During and after the War, noble metals such as gold and platinum were used few amount on account of controll of the government and economical poverty of the people. So, the investigation on substitutes for gold alloy has widely developed and various kinds of substitutive dental alloys have been produced.
In this report, the results on chemical analysis, micro-structure and Vickers hardness of these substitutes are shown and brief discussion on these alloys is stated from the standpoint of metallography.
The results on silver alloys are shown in Table 1. The defect of silver alloys is to be tarnished by sulpher ion. It is well known that addition of palladium and gold prevent this, hewever most of alloys in the market increase their resistance to corrosion by addition of cadmium, zinc and tin. Alloys which contain about 80 % silver are not sufficient to prevent tarnishing, but have comparatively good ductility and high melting point, so they are directed for use as cast crown, swaged plate, etc. Alloys contain 60-70 % silver have good corrosion resistance and are used for cast inlay. Ag-Cu alloys show age-hardening characteristic by quenching and tempering, however maker of these alloys do not, direct to utilize this phenomena. It is doubtful to use silver alloy which contains 27.63 % copper for clasp and bur. For this alloy has eutectic structure and is known as brazing solder.
Cu-Zn-Ni, Cu-Sn-Ni and Cu-Zn alloys are found in the market. (Table 2) They are used for only casting. Cu-Ni-Zn alloy contains more zinc than usual nickel silver to lower the melting temperature. These alloys have some defects, for instance, comparatively high melting point, somewhat poor resistance to corrosion and evaporation of zinc during melting. The evaporation of zink increase the melting point and decrease the hardness and corrosion-resistance. These alloys have dendritic structure when they are cast by investment process. (Photo. 3-5)
The results on Sn-Sb alloy are shown in Table 3. This alloy has very low melting temperature, so care must be taken to prevent the growth of primary phase. To get fine structure, it is necessary to cool down the mould to room temperature. (Photo. 6-8)
As wrought alloys, Ni-Cr, 18-8 stainless steel and Co-Cr alloys are in the market and chemical compositions of these alloys are shown in Table 4, 5 and 6 respectively. Ni-Cr alloy sheets are widely used in this country for crown. Co-Cr alloy is succeedingly used for precise casting. The effort to use this alloy for wrought wire produced the composition of Co-Cr-Fe-Ni system shown in Table 6. A part of cobalt is replaced by nickel and iron to increase their workability. In ferrous alloys, carbon which is contained in material as impurity, forms carbide by heat-treatment and intergranular corrosion takes place for the reason of this carbide. So that, care must be paid to the heat treatment.

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The greater part of the dental grinding wheels on the market in this country are that of vitrified type. The present writer studied on grinding wheel bonded by magnesia cement.
Manufacturing process of this wheel is as follows. Magnesite from Manchuria, or from India calcined at temperature 750°-800°C to magnesia powder containing 3% of CO₂. This powder and abrasive grain (SiC) mixed with solution of magnesium chloride of about 32° Be'. This mixture mould in disk. About two weeks of ageing at room temperature is need to cementation of this moulded mixture. This wheel has excellent grinding power compared with vitrified wheel.

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We are studieing to make a suitable nylon denture before two years, the first report were written in 1954¹⁾, but this time we have produced by way of experiment a new type injection machine for purpose to make nylon dentures. (See Photo 1) This apparatus have a spraying press of ten tons working pressure. The material used was Amilan (6-Nylon), which was manufactured by Toyo Rayon Co, in Tokyo.
The amilan chip is heated in the apparatus to a temperature of 250°C and while liquid, sprayed into the flask and pressed by motor oil pressure. The flasks are special types as they have to withstand the high pressur on the one hand, and must be provided with a filling hole on the other as photo 3. Hard plaster must be used for embedding. The result of experiment were succesfull for dimentions of amilan denture, and it can be well placed in oral. But from the result of using it after about three month, we found out the discoloration of amilan denture in oral. Amilan product has also great expansibility by sorption of water. Therefore we concluded that the amilan was not suitable for denture.
Then we should like to study about other polyamid plastics better than Amilan.

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The life of machinability of commercial round type burs produced in Japan, Germany, America and Denmark were measured by vertical drilling methylmethacryllic resin blocks and aluminium: alloy plate reciprocally. Aluminium alloy plate has the Rockwell hardness number 84.0 to 88.2 in B; scale and 3 mm thickness.
From results of this work, this report might be concluded as follows.
1. Relation between thrust (T) and number of drilling of Al-alloy plates (N) is classified as follows.
i) The more N increases, the more T increases gradually.
ii) As N increases, T increases extremely periodically. This type burs' lives are bad.
iii) T increases parabolically as N increases. This type burs indicate not so good lives.
2. From the minimum N giving be the product of initial thrust Ti and arbitrary constant K, the degree of fall of machinability can be compared with.
3. From the microscopic inspection, the form of blades are classified as follows,
i) No changes are observed.
ii) Dull of the edges are observed partially.
iii) Dull and wear of the blades and edges are observed in all.
4. There is no relation between the initial thrust and life.

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To lower down the abnormal high blood pressure the application of the γ1) preparation is supposed to be the best treatment. However, in the actual treatment, it may be desirable a2) and β3) used jointly.

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Report 1.
The authors intended to study what shades showed the Japanese teeth. It has been compared with the tooth shade guides as a method, because the tooth shade guides are only a standard comparison system made experimentally and sensorily in shades. However, there are no optical connections between them. We can't obtained, therefore, any chracteristic groups from values measured by the tooth shade guides, and we can't conclude the characters of these samples, that is, the average and the deviation value and so forth.
At the beginning of our study, we tried to analyse the optical characters of the tooth shade guides of S. S. W. & Co, in U. S. A, with the automatic recording spectrophotometer of the Central Laboratory, Hitachi Ltd (Japan) . In such a way the authors obtained the data showing the character of the tooth shade guides expressed in numeral.
Report 2.
Before the authors observed the characters of the Japanese tooth shades in different ages, we analyzed the optical characters of the tooth shade guides (S. S. W. & Co., U. S. A.) which is used for a standard, with the automatic recording spectrophotometer. (Report 1.)
With this instrument we measured the Japanese tooth shades of 3, 431 examples in wide distribution of ages (2 to 76 years of age) . It results that the average values in the optical characters of the tooth shade variated characteristically as follows in every groups at the different ages :
1) The chromaticity showed almost white at infancy stage, blueish at youth stage, and increased the reddish shade after manfood stage.
2) The chromaticity of the deciduous teeth is more white than that of the permanent teeth, and we find the inflexion at point of about 10 years of age in chromaticity curve.
3) There is no difference in averages of the chromaticity during groups of 10 to 30 years of age in statistics, so that groups in 10 to 30 years of age showed constant chromaticity.
4) In the chromaticity curve respective averages of groups in more 30 years of age were different values, but every value tended to be reddish.
5) In the luminosity it became darker, with a constant velocity, as the age advances from the youth stage to the old age stage.
6) At 30 to 35 years of age, the luminosity curve, such as the chromaticity curve, showed the second point of inflexion tended darker rapidly than that of groups of younger ages.
7) It has been considered that respectively second points of inflexion in both chromaticityand luminosity-curve show some basic biological meaning.

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A 29-year-old housewife, who had no family history of hereditary psychosis, suffered from marked delusion, hallucination, depression of mental control and obstacle of understanding since the following day after removal of follicular cyst in the area of her upper anterior teeth. She was diagnosed as schizophrenia by a psychiatrist anal has been hospitalized for more than one month so far with no sign of recovery. It may be considered due to her anxiety, astonishment and pain at the time of operation as well as her psychosis-susceptible predisposition.

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Up to this time the chief therapy for the gingiva pigmentation has been the scarification, but we are disappointed that we cannot always have good results by this method.
We, therefore, have applied for the gingiva pigmentation the “Dry ice therapy” which has most frequently been applied on the skin diseases for a long time, and we believe that we have had better results in our dental clinic than in dermatological.

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