Fifteen pregnant rats received about 10 mg of sodium fluoride daily per os. Then each litter were fed in the same manner as their mother. After 250 to 300 days the animals were sacrificed for the microscopic study of jaws, lower extremities and internal organs of them. Histologic examination showed a marked change in the teeth, especially in the incisor enamel, and a severe contracted kidney accompanied with a hypertrophy of the parathyroid glands and bone change similar to diffuse fibrous osteodystrophy. The renal change associated degeneration and atrophy of the tubules followed by proliferafion of the interstitial connective tissues and cystic dilatation of the tubules. The glomeruli showed inconspicuous changes but no change of the blood vessels were demonstrable. Despite of the general acceptance that fluorine has some direct action on the bone tissue, there is good evidence that the skeletal change in these cases are supposed to be induced from the renal damage. Moreover it is suggested that the hypertrophied parathyroid glands play some role in this occasion because of the numerous appearance of dark chief cells in it. A slight atrophic changes were noticed in other endocrine glands.
It has already been demonstrated that fluorine has some influence on the tooth, but histological study was very rarely reported. The main purpose of this investigation was to make a histological study of the changes in the dentin of rabbit tooth which was administrated by fluorine intravenously. The dentin stratification which might be induced by fluorine injection is so resistant to weak acid that it can be easily differentiated from other part of dentin under the microscope. It has been assumed that fluorine would deposit as calcium fluoride or fluoro-apatite. The most part of injected fluorine seems to be excreted rapidly and the rest is effective to the odontoblasts. Very small amount of fluorine, therefore, is sufficient enough to cause the dental changes. Moreover it is believed that fluorine exerts a direct local action on the odontoblasts and that the changes observed in the dentin are not produced primarily by changes in blood calcium and phosphorus. It was also considered fluorine has no effect on the alkaline phosphatase in the dental pulp.
In order to investigate the growth factor of tooth, the author preliminary examined the method to measure the velocity of eruption of the incisor of rabbits and noticed Fuse's method to be favorable for the present aim. The growth of incisor for 10 days was measured under the several experimental conditions. 1. The velocity of eruption of rabbit incisor is from 1.05 to 3.55 mm per days in its normal condition. 2. The eruption of lower tooth is faster than that of upper one. 3. No sexual differences is found. 4. Velocities of eruption are not the same on the left and the right side. 5. Cutting the crown accelerates the eruption. 6. Removal of occlusional stress accelerates the eruption. 7. Fast and removal of a pulp retards the eruption. 8. The pulp may transmit external stimulation on the odontoblast and change the velocity of eruption.
In these three years 48 strains of actinomycetes from the 49 actinomycotic lesions of the human jaw were isolated in the clinic of our university. Depending on the Bergey's Manual (published in 1948) these strains were classified into the following groups. Group A. Genus Actinomyces ………………………31 strains Act. bovis Harz 8……………… strains Act. israeli (Kruse) 23……………… strains Group B. Actinomyces-like organisms 13………………strains a. aerobic types, but not Nocardia 5………………… strains b. anaerobic 3………………strains c. gas production in glucose broth, anaerobic………………5 strains Group C. Corynebacterium 4………………strains a. aerobic 2………………strains b. anaerobic 2………………strains It seems to be interesting that actinomycosis can be caused by such strains in Group B and C. At present, from the clinical viewpoint, there is no difference in their symptome between the cases caused by organisms of belonging to the Group A, B and C, but gene-rally, except one case, there is not recognizable so-called “sulphur granules” in pus from cases caused by strains of Group B-c and Group C.
In order to improve technics on the root canal treatment in applying a high frequency current, the author used three different length of the waves ; short waves, middle short waves and diathermy current, and searched the passage of the current heat distribution of the root of the tooth and the tolerant thermal limit of the periodontal tissue etc. by em-ploying human teeth in situ and extracted ones in models. And the following results were obtained. 1. When a needle shaped electrode is inserted in a root canal and a high frequency is sent to the outer side of the root, the current can easily pass through the root wall. In this case, the diathermy passes mainly as conduction current and the short waves act mainly as displacement current. And it was observed, on the contrary of the previous theory, that the current which passed through an apical foramen was extremely little. 2. When the electrode is inserted in the root canal and the high frequent current is supplied as discribed above, the strongest heating takes place at the end of the electrode and the heating spreads over the canal contents, canal wall and the outer surface of the root by turns. 3. The elevation of the temperature of the canal wall by the short waves is mainly originated in the thermal conduction from the interior of the canal and it is considerable, in the case of the diathermy, that Joule's heat effect produced by the conduction current is also added. 4. As to the burning of the near gingival margin which has been reported repeatedly, it is discussed that a considerable amount of heat derived from the convection of the intra canal liquid accumulates at the upper portion of the root canal and then comes through the tooth snbstance to the periodontal tissue. In the case of the diathermy, by addition of Joule's heat effect, the burning is accelerated. 5. The tolerant thermal limit of the periodontal tissue is considered to be 45°C or so, from the result of the examination of the gingival pocket in situ. 6. When the heating in the root canal is stopped at the tolerant thermal limit of the periodontal tissue, an average temperature of the intra canal liquid, in the case of the short waves, is 56°C and in the diathermy, 50°C. 7. In order to maintain the intra canal temperature to be high and the heating of the periodontal tissue to be under the tolerant thermal limit at the same time, it is recommendable that at first 30-40 mA of the current is to be supplied until the temperature of the root surface reaches to its tolerant thermal limit and then the current is to be supplied intermittently with 5-10 seconds' interval. 8. It is desirable, in pulp coagulation, that the electrode should be inserted to the near region of the would-be coagulation. And it is effective that electrode is inserted to the apical portion of the root canal to elevate equally the temperature of the intra canal medicament. 9. In the root treatment, it is effective to use the short waves which can maintain the intra canal temperature to be high.
A vertical measuring apparatus was devised by Fusayama and used for measuring the free setting expansion of hydrocal. This apparatus is very easy to use and is accurate enough. Perfect curves of dimension, temperature and hardness of hydrocal during setting were made and compared in fig. 2. Plastone and Duroc were used as hydrocal material. Their setting expansions occured at the time of the initial setting. The maximum expansion of Plastone was +0.54% 1 day after pouring, and that of Duroc was +0.05% 6 hours after pouring. The maximum temperature rise from room temperature in the center of a 23×23×50 mm3 block of Plastone was 7.5°C 30 minutes after pouring. That of Duroc was 16°C 13 minutes after pouring. The times requested to reach to these peaks substantially corresponded with those of the highest piches of their setting expansions. At first the hardness increased generally parallel to the curves of their setting expan-sions, and then continued to increase during their drying shrinkage also. They reached B. H. N 7 after 50 minutes in the case of Plastone and B. H. N 8.5 after 30 minutes in the case of Duroc. These results were about 60% of their final hardness measured after 1 week. Elastic hydrocolloid impressions restricted the setting expansion of hydrocal poured in them to some extent. Harder impression colloid supported closer by tray walls restricted it more. The Plastone models poured in various hydrocolloid impressions expanded after one day. This is illustrated in the following data : Technicol-Plastone model +0.26 (±0.06) % Algix-Plastone model +0.51 (±0.10) % Deelastic-Plastone model +0.27 (±0.07) % D. P. Im. Col.-Plastone model +0.35 (±0.09) %
Investiments of silicic acid gel bonded with either quartz or alundum were examined for the dental casting of Co-Cr alloy. Silicic acid is made by hydrolysis of ethyl silicate in the presence of hydrochloric acid and then gelatinized with magnesia mixed in the sand. Test specimens made of various fineness of quartz mixture bonded with silicic acid was fired. at 900°C for 30 minutes and cooled to room temperature to strengthen it against compression. The ratio of 60-100# sand to 200-250# sand : -60: 37 mixture was the hardest. The investiment bonded with concentrated silicic acid was hard. Thermal expansions of quartzsilicic acid investiments and alundum-silicic acid investiment were estimated +1.2-1.3 at, 600-900°C and +0.45% at 800-900°C respectively.
A clinical survey was made from late prognosis of 1139 fixed bridges which were worn for years by patients visiting our clinic during half a year in 1952. 29.3% of them complained about bridges, but actually 40% of the bridges unsatisfatory. Majority of such faulty bridges had supporting teeth suffering from the periodontal disease caused by either ill fitting gingival margins of the over loading upon them. Breakdown of the bridges and secondary decay on supporting teeth were additionally found. These mishaps were also more common on upper anterior bridges. It should be emphasized here that many patients did not know till their bridges or supporting teeth had been incurable.
An eight year-old girl complained difficulty in speaking and in moving tongue because of presence of a small-finger-sized tumor at sublingual mucosa of the left side. The tumor was found there early on a day of one week old infant and has been growing ever since. An examination on the taste could not find any abnormality, but a salty taste. On August 11, 1955 surgical operation removed it successfully and no recurrence as yet. The biopsy found nearly proper tissue elements of the tongue in it.