An experimental study was conducted with dogs into how the functional decline due to complete removal of m. masseter on one side affects the morphological growth of the mandible. The dogs used for the experiment were 1.5 to 2 months old (1.5 to 3.2 kg.) and were operated on the left side, with the right side as control. Forty dogs were divided into seven groups, Group I undergoing the experiment for one month, Group 7 for seven months and were observed by macroscopic, radiographical, osteometrical, and splitting-line methods. The findings are summarized as follows : 1. In Group I, osseous proliferous hypertrophy was observed in the masseteric fossa and the crest of the condyloid process on the experimental side. Radiographically it was found that the osteotrabecula were arranged irregularly and loosely and the splitting lines were irregular. The osseous proliferous hypertrophy increased with the passage at time, reaching the maximum in Group 4. Radiographical examination disclosed increasingly obscure pictures, and splitting-line examination revealed an expansion of the area of irregular lines. But in Groups 5 to 7, the surface of the massetric fossa and the crest of the condyloid process tended to become smooth in the same way as on the control side, and radiographical penetration grew more difficult, while the irregular lines tended to become normal. 2. No difference was observed between the two sides in the eruption of teeth, but the formation of interdental spaces between premolars came later on the experiemntal side. X-ray penetrated through the interradicular alveolar septum of the fourth premolar and the first molar more distinctly on the experimental side. 3. In all groups, a reduction in distance or angle was observed on the experimental side in the length of the mandible (if - cd, cl. cm. goc. crc, crd), the height of the coronoid process (crd - gov, cd -crd), the height of the condyloid process (cd-gov, (cl-gov, cm-gov), the length of the condyloid process (cm-cl), the body angle of the mandible, the inclination angle of the condyloid process, the height of the mandible body of premolars (ap_2^^--a'p_2^^-, ap_3^^--a'p_3^^-, ap_4^^--a'p_4^^-). This was conspicuous especially for if-goc, crd-gov, cd-gov, cl-gov, cm-gov, cm-cl, the body angle of the mandible, and the inclination angle of the condyloid process. An increase was observed in the height of the mandible body of the molars, the angle of the processus coronoideus, and the height of the edge of the incisors. The reduction in the length and angle of the various parts are manifestations of functional morphology due to the incision of the m. masseter. The osseous proliferous hypertrophy in the masseteric fossa and the mandible body of the molars physiological defense reaction to the incision.

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The literatures which were relative to the transplantation of the tooth germs or the developing teeth were reported numerously Sasano (1932), Glasstone (1935), Apfel (1950), Hirakawa (1955), Yamaguchi (1964) and so on. However, the reports that were performed combined transplantation of the mandibular bone block which was contained the deciduous tooth and permanent tooth germ and that examined it's roentogenological and pathohistological responses were fewer. The purpose of this study was to observe and confirm the responses following auto transplantation of the mandibular bone block with the deciduous tooth and permanent tooth germ roentogenologically (some of them soft roentogenologically) and pathohistologically. The results obtained were as follow : 1) About 14 postoperative days, the roentogenologic or ultra soft x-rays examination revealed the enlargement of the periodontal zone, the tendency of the root resorption of the deciduous teeth and the tendency of the resorption of the bony substances. And the examination revealed that these responses progressed according as time passed. 2) About 30 to 60 postoperative days, the radioopaque schadow were observed newly in the bony block. Especially, it appeared in the deciduous tooth pulp, the dental papilla, the outside of the germ crown and the root apex of the deciduous tooth. 3) It was peculiar that the radioopaque schadow were linear and very like to the proper bone trabecula and it was running radially around the tooth germs. 4) About 120 days after operation, the tooth germs were resorpted and disappeared. And also the deciduous teeth were resorpted but only the crowns were remained. 5) Pathohistologically, the degeneration appeared in the deciduous tooth pulp, the periodontal membrane, the dental papilla, the dental sac and the bone mallow at a few days after autotransplantation. 6) About 10 days after operation, the reactive inflammation began and the formation of the young connecive tissue progressed. Gradually, it was changing to the fibrous, connective tissue. The deciduous tooth pulp, the periodontal membrane, the dental papilla, the dental sac and the bone mallow were replaced by the tissue mentioned above. 7) About 21 to 30 days after operation, the resorption of the root of the deciduous tooth and the surrounding bony substances were progressing. And about 60 days after operation, these resorption were remarkable and so the tooth germs began to be resorpted. 8) In addition, about 30 to 60 days after operation, the new formation of the bone began in the part of the deciduous tooth pulp, the periodontal membrane, the dental sac, the dental papilla and the old bony substaces. Then the part were replaced by the new bone. 9) About 120 days after operation, the tooth germs were completely resorpted and disappeared. The resorption in the new bone was progressing remarkably. The author thinks that this resorption of the newbone and the reductive tendency of the transplanted mandibular bone block were extremely influenced by the specialized circumference as the connective tissue of the abdomen.

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A total of 140 teeth was extracted from 37 dogs and pathonervehistological studies were conducted on the extraction wounds from the 1st day to the 70th day of extraction, and behavour (change) of the nerve tissues in the socket and its periphery during the healing process was studied in detail. Results are summarized as follows : 1. The healing process as studied in the present extraction wounds seemed to follow the usual pattern of wound healing. 2. Immediatly after extraction, nerve fibers in the extraction wounds and peripheral tissues suffered the so-called Wallers degeneration, which was most severe until 3rd day of operation, but the degeneration was not seen by the 7th day. 3. The regeneration of the nerve fiber started by the 3rd day, and became most vigorous by the 7th day. By the 5th day, large nerve plexus consisting of fine nerve fibers came to be formed around the bundles of the degenerated nerve fibers in the space between blood vessels at the bottom of socket. 4. By the 6th day after extraction, there were seen in the granulation tissue two distinct groups of nerve fiber bundles, one of which ascended along the wall and the other through the middle of the wound socket. 5. After the 10th day of extraction, both groups of the nerve fibers reached as high as the top of the socket, and several small bundles of nerve fibers and relatively large-sized single fibers were seen branching off in the midway to distribute in the granulation tissues and newly formed bony structure. 6. After the 30th day of extraction, large networks of blood vessel accompanying nerve fibers were seen to destribute in Haversian canals in the new bone as well as in the bone marrow, and by the 40th day the whole picture became indistinguishable from that of nerve distribution in the surrounding alveolar bone. 7. The whole process of nerve distribution in the healing of tooth extraction wound could be distinguished into the following 4 stages. 1. 1st day to 3rd day after extraction : degeneration stage 2. 3rd to 3rd week : regeneration stage 3. 3rd week to 1st month : readjustment stage 4. After 30th day : completion 8. The extremely fine nerve fibers that were observed in great abundance may be of vegetative origin, and these became sparse and finally disappeared with progress and completion of ossification in the tooth socket. 9. The nerve fibers of fairly large size which made appearance at around 7th day of the beginning of granulation when the granulation in the extraction socket was complete proved to be of sensory origin.

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Occurrence of supernumerary root was found in 4 cases among specimens of extracted human teeth as collected in the laboratory of Oral Anatomy, Kyushu Dental College. This report deals with some observations thereon and our view on this anomaly of tooth root. 1st case : Here an upper left 2nd molar had 4 separate roots, two in the buccal side and other two in the lingual side. These roots started to separate from each other at the cervical quarter of the full length ever widening toward apical direction. A variety of the-ories has been proposed as mechanism for such appearance of supernumerary roots. With the present case where the crown part was considerably large in size, there must have been great need to support the pressure of the crown effectively, and we presume that this led to development of the duplicate roots in the lingual side as reinforcement of supporting strength. 2nd case : This is an upper left 2nd molar with 5 roots. It was characteristic of this tooth that the crown had as many as 8 cusps or tubercles, that is, 4 normal cusps, each one of mesial and distal marginal tubercle, a paramolar tubercle and a central cusp. It is natural for this tooth that the crown should be large enough to accommodate such a large number of cusps or tubercles, and the root should be correspondingly reinforced by the supernumerary root to support the heavy load coming from the large crown. 3rd case : This case deals with 2 upper 1st premolars from both sides of the jaw with 3 roots. Both teeth showed very close resemblance in shape, and had 2 buccal and one lingual roots. Mechanism for the production of such anomaly may be somewhat different from that for the above two cases, because premolar with 3 roots is common in the species of anthropoid and moreover the human milk molar which is predecessor of the permanent premolar likewise has 3 roots. In view of these facts, we suggest that the present case represent a case of atavism of the tooth. 4th case : This is a case of lower right 2nd premolar with 2 roots. Although 2-rooted lower premolar is relatively frequent in its occurrence with respect to the 1st premolar, it is seldom encountered with the 2nd premolar. This case too is ascribed to atavism for the same reason with the above, despite the fact that the lower premolars in the anthropoid as well as in the human deciduous dentition have commonly 2 roots.

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