen entering the dental papilla. 5) By 20 days after birth of animal, the 1st molar had begun to erupt and the nerve tissue, now enriched in quantity, had formed a nerve plexus beneath the odontoblast layer and sent terminal branches there. These, however, failed yet to reach the young dentine. In the 2nd molar, on the other hand, the nerve fibers, accompanied by tiny blood vessels, were seen to have reached the odontoblast layer, although fewer in number as compared with those found in the 1st molar. Distribution of the nerve tissues into the dental papilla could not yet be observed with the 3rd molar teeth at this time. 6) By 40 days after birth of animal, the 1st molar was completely erupted and the nerve fibers and also those of the 2nd and 3rd molars likewise became more and more increased and complicated in their amount and running although not to the full extent of nerve development to be attained in the final stage of tooth maturity. In the 3rd molar, the nerve fibers were far less-numbered than in the other two and their running was correspondingly simpler. Even at this time the ends of nerve fibers failed to reach the odontoblast layer.

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Researches on the fibrous architecture of capsule of animal organs based on the splitting line method have been practiced for many years, and a series of reports have been submitted on this subject. However, it is noted that the existence and significance of the irregular splitting lines have not been mentioned in these reports, al hough the line systems are the main concern of their observations. It was by Dr. Nakayama (1956) that the meaning of existence of the irregular splitting lines was taken up and disclosed for the first time. After accumulated studies, he offered the following statements : "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 various 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 defense reaction of the tissue itself. Accordingly, the growing stages of the tissue and organs can be learned by combined observations of the line systems and the irregular splitting lines." In the report of Klaus Niessing (1935) the splitting lines appearing on the kindey capsule of sheep, observations on the line systems were presented but nothing was mentioned on the irregular splitting lines. In this study the author has observed the aging changes of the splitting lines of the fibrous capsule (deep layer) of dog's kidney, respectively at such growing stages as 10 days post-natal, one month, 2 months, 4 months, 6 months, 8 months, 10 months, 1 year, 2 years, 4 years, 6 years, 8 years, 10 years and 12 years, to compare the findings with K. Niessing's opinion. Following conclusions have been obtained by the review that was made based upon Dr. Nakayama's points of view : 1. The splitting lines in the fibrous capsule (deep layer) in the kidney are not merely of the line systems alone as indicated by Niessing, but obviously distinguishable to be the mixture of line systems and irregular splitting lines, or more precisely, the irregular splitting lines are dominant. 2. The tendency of loop formation especially in both abdominal and dorsal surfaces realistically portrays the growing stages of the fibrous capsule itself of the kidney that corresponds to the pulsative volume fluctuation inherent to the appearance of kidney functioning. 3. The indication of K. Niessing that the pulsative volume fluctuation is stronger in the abdominal surface than in the dorsal surface can be analogized from the difference of the splitting line conditions between both surfaces. 4. The irregular splitting lines appear distinctively throughout the whole aging stages and include what may be called even the "irregular splitting line systems". Similar fact by Nakamichi can be observed in the splitting lines on the mucous membrane of the tougue, a muscular organ that demonstrated polymorphic active motions. This is another proof which emphasizes the existence and the meaning of the irregular splitting lines. 5. The kidney growth of the dog is classified into four stages as below by the aging change of the splitting lines in its fibrous capsule : a. Incipient growth stage (10-30 days post-natal) b. Rapid growth stage (2-8 months post-natal) c. Maturation stage (10 months-6 years post-natal) d. Atrophy stage (8-12 years post-natal)

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In Prosthodontic cases, there are some patients who need minor tooth movement because of abnormal tooth position and/or inclination. Recently we had a chance to treat the female patient whose upper left central incisor had been extracted about six years ago and opposite teeth was disarranged. On this case, first, left lower central incisor was extracted according to the X-Ray diagnosis and examination of study model. Then the minor tooth movement was applied to the lower anterior teeth by means of multibanded system. After the orthodontic treatment was finished, the upper right central incisor and left lateral incisor was prepared for the bridge construction and hydrocolloid impression was taken. The working model was made of hard plaster and mounted on the Tsubone's MS type articulator which was improved for the purpose of crown, bridge and partial denture construction and diagnosis of occlusion. According to the diagnosis of occlusion on the articulator, the patient's occlusion was group functioned occlusion. Therefore the same occlusion pattern was given to the metal bonded porcelain bridge and set. In this case, minor tooth movement was not applied to the abutment teeth but to the opposite teeth related to the pontic. This article describe a method of making a satisfactory bridge in occlusion and appearance to this patient.

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The palatal cleft is usually obturated prosthodontically after plastic operation. However, when the patient is too aged, the plastic operation of the cleft palate is impossible and so the improvement of the function or the appearance should be attributed to only the cleft palate prosthesis. For such a case, a useful apparatus having the functional dental arch, periphery and basal surface was fabricated by the application of the flange technique and the dynamic impression method involving replacement of the impression with the elastic rebasing material. This showed good retention and stability in service, and the appearance as well as the masticating, swallowing and sucking efficiency was successfully improved.

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Orthopantomography has been widely used in dentistry. The present report concerns the value and limitation of orthopantomography for the diagnosis of mandibular fractures. Orthopantomography to be a better radiological approach than the other projections as far as the detection of mandibular fractures. But Orthopantomography is not a technique which replaces the other projections in the radiological examination of the mandible. Each technique supplements each other.

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